Circulatory Physiology - AP Biology

Erythrocytes and leukocytes are both produced and mature in bone marrow, with the exception of T cells, a type of white blood cell that matures in the thymus. Unlike leukocytes, red blood cells contain no nuclei or mitochondria, which could interfere with transporting oxygen, carbon dioxide, and nutrients.

Because Jack has blood type B, he will form antibodies against blood types A and AB, as they contain a foreign antigen that his body will reject. Furthermore, he cannot accept any blood types that are Rh+, as this antigen will also seem foreign to his body. He can thus only accept from the blood types B- and O- (the universal donor type).

Arteries carry blood away from the heart, while veins transport blood towards the heart. Because the pulmonary arteries transport blood from the right ventricle towards the lungs to exchange carbon dioxide for oxygen, they contain deoxygenated blood.

The aorta, however, transports oxygenated blood from the left ventricle to the rest of the body for circulation. The pulmonary vein carries oxygenated blood from the lungs to the left ventricle and the vena cavae return deoxygenated blood to the right atrium.

Arteries have thick, muscular walls that allow for constriction and flow direction, while veins have thin walls to carry blood.

Capillaries have extremely thin walls to allow exchange of oxygen, carbon dioxide, and nutrients with tissues, resulting in both oxygenated and deoxygenated blood in these vessels. Pressure in the arteries is always higher than in veins so that blood can be continuously pushed forward, negating the need for valves to prevent backflow. Such valves are present in veins and help to counteract gravity when returning blood to the heart.

Hemoglobin will have varying affinity for oxygen depending on its environment. For example, hemoglobin will have a very high affinity for oxygen in the lungs, where most oxygen is loaded onto the hemoglobin molecules. Once hemoglobin goes to the tissues of the body, there is a much lower oxygen tension. This decreased oxygen causes hemoglobin to have a lower affinity for oxygen and release the oxygen to the tissues.

Hemoglobin is comprised of two alpha and two beta proteins and uses iron to facilitate oxygen transportation. Some variations of hemoglobin, such as fetal hemoglobin, contain gamma proteins that changes the shape of the protein. Consistent with the theme that structure determines function, fetal hemoglobin has a higher affinity for oxygen than does adult hemoglobin. This is necessary since fetuses lack lungs; they obtain all of their oxygen from the hemoglobin of their mothers.

Capillaries are the smallest blood vessels, which allow transport of oxygen and other small molecules. There are capillaries involved in gas exchange in the lungs, but it does not involve transfer of oxygen to the cells. Rather, it involves uptake of oxygen by red blood cells from the air inside the alveoli, and removal of carbon dioxide from the blood into the air in the alveoli to be exhaled. All other blood vessels have walls that are too thick to allow transport of any substances across them. The heart is the muscular pump of the circulatory system, which provides the pressure required to drive blood flow.

As fluid moves through the capillary, the hydrostatic pressure decreases from the arteriole end to the venule end (fluid exits the capillary along the gradient). The osmotic pressure in the interstitium is relatively constant, and will be stronger than capillary hydrostatic pressure near the venule end. As a result, an increase in the interstitial osmotic pressure would cause less fluid to enter the interstitium, because there is less area in the bed where the capillary hydrostatic pressure is greater than the interstitial osmotic pressure.

The capillary is the site of fluid exchange with the body's tissues. This fluid transfer is moderated by two factors: hydrostatic pressure and osmotic pressure. Hydrostatic pressure is the "pushing" force on water due to the presence of more fluid in one region than another. In general, larger fluid volumes generate higher hydrostatic pressure. Osmotic pressure is the "pulling" force on water due to the presence of solutes in solution. Albumin proteins are the main source of osmotic pressure in capillaries, pulling water into the blood.

At the arteriole end of the capillary, the hydrostatic pressure is stronger than the interstitial osmotic pressure and fluid is forced into the interstitium. Osmotic pressure remains relatively constant over the length of the capillary, but hydrostatic pressure drops sharply as it nears the venule end due to the initial loss of fluid volume. At that point, the interstitial osmotic pressure becomes stronger than the capillary's hydrostatic pressure. This forces fluid back into the capillary.

Hydrostatic pressure is the force of the fluid volume against a membrane, while osmotic pressure is related to the protein concentration on either side of a membrane pulling water toward the region of greater concentration.

When fluid enters the capillaries, it is initially pushed out because the hydrostatic pressure pressing outward is greater than the osmotic pressure pushing inward. Although osmotic pressure stays constant throughout the capillary length, hydrostatic pressure decreases towards the venule end of the capillary. This makes the osmotic pressure larger than the hydrostatic pressure, and pushes the fluid back into the capillary.

Ocean water has a higher osmolarity (more units of solute per unit of solvent) than human blood. When James drank the ocean water, it was absorbed into his circulatory system and it pulled water from the cells. Water flows from an area of low osmolarity to an area of high osmolarity. When water was pulled from the cells, the fluid volume in James’ blood increased. As blood reached James’ kidneys, the extra fluid from the tissues was filtered into the urine and caused him to urinate more frequently.

When the body temperature is too high, peripheral vasodilation can help exchange heat from the body to the environment. Warm blood from the center of the body is pumped to the extremities, which have a high surface area. The surface area is used to allow the heat from the blood to dissipate before it returns to the center of the body.

Peripheral vasoconstriction and shivering help increase the body temperature. Hyperventilation have no noticeable effect on body temperature.

The venae cavae are the largest veins in the body. They return deoxygenated blood to the heart. The pulmonary veins bring oxygenated blood from the lungs to the left atrium. The pulmonary arteries bring deoxygenated blood from the right ventricle to the lungs to become oxygenated. The left ventricle hold oxygen-rich blood, and pumps it to the rest of the body. The left atrium is where freshly oxygenated blood is received via the pulmonary veins.

Capillaries are minute blood vessels that connect the arterial and venous systems. The walls of these vessels are extremely thin, allowing easy diffusion of gases, nutrients, and waste particles between the capillary and adjacent cells. Oxygen diffuses into cells from the capillary, and carbon dioxide diffuses into the capillary from the cells.

Vasoconstriction is a function of the smooth muscle that surrounds the vasculature. In order to reroute blood, the vessel needs to have a substantial amount of smooth muscle.

Arterioles have a relatively small diameter and a relatively large amount of smooth muscle. When contracted, this smooth muscle can obstruct the arteriole and route blood away from connected capillary beds. Capillaries do not have smooth muscle linings, and cannot constrict or reroute blood on their own. Arteries have a relatively large diameter; contraction of the surrounding smooth muscle can affect blood pressure, but will rarely be capable of rerouting the blood flow.

Veins contain a series of one way valves that prevent blood from flowing backwards. This is particularly important in larger veins in the legs that are further below the heart, and must oppose gravity to get blood back to the heart. Almost all of the blood pressure produced by the heart is lost along capillaries, thus the blood pressure in the veins is almost zero. Blood is "squished up" a little at a time due to the contraction of the skeletal muscles around veins and the presence unidirectional valves.

The vagus nerve is responsible for slowing down the heart rate, and is able to "override" the faster, natural pace of the sinoatrial node. When the vagus nerve is severed from the heart, the heart will pump at the pace of the SA node.

Note that innervation is not necessary for the heart to continue beating; it is self-sustaining, but can be affected by innervation from the vagus nerve.

The chordae tendinae (tendinous chords or heart strings) are physical structures located in the heart lumen that connect the muscular wall of the heart to the tricuspid and mitral valves via papillary muscles.

The other answer options are examples of cell bundles and tissues that orchestrate the electrical conduction through the heart. Signals begin at the sinoatrial node and transition to the atrioventricular node. They then pass through the atrioventricular bundle (or bundle of His) to the purkinje fibers, which coordinate simultaneous ventricular contraction.

The sinoatrial node is responsible for initiating the contraction of the heart. Depolarization of the sinoatrial node coincides with atrial contraction. The depolarization travels very quickly to the atrioventricular node during this period. The atrioventricular node delays the spread of the impulse, preventing it from triggering ventricular contraction. This time delay allows the atria to fill the ventricles with blood before the impulse causes the ventricles to contract. Without this delay, an inadequate amount of blood would be pumped from the ventricles.