My Chapter 18 A&P

Describe the location and position of the heart in the body

The heart is enclosed within the mediastinum. It lies anterior to the vertebral column and posterior to the sternum. It tips slightly to the left

The Frank-Starling law explains that the critical factor controlling stroke volume is the degree of stretch of the cardiac muscle cells just before they contract.

The important factor in the stretching of cardiac muscle is the amount of blood returning to the heart and distension of the ventricles.

Describe how heart contraction and relaxation influence coronary blood flow.

When the ventricles begin to relax following contraction, blood flows back toward the ventricles, getting caught in the semilunar valves. During this time, the coronary arteries are actively delivering blood to the myocardium. During ventricular contraction, the coronary vessels are compressed and ineffective in blood delivery

The sequence of contraction of the heart chambers is

both atria followed by both ventricles.

Cardiac tamponade is

compression of the heart due to accumulation of blood or inflammatory fluid in the pericardial sac. Such compression reduces the ability of the heart to beat and act as an effective pump, leading to inadequate blood delivery (which results in ischemia and cyanosis) and ultimately cardiogenic shock.

A longer refractory period of cardiac muscle is desirable because

it prevents the heart from going into prolonged or tetanic contractions, which would stop its pumping action

The chordae tendineae

prevent the AV valve flaps from everting.

Cardiac output is

the amount of blood pumped out by the left ventricle in one minute. It can be calculated by the following equation: cardiac output = heart rate × stroke volume.

The activity of the heart depends on intrinsic properties of cardiac muscle and on neural factors. Thus,

vagus nerve stimulation of the heart reduces heart rate, sympathetic nerve stimulation of the heart decreases times available for ventricular filling, sympathetic stimulation of the heart increases its force of contraction

The fact that the left ventricular wall is thicker than the right reveals

that it pumps blood against greater resistance.

The elements of the intrinsic conduction system of the heart, beginning with the pacemaker, are:

the SA node or pacemaker, AV node, AV bundle, right and left bundle branches, and the subendocardial conducting network.

The portion of the intrinsic conduction system located in the superior interventricular septum is the

AV bundle

When the semilunar valves are open, which of the following are occurring?

AV valves are closed, ventricles are in systole, blood enters aorta, and blood enters pulmonary arteries

These abnormal sounds would be heard most clearly during ventricular diastole for the aortic valve and during atrial systole for the mitral valve

An incompetent valve has a swishing sound after the valve has supposedly closed. A stenosed valve has a high-pitched sound when blood is being forced through its constricted opening during systole just before valve closure

In a fetus, the common function of the foramen ovale and the ductus arteriosus is to allow blood to bypass the pulmonary circulation, and move directly into the systemic circulation.

If these shunts remain patent after birth, the opening prevents adequate gas exchange, O2 loading and CO2 unloading, in the pulmonary circulation. This would occur because a large volume of blood returning to the heart would simply bypass the pulmonary circuit.

The cardiac cycle includes all events associated with the flow of blood through the heart during one complete heartbeat.

One cycle includes a period of ventricular filling (mid-to-late diastole at the end of which atrial systole occurs), isovolumetric contraction (early ventricular systole), ventricular ejection (mid to late ventricular systole), and isovolumetric relaxation (early ventricular diastole).

See Figure 18.17.

The P wave results from impulse conduction from the SA node through the atria during atrial depolarization. The QRS complex results from ventricular depolarization and precedes ventricular contraction. Its shape reveals the different size of the two ventricles and the time required for each to depolarize. The T wave is caused by ventricular repolarization.

The pericardium has two layers, a fibrous and a serous layer.

The outer fibrous layer is a fibrous connective tissue that protects the heart and anchors it to surrounding structures. The inner serous layer (squamous epithelial cells) lines the fibrous layer as the parietal serous pericardium and at the base of the heart continues over the heart surface as the visceral serous pericardium. The visceral serous pericardium is the outermost layer of the heart wall, that is, the epicardium

A drop of blood traced from the time it enters the right atrium until it enters the left atrium...

The path from the right atrium to the left atrium is as follows: right atrium, right ventricle, pulmonary trunk, right and left pulmonary arteries, lungs, pulmonary veins, left atrium. This circuit is called the pulmonary circuit

The important function of this conduction system is

This system functions to initiate and distribute impulses throughout the heart so that the myocardium depolarizes and contracts in an orderly, sequential manner from atria to ventricles

To auscultate the aortic valve, place the stethoscope over the second intercostal space at the right sternal margin.

To auscultate the mitral valve, place the stethoscope over the heart apex, in the fifth intercostal space in line with the middle of the clavicle.

The synonyms are as follows:

a. atrioventricular groove: coronary sulcus b. tricuspid valve: right AV valve c. bicuspid valve: left AV or mitral valve d. atrioventricular bundle: bundle of His

In the heart,

action potentials are conducted from cell to cell across the myocardium via gap junctions, the SA node sets the pace for the heart as a whole, and spontaneous depolarization of cardiac cells can occur in the absence of nerve stimulation

Freshly oxygenated blood is first received by the

left atrium

An ECG provides information about

movement of the excitation wave across the heart.

The major branches of the coronary arteries and the areas they serve are as follows:

the left coronary artery runs toward the left side of the heart and divides into the anterior interventricular artery and the circumflex artery. The anterior interventricular artery supplies blood to the interventricular septum and anterior walls of both ventricles, and the circumflex artery serves the left atrium and the posterior walls of the left ventricle. The right coronary artery splits to the right side of the heart, where it divides into the marginal artery and the posterior interventricular artery. The marginal artery serves the myocardium of the lateral part of the right side of the heart and the posterior interventricular artery, which runs to the heart apex and supplies the posterior ventricular walls.