Basics of Cancer

Again, this is just a quick post. The main focus of these two questions appears to be simply defining some of the key terms when talking about cancer.

1. Why is the word potential important in defining the characteristics of invasion and metastases in cancerous tissue?

One of the characteristics of cancer is that it has the potential to invade and metastasise. Not all cancers invade or metastasise but the cancerous cells do need to have the ability to potentially break through the basement membrane of tissues to be considered cancer. Or something. It seems like a bit of a weird definition to me.

2. What is the difference between primary cancers and metastatic cancer?

This one is a bit easier to answer! Primary cancer is the first cancer that appears, while metastatic cancer refers to cancer that has spread around the body from its origin. For example, you can have breast cancer that metastasises to the ovaries. In this case, breast cancer is the primary cancer, while the cancer in the ovaries is metastatic.

The Immune System

The immune system is vastly complex but unfortunately my notes are rather limited. If you wish to learn more about the immune system you'll have to find your own resources for now until I take a microbiology and immunology in 2nd year and can share what I learn with you :P

1. How do natural killer cells differ from T-cells in their recognition of an enemy?

While natural killer cells and T-cells kill off invaders through a similar mechanism (contact followed by release of certain enzymes), they differ in their recognition of an enemy. T-cells have T-cell receptors that recognise particular antigens on the surface of invading cells and are thus relatively specific. Natural killer cells, on the other hand, simply look for whether or not an invader has a "self" marker on the cell surface, and can thus kill a wide variety of invaders. These markers are called major histocompatibility (MHC) antigens, and differ from person to person (except in the case of identical twins).

2. What cells are affected by HIV virus? What is the difference between HIV infection and AIDS?

HIV (Human Immunodeficiency Virus) affects CD4+ cells by entering and multiplying rapidly, destroying the cells in the process. Some of these CD4+ cells are CD4+ lymphocytes, which fight against infection. Hence, HIV weakens the immune system. This condition can lead to AIDS (Acquired Immune Deficiency Syndrome), in which the immune system is too weak to fight off regular infections, leading to otherwise harmless infections to become deadly.

The Musculoskeletal System

Now for some notes on muscles and bones! Don't worry, I won't attempt to name every single one of them :)

1. Describe the chemical reaction at the neuromuscular junction across the synapse.

Communication at the neuromuscular junction is similar to communication between two neurons- the neuron releases neurotransmitters into the synapse, which bind to receptor sites on the other cell, triggering further reactions in the next cell. In the case of muscle contraction, the neurotransmitter released is most commonly ACh (acetylcholine). ACh binds to receptors on the motor end plate (part of the muscle on the other end of the synapse). This opens channels in the muscle cell membrane, allowing Na+ ions to rush in and create a depolarisation potential, stimulating the muscle to contract (well that's how I understand it, anyway). After ACh has had its effect, it is broken down by an enzyme called acetylcholinesterase.

2. Distinguish between isotonic and isometric contraction.

In isotonic contractions, the length of the muscle changes despite the tone and tension remaining the same. An example of an isotonic contraction exercise would be bicep curls- the load (and therefore the muscle tension) remains the same but the length of the bicep changes as you move the weight up and down.

In isometric contractions, the length of the muscle stays the same, but the force changes. An example of an isometric contraction exercise would be pushing hard against a wall. The length of your biceps would remain the same but more tension would be exerted. Believe it or not, isometric exercises can be good at building strength. However, they are not good at building bulk, so if you want to get bulky you'll probably just have to stick with weightlifting.

3. Describe a first-class lever. What muscle group and bone falls into this category?

A first-class lever is generally what first comes to mind when we think of a lever. In a first-class lever, the fulcrum is in the middle, the load is on one end and the force is being exerted on the other. An example of this in the body is the point where the neck articulates with the skull. At this joint, the neck is the fulcrum, the face and head is the load while the muscles at the back of the neck exert force allowing us to lift our head.

4. Why are third-class levers preferred in nature?

A third-class lever is a lever in which the fulcrum is at one end, the load is at the other and force is exerted from somewhere in the middle. There are plenty of third-class levers in our body. One example is the bicep, where the elbow is the fulcrum, the hand (and whatever we might be holding) is the load and the bicep exerts force upwards.

One important point to note about third-class levers (and about levers in general) is that the amount of force and distance that the force is required to move varies depending on the location of the force relative to the fulcrum and load. In the case of a third-class lever, if the force is being exerted closer to the load, the amount of effort required is reduced but the amount of distance required to move to lift the load is large. The inverse is also true: if the force is being exerted at some point closer to the fulcrum, the amount of effort required is significantly increased but the amount of distance required to move to lift the load is small. Many third-class levers in the body, such as the bicep, have the force located close to the fulcrum, allowing for greater speed in movements as well as a greater range of motion but with decreased mechanical advantage (strength).

5. Name and describe at least four functions of the bones.

Movement- Bones provide a point of attachment for skeletal muscles. In this way, bones also allow us to move around.

Storage- Certain substances, such as calcium salts, can be stored in the bones. (Incidentally, storage of calcium is responsible for the hardness of bones.

Protection- Some bones surround organs that need protection. For example, the ribs surround the heart and lungs while the skull surrounds the brain.

Support- Bones help keep us upright.

6. If the radius and ulnar heads are fractured (Colles' fracture), what joints must be immobilised in a cast to control movement until healing takes place?

In a Colles' fracture, treatment generally consists of first trying to move the bones back to their normal positions if they have been displaced. I would assume that then the wrist bones are immobilised to allow the fracture to heal. I'm not a doctor, and taking medical advice over the Internet isn't exactly the wisest idea anyway, so if you get a fracture and do all that and get worse, don't sue me. *disclaimer over*

The Reproductive System

Now we're up to the reproductive system! This is a system that I know a bit more about, since we did a fair bit on it last semester. As usual, though, if you see something wrong, please point it out to me :)

1. Why do the testes need to be outside the body cavity in the scrotum? What structure(s) regulate or affect the distance from the body?

The testes need to be outside the body cavity because the optimal temperature for sperm production is slightly below body temperature. There are several muscles that regulate the distance of the testes from the body. The cremaster muscle can contract to pull the testes up, while the dartos muscle can contract to pull the scrotum against the body and make it wrinkled (possibly to conserve heat?).

2. Describe the pathway taken by sperm from the testes to the urethra.

Sperm production takes place in the seminiferous tubules located within the testes. After sperm are produced, they travel through several ducts. The first one is called the rete testis, which branches into a series of 12 (if I remember correctly) efferent ductules, which combine into the epididymis, a long, coiling duct in which further sperm production takes place. They then move into the vas deferens, a long, muscular tube which runs to the prostate. From there it goes through an ejaculatory duct through to the urethra.

3. What occurs during the preovulatory phase of the menstrual cycle? What is considered day 1?

Day 1 of the menstrual cycle is the first day of bleeding, as that is the easiest to determine. During the preovulatory phase, FSH (follicle-stimulating hormone) stimulates the follicles to grow. Under the influence of LH (luteinising hormone), theca cells on the outside of the follicles increase their number of cholesterol receptors, allowing them to receive more cholesterol which can be converted into androgen (I think that's how it works anyway- can't remember where I read this). Granulosa cells, which are the second layer of the follicle, contain the enzyme aromatase which converts androgens into oestrogens. These oestrogens help to begin rebuilding (proliferating) the functional layer of the endometrium of the uterus after its shedding off during menstruation. Hence the preovulatory phase is also called the proliferative phase.

4. At what stage is there rupture of the corpus luteum? What occurs at this time?

Rupture of the corpus luteum occurs during the end of the menstrual cycle, towards the end of the secretory phase. Since the corpus luteum secretes oestrogen and progesterone which maintains the lining of the uterus, its rupture means that the lining is no longer able to be maintained. The functional layer of the endometrium is then shed during menstruation.

5. What is the purpose of X chromosome inactivation? In which sex does it occur?

X chromosome inactivation, which occurs in females, alleviates the issue of females having "too much genetic information" from two X-chromosomes. If I remember correctly, this phenomena is also known as "dosage compensation." Due to X-chromosome inactivation, only one X-chromosome is active.

6. A father has PKU and the mother does not. Together, they have a child who also has PKU. What is the father's genotype?

PKU (phenylketonuria) is an autosomal recessive disease. To have PKU, therefore, a person must have two recessive alleles for the disease. Hence, the father has two recessive alleles for PKU.

The Urinary System

Now we've moved onto the next system- the urinary system! Once again I don't have that many notes on this system, and whatever notes I have aren't that great, so please a) forgive me and b) correct me if you find any blatant errors.

1. Describe the anatomy of a nephron in detail.

A nephron is basically the functioning unit of the kidney, and as far as I can tell each nephron is basically just a duct surrounded by capillaries. However, it gets a bit more complicated than that (read: a LOT more complicated), but I'll try and describe it as simply as possible.

First, I will describe the shape of the urine-carrying renal tube. At its beginning, located in the renal cortex (the outer region of the kidney), the tube widens out to form a capsule known as Bowman's capsule. The tube then quickly becomes convoluted- the proximal convoluted tubule- as it proceeds downwards. Eventually it forms a long U-shaped loop called the Loop of Henle, which dips down into the renal medulla (the middle portion of the kidney) before going back into the renal cortex again. At this point, it becomes the distal convoluted tubule, which then joins a larger urine-carrying duct.

Next I will describe the blood supply. Fresh blood travels to the nephron in an afferent arteriole. This leads into a convoluted ball of capillaries called the glomerulus, which tucks neatly into the cup-like Bowman's capsule of the renal tube. Blood leaves the glomerulus in an efferent arteriole which is thinner than the afferent arteriole, causing blood in the glomerulus to be at relatively high pressure, which is great for filtration purposes. This blood then branches off into capillaries that surround the other sections of the renal tube, allowing for further transfer of substances between the blood and the urine.

2. Describe the internal blood flow of the kidneys. How is it different from a venous portal system?

I have already described the blood flow of nephrons, the main functioning units of the kidney, in my answer above. I would, however, like to draw attention to one particular point. Did you notice that the blood entering the glomerulus went from an afferent arteriole to capillaries to an efferent arteriole (i.e. arteries to arteries) as opposed to the vein-to-vein systems of the hepatic and hypophyseal portal systems? I would assume that this would result in a higher pressure blood flow due to the arterioles' ability to contract, but I'm not 100% sure so don't quote me on that.

Now I'll mention the more "general" (for lack of a better term) blood flow to the kidneys, which is fortunately much less complex than talking about nephrons. Each kidney has a renal artery and a renal vein. These branch out within the kidney and form circular-like rings so that if one part gets cut off, the rest of the kidney can still survive. This is an example of an anastomosis.

3. Describe the mechanism for water reabsorption and name the locations for reabsorption in the nephron.

Most water reabsorption (around 90%) occurs via osmosis, or the movement of water from an area of higher concentration (i.e. with fewer dissolved solutes) to an area of lower concentration. The remaining 10% of water absorbed is absorbed with the help of hormones such as ADH (antidiuretic hormone) and aldosterone.

4. What is the effect of severe and prolonged hypotension (low blood pressure) on renal filtration? Renal blood flow?

Since filtration requires pressure to push solutes across into the renal tube, severe hypotension would likely decrease the rate of filtration. In fact if the pressure in the capillaries was lower than the pressure in the capsule, perhaps the solutes would filter back across, but I haven't done any physics for around four years now so don't quote me on that. Renal blood flow would likewise decrease, especially since the body is likely to prioritise more critical organs such as the brain and heart over the kidneys. In fact, in very severe cases, blood flow to the kidneys can stop entirely, which can kill the tubules or even the entire kidney.

The Endocrine System

Now we've moved onto the endocrine system! This system is a bit different to the other systems that we've talked about- organs in the endocrine system appear to be grouped together not because they work together but because they send their messages to the rest of the body in the same way. Organs in the endocrine system use the endocrine (!) system of signalling, which is through hormones sent via the blood (as opposed to exocrine in which the chemicals and stuff are dumped into the cavities of organs or onto body surfaces or paracrine in which the stuff diffuses through the interstitial fluid).

Without further ado, here are some notes:

1. How does the venous portal capillary system function in the anterior pituitary gland? Why is this necessary?

There is a small portal system (i.e. veins go to smaller capillaries which go back to being veins again) between the hypothalamus and the anterior pituitary gland. If I remember correctly, this is called the hypophyseal portal system (hypophysis = pituitary). This portal system, with its smaller vessels, allow the hormones to travel in a more concentrated form than they would be in if the vessels had gotten larger as veins normally do. This, in turn, makes communication between the hypothalamus and pituitary more effective.

2. Describe the differences between endocrine control and nervous system control of bodily functions.

While both systems play roles in signalling and communication, there are also several very important differences. One of the main differences is that, while the nervous system uses an electric current to send messages, the endocrine system uses chemical messengers called hormones. The nervous system signalling is therefore much faster than the endocrine system. On the other hand, the effects of the nervous system tend to be much shorter lived than the effects of the endocrine system, which can linger for a long time.

3. Define and describe the differences between exocrine and endocrine glands. In what category is the pancreas?

I kinda already explained this in the introduction, but let me quickly explain again. In an exocrine gland, products are secreted directly into the lumen (cavity) of organs or onto a body surface, such as the skin. In an endocrine gland, on the other hand, products are secreted into the bloodstream to be carried around the body.

The pancreas exists in both categories. 99% of the mass of the pancreas is devoted to its exocrine function, which is the secretion of bile into the duodenum. The remaining 1% of the pancreas is devoted to its endocrine function, which is the secretion of hormones, most notably insulin and glucagon, into the blood where they can regulate blood glucose levels.

4. List as many symptoms as possible in a diabetic patient who has forgotten to eat after taking a normal dose of insulin.

This is the sort of question where I would probably be best off asking a friend of mine who has diabetes, but I don't want to look overly nosy so I'm going to try and answer this question by myself. If a diabetic patient takes insulin, the insulin works to decrease blood glucose levels by increasing the speed of diffusion of glucose into cells, conversion of glucose into glycogen and synthesis of proteins and fatty acids while decreasing the rate of glucose synthesis. If the patient does not eat, they might have an overall net decrease in blood glucose levels. Since glucose is an important form of energy, a patient might go into shock or even into a coma from low blood glucose levels.

5. Describe the function of the thyroid gland.

The thyroid gland secretes hormones that regulate many chemical reactions that take place within the body. These include reactions related to oxygen uptake, body temperature control and the synthesis of molecules in cells.

6. What is a negative feedback mechanism? Describe one such system in detail.

A negative feedback mechanism is a mechanism in which an organ sends out a message to produce a product, and that product sends a message back to the organ to stop producing more. Negative feedback is important for regulating homeostasis. One example of negative feedback is that of glucagon, the hormone in the pancreas that stimulates glucose production. Glucose production, triggered by the release of glucagon, is stimulated by low blood sugar. When enough glucose is produced, the pancreas secretes less glucagon. In this way, blood sugar levels can be maintained. (Glucagon also works closely with insulin, which has the opposite effect on blood sugar levels.)

7. What is a goiter? What is exophthalmos? Are they related? If so, how? If not, why not?

Goiter is a word that basically means "thyroid enlargement." Goiter is not a disease on its own, it's just the name of a symptom that could be triggered by a disease or some other condition such as iodine deficiency. Exophthalmos, on the other hand, is a completely different symptom. It refers to a bulging of the eyes caused by fat deposition behind the eyes. While these symptoms are very different, they do have one thing in common: they can both be caused by Graves' disease. In Graves' disease, patients have antibodies that mimic TSH (thyroid-stimulating hormone) and thus the thyroid becomes overstimulated (a condition known as hyperthyroidism).

The Digestive System part 3: The Small Intestine, Colon and Rectum

This post is the third and final of this short mini-series on the digestive system. Yay!

1. What are the divisions of the small intestine? Which are intraperitoneal?

The divisions of the small intestine are the duodenum (the C-shaped curve at the beginning of the small intestine), the jejunum (the first half of the small intestine) and the ileum (the second half of the small intestine). The division between the jejunum and the ileum is not completely arbitrary, but is determined by the arrangement of blood vessels to these two sections of the intestine. Both the jejunum and ileum are intraperitoneal (i.e. encircled within the peritoneum, which is the membrane lining the abdominal cavity).

2. What would be the effect of removing the entire colon and rectum? Would this be more or less difficult to live with than removing the small intestine? Why?

Some of the functions of the colon and rectum include the absorption of water and, in the case of the rectum, controlling the excretion of waste (since obviously as you know it is a mostly voluntary action). If the colon is removed, the ileum is able to adapt to take on the role of absorption of water. Controlling excretion of waste may be problematic but there are ways around this- for example, in a colostomy, where part of the colon is removed, faeces can be excreted through a hole in the skin into an external bag (which doesn't sound particularly pleasant, but I guess you'd take what you can get if you're in that kind of situation). On the other hand, if the small intestine is removed, the colon would not be able to take on the role of digestion of nutrients. Therefore, removing the colon and rectu would be less difficult to live with than removing the small intestine.

3. Compare and contrast absorption in the small intestine with absorption in the colon.

There are several differences between absorption in the small intestine and absorption in the colon. The colon absorbs only water, while the small intestine absorbs almost everything else. Another difference between absorption in the two areas is that, while both areas have many folds to create a larger surface area, the folds in the small intestine protrude outward and are called villi while those in the colon fold inwards.

4. What are the voluntary and involuntary components of defecation? What would be the effect of completely cutting the external anal sphincter?

We have two anal sphincters- an internal and an external sphincter. The internal sphincter is controlled by the parasympathetic nervous system and is involuntary. The external sphincter, on the other hand, is voluntary. If the external anal sphincter was cut off, then we would lose voluntary control and essentially become incontinent.

The Digestive System part 2: The Pancreas, Liver and the Biliary Tree

Following on from yesterday's post, here's some more notes on the digestive system! By the way, I think I've worked out what the biliary tree is- it appears to refer to the system of bile ducts running down from the liver since they kinda look like a tree.

These questions are (in my opinion) harder than previous questions that I've addressed, so answers to these might not be 100% accurate. Please correct me if you find anything wrong :)

1. Describe the structure of the portal circulation of the liver. Why is this complicated anatomy a necessary evolution of the digestive system?

In the portal circulation of the liver, rather than veins becoming progressively larger as they approach the heart, veins branch out back into capillaries before merging to become veins again. Additionally, if I remember correctly, some arterial blood is mixed with the venous blood in this portal system. The complex bed of capillaries allows for a greater number of hepatocytes (liver cells) to become intertwined with blood vessels, which in turn allows for a greater exchange of nutrients.

2. Trace the route of venous blood in the colon as it enters the inferior mesenteric vein until it comes into the right heart.

The inferior mesenteric vein, along with several other veins such as the superior mesenteric vein, the splenic vein, the gastric veins and the oesophageal veins, all drain into the portal vein. The portal vein enters the liver, and then branches off into capillaries to allow exchanges to take place before returning to the central (portal) veins. Blood then travels through the hepatic veins into the inferior vena cava which leads back to the right side of the heart.

3. Name three hormones secreted by the enteroendocrine glands of the small intestine and describe their target organs and effects.

The enteroendocrine glands of the small intestines secrete several different enzymes, each with somewhat different functions. Some help to slow down the passage of food through the pylorus so that the intestines do not get "overwhelmed," while others stimulate the movement of the intestines.

One hormone is GIP, or gastric inhibitory peptide. It acts on the stomach to inhibit gastric secretion and slow stomach emptying. It also acts on the pancreas to stimulate insulin release, preparing the body for the absorption of glucose.

Another hormone is secretin, which acts on the pancreas, liver and gallbladder to increase the amount of bicarbonate in pancreatic juice. Bicarbonate ions are basic, and hence the rise in bicarbonate increases the pH and neutralises the stomach acid. Secretin, like GIP, also inhibits gastric juice secretion.

A third hormone is CCK, or cholecystokinin. CCK also acts on the pancreas, liver and gallbladder. Functions include increasing bile secretion, stimulating emptying of the gallbladder and providing feelings of satiety.

4. What are the major causes of obstructive jaundice? Which one would you choose to have, if you had a choice? Which would be your last choice?

This is a topic that I'm really not very clear on. Additionally, this is a bloody weird question. If I had a choice, pretty sure I'd choose not to have any kind of obstructive jaundice...?

Anyway as far as I know, obstructive jaundice is basically when the bile ducts get clogged up and all the bile salts back up, making your skin yellow and causing a whole host of other health problems. Some of the major causes of this are gallbladder stones and pancreatic cancer. Obviously if I had to choose between them, I'd choose the stones over the cancer.

The gallbladder is a vestigial organ (that is, it's basically a remnant of some organ passed down to us through evolution) and doesn't always empty that well, resulting in stones forming from the bile salts that have remained in there for too long. Gallbladder stones can be removed and in fact the entire gallbladder can be removed without too many problems.

Pancreatic cancer, on the other hand, is a whole other ball game. The mortality rate is quite high and we don't have effective treatments for it yet. There is surgery that can be done, however the surgery itself has quite a high mortality rate (30-40%), and the survival rate after 5 years is only around 2%. Even more unfortunate is that we still don't know how this cancer can be prevented. Let's hope researchers find something soon to help patients and families affected by this terrible disease :(

The Digestive System part 1: The Mouth, Oesophagus and Stomach

And now we're onto some more notes on the digestive system! This will be in 3 parts, the first being on the mouth, oesophagus and stomach, the second on the pancreas, liver and biliary tree (whatever that is) and the third on the small intestine, colon and rectum.

1. Detail the safeguards that prevent food from entering the airway during swallowing.

There are several safeguards that prevent food from entering the airway. The first involves the uvula (the thing that dangles down at the back of the throat) and the soft palate (the roof of the mouth). When the uvula detects food, the soft palate rises to stop food from going into the nose. The second safeguard involves the epiglottis and the larynx. During swallowing, the larynx moves up, causing the epiglottis to block the opening of the trachea so that food cannot enter.

2. How is gastrin different from the rest of the gastric secretions listed in the lecture (salivary amylase, salivary lipase, gastric lipase etc.)?

Salivary amylase, salivary lipase, gastric lipase and so on are all enzymes, as denoted by the -ase suffix at the end of their names. Enzymes are proteins that catalyse certain chemical reactions in the body- in this case, enzymes help molecules to break down into smaller components. The digestive enzymes are released directly into the lumen (cavity) of the mouth, stomach, intestines etc., where they do their job.

Gastrin, on the other hand, is a hormone. Hormones are distributed through the endocrine system- that is, they travel through the blood to get to their target cells rather than being released directly into the lumen of organs. Rather than assisting in breaking down molecules, the function of gastrin is to stimulate parietal cells in the fundus of the stomach to release hydrochloric acid. (The fundus is an area of the stomach located around the top of the stomach.)

3. Describe the cephalic phase of gastric secretion. What is the mediator in this process?

The cephalic (neural) phase of gastric secretion is mediated by the vagus nerve (cranial nerve X). It is a parasympathetic nerve, meaning that it usually has inhibitory effects on organs- except for those in the digestive tract, on which it has a stimulatory effect. During the cephalic phase, the vagus nerve stimulates muscular contraction and secretion of hydrochloric acid, pepsinogen and mucus. No food has to be in the stomach for this to occur- only thinking about food is required (which is probably why you can feel hungry when thinking about food).

4. Describe the intestinal phase of gastric secretion. Contrast it to the other two phases.

This is the area that I'm a bit hazy on. From what I understand the intestinal phase runs pretty much at the same time as the other two phases (in fact reading over my notes I see that there is a lot of overlap between the three phases). The intestinal phase mainly inhibits the action of the other two phases- while the cephalic and gastric phases are both stimulating contraction and trying to push food out of the stomach (particularly in the gastric phase), the intestinal phase tries to slow these processes down in order to give the intestines more time to prepare for food. Also, unlike the first two phases, which are mediated somewhat by the vagus nerve (the cephalic phase more directly and the gastric phase more indirectly, as the latter is initiated by stretching of the stomach which is mediated by the vagus nerve), the intestinal phase appears to be mediated more through the hormones that are released by the entry of chyme into the duodenum. These hormones include GIP (gastric inhibitory hormone), which inhibits gastric secretion and motility, secretin, which inhibits gastric secretion and CCK (cholecystokinin), which inhibits gastric emptying.

Nervous system notes part 2: The autonomic nervous system, eyes, ears and memory

I know it's been a long time since I last posted, but here's some more notes that I forgot (or more likely couldn't be bothered) to upload earlier.

1. How does sympathetic stimulation prepare an individual for fight?

The actions of the sympathetic nervous system speed up the heart rate, dilate the pupils to increase the amount of light entering the eye, increases the rate of breathing and so on, in order to get more oxygen and nutrients to the brain and muscles and thus prepare the body to respond to whatever stimulus has initiated the fight-or-flight response.

2. What is the effect of parasympathetic stimulation on the cardiac muscles? On respiration?

The parasympathetic nervous system has the opposite effect of the sympathetic nervous system: that is, it slows down heart and respiration rates.

3. What does the presence of more rods at the periphery of the visual field do to acuity of vision in that area?

Rods are photoreceptors (light receptors) that work best in dim light, though only see in black and white. Their location at the periphery of the visual field mean that, at night, our peripheral vision is better than our normal vision. This allows us to detect predators and other things moving around in the darkness.

4. Discuss convergence and divergence as they refer to the circuits of the rods and cones. Which confers greater visual acuity? Sensitivity?

Multiple rods "converge" into one nerve cell- i.e. information from multiple rods is sent to the same nerve cell. This gives better sensitivity at the expense of visual acuity. On the other hand, cones have a lot of receptors to gain the light that they need to function, which provides higher visual acuity at the expense of sensitivity.

5. Describe the components of the middle ear.

The middle ear is home to some of the smallest bones and muscles in the body. The boundary between the outer ear and middle ear is the tympanic membrane, or eardrum, which vibrates in response to sound. Attached to this is the first ossicle (small bone): the malleus (or hammer). This articulates with the incus (anvil), which in turn articulates with the stapes (stirrup). The stapes is then attached to the oval window, which is the membrane forming the boundary between the middle and inner ear.

There are several small muscles that can contract to hold the bones steady during prolonged exposure to loud sounds. One of these is the tensor tympani muscle controlled by cranial nerve V. This muscle holds the malleus steady. Another of these is the stapedius muscle, which is the smallest muscle in the body. It is attached to the stapes and is controlled by cranial nerve VII.

Another important component of the middle ear is the eustachian tube, which connects the middle ear to the back of the mouth. Air can travel through here to equalise the pressure in the ears. This is why blocking your nose and blowing hard can help relieve pain when dealing with pressure changes (such as during takeoff and landing on an aeroplane).

6. How is balance transmitted from the semicircular canals to the brain? Is this static or dynamic equilibrium?

There are three semicircular canals in each ear, oriented in different directions. These canals detect dynamic equilibrium, which is changes in motion (as opposed to static equilibrium, which refers to the orientation of the body). The canals are filled with fluid and lined with cilia, and when the body moves, the fluid in the canals pushes the cilia. A structure called the crista, located in the ampulla (widest section of the canal) detects motion and sends off impulses via its nerve fibres to the brain. (I think that's how it works, anyway- I'm not 100% sure.)

7. What is the anatomic basis of the differences between short-term and long-term memory?

In short-term memory, there are no anatomical changes (as far as we know). No neurons are added and the structure of the neurons does not change. Short-term memory is probably simply a result of short-lived electrical and chemical reactions in the brain. Long-term memory, on the other hand, is signalled by certain anatomical changes, such as more and larger presynaptic terminals capable of carrying more neurotransmitters. Long-term potentiation (LTP) is an enduring increase in synaptic strength in which connections are activated more easily.

8. Describe the differences between movements in patients with Parkinson's disease (rest tremor) and cerebellar ataxia (intention tremor).

Patients with Parkinson's sometimes exhibit rest tremor, which consists of small, shaky movements when the patient is at rest. These tremors, however, go away when the patient carries out some action intentionally, such as reaching out to grab something. Patients with cerebellar ataxia (damage to the cerebellum), on the other hand, exhibit intention tremor, which occurs when patients are carrying out an action intentionally. Since the cerebellum is not functioning properly, patients with cerebellar ataxia find it difficult to judge how much movement they need to carry out some task, so they may continuously over-correct their movements. For instance, if they reach out to grab something and their first movement is a little bit too far over to the left, they might swing their arm wildly over to the right, then wildly over to the left, and so on.

Nervous system notes- the brain and spinal cord

It's been a few days since my last post, but that's mainly because 1) I've finally started uni and 2) the nervous system confuses the hell out of me. I realise that I've written hardly anything about the nervous system before, but maybe I will in the future (read: not actually very likely to, but could happen if anyone actually requests for me to do so, which again is not very likely).

So without further ado, here are my notes so far. There will be a part 2 later on.

1. What are the three layers of tissue that cover the brain? Describe the function of any two of them.

The brain is covered by three layers of tissue known as the meninges.

The outermost layer, the dura mater, is quite hard and offers the most protection of the three layers. It also separates the two halves of the brain by forming a falx cerebri in the middle.

The arachnoid, containing blood vessels and so on, lies underneath the dura mater. It also contains arachnoid villi, which secrete cerebrospinal fluid (CSF).

The innermost layer is the pia mater. This layer is quite thin and is attached to the bain itself.

2. How does the circle of Willis provide insurance against brain infarction?

The circle of Willis, which is essentially a circle of arteries, provides insurance against brain infarction by providing an anastomosis (i.e. if a blockage forms in one part, blood can come in from a different direction).

3. What is the difference between the sympathetic nervous system and the parasympathetic nervous system?

The sympathetic nervous system, located along the spinal cord, is concerned mainly with the fight/flight/freeze survival instincts. The parasympathetic nervous system, on the other hand, is concerned mainly with rest, recovery and regulation.

4. How are the endocrine system and the nervous system different in their regulation of homeostasis?

The endocrine and nervous system are similar in that they both help regulate homeostasis by sending out messages to required parts of the body. They differ, however, in how they send these messages. The chemical-based endocrine system is slower (signalling takes seconds to days) and is less specific, while the electrical-based nervous system is faster (signalling takes only milliseconds) and is very specific.

5. What is the evolutionary purpose of the reflex arc? How might it aid in survival?

The reflex arc reduces the amount of time required for a response to occur. This allows us to avoid dangerous situations or minimise harm done to the body.

6. Describe the steps in the knee jerk (patellar tendon) reflex.

When the knee is tapped, stretch receptors in the muscles send messages to the spinal cord where they are then sent to the brain and to motor neurons. One of these motor neurons sends a message to the femoral muscle to cause the leg to kick out. To stop the hamstrings from tensing up and getting in the way of the reflex action, another motor neuron sends a message to inhibit the hamstrings.

Some more notes on the respiratory system

As I promised in my last post, here are some notes on the respiratory system.

1. Define the pleural space anatomically.

The pleural space is the area between the parietal pleura and the visceral pleura (the connective tissue lining the chest wall and lungs, respectively). It is filled with a lubricating fluid to allow the lungs to expand and contract.

2. Would tracheostomy help in the case of a severe asthma attack? If so, why? If not, why not?

Tracheostomy would not help in the case of an asthma attack. A tracheostomy is an operation which allows patients with blocked larynxes to breathe by inserting a tube lower down in the trachea, allowing air to bypass the larynx. Asthma, however, affects the smooth muscles near the alveoli, which is far past the area bypassed by a tracheostomy.

3. What muscles are involved in respiration during severe exertion? How is that different from respiration at rest?

During severe exertion, the accessory muscles of respiration are also involved (as opposed to only the diaphragm being involved as during rest). These muscles include the external and internal intercostal muscles, the sternocleidomastoid muscle, the scalene muscles and the rectus abdominus.

4. What is a pneumothorax? Describe the events that occur in the chest after a gunshot wound that creates a hole in the chest wall.

A pneumothorax is a loss of the vacuum in the pleural cavity following a tear in the visercal and/or parietal pleura. This loss of vacuum causes the lung to collapse.

After a gunshot wound causing damage to the parietal pleura and probably the visceral pleura as well, air rushes into the pleural cavity, causing a loss in vacuum. The decreased pressure causes the lung to collapse, which in turn stops gas exchange in the lung.

Some more notes on the cardiovascular system

It's been a rather long time since I last posted.

I don't really have that much to say, since it's been holidays and I've been on gap year and all. A couple of months ago I got Understanding the Human Body: An Introduction to Anatomy and Physiology as a gift of sorts, but you know what holiday mode is like- I watched some of the lectures but then didn't keep up with it for a while. Well, now that uni is about to start, I finally got the motivation to do so, and to answer some of the chapter questions in the book. Here goes...

1. Describe the route of blood flow, starting at the entry into the left atrium through its return to the left atrium.

Blood flows from the left atrium into the left ventricle, where it is pumped into the aorta for transport around the body. The aorta branches off into arteries supplying various parts of the body with blood, which then branch out into smaller and smaller arteries, which eventually branch out into arterioles, which then branch out further into capillaries which are only thick enough for one red blood cell to pass through at a time. The capillaries eventually combine into small venules, which combine to form larger and larger venules until you get veins, which get progressively larger and larger until you get to the level of the superior and inferior vena cava. Blood flows through these very large veins into the right atrium.

Blood then flows from the right atrium into the right ventricle, where it is pumped into the pulmonary arteries. These arteries also divide into smaller and smaller vessels until the capillary beds in the lungs. The vessels then get larger and larger, progressing through the venule and vein stages, eventually getting to the pulmonary vein, which brings blood back to the left atrium.

2. Define the physical borders of the mediastinum.

The mediastinum is essentially the space between the lungs in the chest cavity. It is also the heart's enclosure.

The tough fibrous tissue that covers the heart is called the pericardium, and is made up of two layers with a lubricating fluid between them. The outer layer of the pericardium is called the parietal pericardium. The inner layer is called the visceral pericardium and is very thin and can be torn easily.

The heart wall itself also has several layers. The outer layer, the epicardium, is essentially also the visceral pericardium. The middle layer is quite muscular, and is called the myocardium, or heart muscle. The inner layer is known as the endocardium. This inner layer also extends into the vessels, where it lines the vessels and is called the endothelium. (The endocardium and endothelium are pretty much the same- the name just changes depending on the location.)

3. Describe the events during the phases of the cardiac cycle.

The first phase of the cardiac cycle is relaxation, where both the atria and ventricles are in diastole (i.e. their muscles are relaxed, allowing atria and ventricles to expand). Blood fills the atria on both sides, and when the pressure is high enough, the mitral and tricuspid valves open, marking the start of the second phase of the cardiac cycle.

During the second phase of the cardiac cycle, the ventricles fill. At first, they fill passively due to the opening of the valves. After that, atrial systole (contraction of the atria) occurs, pushing any blood remaining in the atria into the ventricles. Throughout this phase, the atrioventricular valves (i.e. the mitral and tricuspid valves) remain open, while the semilunar valves (i.e. those leading into the pulmonary artery and aorta) remain closed.

The third and final phase of the cardiac cycle is ejection, where the atrioventricular valves close (all valves are closed for a fraction of a second), the aortic and pulmonary semilunar valves open, and the blood is ejected out into the main arteries. The aortic and pulmonary valves then close in order to start the cycle all over again.

4. Define cardiac output. What is stroke volume, and how does it affect cardiac output? What is the cardiac output in a man with a stroke volume of 90 mL and a heart rate of 85 beats per minute?

Cardiac output is the volume of blood pumped out per minute in millilitres. Stroke volume is the volume of blood (in mL) pumped out per beat, and a higher or lower stroke volume will obviously cause an increase or decrease in cardiac output.

e.g. In a man with stroke volume 90 mL and heart rate 85bpm

Cardiac output = 90 x 85 = 7 650

5. How is the portal circulation different from a systemic capillary bed?

The portal circulation, such as in the liver and surrounding organs, is different in that venous systems feed into each other (i.e. veins are going into other veins, rather than arteries going to veins). Also instead of progressively getting bigger or progressively getting smaller, the vessels may get bigger then smaller than bigger again.

6. How is blood shunted from one organ system to another?

Blood is shunted from one organ system to another via the constriction of vessels, which is in turn controlled by the brain.

7. Define shock.

Shock is a state in which the body cannot maintain sufficient cardiac output to carry out its fnctions effectively.

8. What are the three stages of shock, and which (if any) are treatable?

The first stage of shock is compensated non-progressive shock, in which no permanent damage or cell death occurs. Only transient fainting is experienced by the patient, who generally recovers naturally.

The second stage of shock is decompensated progressive shock, in which cells are injured. It can be treated, but not without medical assistance.

The third stage of shock is irreversible shock, in which organs are damaged, the blood becomes acidic and the patient dies within hours. It is untreatable.

That's it for now on the cardiovascular system. Later on I'll put up a couple more notes regarding the respiratory system.

Year 11 Human Bio Glossary U - Z

Other glossary sections: (A - E) (F - J) (K - O) (P - T)

U

Ulna- One of the bones on the lower arm. It forms the point of the elbow and joins the wrist on the small finger side.
Umbilical arteries- Arteries that carry blood to the capillaries of the chorionic villi.
Umbilical cord- The structure that attaches the foetus to the placenta.
Umbilical vein- The vein that carries blood from the placenta to the foetus.
Umbilicus- The navel.
Uracil- One of the nitrogen bases present in RNA (but is not present in DNA). Pairs up with adenine.
Urethra- The tube that transports urine (as well as sperm, in the case of males) to outside the body.
Uterine arteries- Arteries that carry the mother's blood to the placenta.
Uterine tube- A tube that carries the ovum from an ovary to the uterus. Also known as the Fallopian tube or oviduct.
Uterine veins- Veins that carry the mother's blood away from the placenta.
Uterus- The womb in which the foetus develops. Held behind the urinary bladder and in front of the rectum by ligaments.

V

Vagina- The tube that leads from the uterus to the outside of the body. It is muscular and lined with mucous membranes.
Varicose veins- Enlarged and lengthened veins which cannot carry blood back to the heart efficiently, potentially resulting in the accumulation of blood in lower limbs.
Vas deferens- The sperm duct. Takes the sperm away from a testis, into the abdominal cavity, across the upper surface of the bladder and around to the back of the bladder, where it meets up with the vas deferens of the other testis and joins the urethra.
Vasectomy- A form of sterilisation. A small piece of each vas deferens is removed and the cut ends are tied. Another method includes using high frequency ultrasound to kill the cells in the wall of the vas deferens, causing dead cells to coagulate and form an obstruction in the tube.
Veins- Relatively large blood vessels that take blood back to the heart. They have relatively thin walls as they carry low-pressure blood. They contain valves that prevent backflow of blood. The veins are squeezed, pushing blood along, when surrounding muscles contract.
Ventilation- A fancy word for "breathing."
Ventricle- The chamber of the heart that blood passes through after passing through the atrium. It has thick muscular walls, particularly on the left side of the heart, in order to pump blood around the lungs and body.
Ventricular systole- A stage of the cardiac cycle that lasts roughly 0.3 seconds. During this stage, blood is forced into the arteries from the ventricles.
Venules- Small veins.
Vernix- The protective waxy layer that covers newborn babies.
Vertebrae (singular: vertebra)- The bones making up the vertebral column. The top seven are the cervical vertebrae, the next twelve are the thoracic vertebrae, the next five are the lumbar vertebrae, and then the sacrum and coccyx are located at the bottom.
Vertebral column- The backbone.
Vertebrata- A subphylum that includes animals with backbones.
Villus (plural: villi)- A bristle-like projection, about 1mm long, that has smaller projections called microvilli. Inside each villus are blood capillaries and lacteals (a type of lymph capillary). Villi only have one layer of cells on their surfaces, allowing for easy diffusion of substances.
Vital capacity- The maximum amount of air that can be exhaled after inhaling as much air as possible.
Vitamins- Molecules that are essential for regulating cellular reactions and allowing cells to gain energy from proteins, carbohydrates and fatty acids. They cannot be manufactured in the body, but a balanced diet should give you all of the vitamins that you need.
Vocal cords- The edges of the vocal folds. They have elastic ligaments that can vibrate.
Vocal folds- The mucous membranes stretched between the pieces of cartilage making up the larynx.
Vulva- The region surrounding the opening of the vagina and urethra (in females).

W

Weaning- Moving onto solid foods.
Whiplash- The head flings back and forth during a sharp impact, causing ligaments to tear and internal bleeding to occur. Nerves may also be injured. There are many symptoms of whiplash, including headaches, dizziness, nausea, pain and weakness. If the injury is such that the axis is driven into the brain stem, death may occur.
White blood cells- Blood cells that defend the body against invading microorganisms and remove dead or injured cells. They are (obviously) white.

X

Y

Yellow bone marrow cavity- A fat storage site within bones.
Yolk sac- One of the embryonic membranes. Forms red blood cells and will become part of the umbilical cord.

Z

Zygote- The single diploid cell formed from the fertilisation of a sperm and ovum.
Zygote intrafallopian transfer (ZIFT)- A form of ART where the eggs are fertilised in the lab. At the zygote stage, normally a day after fertilisation, the zygote is transferred to the woman's uterine tubes.

Year 11 Human Bio Glossary P - T

Other glossary sections: (A - E) (F - J) (K - O) (U - Z)

P

Palliation- Treatment focused on reducing the symptoms (if there is no cure available).
Pancreas- An organ located just beneath the stomach, in the curve of the duodenum. It secretes pancreatic juice, which contains enzymes that aid in digestion, as well as the hormones insulin and glucagon, which regulate sugar levels in the blood.
Pancreatic amylase- A digestive enzyme in the pancreatic juice that breaks down starch into disaccharides, particularly maltose.
Pancreatic duct- A duct in the pancreas that the pancreatic juice travels through. Joins up to the common bile duct, which then enters the duodenum.
Pancreatic juice- A liquid secreted by the pancreas that contains digestive enzymes including pancreatic amylase, trypsin (a.k.a. pancreatic protease), ribonuclease, deoxyribonuclease and pancreatic lipases. It is slightly basic, thus neutralising any HCl that might still be in the chyme (the mixture formed after digestion in the stomach).
Pancreatic lipase- A digestive enzyme in the pancreatic juice that breaks down fats into fatty acids and glycerol.
Pancreatic protease- A digestive enzyme in the pancreatic juice that breaks down proteins into smaller peptide chains. Also known as trypsin.
Paraplegia- Paralysis of both of the lower limbs.
Parent cell- A term used to refer to the original cell (after cell division has occurred).
Parturition- Birth of a newborn baby.
Patella- A triangular bone also known as the "kneecap."
Pectoral girdle- The shoulder girdle. Consists of the clavicle and scapula.
Pelvic bones- The two main bones of the pelvic girdle. Also known as the hip bones.
Pelvic girdle- The hip girdle or pelvis. Consists of the pelvic bones.
Pelvic inflammatory disease (PID)- An infection of the pelvic organs of the female reproductive tract.
Pentadactyl- Animals that have five mobile digits on each limb.
Pepsin- An enzyme that breaks proteins and other long chains of amino acids down into shorter chains, or polypeptides. Also known as gastric protease.
Pepsinogen- An inactive form of pepsin. Pepsin is secreted in this form so that digestion does not occur in the lining of the stomach. Pepsinogen is inactive in alkaline surroundings and requires contact with HCl to activate.
Peptidase- An enzyme in the intestinal juice that breaks down peptide chains.
Peptide bond- The bond between two amino acids.
Pericardium- A membrane that surrounds the entire heart in order to hold it in place and prevent it from over-beating while still giving it some freedom to move while beating.
Periosteum- A dense, white fibrous covering on the outer surface of bones.
Peripheral vascular diseases- Cardiovascular diseases affecting the limbs. Includes phlebitis, varicose veins and arteriosclerosis in the limb arteries.
Peristalsis- Muscle movements in the alimentary canal that push the food along.
Pernicious anaemia- Anaemia caused by inadequate B12.
Phagocytosis- A process in which a cell surrounds and engulfs bacteria, dead cells, fragments and so on. If the substance is liquid, the process is called pinocytosis instead.
Phalanges- Bones in the fingers and toes.
Pharyngeal pouches- The "gill slits" present in the early embryonic stage.
Pharynx- A cavity in the back of the mouth. It is roughly 13 centimetres long and extends from the nasal cavity downwards.
Phenylketonuria (PKU)- A genetic disorder that can result in severe mental retardation. The gene controlling the production of an enzyme that breaks phenylalanine down is affected, so toxic levels accumulate in the blood, resulting in damage to the growing brain.
Phlebitis- Inflammation of a vein. May cause blood clots.
Phospholipid- A lipid that is a part of cell membranes.
Pinocytosis- A form of endocytosis in which the substances taken into the cell are liquid.
Pituitary gland- An endocrine gland located below the brain and above the mouth. Secretes a variety of hormones, including the gonadotropic hormones.
Pivot joint- Joint in which one bone has a circular, pointed or conical end, which rotates upon the axis of another bone. A prime example of this is the joint between the first vertebra (on which the head is balanced) and the second vertebra.
Placenta- A structure that supplies the foetus with nutrients while removing its wastes. Other functions include producing oestrogen and progesterone. Fully formed by the end of the third month of pregnancy.
Plasma- One of the components of the blood, comprising of 55% of the blood. Plasma is 91% water and 7% plasma proteins and also contains ions and some other substances such as dissolved nutrients and gases, hormones and waste products from cells.
Plasma membrane- A structure that separates the cell from neighbouring cells and the external environment. It is made up of a double layer of lipid molecules as well as various proteins associated with the lipids. Allows some substances to get through but not others. Also known as the cell membrane.
Plasma proteins- Proteins in the plasma.
Platelet- A type of blood cell that forms blood clots when blood vessels are damaged. Also known as a thrombocyte.
Pleura- The two-layered membrane surrounding the lungs. The outer layer adheres to the inner wall of the chest cavity, while the inner layer covers the inner surface of the lungs. Also known as the pleural membrane.
Pleural cavity- The space between the two layers of the pleural membrane.
Pleural fluid- The fluid inside the pleural cavity. Provides lubrication, allowing the two layers to slide against each other. Also holds the lungs in place.
Pleural membrane- The two-layered membrane surrounding the lungs. The outer layer adheres to the inner wall of the chest cavity, while the inner layer covers the inner surface of the lungs. Also known as the pleura.
Pneumonia- An infection caused by some bacteria, viruses or fungi, most notably the pneumococcus bacterium. The inflammation causes fluid to accumulate in the alveoli.
Polypeptide- Ten or more amino acids joined together.
Polysaccharide- Long chains of simple sugars (monosaccharides). One example is glycogen, the form in which carbohydrates are stored in the body.
Polyunsaturated fat- A fat in which there are multiple double bonds between C atoms.
Postural reflexes- Movements involved in adjusting stance so as to maintain balance. Occur without conscious thought.
Power grip- The grip involved in holding objects.
Precision grip- The grip involved in fine movements such as writing or se
Prehensile- Capable of grasping.
Preimplantation genetic diagnosis (PGD)- A technique that can be used to test embryos for genetic defects. Banned in some places due to ethical issues.
Pre-menstrual syndrome (PMS)- A range of symptoms that some women experience prior to menstruation. Symptoms are varied, ranging from mood swings to bloating to joint pain, and so on.
Premolars- Teeth used for crushing and grinding (along with the molars).
Primary amenorrhoea- A menstrual abnormality in which menstruation does not begin during adolescence.
Primary bronchi- The pair of bronchi that enter the lungs. These then divide into secondary bronchi, which divide into tertiary bronchi etc.
Primary follicle- An ovum surrounded by a single layer of cells.
Primary germ layers- The ectoderm, mesoderm and endoderm. Formed by the cells of the inner cell mass. Will develop into all of the tissues and organs of the body.
Primary oocyte- A grown oogonium. Surrounded by a single layer of cells, forming a primary follicle.
Primary spermatocytes- Diploid cells formed when spermatogonia are pushed into the centre of the seminiferous tubules.
Primates- An order (taxonomic rank) within the Mammalia class that consists of animals with forward-facing eyes and nails instead of claws.
Prime mover- The muscle in the pair that carries out the desired action. Opposite to this is the antagonist. The prime mover is also known as the agonist.
Progestagen- A substitute for progesterone which is used in some types of hormonal contraception.
Progesterone- One of the sex hormones in females.
Prolactin- Hormones secreted by the pituitary gland that affect the breasts of women. Important in milk production. Also known as lactogenic hormones.
Promotion stage- The second stage of tumour development. The initiated cells start dividing and become a malignant tumour.
Prophase- The first actual stage of mitosis. The spindle forms, the nuclear membrane breaks down and the chromatin threads coil up to become chromosomes.
Prosimians- A suborder within the primates. Include lemurs, lorises, pottos and galagos.
Prostate gland- A doughnut-shaped gland that surrounds the urethra just below the bladder. Secretes a thin, milky, alkaline fluid.
Protein- A structure made up of over 100 amino acids joined together. They make up much of the structure of body cells and take part in many chemical reactions in the body. They contain the elements C, H, O and N, and sometimes S or P as well.
Protoplasm- The nucleus and cytoplasm together (i.e. all of the cell's contents).
Proximodistal pattern- A pattern involved in motor development. Parts of limbs closer to the body are able to be controlled before parts of limbs further away from the body.
Puberty- The time during which sexual maturity (physically) is attained.
Puerperium- The period of time following pregnancy, during which the organs return to their non-pregnant state.
Pulmonary artery- The artery flowing from the right side of the heart to the lungs. Splits into the left and right pulmonary arteries.
Pulmonary circulation- Circulation of blood through the lungs.
Pulmonary vein- The vein that flows from the lungs to the left side of the heart.
Pulp cavity- The inside of the tooth. Contains nerves, blood vessels and a soft tissue called pulp.
Pyloric sphincter- A thick circular muscle at the lower end of the stomach. Stops stomach contents from leaving prematurely.

Q

Quadriceps- One of the main muscle groups of the thigh. Straightens the lower leg. All quadriceps muscles have a common tendon which crosses the knee joint to join with the tibia.
Quadriplegia- Paralysis of all four limbs.
Quadrupedal- Walks on four legs.

R

Radius- One of two lower arm bones. Joins the wrist on the thumb side and forms the wrist joint.
Recovery oxygen- The extra oxygen that needs to be breathed in following a period of anaerobic respiration.
Rectum- A section at the end of the large intestine. It can contract (in conjunction with relaxation of the anal sphincter) to allow defecation to take place.
Red blood cells- Blood cells that transport oxygen to the cells. They are (obviously) red in colour.
Red bone marrow- A type of bone marrow in which many blood cells are produced.
Red cell concentrate- A transfusion containing mainly red blood cells which have been separated out. The transfusion may also contain platelets and leucocytes.
Renal arteries- Arteries that take blood to the kidneys.
Rennin- An enzyme only found in the gastric juice of infants. Makes milk proteins coagulate (become solid or semi-solid), allowing the stomach more time to break down the milk proteins.
Residual volume (of air)- The volume of air remaining in the lungs after maximum expiration.
Respiration- The process by which carbohydrates, lipids and proteins are broken down to provide energy.
Retrovirus- A virus that contains an RNA core instead of a DNA core and cannot reproduce itself.
Rheumatoid arthritis- A severe form of arthritis involving inflammation of the joint, swelling, pain and loss of function.
Rhythm method- A method of contraception. "Unsafe days" for intercourse are considered to be between days 10-17 of a 28-day cycle. This is the least reliable of the ovulation detection methods.
Ribonuclease- A digestive enzyme in the pancreatic juice that breaks down RNA.
Ribosomes- Very small, spherical organelles that can be found either floating around in the cytoplasm or attached to membranes within the cells. At the ribosomes, amino acids combine into proteins according to instructions in the DNA.
Rickets- A condition in which the bones are soft.
Right lymphatic duct- A duct of the lymphatic system.
Roots- One or two long thin bits of the tooth that extend into the sockets in the jaw bones.
Rotation- Movement in which a bone rotates around its long axis.
Roughage- Food, such as cellulose, that cannot be digested by humans, but stimulates the contraction of the muscular walls of the intestine. Also known as insoluble fibre.

S

Saddle joint- Joint in which the two bones are saddle-shaped (i.e. concave in one direction, convex in the other). This allows both side-to-side and back-and-forth movements. Pretty much only seen in the joint between the thumb and the palm of the hand.
Saliva- A substance secreted into the mouth by the salivary glands. Contains mucus to lubricate the mouth and hold the food together; a digestive enzyme called salivary amylase, which breaks carbohydrates down into shorter chains; and antibodies, which kill bacteria in the food.
Salivary amylase- A digestive enzyme that breaks down carbohydrates into smaller chains.
Salivary glands- Three pairs of glands that secrete saliva into the mouth.
Sarcolemma- The thin, transparent plasma membrane surrounding muscle cells. Contains sarcoplasm.
Sarcoma- A type of cancer that forms from supporting tissues such as cartilage, fatty tissues, bones and muscles. Around 5% of cancers are sarcomas.
Sarcomeres- Units of the myofibrils. Contain many myofilaments, which come in two varieties: thick myofilaments containing the protein myosin, and thin ones containing the protein actin.
Sarcoplasm- A kind of cell fluid present in the sarcolemma. Contains hundreds to several thousands of myofibrils.
Saturated fat- A fat in which there are no double bonds between carbon atoms.
Scapula- Shoulder blade.
Scrotum- Skin-covered pouch that holds the testes. Divided into two sacs, each containing a single testis. Contains smooth muscle fibres allowing the scrotum to move towards or away from the body, depending on the temperature.
Secondary amenorrhoea- One or more menstrual periods are missed. This is quite common and happens to nearly all women at some point.
Secondary follicle- The second stage of the development of an ovum-containing follicle. The cells surrounding the original primary follicle have grown, divided and secreted fluids, forming a fluid-filled space forcing the egg to move towards the edge of the follicle, forming a secondary follicle.
Secondary oocyte- The larger product of the first meiotic division of a primary oocyte. Does not proceed past metaphase unless the sperm meets the ovum.
Secondary sexual characteristics- Characteristics associated with a person's gender but aren't related to sexual reproduction. In females, these include breast growth and broadening of the hips. In boys, it includes an increase in the size of the larynx. In both genders, it includes the growth of body hair in various places.
Secondary spermatocytes- Haploid cells that form after the primary spermatocytes undergo meiosis.
Second-class proteins- Proteins that do not contain sufficient quantities of essential amino acids. Same as incomplete proteins.
Second polar body- The smaller product of the division of a secondary oocyte. Eventually disintegrates.
Segmentation- Movements of the muscles of the small intestine that allow food to move back and forth and mix well with the digestive juices.
Semen- A liquid that nourishes and aids the transport of sperm. Also known as the seminal fluid.
Semilunar valve- Valves at the bottom of the aorta and pulmonary artery. Consist of three cusps that hold any blood that tries to flow back, preventing backflow.
Seminal fluid- A liquid that nourishes and aids the transport of sperm. Also known as semen.
Seminal vesicles- Vesicles located behind the urinary bladder. Secrete a thick sugar-rich fluid that makes up 60% of the volume of semen.
Seminiferous tubules- Tubules located in the lobules of the testes. Lined with cells that can divide to produce sperm.
Senescence- A decline in the performance of all the organ systems.
Septum- The "wall" dividing the heart into two halves.
Seroconversion illness- An illness that may develop within two weeks of exposure to HIV. Symptoms include lack of energy, fevers, headaches, dry cough, swollen lymph nodes and pain in muscles and joints.
Serosa- The outer layer of the alimentary canal, consisting of connective tissue.
Serum- A fluid that is squeezed out during the process of clot retraction.
Sexually transmitted diseases (STDs)- Diseases that can be transmitted through exchange of bodily fluids. Also known as sexually transmitted infections (STIs).
Sickle cell anaemia- A genetic condition resulting in deformed red blood cells.
Simple epithelium- Epithelium with only a single layer of cells.
Skeletal muscles- Muscles that allow movement at the joints. Also known as striated muscles due to their appearance under a microscope, or as voluntary muscles since they can only be contracted voluntarily.
Slightly moveable joints- Joints in which bones are held together by cartilage. Slight movement can occur, but not a lot. Also known as cartilaginous joints.
Slipped disk- Part of the invertebral disc (fibrocartilage between vertebrae) is squeezed to one side, displacing the disc. Depending on how the disc has "slipped," it can put pressure on spinal nerves of the spinal cord, causing severe pain and numbness. This can then result in nerve damage, which then causes weakness and possible degeneration to the tissue of the muscles supplied by the damaged nerves.
Smooth muscles- Muscles in the internal organs. Do not have striations. Also known as involuntary muscles.
Social smiles- Actions that babies perform to respond to people, such as smiles, sounds, smiling, kicking or waving their hands.
Spasms- Short, sudden, involuntary muscle contractions.
Spermatids- Haploid cells formed after the secondary spermatocytes divide.
Spermatogenesis- The process of sperm production.
Spermatogonia- Sperm "mother cells" that are immature cells containing full sets of 46 chromosomes. These cells line the seminiferous tubules of each testis. When puberty begins, most of these cells begin to divide by mitosis, resulting in a continuous source of spermatogonia for the production of sperm.
Spermatozoa (sperm)- The male gametes. They are around 0.06mm long and are made up of a head, neck, middle piece and tail. The tip of the head contains a fluid filled vesicle which, in turn, contains enzymes which help to break down the layers surrounding the ovum. The head also contains the nuclear material. The middle piece contains mitochondria and a tiny bit of cytoplasm, while the tail's function is to propel the cell forward.
Spina bifida- A birth defect where the spine fails to join together at the back, resulting in a gap that membranes and parts of the spinal cord may push through.
Spindle- A framework of fibres formed during the prophase stage of cell division.
Spongy bone- Porous bone tissue that contains many large spaces. Also known as cancellous bone.
Sprain- A ligament is torn from the bones. Blood vessels, muscles, tendons, ligaments and nerves may also be damaged. Symptoms include swelling, pain and discolouration due to ruptured blood vessels.
Stance phase- The phase of walking during which the leg starts to support the body weight. Also known as the supporting leg phase.
Starch- A long-chain carbohydrate that is found in cereals, wheat, rice, oat, corn, bread and certain vegetables such as potatoes, peas and dried beans.
Sternum- The breastbone.
Steroid- A type of lipid. Examples include cholesterol and the sex hormones.
Strain- Symptoms include a sudden pain and loss of power in the limb. Normally occurs when a muscle or tendon is overstretched.
Stratified epithelium- Epithelium with multiple layers of cells.
Stretch receptors- Sense organs located in the joints, ligaments and tendons that give the brain input regarding balance.
Striated muscle- Another name for skeletal muscles. The name comes from the appearance of the muscles when viewed under a microscope.
Stroke- Occurs when atherosclerosis affects the cerebral arteries, causing part of the brain tissue to die. Aside from blocked arteries, cerebral haemorrhage (bleeding at a weak point in one of the arteries), can cause strokes. Strokes range in severity from mild to severe.
Stroma- The connective tissue that ovaries are composed of. Surrounded by a layer of cells containing some germ cells.
Subclavian arteries- Arteries that take blood to the arms.
Submucosa- The second innermost layer of the alimentary canal. Contains glands and connective tissue, the latter of which contains blood vessels, lymph vessels and nerves. The small intestine submucosa has many folds, increasing surface area.
Substrates- Molecules that are involved in a reaction.
Sucrase- An enzyme in the intestinal juice that breaks sucrose down into monosaccharides.
Superior vena cava- One of the main veins of the body. Takes blood from the upper body to the right side of the heart.
Supporting leg phase- The phase of walking during which the leg starts to support the body weight. Also known as the stance phase.
Swinging leg phase- The phase of walking during which the leg swings forward.
Symphysis pubis- The cartilaginous joint joining the two pelvic bones together at the front.
Symptothermal method- A method of contraception involving elements of the rhythm method, the temperature method and the mucus method.
Synapsis- A process that occurs during the prophase stage of cell division. The chromosomes pair off, each pair appearing as four strands twisted together.
Synovial fluid- Fluid secreted by the synovial membrane. Lubricates the joint, provides nourishment for the cells of the articular cartilage, and carries phagocytic cells that remove microorganisms and debris resulting from wear-and-tear. Only a small amount of fluid is usually present, but if the joint is injured or inflamed, more fluid may be produced, resulting in swelling and discomfort.
Synovial joints- Joints with a relatively large range of movement. (Movement is, however, restricted by the shape of the bones.) Also known as freely moveable joints.
Synovial membrane- The inner layer of the capsule surrounding freely moving (synovial) joints. It consists of loose connective tissue with blood capillaries. The synovial membrane lines the entire joint cavity aside from the articular cartilages and the articular discs.
Synthesis- The process of building complex molecules by combining smaller ones.
Syphilis- An STD that affects many different areas of the body throughout the course of the disease. In the first stage, small sores appear, mainly on the sex organs but also on other parts of hte body. In the second stage, there are many possible symptoms, including rashes, mild fevers, sore or ulcerated mouth or throat and disorders of the bones or eyes. In the third stage, which may occur many years later, many tissues of the body are damaged, causing a variety of severe symptoms.
Systemic circulation- Circulation of blood throughout the whole body.

T

Talus- One of the tarsals. The only ankle bone to articulate with the fibula and tibia.
Tarsals- Ankle bones. There are seven in each ankle.
Tarsiers- A suborder within the primates. Only contains tarsiers.
Taxonomic Rank- The different levels of classification in Bloom's taxonomy (the system used for classifying all living matter).
Telophase- The final step of cell division. The two sets of chromosomes group together at opposite ends of the cell, nuclear membranes form around each group, a nucleolus appears in each new nucleus, the spindle fibres disappear, and the chromosomes uncoil to become chromatin threads again. The centrioles then duplicate, ready for the next division. The cytoplasm also begins to divide during telophase: a furrow appears between the two nuclei, which gradually deepens until the cell is split in two.
Temperature method- A method of contraception based on fluctuations in temperature surrounding ovulation.
Tendinitis- Inflammation of the tendon sheaths surrounding certain joints. Symptoms include swelling and pain upon movement of the affected joint.
Tendons- Fibrous, inelastic connective tissue that attach skeletal muscles to the skeleton.
Teratogenic agent- A chemical that causes physical defects in the developing embryo. Includes alcohol, thalidomide, heroin, LSD and many medicinal drugs.
Testis (plural: testes)- Male gonads in which the sperm is produced.
Testosterone- A sex hormone in males.
Thalassaemia- A genetic form of anaemia in which there are defects in the formation of the haemoglobin molecule. People with thalassaemia need frequent blood transfusions, as well as medication to remove the excess iron in their bodies.
Thoracic cavity- The area bounded by the ribs and diaphragm. Includes the lungs, heart, aorta, venae cavae, pulmonary veins and arteries, oesophagus, thymus gland and part of the trachea and bronchi.
Thoracic duct- A duct of the lymphatic system.
Thorax- The chest.
Thrombocyte- A type of blood cell that forms blood clots when blood vessels are damaged. Also known as a platelet.
Thymine- One of the nitrogen bases present in DNA (but is not present in RNA). Pairs up with adenine.
Tibia- The larger of the two lower leg bones.
Tics- Involuntary, spasmodic twitching of muscles.
Tidal volume- The amount of air that moves in and out with every regular breath.
Tissue fluid- Fluid found between cells in the tissues. Also known as interstitial fluid or intercellular fluid.
Trabeculae- An irregular arrangement of thin, bony plates. The spaces contain bone cells, nerves and blood vessels. Found in spongy bone.
Trachea- A tube around 12cm long and 2.5cm in diameter. Air travels through here to get to the bronchi in the lungs. Contains C-shaped bands of cartilage, which allow the trachea to be flexible without collapsing. Also contain cilia, which push mucus and other solids towards the pharynx, where they can then be swallowed.
Transfer RNA- A type of RNA that brings the amino acids to the ribosomes.
Transient ischaemic attack (TIA)- A cardiovascular disease that is like a stroke but shorter and less severe.
Transverse arch- The side to side arch of the foot.
Transverse colon- The section of the colon that goes from the person's right to their left.
Trapezius- Muscle that attaches scapula to axial skeleton. Allows us to move our shoulders in various ways (e.g. shrugging).
Tricuspid valve- The atrioventricular valve on the right side of the heart, so called due to its three cusps.
Triglyceride- A fat formed from the product of glycerol and three fatty acids.
Trisomy-21- A birth defect caused by having three of the chromosome number 21. Symptoms include mental retardation and malformation of the heart, ears, hands and feet. The risk increases as the mother reaches the end of her child-bearing period. Also known as Down Syndrome.
True ribs- Ribs directly attached to the sternum by some costal cartilage.
Trypsin- A digestive enzyme in the pancreatic juice that breaks down proteins into smaller peptide chains. Also known as pancreatic protease.
Tubal embryo transfer (TET)- A form of ART in which the eggs are fertilised in the lab. The resulting zygote is allowed to divide into the 2-cell to 4-cell stage before being implanted into the woman's uterine tubes.
Tubal ligation- A form of sterilisation in which a small piece of each uterine tube is removed and the cut ends are tied.

Year 11 Human Bio Glossary K - O

Other glossary sections: (A - E) (F - J) (P - T) (U - Z)

K

Karyotype- A photograph of all of the chromosomes displayed in order.

L

Labia majora- Two fleshy folds of skin located in the vulva. Comprised of fat and fibrous tissue.
Labia minora- Two smaller folds of skin located between and beneath the labia majora. Lack fat and are pinkish in colour. Surround the openings of the urethra, vagina and the clitoris.
Lactase- An enzyme in intestinal juice that breaks lactose down into monosaccharides.
Lacteal- A lymph capillary located in the villi.
Lactogenic hormones- Hormones secreted by the pituitary gland that affect the breasts of women. Important in milk production. Also known as prolactin.
Lacunae (singular: lacuna)- Spaces between the lamellae in compact bone. Contain bone cells.
Lamellae (singular: lamella)- A bony matrix consisting of bone cells as well as non-cellular material, including inorganic salts.
Laryngitis- Swelling of the mucous membrane covering the vocal cords, making it difficult for them to vibrate.
Larynx- An organ that connects the pharynx with the trachea. Also known as the "voice box" as it has a role in producing sounds.
Leucocytes- Blood cells that defend the body against invading microorganisms and remove dead or injured cells. They are white, hence their common name, white blood cells.
Leukaemia- An abnormal number of white blood cells are produced. These white blood cells fill the red bone marrow, inhibiting the production of the red blood cells, which can lead to anaemia.
Lipase- An enzyme in intestinal juice that breaks down lipids.
Lipids- Water-insoluble molecules stored in the body as energy reserves.
Liver- A rather large organ located just below the diaphragm on the right side of the body. It has many known functions, including blood glucose regulation, deamination, fat conversion, plasma protein production, production of blood-clotting factors, storage of various substances, toxin breakdown, hormone inactivation and heat production.
Lobes- Sections of the breast. There are around 15-25 per breast. Surrounded by fatty connective tissue.
Lobules- Sub-sections of the breasts. Surrounded by fatty connective tissue. The walls are made up of lots of glandular alveoli, which secrete milk. Lead into ducts, which open up into milk spaces, which then lead into short, straight ducts to the nipple.
Longitudinal arch- The front to back arch of the foot.
Longitudinal muscle- Muscle in which the muscle fibres are arranged along the length of something else (such as the alimentary canal).
Loose connective tissue- A type of connective tissue that supports and connects other tissues. Made up of fibres and cells in a semi-fluid matrix.
Lung cancer- Involves the development of a tumour, just like other cancers. Normally begins in the walls of the bronchi- excessive production of mucus is caused by irritation of the mucous membrane lining. Trapped mucus causes alveoli to rupture, resulting in emphysema. Eventually a cancerous growth develops in a bronchus and may spread to other parts of the body.
Luteinising hormone (LH)- A gonadotropic hormone secreted by the pituitary gland. In females, LH promotes final maturation of the ovarian follicle, ovulation and the formation of the corpus luteum. Less LH is secreted as progesterone levels rise. In males, LH stimulates ccells in the testes to secrete the hormone testosterone, which is important for sperm production.
Lymph- The fluid inside the lymph capillaries. Composition is essentially the same as tissue fluid.
Lymph capillaries- Small lymph vessels that eventually join up to form lymphatic vessels.
Lymph nodes- Nodes located along the lymphatic vessels that remove bacteria and foreign particles from the lymph.
Lymphatic system- The system that drains fluid from the tissues. Consists of lymph vessels as well as the lymphoid organs.
Lymphomas- Solid tumour masses formed from cells of blood and/or lymphatic origin.
Lymph vessels- Consist of the lymph capillaries, lymphatic vessels and other ducts of the lymph system. They are squeezed when surrounding muscles contract, pushing the lymph along. They have valves to ensure that the lymph only moves in one direction.
Lymphatic vessels- Lymph vessels that eventually join up to become even bigger lymphatic vessels, which then join in to the thoracic duct and the right lymphatic duct.
Lymphoid organs- The tonsils, thymus and spleen. Are involved in specific immune responses.
Lysosomes- Small membrane-bounded spheres formed by the Golgi apparatus. Contain digestive enzymes which break down material transported into the cell via vesicles as well as worn-out organelles.

M

Male pronucleus- The head of the sperm once it has entered the egg and had its tail absorbed.
Malignant neoplasm- An abnormal mass of tissue formed from the uncontrolled division of cells. Also known as a malignant tumour.
Malignant tumour- An abnormal mass of tissue formed from the uncontrolled division of cells. Also known as a malignant neoplasm.
Mammalia- A class (taxonomic rank) that includes warm-blooded hairy creatures that produce milk.
Mandible- The bone that makes up the lower jaw.  It is the only bone in the jaw with a moveable joint.
Matrix- The name for the intercellular material inside tissues.
Maxilla- The bone that forms the upper jaw, as well as part of the mouth, eye sockets and nasal cavities.
Mediastinum- The space between the two lungs.
Meiosis- A type of cell division that results in four haploid "daughter" cells. Used to form the gametes.
Melanocyte- A pigment cell.
Melanoma- A type of cancer that forms from melanocytes. Grow and spread very quickly.
Menarche- The time at which a woman first begins to menstruate. Normally between 9-16 years of age.
Menisci (singular: meniscus)-  Articular discs in the knee joint. Consist of fibrocartilage which extends inwards from the articular capsule.
Menopause- The time at which menstruation no longer occurs. Normally occurs around 35 years after menarche, between the ages of 40 and 50.
Menstruation- The expulsion of blood, mucous secretions and cell debris from the uterine lining through the vagina. Occurs roughly once every month.
Mesenteric artery- An artery that takes blood to the intestines.
Messenger RNA- A type of RNA used to transfer the genetic code from the DNA to the ribosomes.
Metabolism- The chemical reactions that take place within cells.
Metacarpals- Bones in the palm of the hand.
Metaphase- The second stage of mitosis. During this stage, the chromosomes line up on the equator of the spindle. The centromere of each chromosome is attached to a spindle fibre.
Metastasis- The process in which malignant cells spread to other parts of the body, forming secondary tumours.
Metatarsals- Foot bones.
Microfilaments- One of the structures of the cytoskeleton. Moves materials around the cytoplasm or moves the entire cell.
Microtubules- One of the structures of the cytoskeleton. Keeps organelles in place or moves them around the cell.
Microvilli (singular: microvillus)- Small projections located on the villi.
Minerals- Elements such as calcium, ion, iodine, zinc and fluorine that are necessary for the body. Different minerals have different functions within the body.
Mitochondria (singular: mitochondrion)- The energy centres of the cell. They have two membranes, which contain enzymes which are involved in energy-releasing cellular reactions. The inner membrane has a series of folds (which the outer membrane lacks), increasing the surface area for chemical reactions.
Mitosis- A type of cell division which results in two diploid "daughter" cells.
Molars- Teeth used for crushing and grinding (along with the premolars). The cusps on the crowns of the molars fit into the depressions of the crowns of the molars on the opposite site, making crushing and grinding more efficient.
Monosaccharide- Simple sugars (e.g. glucose, fructose, galactose) that only consist of one ring of C, H and O atoms. Can combine to form disaccharides or polysaccharides.
Monounsaturated fat- A fat in which there is only one double bond between carbon atoms.
Morula- A ball of cells formed from the zygote dividing. It is roughly the same size as the original zygote as no new cytoplasm is produced, but has many more nuclei due to the increased number of cells.
Mountain sickness- Higher altitudes contain lower pressure air (i.e. fewer gas molecules in the same amount of space as compared to lower altitudes). People who aren't used to the lower pressures may feel sick as their bodies are unable to absorb enough oxygen. Also known as altitude sickness.
Mucosa- The innermost layer of the alimentary canal. In the oesophagus, it secretes mucus, making it easier for the food to move through. In the stomach, it secretes gastric juice, which contains digestive enzymes, among other things. The stomach mucosa can also secrete mucus to protect itself from the hydrochloric acid in the gastric juice. The small intestine mucosa has many folds as well as finger-like projections called villi, increasing surface area. It also contains glands that secrete intestinal juice.
Mucus method- A method of contraception that relies on observing changes in the mucus of the cervix.
Muscle tone- The partial contraction of skeletal muscles.
Muscular dystrophy- Inherited diseases in which individual muscle cells degenerate. Leads to a progressive reduction in the size of the skeletal muscle, an increase in connective tissue and possibly the replacement of muscle fibres with fatty tissue. There are two forms: the Duchenne form and the fascioscapulohumeral form.
Muscular endurance- The ability of a muscle to contract repeatedly or sustain a contraction for an extended period of time.
Muscular strength- The force that a muscle group can exert against a resistance.
Muscle tone- The maintenance of partial contraction of muscles.
Mutagens- Agents that can increase the rate at which mutations occur (though do not cause mutations). Include mustard gas, sulfur dioxide, X-rays, radiation, and so on.
Myocardial infarction- A complete stop in blood flow to a part of the heart muscle, resulting in death of the muscle in that area. This causes sudden and severe chest pain. Can heal if only a small area is affected; adverse effects and death can also occur. Symptoms include chest pain, pain radiating to the left arm, shoulder, neck or jaw, sweating, breathlessness, faintness and palpitations. Also known as a heart attack.
Myofibrils- Thread-like structures found within the sarcoplasm.

N

Nasal cavity- The part of the nose inside the skull.
Neck (part of tooth)- The part of the tooth between the crown and the roots.
Net diffusion- The overall movement of particles along a diffusion gradient.
Neurons- Nerve cells.
Non-specific urethritis (NSU)- An infection of the urethra. Can be caused by the Chlamydia bacteria, though there are many other causes.
Nuclear membrane- The membrane surrounding the nucleus. It is actually a double membrane- two membranes separated by a space.
Nucleic acids- Molecules consisting of chains of nucleotides. RNA (ribonucleic acid) has one chain, while DNA (deoxyribonucleic acid) has two chains.
Nuclear pores- Gaps in the nuclear membrane which allow substances to pass through.
Nucleolus- An area in the nucleus that contains RNA, which plays a role in synthesising proteins.
Nucleoplasm- The fluid inside the nucleus. Suspended in it are chromatin threads and the nucleolus.
Nucleotide- A small molecule consisting of a nitrogen base, a sugar and a phosphate group. RNA (ribonucleic acid) has ribose sugar, while DNA (deoxyribonucleic acid) has deoxyribose sugar.
Nucleus- One of the organelles of the cell. Nearly all cells contain one, though some contain more, and some don't have a nucleus at all. It is the largest organelle, is normally oval or spherical in shape, and is surrounded by a nuclear membrane. The nucleus is often thought of as the "control centre" for the cell as it contains DNA (deoxyribonucleic acid), which determine which proteins and enzymes a cell can make, which then determine which chemical reactions can take place in the cell.

O

Oblique muscle layer- A layer of muscles in the stomach that provide the stomach with more ways in which it can churn the food.
Oestrogen- One of the sex hormones in females.
Olfactory receptors- Nerve endings located in the upper part of the nasal cavity. Are sensitive enough to distinguish different smells.
Oogenesis- The process in which ova are produced.
Oogonia (singular: oogonium)- "Egg mother cells." Diploid cells that will eventually divide to form ova. Millions are already present at birth.
Oophorectomy- Removal of ovaries.
Opposability- The ability of the thumb to reach across and touch the tips of the other fingers of the same hand.
Organelles- Small structures within the cell that carry out various functions.
Origin- The end of the muscle attached to the stationary bone.
Osmosis- The diffusion of water across differentially permeable membranes (e.g. the membranes of cells).
Osmotic pressure- The pressure caused by osmosis when solutes that can't pass through a differentially permeable membrane are added.
Osteoarthritis- A much more common, but much less damaging form of arthritis (as opposed to rheumatoid arthritis). It involves deterioration of the articular cartilage, causing bony spurs to develop from the ends of the bone forming the joint. Due to these spurs, the space in the joint is decreased, which in turn restricts the movement of the joint.
Osteoblast- Bone-forming cell that allows bones to repair themselves after a fracture. Stimulated when the bone is used for support and movement.
Osteocyte- Bone cell
Osteoporosis- A gradual reduction in the rate of bone formation while the rate of bone absorption remains normal. This results in the bones becoming porous, fragile and relatively easily broken.
Ova (singular: ovum)- The female gametes.
Ovarian cyst- A fluid-filled tumour in the ovary that is usually not cancerous.
Ovary- The organ in which ova are produced. They are located within the body, on either side of the pelvic cavity, and are supported by ligaments.
Oviduct- A tube that carries the ovum from an ovary to the uterus. Also known as the Fallopian tube or uterine tube.
Ovulation- The expulsion of an ovum from the mature follicle into the uterine tube.
Oxyhaemoglobin- A bright red compound produced when oxygen and haemoglobin combine.
Oxytocin- A hormone secreted by the pituitary gland. Causes the small muscles around the milk-filled lobules in the breast to contract, pushing milk through the openings on the nipple.