Answers Problem Set #8
1. Pressure on neck exerts pressure on carotid sinus where baroreceptor is located. This increases firing rate of afferent neuron to cardiovascular center in medulla oblongata, which in turn, sends more parasympathetic stimulation to the SA node and the heart rate decreases.
2. a 3. c 4. b
5. Framingham: Longitudinal (long-term) study: Advantages: see development of disease over time in same individual. All people here lived in same geographical area, so environmental and ethnic variables were minimized. Disadvantage: takes long time, expensive. Can't see effects of diet and race, since group was so homogeneous. Seven Countries (crosscultural) Advantages: get results more quickly, probably more representative of "people in general". Disadvantages: use of several cultures mean that the variable of interest (dietary fat intake) is confounded with other varialbes (genetic differences, climate, stresses, etc). Also, this looks at current behavior only, and it's possible that what's important is what people ate 10-20 years before they developed the disease, which can't be ascertained from this study.
6. A. They were interested in the effect of dietary lipid on behavior. Had they varied lipids over a small range, say, 300 to 500 mg/day, they would have had to study the animals for a very long time, or to use a lot of animals, before they could expect to see statistically significant results. By using extreme categories, they're more likely to see an effect, especially when the effect is small. (Also, the Framingham study had found that there was no relationship between dietary fat and heart disease in a population where there were only small variations in fat content, while the Seven Countries study had found tht larger variations in fat content were related to development of heart disease. B. Not necessarily. Could be that there are species differences and monkeys but not humans become more aggressive when cholesterol is low. However, it's hard to draw such conclusions without additional information: How old were the monkey? (turns out they were juveniles, and data from young animals may not be applicable to adults, even in the same species) What were the endpoints that were used as measurements of "aggression"? (Behavior patterns of aggression differ in different species, and turns out that for the monkeys, the researchers used "amount of time spent sitting near another animal" as an indication of how friendly/aggressive the subjects were.) How was the sample of Finns selected? What other dietary/climatic/social factors affected the behavior of this group of humans? (Note: This question was actually referring to a research article that the students read last year.)
7. Hemophiliacs are missing one or another of the clotting factors. Apparently Plonie and Almonie are missing different factors, so in a testtube, Plonie 's blood has the factor that Almonie is lacking (and vice versa) so the blood clots.
8. The clotting factors are synthesized by the liver. Dysfunctional liver may produce insufficient clotting factors and damaged blood vessel will not have the clotting factors, prothrombin, fibrinogen needed for the process of clot formation.
9. Increase. Activation of these neurons by high blood pressure normally causes heart rate to decrease. Cutting these neurons will prevent further stimulation of the medulla, and cause heart rate to increase.
12.The rate of flow of fluid in a tube is inversely proportional to the Resistance, or directly proportional to the radius to the 4th, so a small increase in r will lead to a large increase in blood flow. So even a small decrease in blockage of arteries would lead to a large increase in blood flow through the coronary arteries.
13. Pressure of exercising muscles ==> compresses veins==> increase blood returning to heart ==> increase EDV ==> increase stretch on muscle ==> increase force of contraction ==> increase stroke volume. (following Frank-Starling law of the heart)
14. Usually, standing up causes a sudden decrease in blood pressure, sensed by baroreceptors, which send messages to the medulla oblongata, which in turn send messages via sympathetic neurons to arterioles and veins, constricting them, and to the heart, increasing its heart rate and stroke volume. All this leads to a reversal of the falling blood pressure. These messages are conveyed by sympathetic neurons, which release norepinephrine from their terminals. With DBH deficiency, there is a decrease in the ability to rapidly reverse this fall in blood pressure and the person feels dizzy because there is less blood flow to the brain.
15. a. 16. a