Ch12 - Heart

Essentials of Anatomy and Physiology, Seventh Edition
Valerie C. Scanlon and Tina Sanders
Copyright © F.A. Davis Company 2015
Chapter 12
The Heart

The heart pumps blood, which creates blood pressure
in the vascular system.
The pumping of the heart circulates oxygen, nutrients, and
other substances.
The cone-shaped heart is located in a thoracic area called
the mediastinum.
Question: Describe the location of the heart in terms of surrounding organs.

Answer
The heart is medial to the lungs and superior to the diaphragm.
The rib cage protects the heart from mechanical injury.

Cardiac Muscle Tissue—myocardium
Cardiac muscle fibers—units of contraction are sarcomeres:
myosin and actin
Mitochondria:
Cardiac myocytes generate their own action potentials.
Intercalated discs—
Atrial natriuretic peptide (ANP)—produced when the atrial
walls are stretched by greater blood volume
Function:

Pericardial Membranes—three layers that enclose
the heart
Fibrous pericardium—the outer layer, a loose-fitting sac:
Parietal pericardium—a serous membrane; lines the fibrous
pericardium
Visceral pericardium or epicardium—a serous membrane on
the surface of the myocardium
Serous fluid—

Chambers of the Heart—the walls of the four chambers
are made of myocardium
Endocardium—simple squamous epithelium that lines the
chambers and covers the valves
Function:
Right and left atria—upper chambers:
Interatrial septum—
Right and left ventricles—lower chambers:
Interventricular septum—

Right Atrium (see Table 12–1)
Receives blood from:
Superior vena cava—
Inferior vena cava—
The tricuspid valve (right AV valve)—at the opening of the
atrium to the right ventricle
Function:

Left Atrium
Receives blood from the pulmonary veins—
The mitral valve (left AV or bicuspid valve)—at the opening
of the atrium to the left ventricle
Function:

Right Ventricle—has relatively thin walls
Pumps blood into the pulmonary artery—
The pulmonary semilunar valve is at the junction of the
artery with the ventricle.
Function:
Papillary muscles and chordae tendineae—anchor the AV
valve flaps to the floor of the ventricle
Function:

Left Ventricle—has relatively thick walls
Pumps blood into the aorta—
The aortic semilunar valve is at the junction of the aorta with
the ventricle.
Function:
The heart is a double pump; both pumps work
simultaneously. The right side receives blood from the
body and pumps it to the lungs.
Question: What does the left side of the heart do?

Answer
The left side of the heart receives blood from the lungs and
pumps it to the body.

Coronary Vessels
Pathway: ascending aorta  coronary arteries  coronary
capillaries  coronary veins  coronary sinus  right
atrium
Purpose: the system of coronary vessels circulates
oxygenated blood throughout the myocardium.
Myocardial infarction—

Cardiac Cycle—the sequence of events in one
heartbeat
Systole—
Diastole—
1. The atria continually receive blood from the veins;
pressure within the atria increases. The AV valves are
opened.
2. Two-thirds of atrial blood flows passively into the
ventricles. Atrial systole—

Cardiac Cycle (continued)
3. The beginning of ventricular systole closes the AV valves
and opens the arterial semilunar valves.
4. All blood that enters the pulmonary artery and aorta is
pumped by ventricular systole.
5. The ventricles relax, and because blood is flowing into the
atria, the cycle begins again.
Question: The events of the cardiac cycle keep blood moving from the veins,
through the heart, and into the arteries. Are these events electrical, chemical,
or mechanical?

Answer
The events of the cardiac cycle are mechanical.

Heart Sounds—two sounds per heartbeat
First sound—created by the closure of the AV valves during
ventricular systole
Second sound—created by closure of the aortic and
pulmonary semilunar valves
Heart murmur—

Cardiac Conduction Pathway—the pathway of
electrical impulses (action potentials) during the
cardiac cycle
1. Sinoatrial (SA) node—in the wall of the right atrium
Cells of the SA node are more permeable than other
cardiac cells to Na+
ions—
2. Atrioventricular (AV) node—in the lower interatrial septum

Cardiac Conduction Pathway (continued)
3. The atrioventricular (AV) bundle, or bundle of His, is in
the upper interventricular septum.
4. Right and left bundle branches—
5. Purkinje fibers—
If part of the pathway malfunctions, the next part will initiate
the heartbeat—
Question: What is an arrhythmia?

Answer
An arrhythmia is an irregular heartbeat caused by damage
to part of the conduction pathway, or by a beat generated
in another part (usually damaged) of the myocardium.

Heart Rate
Healthy adult—heart rate of 60 to 80 beats per minute
Bradycardia:
Tachycardia:
Children and infants—faster heart rates:
This is a size factor.
An adult in excellent physical condition—the heart is a
more efficient pump, therefore:

Cardiac Output (see Table 12–2)
Cardiac output (CO) is the amount of blood pumped by a
ventricle in 1 minute.
CO depends on pulse and stroke volume.
Stroke volume is the amount of blood pumped by a
ventricle in one beat; average: 60 to 80 mL.
Cardiac output = stroke volume × pulse
Example: stroke volume, 70 mL; pulse, 70 bpm
Cardiac output =

Cardiac Output (continued)
For the athlete:
Resting cardiac output: 5000 mL
Resting pulse: 50 bpm
Therefore, resting stroke volume =
The athlete’s more efficient heart pumps more blood per
beat and, therefore, needs fewer bpm to provide sufficient
cardiac output.

Cardiac Output (continued)
During exercise:
Stroke volume: 100 mL
Pulse: 100 bpm
Exercise cardiac output =
Cardiac reserve: the difference between
resting cardiac output and maximum
cardiac output:

Regulation of Heart Rate—the heart generates its own
beat; rate may be changed by the nervous system
Medulla: cardiac centers:
Accelerator
Inhibitory
Sympathetic impulses to the heart:
Parasympathetic (vagus nerves) impulses:
Information for changes in rate comes from pressoreceptors
and chemoreceptors.

Regulation of Heart Rate (continued)
Pressoreceptors—detect changes in blood pressure;
located in the carotid sinuses and the aortic sinus
Sensory nerves: carotid— aortic—
Chemoreceptors—detect changes in blood oxygen level;
located in the carotid bodies and the aortic body
Sensory nerves:

If BP to the brain decreases:
Carotid pressoreceptors detect the change.
Fewer impulses are sent along glossopharyngeal nerves
to the medulla.
Accelerator center is stimulated, sends motor impulses
along sympathetic nerves to increase heart rate and force
of contraction.
Result:

Hormonal regulation
Questions: Name the hormone that stimulates increased heart rate and force of
contraction.
Name the gland that produces this hormone, and state when it does so.

Answers
Epinephrine stimulates increased heart rate and force of
contraction.
The adrenal medulla secretes epinephrine during stressful
situations (fear, anger, exertion).

Wrap-Up Question
Name the part or aspect of the heart described.
1. Initiates each heartbeat
2. On the surface of the myocardium
3. Tracing of the electrical activity of the heart
4. Volume of blood pumped by LV in 1 minute
5. Left AV valve
6. Nerves to slow the heart rate
7. Lining of chambers
8. CNS center for heart rate

Answers
1. Initiates each heartbeat—SA node
2. On the surface of the myocardium—epicardium
3. Tracing of the electrical activity—electrocardiogram
4. Volume pumped by LV in 1 minute—cardiac output
5. Left AV valve—mitral valve
6. Nerves to slow the heart rate—vagus nerves
7. Lining of chambers—endocardium
8. CNS center for heart rate—medulla

Ch12 - Heart

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