Download The_Circulatory_System

Location, Size, and Position of the Heart
The heart is a triangular organ located in the mediastinum, with two thirds of the mass to the
left of the body midline, and one third to the right; the apex is on the diaphragm; it is the size
and shape of a closed fist
Anatomy of the Heart
Heart chambers
The two upper chambers are called atria (receiving chambers)—right and left atria
The two lower chambers are called ventricles (discharging chambers)—right and left ventricles
The wall of each heart chamber is composed of cardiac muscle tissue called myocardium
The endocardium is the smooth lining of each heart chamber
Inflammation of endocardium called endocarditis
The pericardium and pericarditis
The pericardium is a two-layered fibrous sac with a lubricated space between the two layers
Pericarditis is inflammation of the pericardium
Cardiac tamponade: compression of the heart caused by fluid building up between the layers of
the pericardium
Four valves keep blood flowing through the heart and prevent backflow
Incompetent valves “leak,” allowing some blood back into the chamber from which it came
Coronary Circulation and Coronary Heart Disease
Blood, which supplies oxygen and nutrients to the myocardium of the heart, flows through the
right and left coronary arteries
Blockage of blood flow through the coronary arteries can cause myocardial infarction (heart
attack)
Atherosclerosis (a type of “hardening of the arteries” in which lipids build up on the inside wall
of blood vessels) can partially or totally block coronary blood flow
Angina pectoris: chest pain caused by inadequate oxygen to the heart
Cardiac Cycle
The heart beat is regular and rhythmic—each complete beat called a cardiac cycle—averaging
about 72 beats per minute
Each cycle, about 0.8 seconds long, is subdivided into systole (contraction phase) and diastole
(relaxation phase)
Stroke volume is the volume of blood ejected from one ventricle with each beat
Cardiac output is the amount of blood that one ventricle can pump each minute—the average
is about 5 L per minute at rest
Conduction System of the Heart
Cardiac dysrhythmia refers to an abnormality in heart rhythm
Heart block: conduction of electrical impulses is blocked
Can be treated by implanting an artificial pacemaker
Bradycardia: slow heart rate (under 60 beats/min)
Tachycardia: rapid heart rate (over 100 beats/min)
Sinus dysrhythmia: a variation in heart rate during breathing cycle
Premature contraction (extrasystole): contraction that occurs sooner than expected in a normal
rhythm
Fibrillation—condition in which cardiac muscle fibers are “out of step,” producing no effective
pumping action
Heart Failure
Heart failure: the inability to pump enough returned blood to sustain life; it can be caused by
many different heart diseases
Right-sided heart failure: failure of the right side of the heart to pump blood, usually because
the left side of the heart is not pumping effectively
Left-sided heart failure (congestive heart failure) involves an inability of the left ventricle to
pump effectively, resulting in congestion of the systemic and pulmonary circulations
Diseased hearts can be replaced by donated living hearts (transplants) or by artificial hearts
(implants), although both procedures have yet to be perfected
Blood Vessels
Types:
Arteries carry blood away from the heart
Veins carry blood toward the heart
Capillaries carry blood from the arterioles to the venules
Functions
Arteries: distribution of nutrients, gases, etc., with movement of blood under high pressure
Capillaries: serve as exchange vessels for nutrients, wastes, and fluids
Veins: collect blood for return to the heart; low pressure vessels
Disorders of Blood Vessels
Disorders of arteries
Arteries must withstand high pressure and remain free of blockage
Arteriosclerosis: hardening of the arteries; reduces flow of blood, possibly causing ischemia that
may progress to necrosis (or gangrene)
Atherosclerosis: a disorder in which lipids and other matter blocks arteries
May be corrected by vasodilators, angioplasty, or surgical replacement
Aneurysm: an abnormal widening of the arterial wall
Aneurysms promote formation of thrombi that may obstruct vital tissues; may burst, resulting
in life-threatening hemorrhaging
Cerebrovascular accident (CVA) or stroke: ischemia of brain tissue caused by embolism or
hemorrhage
Disorders of Blood Vessels
Disorders of veins
Veins are low-pressure vessels
Varicose veins (varices) are enlarged veins in which blood pools
Hemorrhoids are varicose veins in the rectum
Treatments include supporting affected veins and surgical removal
Thrombophlebitis: vein inflammation (phlebitis) accompanied by clot (thrombus) formation;
may result in fatal pulmonary embolism
Circulation of Blood
Systemic circulation
Carries blood throughout the body
Path goes from left ventricle through the aorta, smaller arteries, arterioles, capillaries, venules,
venae cavae, to right atrium
Pulmonary circulation
Carries blood to and from the lungs; arteries deliver deoxygenated blood to the lungs for gas
exchange
Path goes from right ventricle through pulmonary arteries, lungs, pulmonary veins, to left
atrium
Hepatic portal circulation
Unique blood route through the liver
Assists with homeostasis of blood glucose
Blood Pressure
Blood pressure is push or force of blood in the blood vessels
Highest in the arteries, lowest in the veins
A blood pressure gradient causes blood to circulate; liquids can flow only from the area where
pressure is higher to where it is lower
Blood volume, heartbeat, and blood viscosity are the main factors determining blood pressure
Blood pressure varies within normal range from time to time
Venous return of blood to the heart depends on five mechanisms: a strongly beating heart, an
adequate arterial blood pressure, valves in the veins, pumping action of skeletal muscles as
they contract, and changing pressures in the chest cavity caused by breathing
Circulatory Shock
Circulatory shock: failure of the circulatory system to deliver oxygen to the tissues adequately,
resulting in cell impairment
When the cause is known, shock can be classified by this scheme:
Cardiogenic shock is caused by heart failure
Hypovolemic shock is caused by a drop in blood volume that causes blood pressure (and blood
flow) to drop
Neurogenic shock is caused by a nerve condition that relaxes (dilates) blood vessels and thus
reduces blood flow
Anaphylactic shock is caused by a type of severe allergic reaction characterized by blood vessel
dilation
Septic shock results from complications of septicemia (toxins in blood resulting from infection)