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.
Wednesday, July 1, 2015
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.
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.
Tuesday, June 30, 2015
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*
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*
Monday, June 29, 2015
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.
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.
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.
Friday, June 26, 2015
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).
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).
Thursday, June 25, 2015
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.
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.
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