Download Answers to Mastering Concepts Questions

Answers to Mastering Concepts Questions
Chapter 32
32.1
1. The components of a circulatory system are a heart, blood, and vessels that transport the
blood throughout the body.
2. Vertebrates have closed circulatory systems, as do earthworms and mollusks. Most other
invertebrates have open circulatory systems.
3. Arteries bring blood away from the heart; veins return blood to the heart. Arterioles are smaller
branches of arteries; venules are smaller branches of veins. Capillaries link arterioles and
venules. They are the smallest blood vessels, which exchange substances with the surrounding
cells and interstitial fluid.
4. Vertebrate circulatory systems are closed.
5. The circulatory system of fishes has a single circuit in which a two-chambered heart pumps
blood to the gills, where the blood absorbs O2 and releases CO2. The oxygenated blood
circulates to tissues and then back to the heart to be pumped back to the gills. Amphibians and
most reptiles have a three-chambered heart that pumps blood separately in two circuits, one
going to the lungs and one going to other body tissues. Oxygenated blood from the lungs and
deoxygenated blood from the tissues mix in the single ventricle. The circulatory system of birds
and mammals features a four-chambered heart. Each side of the heart pumps blood separately to
the lungs (right side of the heart) or to the body tissues (left side of the heart).
32.2
1. Blood flows along this pathway: right atrium, right AV valve, right ventricle, semilunar valve, to
the lungs via the pulmonary artery, to the capillaries of the lungs, and then back to the heart via
the pulmonary veins. The pulmonary veins empty into the left atrium, from where blood passes
through the left AV valve, left ventricle, and semilunar valve, and then to the tissues via the aorta.
2. The heartbeat originates in the sinoatrial node. It spreads across the atria to the atrioventricular
node that sends an electrical signal to the ventricle walls.
3. Exercise affects the circulatory system in several ways. It strengthens the heart, increases its
cardiac output, allows it to pump out a greater volume of blood each minute, and allows it to
increase the rate at which it beats. Exercise can also cause extra blood vessels to develop within
the walls of the heart.
4. Exercise makes the heart beat faster first because during exercise, muscles squeeze against
the veins, returning blood to the heart more quickly. Stroke volume does not increase during a
single exercise session, so the only way to increase cardiac output would be to increase the rate
at which the heart beats.
32.3
1. Arteries, veins, and capillaries are similar in that all are blood vessels and all have an inner
layer of endothelial cells. Capillaries are the smallest vessels, consisting of only a single layer of
endothelial cells. Arteries and veins are much larger and differ in their functions, the thickness of
their layer of smooth muscle tissue, and in internal specializations. Arteries take blood away from
the heart, whereas veins bring blood to the heart. Arteries have a thicker wall of smooth muscle
than do veins. Large and medium-sized veins of the legs have venous valves that prevent
backflow of blood. When muscles squeeze on veins they help return blood to the heart. The force
of heart contractions moves blood in arteries.
2. Here is the path of blood from the heart to a capillary bed in the foot and back to the heart:
Aorta – femoral artery – artery to foot – arteriole – capillary bed in the foot – venule – vein from
foot – femoral vein – inferior vena cava – right atrium
3. Blood pressure and velocity are greatest in the largest arteries, and blood pressure is lowest in
the veins. Vessel diameter is smallest in the capillaries, but capillaries have the greatest crosssectional area, so blood velocity is lowest in the capillaries.
4. When blood pressure is too high, the autonomic nervous system will dilate arterioles in the skin
and decrease the heart rate. These have the net effect of decreasing blood pressure, bringing it
back to normal. In contrast, if blood pressure is too low, the arterioles in the skin will constrict and
the heart rate will increase, with the net effect of increasing blood pressure. In addition, the body
raises or lowers blood volume through control of the amount of fluid lost through the kidneys.
32.4
1. The following substances are dissolved in blood plasma: oxygen, carbon dioxide, other
dissolved gases, proteins, salts, wastes, nutrients, hormones
2. Erythrocytes (red blood cells) carry hemoglobin. Its function is to bind and release oxygen.
3. Red and white blood cells originate in red bone marrow.
4. The basis for the ABO and Rh blood groups in humans are molecules in the membranes of red
blood cells that cause blood to clump in the presence of antibodies in the blood.
5. Blood clots when a wound causes blood to escape from a vessel. As the vessel constricts,
platelets adhere to the wounded area, forming a plug that helps control blood loss. In the
meantime, exposure of blood to the surrounding tissue activates clotting factors that trigger clot
formation.
6. Blood clotting that is too slow will allow unnecessary bleeding, and wounds will heal slowly.
Blood clotting that is too fast will produce dangerous clots within the blood vessels.
32.5
1. Lymph is blood plasma that leaks out of capillaries.
2. Lymph capillaries absorb lymphatic fluid from tissues and send it on to lymph nodes. At lymph
nodes, white blood cells are added to the blood stream. In addition, lymphatic fluid is filtered in
lymph nodes, which remove bacteria and tissue debris. Eventually, lymph vessels empty
lymphatic fluid into the bloodstream in veins in the chest. The spleen is an organ of the lymphatic
system that destroys damaged red cells, filters and stores blood, and releases white blood cells.
In the thymus, T cells learn to distinguish body cells from foreign substances.
3. The blood and lymph circulatory systems work together to collect blood plasma that has leaked
from capillaries, clean it of bacteria and tissue debris, and return it to the bloodstream.