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CHAPTER 12: CARDIOVASCULAR SYSTEM
LECTURE OUTLINE
12.1 The Blood Vessels
The cardiovascular system has three types of blood vessels: the arteries, the capillaries, and the
veins.
The Arteries
An arterial wall has three layers including a layer of smooth muscle that can contract to
regulate blood flow and blood pressure. Smaller arteries branch into a number of
arterioles.
The Capillaries
Capillaries join arterioles to venules. They are extremely narrow and have thin walls.
The exchange of substances takes place in the capillaries.
The Veins
Veins and venules take blood from the capillary beds to the heart. Veins often have
valves which prevent blood from flowing backward when closed.
12.2 The Human Heart
The heart is a cone-shaped, muscular organ about the size of a fist. The major portion of the
heart, called the myocardium, consists largely of cardiac muscle tissue. Internally, the heart has
four chambers: two thin-walled atria, and two thick-walled ventricles.
Path of Blood through the Heart
There is a specific pathway whereby blood flows through the heart such that oxygen-poor
blood never mixes with oxygen-rich blood. The pumping of the heart sends blood out to
the rest of the body under pressure.
The Heartbeat
When the heart beats, first the two atria contract at the same time; then the two ventricles
contract at the same time. Then all the chambers relax. The word systole refers to
contraction of heart muscle, and the word diastole refers to relaxation of heart muscle.
Intrinsic Control of Heartbeat
The rhythmic contraction of the atria and ventricles is due to the intrinsic
conduction system of the heart. Nodal tissue, which has both muscular and
nervous characteristics, is located in two regions of the heart.
Extrinsic Control of Heartbeat
The body also has extrinsic ways to regulate the heartbeat. A cardiac control
center exists in the medulla oblongata of the brain. Hormones can also stimulate
the heart.
The Electrocardiogram
The electrocardiogram is a recording of the electrical changes that occur in the
myocardium during a cardiac cycle. Body fluids contain ions that conduct electrical
currents.
12.3 The Vascular Pathways
The cardiovascular system includes two circuits: the pulmonary and the systemic circuit.
The Pulmonary Circuit
The pulmonary arteries take oxygen-poor blood from the right ventricle to the lungs and
the pulmonary veins return oxygen-rich blood to the left atrium.
The Systemic Circuit
The systemic circuit includes all the arteries and veins that feed the head, chest, arms, and
lower body regions.
Blood Pressure
Systolic pressure results from blood being forced into the arteries during
ventricular systole, and diastolic pressure is the pressure in the arteries during
ventricular diastole. A blood pressure reading consists of these two numbers: for
example, 120/80 (systolic/diastolic).
12.4 Blood
Blood has transport functions, regulatory functions, and protective functions. It consists of
plasma, the liquid portion of the blood, and the formed elements.
Plasma
Plasma contains a variety of inorganic and organic substances dissolved or suspended in
water.
The Red Blood Cells
Mature red blood cells don’t have a nucleus and are biconcave disks. Their shape
increases their flexibility for moving through capillary beds and their surface area for
diffusion of gases. Red blood cells carry oxygen.
The White Blood Cells
White blood cells differ from red blood cells in that they are usually larger, have a
nucleus, lack hemoglobin, and without staining appear translucent. They fight infection
and play a role in the development of immunity.
The Platelets and Blood Clotting
Platelets are fragments of certain large cells and are involved in the process of blood
clotting. There are at least 12 clotting factors in the blood that participate in the
formation of a blood clot.
Blood Clotting
There are several steps involved in blood clotting. First, platelets clump at the
site of the puncture. This and the damaged tissue activate several factors that
result in a cascade of enzymatic reactions, eventually resulting in a fibrin clot.
Hemophilia
Hemophilia is an inherited clotting disorder caused by a deficiency in a clotting
factor.
Bone Marrow Stem Cells
A stem cell is a cell that is ever capable of dividing and producing new cells that go on to
differentiate into particular types of cells. Bone marrow contains multipotent stem cells.
Capillary Exchange
Two forces primarily control movement of fluid through the capillary wall: osmotic
pressure and blood pressure.
12.5 Cardiovascular Disorders
Cardiovascular disease is the leading cause of untimely death in Western countries.
Atherosclerosis
Atherosclerosis is an accumulation of soft masses of fatty materials beneath the inner
lining of arteries.
Stroke, Heart Attack, and Aneurysm
A stroke results when a small cranial arteriole bursts or is blocked. If a coronary artery
becomes blocked, a portion of the heart muscle dies due to lack of oxygen and a heart
attack occurs. An aneurysm is a ballooning of a blood vessel.
Coronary Bypass Operations
During this operation, a surgeon bypasses an obstructed coronary artery with a
segment from another blood vessel.
Clearing Clogged Arteries
In angioplasty, a cardiologist uses a catheter to open a clogged artery.
Dissolving Blood Clots
Tissue plasminogen activator is converted into an enzyme that dissolves blood
clots.
Heart Transplants and Artificial Hearts
Although heart transplants are usually successful, the need for hearts is greater
than the supply. Only a few patients have received a total artificial heart.
Hypertension
Hypertension, or high blood pressure, is sometimes called “the silent killer” because it
may not be detected until a stroke or heart attack occurs. Hypertension is most often due
to a narrowing of the arteries.