ch 12 a&p
CHAPTER 12-THE CARDIOVASCULAR SYSTEM
I. THE HEART
A. The heart serves as the primary pump for the human body. It pumps blood through a
closed system of blood vessels.
B. The heart is a hollow, four-chambered, muscular pump located between the lungs in the
mediastinum of the thoracic cavity.
C. The heart is about the size of a fist (weighs less than 1 pound).
C. About 2/3rds of the heart is to the left of the midsternal line. The base of the heart is
located at the top of the heart, the apex of the heart points towards the left hip.
II. COVERINGS AROUND THE HEART
A. The heart is enclosed and held in place by a double-walled sac known as the pericardium.
B. The Pericardium
1. Is composed of 2 layers:
a. The Fibrous Pericardium-composed of dense connective tissue. This is a
bag that encloses and anchors the heart in place.
b. The Serous Pericardium-inner membrane that is composed of two layers:
1) A Parietal layer-lines the internal surface of the fibrous pericardium.
2) A Visceral layer (epicardium)-this layer attaches to the heart
muscle (myocardium).
3) Pericardial cavity-space between the parietal and visceral layers.
This cavity is filled with serous fluid which prevents friction
between the layers as the heart moves.
2. Pericarditis-inflammation of the pericardium. Is caused by bacteria, viruses.
a. In this illness, serous fluid production is reduced; therefore, the layers of
the pericardium stick together. This restricts heart movements.
III. LAYERS OF THE HEART WALL
A. The Epicardium-also known as the visceral layer of the serous pericardium.
1. This is a thin, outer, protective layer around the heart.
B. The Myocardium-middle layer; composed of cardiac muscle tissue. This layer forms the
bulk of the heart wall.
C. The Endocardium-lines the inside of the heart (including the chambers) and it covers the
heart valves. This layer is composed of epithelial and connective tissue.
IV. HEART CHAMBERS
A. The heart is composed of 4 chambers:
1. 2 superior atria (which are separated by the interatrial septum).
2. 2 inferior ventricles (which are separated by the interventricular septum).
B. The Atria (singular: atrium). These are the small, thin-walled upper chambers.
1. Their primary function is to receive incoming blood from the body. This blood is
then pumped into the ventricles.
C. Ventricles-lower heart chambers; these make up most of the mass of the heart.
1. 2 of these: right and left. These are the lower chambers.
2. The ventricles are separated from each other by a wall known as the
Interventricular Septum.
3. The ventricles pump blood to the body; therefore, they are much more muscular
than the atria.
V. HEART VALVES
A. There are 4 valves in the heart.
1. These ensure that blood flows in one direction through the heart (from atria to
ventricles and out of the arteries that attach to the heart).
2. The valves open and close in response to differences in blood pressure on their 2
sides.
3. There are 2 atrioventricular valves and 2 semilunar valves in the heart.
B. Atrioventricular (AV) Valves-2 of these; 1 located between each atrium and ventricle.
1. These prevent blood backflow into the atria when the ventricles contract.
2. 2 AV Valves:
a. The Tricuspid Valve-consists of 3 flaps or cusps and is located between the
right atrium and right ventricle. The flaps are primarily connective tissue.
b. The Bicuspid Valve-consists of only 2 flaps and it is located between the
left atrium and left ventricle. It is also known as the Mitral Valve.
3. The flaps of the valves are attached to cordlike chordae tendinae that attach to the
papillary muscles that line the inside of the ventricles. The chordae tendinae and
papillary muscles together control the AV valves.
4. When the heart is relaxed, the AV valves hang down into the ventricular chamber.
a. During contraction, pressure rises in the ventricles; thus, forcing the valves
to close (the cusps are forced together). The chordae tendinae and
papillary muscles anchor the valves in the closed position, which prevents
the upward movement of blood.
C. Semilunar (SL)Valves-2 of these, located between the ventricles and the major arteries
attached to the heart. These prevent blood from back flowing into the ventricles.
1. Each SL valve is composed of 3 half-moon shaped cusps.
2. When the ventricles contract, the blood pushes the SL valves open (against the
wall of the arteries). When the ventricles relax, blood in the arteries pushes the
valves closed, thus, preventing blood from flowing backwards.
3. The Pulmonary Semilunar Valve and the Aortic Semilunar Valve are the 2 SL valves.
D. Valve-Related Disorders
1. Incompetent Valve-the valve does not open and close. Due to this, the heart has to
pump the same blood over and over again. This is very inefficient.
2. Valvular Stenosis-valve flaps become stiff and constrict the opening. The heart
work harder in this case.
3. Mitral Valve Prolapse-in about 1% of the population. Most common in young women.
In this situation, the flaps become incompetent. This position can be genetic.
Again, this causes great inefficiency in the heart. In most cases, the faulty valves
are replaced with synthetic valves or pig heart valves.
VI. BLOOD CIRCULATION THROUGH THE HEART
A. Circulation Patterns in the Heart:
1. Pulmonary Circulation-carried out by the right side of the heart. In this circulation,
blood is pumped to the lungs and back to the left side of the heart.
2. Systemic Circulation-carried out by the left side of the heart. In this circulation
pattern, blood is pumped to and from the body.
3. Coronary Circulation-blood flow to and from the heart muscle.
B. Events in Blood Circulation Through the Heart
1. Blood enters the right atrium via the superior and inferior vena cava. This is
deoxygenated blood.
2. The right atrium contracts. This pushes blood past the tricuspid valve to the right
ventricle. Once blood fills the right ventricle, then the tricuspid valve closes to
prevent the backflow of blood.
3. The right ventricle contracts to push blood past the pulmonary semilunar valve
through the pulmonary trunk(artery) into the lungs.
a. In the capillaries of the lungs, the blood gives up carbon dioxide and picks up
oxygen.
4. This oxygenated blood returns to the left atrium via the pulmonary veins.
a. This ends pulmonary circulation.
5. Next, the left atrium contacts to force blood past the mitral (bicuspid) valve into the left
ventricle. Once the left ventricle is filled with blood, the mitral valve closes to prevent
the backflow of blood.
6. The left ventricle contracts to force blood past the aortic semilunar valve into the aorta and
on to all parts of the body. This is systemic circulation.
7. Coronary Arteries-carry oxygenated blood to the myocardium. These arteries encircle the
heart. These branch into the anterior interventricular arteryand the circumflex artery. The
circumflex artery supplies the external portions of the left atrium and left ventricle with
oxygen.
a. Deoxygenated blood from the myocardium empties into cardiac veins which
empty into the right atrium. This is Coronary Circulation.
C. Disorders associated with blood flow through the heart
1. Angina pectoris-inadequate blood supply to the myocardium. This leads to pain and
tightness in the chest and arm. This is treated with nitrates which dilate blood vessels.
Stress and/or increased physical demands on the heart can cause this.
2. Ischemia-reduced oxygen supply to the heart.
3. Myocardial infarction-heart attack or coronary.
a. Infarction-death of tissue due to interrupted blood supply.
b. This is often caused by a blockage in one of the coronary arteries. The
blockage can be caused by a blood clot, fat etc..
c. Can be treated with streptokinase (thru a catheter) which dissolves clots.
d. Surgery may also be an option.
VII. PROPERTIES OF CARDIAC MUSCLE FIBERS
A. Cardiac muscle is striated and involuntary. It contracts via the sliding filament mechanism.
B. Intercalated discs-only in cardiac muscle fibers. These provide support and strength to
contracting muscle fibers.
C. Cardiac fibers exhibit autorhythmicity, that is, the fibers contract in a coordinated fashion.
D. Cardiac muscle fibers contain numerous mitochondria which are involved in ATP production
(By Aerobic Cellular Respiration).
VIII. HEART PHYSIOLOGY
A. The Cardiac Conduction System-ensures that heart contractions (beats) are well-coordinated.
1. In a normal heartbeat: the 2 atria contract (while the 2 ventricles relax), then the 2
ventricles contract (while the 2 atria relax).
2. Autorhythmic Cells make up the cardiac conduction system. These are specialized
neurons. These cells make up the following structures:
a. Sinoatrial node (SA Node)
b. Atrioventricular node (AV Node)
c. Atrioventricular Bundle (Bundle of His)
d. Right and Left Bundle Branches
e. Purkinje Fibers
3. Nerve impulses travel over the heart in the structures listed above. The impulses
travel through the structures in the exact order listed above.
4. Events in the Cardiac Conduction System:
a. Impulses (electrical signals) produce contractions of heart muscle (also known
as the heartbeat).
b. The Sinoatrial Node (SA Node)-located in the right atrial wall. This structure
produces impulses that begin heart muscle contraction.
1) The SA Node is the pacemaker of the heart. It generates about 75
impulses per minute in a resting individual.
2) The impulses produced here spread to both atria.
3) The SA Node also sets the rhythm for the entire heart. It can speed up or
slow down heartbeat in response to body activity.
c. Next, impulses (and contractions) pass to the Atrioventricular Node (AV Node).
1) The AV Node is located in the lower portion of the interatrial septum.
2) At the AV Node, impulses are briefly delayed. This allows the atria to
complete their contraction before the ventricles contract.
d. From the AV Node, impulses spread quickly to the Atrioventricular Bundle which
is located in the inferior portion of the interatrial septum.
1) The AV Bundle is the only connection between the atria and ventricles.
e. Impulses then move into and through the interventricular septum via the Right
and Left Bundle Branches.
f. Purkinje Fibers carry impulses completely through the interventricular septum
and to the apex of the heart.
5. Problems/Disorders Associated with the Cardiac Conduction System
a. Arrythmias-irregular heart rhythm. This includes:
1) Tachycardia-abnormally fast heart rate; greater than 100 beats/minute.
2) Bradycardia-slow heart rate; less than 60 beats/minute.
3) Some arrythmias can be treated with artificial pacemakers.
b. Fibrillation-rapid, irregular and uncoordinated heart contractions. This interrupts
blood flow out of the heart. Is treated with electrical shock.
c. Ectopic focus-abnormal pacemaker. In some cases, the AV Node will assume
control of the heart.
B. Control of Heart Activity
1. The Medulla oblongata controls and regulates much of the heart’s activity. Specifically,
the medulla contains: the cardiovascular center and the cardioaccelerating center.
C. The Cardiac Cycle-refers to the events that occur during one complete heart beat.
1. On average, the heart beats 72 times per minute.
2. Key Terms:
a. Systole-refers to contraction and emptying of heart chambers.
b. Diastole-refers to relaxing and filling of heart chambers.
D. Heart Sounds
1. 2 distinct heart sounds: Lubb and Dubb.
2. The sounds are the result of the closing of the heart valves.
3. What produces the heart sounds?
a. Lubb-produced by the closing of the atrioventricular valves during ventricular
systole. Ventricular pressure is greater than atrial pressure at this point.
b. Dubb-2nd heart sound. Occurs at the end of ventricular systole as the semilunar
valves close.
4. Heart murmurs-an abnormal heart sound caused by incomplete closing of the valves.
a. Stenosis-change in valve shape.
E. Electrocardiogram (ECG or EKG)-a measurement of the electrical impulses through the heart.
1. A typical ECG consists of three distinct waves:
a. P Wave-1st wave, is very small. This wave is the result of atrial depolarization.
1) The P wave represents atrial contraction.
b. QRS Complex-large, results from ventricular depolarization.
1) This represents ventricular contraction.
c. T Wave-3rd wave, represents ventricular repolarization.
2. The waves in a normal ECG tend to be very consistent. Any changes indicate heart issues.
F. Cardiac Output (CO)-the amount of blood pumped out by each ventricle in one minute.
G. Regulation of Heart Rate
1. Autonomic Nervous System (ANS)
a. Nerves from here run to the SA and AV Nodes.
b. 2 Divisions of the ANS:
1) Sympathetic Division-under stress or fear, nerves in this division
force the release of norepinephrine and epinephrine from the
adrenal glands. These two hormones increase SA Node activity;
thus, increasing overall heart activity.
2) Parasympathetic Division-reduces heart rate following stress.
c. Baroreceptors-in some blood vessels; can respond to blood pressure
changes. This forces the brain to adjust SA Node activity as needed.
2. Chemical Regulation-Including:
a. Hormones
1) Norepinephrine/epinephrine-from above.
2) Thyroxine-from thyroid gland, regulates overall body metabolism.
b. Ions-Including:
1) Calcium Ion-decreased calcium ion levels depresses heart activity
(the opposite is also true).
2) Sodium and Potassium Ions-also regulate heart activity.
IX. HOMEOSTATIC IMBALANCES OF THE HEART
A. Tachycardia, Bradycardia-from earlier in notes.
B. Congestive heart failure-occurs when the pumping efficiency of the heart is so low that
blood circulation is inadequate to meet tissue needs. Can be caused by high BP,
blockages.
X. HEART DISORDERS:
A. Circulatory Shock-cardiac output is reduced so that body tissues do not receive an
adequate blood (oxygen) supply. Symptoms include pale skin, cyanosis.
B. Diagnosing Heart Disorders:
1. Catheterization-catheter is introduced into a blood vessel and worked up to the
heart.
2. Echocardiography-use of ultrasound to take pictures of the heart.
C. Risk Factors in Heart Disease:
1. High cholesterol
2. High blood pressure
3. Smoking
4. Obesity
5. Lack of exercise
6. Age
7. Genetics
8. Gender
9. Diabetes
XI. BLOOD VESSELS-are responsible for delivering blood to all parts of the human body.
A. As the heart contracts it forces blood into arteries which branch into smaller arteries that
branch to from smaller arterioles. Arterioles carry blood into capillaries (capillary beds)
which carry blood into body tissues.
B. Blood returning from the capillary beds empties into venules that merge to form veins.
Veins ultimately empty into the heart.
XII. ARTERIES-carry blood away from the heart.
A. In general, arteries carry oxygenated blood.
B. Structure of the Wall of Arteries:
1. 3 Layers in arterial walls (are also known as tunics):
a. Tunica interna-innermost layer. Also known as the tunica intima.
1) Surrounds a central blood-containing space known as the lumen.
b. Tunica media-composed primarily of smooth muscle tissue.
1) Vasoconstriction (reduction in lumen diameter due to smooth
muscle contraction) and Vasodilation(widening of the lumen due
to smooth muscle relaxation) both occur in the tunica media.
3) This layer is typically the thickest layer in the walls of arteries. This
layer also helps to regulate blood pressure and blood flow.
c. Tunica externa (tunica adventitia)-outermost layer of the arterial wall.
1) Is primarily connective tissue in structure
XIII. CAPILLARIES-microscopic blood vessels. Are the smallest vessels in the body.
A. Their walls consist of only a tunica interna and their walls are typically only one cell layer thick.
B. Capillaries are the primary sites for the exchange of materials (gases, nutrients, hormones)
between the blood and body tissues and interstitial fluid.
XIV. VEINS-carry deoxygenated blood back to the heart.
A. Blood flow is sluggish at best in veins.
B. Veins have 3 distinct tunics, but their walls are always thinner and their lumens larger than
those of arteries.
C. Veins contain Valves along their tunica interna. These valves prevent the backflow of blood in
the veins of the body. The valves are most numerous in the veins of the limbs.
E. Veins collapse when cut.
F. Varicose veins-occur when veins dilate. Is usually caused by incompetent valves.
1. Prolonged standing, obesity, genetic factors all contribute to varicose veins.
2. Treatment often includes surgical removal of the veins.
H. Hemorrhoids-occur when blood does not exit the veins of the anal canal. These veins fill with
blood and swell. Causes include pregnancy, prolonged sitting.
I. Phlebitis-inflammation or injury to a vein. Blood clots may form in the vein.
J. As a rule, in adults, arteries carry oxygenated blood and veins carry deoxygenated blood.
1. Sole Exception in adults: pulmonary artery carries deoxygenated blood and the
pulmonary vein carries oxygenated blood.
XV. PHYSIOLOGY OF CIRCULATION
A. Blood must be kept circulating for us to survive.
B. Key Terms Relating To Circulation:
1. Blood Flow-volume of blood flowing through a vessel or organ in a given period of time
(ml/min). Is equivalent to cardiac output.
2. Blood Pressure (BP)-the force per unit area exerted on the wall of a blood vessel by its
contained blood. Is expressed in mm Hg.
3. Resistance-the opposition to blood flow. This also includes any friction blood faces as it
travels through the body.
4. Blood Viscosity-refers to the thickness of blood.
C. Blood Pressure (BP)-is uassociated with arteries. Is measured with a sphygmomanometer.
1. Systolic Pressure
a. This is caused by ventricular contraction (or systole).
b. This typically measures around 120 mmHg.
2. Diastolic Pressure-the lowest blood pressure reading.
a. This occurs during ventricular diastole (filling).
b. It usually measures 60-80 mmHg.
3. BP is expressed systolic/diastolic. For example: 120/80.
4. There is a wide variation in blood pressure in different individuals.
a. Hypertension-high blood pressure. Occurs when BP is greater than 140/95.
1) Causes include: atherosclerosis and kidney disease (the kidney releases
renin which increases BP).
6. Controls that act to maintain normal blood pressure:
a. Vasomotor center-in the medulla of the brain.
b. Baroreceptors-located in most large arteries.
1) These stretch when BP increases which creates impulses that are sent
to the vasomotor center. The vasomotor center responds by decreasing
blood pressure.
XVI. 2 MAJOR CIRCULATORY ROUTES IN THE BODY
A. Systemic Circulation-oxygenated blood leaves the left ventricle through the aorta and travels to
systemic arteries. Deoxygenated blood from the organs returns via systemic veins into the
superior or inferior vena cava then into the right atrium.
1. 2 Specialized Circulatory Routes in the Systemic Circulation:
a. Coronary Circulation-to myocardium of the heart.
b. Hepatic Portal Circulation-blood flow to/from the liver. The liver regulates nutrients
in the blood and it removes foreign debris from the blood.
1) In the hepatic portal circulation, the following events occur:
a) Hepatic Portal Vein-carries blood from the GI tract to the liver.
b) In the liver, the blood passes through enlarged venous areas known
as hepatic sinusoids.
c) Kupffer Cells in the sinusoids remove bacteria from the blood and
enzymes in the sinusoids remove certain chemicals from the blood.
2. The Aorta-the largest artery in the body. It exits the left ventricle of the heart.
a. 4 Portions of the Aorta:
1) Ascending Aorta-posterior and to the right of the pulmonary trunk. This runs
from the left ventricle to the sternal angle.
2) Aortic Arch-begins and ends at the sternal angle.
3) Descending (Thoracic) Aorta-runs from T5 to T12 along the spine. It sends
off many small arteries to the thorax and viscera before it runs through the
diaphragm.
4) Abdominal Aorta-begins at the entrance of the abdominal cavity (T12 or
diaphragm). It supplies viscera and the abdominal walls in the abdominal
cavity. It ends at L4-where it branches.
B. Pulmonary Circulation-carries deoxygenated blood from the right ventricle through the pulmonary
artery to the lungs.