Circulatory System - AP Biology

The left ventricle is responsible for pumping blood to all body tissues. Because it needs to pump blood a farther distance than the right ventricle (which pumps blood to the lungs), it requires a thicker myocardial wall. This provides it with a more powerful contraction in order to send blood throughout the body. The left ventriclar wall is approximately three times thicker than the right ventricular wall.

The atria generally have the thinnest myocardium, as they are only responsible for receiving blood and transferring it to the ventricles.

A centrifuge will organize a solution into distinct sections, separating them based on their density. The least dense sections will rise to the top, while the most dense compounds will settle at the bottom. Plasma is the least dense section, so it will rise to the top section in the tube. It will be followed by the buffy coat, and the dense red blood cells will settle at the bottom of the tube.

Plasma is composed mostly of water and proteins. The buffy coat contains most white blood cells and platelets.

The foramen ovale is needed to shunt blood away from the lungs, which are still developing in the fetus. The ductus venosus connects the umbilical vein to the inferior vena cava, while the ductus arteriosus connects the pulmonary artery to the aorta. The pulmonic semilunar valve is used in developed circulatory systems between the right ventricle and the pulmonary artery.

When blood enters the heart from systemic circulation, it is first collected in the right atrium. It then passes through the tricuspid valve into the right ventricle. To understand where the blood travels next, we must remember that this blood is deoxygenated after its passage through the body; it must pass to the lungs for oxygenation. It does so by entering the pulmonary arteries, which carry the blood away from the heart to the lungs. The pulmonary veins later return the oxygenated blood to the left side of the heart.

The major function of heart valves between the chambers of the heart is to restrict blood flow to one direction. This unidirectional flow prevents backflow and mixing of blood between chambers. This allows blood to deliver nutrients and oxygen to the peripheral tissues, return carbon dioxide to the lungs, become reoxygenated in the lungs, and maintain the circulatory system cycle without traveling backward at any point in the process. The patterns of valve opening and closing ensure that the contraction of a chamber will only expel blood in one direction, rather than allowing it to exit from both opening in the chamber.

The amount of pumped blood, also known as cardiac output, is controlled by the strength and rate of heart contractions. Since the heart valves are not constructed from muscle, they are unable to contract and propel blood. The valves are passive structures composed of connective tissue.

The atria and ventricles of the heart are separated by two valves, one on each side of the heart. The left atrium and left ventricle is separated by the mitral valve, also known as the bicuspid valve. The right atrium and right ventricle is separated by the tricuspid valve, named for its three flaps that work together to form the valve.

The semilunar valves separate the aorta from the left ventricle and the pulmonary artery from the right ventricle. They are commonly called the "aortic valve" and "pulmonary valve."

The right atrium receives blood that is returning to the heart from the body. The vena cavae are responsible for collecting the blood from the rest of the body and depositing it in this heart chamber. The superior vena cava collects blood from the head and upper extremities, while the inferior vena cava collects blood from the lower trunk and lower extremities.

The aorta is the artery that exits the left ventricle to deliver blood back to the body's tissues. The carotid artery carries blood to the head; the left branch is derived from the aorta, while the right branch is derived from the brachiocephalic artery.

The left ventricle is the chamber responsible for pumping oxygen-rich blood throughout the entire system, as opposed to the right ventricle, which only pumps oxygen-poor blood to the lungs. This requires the cardiac muscle that makes up the walls of the left ventricle to be much thicker, and thus stronger, than that of the rest of the heart chambers.

The coronary arteries supply blood to the heart. These vessels wrap around the heart muscle. Heart attacks often occur when these blood vessels become clogged, thus inhibiting blood flow to the heart, resulting in necrosis of cardiac cells. Note that the blood in the chambers of the heart is not involved in any nutrient exchange within the heart, rather, it must be pumped through capillaries where blood can supply nutrients to cells.

The right side of the heart contains oxygen-poor blood. The right atrium receives oxygen-poor blood from the body through the superior and inferior vena cavae. This blood then flows into the right ventricle and then out the pulmonary valve into the lungs where the blood becomes oxygen-rich. The oxygen-rich blood goes to the right atrium then to the right ventricle where it is pumped to the system to provide oxygen to the cells of the body.

Oxygen-poor blood leaves the heart towards the lungs via the pulmonary arteries and returns oxygen-rich blood from the lungs to the heart via the pulmonary veins. Any blood vessel that transports blood away from the heart is an artery. Any blood vessel that transports blood towards the heart is a vein.

There are four valves in the heart. The tricuspid valve separates the right atrium from the right ventricle. The pulmonary valve separates the right ventricle from the pulmonary arteries. The bicuspid valve separates the left atrium from the left ventricle. The aortic valve separates the left ventricle from the aorta. These valves separate the chambers of the heart, and prevent back flow from one chamber to the other. The tricuspid valve is also known as the right atrioventricular valve, and the bicuspid valve is also known as the left atrioventricular valve, and the mitral valve.

Blood flows from the vena cavae into the right atrium, then into the right ventricle through the tricuspid valve. From here, blood is pumped into the pulmonary artery through the pulmonary semilunar valve. Oxygen-rich blood returns to the left atrium via the pulmonary veins. Blood flows from the right atrium into the right ventricle through the bicuspid valve. From the left ventricle, blood is pumped into the aorta, through the aortic semilunar valve.

The heart is composed of cardiac muscle. This is the only location in the entire body that contains this type of muscle. Skeletal muscles are those attached to bones, and are under voluntary control. While contraction and relaxation of smooth muscle is involuntary, it is not found in the heart. Cardiac muscle is unique in that the cells are connected via gap junctions, which allows rapid electrical conduction between them, producing wavelike contractions of the heart, essential to its function.

The first sound (“lub”) occurs when the mitral and the tricuspid valves close. The second sound (“dub”) occurs when the pulmonary and the aortic valves close. The mitral and tricuspid valves close after both the left and the right atrias have contracted and have released blood into the ventricles. Transitioning towards the second heart sound, the ventricles contract and release blood into the systemic and pulmonary circulatory systems. If an extra noise is heard between the “lub” and the “dub” sounds, then it meant that while the ventricle is contracting, some blood is being pushed back into the atria(s) because the tricuspid valve and/or the mitral valve(s) did not completely close, resulting in regurgitation.

The "lub" heart sound occurs when both the mitral and the tricuspid valves close at the same time. If one hears a split sound, then it indicates that one of the two valves closed late.

The “dub” sound occurs when both the aortic and the pulmonary valves close at the same time. When one closes later than the other, then the valve that closed late will create a splitting sound; therefore, creating an extra sound close to the first sound.

The pulmonary circulation carries oxygenated blood from the lungs to the left atrium via the pulmonary veins. From there it enters the left ventricle, then it is pumped out through the aorta to serve organs of the body.

The right ventricle pumps oxygen-poor blood into the pulmonary circulation, not oxygen-rich blood. This blood leaves the right ventricle through the pulmonary artery and reaches the lungs. All other answer choices are true statements.