Circulation Blood And Immunity Page 3

Question 1

What is myogenic?

Answer 1

Heart muscle is myogenic ie. It can contract without nerve stimulus. Separated heart cells will beat in sync. if placed together and touching.

Example: Heart muscle cells contracting without external stimulus

Question 2

What is the pacemaker or SA node?

Answer 2

The pacemaker or sinoatrial node (SA node) is made of specialized nerves that set the heart tempo at about 70 beats/min. Situated in the right atria near the entrance of the vena cava.

Example: SA node setting heart tempo

Question 3

What is the AV node?

Answer 3

Heart contractions travel to a second node the AV node or atrioventricular node which is the impulse carrier between the atrium and ventricles.

Example: AV node as impulse carrier

Question 4

How is the pacemaker controlled by nerves?

Answer 4

The pacemaker is controlled by nerve impulses. In times of stress or exercise the sympathetic nerves stimulate the SA node to increase heart rate (called tachycardia). During relaxation the parasympathetic nerves slow heart rate (called bradycardia).

Example: Sympathetic and parasympathetic nerves controlling heart rate

Question 5

What causes the “lubb-dubb” sound of the heart?

Answer 5

The “lubb-dubb” sound of the heart are caused by valves closing under pressure.

Example: Valves closing causing heart sounds

Question 6

What happens when blood flows from the atria to the ventricles?

Answer 6

As blood flows from the atria to the ventricles AV valves open letting blood flow through. The atria will relax (diastole) and ventricles will contract. The AV valves will close not allowing blood back into the atria. This closing causes the “lubb” (weaker) sound.

Example: AV valves opening and closing during heart cycle