Cardiac Output (Lecture 4)

Question 1

What are the three layers of the heart and what are they made up of?

Answer 1

Epicardium- fat and connective tissue
Myocardium- cardiac muscle fibres
Endocardium- endothelium

Question 2

How does the force of contraction change with extracellular calcium ion concentration?

Answer 2

Contraction force increases with increased calcium concentration.

Question 3

What is the site that calcium binds to on troponin called?

Answer 3

Troponin C

Question 4

Why is calcium required for muscular contraction?

Answer 4

It binds to troponin C, causing tropomyosin to expose the myosin binding site on actin.

Question 5

During excitation, at what voltage do voltage-gated calcium channels open?

Answer 5

-40mV

Question 6

Once extracellular calcium enters the cell it interacts with receptors to open pore to release internal calcium into the cytosol. What are these receptors called?

Answer 6

Ryanodine receptors.

Question 7

What is cardiac output and how is it calculated?

Answer 7

The amount of blood released per minute.

CO = SV (L/contraction) x HR (contractions/min)

Question 8

What are the values for average heart rate, stroke volume and cardiac output?

Answer 8

HR: 70 bpm
SV: 70mL/beat
CO: 4.9L/min

Question 9

What is the cardiac output during strenuous exercise?

Answer 9

20-25 L

Question 10

What two factors can be changed to change cardiac output?

Answer 10

Heart rate and/or stroke volume.

Question 11

How can heart rate be increased?

Answer 11

By decreasing parasympathetic activation, increasing sympathetic activation, increasing plasma epinephrine. This increase the heart rate by effecting the SA node.

Question 12

How can stroke volume be increased?

Answer 12

By increasing muscle fibre length and/or by increasing calcium release.

Question 13

Is all blood that the left ventricle is filled with ejected from the heart during systole?

Answer 13

No

Question 14

How is the ejection fraction calculated?

Answer 14

Volume ejected/ EDV x 100.

Question 15

Explain how an increase in EDV increases SV and therefore CO

Answer 15

Increased EDV increases pressure in ventricles, which increases the muscle fibre length, increasing the force of contraction. This increases the SV and therefore, the CO.

Question 16

What two factors influence EDV?

Answer 16

Filling time of the ventricle and venous pressure (venous return). An increase in either increases EDV.

Question 17

What is pulmonary congestion?

Answer 17

Build up of fluid due to cardiac input and output not being matched.

Question 18

How do increased noradrenaline levels increase SV?

Answer 18

With increased sympathetic activation, the amount of noradrenaline interacting with Beta receptors on the heart increases. This causes activation of membrane bound adenylyl cyclase, which converts ATP to cAMP. This activates cAMP-dependent protein kinase, which phosphorylates L-type Ca2+ channels so they remain open for longer. Calcium influx increases, increasing calcium-induced calcium release and contraction force.