BIO 3520 Notes, 10/24/08
CARDIOVASCULAR SYSTEM I
I. Functions. [Widmaier, pg. 360]
A. Transportation.
1. Delivery of oxygen and nutrients to cells.
2. Removal of waste products from cells to organs of excretion.
3. Transport of hormones.
B. Distribution of body heat.
1. Important for thermoregulation.
C. Protection.
1. Defense against disease-causing organisms.
II. Organization of the Circulatory System. [Widmaier, pp. 360-362]
A. Components.
1. Muscular pump -- heart.
2. Closed network of tubes -- blood vessels.
3. Liquid -- blood.
B. Types of blood vessels (table 12-1, figure).
1. Arteries.
a. Large, thick-walled, elastic tubes.
b. Carry blood away from the heart.
2. Arterioles.
a. Much smaller, very muscular.
b. Microscopic identification (frog web).
1. Diverge.
2. Pulsatile flow of red blood cells.
c. Major role in control of blood pressure.
3. Capillaries.
a. Very small, thin-walled.
b. Microscopic identification.
1. RBC's in single file (figure).
2. Slowest velocity.
c. Exchange gases and nutrients with cells or lungs.
4. Venules.
a. Same size as arterioles, less muscular.
b. Microscopic identification.
1. Smooth flow.
2. Converge.
c. Carry blood towards the heart.
5. Veins.
a. Large, like arteries, thinner walls.
b. Carry blood back to heart.
III. Anatomy of the Heart. [pp. 365-367]
A. Muscular organ located in chest cavity (figure).
B. Tissue layers (figure).
1. Thin inner walls of epithelial cells -- endocardium.
2. Thick walls of cardiac muscle -- myocardium.
3. Thin outer layer of connective tissue -- epicardium.
4. Enclosed in thin connective tissue sac -- pericardium.
C. Chambers.
1. Fish have a two-chambered heart (figure).
a. Atrium above -- receives blood from veins.
b. Ventricle below -- primary pump of the heart.
c. Heart
> gills> body tissues> heart.
2. Amphibians and most reptiles have three-chambered heart.
a. Two atria, one ventricle.
b. Oxygenated blood from lungs enters left atrium.
c. Oxygen-poor blood from tissues enters right atrium.
d. Oxygenated blood and oxygen-poor blood mix in ventricle.
e. Reptiles have an incomplete septum in the ventricle.
3. Crocodilians, birds, and mammals have four-chambered heart.
a. Two atria and two ventricles.
b. Left and right ventricles are separated by a septum.
c. Complete separation of left and right hearts.
4. What about dinosaurs?
D. Valves (figs. 12-6, 12-7, figure).
1. Atrioventricular (AV) valves open from atria into ventricles.
a. Right side -- tricuspid valve.
b. Left side -- bicuspid or mitral valve.
2. Semilunar valves open from ventricles into great arteries.
a. Right side -- pulmonary valve (fig. 12-7b).
b. Left side -- aortic valve.
IV. Divisions of the Circulatory System. [pp. 361-362, 365-366]
A. Systemic loop.
1. Left ventricle
> body tissues> right atrium.
2. Major artery -- aorta (fig.12-6)
3. Major veins.
a. Superior vena cava from head, neck, and arms.
b. Inferior vena cava from lower body.
B. Pulmonary loop.
1. Right ventricle
> lungs> left atrium.
2. Major arteries -- pulmonary arteries.
3. Major veins -- pulmonary veins.
C. Left-to-right shunts.
1. A portion of left ventricular output goes back to lungs instead of
systemic circulation.
2. Septal defect -- hole in interventricular septum (figure).
a. Blood flows from left ventricle to right ventricle.
3. Patent ductus arteriosus (figure).
a. Ductus arteriosus connects pulmonary artery with aorta in fetal
circulation (figure).
b. Reversal of blood flow through ductus arteriosus at birth causes
its closure within a few hours.
c. If it remains open (patent) then blood flows from aorta into
pulmonary artery.
4. Both conditions are surgically correctable (figure).
V. Cardiac Muscle. [pp. 290-291, 366-367, 373]
A. Cardiac muscle fibers (9-39a).
1. Shorter than skeletal muscle fibers.
2. Several branching processes.
3. Fibers are irregularly striated.
4. Cells joined together end to end (9-39b).
a. Desmosomes --
b. Gap junctions --
B. Action potential (fig. 12-12).
1. Rising phase -- depolarization due to opening of Na+ channels.
2. Plateau phase -- delay before repolarization.
a. Delay in opening K+ channels.
b. Opening of slow Ca++ channels on cell membrane and
sarcoplasmic reticulum.
3. Falling phase -- opening of K+ channels.
4. Tension development.
a. Increased Ca++ in cytoplasm binds to troponin and causes
contraction.
b. Sliding filament mechanism similar to skeletal muscle.
c. Tension develops slowly (150 msec to peak tension) (fig. 12-17).
d. Ca++ is pumped back into S.R.
> relaxation.
5. Long refractory period.
a. Skeletal = 2 msec; cardiac = 250 msec (fig. 9-41).
b. Allows full contraction and relaxation of fibers.
c. No tetanus.
VI. Impulse Conduction Through the Heart. [pp. 367-370]
A. 99% of cardiac muscle cells are specialized for contraction.
B. 1% are specialized for initiating and conducting action potentials.
1. Capable of self-excitation.
2. Contain few contractile proteins.
3. Make up specific conduction pathway.
C. Pacemaker cells.
1. Normal pacemaker in heart is sinoatrial (SA) node.
2. Electrical activity of pacemaker cells (fig. 12-13).
a. Pacemaker potential = Gradual spontaneous depolarization of
cardiac pacemaker cells.
1. Due to slow leak of Na+ into cell.
b. Reaches threshold
> action potential.1. Action potential is due to opening of Ca++ channels
(unlike all other excitable cells in which Na+ channels open).
D. Conduction pathway (figs. 12-10, 12-11).
1. SA node spontaneously depolarizes.
2. Impulse spreads downward and to the left across both atria by way of
gap junctions -- both atria depolarize and contract.
3. Only conducting path to ventricles is the atrioventricular (AV) node.
a. Slow conduction through AV node delays ventricular contraction by
100 msec.
4. Down bundle of His to apex of heart.
5. Along Purkinje fibers and across both ventricles -- both ventricles
depolarize and contract.
6. If SA node is blocked, another portion of the conducting system will
take over as pacemaker.
VII. Electrocardiogram (ECG). [pp. 370-371]
A. ECG is a recording of the electrical activity of the heart.
B. Origin of ECG.
1. Action potentials originate in cardiac muscle.
2. Can be measured at skin surface using surface electrodes.
3. Record potential difference between two points of body using bipolar
electrodes (fig. 12-15, figure).
C. Shape of the ECG (fig. 12-14).
1. P wave = atrial depolarization.
2. QRS complex = ventricular depolarization.
3. T wave = ventricular repolarization.
D. Normal ECG values (figure).
1. Normal heart rate = 60 - 100 beats/min.
2. Normal sequence is atrial depolarization, followed each time by
ventricular depolarization.
E. Arrhythmias.
1. Bradycardia = Heart rate less than 60 beats/min (figure).
a. Ex. athlete's bradycardia.
2. Tachycardia = Heart rate greater than 100 beats/min (figure).
a. Activation of sympathetic nervous system.
b. Exercise.
c. Drugs.
1. Caffeine -- stimulates SA node.
2. Cocaine -- stimulates sympathetic n.s.
3. Premature ventricular contractions (PVC's) = Extra beats
originating in the ventricles (extrasystoles) (figure).
a. Most common type of arrhythmia.
4. AV block (heart block) = Interference with conduction
through AV node (fig. 12-16).
a. Partial AV block -- Some action potentials are conducted through
AV node while others are not (figure).
1. Some P waves do not have QRS complexes following
b. Complete AV block -- No conduction through AV node (figure).
1. No synchrony between P waves and QRS complexes
2. Pacemaker cells in ventricle establish their own rhythm --
slower than atria.
5. Atrial flutter = Very rapid, coordinated contractions of the atria (figure).
a. Atrial rate greater than 200 beats/min.
b. Multiple P waves.
c. Ventricular rate normal due to long refractory period of AV node.
6. Atrial fibrillation = Very rapid, uncoordinated contractions of the atria
(figure).
a. No P waves, irregular QRS complexes .
b. Blood clots form in atria -- increased risk of stroke.
7. Ventricular fibrillation = Very rapid, uncoordinated contractions of
the ventricles (figure).
a. No recognizable rhythm .
b. Ventricles are ineffective as pumps
> rapidly fatal.c. Treatment.
1. Cardiopulmonary resuscitation (CPR) (figure).
2. Electrical defibrillation (figure).
VIII. The Cardiac Cycle. [pp. 373-377]
A. General principles.
1. Contraction of the myocardium generates pressure changes that
result in the orderly movement of blood.
2. Blood flows from area of high pressure to area of low pressure,
unless flow is blocked by a valve.
3. Events on the right and left side are the same, except pressures are
lower on the right side.
B. Definitions.
1. Systole = Period of ventricular contraction.
2. Diastole = Period of ventricular relaxation.
C. Phases (figs. 12-18 and 12-19).
1. Passive filling (mid-diastole).
a. Atria and ventricles are both relaxed.
b. Ventricular pressure = 0.
c. AV valves are open because atrial pressure is greater than
ventricular pressure.
d. Blood is flowing from veins into atria and into ventricles.
1. 80% of ventricular filling occurs during this phase.
e. Semilunar valves are closed because arterial pressure is greater
than ventricular pressure.
2. Atrial contraction (late diastole).
a. SA node depolarizes.
b. Wave of depolarization spreads across both atria
>reaches AV node.
c. P wave of ECG.
d. Atria contract.
e. Slight increase in ventricular pressure.
f. Completion of ventricular filling.
1. End-diastolic volume (EDV) = Volume of each ventricle at
the end of diastole (~135 ml).
g. Arterial blood pressure is lowest.
1. Diastolic blood pressure = Arterial blood pressure at its
lowest point in the cardiac cycle (80 mmHg).
3. Isovolumetric ventricular contraction (early systole).
a. Action potential is conducted through AV node, down bundle of His,
and along Purkinje fibers
> ventricular depolarization.
b. QRS complex of ECG.
c. Ventricles contract.
d. Increasing pressure in ventricles causes AV valves to close,
preventing backflow into atria.
1. First heart sound ("lub").
4. Ejection (most of systole).
a. Ventricular pressure exceeds arterial pressure
>semilunar valves open.
b. About 2/3 of blood is ejected from each ventricle.
1. Stroke volume (SV) = Volume of blood ejected from each
ventricle in a single beat (~90 ml).
2. SV/EDV = ejection fraction.
c. Arterial blood pressure rises to its highest point.
1. Systolic blood pressure = arterial blood pressure at its
highest point in the cardiac cycle (120 mmHg).
5. Isovolumetric ventricular relaxation (early diastole).
a. Wave of repolarization across ventricles.
b. T wave of ECG.
c. Ventricles relax.
d. Ventricular pressure falls below arterial pressure
>semilunar valves close.
1. Second heart sound ("dub").
6. Passive filling.
a. Ventricular pressure falls below atrial pressure
> AV valvesopen.
b. Ventricles begin to refill.
E. Timing.
1. Normal systole = 0.3 sec.
2. Normal diastole = 0.5 sec.
F. Pressures.
1. Systemic arterial BP = 120/80 mmHg.
a. Lower pressure would not provide adequate blood flow to all
organs.
2. Pulmonary arterial BP = 25/8 mmHg (fig. 12-20).
a. Higher pressure would force fluid into lungs.
G. Stroke volume is the same for either side.
1. Why is this important?
2. Left ventricle is pumping the same amount of blood against
higher pressures.
IX. Coronary Heart Disease. [pp. 422-424]
A. Coronary circulation (branch of the systemic loop).
1. Blood supply to the myocardium.
2. Coronary arteries branch off of the base of the aorta (fig. 12-66a).
3. Any narrowing or blockage of a coronary artery interferes with the
blood supply to the myocardium
> coronary heart disease.
B. Myocardial ischemia.
1. Ischemia = Insufficient blood flow to an organ.
2. Myocardial ischemia = Insufficient blood flow to part of the
myocardium.
3. Due to partial blockage of coronary artery.
4. Silent ischemia.
a. 75 - 80% of ischemic episodes are not painful.
b. Heart rate higher than normal.
5. Angina pectoris.
a. Severe pain to chest and left arm.
b. Attacks are short, but very frightening.
c. Prevent or control attacks with nitrates.
C. Heart attack (myocardial infarction).
1. Heart attack is the number one killer of men and women in the U.S.
2. Complete blockage of blood flow to a part of myocardium.
3. Most common cause of myocardial infarction is atherosclerosis
(figure).
a. Clot may lodge in narrowed area
> complete blockage (figure).
4. Consequences.
a. Impaired impulse conduction through heart
> may lead toventricular fibrillation.
b. Weakens heart muscle
> may lead to heart failure.
5. Intervention.
a. Seek medical help immediately.
b. Cardiopulmonary resuscitation (CPR), if necessary.
c. Electrical defibrillation, if necessary.
d. Injection of clot-dissolving drugs.
D. Diagnosis and treatment of coronary heart disease.
1. Angiogram (figure).
a. Inject dye into coronary circulation.
b. X-ray heart for blocked arteries.
2. Angioplasty -- Insert catheter into coronary artery to open blocked
area (fig. 12-66).
a. Balloon (figure).
b. Stent (figure).
c. Drill (figure).
d. Laser (figure).
3. Coronary artery bypass surgery (figure).
a. Bypass blocked artery by attaching vein from the leg or arm
>restores blood flow.
