Question

An average adult has approximately 5L of blood. Because there is not enough blood to for equal distribution to all tissues simultaneously, blood flow is continuously redistributed to more active tissues.

1. Identify a specific organ in which blood supply remains relatively unchanged despite changes in activity level.
2. Describe the effect of exercise on vascular homeostasis.
3. Describe the mechanism by which the body attempts to restore homeostasis when an abdominal aortic aneurysm ruptures. Be sure to include the stimulus, effector, target organs, and effect.

Answer 1

A] Exercises and high levels of activity have a direct effect on the blood flow through the body. There is an increase in blood flow to the skeletal muscles, lungs, heart, brain and even the skin, while the blood flow to the gastrointestinal tract and kidneys decreases. One organ system which remains relatively unaffected by the level of activity is the reproductive system. So, blood flow to the uterus will remain relatively unaffected by the level of activity.

B] Exercises increase heart rate and blood flow at the beginning but then slowly homeostasis takes over and the cardiovascular system stabilizes. Autoregulation or the local control of vasodilation and vasoconstriction is achieved by chemical signals and the myogenic response. Also, to accomodate the increased metabolic activity in the skeletal muscles the circulatory system has to control the transport of oxygen and CO2, as well as help to buffer the pH level of active tissues. All this is achieved by balancing the blood pressure, heart rate and blood flow through the body.

C] An abdominal aortic aneurysm [AAA] is an enlargement of the aorta at the level of the abdomen. The aorta is the largest vein and carries pure blood out of the heart, branching to supply blood to all the body parts. If the aortic aneurism bursts then it can be life threatening. A ruptured aneurism can cause massive internal bleeding. If the bleeding continues there will be a sharp drop in the blood pressure. In response to this, the blood vessels will begin to constrict and the clotting mechanism of the blood will be activated. Since the blood flows at high pressure in the aorta, bleeding will occur at a fast rate, giving very little time to the body to bring a blood pressure homeostasis and in the formation of clot at the rupture site. This is why almost 80% of the people with a AAA rupture die before any medical aid can be given to them or do not survive surgery even if they reach the hospital.