Circulatory System

Question 1

Arteries

Answer 1

Arteries are blood vessels that carry blood away from the heart (except for the arteries that actually supply blood to the heart muscle). Most arteries carry oxygen-rich blood, and one of their main functions is distributing oxygen to tissues throughout the body. The smallest arteries are called arterioles.

Question 2

Veins

Answer 2

Veins are blood vessels that carry blood toward the heart. Most veins carry deoxygenated blood. The smallest veins are called venules.

Question 3

Capillaries

Answer 3

Capillaries are the smallest blood vessels, and they connect arterioles and venules. As they pass through tissues, they exchange substances (including oxygen) with cells.

Question 4

Pulmonary Circulation

Answer 4

The pulmonary circulation involves only the heart, the lungs, and the major blood vessels that connect them. Blood moves through the pulmonary circulation from the heart, to the lungs, and then back to the heart again, becoming oxygenated in the process.

Question 5

Systemic Circulation

Answer 5

The oxygenated blood that enters the left atrium of the heart in the pulmonary circulation then passes into the systemic circulation. This is the part of the cardiovascular system that transports blood to and from all of the tissues of the body to provide oxygen and nutrients, and to pick up wastes. It consists of the heart and blood vessels that supply the metabolic needs of all the cells in the body, including those of the heart and lungs.

Question 6

Plasma

Answer 6

The fluid part of blood is called plasma. It is a yellowish, watery liquid that contains many dissolved substances and blood cells. Types of blood cells in plasma include red blood cells, white blood cells, and platelets.

Question 7

Red Blood Cells

Answer 7

Red blood cells have the main function of carrying oxygen in the blood. Red blood cells consist mostly of hemoglobin, a protein containing iron that binds with oxygen.

Question 8

White Blood Cells

Answer 8

White blood cells are far fewer in number than red blood cells. They defend the body in various ways. White blood cells called phagocytes, for example, swallow and destroy pathogens, dead cells, and other debris in the blood.

Question 9

Platelets

Answer 9

Platelets are cell fragments involved in blood clotting. They stick to tears in blood vessels and to each other, forming a plug at the site of injury. They also release chemicals that are needed for clotting to occur.

Question 10

Endocardium

Answer 10

The endocardium is the innermost layer of the heart wall. It is made up primarily of simple epithelial cells. It covers the heart chambers and valves. A thin layer of connective tissue joins the endocardium to the myocardium.

Question 11

Myocardium

Answer 11

The myocardium is the middle and thickest layer of the heart wall. It consists of cardiac muscle surrounded by a framework of collagen. There are two types of cardiac muscle cells in the myocardium: cardiomyocytes — which have the ability to contract easily — and pacemaker cells, which conduct electrical impulses that cause the cardiomyocytes to contract. About 99 percent of cardiac muscle cells are cardiomyocytes, and the remaining one percent is pacemaker cells. The myocardium is supplied with blood vessels and nerve fibers via the pericardium.

Question 12

Pericardium

Answer 12

The pericardium is a protective sac that encloses and protects the heart. The pericardium consists of two membranes (visceral pericardium and parietal pericardium), between which there is a fluid-filled cavity. The fluid helps to cushion the heart, and also lubricates its outer surface.

Question 13

Atria

Answer 13

As shown in the diagram below, the four chambers of the heart include two upper chambers called atria (singular, atrium), and two lower chambers called ventricles. The atria are also referred to as receiving chambers, because blood coming into the heart first enters these two chambers. The right atrium receives blood from the upper and lower body through the superior vena cava and inferior vena cava, respectively. The left atrium receives blood from the lungs through the pulmonary veins.

Question 14

Ventricles

Answer 14

As shown in the diagram below, the four chambers of the heart include two upper chambers called atria (singular, atrium), and two lower chambers called ventricles. The ventricles are also referred to as discharging chambers, because blood leaving the heart passes out through these two chambers. The right ventricle discharges blood to the lungs through the pulmonary artery, and the left ventricle discharges blood to the rest of the body through the aorta. The four chambers are separated from each other by dense connective tissue consisting mainly of collagen.

Question 15

Valves

Answer 15

The heart valves allow blood to flow from the atria to the ventricles, and from the ventricles to the pulmonary artery and aorta. The valves are constructed in such a way that blood can flow through them in only one direction, thus preventing the backflow of blood. The four valves are the:
tricuspid valve, which allows blood to flow from the right atrium to the right ventricle
mitral valve, which allows blood to flow from the left atrium to the left ventricle
pulmonary valve, which allows blood to flow from the right ventricle to the pulmonary artery
aortic valve, which allows blood to flow from the left ventricle to the aorta

Question 16

Diastole

Answer 16

During diastole, the atria contract and pump blood into the ventricles, while the ventricles relax and fill with blood from the atria. Diastole is referred to the filling stage, because this is when the ventricles fill with blood.

Question 17

Systole

Answer 17

During systole, the atria relax and collect blood from the lungs and body, while the ventricles contract and pump blood out of the heart. Systole is referred to the pumping stage because this is when the ventricles pump blood out of the heart.