Organismal Biology/Physiology Thread

[QofQuimica]

All users may post questions about MCAT, DAT, OAT, or PCAT organismal biology (anatomy, physiology, development, embryology, and evolution) here. Cellular bio, molecular bio, and biochemistry questions should be posted in the other biology thread. We will answer the questions as soon as we reasonably can. If you would like to know what biology topics appear on the MCAT, you should check the MCAT Student Manual (http://www.aamc.org/students/mcat/studentmanual/start.htm)

Acceptable topics:
-general, MCAT-level biology.
-particular MCAT-level biology problems, whether your own or from study material
-what you need to know about biology for the MCAT
-how best to approach to MCAT biology passages
-how best to study MCAT biology
-how best to tackle the MCAT biological sciences section

Unacceptable topics:
-actual MCAT questions or passages, or close paraphrasings thereof
-anything you know to be beyond the scope of the MCAT

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If you really know your organismal biology, I can use your help. If you are willing to help answer questions on this thread, please let me know. Here are the current members of the Organismal Biology Team:

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[DiverDoc]

probably due to gravity's (or the acceleration of gravity's) direct relation to force. Recall fluid dynamics: P=F/A

The way I look at it is just the P is related (in this sense) to h the height of fluid above it.

 

[deleted92121]

What are positive and negative Modulators

Acid= H+ increase=low ph
Alkaline/Base=H+ decrease=high ph
..is this correct?

thanks,
dxu

 

[deleted92121]

could somebody please answer this quickly?

i'd appreciate it

dxu

 

[QofQuimica]

could somebody please answer this quickly?

i'd appreciate it

dxu

A few things:

1) Please do not start new threads in the MCAT subforum. You should post your question in the appropriate already existing thread.

2) I am a medical student, and thus, I am not on SDN 24-7 ready and waiting to answer questions the moment someone posts them in the subforum. I do log on every day, so your questions will generally be answered within 24 hours. But FYI, you should not expect to get a question answered right away unless you and I happen to be on at the same time. The same goes for all of the other subforum volunteers; this is a hobby, not our day job. We appreciate your patience and understanding on this issue.

3) Positive modulators are things that activate a receptor or enzyme. Negative ones then will do the opposite. Your analysis of acids versus bases and pH is correct.

 

[deleted92121]

A few things:

1) Please do not start new threads in the MCAT subforum. You should post your question in the appropriate already existing thread.

2) I am a medical student, and thus, I am not on SDN 24-7 ready and waiting to answer questions the moment someone posts them in the subforum. I do log on every day, so your questions will generally be answered within 24 hours. But FYI, you should not expect to get a question answered right away unless you and I happen to be on at the same time. The same goes for all of the other subforum volunteers; this is a hobby, not our day job. We appreciate your patience and understanding on this issue.

3) Positive modulators are things that activate a receptor or enzyme. Negative ones then will do the opposite. Your analysis of acids versus bases and pH is correct.

First off, I did not move this thread here, the mod did, so thank them. I posted it in the pre-osteopathic thread for the specific purpose of ppl are in there more than here and I didnt believe this to be the correct forum.

Secondly, I realize that you have other things and this is a hobby. I wasn't trying to pushy or impatient. I just had a test and was hoping someone that was looking at my post would answer it instead of just read it and not answer.

Lastly, thank you for the answer to my question. I appreciate it.

dxu

 

[QofQuimica]

First off, I did not move this thread here, the mod did, so thank them. I posted it in the pre-osteopathic thread for the specific purpose of ppl are in there more than here and I didnt believe this to be the correct forum.

Secondly, I realize that you have other things and this is a hobby. I wasn't trying to pushy or impatient. I just had a test and was hoping someone that was looking at my post would answer it instead of just read it and not answer.

Lastly, thank you for the answer to my question. I appreciate it.

dxu

You're welcome on both accounts. I apologize if my previous post sounded testy; it's just been a rough week.

 

[Chairman Natto]

Hey guys,

Where do B cells mature? I know that T cells mature in the thymus, but I can't find where B cells mature.

Thanks!

I got the text books for the protocols for creating artificial white blood cells. If you would like to discuss artificial white blood cells let me know. Its all about Cloned Lymphocytes that are produced outside of the body. (Ex-vivo production)

http://khalidnatto.tripod.com

 

[alex1231]

Where is a refractory period on action potential curve?
Is it on the repolarizaton or hyperpolarization?
Thanks

 

[alex1231]

I got it.
Here is a link for people who are interested:
http://www.mfi.ku.dk/ppaulev/chapter1/Chapter 1.htm

 

[QofQuimica]

Where is a refractory period on action potential curve?
Is it on the repolarizaton or hyperpolarization?
Thanks

Great link; thanks for posting it. For anyone who doesn't want to wade through an entire chapter, the short answer is that there are actually two refractory periods. One is during the action potential itself (absolute refractory period), and one is during the hyperpolarization phase (relative refractory period). During the absolute refractory period while the action potential is occurring, no further action potentials can be initiated. In other words, once the action potential begins, the cell cannot fire again until after that action potential is over. The relative refractory period occurs during hyperpolarization. During the relative refractory period, the cell can initiate a new action potential, but a greater than normal stimulus is required to do this. Both refractory periods are labeled in the figure below.

 

[QofQuimica]

bump

 

[lisichka]

,

 

[rcd]

Hi
i have a Q about a reflex arch. In the kaplan review notes, it is noted "the sensory neuron synapses with motor neuron in the spinal cord" i take it means that they directly synapse with each other with one synapse in between them. and the pic in the book is drawn to confirm this. just one direct synapse.

But in one of their quizzes they mention that in a reflex arch a minimum of 3 neurons must participate (i assume the 3rd one is interneuron in the spinal cord), meaning that there is discrepancy between the book explanation and the quiz.
may be there is a difference between a simple reflex arch and some other arch. hmmm?

what is really going on there? am i missing something? please help.
thank you very much

Kaplan is over-simplifying the reflex arch.

The fact as I see it is: you have your monosynaptic and polysynaptic reflexes.

Monosynaptic:

sensory -> motor neuron (this corresponds to what you quoted the Kaplan Review as saying first)

Polysynaptic:

sensory -> motor neuron 1
and
sensory -> motor neuron 2

Sorry, I can't draw these out well, but in polysynaptic (this corresponds to what Kaplan says about a min. of 3 neurons) the sensory innervates 2 motor neurons. The end result is recruiting two muscles to perform the reflex. Think: antagonistic muscle pairs.

I don't _think_ that other interneurons are present in the reflex arch, mainly because they don't provide much benefit -- reflexes are very simple and an organism needs them to be fast.

 

[lisichka]

.

 

[rcd]

but how do we know whether they mean poly or mono synaptic when they are asking about the arch? they just ask what is true about the arch--> minimum 3 neurons is their answer.?

Not my problem . MCAT questions will be more clear.

BTW, my diagram for the polysynaptic reflex arc is wrong. There's always at least one interneuron thrown in the mix for polysnaptic arcs.

 

[rcd]

repost. repost. repost. whoops

 

[commuter9]

Some passages in the respiratory tract do not participate in gas exchange; these passages are known as physiological dead space. Compared to air in the alveoli, air in the physiological dead space will have:

A. a higher partial pressure of carbon dioxide and oxygen.
B. a higher partial pressure of carbon dioxide and a lower partial pressure of oxygen.
C. a lower partial pressure of carbon dioxide and a higher partial pressure of oxygen.
D. the same partial pressure of carbon dioxide and oxygen.

The answer is C. The explanation says that the physiological dead space is not involved in gas exchange. This means that the composition of air in the dead space is virtually identical to that of atmospheric air.

Why? I mean why wouldn't the answer be D since no gas exchange is happening. I don't exactly see why we can treat it like air outside the body.

 

[estairella]

Why? I mean why wouldn't the answer be D since no gas exchange is happening. I don't exactly see why we can treat it like air outside the body.

*scratches head* Well, it is air from outside the body, and because no gas exchange is occurring, it hasn't changed from "outside-air". That's the best explanation I can provide... unless you can explain in more detail why you think the answer should be D? First of all, you can eliminate D completely because you know that alveoli DOES participate in gas exchange (in contrast to dead space air). Therefore your above reasoning is wrong from the start.

 

[endofevangelion]

Since all bacteria lack mitochondria, do all of them make 2 ATP per glucose via glycolysis? What about those aerobic bacteria? I mean since some have electron transport chains, and oxygen, which is very high in electron affinity, shouldn't they make more ATP than the amount from glycolysis?

This was confusing to me because I was doing one of the kaplan qbank problems and it stated that bacteria can only make 2 ATP per glucose

 

[commuter9]

*scratches head* Well, it is air from outside the body, and because no gas exchange is occurring, it hasn't changed from "outside-air". That's the best explanation I can provide... unless you can explain in more detail why you think the answer should be D? First of all, you can eliminate D completely because you know that alveoli DOES participate in gas exchange (in contrast to dead space air). Therefore your above reasoning is wrong from the start.

hey trozman...thanks for the help. what you said totally made sense. my reasoning was just off. i was thinking since to exchange was happening that the partial pressure of oxygen and CO2 should be the same (i wasn't comparing it to the alveoli, but i see that even if i was thinking that my answer would still be wrong).

 

[lisichka]

double post sorry

 

[5moreminutes]

Can someone please explain me the concept behind this. I am totally confused about how hypotonicity and hypertopnicity relate to these

thanks

 

[awk]

Glucose is a charged molecule so it can't pass through the cell membrane on its own. Normal cells have facilitated proteins to carry Glucose across their membrane. Intestinal and Kidney cells have Na+/Glucose symporters which concentrate glucose inside the cells, using the energy provided by cotransport of Na+ ions down their electrochemical gradient (meaning its energentically favorable for Na+ to leave the cell. When it does it "powers" in a glucose.

 

[CATallergy]

*scratches head* Well, it is air from outside the body, and because no gas exchange is occurring, it hasn't changed from "outside-air". That's the best explanation I can provide... unless you can explain in more detail why you think the answer should be D? First of all, you can eliminate D completely because you know that alveoli DOES participate in gas exchange (in contrast to dead space air). Therefore your above reasoning is wrong from the start.

Even though no gas exchange is occuring, how do we know that the air contents have not previously been dissolved? Couldn't it be either on the way in or on the way out? Where is this air? Maybe this question is based on a last-in-first-out argument, and that the last air of each breath is inspired and expired before reaching alveoli?

 

[amestramgram]

Since all bacteria lack mitochondria, do all of them make 2 ATP per glucose via glycolysis? What about those aerobic bacteria? I mean since some have electron transport chains, and oxygen, which is very high in electron affinity, shouldn't they make more ATP than the amount from glycolysis?

This was confusing to me because I was doing one of the kaplan qbank problems and it stated that bacteria can only make 2 ATP per glucose

That statement is an overgeneralization from Kaplan

There are bacteria that can carry out photosynthesis, and make 30 or so ATP per glucose

There are others who can carry a proton gradient, and make 30 or so ATP as well

However, there are also those unfortunate bacteria who can only make 2ATP per glucose; they are called anaerobic.

Glucose is a charged molecule so it can't pass through the cell membrane on its own. Normal cells have facilitated proteins to carry Glucose across their membrane. Intestinal and Kidney cells have Na+/Glucose symporters which concentrate glucose inside the cells, using the energy provided by cotransport of Na+ ions down their electrochemical gradient (meaning its energentically favorable for Na+ to leave the cell. When it does it "powers" in a glucose.

no glucose is not a charged molecule. It never is. It just takes the potential energy of the sodium concentration gradient to build up a glucose concentration gradient higher in the cell than outside.

 

[awk]

Since all bacteria lack mitochondria, do all of them make 2 ATP per glucose via glycolysis? What about those aerobic bacteria? I mean since some have electron transport chains, and oxygen, which is very high in electron affinity, shouldn't they make more ATP than the amount from glycolysis?

This was confusing to me because I was doing one of the kaplan qbank problems and it stated that bacteria can only make 2 ATP per glucose

Bacteria don't lack mitochodria, they ARE mitochondria in theory. Remember they can produce proton gradients and ETCs on their outer membrane and run ATP pumps just like mito can. They are running 32-36 ATP/Glucose like you are.

 

[awk]

no glucose is not a charged molecule. It never is. It just takes the potential energy of the sodium concentration gradient to build up a glucose concentration gradient higher in the cell than outside.

I meant to say POLAR molecule....but the same principle applies. It can't cross a membrane on its own.

 

[HippocratesX]

"Hyper" means there is more solutes inside the cell then outside the cell, "Hypo" means there is less inside the cell then its environment....therefore, in membrane transport, things like to go DOWN the electrochemical gradient from a region of high concentration or charge, to low. If those molecules cannot pass thru to the lower concentration side, then water will move in to the high concentration side (water is still going down its electrochemical gradient).

In regular active transport, you are moving molecules AGAINST the electrochemical gradient (using ATP). In SEcondary active transport (co-transport) however, you are using the ATP to create the electrochemical gradient that you desire (high---> low), instead of moving molecules against their gradient. So in co-transport, you use the ATP to make the molecule go in the direction of high to low electrochemically.

So I'm not sure if this answers your question? Am I even correct in my thinking? Anyone please correct me if I'm wrong?

Can someone please explain me the concept behind this. I am totally confused about how hypotonicity and hypertopnicity relate to these

thanks

 

[BrokenGlass]

"Hyper" means there is more solutes inside the cell then outside the cell, "Hypo" means there is less inside the cell then its environment....therefore, in membrane transport, things like to go DOWN the electrochemical gradient from a region of high concentration or charge, to low. If those molecules cannot pass thru to the lower concentration side, then water will move in to the high concentration side (water is still going down its electrochemical gradient).

In regular active transport, you are moving molecules AGAINST the electrochemical gradient (using ATP). In SEcondary active transport (co-transport) however, you are using the ATP to create the electrochemical gradient that you desire (high---> low), instead of moving molecules against their gradient. So in co-transport, you use the ATP to make the molecule go in the direction of high to low electrochemically.

So I'm not sure if this answers your question? Am I even correct in my thinking? Anyone please correct me if I'm wrong?

Secondary active transport does NOT use ATP directly but takes advantage of a previously existing electrochemical gradient. So the transport of one solute AGAINST its electrochemical gradient is coupled to the transport of another solute DOWN its electrochemical
gradient.

Primary active transport uses (energy of) ATP directly.

 

[HippocratesX]

BrokenGlass, thanks for clearing that up!! Makes alot more sense now; the term 'co-transport'.

 

[HippocratesX]

The way I look at it is just the P is related (in this sense) to h the height of fluid above it.

Right...so...is in the blood vessels, the fluid (blood) is moving, ....so does the equation for resting fluid pressure (P = density x gravity x height) apply to this situation where the fluid is moving also? So, if you take a point in the tube below another point in the tube (lets say P2 is at a lower height), then its pressure would be P2 + P1?

note: the original question asked why the blood pressure in the legs is higher than the pressure in the arms

 

[gridiron]

Right...so...is in the blood vessels, the fluid (blood) is moving, ....so does the equation for resting fluid pressure (P = density x gravity x height) apply to this situation where the fluid is moving also? So, if you take a point in the tube below another point in the tube (lets say P2 is at a lower height), then its pressure would be P2 + P1?

note: the original question asked why the blood pressure in the legs is higher than the pressure in the arms

Hey! If you are considering only pressure, and neglect the concept of a moving fluid or medium, then the pressure will be greater in the legs compared to the arms--this has to do with the concept that pressure is proportional to a change in height. However, when you are considering a moving fluid you have to use Bernoulli's equation to explain pressure differences, height differences or velocity differences. Bernoulli's equation only applies to ideal fluids. Blood isn't an ideal fluid, but to explain the pressure differences, Bernoulli's equation is useful. Bernoulli's equation is derived from the conservation of mechanical energy for fluids. On the MCAT, one term will always cancel when you are using/dealing with Bernoulli's equation (velocity, pressure or height). If we consider the case of a tube with the same diameter throughout, the velocity changes are negligible. So, you are dealing with only pressure and height changes. Let's reverse the question you have at hand and consider the pressure changes as the height increases. According to Bernoulli's equation:

P1 + rho*g*h1 = P2 + rho*g*h2 (when velocity changes are negligible)

As the height increases, h2 > h1. In order to satisfy the proportion, what happens to one side must be balanced on the other. So, P1 > P2. I hope this helps and good .

 

[KnuxNole]

2 questions concerning the reproductive system

1) How much detail should I pay attention to in studying the menstrual cycle? I know that understanding the hormonal levels for each stage is essential, but do I have to know the names of each stage and what happens at each part?

2) Can someone explain briefly the steps of oogenesis. I tried reading the EK explanation, but it is a bit confusing.

Thanks.

 

[BrokenGlass]

2 questions concerning the reproductive system

1) How much detail should I pay attention to in studying the menstrual cycle? I know that understanding the hormonal levels for each stage is essential, but do I have to know the names of each stage and what happens at each part?

2) Can someone explain briefly the steps of oogenesis. I tried reading the EK explanation, but it is a bit confusing.

Thanks.

Try this http://forums.studentdoctor.net/showpost.php?p=2890315&postcount=4

 

[KnuxNole]

Thank you for posting that link. I didn't realize someone already explained it on this same thread, but it was a clear description.

 

[minsoox1983]

I do not understand why would the bp in the pulmonary artery not influence the oxygenation of blood. More blood pumping to the pulmonary artery will mean a faster O2/CO2 exchange. Isn't it ?

Here's the question I am struggling.
Thanks for your help!


Q.Which of the following factors will NOT influence the oxygenation of blood in the pulmonary circulation?

A) Rate and depth of breathing

B) Hemoglobin concentration of the blood

**C) Blood pressure in the pulmonary artery
A, B and D are incorrect because the oxygen level in the blood would be increased by rapid turnover of air in the lungs, by high hemoglobin content, which would increase the carrying capacity of the blood, and by increased surface area of the alveoli, which would allow for more rapid loading of the blood with oxygen. The pressure of the blood flowing to the lung should not in itself affect the oxygen content, so option C is the best answer.

D) Surface area of the alveoli

 

[MSTPbound]

...Here's the question I am struggling.
Thanks for your help!


Q.Which of the following factors will NOT influence the oxygenation of blood in the pulmonary circulation?

A) Rate and depth of breathing

B) Hemoglobin concentration of the blood

**C) Blood pressure in the pulmonary artery
A, B and D are incorrect because the oxygen level in the blood would be increased by rapid turnover of air in the lungs, by high hemoglobin content, which would increase the carrying capacity of the blood, and by increased surface area of the alveoli, which would allow for more rapid loading of the blood with oxygen. The pressure of the blood flowing to the lung should not in itself affect the oxygen content, so option C is the best answer.

D) Surface area of the alveoli

You pose a good question; if I got this question, I would have chosen C by eliminating choices A, B, and D.

...More blood pumping to the pulmonary artery will mean a faster O2/CO2 exchange. Isn't it ?

I don't think so (someone who knows better will probably respond...)... higher blood pressure will lead to greater cardiac output... greater peripheral resistance against circulation. Whether this would increase the exchange rate of O2/CO2 doesn't seem to intuitively follow as a result.

Rate of gas exchange would be a function of surface area available for differential gas exchange, partial pressures of the gases on each side of the membrane and, of course, chemical considerations (i.e. hemoglobin content of blood). Differences in pulmonary arterial pressure probably wouldn't directly affect any of these factors.

If I'm wrong, or missing something, hopefully someone will correct soon... otherwise, hope this helps!

 

[BrokenGlass]

I do not understand why would the bp in the pulmonary artery not influence the oxygenation of blood. More blood pumping to the pulmonary artery will mean a faster O2/CO2 exchange. Isn't it ?

Here's the question I am struggling.
Thanks for your help!


Q.Which of the following factors will NOT influence the oxygenation of blood in the pulmonary circulation?

A) Rate and depth of breathing

B) Hemoglobin concentration of the blood

**C) Blood pressure in the pulmonary artery
A, B and D are incorrect because the oxygen level in the blood would be increased by rapid turnover of air in the lungs, by high hemoglobin content, which would increase the carrying capacity of the blood, and by increased surface area of the alveoli, which would allow for more rapid loading of the blood with oxygen. The pressure of the blood flowing to the lung should not in itself affect the oxygen content, so option C is the best answer.

D) Surface area of the alveoli

The pulmonary artery is a blood vessel carrying oxygen-poor blood from the right ventricle (one of the heart's pumping chambers) to the lungs to be oxygenated. Higher blood pressure in the pulmonary artery doesn't automatically mean more blood will reach the lungs per unit time.

For example, blood pressure in the pulmonary artery could increase due to constriction (narrowing) of the pulmonary capillaries, which means
there is more resistance to blood flow. This increased resistance puts a strain on the right ventricle, which now must work harder than usual
to move enough blood (NOT an increased amount of blood) to and through the lungs per unit time. This would increase pressure in the pulmonary artery, but the amount of blood reaching the lungs will be the same. So if the same amount of blood reaches the lungs per unit time, oxygenation of blood will not be influenced.

But it's definitely easier to answer this question by eliminating answer choices A, B, and D.

 

[minsoox1983]

Thanks for your explanations ! It has been very helpful and easy to understand!

I have some questions about the osmotic pressure.
1) I do understand the artery-capillary-vein system but I 'm not sure about the blockage in the vein resulting in the fluid flowing into interstiatial spaces.
2) How do osmotic and hydrostatic pressure differ and how do they work in the capillary system ?

hydrostatic vs osmotic.. they're all pressure of the solvent.. isn't it ?


3) Would you be able to clarify the explanation below please?

Thanks!


Question. Capillaries in the kidney and elsewhere in the body maintain fluid homeostasis by balancing hydrostatic and osmotic pressures. Which of the following is the initial effect of a blood clot forming on the venous side of a capillary bed?

**A) Net fluid flow in the direction of interstitial spaces will increase.
After introducing the idea of fluid homeostasis, which is obtained by balancing hydrostatic and osmotic pressures, the question asks the examinee to predict the consequences of a blood clot on the venous side of a capillary bed. To answer this, it is necessary to know that blood flows from arteries to capillaries and then to veins. If flow is blocked at the venous side, blood would accumulate in the capillaries. Thus, hydrostatic pressure would build up in the capillaries, causing a net increase in fluid flow into the interstitial spaces. A is therefore correct. B is incorrect because there will be an increase in net fluid flow into the interstitial spaces, not a decrease. C is not the best answer because the increase in osmotic pressure in the capillaries would be an indirect result of the fluid flow out of the capillaries. D is incorrect because the flow of fluid out of the capillaries would slightly increase, not decrease, the osmotic pressure. Thus, A is the best answer.

B) Net fluid flow in the direction of interstitial spaces will decrease.

C) Capillary osmotic pressure will increase.

D) Capillary osmotic pressure will decrease.

 

[HippocratesX]

osmotic pressure is not really pressure at all. Its just easier to think of it as a type of pressure intuitively, that "sucks in" or pulls into the liquid, instead of the liquid pushing against the material/surface that's enclosing the liquid(which is the normal type of pressure we know, ie..hydrostatic pressure)

So basically the only place where nutrient and gas exchange take place (besides the lungs) is in the capillaries and not across arterioles or venules. This happens by 4 possible methods, 1. pinocytosis, 2. diffusion , 3. movement thru pores in the cells called fenestrations, 4. movement thru the space between cells . As blood flows into a capillary, hydrostatic pressure is greater than osmotic pressure. So this means that the force is pushing out of the capillaries and into the interstitium. This hydrostatic pressure takes a nose-dive drop from the arteriole end to the venule end. So during that area where hydrostatic pressure is very low (toward the venule side of the capillary), the osmotic or "sucking-in" pressure overcomes the hydrostatic pressure and so the net result is that the fluid is sucked into the venules and to the veins in circulation. So the nutrients/gas/fluid is exchanged from a pushing in to the interstitium space through hydrostatic pressure (ie..delivery is made) and a sucking-out of the capillaries by osmotic pressure (trash is taken out). So this is how the pressure stuff works to exchange materials in the arteries/capillaries/veins.

Also remember that the net result of fluid exchange by the capillaries is a 10% loss of fluid to the interstitium. You can remember this by knowing what the purpose of the lymph system is, which is to collect and return excess interstitial fluid back to the blood after it recycles it by passing the excess fluid thru the lymph nodes. The other purpose of the lymph system is to moniter the blood for infection, but that's another story...

So then it follows that when there is a blood clot on the venule side of the capillary....there is a build up of fluid in the capillary. This causes more fluid to be pushed into the interstitium by hydrostatic pressure. The osmotic pressure will also increase, but only to try and balance this extra fluid that's being placed into the interstitium by the hydrostatic pressure, due to the blood clot.

 

[minsoox1983]

ok.. so let me rephrase what you said..

in arteriole-capillary, the hydrostatic is greater than the osmotic pressure.. therefore the blood is pushing out to the interstitial space..

in capillary-venule the there is only osmotic pressure present, therefore sucking contents into the venule..

so.. can i call the hydrostatic pressure is the pressure exerted by the blood exerting to the wall of artery vessels, and the osmotic pressure as the pressure of the interstitial fluid (outside) ?


Thank you!

 

[BrokenGlass]

Thanks for your explanations ! It has been very helpful and easy to understand!

I have some questions about the osmotic pressure.
1) I do understand the artery-capillary-vein system but I 'm not sure about the blockage in the vein resulting in the fluid flowing into interstiatial spaces.
2) How do osmotic and hydrostatic pressure differ and how do they work in the capillary system ?

hydrostatic vs osmotic.. they're all pressure of the solvent.. isn't it ?


3) Would you be able to clarify the explanation below please?

Thanks!


Question. Capillaries in the kidney and elsewhere in the body maintain fluid homeostasis by balancing hydrostatic and osmotic pressures. Which of the following is the initial effect of a blood clot forming on the venous side of a capillary bed?

**A) Net fluid flow in the direction of interstitial spaces will increase.
After introducing the idea of fluid homeostasis, which is obtained by balancing hydrostatic and osmotic pressures, the question asks the examinee to predict the consequences of a blood clot on the venous side of a capillary bed. To answer this, it is necessary to know that blood flows from arteries to capillaries and then to veins. If flow is blocked at the venous side, blood would accumulate in the capillaries. Thus, hydrostatic pressure would build up in the capillaries, causing a net increase in fluid flow into the interstitial spaces. A is therefore correct. B is incorrect because there will be an increase in net fluid flow into the interstitial spaces, not a decrease. C is not the best answer because the increase in osmotic pressure in the capillaries would be an indirect result of the fluid flow out of the capillaries. D is incorrect because the flow of fluid out of the capillaries would slightly increase, not decrease, the osmotic pressure. Thus, A is the best answer.

B) Net fluid flow in the direction of interstitial spaces will decrease.

C) Capillary osmotic pressure will increase.

D) Capillary osmotic pressure will decrease.

http://www.dlt.ncssm.edu/core/Chapt...ies/Chapter12-Animations/OsmoticPressure.html

Osmosis always moves a solvent from a less concentrated solution to a more concentrated solution. As osmosis proceeds, hydrostatic
pressure builds up on the side of the membrane where volume has increased. Ultimately, this pressure prevents more solvent from entering
and osmosis stops. The osmotic pressure of a solution is the difference in hydrostatic pressures between two sides of a U tube with a
semi-permiable membrane at a point in time where osmosis stops. This should give you some intuition about osmotic pressure.

We can think of blood vessels as semi-permeable membranes (i.e. fluid can move across the membrane, but solutes cannot).

Ventricles pump blood away from the heart and pressure due to ventricular pumping drops as blood flows further away from the heart.
The portion of the path taken by blood as it moves away from the heart is arteries -> arterioles -> capillaries -> venules -> veins.
So blood pressure generated by ventricles is higher on the arterial side than on the venuos side of capillaries. The osmotic pressure is pretty
much constant across the entire length of a capillary (because the solute concentration gradient is pretty much constant across the
entire length of a capillary).

In this problem the effect of hydrostatic pressure is to try to force fluid out of the capillaries and the effect of osmotic pressure is to try
to force fluid into the capillaries.

It turns out that hydrostatic pressure is higher than osmotic pressure on the arterial side of the capillaries, but hydrostatic pressure is lower than osmotic pressure on the venous side of the capillaries. So fluid is forced out of capillaries and into interstitial space (i.e. space between the cells) on the arterial side and fluid is forced into capillaries from interstitial space on the venuos side of the capillaries.

As stated by the solution, if blood flow is blocked at the venous side, blood would accumulate in the capillaries. Thus, hydrostatic pressure would build up in the capillaries, causing a net increase in fluid flow into the interstitial space.

It's easier for fluids than for solutes to move across blood vessels. So due to net increase in fluid flow into interstitial space, osmolarity (i.e. total solute concentration) in the capillaries relative to interstitial space rises (because fluid is leaving while solutes are staying). So the flow of fluid out of the capillaries would increase the osmotic pressure slightly because the solute concentration gradient (which points from the interstitial space into the capillaries) increases slightly.

 

[googlinggoogler]

"If chromosomal duplication before tetrad formation occured twice during spermatogenesis, while the other steps of meiosis proceeded normally, which of the following would result from a single spermatocyte?"

Answer: 4 diploid sperm

I got confused by this question because I do not completely understand the definition of "diploid/haploid" and "2N/N". I think in this situation, each resulting sperm will contain two sister chromatids. However, since these sister chromatids are identical, would they be considered diploid or haploid?

In my book describing meoisis, it says that in telophase I, "the cell divides into two daughter cells, each of which receives a nucleus containing the haploid number of chromosomes." I imagine the sperm produced in the question stem would look like the result of a normal situation where telophase I takes place (chromosomal duplication did not occur twice). Therefore, the book calls two sister chromatids "haploid." But this question from AAMC cbt 9 calls it "diploid." What's going on?

 

[BrokenGlass]

"If chromosomal duplication before tetrad formation occured twice during spermatogenesis, while the other steps of meiosis proceeded normally, which of the following would result from a single spermatocyte?"

Answer: 4 diploid sperm

I got confused by this question because I do not completely understand the definition of "diploid/haploid" and "2N/N". I think in this situation, each resulting sperm will contain two sister chromatids. However, since these sister chromatids are identical, would they be considered diploid or haploid?

In my book describing meoisis, it says that in telophase I, "the cell divides into two daughter cells, each of which receives a nucleus containing the haploid number of chromosomes." I imagine the sperm produced in the question stem would look like the result of a normal situation where telophase I takes place (chromosomal duplication did not occur twice). Therefore, the book calls two sister chromatids "haploid." But this question from AAMC cbt 9 calls it "diploid." What's going on?

2N means diploid (i.e. the cell has homologous chromosomes). N means haploid (i.e. the cell has NO homologous chromososmes).

Cell cycle consists of interphase and meiosis (or mitosis). Interphase consists of G1, S, and G2. G1 is growth phase 1, S is DNA synthesis
(a.k.a. DNA replicaion), and G2 is growth phase 2.

Under normal conditions, before a cell enters meiosis its DNA is replicated once. If before DNA replication the cell is diploid, then after
DNA replication the cell is still diploid. It has twice the amount of chromosomal material but the same number of chromosomes. Before
replication each chromosome looks like half of a butterfly, but after replication each chromosome looks like a full butterfly. Since the
number of centromeres before replication is the same as the number of centromeres after replication, the number of chromosomes doesn't
change.

In meiosis I, homologous chromosomes are separated from each other (reduction division, i.e. from diploid to hapoid).
In meiosis II, sister chromatids are separated from each other.
So under normal conditions, spermatogenesis (meiosis of spermatogonium) produces 4 haploid sperm cells.


Now, if DNA were replicated TWICE before a cell enters meiosis, 4 diploid cells would be produced.

This could be of some use: http://www.lewport.wnyric.org/jwanamaker/animations/meiosis.html

Try single stepping through this animation and meiosis should be clear to you: http://www.stolaf.edu/people/giannini/flashanimat/celldivision/meiosis.swf

And last but not least: http://www-rcf.usc.edu/~forsburg/meiosis.html

 

[googlinggoogler]

Thanks so much for giving me such a nice explanation. This question has been bugging me for a long time. Unfortuneatly, I still feel confused. I think I understand meosis pretty well. What I have trouble with is the vocabulary.

In normal meoisis, after S phase, you get a tetrad (a row of two full butterflies). However, in the AAMC question, the DNA is duplicated twice. Thus, you get a row of four full butterflies. After the meosis I, you get two full butterflies per cell. After meosis II, you get one full butterfly per sperm. (a "butterfly" is two sister chromatids held at the centromere)

Therefore, in my mind, the answer to this AAMC question is 4 sperm, each sperm containing a full butterfly (2 sister chromatids held at the centromere). Am I wrong? AAMC calls this "diploid."

However, if you follow this link:
http://www.phschool.com/science/biology_place/biocoach/images/meiosis/mediagr.gif
Look at the second row down, accross from the caption that says "two haploid cells with each chromosome still consisting of two chromatids." Doesn't this picture call two sister chromatids held at the centromere "haploid"?

So, do you see the discrepancy I see? AAMC calls 2 sister chromatids held at the centromere "diploid" while this picture calls the same thing "haploid." If there is something I am not understanding, please let me know. I'd really appreciate it. Thanks

 

[BrokenGlass]

Thanks so much for giving me such a nice explanation. This question has been bugging me for a long time. Unfortuneatly, I still feel confused. I think I understand meosis pretty well. What I have trouble with is the vocabulary.

In normal meoisis, after S phase, you get a tetrad (a row of two full butterflies). However, in the AAMC question, the DNA is duplicated twice. Thus, you get a row of four full butterflies. After the meosis I, you get two full butterflies per cell. After meosis II, you get one full butterfly per sperm. (a "butterfly" is two sister chromatids held at the centromere)

Therefore, in my mind, the answer to this AAMC question is 4 sperm, each sperm containing a full butterfly (2 sister chromatids held at the centromere). Am I wrong? AAMC calls this "diploid."

However, if you follow this link:
http://www.phschool.com/science/biology_place/biocoach/images/meiosis/mediagr.gif
Look at the second row down, accross from the caption that says "two haploid cells with each chromosome still consisting of two chromatids." Doesn't this picture call two sister chromatids held at the centromere "haploid"?

So, do you see the discrepancy I see? AAMC calls 2 sister chromatids held at the centromere "diploid" while this picture calls the same thing "haploid." If there is something I am not understanding, please let me know. I'd really appreciate it. Thanks

You were doing fine until you started talking about meiosis II. Remember that in meiosis II, you are separating sister chromatids (i.e. making half butterflies out of full butterflies). You are NOT separating homologous chromosomes in Meiosis II.

So for instance, suppose you have a pair of homologous chromosomes "A" and "a". Each of them is a half butterfly before replication. After 2 rounds of replication, you have "A", "A", "a", "a", and each of them is a full butterfly.

After meiosis I, you have 2 cells, one containing "A", "A" and the other containing "a", "a." Each of these 2 cells is diploid and all chromosomes are still full butteflies. Remember that meiosis I separates homologues.

After meiosis II, you have 4 cells, two of which contain "A", "A" and the other two contain "a", "a." Each of these 4 cells is diploid (there are 2 centromeres in each cell). Each chromosome is now half a butterfly. Remember that meiosis II separates sister chromatids.

I hope it's clear now why AAMC calls these cells "diploid."

In the picture you posted (i.e. under normal conditions, i.e. one round of replication), the cells are haploid because homologues separate in meiosis I and each of 2 resulting cells gets 1 chromosome (for simplicity we consider 1 pair of homologous chromosomes going through meiosis; as you know, it's actually 23 pairs of homologous chromosomes in humans, so after meiosis I each cell would get 23 chromosomes, and each of these 23 chromosomes would be a full butterfly).

So again, consider just a single pair of homologous chromosomes going through meiosis. To tell diploid from haploid count number of centromeres. 1 centromere means haploid (N), 2 centromeres means diploid (2N).

Full butterfly vs. half butterfly represent amount of chromosomal material, they should not be used to tell diploid from haploid.

 

[googlinggoogler]

awesome! Thank you so much BrokenGlass!

 

[minsoox1983]

I keep getting simple math question wrong. Can anyone clarify me the explanation below please ? What do they mean by different kinds of haploid ? Do they mean like.. ABC, AbC, Abc, ABc, BAC, BaC, BAc, Bac, ACB, AcB, ACb, Acb..etc ? with that method i found 12 ?



Question. Consider an organism that has three pairs of chromosomes, AaBbCc, in its diploid cells. How many genotypically different kinds of haploid cells can it produce?

A) 4
**B) 8
The number of different possible gametes that can be formed by diploid organisms as a result of independent assortment of chromosomes during meiosis can be calculated using the formula 2^n where n is the haploid number of chromosomes. In this case, the haploid number is 3, making the number of different haploid cells 23, or 8. Thus, B is the best answer.

C) 16
D) 32


Thanks in advance,

 

[BrokenGlass]

I keep getting simple math question wrong. Can anyone clarify me the explanation below please ? What do they mean by different kinds of haploid ? Do they mean like.. ABC, AbC, Abc, ABc, BAC, BaC, BAc, Bac, ACB, AcB, ACb, Acb..etc ? with that method i found 12 ?



Question. Consider an organism that has three pairs of chromosomes, AaBbCc, in its diploid cells. How many genotypically different kinds of haploid cells can it produce?

A) 4
**B) 8
The number of different possible gametes that can be formed by diploid organisms as a result of independent assortment of chromosomes during meiosis can be calculated using the formula 2^n where n is the haploid number of chromosomes. In this case, the haploid number is 3, making the number of different haploid cells 23, or 8. Thus, B is the best answer.

C) 16
D) 32


Thanks in advance,

You are on the right track, but you are double counting. For instance, ABC and BAC are the same genotype. Basically, you are counting
permutations, but you should be counting combinations. With combinations, the order doesn't matter. Don't write out all the possibilities because that's too time consuming. Instead, realize that you have AaBbCc and you need a genotype with 3 chromosomes. So for chromosome 1 one can you choose a or A, for chromosome 2 you can choose b or B, and for chromosome 3 you can choose c or C. So the "base" is number of choices for each chromosome and the "exponent" is the number of chromosomes the genotype needs.

2*2*2 = 2^3 = 8.

 

[minsoox1983]

You are on the right track, but you are double counting. For instance, ABC and BAC are the same genotype. Basically, you are counting
permutations, but you should be counting combinations. With combinations, the order doesn't matter. Don't write out all the possibilities because that's too time consuming. Instead, realize that you have AaBbCc and you need a genotype with 3 chromosomes. So for chromosome 1 one can you choose a or A, for chromosome 2 you can choose b or B, and for chromosome 3 you can choose c or C. So the "base" is number of choices for each chromosome and the "exponent" is the number of chromosomes the genotype needs.

2*2*2 = 2^3 = 8.

thank you! now i see that ABC and BAC are same.. wasn't sure if the order didn't matter..

hey
thank you!