Physiology of the heart - 2

Question 1

What is meant by the ejection fraction and how much is it at rest for the average person?

Answer 1

The percentage of volume of blood ejected with each contraction of the heart - 55-60% for each person

Question 2

What is meant by the residual volume and what is the value for the average person?

Answer 2

Leftover volume of blood in heart left after ejection - around 70mls

Question 3

What is the cardiac output and amount of blood in the body on average?

Answer 3

Around 5L of blood

HR x SV, around 4.9l/min

Question 4

What factors impact 1) heart rate and 2) stroke volume?

Answer 4

HR - drugs, the autonomic NS and circulating catecholamines

SV - pre and after load, contractility of the heart (controlled by O2, FFAs, Ca2+, ATP)

Question 5

What is meant by the preload and afterload ?

Answer 5

Preload - volume / pressure of fluid entering the heart

Afterload - resistance to ejection of blood, dependant normally on the contractility of blood vessels

Question 6

Role of calcium in the heart - where is it stored, where does it attach, what happens to cause contraction?

Answer 6

Stored in the sarcoplasmic reticulum
Upon propogation of AP, Ca2+ is released, attaches to Ryanodine receptors , which in turn results in more release of Ca2+
This second wave of Ca2+ release binds to troponin which leads to a change in the configuration of Troponin which leads to contraction.
ENERGY DEPENDANT (ATP) REACTION

Question 7

How are cardiac muscles laid out and why?

Answer 7

They branch allowing them to link each other sideways this allows synchronous contraction of cells

Question 8

What does the frank starling mechanism refer to?

Answer 8

‘Change in heart contractility in response to a change in venous return’
The increase of filling pressure causes cardiac muscle cells to stretch. More stretch = more powerful contractions

Question 9

How does decreasing venous return impact stroke volume?

Answer 9

Less venous return = decrease in end diastolic pressure = decreased stroke volume

Question 10

How does increasing venous return impact stroke volume?

Answer 10

Increase in stroke volume due to an increase in filling volume and pressure in the heart

Question 11

Afterload/contractility curve –> how do problems with heart change position on curve?

Answer 11

Produces a lower, flatter curve > higher end diastolic pressure is needed to maintain the same stroke volume in the heart

Question 12

how does increased afterload impact SV?

Answer 12

Same or increased resistance produces a smaller SV

Question 13

How does increased contractility of the heart impact the afterload?

Answer 13

Increased contractility = decreased afterload! Less resistance to ejection is seen –> shifts different curve (to left hand side and steeper curve –> less resistance needed for the same stroke volume)

Question 14

How does sympathetic stimulation impact heart contractility?

Answer 14

Shifts curve to LHS > more SV for less pressure

Question 15

How are diuretics used in treatment of Heart failure – how do they impact the graph

Answer 15

Decrease total blood volume by increasing production of urine –> this causes a reduction in filling pressure and shifts back the end diastolic pressure on the curve

Question 16

How are vasodilators used in treatment of Heart failure – how do they impact the graph

Answer 16

Vasodilators (such as ACE inhibitors) cause a reduction in end diastolic pressure and therefore shift the curve to the left and up > lower pressure produces higher stroke volume

Question 17

How does heart failure impact frank starling curve?

Answer 17

In heart failure tend to see an increase in filling pressure –> the heart operates at a higher pressure to increase the stroke volume

Question 18

How is Digoxin used in treatment of heart failure

Answer 18

Inhibits the Na+/K+ pump –> this reduces gradient for Na+ efflux –> decreases efflux of Ca2+ allowing sustained contraction of cardiac muscle