Chapter 19 - The Heart

Question 1

Define the pulmonary circuit?

Answer 1

The circuit begins with deoxygenated blood returned from the body to the right atrium of the heart where it is pumped out from the right ventricle to the lungs.

Question 2

Define the systemic circuit

Answer 2

The routes through which oxygenated blood flows from the left ventricle through the aorta to all the organs of the body and deoxygenated blood returns to the right atrium.

Question 3

describe the general location, size, and shape of the heart

Answer 3

The heart is located within the thoracic cavity, medially between the lungs.
It is about the size of a fist, is broad at the top, and tapers toward the base.

Question 4

describe the pericardial sac that encloses the heart.

Answer 4

Allows heart to beat without friction, provides room to expand, yet resists excessive expansion

Question 5

What are the three layers of the heart wall?

Answer 5

(inner) Endocardium.
(Middle) Myocardium
(outer) Epicardium

Question 6

Define endocardium

Answer 6

-Smooth inner lining of heart and blood vessels
-Covers the valve surfaces and is continuous with endothelium of blood vessels

Question 7

Define Myocardium

Answer 7

-Provides structural support and attachment for cardiac muscle and anchor for valve tissue
-Electrical insulation between atria and ventricles; important in timing and coordination of contractile activity

Question 8

Define Epicardium

Answer 8

-Serous membrane covering heart
-Adipose in thick layer in some places
-Coronary blood vessels travel through this layer

Question 9

Identify the four chambers of the heart.

Answer 9

-Right and left atria
*Two superior chambers
*Receive blood returning to heart
*Auricles (seen on surface) enlarge chamber

-Right and left ventricles
*Two inferior chambers
*Pump blood into arteries

Question 10

Identify the surface features of the heart

Answer 10

*Atrioventricular sulcus—separates atria and ventricles

*Interventricular sulcus—overlies the interventricular septum that divides the right ventricle from the left

*Sulci contain coronary arteries

*Interatrial septum
-Wall that separates atria

*Pectinate muscles
-Internal ridges of myocardium in right atrium and both auricles

*Interventricular septum
-Muscular wall that separates ventricles

*Trabeculae carneae
-Internal ridges in both ventricles
-May prevent ventricle walls from sticking together after contraction

Question 11

Identify the four valves of the heart.

Answer 11

*Atrioventricular (AV) valves—control blood flow between atria and ventricles
-Right AV valve has three cusps (tricuspid valve)
-Left AV valve has two cusps (mitral valve, formerly ‘bicuspid’)
-Chordae tendineae: cords connect AV valves to papillary muscles on floor of ventricles
*Prevent AV valves from flipping or bulging into atria when ventricles contract
*Each papillary muscle has 2-3 attachments to heart floor (like Eiffel Tower) to distribute physical stress, coordinate timing of electrical conduction, and provide redundancy

*Semilunar valves—control flow into great arteries; open and close because of blood flow and pressure
-Pulmonary semilunar valve: in opening between right ventricle and pulmonary trunk
-Aortic semilunar valve: in opening between left ventricle and aorta

Question 12

Trace the flow of blood through the four chambers and valves of the heart and adjacent blood vessels.

Answer 12

*Ventricles relax
-Pressure drops inside the ventricles
-Semilunar valves close as blood attempts to back up into the ventricles from the vessels
-AV valves open
-Blood flows from atria to ventricles

*Ventricles contract
-AV valves close as blood attempts to back up into the atria
-Pressure rises inside of the ventricles
-Semilunar valves open and blood flows into great vessels

Question 13

Describe the arteries that nourish the myocardium and the veins that drain it.

Answer 13

**Left Coronary Artery
– Anterior interventricular branch (Left anterior descending)
– Circumflex branch

**Right coronary Artery
– Right marginal branch
– Posterior interventricular branch

Question 14

Describe the unique structure of cardiac muscle

Answer 14

Cardiac muscle cells (cardiomyocytes) are striated, branched, contain many mitochondria, and are under involuntary control.

Question 15

Describe the metabolic characteristics of cardiac muscle

Answer 15

Cardiac muscle depends almost exclusively on aerobic respiration to make ATP
-Rich in myoglobin and glycogen

Question 16

Explain the nature and functional significance of the intercellular junctions between cardiac muscle cells.

Answer 16

-Composed of an internal pacemaker and nerve-
like conduction pathways through myocardium.
-Gap junctions ensure the heart contracts as a unit

Question 17

Name the major cardiac vein

Answer 17

Coronary Sinus

Question 18

Describe the heart’s pacemaker and internal electrical conduction system.

Answer 18

1) SA node fires.
2) Excitation spreads through
atrial myocardium.
3) AV node fires.
4) Excitation spreads down AV
bundle.
5) Subendocardial conducting
network distributes
excitation through
ventricular myocardium.

Question 19

What is the nerves supplying the heart called?

Answer 19

Cardiac plexus

Question 20

What is cardiac plexus responsible for?

Answer 20

These are responsible for influencing heart rate, cardiac output, and contraction forces of the heart.

Question 21

interpret a normal electrocardiogram.

Answer 21

*P wave
-SA node fires, atria depolarize and contract
-Atrial systole begins 100 ms after SA signal

*QRS complex
-Ventricular depolarization
-Complex shape of spike due to different thickness and shape of the two ventricles

*ST segment—ventricular systole
-Corresponds to plateau in myocardial action potential

*T wave
-Ventricular repolarization and relaxation

Question 22

describe how changes in blood pressure operate the heart valves

Answer 22

As the ventricles contract, ventricular pressure exceeds arterial pressure, the semilunar valves open and blood is pumped into the major arteries. However, when the ventricles relax, arterial pressure exceeds ventricular pressure and the semilunar valves snap shut.

Question 23

relate the events of the cardiac cycle to the volume of blood entering and leaving the heart.

Answer 23

*In a resting person
-Atrial systole lasts about 0.1 second
-Ventricular systole lasts about 0.3 second
-Quiescent period, when all four chambers are in diastole, lasts about 0.4 second
*Total duration of the cardiac cycle is therefore 0.8 second in a heart beating 75 bpm

Question 24

Define cardiac output and explain its importance.

Answer 24

*Cardiac output (CO)—amount ejected by each ventricle in 1 minute
*Cardiac output = heart rate x stroke volume
-About 4 to 6 L/min at rest
-A RBC leaving the left ventricle will arrive back at the left ventricle in about 1 minute

Question 25

Identify the factors that govern cardiac output.

Answer 25

-Vigorous exercise increases CO to 21 L/min for a fit person and up to 35 L/min for a world-class athlete
*Cardiac reserve—the difference between a person’s maximum and resting CO
-Increases with fitness, decreases with disease

Question 26

Which cells are called contractile cells?

Answer 26

Myocytes which make up the myocardium

Question 27

Where are pacemaker cells present?

Answer 27

in the Sinoatrial Node

Question 28

The depolarization or repolarization cause muscle contraction

Answer 28

depolarization

Question 29

Electric conduction pathway of the heart?

Answer 29

Starts from the AV node -> bundle of His -> Left and right bundle branches -> Purkinje Fibers (then to the rest of the heart)

Question 30

A cardiac action potential spreads from the sinoatrial node to the right and left atria via the

Answer 30

atrial internodal tracts

Question 31

The resting membrane potential of cardiac cells is primarily determined by ______ ions.

Answer 31

The resting membrane potential of cardiac cells is primarily determined by potassium ions.