Lecture 16

Question 1

What does syncytium mean?

Answer 1

The cells are electrically coupled to each other at intercalated discs.
These discs consist of gap junctions (allowing ions through) and desmosomes (which are involved in mechanical coupling)

Question 2

What is the difference between the relative and absolute refractory period?

Answer 2

The absolute refractory period is when nearly all sodium channels are inactivated.
Relative refractory period occurs when less sodium channels are inactivated and the excitability is returning to normal

Question 3

What is Frank-Starling’s law of the hear?

Answer 3

The amount of stretch of the cardiac muscles determines the amount of force generated during contraction

Question 4

Give some examples of positive and negative inotropic drugs

Answer 4

+ve:
Adrenaline and noradrenaline interacting with B-adrenorecptors to increase contractile force. They raise cAMP levels and activate protein kinase A.
Cardiac glycosides inhibit Na/K ATPases

-ve:
Calcium channel blockers, used to treat arrhythmias and angina
B-adrenorecptors antagonists

Question 5

What is force regulated by?

Answer 5

Blood flow into the heart and activation of B-adrenorecptors