Chapter 20 - The Heart

Question 1

20.1

Question 2

The Heart

Answer 2

A hollow muscular organ that pumps oxygen-poor blood to the lungs within the pulmonary circuit and oxygen-rich blood to the rest of the body within the systemic circuit
-Systemic arteries carry oxygenated blood from heart to tissues, systemic veins carry deoxygenated blood from tissues to heart
-Pulmonary artery carries deoxygenated blood from heart to lungs, and pulmonary vein carries oxygenated blood from lungs to heart

-***When the heart beats, first the atria contract, and then the ventricles contract. The two ventricles contract at the same time and eject equal volumes of blood into the pulmonary and systemic circuits.

Question 3

Great vessels

Answer 3

the largest veins and arteries in the body, those connected to the heart

Question 4

Capillaries

Answer 4

Microscopic thin-walled vessels that interconnect the smallest arteries and the smallest veins. Capillaries are called exchange vessels, because their thin walls permit the exchange of nutrients, dissolved gases (called gas exchange), and wastes between the blood and surrounding tissues

Question 5

Base

Answer 5

This area is the “top” of the heart, where the great vessels, both veins and arteries, are connected to the superior end of the heart. The base sits posterior to the sternum at the level of the third costal cartilage

Question 6

Apex

Answer 6

The inferior, pointed tip of the heart.

Question 7

Pulmonary arteries (trunk)

Answer 7

Transport deoxygenated blood from right ventricle to lungs

Question 8

Coronary Sulcus

Answer 8

Separates right atrium from right ventricle

Question 9

Anterior Interventricular Sulcus

Answer 9

Separates right from left ventricle (from anterior view; but posterior interventricular sulcus would separate left from right ventricle as seen from posterior view)

Question 10

Mediastinum

Answer 10

Region between the two pleural cavities. Contains thymus, esophagus, trachea, and great vessels (which attach to base of heart).

Question 11

Layers of heart, from deep to superficial:

Answer 11

1) Endocardium: innermost layer whose simple squamous epithelium is continuous with the endothelial lining of blood vessels
2) Myocardium: spiral bundles of cardiac muscle cells
3) Pericardium: outermost layer that anchors and protects, composed of BOTH fibrous (collaganeous) and serous pericardium (The two-layered serous pericardium is made up of a parietal layer and a visceral layer (epicardium). These layers are separated by a fluid-filled pericardial cavity)

***Do NOT confuse endocardium (one of three main layers of heart) with epicardium (visceral layer of serous pericardium)

Question 12

Cardiac skeleton

Answer 12

a crisscrossing, interlacing layer of dense connective tissue that anchors muscle fibers, supports the great vessels and heart valves, and limits the spread of action potentials

-consists of four dense bands of tough elastic tissue that encircle the heart valves and the bases of the pulmonary trunk and aorta (look ahead to Figure 20–7). These bands stabilize the positions of the heart valves and ventricular muscle cells. They also electrically insulate the ventricular cells from the atrial cells.

Question 13

Heart layers: Pericardium

Answer 13

• outermost layer of heart, with outer part being fibrous pericardium and inner part being serous pericardium
• fibrous pericardium contains a dense network of collagen fibers that help to stabilize the position of the heart and associated vessels
• serous pericardium is two-layered membrane, with a parietal pleura and visceral (inner, epicardium) layer
• visceral layer (epicardium) covers surface of heart
• pericardial cavity lies between the parietal and visceral layers, and it’s filled with lubricant (produced by pericardial membranes) which prevent friction between these two layers

Question 14

Pericarditis

Answer 14

Condition where pathogens infect the pericardium, producing inflammation and causing the visceral and parietal layers to rub against one another. This inflammation can also commonly result in increased lubrication production within the pericardial cavity, which can lead to fluid building within the pericardial cavity (called a cardiac tamponade).

Question 15

(Peri)Cardiac tamponade

Answer 15

Can come about due to infection from pathogens or from trauma. This condition occurs when fluid builds up within the pericardial sac, compressing on the heart and limiting its contracting ability. Can be relieved via pericardiocentesis.

Question 16

Two Atria of Heart

Answer 16

• have thin muscular walls but are highly expandable
• auricle surrounds each atria, and can expand upon the filling up blood (and looks wrinkled when there is no blood filling up atria)

Question 17

Coronary sulcus

Answer 17

Deep groove that marks the border between the atria and the ventricles

-this, alongside the interventricular sulci, typically contains large amounts of fat and also the coronary arteries/veins (that supply the cardiac muscle)

Question 18

Anterior and posterior interventricular sulci

Answer 18

Shallower depressions that mark the border between both ventricles (on anterior and posterior sides of heart)

= these, alongside the coronary sulcus, typically contain large amounts of fat and also the coronary arteries/veins (that supply the cardiac muscle)

Question 19

Heart layers - structure/organization

Answer 19

1) The visceral layer of serous pericardium (epicardium) covers the surface of the heart. This serous membrane consists of an exposed mesothelium and an underlying layer of areolar connective tissue that is attached to the myocardium. The parietal layer of serous pericardium consists of an outer dense fibrous layer, an areolar layer, and an inner mesothelium.

2) The myocardium is cardiac muscle tissue that forms the atria and ventricles. This muscular layer contains cardiac muscle cells, connective tissues, blood vessels, and nerves. The atrial myocardium contains muscle bundles that wrap around the atria and form figure eights that encircle the great vessels (Figure 20–4b). Superficial ventricular muscles wrap around both ventricles, and deeper muscle layers spiral around and between the ventricles toward the apex in a figure-eight pattern.

3) The endocardium covers the inner surfaces of the heart, including those of the heart valves. It is made up of a simple squamous epithelium and underlying areolar tissue. This simple squamous epithelium, or endothelium, is continuous with the endothelium of the attached great vessels.

Question 20

Connective Tissues of the Heart

Answer 20

Mainly collagen and elastic fibers, help to:
1) provide physical support for cardiac muscle fibers, blood vessels, and nerves of the myocardium
2) help distribute forces of contraction
3) add strength and prevent over-expansion of heart
4) provide elasticity that allow heart to return to original position following contraction

Question 21

Septum (plural: septa)

Answer 21

Muscular walls that separate the chambers of the heart

Question 22

Interatrial septum

Answer 22

separates the atria; very thin

Question 23

Interventricular septum

Answer 23

separates the ventricles; very thick

Question 24

Valves

Answer 24

Covered openings that direct the flow of blood between chambers and vessels (the cardiac skeleton stabilizes the positions of these valves)

Question 25

Atrioventricular Valves (AV Valves)

Answer 25

tricuspid (right) and mitral (also called bicuspid; left) valves
- these valves permit blood to only flow in one direction, from atria to ventricles

-**papillary muscles and chordae tendinae support the mitral and tricuspid valves

(right atrium -> tricuspid valve -> right ventricle -> pulmonary valve -> pulmonary artery -> lungs -> pulmonary vein -> left atrium -> mitral valve -> left ventricle -> aortic valve -> aortic arch)

Question 26

Semilunar Valves

Answer 26

pulmonary and aortic valves
- these valves permit blood to only flow in one direction, from ventricles to vessels (either the pulmonary artery or the aorta)

Question 27

Foramen ovale

Answer 27

In the embryonic heart, from the fifth week of development until birth, an opening exists between the right and left atria whilst the lungs develop. This opening, called the foramen ovale, remains until birth during which it closes off, and it permanently seals off within three months of delivery.

Question 28

Fossa ovalis

Answer 28

A small, shallow depression that remains in place of where the embryonic foramen ovale used to be, within the adult human heart.

Question 29

Pectinate muscles

Answer 29

Prominent muscular ridges on the inner surface of the auricle as well as the anterior atrial wall

Question 30

Tricuspid valve

Answer 30

Blood travels from the right atrium into the right ventricle through a broad opening bordered by three fibrous flaps. These flaps, called cusps, are part of the tricuspid (trī-KUS-pid; tri, three) valve, also known as the right atrioventricular (AV) valve. The free edge of each cusp is attached to connective tissue fibers called the chordae tendineae (KOR-dē TEN-dih-nē-ē; tendinous cords). The fibers originate at the papillary (PAP-ih-lehr-ē) muscles, conical muscular projections that arise from the inner surface of the right ventricle

–***FUNCTION: Contractions of the papillary muscles pull on the chordae tendineae, which “tug” on your heart’s valves

Question 31

Trabeculae carnae

Answer 31

Muscular ridges that exist on inner surface of right ventricle

Question 32

Moderator band

Answer 32

The moderator band is a muscular ridge that extends horizontally from the inferior portion of the interventricular septum and connects to the anterior papillary muscle. The moderator band delivers the stimulus for contraction to the papillary muscles. As a result, they begin tensing the chordae tendineae before the rest of the ventricle contracts.

Question 33

Conus arteriosus

Answer 33

The superior end of the right ventricle tapers to the conus arteriosus, a cone-shaped pouch that ends at the pulmonary valve, or pulmonary semilunar valve.

Question 34

Pulmonary valve

Answer 34

Consists of three semilunar (half-moon shaped) cusps of thick connective tissue. Blood flowing from the right ventricle passes through this valve into the pulmonary trunk, the start of the pulmonary circuit

Question 35

Lungs -> pulmonary veins -> left atrium

Answer 35

From the respiratory capillaries, blood collects into small veins that ultimately unite to form the four pulmonary veins. The posterior wall of the left atrium receives blood from two left and two right pulmonary veins. Again there is no valve between the pulmonary veins and the left atrium. Like the right atrium, however, the left atrium has an auricle.

Question 36

Left ventricle

Answer 36

The internal organization of the left ventricle resembles that of the right ventricle, but it has no moderator band (see Figure 20–5a). The trabeculae carneae are prominent. A pair of large papillary muscles tenses the chordae tendineae that anchor the cusps of the mitral valve and prevent blood from flowing back into the left atrium.

Question 37

Ligamentum arteriosum

Answer 37

A fibrous band connecting the pulmonary trunk to the aortic arch. This structure is a fibrous band left over from an important fetal blood vessel.

Question 38

Differences between the left and right ventricles

Answer 38

The function of the atria is to collect blood that is returning to the heart and to convey it to the ventricles. The demands on the right and left atria are similar, and the two chambers look almost identical. The demands on the right and left ventricles, however, are very different, and the two have significant structural differences. Even though the two ventricles hold and pump equal amounts of blood, the left ventricle is much larger than the right ventricle. What’s the reason? It has thicker walls. These thick, muscular walls enable the left ventricle to push blood through the body’s extensive systemic circuit. In contrast, the right ventricle needs to pump blood, at lower pressure, only about 15 cm (6 in.) to and from the lungs.

Question 39

If an individual were to have a damaged right ventricle, would it affect their circulation greatly?

Answer 39

Not greatly. As the powerful left ventricle contracts, it bulges into the right ventricular cavity (Figure 20–6b). This action increases the pumping efficiency of the right ventricle. Individuals with severe damage to the right ventricle may survive, because the contraction of the left ventricle helps push blood into the pulmonary circuit.

Question 40

*******The AV Valves: Atria to Ventricles

Answer 40

The atrioventricular (AV) valves prevent the backflow of blood from the ventricles to the atria when the ventricles are contracting. The chordae tendineae and papillary muscles play important roles in the normal function of the AV valves. When the ventricles are relaxed, the chordae tendineae are loose, and the AV valves offer no resistance as blood flows from the atria into the ventricles (Figure 20–7a). When the ventricles contract, blood moving back toward the atria swings the cusps together, closing the valves (Figure 20–7b). At the same time, the contraction of the papillary muscles tenses the chordae tendineae, stopping the cusps before they swing into the atria. If the chordae tendineae were cut or the papillary muscles were damaged, backflow, called regurgitation, of blood into the atria would occur each time the ventricles contracted.

Question 41

SLIDE 10!!!!!!!!!!!!!

Question 42

Faulty Heart Valves

Answer 42

Each of the four heart valves must open and close crisply and precisely to permit the proper flow of blood through the heart.
The most common valve to falter is the mitral valve. One scenario responsible for mitral malfunction is an untreated bacterial or viral infection that infiltrates the valve cusps. The cusps become inflamed and later scar, resulting in a faulty valve.
A valve can malfunction in one of three ways: (1) It can become rigid (a stenotic valve) so that it does not open fully, (2) it can fail to close properly (a regurgitant valve), or (3) it can actually flop backwards (a prolapsed valve). Faulty valves are heard as heart murmurs with a stethoscope.

Question 43

SLIDE 12!!!!!!!!!!

Question 44

Coronary arteries

Answer 44

The left and right coronary arteries originate at the base of the ascending aorta, at the aortic sinuses (Figure 20–8a). Blood pressure here is the highest in the systemic circuit. When the left ventricle contracts and forces blood into the aorta, the high pressure of this blood stretches the elastic walls of the aorta. When the left ventricle relaxes, blood no longer flows into the aorta, pressure declines, and the walls of the aorta recoil. This recoil, called elastic rebound, pushes blood both forward, into the systemic circuit, and backward, through the left and right aortic sinuses and then into the respective coronary arteries. In this way, the combination of elevated blood pressure and elastic rebound ensures a continuous flow of blood to meet the demands of active cardiac muscle tissue.

The right and left coronary arteries, which deliver blood to the myocardium, originate at the right and left aortic sinuses. The right coronary artery follows the coronary sulcus around the heart (see Figure 20–8). It supplies blood to (1) the right atrium, (2) portions of both ventricles, and (3) portions of the electrical conducting system of the heart. Inferior to the right atrium, the right coronary artery generally gives rise to one or more marginal arteries, which extend across the surface of the right ventricle. The right coronary artery then continues across the posterior surface of the heart. It supplies the posterior interventricular artery, or posterior descending artery, which runs toward the apex within the posterior interventricular sulcus. The posterior interventricular artery supplies blood to the interventricular septum and adjacent portions of the ventricles.

The left coronary artery supplies blood to the left ventricle, left atrium, and interventricular septum (see Figure 20–8). As it reaches the anterior surface of the heart, it gives rise to a circumflex branch and an anterior interventricular branch. The circumflex artery curves to the left around the coronary sulcus. It eventually meets and fuses with small branches of the right coronary artery.

The much larger anterior interventricular artery, or left anterior descending artery (LAD), swings around the pulmonary trunk and runs along the surface within the anterior interventricular sulcus. The anterior interventricular artery supplies small tributaries continuous with those of the posterior interventricular artery. Such interconnections between arteries are called arterial anastomoses (ah-nas-tō-MŌ-sē z; anastomosis, outlet). Because the arteries are interconnected in this way, the blood supply to the cardiac muscle remains relatively constant despite pressure fluctuations in the left and right coronary arteries as the heart beats.

Question 45

Arterial anastomoses

Answer 45

The anterior. interventricular artery supplies small tributaries continuous with those of the posterior interventricular artery. Such interconnections between arteries are called arterial anastomoses

Question 46

Coronary artery disease (CAD)

Answer 46

Interrupted blood flow to the myocardium (see slides)

Question 47

Angina pectoris

Answer 47

chest pain; symptom

Question 48

Myocardial infarction (MI)

Answer 48

condition in which part of coronary circulation is blocked, and myocardial cells begin to die - death of affected tissue creates a nonfunctional area known as an “infarct”
- can result from severe CAD
-can be detected with an electrocardiogram (ECG) or diagnostic tests revealing elevated cardiac troponin T/I levels (these are enzymes released by damaged cardiac muscle cells)

Question 49

Atherosclerosis

Answer 49

narrowing of arteries due to plaque buildup

Question 50

Coronary veins

Answer 50

The cardiac veins draining the myocardium return blood to the coronary sinus, a large, thin-walled vein. The coronary sinus opens into the right atrium near the base of the inferior vena cava.
Other cardiac veins empty into the great cardiac vein or the coronary sinus. These veins include (1) the posterior vein of left ventricle, draining the area served by the circumflex artery; (2) the middle cardiac vein, draining the area supplied by the posterior interventricular artery; and (3) the small cardiac vein, which receives blood from the posterior surfaces of the right atrium and ventricle. The anterior cardiac veins (also called the anterior veins of right ventricle), which drain the anterior surface of the right ventricle, empty directly into the right atrium.

Question 51

2 types of cardiac muscle cells involved in a contraction:

Answer 51

1) autorhythmic cells (of the conducting system)
-pacemaker
-conducting
2) contractile cells

Action potential generated by autorythmic cells of the conducting system (also carried across via conducting cells) reaches target contractile cells, which then stimulate contraction

Question 52

Autorhythmicity

Answer 52

the property of cardiac muscle cells to contract on their own without a neural/hormonal stimulus (unlike skeletal muscle cells)

Question 53

Conducting system

Answer 53

System of heart which contain cells that drive the heartbeat/contraction
- these are the autorhythmic cells (pacemaker and conducting cells); they initiate and distribute electrical impulses for the contractile cells to later use

Question 54

Heartbeat

Answer 54

Each heartbeat begins with an action potential generated by cells of the conducting system. Other cells of this system then propagate and distribute this electrical impulse to stimulate contractile cells to push blood in the right direction at the proper time. The arrival of an electrical impulse at a cardiac contractile cell’s plasma membrane produces an action potential that is comparable to an action potential in a skeletal muscle fiber. As in a skeletal muscle fiber, this action potential triggers the contraction of the cardiac contractile cell. The actual contraction lags behind the beginning of the action potential. Because of the coordination provided by the conducting system, the atria contract first, driving blood into the ventricles through the AV valves, and the ventricles contract next, driving blood out of the heart through the semilunar valves.

Question 55

Pacemaker cells

Answer 55

Cells of the SA node that set the pace for contraction

Question 56

SInoatrial node (SA node)

Answer 56

• primary driver of heart rate, also called cardiac pacemaker
• located in right atrium near superior vena cava

Question 57

Atrioventricular node (AV node)

Answer 57

• continue on signals sent by SA node, and act as backup to SA node pacemaker cells
• located near coronary sinus

Question 58

Conducting cells interconnect the SA and AV nodes, and distribute the contractile stimulus throughout the myocardium:

Answer 58

• In the atria, these conducting cells are found within the internodal pathways. As the contractile stimulus travels from SA to AV node, conducting cells distribute the stimulus to the atrial muscle cells.
• In the ventricles, these conducting cells are found within the AV bundle (also known as “Bundle of His”), the bundle branches, and the Purjinke fibers.

Question 59

Pacemaker potential

Answer 59

Pacemaker cells of the SA and AV nodes share a special characteristic: Their excitable membranes do not have a stable resting membrane potential. Each time a pacemaker cell repolarizes, its membrane potential drifts toward threshold. This gradual depolarization is called a pacemaker potential (Figure 20–10b). The pacemaker potential results from a slow inflow of Na+ without a compensating outflow of K+

Question 60

Where is the rate of spontaneous depolarization fastest within the conducting system?

Answer 60

The sinoatrial node:
Without neural or hormonal stimulation, the SA node generates action potentials at a rate of 60–100 per minute. Isolated cells of the AV node depolarize more slowly, generating 40–60 action potentials per minute. Because the SA node reaches threshold first, it establishes the basic heart rhythm, or sinus rhythm.

**In other words, the impulse generated by the SA node brings the AV pacemaker cells to threshold faster than does the pacemaker potential of the AV pacemaker cells

Question 61

Why is the 100 msec delay important, with regards to impulse passing through pacemaker cells of AV node?

Answer 61

This allows the atria to contract before the ventricles do.
(The delay is a result of the time it takes for calcium ions to enter the sarcoplasm and activate the contraction process)

Question 62

At an intercalated disc, the interlocking membranes of adjacent cells are held together by desmosomes and linked by gap junctions (Figure 20–14b,c). The desmosomes prevent cells from separating during contraction, while the gap junctions allow ions to pass and electrically couple adjacent cells. This allows the heart muscle to behave as a functional syncytium (sin-SI-shē-um), a mechanically, chemically, and electrically coupled, multinucleate tissue.

Question 63

WATCH VIDEO ON STEPS OF EKG!!! (on etext)

Question 64

Process

Answer 64

After the brief delay at the AV node, the impulse is conducted along the AV bundle and the bundle branches to the Purkinje fibers and the papillary muscles (Figure 20–11). The connection between the AV node and the AV bundle is normally the only electrical connection between the atria and the ventricles. Once an impulse enters the AV bundle, it travels to the interventricular septum and enters the right and left bundle branches. The left bundle branch, which supplies the massive left ventricle, is much larger than the right bundle branch. Both branches extend toward the apex of the heart, turn, and fan out deep to the endocardial surface.
As the bundle branches diverge, they conduct the impulse to both the Purkinje fibers and, through the moderator band, to the papillary muscles of the right ventricle. Because the impulse is delivered to the papillary muscles directly, these muscles begin contracting before the rest of the ventricular musculature does. Contraction of the papillary muscles applies tension to the chordae tendineae, bracing the AV valves. This tension limits the movement of the cusps, preventing the backflow of blood into the atria when the ventricles contract.
The Purkinje fibers then distribute the impulse to the ventricular myocardium (Figure 20–11 ). Purkinje fibers, which radiate from the apex toward the base of the heart, conduct action potentials very rapidly—as fast as small myelinated axons. Within about 75 msec, the signal to begin a contraction has reached all the ventricular cardiac contractile cells, and ventricular contraction begins. By this time, the atria have completed their contractions and ventricular contraction can safely occur. Because of the location of the Purkinje fibers, the ventricles contract in a wave that begins at the apex of the heart and spreads toward the base. The contraction pushes blood toward the base, into the aorta and pulmonary trunk.
In summary, each time the heart beats, a wave of depolarization spreads through the atria, pauses at the AV node, then travels down the interventricular septum to the apex, turns, and spreads through the ventricular myocardium toward the base (see Figure 20–11). The entire process, from the generation of an impulse at the SA node to the complete depolarization of the ventricular myocardium, normally takes around 225 msec.

Question 65

Intercalated discs

Answer 65

Interconnect cardiac CONTRACTILE cells
- they transfer the force of contraction from cell to cell and propagate the action potential that is sent via the conducting cells

Question 66

The appearance of an action potential in the cardiac contractile cell plasma membrane produces a contraction by causing an increase in the concentration of Ca2+ around the myofibrils. This process takes place in two steps:

Answer 66

1) Extracellular calcium ions crossing the plasma membrane during the plateau phase of the action potential provide roughly 20 percent of the Ca2+ required for a contraction.
2) The arrival of extracellular Ca2+ triggers the release of additional Ca2+ from reserves in the sarcoplasmic reticulum (SR).

Question 67

20.3

Question 68

Pressure changes within the heart

Answer 68

In the heart chamber, the pressure rises during systole and falls during diastole. Valves between adjacent chambers help ensure that blood flows in the required direction, but blood flows from one chamber to another only if the pressure in the first chamber exceeds that in the second. This basic principle governs the movement of blood between atria and ventricles, between ventricles and arterial trunks, and between major veins and atria.

Question 69

Phases of the Cardiac Cycle

Answer 69

• Atrial Systole
• Atrial Diastole
• Ventricular Systole
• Ventricular Diastole

When the cardiac cycle begins, all four chambers are relaxed, and the ventricles are partially filled with blood.

Question 70

(go over more on text and presentation slide)

Question 71

20.4

Answer 71

review ->

Question 72

REVIEW ALL OF THIS SECTION