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*
Tuesday, June 30, 2015
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.
Tuesday, June 23, 2015
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 :(
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 :(
Sunday, June 21, 2015
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.
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.
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.
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