Control Of Cardiac Output

Question 1

What are the two factors which determine arterial pressure?

Answer 1

Cardiac output and total peripheral resistance

Question 2

What determines venous pressure?

Answer 2

This is a balance between the rate at which blood enters the venous system and the rate at which it is pumped out of the heart.

Question 3

What can be said about changes to arterial and venous pressure and how the other responds?

Answer 3

When arterial pressure increases, venous pressure decreases and vice versa.

Question 4

What is the relationship between TPR and the body’s need for blood?

Answer 4

Inversely proportional, as the body’s need for blood increases, there needs to be vasodilation and so a decrease in TPR.

Question 5

How do changes in metabolism cause changes at the heart?

Answer 5

Changes in metabolism cause changes in TPR which affects both arterial and venous pressure. These generates signals which lead to changes at the heart.

Question 6

How can we calculate stroke volume?

Answer 6

End diastolic volume - end systolic volume.

Question 7

What effect does higher venous pressure have in the ventricles?

Answer 7

Higher venous pressure leads to increased ventricular filling as there is an increased pressure gradient.

Question 8

What is starlings law of the heart about stretching cardiac tissue?

Answer 8

The more the heart muscle is stretched, the more it pumps.

Question 9

What is the relationship between venous pressure and Stroke volume?

Answer 9

Increased venous pressure leads to increased stroke volume.

Question 10

What are alterations in contractility called?

Answer 10

This is called positive and negative inotropy.

Question 11

What two factors determine force of contraction?

Answer 11

End diastolic volume and contractility

Question 12

On a graph of stroke volume against end diastolic volume, what is the effect of altered contractility?

Answer 12

This leads to shifting of the curve left to right.

Question 13

What is aortic impedance?

Answer 13

This is where there is high aortic pressure and so this makes it harder to eject blood.

Question 14

What is preload?

Answer 14

This is the volume of blood in the ventricles at the end of diastole

Question 15

Name some factors which can lead to increased preload.

Answer 15

Hypervolemia, regurgitation of cardiac valves, heart failure

Question 16

What is afterload?

Answer 16

The resistance the LV must overcome to circulate blood

Question 17

Under what circumstances will afterload be increased?

Answer 17

Hypertension and increased total peripheral resistance.

Question 18

What detects arterial blood pressure?

Answer 18

Baroreceptors. These cause autonomic control over the heart.

Question 19

When blood pressure decreases, how does the autonomic nervous system correct this?

Answer 19

There is an increase in sympathetic drive which increases heart rate and contractility, and a decrease in parasympathetic action on pulse.

Question 20

What detects increase in venous pressure?

Answer 20

The bainbridge reflex, which results in a parasympathetic drive and an increase in heart rate.

Question 21

Name the organs which always require a stable perfusion.

Answer 21

Heart, brain and kidneys.

Question 22

How does blood flow change with intense exercise?

Answer 22

There is increased blood flow to the skeletal muscle and skin and decreased blood flow to the gut.

Question 23

Why does cardiac fitness effect cardiac output?

Answer 23

If someone is more cardiac fit, then they will have a greater ventricular distensibility and contractility.

Question 24

Where in the body are baroreceptors found?

Answer 24

Carotid sinus and aortic arch.

Question 25

What blood vessels are responsible for TPR?

Answer 25

Arterioles

Question 26

What vessels can control RA filling and therefore stroke volume?

Answer 26

The veins/ great veins which are reservoirs for blood with large volumes and low pressures.

Question 27

What is the functional reserve in the CVS?

Answer 27

There are many capillary beds which are not perfused and so these serve as a functional reserve.

Question 28

At what mean arterial blood pressure does perfusion become inadequate?

Answer 28

65mmHg.

Question 29

What happens immediately in the CVS when a person stands up?

Answer 29

There is a drop in central venous pressure which leads to reduced atrial filling and therefore a drop in mean arterial blood pressure.

Question 30

Hat is the orthostatic response to standing up?

Answer 30

Heart rate will increase and so will TPR to increase mean arterial blood pressure.

Question 31

What is the importance of smooth muscle tone of the veins on standing up?

Answer 31

This means that there is less pooling of blood to the legs which increases CVP because more blood is pumped back to the heart.

Question 32

When the body has a delayed CVS response to standing up, what happens?

Answer 32

When there is a delayed CVS response, this leads to dizziness and fainting which can result in syncope. This is due to inadequate cerebral blood flow.

Question 33

What is the systemic effect of eating a large meal?

Answer 33

This causes an increase in action of the parasympathetic nervous system.

Question 34

What is the effect on eating a large meal on TPR?

Answer 34

There is decreased TPR because there are more local dilators and autacoids and also an increased activity of the parasympathetic nervous system.

Question 35

What two changes occur to the CVS as a result of eating a large meal?

Answer 35

There is an increase in cardiac output due to increased RA filling and there is also a decrease in arterial pressure.

Question 36

What response do baroreceptors initiate to eating a large meal?

Answer 36

They detect the fall in MABP and so increase cardiac output which reduces CVP and increases arterial pressure.

Question 37

What changes occur to the heart during strenuous exercise?

Answer 37

There is increased cardiac output due to an increase in pulse and Stroke volume.

Question 38

What happens the instance exercise begins?

Answer 38

Vasodilation leads to an increased central venous pressure. This causes a fall in blood pressure.

Question 39

In exercise, what is the benefit of muscle contraction?

Answer 39

Muscle contraction for the exercise also aids circulation.

Question 40

What happens during haemorrhage?

Answer 40

This is stopped by clotting, and when there is blood loss this leads to hypovolaemia shock. Blood loss causes decreased CVP, Sv, CO and MABP.

Question 41

What occurs in the tissue during haemorrhage which makes the situation worse?

Answer 41

Locally, there is metabolite build up and so this causes vasodilation which lowers TPR and causes a further drop in MABP

Question 42

What is the major influence of baroreceptors in haemorrhage?

Answer 42

They increase sympathetic activity on the heart, particularly to increase pulse rate.

Question 43

What can occur to major organs as a result of haemorrhage?

Answer 43

They can experience reduced perfusion which can lead to delayed death due to inability to maintain MABP.

Question 44

Where in the brain does control of cardiac output occur?

Answer 44

In the medulla. Information from baroreceptors is sent here and then this coordinates the autonomic nervous system response.