Biology: The Vascular System

Question 1

The human cardiovascular system is composed of…

Answer 1

…a muscular, four-chambered heart, a network of blood vessels, and the blood itself.

Question 2

Heart Function & Anatomy

Answer 2

The heart is the driving force of the circulatory system. The right and left halves can be viewed as two separate pumps: the right side of the heart pumped deoxygenated blood into pulmonary circulation (toward the lungs), whereas the left side pumps oxygenated blood into systemic circulation (throughout the body). The two upper chambers are called atria, and the two lower chambers are called ventricles. The atria are thin-walled, whereas the ventricles are extremely muscular. The left ventricle is more muscular than the right ventricle because it is responsible for generating the force that propels systemic circulation and because it pumps against a higher resistance.I

Question 3

Heart’s Network of Blood Vessels

Answer 3

Blood is pumped into the aorta, which branches into a series of arteries. The arteries branch into arterioles and then into microscopic capillaries. Exchange of gases, nutrients, and cellular waste products occurs via diffusion across capillary walls. The capillaries then converge into venules and eventually into veins, leading deoxygenated blood back toward the heart.

Question 4

Atrioventricular Valves

Answer 4

The atrioventricular valves, located between the atria and ventricles on both sides of the heart, prevent backflow of blood into the atria.

The valve on the right side of the heart has three cusps and is called the tricuspid valve.

The valve on the left side of the heart has two cusps and is called the mitral valve.

Question 5

Semilunar Valves

Answer 5

The semilunar valves have three cusps and are located between the left ventricle and the aorta (the aortic valve) and between the right ventricle and the pulmonary artery (the pulmonic valve).

Question 6

Systole & Diastole

Answer 6

The heart’s pumping cycle is divided into two alternating phases, systole and diastole, which together make up the heartbeat. Systole is the period during which the ventricles contract. Diastole is the period of cardiac muscle relaxation during which blood drains into all four chambers.

Question 7

Cardiac Output

Answer 7

Cardiac output is defined as the total volume of blood the left ventricle pumps out perminute. Cardiac output = heart rate (number of beats per minute) x stroke volume (volume of blood pumped out of the left ventricle per contraction).

Question 8

Mechanism and Control of Heart

Answer 8

Cardiac muscle contracts rhythmically without stimulation from the nervous system, producing impulses that spread through its internal conducting system. An ordinary cardiac contraction originates in, and is regulated by, the sinoatrial (SA) node (the pacemaker), a small mass of specialized tissue located in the wall of the right atrium.

The SA node spreads impulses through both atria, stimulating them to contract simultaneously. The impulse arrives at the atrioventricular (AV) node, which conducts slowly, allowing enough time for atrial contraction and for the ventricles to fill with blood.

The impulse is then carried by the bundle of His (AV bundle), which branches into the right and left bundle branches, and finally through the Purkinje fibers, in the walls of both ventricles, generating a strong contraction.

Question 9

Autonomic Nervous System Role in Heart

Answer 9

Modifies the rate of heart contraction.

The parasympathetic system innervates the heart via the vagus nerve and causes a decrease in the heart rate.

The sympathetic system innervates the heart via the cervical and upper thoracic ganglia and causes an increase in the heart rate.

The adrenal medulla exerts hormonal control via epinephrine (adrenaline) secretion, which causes an increase in heart rate.

Question 10

Blood Vessels

Answer 10

The 3 types of blood vessels are arteries, veins, and capillaries.

Arteries are thick-walled, muscular, elastic vessels that transport oxygenated blood away from the heart-except for the pulmonary arteries, which transport deoxygenated blood from the heart to the lungs.

Veins are relatively thinly walled, inelastic vessels that conduct deoxygenated blood toward the heart-except for the pulmonary veins, which carry oxygenated blood from the lungs to the heart. Much of the blood flow in veins depends on their compression by skeletal muscles during movement, rather than on the pumping of the heart. Venous circulation is often at odds with gravity; thus, larger, veins, especially those in the legs, have valves that prevent backflow.

Capillaries have very thin walls composed of a single layer of endothelial cells, across which respiratory gases, nutrients, enzymes, hormones, and wastes can readily diffuse. Capillaries have the smallest diameter of all 3 types of vessels; red blood cells must often travel through them single file.

Question 11

Lymphatic System & Vessels

Answer 11

The lymphatic system is a secondary circulatory system distinct from the cardiovascular circulation.

Its vessels transport excess interstitial fluid, called lymph, to the cardiovascular system, thereby keeping fluid levels in the body constant.

Question 12

Lacteals

Answer 12

The smallest lymphatic vessels (lacteals) collect fats in the form of chylomicrons from the villi in the small intestine and deliver them into the bloodstream, bypassing the liver.

Question 13

Lymph Nodes

Answer 13

Lymph nodes are swellings along lymph vessels containing phagocytic cells (lymphocytes) that filter the lymph, removing and destroying foreign particles and pathogens.

Question 14

Blood

Answer 14

On the average, the human body contains 4-6 liters of blood. Blood has both liquid (55 percent) and cellular components (45 percent). Plasma is the liquid portion of the blood. It is an aquous mixture of nutrients, salts, respiratory gases, wastes, hormones, and blood proteins (e.g. immunoglobulins, albumin, and fibrinogen). The cellular components of the blood and erythrocytes, leukocytes, and platelets.

Question 15

Erythrocytes (RBCs)

Answer 15

The oxygen-carrying components of blood. An erythrocyte contains approximately 250 million molecules of hemoglobin, each of which can bind up to four molecules of oxygen.

When hemoglobin binds oxygen, it is called oxygemoglobin. This is the primary form of oxygen transport in the blood.

Erythrocytes have a distinct biconcave, disklike shape, which gives them both increased surface area for gas exchange and greater flexibility for movement through those tiny capillaries.

Erythrocytes are formed from stem cells in the bone marrow, where they lose their nuclei, mitochondria, and membranous organelles.

Once mature, RBCs circulate in the blood for about 120 days, after which they are phagocytized by special cells int he spleen and liver.

Question 16

Leukocytes (WBCs)

Answer 16

Larger than erythrocytes and serve protective functions. Some white blood cells (WBCs) phagocytize foreign matter and organisms such as bacteria. Others migrate from the blood to tissue, where they mature into stationary cells called macrophages. Other WBCs, called lymphocytes, are involved in immune response and the production of antibodies (B cells) or cytolysis of infected cells (T cells).

Question 17

Platelets

Answer 17

Cell fragments that lack nuclei and are involved in clot formation.

Question 18

Transport of Gases

Answer 18

Erythrocytes transport oxygen throughout the circulatory system. Actually, the hemoglobin molecules in erythrocytes bind to oxygen. Each hemoglobin molecule is capable of binding to four molecules of oxygen. Hemoglobin also binds to carbon dioxide and is referred to as deoxyhemoglobin.

Question 19

Transport of Nutrients and Waste

Answer 19

Amino acids and simple sugars are absorbed into the bloodstream at the intestinal capillaries and, after processing, are transported throughout the body. Throughout the body, metabolic waste products (e.g., water, urea, and carbon dioxide) diffuse into capillaries from surrounded cells; these wastes are then delivered to the appropriate excretory organs.

Question 20

Clotting

Answer 20

When platelets come into contact with the exposed collagen of a damaged vessel, they release a chemical that causes neighboring platelets to adhere to one another, forming a platelet plug.

Subsequently, both the platelets and the damaged tissue release the clotting factor thromboplastin. Thromboplastin, with the aid of its cofactors calcium and vitamin K, converts the inactive plasma protein prothrombin to its active form, thrombin.

Thrombin then converts fibrinogen (another plasma protein) into fibrin. Threads of fribin coat the damaged area and trap blood cells to form a clot.

Clots prevent extensive blood loss while the damaged vessel heals itself. The fluid left after blood clotting is called serum.

Question 21

The Human Immune System

Answer 21

The body has the ability to distinguish between “self” and “nonself” and to “remember” nonself entities (antigens) that it has previously encountered. These defense mechanisms are an integral part of the immune system.

The immune system is composed of nonspecific and specific defense mechanisms.

The specific immune system comprises humoral immunity, which involves the production of antibodies, and cell-mediated immunity, which involes cells that combat fungal and viral infection. Lymphocytes are responsible for both of these immune mechanisms.

The body also has a number of nonspecific defense mechanisms.

Question 22

Nonspecific Defense Mechanisms

Answer 22

The body uses several nonspecific defenses against foreign material.

Skin is a physical barrier against bacterial invasion. In addition, pores on the skin’s surface secrete sweat, which contains an enzyme that attacks bacterial cell walls.

Passages (e.g., the respiratory tract) are lined with ciliated mucus-coated epithealia, which filter and trap foreign particles.

Macrophages engulf and destroy foreign particles.

The inflammatory response is initiated by the body in response to physical damage: Injured cells release histamine, which causes blood vessels to dilate, thereby increasing blood flow to the damaged region. Granulocytes attracted to the injury site phagocutize antigenic material.

An inflammatory response is often accompanied by a fever. Proteins called interferons are produced by cells under viral attack. Interferons diffuse to other cells, where they help prevent the spread of the virus.

Inappropriate response to certain foods and pollen can cause the body to form antibodies and release histamine. These responses are called allergic reactions.

Question 23

Antibodies

Answer 23

One of the body’s defense mechanisms is the production of antibodies. These responses are very specific to the antigen involved.

Humoral immunity is responsible for the proliferation of antibodies after exposure to antigens.

Antibodies, also called immunoglobulins (Igs), are complex proteins that recognize and bind to specific antigens and trigger the immune system to remove them.

Antibodies either attract other cells (such as leukocytes) to phagocytize the antigen or cause the antigens to clump together (agglutinate) and form large insoluble complexes, facilitating their removal by phagocytic cells.

Question 24

Active Immunity

Answer 24

Refers to the production of antibodies during an immune response. Active immunity can be conferred by vaccination; an individual is injected with a weakened, inactive, or related form of a particular antigen, which stimulates the immune system to produce specific antibodies against it. Active immunity may require weeks to build up.

Question 25

Passive Immunity

Answer 25

Involves the transfer of antibodies produced by another individual or organism. Passive immunity is acquired either passively or by injection. For example, during pregnancy, some maternal antibodies cross the placenta and enter fetal circulation, conferring passive immunity upon the fetus. Although passive immunity is acquired immediately, it is very short-lived, lasting only as long as the antibodies circulate in the blood system. Usually it is not very specific.

Question 26

Gamme Globulin

Answer 26

The fraction of the blood containing a wide variety of antibodies. Can be used to cofer temporary protection against hepatitis and other diseases by passive immunity.

Question 27

Rejection of Transplants

Answer 27

Transplanted tissues or organs are detected as foreign bodies by the recipient’s immune system. The resulting immune response can cause the transplant to be rejected. Immunosuppressing drugs can be used to lower the immune response to transplants and decrease the likelihood of rejection.

Question 28

ABO Blood Types

Answer 28

Erythrocytes have characteristic cell-surface proteins (antigens). Antigens are macromolecules that are foreign to the host organism and trigger an immune response. The two major groups of red blood cell antigens are the ABO group and the Rh factor.

It is extremely important during blood transfusions that donor and recipient blood types be appropriately matched. The aim is to avoid transfusion of red blood cells that will be clumped (“rejected”) by antibodies (proteins int he immune system that bind specifically to antigens) present in the recipient’s plasma. The rule of blood matching is as follows: if the donor’s antigens are already in the recipient’s blood, no clumping occurs. Type AB blood is termed the “universal recipient,” as it has neither anti-A nor anti-B antibodies. Type O blood is the “universal donor”; it will not elicit a response from the recipient’s immune system because it does not possess any surface antigens.

Question 29

Rh Factor

Answer 29

Another antigen that may be present on the surface of red blood cells. Individuals may be Rh+, possessing the Rh antigen, or Rh-, lacking the Rh antigen.

Consideration of the Rh factor is particularly important during pregnancy. An Rh- woman can be sensitized by an Rh+ fetus if fetal red blood cells (which will have the Rh factor) enter maternal circulation during birth. If this woman subsequently carries another Rh+ fetus, the anti-Rh antibodies she produced when sensitized by the first birth may cross the placenta and destroy fetal red blood cells. This results in a severe anemia for the fetus, known as erythroblastosis fetalis.

Erythroblastosis is not caused by ABO blood-type mismatches between mother and fetus because anti-A and anti-B antibodies cannot cross the placenta.