lecture 7 - cardiac muscle & function

Question 1

What feature connects adjoining cardiomyocytes?

Answer 1

Intercalated discs

Question 2

What are the steps in excitation-contraction coupling in a cardiomyocyte?

Answer 2

1.) Cell depolarised
2.) L-type Ca2+ channels reach threshold and open
3.) influx of Ca2+ is small but triggers Ca2+ release from sarcoplasmic reticulum (Calcium-Induced calcium release),
5.) Ca2+ binds to troponin,
6.) tropomyosin moves
7.) actin-myosin interaction occurs causing a contraction

Question 3

What are the 3 mechanisms through which Ca2+ is removed from cardiomyocytes during cardiac muscle relaxation?

Answer 3

1.) SERCA - pump Ca2+ into SR (majority of Ca2+)
2.) Sodium-Calcium exchange pump on cell membrane
3.) Cell membrane ATP-dependent Ca2+ pump

Question 4

What is a positive inotropic effect?

Answer 4

Improving the pumping action of the heart - making contractions stronger

Question 5

What are the effects of sympathetic stimulation on cardiac muscle?

Answer 5

Increased active tension, increased rate of tension development, increased rate of relaxation (shorter contraction) - ultimately a positive inotropic effect & increased heart rate

Question 6

What does noradrenaline bind to sympathetically stimulate the heart?

Answer 6

Beta-1-adrenoreceptors in cardiomyocytes

Question 7

What is the effect of Beta-adrenergic stimulation on the heart?

Answer 7

Increased contractility - positive inotropic

Question 8

What is the length-tension relationship of the heart?

Answer 8

The ability of cardiac muscle to increase its contractile force with a slight increase in its length, thus allowing it to control stroke volume without changing the underlying biochemistry

Question 9

What is Starling’s Law?

Answer 9

As End diastolic volume (filling of the heart) increases, stroke volume increases

Question 10

What is the effect of increased contractility on a Starling Curve?

Answer 10

Shifts upwards - the same EDV results in a higher stroke volume

Question 11

What are the key examples of inotropic agents?

Answer 11

Noradrenaline, adrenaline, digoxin (drug)

Question 12

What pathological states can cause the release of negative inotropic agents?

Answer 12

Hypoxia, sepsis

Question 13

What processes can occur to improve heart function in response to acute cardiac failure?

Answer 13

sympathetic stimulation -> increased contractility -> increased SV for same EDV -> maintain Mean arterial blood pressure.
Also, RAAS can increase plasma volume to increase BP in short term