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:

Maddscientist (thread moderator): Maddscientist is a Ph.D. student in developmental biology.

TheDarkSide: TheDarkSide has several years of experience working as a nurse. She scored 12 on the BS portion of the MCAT, and 37 overall.

Occasional moderator: Shrike. Shrike is a full-time instructor for The Princeton Review. His primary expertise is in other subjects; he knows just enough biology to have scored 12 on the BS section without ever having studied organic chemistry.

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[dreambig2night]

Are centrioles found only in animal cells?

and are vacuoles found on both plant and animal cells?

 

[kevin86]

sympa vs parasympa, please help

which is vasocontriction and which is vasodilation, or is it all differently.

 

[MollyMalone]

Are centrioles found only in animal cells?

and are vacuoles found on both plant and animal cells?

Yes and yes.

 

[MollyMalone]

sympa vs parasympa, please help

which is vasocontriction and which is vasodilation, or is it all differently.

Sympathetic constricts circulation to the skin and the GI tract while increasing circulation to the lungs and the skeletal muscle. Parasympathetic is the opposite.

 

[Krazykritter]

Easy and quick way to remember:

Parasympathetic = Restin & Digesting (aka increases circulation to the GI)...Think Homer Simpson sitting on the couch

Sympathetic = Flight or Fight mechanisms (bronchodilate, pupil dilation, increase circulation to skeletal m.)...Think here of Lance Armstrong on his bike

 

[Krazykritter]

This may be beyond MCAT, but;

Sympathetic you can think of as "Running from a bear through the woods at night"
This gives you the bronchodilation, pupil dilation, increase circulation to skin and skeletal m. etc.

Hope this helps

 

[kevin86]

yeah yeah this is where i am confused on, so when you increase your blood flow, do you constrict blood vessels or dialate them. and is it always the same?

 

[Krazykritter]

Increasing blood flow necessitates an increase in diameter (aka dilation) or an increase in pressure (however the body likes to keep this as constant as possible).

 

[kevin86]

so it depends then? ooh then how about a simpler question does epinepherine do anything to blood vessels, if not then which other sympathetic hormons does and how.

 

[MAXHARDC]

Testosterone is thought to have small role in stimulation of spermatogenesis by stimulating maturation of germ cells (this may be what the TPR book was referring to). FSH is, however, the major hormone that stimulates spermatogenesis. When FSH stimulates the Sertoli cells to both increase spermatogenesis and also increase the release of Testosterone and inhibin. The testosterone directly inhibits the Hypothalamus which releases the tropic hormone GnRH. GnRH is the hormone that causes the release of FSH & LH from the Ant. Pituitary. W/out FSH, you cannot produce sperm and thus become sterile.

Actually, HCG has been used successfully for treating infertility, in absence of FSH. There seems to be some debate on this very question within fertility medicine, by my readings. The usual protocol is a long (many months) course of HCG before adding in the HMG (FSH). Of course, it takes 80-90 days to get a swimmer (medical lingo) ready for his big trip.

Other studies show it is FSH operating in an environment of testosterone (via LH stimulation) which produces sperm.

Max

 

[MAXHARDC]

is this the right thread? Ok I have a question about testesterone. Since it inhibits FSH secretion, wouldnt it inhibit spermatogenesis? Like those body builders who took too much testesterone. But why does the TPR book and another book say it also facilitates spermatogenesis. Is there something I'm missing here?

Also the same goes for estrogen right, that it inhibits FSH, which inhibits ovary. Is that what happens in a birth control pill?

Just a bit confused.

Kevin,


The suppression is surely produced by the induced T. I am not aware that LH directly suppresses at the hypothalamus or pituitary. However, we are finding more and more sites where LH is bioactive, and this is also a good reason to use HCG throughout the steroid cycle in cases where LH production is reduced.

HCG is "to suppressive' only when itr is being administered while we are trying to recover the HPTA. Then it is, just as Androgel or 100mg pf test cyp per week would be. IOW, you cannot "hide" androgens from the HP.

DHT, Testosterone, Estrogen, Progestins, Prolactin, can all act on the HP negatively.

There are two potential feedback loops: a long loop and a short one. The long loop involves LH stimulating testosterone production, which along with estrogen suppress GnRH/LH production.

The short loop has LH or its synthetic analog hCG acting directly back on the hypothalamus to blunt GnRH, or acting on the pituitary to block LH production.


Max

 

[QofQuimica]

bump

 

[QofQuimica]

bump

 

[Lindyhopper]

The simplified schematic of the ANS neurotransmitters generally has the Sympathetic branch's preganglionic neuron releasing Ach & the postganglionic neuron releasing epine. or norepine.
In the parasympathetic both pre & postganglionic releasing Ach.
The somatic system relases Ach at the neuromuscular junction.

There are than a host of questions in which altering the levels of Ach effect the Parasym & somatic ONLY while changes in norepine. effect the sympathetic?

As the sympathetic NS also has a Ach mediated synpase why isn't it's function also mediated by changes in Ach?

 

[Wildstang]

What exactly is the point of the loop of henle?

Thanks.

 

[QofQuimica]

What exactly is the point of the loop of henle?

Thanks.

Please don't start new threads in the subforum. Just post your question in the appropriate question thread.

I don't really understand your question. The loop of henle is a part of the nephron and is involved with reabsorption of salts and water.

 

[anhu]

What is the difference between an absolute refractory period and a relative refractory period? At what points on the action potential graph do they occur? When are they over?

 

[Dr Durden]

The refractory period allows the voltage sensitive ion channels to restore their original polarity. The absolute refractory period of approximately 1 millisec is when the Na+ channels are open. This is the left half of the sharp upward peak on the graph. No new action potentials can be generated during this period. The relative refractory period occurs largely when the membrane is hyperpolarized (-80 mV), when the K+ channels are open and the Na+ channels are recovering in a random order. The action potential is more difficult to generate during this period because a greater stimulus is required to reach the threshold as opposed to the resting potential (-70 mV). On the graph, this is the dip immediately following the large spike. Yet it can also happen on the right half of the spike as well, but the closer in time to the peak voltage, the greater the stimulus required. These refractory period are both over after approximately 5 milliseconds.

 

[Lindyhopper]

Nice answer Dr. D, would you like to take a whack at post 114.

 

[akinf]

How important is human physiology (i think the same thing as organismal biology) on the mcat?

 

[QofQuimica]

How important is human physiology (i think the same thing as organismal biology) on the mcat?

This is a tough question to answer. Physiology is definitely not my strength either (yet, anyway!), so I spent quite a bit of time studying for it. I would say that it's advisable to make sure that you are comfortable with all of the AAMC topics in biology. If there are things on that list that you don't know, you should study them. That being said, you aren't in med school yet, and they don't expect you to know as much physiology as a med student does. So you don't have to have more than a basic understanding of each topic.

Lindy, I'm sorry, but I don't think any of us know the answer to your question. FWIW, it's definitely beyond the scope of the MCAT.

 

[H and D]

I am having some trouble deciphering passages that deal with kidney topics like Renal Clearance, renal plasma flow, glomerular filtration rate and filtration fraction. I have come across two passage like this so far (one in EK and one in an AAMC test). I have a lot of trouble even reading these passages and understanding what these terms mean.
I have spent a lot of time learning about the nephron and its anatomy plus different hormones that act on the nephron but my review books (like EK) do not cover these filtration rate type topics.
Does anyone know any good websites or references that simply, and comprehensively cover these topics?
I am really scared I will get a filtration passage on my MCAT and get 90% of these questions wrong.

Thanks so much!

 

[hopster]

I am having some trouble deciphering passages that deal with kidney topics like Renal Clearance, renal plasma flow, glomerular filtration rate and filtration fraction. I have come across two passage like this so far (one in EK and one in an AAMC test). I have a lot of trouble even reading these passages and understanding what these terms mean.
I have spent a lot of time learning about the nephron and its anatomy plus different hormones that act on the nephron but my review books (like EK) do not cover these filtration rate type topics.
Does anyone know any good websites or references that simply, and comprehensively cover these topics?
I am really scared I will get a filtration passage on my MCAT and get 90% of these questions wrong.

Thanks so much!

Are you using the EK 1001 bio book? I think this had a lot of questions about this kind of stuff.

 

[H and D]

Are you using the EK 1001 bio book? I think this had a lot of questions about this kind of stuff.

I do not have the EK 1001 bio book. Any other suggestions?

Thanks.

 

[googlinggoogler]

Hi, quick question. Is aldosterone release stimulated by ACTH (which stimulates adrenal cortex to release hormones) or angiotensin II (the renin cascade)??

 

[vtrain]

Hi, quick question. Is aldosterone release stimulated by ACTH (which stimulates adrenal cortex to release hormones) or angiotensin II (the renin cascade)??

both - however the major regulator of aldosterone secretion lies in the Renin-Angio system

 

[googlinggoogler]

both - however the major regulator of aldosterone secretion lies in the Renin-Angio system

great, thanks!

 

[seanth]

In the EK Bio book, they bolded and underlined a number of different dissacharides (sp?). I was just wondering, for the MCAT do we need to know which two monosacharides make up a particular dissacharide?

Thanks!

 

[Krazykritter]

I can't be sure, but I think I remember having a passage about Lactose on my MCAT that required me to know the constituents. This was a few years ago, but I do not think that it would be the type of thing that is out of the testing realm.

 

[harrypotter]

On my tests, I've seen lactose, sucrose, and maltose show up. I would memorize those. I took the test last August and lactose was a free standing question.

 

[4s4]

I'm having trouble linking effect of blood pressure on glomerular filtration rate. When the blood pressure increases, the parasympathetic system should be activated to decrease the blood pressure, and this may cause an increase or decrease in the GFR? My logic is that increased blood pressure usually means high blood V, so to increase blood V, you increase GFR? How exactly does GFR do this?

And when body temp is low, the sympathetic system is activated right? Thanks!

 

[harrypotter]

In a pedigree chart, how do you figure out if it's a domnant or recessive inheritance? My notes says to check if it skips generations but I have no idea what that means.

Thank you!

 

[4s4]

For recessive inheritance, usually the parents don't have the disease phenotype, but the children have it, so it "skips" a generation. But for dominant dominant inheritance, both the parents and children will have the disease phenotype.

 

[harrypotter]

Thanks 4s4 for the quick reply!!!

 

[wannaberockstar]

I have two questions:

1. Do the parasympathetic and sympathetic divisions of the autonomic system have both sensory and motor divisions? Because it seems books only talk about the motor (efferent) parts.

2. What hormones does the hypothalamus synthesize? I know it makes the posterior pituitary hormones, ADH and oxytocin, but what about the anterior pituitary hormones?

Thanks!

 

[grapeflavorsoda]

I have two questions:

1. Do the parasympathetic and sympathetic divisions of the autonomic system have both sensory and motor divisions? Because it seems books only talk about the motor (efferent) parts.

2. What hormones does the hypothalamus synthesize? I know it makes the posterior pituitary hormones, ADH and oxytocin, but what about the anterior pituitary hormones?

Thanks!

1)as far as i know, motor only.

2)ADH, oxytocin, GnRH, and other releasing hormones.
anterior makes their own hormones.

 

[Krazykritter]

I have two questions:

1. Do the parasympathetic and sympathetic divisions of the autonomic system have both sensory and motor divisions? Because it seems books only talk about the motor (efferent) parts.

2. What hormones does the hypothalamus synthesize? I know it makes the posterior pituitary hormones, ADH and oxytocin, but what about the anterior pituitary hormones?

Thanks!

1. Both sympathetic & parasympathetic nervous systems have an afferent (sensory) & an efferent (effector/motor) component.

2. First, you got the Post. Pituitary hormones correct (the post. pituitary is more or less a continuation of the hypothalamus caudally). The Ant. Pituitary is a gland in traditional sense. It secretes; GH (Growth Hormone), ACTH (Adrenocorticotropic Hormone), TSH (Thyroid Stimulating Hormone), Prolactin, & the Gonadotropins (LH & FSH).

I did not provide any detail to the first as your question did not see to need much.

 

[sj786]

Why is arterial blood pressure in legs greater than the arms?

 

[Heyeon]

In a pedigree chart, how do you figure out if it's a domnant or recessive inheritance? My notes says to check if it skips generations but I have no idea what that means.

Thank you!

From what i know, A recessive trait is carried genotypically through generations but wont appear phynotypically unless its homozygous..So when they say that the trait has skipped generations means tht its there in heterozygous form and hence not expressed phynotypically

 

[tracy34]

I have a really difficult time understanding how to tell whether a response is the results of sympathetic or parasympathetic autonomic nervous system activity. I am a biochem major and I never took a physiology class. The Examcrackers books says that sympathetic is "fight or flight" and parasympathetic is "rest or digest," but this is not very helpful.

 

[redsoxfan]

I have a really difficult time understanding how to tell whether a response is the results of sympathetic or parasympathetic autonomic nervous system activity. I am a biochem major and I never took a physiology class. The Examcrackers books says that sympathetic is "fight or flight" and parasympathetic is "rest or digest," but this is not very helpful.

well try to break it up into body parts:

Sympathetic Parasympathetic

blood flow to gut + kidneys decr incr
blood flow to skeletal muscles incr decr
iris dilate constrict
lung bronchioles dilate constrict
cardiac output incr decr
liver glycogen breakdown ----

hope these help

 

[Krazykritter]

Here is a really good way to remember Parasymp. vs Sympathetic:

Sympathetic = RUNNING FROM A BEAR IN THE WOODS AT NIGHT...Meaning you are going to have eyes dilating to see trees (mydriasis) + all your fight or flight responses of increased HR, vasodilation to muscles, & glycogenolysis. Also negative GI effects

Parasympathetic = Resting & Digesting...Pupillary constriction (miosis) increased GI function, & your SLUDE effects (Salivation, Lacrimation, Urination, Defecation & Emesis). So again, Parasympathetic is rest & digest + SLUDE.

P.S.--SLUDE may be beyond the scope of the MCAT.

 

[87138]

Kind of a dumb/basic question, but:

When bicarbonate (HCO3-) is present in tissues/blood in high amounts, is this considered alkalosis or acidosis? I would assume since it would act mostly as a base, that it would cause a pH increase? For some reason I keep mixing this up.

 

[sj786]

Look at the [H+] concentration only. if its increased then its acidosis, if its decreased its alkalosis.



I used to get confused about this a lot too. hope that helps

 

[tracy34]

Hey, thanks for the replies above about parasympathetic vs. sympathetic. They really helped. =)

Another topic that I'm shaky on is action potentials. I know that the resting potential of a neuron is always negative on the outside and positive on the outside, and a depolarized neuron will be positive on the inside and negative on the outside. I just have trouble understanding the proton pumps and exactly why pumping out three Na "protons" per two Potassium "protons" is creating the resting negative potential inside the cell.
Thanks again guys

 

[87138]

Hey, thanks for the replies above about parasympathetic vs. sympathetic. They really helped. =)

Another topic that I'm shaky on is action potentials. I know that the resting potential of a neuron is always negative on the outside and positive on the outside, and a depolarized neuron will be positive on the inside and negative on the outside. I just have trouble understanding the proton pumps and exactly why pumping out three Na "protons" per two Potassium "protons" is creating the resting negative potential inside the cell.
Thanks again guys

The "simple" answer is:

3 Na+ out = loss of "3"
2 K+ in = gain of "2"

Net loss of "1", which leads to an overall negative charge.

 

[sssddd]

new question please help very appreciated.

Under what conditions would the flow the Na/K pump be reversed, and why or how

Also with refractory periods, does it raise or lower the threshold, and how.

 

[QofQuimica]

new question please help very appreciated.

Under what conditions would the flow the Na/K pump be reversed, and why or how

Also with refractory periods, does it raise or lower the threshold, and how.

You mean to pump the ions in the opposite directions? I've never heard of that happening, but maybe one of the bio people can come up with an example. Refractory periods occur after an action potential, and they are a period when the neuron is not able to fire. Basically what is happening is that when the potassium leaves the cell through the potassium channels, the cell "overshoots" and becomes more negative on the inside with respect to the outside (hyperpolarized). So the threshold level itself does not move, but what does move is the place where you're starting from, which is now lower than the normal resting level. Take a look at this picture, and it should help you see what I mean. You will see that the refractory period level is in an energy "well," but the threshold is at the same level that it always was.

 

[MaximusD]

Why is arterial blood pressure in legs greater than the arms?

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

 

[QofQuimica]

bump