Chapter 19: Cardiovascular System: The Heart

Question 1

Describe the general function of the cardiovascular system.

Answer 1

The general function of the cardiovascular system is to transport blood throughout the body to allow the exchange of substances (e.g., respiratory gases, nutrients, and waste products) between the blood of capillaries and the body’s cells.

The “goal” of the cardiovascular system is to provide adequate perfusion to all body tissues.

Question 2

Differentiate among the three primary types of blood vessels.

Answer 2

1. Arteries: carry blood away from the heart
2. Veins: carry blood back to the heart
3. Capillaries: exchange sites between either the blood and the air sacs (alveoli) of the lungs or the blood and the body cells.

Question 3

Describe the general structure and function of the heart.

Answer 3

1. Two pumps:
   Each pump has a receiving chamber (atrium) and a pumping chamber (ventricle).
   - Right side: pumps deoxygenated blood to the lungs.
   - Left side: pumps oxygenated blood to the body.
2. Great vessels:
   Arteries (arterial trunks) transport blood away from the heart.
   - Pulmonary trunk transports from right side.
   - Aorta transports from left side.
   Veins transport blood toward the heart.
   - Vena cavae (SVC and IVC) drain into the right side.
   - Pulmonary veins drain into left side.
3. Valves:
   Heart valves prevent back flow to ensure one-way blood flow.
   - Atrioventricular (AV) valves (i.e., right AV valve and left AV valve) are between the atrium and ventricle.
   - Semilunar valves (i.e., pulmonary semilunar valve and aortic semilunar valve) are between ventricle and arterial trunk.

Question 4

Compare and contrast pulmonary circulation and systemic circulation of the cardiovascular system. Trace blood flow through both circulations.

Answer 4

The pulmonary circulation convert deoxygenated blood from the right side of the heart through blood vessels to the lungs for the pickup of oxygen and the release of carbon dioxide, and then back through blood vessels to the left side of the heart.

The systemic circulation moves oxygenated blood from the left side of the heart. The blood vessels to the systemic cells such as those of the liver, skin, muscle, and brain for the exchange of nutrients, respiratory gases, and wastes before returning the blood in vessels that enter the right side of the heart.

Thus, the basic pattern of blood flow is the right side of the heart—> lungs—> the left side of the heart—> systemic tissues of the body —> back to the right side

Question 5

Describe the location and position of the heart in the thoracic cavity.

Answer 5

The heart is located posterior to the sternum left of the body midline between the lungs in the mediastinum. The posterosuperior surface of the heart is called the base. The inferior, conical end of the heart is called the apex.

*Think of the heart’s position like an “upside down” pyramid with the apex below the base.

Question 6

List the structural components of the pericardium.

Answer 6

The pericardium that encloses the heart includes the pericardial sac, which has an outer fibrous pericardium and an inner parietal layer of serious pericardium, and a visceral layer of serous pericardium (epicardium) that forms the outer layer of the heart wall.

Question 7

Describe the function of the pericardium and the purpose of the serous fluid within the pericardial cavity.

Answer 7

The pericardial cavity is a potential space between the layers of the serous pericardium that contain serous fluid, which is produced by the serous membranes and lubricates the surfaces to reduce friction.

Question 8

Compare the superficial features of the anterior and posterior aspects of the heart

Answer 8

The right side of the heart is more visible from the anterior view, and the left side of the heart is more visible from the posterior view.

Question 9

Name the three layers of the heart wall and the tissue components of each.

Answer 9

1. Epicardium: outermost layer that is also called the visceral layer of serous pericardium.
2. Myocardium: the middle and thickest layer. Contraction of the cardiac muscle in the myocardium generates the force necessary to pump blood.
3. Endocardium: covers the internal surface of the heart and the external surfaces of the heart valves. It is continuous with the inner lining of blood vessels.

Question 10

Characterize the four chambers of the heart and their functions.

Answer 10

• The right atrium

Receives deoxygenated blood from the superior and inferior vena cava and the coronary sinus and pumps it into the right ventricle through the tricuspid valve

• The left atrium
  Receives oxygenated blood from the pulmonary veins and pumps it into the left ventricle using the atrioventricular valve
• The right ventricle
  Receives deoxygenated blood from the right atrium via the tricuspid valve and pumps it into the pulmonary artery via the pulmonary valve and pulmonary trunk.
• The left ventricle
  Receives oxygenated blood from the left atrium via the mitral valve, and pumps it into the aorta via the aortic valve.

Question 11

Compare and contrast the structure and function of the two types of heart valves.

Answer 11

Each valve consists of endothelium-lined fibrous connective tissue flaps called cusps, or leaflets.

1. Atrioventricular valves
   - the right AV valve covers the right atrioventricular opening, and it has three cusps; the left AV valve covers the left atrioventricular opening, but it only has two cusps.

• When open, the cusps of the valve extend into the ventricles, allowing blood to move from an atrium into the opening of a ventricle. This causes the AV valves to close.
• The papillary muscles secure the thin chordae tendineae that attach to the lower surface of each AV valve cusp, preventing blood flow back into the atrium

2. Semilunar valves
   - the pulmonary semilunar valve is located between the right ventricle and the pulmonary trunk, and the aortic semilunar valve is located between the left ventricle and the aorta.

• each valve is composed of three cusps
• neither papillary muscles nor chord tendineae are associated with these valves.
• The semilunar valves open when the ventricles contract and the force of the blood pushes the AV valves open and blood enters the arterial trunks.
• The valves close when the ventricles relax and the pressure in the ventricle becomes less than the pressure in a great arterial trunk.
• Blood in the arteries begins to fall backward toward the ventricle and is caught in the cusps of the semilunar valves, and they close, preventing the back flow of blood into the ventricle.

Question 12

Describe the location and function of the fibrous skeleton.

Answer 12

The fibrous skeleton provides an attachment site for heart valves and cardiac muscle and prevents action potentials from spreading between the atria and ventricles except through the AV node.

Question 13

Describe the general structure of cardiac muscle.

Answer 13

Cardiac muscle cells are small, have one or two centrally located nuclei, and are branched.

Question 14

Explain the intercellular structures of cardiac muscle.

Answer 14

Intercalated discs tightly link the cardiac muscle cells together and permit the passage of action potentials.

• Desmosomes act as mechanical junctions to prevent cardiac muscle cells from pulling apart.
• Gap junctions provide a low-resistance pathway for the flow of ions between cardiac cells. They allow an action potential to move continuously along the sarcolemma of cardiac muscle cells, resulting in synchronous contraction of that chamber.

Question 15

Discuss how cardiac muscle meets its energy needs.

Answer 15

Cardiac muscle cells rely almost exclusively on aerobic cellular respiration for supplying ATP.

• It is also versatile in being able to use different types of fuel molecules, including fatty acids, glucose, lactic acid, amino acids, and ketone bodies.

Question 16

Identify the coronary arteries, and describe the specific areas of the heart supplied by their major branches.

Answer 16

Coronary arteries supply oxygenated blood to the heart wall and include the left and right coronary arteries that branch off the aorta.

• three major coronary arteries off the right side of the heart (RMP): the right coronary artery splits into the right marginal artery and posterior inter ventricular artery
• three major coronary arteries off the left side of the heart (LAC): the left coronary artery, the anterior inter ventricular artery, and circumflex artery.

Question 17

Explain the significance of coronary arteries as functional end arteries.

Answer 17

Some arteries may share connections, called arterial anastomoses. Other arteries terminate in capillary beds only, and are called end arteries. The left and right coronary arteries are considered functional end arteries because, although there coronary arteries have anastomoses, if one of the arteries becomes blocked these anastomoses are too tiny to shunt sufficient blood from one artery to the other. As a result, the part of the heart wall that was supplied by one coronary artery branch will die due to lack of blood flow to the tissue.

Question 18

Describe blood flow through the coronary arteries.

Answer 18

Blood flow to the heart wall is not a steady stream; it is impeded and then flows, as the heart rhythmically contracts and relaxes.

Question 19

Identify the coronary veins, and describe the specific areas of the heart drained by their major branches.

Answer 19

Venous return is through the cardiac veins (great, middle, and small) into the coronary sinus, which collects venous blood and drains deoxygenated blood from the heart wall directly into the right atrium of the heart.

Question 20

Identify and locate the components of the heart’s conduction system.

Answer 20

Stimulation of the heart involves the initiation of an action potential at the SA node and its transmission through the conduction system.

The conducting system includes sinoatrial (SA) node, atrioventricular (AV) node, AV bundle, and Purkinje fibers, which are composed of specialized cardiac cells that initiate and conduct action potentials resulting in a heartbeat.

Question 21

Compare and contrast parasympathetic and sympathetic innervation of the heart.

Answer 21

Parasympathetic innervation comes from the cardioinhibitory center to decrease the heart rate..

Sympathetic innervation comes from the cardioacceleratory center to increase the heart rate and increase force of contraction.

Question 22

Describe a nodal cell at rest.

Answer 22

The nodal cells are at rest when the cytosol inside the the nodal cells is relatively negative in comparison to the fluid outside the cells.

Question 23

Define autorhythmicity.

Answer 23

SA nodal cells are unique in that they exhibit autorhythmicity, meaning that they are capable of depolarizing and firing an action potential spontaneously without external influence.

Question 24

Describe the steps for SA nodal cells to spontaneously depolarize and serve as the pacemaker cells.

Answer 24

1. Reaching threshold as Na+ enters the nodal cells through open voltage-gated Na+ channels
2. depolarization as Ca2+ enters the nodal cells through open voltage-gated Ca2+ channels
3. Repolarization as K+ exits the nodal cells through voltage-gated K+ channels

At rest, the parasympathetic nervous system decreases the inherent rhythm of nodal cells from a firing rate of 100 per minute to 75 per minute.

Question 25

Describe the spread of the action potential through the heart’s conduction system.

Answer 25

The action potential travels through the conduction system as follows:
1. SA node
2. AV node
3. AV bundle
4. bundle branches
5. Purkinje fibers

Following stimulation by the conduction system, there is a propagation of the action potential at the sarcolemma and contraction of sarcomeres within the cardiac muscle cells.

Question 26

Describe the conditions at the sarcolemma of cardiac muscle cells at rest.

Answer 26

1. RMP is -90 mV.
2. Contains fast voltage-gated Na+ channels for depolarization and K+ voltage-gated channels for repolarization of membrane.
3. Also contains slow voltage-gated Ca+ channels.

Question 27

List the electrical events of an action potential that occur at the sarcolemma.

Answer 27

The electrical events of cardiac muscle include depolarization, plateau, and depolarization at the sarcolemma.

Question 28

Briefly summarize the mechanical events of muscle contraction.

Answer 28

The mechanical events are similar to those of skeletal muscle fibers and involve cross bridge cycling and the shortening of sarcomeres within cardiac muscle cells.

Question 29

Define the refractory period.

Answer 29

Cardiac muscle exhibits a longer refractory period than skeletal muscle fibers to allow time for contraction and relaxation of the muscle cells before they are stimulated again- a necessary requirement for the “pumping action” of the heart.

Question 30

Explain the significance of the plateau phase.

Answer 30

The plateau phase delays repolarization and allows the sarcomeres of cardiac muscle cells to fully contract and relax before following each stimulation. This prevents cardiac muscle cells from exhibiting tetany which would result in the locking up of heart chambers.

Question 31

Identify the components of an ECG recording.

Answer 31

An electrocardiogram (ECG) is a graphic recording of the electrical changes in the heart and is used in the diagnosis and treatment of abnormal heart function.

Question 32

Identify the two processes within the heart that occur due to pressure changes associated with the cardiac cycle.

Answer 32

A cardiac cycle is the inclusive period of time from initiation of one heartbeat to the start of the next.

1. Systole: contraction of a chamber
2. Diastole: relaxation of a chamber

Question 33

List the five phases of the cardiac cycle.

Answer 33

1. Atrial systole
2. Early ventricular systole
3. Late ventricular systole
4. Early ventricular diastole
5. Late ventricular diastole

Question 34

List and describe what occurs during the five phases of the cardiac cycle.

Answer 34

1. Atrial systole is the contraction of atria to finish filling the ventricles, which are in diastole.
2. Early ventricular systole is a time of isovolumetric contraction: Ventricles begin to contract, AV valves are pushed closed, and no blood leaves the ventricles yet.
3. Late ventricular systole is the time of ventricular ejection: Semilunar valves are pushed open, and blood is forced through the semilunar valves into the arterial trunk.
4. Early ventricular diastole is the beginning of ventricular relaxation: AV valves remain closed, and semilunar valves close.
5. Late ventricular diastole is a time to begin ventricular filling as AV valves open and passive filling of the ventricle begins.

Question 35

Explain the significance of ventricular balance.

Answer 35

equal amounts of blood pumped by two ventricles. If sustained pumping in unequal amounts.

Question 36

Define cardiac output.

Answer 36

Cardiac output is a measure of how effective the cardiovascular system is in transporting substances through the body.

It is defined as the amount of blood pumped by a single ventricle in 1 minute.

Cardiac output is the heart rate multiplied by the stroke volume.

Question 37

Explain what is meant by cardiac reserve.

Answer 37

Cardiac reserve is a measure of the ability of the heart to increase pumping capacity beyond the normal resting cardiac output (CO).

Question 38

Define chronotropic agents, and describe how they affect heart rate.

Answer 38

Heart rate is altered through chronotropic agents, which change SA node and AV node activity.

Positive chronotropic agents increase the heart rate and the negative chronotropic agents decrease the heart rate.

Question 39

Discuss how autonomic reflexes alter heart rate.

Answer 39

The sympathetic nervous system (SNS) releases the hormones (catecholamines - epinephrine and norepinephrine) to accelerate the heart rate.

Question 40

List the three variables that may influence stroke volume.

Answer 40

Stroke volume is influenced by venous return, inotropic agents, and afterload.

Question 41

Define each of the three variables, describe the factors that influence each variable and how each variable affects stroke volume.

Answer 41

Venous return is directly correlated with store volume.

Positive inotropic agents increase stroke volume, negative inotropic agents decrease stroke volume.

Afterload is inversely related to stroke volume.

Question 42

Summarize the variables that influence cardiac output

Answer 42

heart rate, contractility, preload, and afterload.

Question 43

Explain how postnatal heart structures develop from the primitive heart tube.

Answer 43

The primitive heart tube develops into sinus venosus, primitive atrium and ventricle, bulbus cordis postnatal heart structures by 28 days of embryonic development.

Question 44

Describe septal defects that may occur during development.

Answer 44

As a baby’s heart develops during pregnancy, there are normally several openings in the wall dividing the upper chambers of the heart (atria). These usually close during pregnancy or shortly after birth. If one of these openings does not close, a hole is left, and it is called an atrial septal defect