CHAPTER 7: CARDIOVASCULAR SYSTEM

I. The Blood Vessels
Chapter 5: Cardiovascular System –– Heart and Blood Vessels
A. The cardiovascular system has 3 types of blood vessels:
1. Arteries (and arterioles) which carry blood away from the heart to the capillaries.
2. The capillaries which permit exchange of nutrients, wastes, and gases with the
tissues.
3. Veins (and venules) which return blood from the capillaries to the heart.
B. The Arteries
The arterial wall has 3 layers which are thick and resilient.
The strong walls of an artery give it support when blood enters under pressure.
Divide into smaller arterioles –– small arteries just visible to the naked eye.
C. The Capillaries
D. The Veins
Middle layer has some elastic tissue, but is composed mostly of smooth
muscle fibers.
When these muscle fibers are contracted, the vessel is constricted. When they
are relaxed, the vessel is dilated.
Arteriole constriction or dilation affects blood pressure.
Arterioles branch into capillaries.
Capillaries are extremely narrow, microscopic blood vessels with a wall formed of
one layer of simple squamous cells.
Capillary beds (networks of many capillaries) are present in all regions of the body.
Gas, nutrient, and waste exchange occur across their thin walls.
Only certain capillaries are open at any given time. After eating, the capillaries that
serve the digestive system are open and those that serve the muscles are closed.
Venules are small veins that drain blood from the capillaries and then join to form a
vein.

II. The Heart
The walls of veins and venules have the same 3 layers as arteries, but they are much
thinner.
Thinner walls allow veins to expand to a greater extent.
Veins often have valves which allow blood to flow only toward the heart when open
and prevent the backward flow of blood when closed.
A. The heart is a cone-shaped, muscular organ about the size of a fist.
B. It is located between the lungs directly behind the sternum (breast bone) and is tilted so
the apex (pointed end) is directed left.
C. Myocardium is the major portion of the heart consisting of cardiac muscle tissue.
D. Heart lies within a pericardium sac that contains pericardial fluid which provides
cushioning.
E. Endocardium lines inner surface of the heart.
F. Internal wall called the septum separates heart into right and left halves.
G. Heart has 2 upper, thin-walled atria and 2 lower, thick-walled ventricles.
Atria receive blood from the venous portion of the cardiovascular system.
Atria are much smaller and weaker than muscular ventricles, but hold the same
volume of blood.
Ventricles pump blood into arterial portion of cardiovascular system.
H. Heart valves direct flow of blood and prevent backward movement.
Valves are supported by strong, fibrous tendons attached to muscular projections of
ventricular walls. They support the valves and prevent them from inverting when the
heart contracts.
Atrioventricular valves occur between atria and ventricles and prevent back flow of
blood from ventricle to atrium.
Right atrioventricular or tricuspid valve on right side of heart consists of 3
cusps or flaps.
Left atrioventricular or bicuspid (mitral) valve on left side of heart consists of
2 cusps or flaps.

Semilunar valves have flaps that resemble half-moons and are located between the
ventricles and their attached vessels.
III. Passage of Blood through the Heart
The pulmonary semilunar valve lies between the right ventricle and the
pulmonary trunk.
The aortic semilunar valve lies between the left ventricle and the aorta.
A. Oxygen-poor (deoxygenated) blood enters right atrium from both superior and inferior
vena cava.
B. Right atrium sends blood through right atrioventricular valve (tricuspid valve) to right
ventricle.
C. Right ventricle sends blood through pulmonary semilunar valve into pulmonary trunk.
The pulmonary trunk divides into two pulmonary arteries that go to the lungs.
D. Oxygen-rich (oxygenated) blood returns from lungs through pulmonary veins and is
delivered to the left atrium.
E. Left atrium sends blood through left atrioventricular valve (bicuspid or mitral valve) to
left ventricle.
F. Left ventricle sends blood through aortic semilunar valve into the aorta to the body proper
through arteries.
G. Oxygen-poor blood never mixes with oxygen-rich blood.
H. Blood must go through the lungs in order to pass from the right side to the left side of the
heart.
I. The heart is a double pump serving the lungs and the body circulations simultaneously.
J. Since the left ventricle has the harder job of pumping blood throughout the body, its walls
are thicker than those of the right ventricle.
K. The Heartbeat
Each heartbeat is called a cardiac cycle.
The heart contracts or beats about 70 times a minute.
Each heartbeat lasts about 0.85 seconds.
A normal adult heart rate at rest can vary from 60 to 80 beats per minute.

The heartbeat consists of phases: Systole refers to contraction of heart chambers and
Diastole is relaxation of heart chambers.
Atria contract first while ventricles relax (0.15 sec), then ventricles contract while
atria relax (0.30 sec), then all chambers rest (0.40 sec).
When the heart beats, the familiar lub-dup sound is heard as valves of the heart close.
Lub is caused by vibrations occurring when the atrioventricular valves close
due to ventricular contraction.
Dup is heard when the semilunar valves close due to back pressure of blood
in the arteries.
A heart murmur is often due to ineffective valves, which allow blood to pass back
into the atria after the atrioventricular valves have closed
Rhythmical contraction of the atria and ventricles is due to the intrinsic conduction
system of the heart.
SA (Sinoatrial) node is found in the upper dorsal wall of the right atrium. It
initiates the heartbeat by sending out an excitatory impulse every 0.85
seconds that cause atria to contract. It is called the pacemaker because it
serves to keep the heartbeat regular.
AV (Atrioventricular) node is found at the base of the right atrium very near
the septum. When stimulated by impulses from SA node, it sends out
impulses through septum to cause ventricles to contract.
An electrocardiogram (ECG) is a recording of the electrical changes that occur in
myocardium during a cardiac cycle.
An abnormality called ventricular fibrillation can be detected using an ECG.
Ventricular fibrillation is the most common cause of sudden cardiac death in
seemingly healthy individuals over the age of 35.
IV. Features of the Cardiovascular System
A. Pulse
Causes uncoordinated contraction of the ventricles.
Can be caused by injury or drug overdose.
The surge of blood entering the arteries causes their elastic walls to stretch and then
recoil. This alternating stretching and recoiling of an arterial wall can be felt as a
pulse in any artery that runs close to the body’s surface.

Pulse can be felt by placing several fingers on the radial artery which lies near the
outer border of the palm side of a wrist. A carotid artery, on either side of the trachea
in the neck, is another accessible location for feeling the pulse.
Normally the pulse rate indicates the rate of heartbeat because the arterial walls pulse
whenever the left ventricle contracts.
B. Blood Flow
The pulse rate is usually 60–80 beats per minute.
Blood pressure is the pressure of blood against the wall of a blood vessel.
A sphygmomanometer which has a pressure cuff is used to measure blood pressure
in the brachial artery of the arm.
Systolic pressure is the highest arterial pressure reached during ejection of blood
from the heart.
Diastolic pressure is the lowest arterial pressure that occurs while the heart ventricles
are relaxing.
Normal resting blood pressure for a young adult is 120mm mercury (Hg) over 80
mm Hg or 120/80.
The higher number is the systolic pressure and the lower number is the
diastolic pressure.
Blood pressure varies throughout the body. It is highest in the aorta and lowest in the
vena cava.
Both systolic and diastolic pressure decrease with distance from the left ventricle.
Blood pressure is minimal in venules and veins.
Instead of blood pressure, venous return is dependent on skeletal muscle contraction,
the presence of valves in veins, and respiratory movements.
V. The Cardiovascular Pathways
A. The cardiovascular system has 2 major circular pathways: The pulmonary circuit which
circulates blood through the lungs and the systemic circuit which serves the needs of the
body tissues.
B. The Pulmonary Circuit
Deoxygenated blood from the body collects in the right atrium and then passes into
the right ventricle, which pumps it to pulmonary trunk.

Pulmonary trunk divides into right and left pulmonary arteries to carry blood to each
lung.
In the pulmonary capillaries of the lungs, carbon dioxide is unloaded and oxygen is
picked up by blood.
Oxygenated blood from lungs is returned through pulmonary veins to left atrium.
Not all arteries carry oxygenated blood and not all veins carry deoxygenated blood.
Since blood in the pulmonary arteries is oxygen poor and blood in the pulmonary
veins is oxygen rich they serve as the exception.
C. The Systemic Circuit
The aorta (artery) and vena cava (veins) are the main pathways for blood in the
systemic circuit.
The superior vena cava collects blood from the head, chest, and arms while
the inferior vena cava collects blood from the lower body regions.
Transport of oxygenated blood moves from left ventricle through aorta out to all
tissues.
Deoxygenated blood returns from all tissues via vena cava.
The coronary arteries serve the heart muscle itself and are the first branches off the
aorta.
Coronary arteries lie on the external surface of the heart, where they divide into
arterioles.
Coronary veins collect deoxygenated blood from capillaries and empty into the right
atrium.
VI. Cardiovascular Disorders
A. Cardiovascular Disease (CVD) is the leading cause of untimely deaths in the U.S.
B. Risk of CVD can be reduced by following guidelines for a heart-healthy life style.
C. Hypertension (High Blood Pressure)
Occurs when blood moves through the arteries at a higher pressure than normal.
Hypertension is present when the systolic blood pressure is 140 or greater or the
diastolic blood pressure is 90 or greater.

Sometimes called the silent killer because it may not be detected until a stroke or
heart attack occurs.
Genetic predisposition.
D. Atherosclerosis
An accumulation of soft masses of fatty materials, including cholesterol, beneath the
inner linings of arteries –– plaque.
As plaque develops, it tends to protrude into a vessel interfering with blood flow.
Atherosclerosis begins in early adulthood and develops progressively through middle
age, but symptoms may not appear until an individual is age 50 or older. Plaque can
cause a clot to form on the arterial wall.
As long as the clot remains stationary, it is called a thrombus.
If a clot dislodges and moves along with the blood, it is called an embolus.
Aspirin reduces the stickiness of platelets and thereby lowers the probability that a
clot will form.
E. Stroke, Heart Attack, and Aneurysm
A cerebrovascular accident (CVA) also called a stroke, often results when a small
cranial arteriole bursts or is blocked by an embolus.
A lack of oxygen causes a portion of the brain to die, and paralysis or death
can result.
A myocardial infarction (MI), also called a heart attack, occurs when a portion of the
heart muscle dies due to a lack of oxygen.
If a coronary artery becomes partially blocked, the individual may then suffer
from angina pectoris, characterized by radiating pain in the left arm.
When a coronary artery is completely blocked, a heart attack occurs.
An aneurysm is a ballooning of a blood vessel, most often the abdominal artery or
the arteries leading to the brain.
Atherosclerosis and hypertension can weaken the wall of an artery to the
point that an aneurysm develops.
F. Varicose veins develop when the valves of veins become weak and ineffective due to the
backward pressure of blood.

VII. The Lymphatic System Helps the Cardiovascular System
A. The lymphatic system consists of lymphatic vessels and the lymphatic organs.
B. The lymphatic system has three main functions that contribute to homeostasis:
Lymphatic capillaries take up excess tissue fluid and return it to the bloodstream; lacteals
receive fat molecules at the intestinal villi and transport them to the bloodstream; the
lymphatic system helps defend the body against disease.
C. The lymphatic vessels carry lymph which has the same composition as tissue fluid.
The lymphatic vessels merge before entering one of two ducts: the thoracic duct or
the right lymphatic duct. The lymphatic ducts enter the subclavian veins, which are
cardiovascular veins in the thoracic region.