Resp. to Changes in Blood Volume & Pressure

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Resp. to Changes in Blood Volume & Pressure


Lecture number:
39
Pages:
8
Type:
Lecture Note
School:
University of Southern California
Course:
Bisc 307l - General Physiology
Edition:
2
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BISC 307L 2nd Edition Lecture 39 Current Lecture On left are the responses of the body to a decrease in blood volume and blood pressure. The most common causes of this are dehydration and hemorrhage. Decreased blood volume and blood pressure will boost cardiac output and the hypothalamus will stimulate a desire to find and drink water. The kidneys play a very important role as well because they can minimize water loss through the urine. The ultimate solution to the problem is drinking and getting more water. But the kidney can at least prevent further loss of water. It is not obvious from this diagram, but there are two different types of pressure receptors, or baroreceptors, in the body. They are in the carotid body and aortic body. They are referred to as the high pressure baroreceptors. But in addition to that, there are a set of low pressure baroreceptors. They are stretch sensitive nerves in the atria, the pulmonary vasculature, and the big veins. So these are highly compliant parts of the vascular system. And because these are low pressure, highly compliant parts, they tend to expand. So these low pressure baroreceptors are often called volume receptors. Whereas the high pressure baroreceptors are called pressure receptors. The reflexes that get activated when pressure is too high or low are one set – they overlap, but they are distinctive in other ways from the reflexes that kick in when blood volume is too high or too low, and these two sets of receptors is what sense those differences. Water Balance in the Body In order to not gain or lose water, the body has to be in water balance. You would gain 2.5 liters of water a day. Notes: 1 Not including intravenous infusion 2 Mostly from aerobic respiration (fuel molecules + O2  CO2 + H2O) 3 Not including diarrhea, vomiting So water input has to equal water output, and things need to be in balance. No matter how much water one drinks, we’ve already seen that a variable amount of plasma gets filtered into the kidneys. So way over 99% of that water has to be reclaimed. Most of that reclamation happens in the proximal tubule. A little more happens in the loop of henle and part of the distal tubule, which leaves the rest of the distal tubule and the collecting duct as the places that do the final adjustment of how much water is excreted from the body. Osmolarity Within Kidney This is a picture of the osmolarity within the kidney. Can see the juxtamedullary capillary with the long loop of henle, and as you know, the kidney has this osmotic gradient in it where the cortex and outer medulla have an osmolarity of about 300 mOs/M, which is about the same as blood. But as you go deeper away from the outer medulla, it gets more osmotically concentrated. It gets up to 1200 at the deepest part, due mainly to high concentrations of salt and ...


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