
Lewis: Medical-Surgical Nursing, 9th Edition
Chapter 32
Nursing Assessment: Cardiovascular System
KEY POINTS
Structures and Functions of CARDIOVASCULAR SYSTEM
Heart
•The heart
•oHas four chambers: the right and left atrium and right and left ventricles.
•oIs composed of three layers: endocardium, myocardium, and epicardium.
•oIs surrounded by a fibroserous sac called the pericardium.
•oHas four valves: mitral, aortic, tricuspid, and pulmonary. These serve to maintain
the one-way flow of blood.
•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.
•The coronary circulation provides blood to the myocardium (heart muscle). The right and
left coronary arteries are the first two branches off the aorta.
•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.
•oEach 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 terminating in
the Purkinje fibers.
•oThe electrical activity of the heart is recorded on an electrocardiogram (ECG).
•Contraction of the myocardium, or systole, results in ejection of blood from the
ventricles. Relaxation of the myocardium, or diastole, allows for filling of the ventricles.
•Cardiac output (CO) is the amount of blood pumped by each ventricle in 1 minute. It is
calculated by multiplying the amount of blood ejected from the ventricle with each heartbeat
(stroke volume [SV]) by the heart rate (HR) per minute: CO = SV HR.
•Factors affecting SV are preload, contractility, and afterload. Preload is the volume of
blood in the ventricles at the end of diastole, and afterload represents the systemic resistance
against which the left ventricle must pump.
Regulation of Cardiovascular System
•Stimulation of the sympathetic nervous system increases HR, speed of conduction
through the AV node, and force of atrial and ventricular contractions, whereas stimulation of the
parasympathetic nervous system decreases HR.
•Stimulation of baroreceptors and chemoreceptors, located in the aortic arch and carotid
sinus, can initiate changes in HR and arterial pressure.
•Normal BP is systolic BP less than 120 mm Hg and diastolic BP less than 80 mm Hg.