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1

The heart
♣ Has four chambers:
♣ Is composed of three layers:
o Is surrounded by a?
o Has four valves:

♣ Has four chambers: the right and left atrium and right and left ventricles.
♣ Is composed of three layers: endocardium (thin inner lining), myocardium (layer of muscle), and epicardium (outer layer).
o Is surrounded by a fibroserous sac called the pericardium.
o Has four valves: mitral, aortic, tricuspid, and pulmonary. These maintain the one-way flow of blood.

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Heart: The thickness of the wall of each chamber is different. The atrial myocardium is thinner than that of the ventricles, and the left ventricular wall is two or three times thicker than the right ventricular wall. The thickness of the left ventricle is necessary to?

produce the force needed to pump the blood into the systemic circulation.

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Blood flow:

1, The right atrium receives venous blood from the inferior and superior venae cavae and the coronary sinus. The blood then passes through the tricuspid valve into the right ventricle.
2, With each contraction, the right ventricle pumps blood through the pulmonic valve into the pulmonary artery and to the lungs.
3, Oxygenated blood flows from the lungs to the left atrium by way of the pulmonary veins.
4, It then passes through the mitral valve and into the left ventricle.
5, As the heart contracts, blood is ejected through the aortic valve into the aorta and thus enters the systemic circulation.

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The right side of the heart receives venous blood from the body (via the vena cava) and pumps it to the lungs where it is oxygenated. Blood returns to the?

left side of the heart (via the pulmonary veins) and is pumped to the body via the aorta.

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The pulmonic and aortic valves (also known as semilunar valves) prevent blood from?.

regurgitating into the ventricles at the end of each ventricular contraction.

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Blood supply to myocardium: The myocardium has its own blood supply, the coronary circulation. Blood flow into the two major coronary arteries occurs primarily during diastole (relaxation of the myocardium). The left coronary artery arises from the aorta and divides into two main branches: the left anterior descending artery and left circumflex artery. These arteries supply the left atrium, left ventricle, interventricular septum, and a portion of the right ventricle. The right coronary artery also arises from the aorta, and its branches supply the right atrium, right ventricle, and a portion of the posterior wall of the left ventricle. In 90% of people the atrioventricular (AV) node and the bundle of His receive blood supply from the?

right coronary artery. For this reason, blockage of this artery often causes serious defects in cardiac conduction.

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Blood flow into the two major coronary arteries occurs primarily during?

diastole (relaxation of the myocardium)

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Blood supply to myocardium: The divisions of coronary veins parallel the coronary arteries. Most of the blood from the coronary system drains into the?

coronary sinus (a large channel), which empties into the right atrium near the entrance of the inferior vena cava.

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Conduction system: consists of specialized tissue responsible for creating and transporting electrical impulse (action potential). This impulse starts depolarization of the heart cells and subsequently heart contraction. The electrical impulse begins in the?

1) sinoatrial (SA) node (pacemaker of the heart). Each impulse coming from SA node travels through interatrial pathways to depolarize the atria, resulting in a contraction.
2) electrical impulse travels from atria to AV node through internodal pathways.
3) signal then moves through bundle of His and left and right bundle branches. left bundle branch has two fascicles (divisions): anterior and posterior. action potential moves through walls of both ventricles by means of Purkinje fibers.
4) ventricular conduction system delivers the impulse within 0.12 second. This triggers a synchronized right and left ventricular contraction and ejection of blood into the pulmonary and systemic circulations.
5) repolarization occurs when contractile fiber cells and conduction pathway cells regain resting polarized condition. Heart muscle cells have a compensatory mechanism that makes them unresponsive or refractory to restimulation during the action potential. During ventricular contraction, there is an absolute refractory period during which heart muscle does not respond to any stimuli. After this period, heart muscle gradually recovers its excitability, and a relative refractory period occurs by early diastole.

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The coronary circulation provides blood to the myocardium (heart muscle). The right and left coronary arteries are the?

first two branches off the aorta.

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The conduction system consists of specialized cells that create and transport electrical impulses. These electrical impulses initiate?

depolarization of the myocardium. This triggers a cardiac contraction.

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Each electrical impulse starts at the?

SA node (located in the right atrium), travels to the AV node (located at the atrioventricular junction), through the bundle of His, down the right and left bundle branches (located in the ventricular septum), and ends in the Purkinje fibers.

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Electrocardiogram: The letters P, QRS, T, and U are used to identify the separate waveforms.

1) P wave, begins with the firing of the SA node and represents depolarization of the atria.
2) The QRS complex represents depolarization from the AV node throughout the ventricles.
* There is a delay of impulse transmission through the AV node that accounts for the time between the beginning of the P wave and the beginning of the QRS wave.
3) The T wave represents repolarization of the ventricles. 4) The U wave, if seen, may represent repolarization of the Purkinje fibers, or it may be associated with hypokalemia.

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Electrocardiogram: Intervals between these waves (PR, QRS, and QT intervals) reflect the time it takes for the signal to travel from one area of the heart to another. These time intervals are?

measured, and changes from these time references often indicate pathologic conditions

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Mechanical System.
Depolarization triggers mechanical activity.
1) Systole, contraction of the heart muscle, results in?
2) Relaxation of the heart muscle, diastole, allows for?
3) Cardiac output (CO), the amount of?

1) ejection of blood from the ventricles.
2) filling of the ventricles.
3) blood pumped by each ventricle in 1 minute, is calculated by multiplying the amount of blood ejected from the ventricle with each heartbeat: stroke volume (SV) times heart rate (HR) per minute: CO = SV x HR

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1) For the normal adult at rest, CO is maintained in the range of?
2) Cardiac index (CI) is the?
3) The CI adjusts the CO to the body size. The normal CI is?

1) 4 to 8 L/min
2) CO divided by the body surface area (BSA).
3) 2.8 to 4.2 L per minute per meter squared (L/min/m2)

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Amount of blood ejected with each heart beat

Stroke volume

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Amount of blood pumped by each ventricle in 1 minute
Normal:

Cardiac output: Amount of blood pumped by each ventricle in 1 minute
Normal 4-8 L/min

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Cardiac index:
Normal:

Cardiac index: CO divided by body surface area
Normal 2.8-4.2 L/min/m2

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Factors Affecting Cardiac Output.
Numerous factors can affect either the HR or SV, and thus the CO. The HR, which is controlled primarily by the autonomic nervous system, can reach as high as 180 beats/min for short periods without harmful effects. The factors affecting the SV are?

preload, contractility, and afterload. Increasing preload, contractility, and afterload increases the workload of the heart muscle, resulting in increased O2 demand.

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Frank-Starling law states that, to a point, the more the myocardial fibers are stretched, the greater their force of contraction. The volume of blood in the ventricles at the end of diastole, before the next contraction, is called preload. Preload determines the amount of?

stretch placed on myocardial fibers. Preload can be increased by a number of conditions such as hypertension, aortic valve disease, and hypervolemia

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Factors affecting cardiac output: Contractility can be increased by?

epinephrine and norepinephrine released by the sympathetic nervous system. Increasing contractility raises the SV by increasing ventricular emptying.

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Factors affecting cardiac output:
1) Afterload is the?
2) Afterload is affected by the?

1) peripheral resistance against which the left ventricle must pump.
2) size of the ventricle, wall tension, and arterial blood pressure (BP). If the arterial BP is elevated, the ventricles meet increased resistance to ejection of blood, increasing the work demand. Eventually this results in ventricular hypertrophy, an enlargement of the heart muscle without an increase in CO or the size of chambers

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Factors Affecting Cardiac Output

1) Preload: Volume of blood in ventricles at the end of diastole
2) Contractility
3) Afterload: Peripheral resistance against which the left ventricle must pump

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A patient is receiving a drug that decreases afterload. To evaluate the patient's response to this drug, what is most important for the nurse to assess?
A. Heart rate
B. Lung sounds
C. Blood pressure
D. Jugular venous distention

C. Blood pressure (trying to reduce afterload so we must reduce BP)

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The cardiovascular system must respond to numerous situations in health and illness (e.g., exercise, stress, hypovolemia). The ability to respond to these demands by altering CO is termed?

cardiac reserve

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Factors affecting SV are preload, contractility, and afterload.

- Preload is the volume of blood in the ventricles at the end of diastole
- afterload represents the systemic resistance against which the left ventricle must pump.

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Blood Vessels.
The three major types of blood vessels in the vascular system are the arteries, veins, and capillaries.

- Arteries, except for the pulmonary artery, carry oxygenated blood away from the heart.
- Veins, except for the pulmonary veins, carry deoxygenated blood toward the heart.
- Small branches of arteries and veins are arterioles and venules.
- Blood circulates from the left side of the heart into arteries, arterioles, capillaries, venules, and veins, and then back to the right side of the heart.

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Heart structure: The arterial system differs from the venous system by the amount and type of tissue that make up arterial walls. The large arteries have thick walls composed mainly of elastic tissue. This elastic property cushions the impact of the pressure created by ventricular con­traction and provides recoil that propels blood forward into the circulation. Large arteries also contain some?

smooth muscle. Examples of large arteries are the aorta and pulmonary artery.

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Arterioles have relatively little elastic tissue and more smooth muscle. Arterioles serve as the major control of?

arterial BP and distribution of blood flow. They respond readily to local conditions such as low O2 and increasing levels of CO2 by dilating or constricting.