W3006 Physiology Problem set #8 - Blood pressure regulation and atherosclerosis

1. An enzyme found in the liver catalyzes the rate determining step in the synthesis of cholesterol. If these people have a particular allele that produces a slow-working enzyme or an enzyme that does not work at all, they’ll produce less cholesterol. This in turn will reduce the down regulation of LDL receptors. The presence of these extra receptors will increase the amount of dietary cholesterol that will be absorbed form the blood.

2.a. decrease in cardiac output. Beta-1 receptors are the receptors on the heart for norepinephrine from the sympathetic nervous system. Norepinephrine will cause an increase in HR, and blocking the receptors will decrease HR and will lower the CO because CO= SV x HR

b.decrease in peripheral resistance – Nitric oxide causes local vasodialtation, an increase in the radius of the arterioles. Resistance is proportional to 1/r^4 so an increase in the radius greatly decreases peripheral resistance.

c. decrease in cardiac output. Aldosterone usually increases sodium reabsorption in the kidney. Here it is blocked by an antagonists, so less sodium will be reabsorbed, less water will follow, and the blood volume will decrease. The less blood entering the heart, the lower the stroke volume (Frank Starling law) and the lower the CO. CO= SVxHR.

Question 3. was on "Problem Set 7"

4. a

Questions 5. through 12. were on "Problem Set #7"

13.a

14. Y. Frank Starling Law -> The greater the heart muscle is stretched, i.e the greater volume of blood that enters, the stronger the contraction, and the greater the volume of blood ejected in one stroke.

15. A. Adrenal cortex. B. Cholesterol is needed there to synthesize steroid hormones such as cortisol. HDL may bring cholesterol to adrenal,

16. For this question, I expected students to include a summary of some of the mechanisms by which stress might increase the risk of heart disease or cancer, but to also consider this quantitatively, that is, the magnitude of the stress that results from steak-avoidance is probably not sufficient to cause the long-term ill effects we discussed.

17. decrease, decreases, sympathetic, arterioles, veins, increase

18.As in the veins, lymph from the foot is normally forced through the lymphatic vessels by pressure of the surrounding muscle contraction(as in exercise) which can be mimicked by external pressure (as in a massage).

19. decreases. decrease. Angiotensin-converting enzyme usually converts angiotensin I into angiontensin II. Angiotensin II acts on the arterioles to cause vasoconstriction (in addition to its role in increasing sodium reabsorption). Without angiontensinII, the radius of the arterioles will increase. Resistance is proportional to 1/r^4 (where r = radius), so an increase in radius cause a large decrease in resistance (or you could use R=(8*P*n*L)/(Pi*r^4). Since Blood Pressure = COxResistance a drop in resistance will also cause a drop in BP. Summary: Block ACE-> less angio II -> a larger radius-> lower resistance-> lower bp.

20. Not affected because Epinephrine receptors on the heart are Beta one receptor (not alpha–1 )

21. Possible answers include: could be one group of patients has poorer memory for food intake; sugar is often found in high fat foods (cakes, ice cream), and could be those eating much sugar are also eating much fat; those people eating those cakes and ice cream may also be smoking cigarettes afterwards; sample size is relatively small.

22. Usually 60% of the blood is stored in the veins. Body regulates amount in different regions by vasoconstriction. Usually some overall vasoconstriction, if suddenly have extensive vasodilation, the same amount of blood is now spread over a much larger space, leading to a decrease in blood pressure.

23. decreased. The increase in blood pressure is sensed by the baroreceptor in the carotid sinus, which sends a message to the medulla oblongata to relax arteriolar smooth muscle, and to decrease rate of the heart beat, both of which will lead to a decrease in blood pressure. These effects are dependent on increased parasympathetic activity, and decreased sympathetic activity.

24. (I didn't mention these receptors this year.) Muscarinic Receptors. Acetylcholine will combine with muscarinic receptors in the digestive system and on the heart. When Ach combines with heart receptors, the heart rate is lowered. Usually the release of ACh balances the effects of norepinephrine which would by itself increase HR. In nightshade poisoning, the heart rate can not be slowed because the Ach receptors are blocked. Ach acting through muscarinic receptors also aids digestion by for example increasing release of acid in the stomach. Here too this effect is blocked by the poison.