Physiology Questionnaire Regarding Circulation, Cells, etc

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1. Compare & contrast the structure, function, & roles of arterioles and veins in the regulation of circulation. Include their regulation by local factors, hormones, and the autonomic nervous system.

Veins are soft and thin walled since the pressure is steady. They collapse when empty but can expand easily and accommodate different volumes of blood. Arterioles are more muscular with one to three layers and little elastic tissue. Matched to the larger arties, they have thicker ratio of tunica media to lumen. Arterioles are the primary location of vascular resistance, also, large changes in blood pressure/velocity occurs at the location of transition between arterioles and capillaries.
For local factors, there are vasoactive chemicals such as histamine, bradykinin, and prostaglandins. There are also prostacyclin and nitric oxide that are secreted by blood rubbing against the endothelial cells (shear stress) which cause vasodilation. Reactive hyperemia results when a tissue’s blood supply is restricted for a period and then returned to normal. Three autonomic reflexes (baroreflexes, chemoreflexes, and medullary ischemic reflex) are integrated by the vasomotor center. For example, the baroreflex causes a negative feedback response to changes in the blood pressure. When glossopharyngeal nerve fibers transmit signals to the brainstem, it results in a reduced heart rate, cardiac output, and reduces the size of vessels. Chemoreflex responds to changes in the blood chemistry especially pH and concentrations of O2 and CO2.Their role is to adjust respiration and stimulate vasomotion. The medullary ischemic reflex responds to reduce perfusion of the brain checked by the medulla oblongata. If there is a drop in perfusion, within a matter of...

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...ers. This happens by promoting weakening of nerve cells in the hippocampus, which is vital for verbal and visual memory.

10. For the astronauts on the space station, where there is essentially zero gravity, what happens, if anything, to their circulation and blood pressure?

In space, there is a shift in fluid because the cardiovascular system does not have to work hard like it does on earth to fight gravity. Our bodies are equipped with several mechanisms to go against gravity to maintain a blood flow to our brains. When fluid moves up from legs to trunk of your body, the heart rate increases and pressure rises. Almost half of astronauts experience a ‘space sickness’ partially because of the circulation changes. Also, some studies show that in space red blood cells change to a more spherical shape and less inhabit bone marrow that when they are on Earth.

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