Test 83    (cardiac physiology)

1. The following are true about cardiac contraction:

a. the P wave initiates the atrial contraction

b. atrial contribution to ventricular filling is most
    effective at fast heart rate.

c. b wave is generated by atrial contraction

d. fourth heart sound occurs during atrial contraction

e. atrial natriuretic peptide (ANP) is released when the 
    atria are distended by increases in blood volume

Answera.T   b.T  c.F  d.T  e.T
a wave is generated by atrial contraction.
ANP causes natriuresis ie increase secretion
of sodium and water by the kidneys and vasodilatation.

2. True statements about ECG include:

a. the P-R interval corresponds to the duration of atrial systole

b. the T-wave ends at the time of aortic valve closure

c. the ST segment represents repolarization of the 
    ventricles

d. the QRS complex represents atrial repolarization

e. P-wave represents depolarization of the atrium

Answera.T   b.T   c.T  d.F   e.T
QRS complex represents ventricular depolarization.

3. The following are true about micro-circulation:

a. arterioles have no muscle

b. capillaries have walls made up of a single layer of cells

c. capillaries have no innervation

d. the capillaries contain 5% of the total blood volume 
    at any one time

e. the capillaries contain gaps measuring 5-9um wide

Answera.F   b.T  c.T   d.T   e.T
Arterioles contains muscle but no capillaries.

4. Differences between myocardial muscles and normal muscles
    in that myocardial muscles:

a. can incur a greater oxygen debt

b. can metabolize lactic acid

c. contains no striated muscles

d. contains no glycogen

e. has a longer refractory period

Answera.F  b.T  c.F  d.F   e.T
In normal time, the metabolism of the cardiac 
muscle is less than 1% anaerobic but in times 
of hypoxia up to 10% may be anaerobic. However, 
compared with skeletal muscles, it incur less oxygen debt.
A longer refractory period is essential for cardiac 
muscle otherwise it runs the risk of tetany.

5. Oxygen blood supply to the heart depends on:

a. blood acidity

b. sympathetic tone

c. blood viscosity

d. heart rate

e. haemoglobin concentration

Answera.T   b.T   c.T   d.T   e.T
Acidosis, hypoxia and hypercarbia increases
the diameter of the coronary arteries and hence greater blood flow.

 
 

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