Control of Cardiac Output in Systemic Circulation

Question 1

What happens to arterial and venous pressure when total peripheral resistance is decreased with no change to cardiac output?

Answer 1

Arterial decreases

Venous increases

Question 2

What happens to arterial and venous pressure when total peripheral resistance is increased with no change to cardiac output?

Answer 2

Arterial increases

Venous decreases

Question 3

What happens to arterial and venous pressure when cardiac output is decreased with no change to total peripheral resistance?

Answer 3

Arterial increases

Venous decreases

Question 4

What happens to arterial and venous pressure when cardiac output is increased with no change to total peripheral resistance?

Answer 4

Arterial decreases

Venous decreases

Question 5

Describe demand-led pumping

Answer 5

The heart responds to changes in arterial/venous pressure (key signals) which indicate the body’s need for blood.

Question 6

Describe stroke volume

Answer 6

The difference between end diastolic volume and end systolic volume

Question 7

How does vein pressure determine the end diastolic volume?

Answer 7

The pressure in the veins determines atrial pressure as there is no valve.
Blood passes from the atria to ventricles, causing the walls to stretch and pressure to rise.
Filling of the ventricles continues until the interventricular pressure is equal to that in the atria.

Question 8

What is Starlings law of the heart?

Answer 8

Stroke volume is proportional to ventricular pressure, until the pericardium restricts filling.

Question 9

What does the end systolic volume depend on?

Answer 9

Force of contraction

How hard it is to eject blood

Question 10

What effect does noradrenaline have on the Starlings curve?

Answer 10

It will steepen the gradient as it improves contractility

Question 11

Describe what is meant by contractility of the heart

Answer 11

It’s intrinsic ability to contract.

Changes in ability to produce force of contraction result from incremental degrees of binding between actin and myosin filaments.

Question 12

What is ease of ejection of blood from the heart dependent on?

Answer 12

Aortic impedance (sum of external factors that oppose ventricular ejection)
Total peripheral resistance (small effect)

Question 13

Describe the Bainbridge reflex

Answer 13

High ventricular pressure sensed in the right atrium. Low parasympathetic activity increases heart rate but has no effect on force of contraction.

Question 14

Describe pressure changes caused by eating a meal and how they are then returned to normal.

Answer 14

Increased activity of gut causes local vasodilation
TPR decreases causing venous pressure to increase and arterial pressure to decrease.
VP increasing causes CO to rise, and AP decreases causes increased heart rate and therefore CO.
Ventricular pressure reduced by extra pumping of the heart which increases atrial pressure.

Question 15

If the heart rate alone was increased, describe the changes that occur.

Answer 15

CO increase, TPR remains the same

High CO decreases venous pressure and therefore stroke volume. CO returns to original value.

Question 16

Describe how significant exercises changes pressure and heart rate.

Answer 16

Increase in demand and muscle pumping forces extra blood back to the heart.
Venous pressure will be high and arterial pressure will be low.
The heart rate rises as exercise begins, driven by the brain (CVS centres in medulla). This means that when VP is increased, heart rate is already high which keeps stroke volume down.

Question 17

Describe how excessive exercise can cause pulmonary oedema

Answer 17

Output of the right and left ventricles can’t be matched and there is more entering the right. Causes increased pressure in the lungs, leading to pulmonary oedema

Question 18

Describe the normal processes that occur when standing up to keep blood pressure constant.

Answer 18

Blood pools in superficial veins in legs due to gravity so venous pressure falls. CO decreases due to Starlings law so arterial pressure also falls.
Baroreceptors sense the low AP, causing heart rate to increase. TPR increases to defend the arterial pressure.
Muscle pumping in the legs increases venous return.

Question 19

Describe what happens to cause postural hypotension.

Answer 19

When the normal processes used when standing up don’t work properly e.g. due to haemorrhage, hypovolaemia, ANS dysfunction causing a transient drop in blood pressure.

Question 20

Describe the look of a patient with haemorrhage

Answer 20

Pale, high heart rate, sweating, no force to their pulse

Question 21

Describe the changes to the CVS with a haemorrhage

Answer 21

Low blood volume and venous pressure. CO and arterial pressure also falls.
Volume mostly lost from veins
Increased TPR to increase arterial pressure along with heart rate
Need to increase venous pressure by venoconstriction and autotransfusion.

Question 22

Describe autotransfusion

Answer 22

Fluid from the ECM is taken up into the CVS to increase circulatory volume

Question 23

Describe how long term high blood volume can occur

Answer 23

Increased sodium reabsorption in the kidney which causes increased water reabsorption

Question 24

Describe the effect that long term high blood volume has on the CVS

Answer 24

Increased CO, increasing arterial pressure so VP and AP increased as TPR stays the same.
Overperfusion occurs, autoregulation by metabolite concentration increases TPR so arterial pressure is pushed further up and stayed up.
Average pressure is proportional to volume of the blood.
Causes turbulent flow which can damage the endothelium and increase the risk of atheroma formation

Question 25

Give some drugs used as treatments for a person with long term high blood volume

Answer 25

Potassium sparing diuretics - amiloride
Thiazide diuretics - chlorothiazide
Loop diuretics