Topic 3 Circulatory System: Cardiac Cycle

Question 1

• Not all blood leaves ventricles when heart pumps
• The % that does is called ejection fraction
• This cycle is the rate regulated cycle by autorhythmic cells of the autonomic nervous system, but contractions are initiated independently of the autonomic nervous system
• Instead, the heart contracts automatically

Answer 1

Cardiac Cycle

Question 2

• Located in upper wall of the right atrium, the SA node is a group of specialized cardiac muscle cells that initiate by contracting both atria and sending an impulse that stimulates the AV node
  a. At the AV node, the impulse is briefly delayed to allow the atria to completely empty, and to allow the ventricles to fill with blood
  b. The impulse spreads the contraction to surrounding cardiac muscles via electrical synapses made from gap junctions
  c. The pace of the SA node is faster than the normal heartbeat, but the parasympathetic vagus nerve innervates the SA node and slows contractions
• The vagus nerve also increases digestive activity of intestines

Answer 2

1. SA (sinoatrial) node/pacemaker

Question 3

• Located in lower wall of right atrium / interatrial septa; sends impulse through the Bundle of His -> passes between both ventricles -> branches into ventricles via the purkinje fibers which results in contraction of both ventricles simultaneously

Answer 3

2. AV node

Question 4

• When the ventricles contract) ventricular systole phase), blood is forced through the pulmonary arteries and aorta

Answer 4

3. Ventricular Contraction

Question 5

• Papillary muscles and chordae tendinae are attached to cardiac valves and force them closed during systole

Answer 5

Note