Questions for review (submitted by you) and their answers. These are not all of the questions, but they are the ones which I thought were not as straightforward (in terms of answers). So, if you submitted a question to which you really wanted to know the answer, and do not see it listed here, please feel free to contact me. I will be available Monday through Thursday (before the exam). It's probably best to make an appointment so that I will be expecting you and won't be occupied with something else when you come in.

1. In digestion, when food molecules are endocytosed, are the vesicles containing these molecules marked for transport to specific organelles the way secretory vesicles are marked? In endocytosis of food particles it would not be likely that this marking would occur if the components are a random mix. However, in the endocytosis of a specific group (eg proteins binding to a cluster of receptors) there would be some form of marking to ensure that the proteins could reach their destination. There is evidence that antibodies are endocytosed (especially in nursing animals who receive antibodies from their mother's milk) as well as the digestive enzyme trypsin (for re-use).
2. Do lipid soluble hormones ever have an amplification system? Lipid soluble hormones do not have the same amplification systems that are used by lipid insoluble hormones. However, amplification does occur. When the receptor-hormone complex is bound to the promoter of a specific gene, it causes more than one copy of mRNA to be produced (first round of amplification). Each mRNA can then be used as a template for translation (protein production) about ten times. (second round of amplification)
3. Is estrogen the only chemical (hormone) required for bone formation, and if so, how does it bind calcium? There are many hormones required for bone formation: Calcitonin, growth factors, growth hormone, vitamin D (calciferol). Additionally, parathyroid hormone helps maintain plasma calcium levels by removing calcium from the bones. There is a great deal of research to try to determine what role estrogen plays in deposition of calcium to the bones and why it seems to be more important in women than men.
4. Since estrogen is required (at least in women) for calcium deposition, wouldn't hormone replacement therapy reduce or slow the effects of calcium depletion and osteoporosis? Yes, it would. However, there is still a great deal of debate about the side effects of hormone replacement therapy and whether or not it may be linked to an increased risk of some forms of cancer. So, the very best defense is to consume plenty of dairy products (including my favorite, ice cream!) before and after menopause so that the bone is does not become depleted.
5. When exercising, why are you supposed to breathe in through your nose and out through your mouth? How is this related to heating incoming air and cooling the body? As air is breathed in the nose, it is warmed and humidified: two necessary conditions to ensure the best exchange of gases at the respiratory surface. Breathing out via the mouth will increase the loss of both heat and moisture. While one does not necessarily want to lose fluids, it is better than letting heat build up while you exercise. This is why it is important to drink plenty of fluid while exercising: it allows the necessary cooling processes (loss of fluid via sweat and exhalation) to maintain proper body temperature. Additionally, if severe dehydration occurs, one's circulatory fluid would become hyperosmotic.
6. What is the function of the juxtaglomerular apparatus and why does it have different types of cells? Just like everything else in physiology, a structure/function relationship exists here. The function of the JGA is to sense pressure and osmotic changes in the blood. If the pressure or osmolarity is too low, the JGA secretes renin that will eventually cause the release of aldosterone. The three cell types each have a different function. The extraglomerular mesangil cells (or juxtaglomerular cells) sense pressure changes and release renin. The granular (or lacis) cells synthesize and release renin. The macula densa senses the concentrations of sodium and chloride by monitoring their transport rate.
7. How often and under what stimuli are male sex hormones released? They are released every couple of hours in response to pulses of LH, which is released by pulses of GnRH. There really is not a definite pattern to the secretion of male hormones, as there is with female. In general the levels of testosterone are 25% higher in the morning than they are in the evening.

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