Control of cardiac output

Question 1

Define cardiac output

Answer 1

• the amount of blood that is pumped through the circulatory system per minute

Question 2

Define afterload

Answer 2

The load the heart must eject blood against

Question 3

Define pre load

Answer 3

Amount the ventricles are stretched in diastole - related to end diastolic volume

Question 4

Define total peripheral resistance

Answer 4

Resistance to blood flow offered by all the systemic vasculature

Question 5

What blood vessels offer the greatest resistance ?

Answer 5

Arterioles because they play a crucial role in regulating blood pressure using their layer of smooth muscle.

Question 6

Why is there a drop in pressure as blood flows through the arteries into arterioles ?

Answer 6

• the constriction of arterioles increases resistance , this would cause a reduction in the flow of blood to downstream capillaries and veins thus a decrease in blood pressure in capillaries and veins BUT will cause pressure on arterial side

Question 7

If total resistance pressure increases, but cardiac output remains the same , what are the effects on venous and arterial pressure ?

Answer 7

1) arterial pressure would increase
2) venous pressure would decrease

This is because there is more resistance in the arteries so less blood would effectively flow out of the arteries in the veins so there is less blood in the veins,

Question 8

If total peripheral resistance falls , and cardiac output remains unchanged , what are the effects on venous and arterial pressure?

Answer 8

• arterial pressure decreases
• venous pressure increases

This is because there is less resistance in the arteries , so flow of blood from the arteries in the veins increases. So there is less blood in the arteries hence the decrease in the pressure but more blood in the veins which causes an increase in venous pressure.

Question 9

If cardiac output increases but TPR is unchanged , what are the effects on venous pressure and arterial ?

Answer 9

• arterial pressure increases

- but venous pressure decreases because you are emptying the heart more.

Question 10

If a tissue requires more blood , how will the arterioles and precapillary sphincters accomadate to this ?

Answer 10

• 1) arterioles would dilate
  2) pre capillary sphincters would also dilate
• this would lead to peripheral resistance falling , which would cause arterial to also fall , the heart needs to pump more so that arterial pressure does not fall and venous pressure does not rise,

Question 11

How to calculate stroke volume ?

Answer 11

End diastolic volume - end systolic volume

Question 12

When does ventricular filling occur ?

Answer 12

During diastole

Question 13

Define compliance

Answer 13

How easily a chamber of the heart fills with blood

• change in volume / change in pressure

Question 14

When the ventricles fill with blood during diastole , what must the intraventrocular pressure equal to ?

Answer 14

Venous pressure - the ventricles stretch enough so that IV pressure is the same to venous pressure

Question 15

What does an increased compliance mean ?

Answer 15

Dilated heart - stretched more which ,ends to lower left ventricle pressure

Question 16

What does a decreased compliance mean ?

Answer 16

• heart has stiffened for example due to hypertrophy as muscular walls have thickened too much.
• this leads to an increased end diastolic pressure

Question 17

What is frank-starling law of the heart

Answer 17

An increase in venous pressure would result in the heart filling more , the harder it contracts

• the harder it contracts , the bigger the stroke volume

Question 18

The starling curve

Answer 18

• linear graph
• insert image
• x axis : left ventricular end diastolic pressure (mm hg)
• y axis : stroke volume (ml)
• increasing venous return would increase left ventricular end diastolic pressure which would cause an increase in stroke volume

Question 19

What are the two mechanisms by which the volume of blood pumped out is regulated?

Answer 19

1) intrinsic control - heart is able to control the volume of blood ejected within itself.
2) extrinsic : autonomic nervous system control

Question 20

Define contractility

Answer 20

The force of contraction for a given fibre length

Question 21

What type of factors can increase contractility ?

Answer 21

Extrinsic factors such as sympathetic stimulation and circulating adrenaline

Question 22

What do intrinsic control mechanism ensure ? According to frank sterling law of the heart

Answer 22

Ensures that the output of the left and right ventricles match

Question 23

3=Factors determining cardiac output

Answer 23

1) stroke volume , heart rate
2) how hard it contracts - determined by contractility , EDV
3) how hard to eject blood ( aortic pressure increases decreases this ability)

Question 24

How would the CV system respond by metabolism in the body increasing ?

Answer 24

1) TPR will fall by arteries dilating and precapillary sphincters. This would cause arterial pressure to decrease and an increase in venous pressure
- this results in the heart stretching more , so harder contractions and more blood pumped

Question 25

How to measure jugular venous pulse ?

Answer 25

Measured in the right internal jugular vein