CVS Session 5 (Lecture 5.2)

Question 1

What is the formula for cardiac output?

Answer 1

CO = SV . HR

Question 2

What is the normal SV and HR for a 70kg man?

Answer 2

80ml and 60bpm

Question 3

Describe the flow of blood as the heart pumps?

Answer 3

Heart ejects blood intermittently - pulsatile flow

Question 4

Describe the flow of blood though arteries with distensible walls.

Answer 4

In systole, arteries stretch
More blood flows in than out
Pressure does not rise so much
Arteries recoil in diastole, flow continues through the arterioles

Question 5

What factors affect the systolic pressure?

Answer 5

Force of contraction
TPR
Stretchiness of the arteries (increased stiffness increases peak pressure)

Question 6

What factors affect the diastolic pressure?

Answer 6

Systolic pressure

TPR

Question 7

Which pressure is the better indicator of TPR?

Answer 7

Diastolic pressure

Question 8

What is a pulse pressure?

Answer 8

Difference between systolic and diastolic (around 40 mmHg)

Question 9

What is the formula to calculate average pressure?

Answer 9

AVP = DP + 1/3 (PP) becasue diastole is 2/3 of heartbeat

Question 10

What are the resistance vessels?

Answer 10

Arterioles and pre-capillary sphincters

Question 11

What is vasomotor tone?

Answer 11

Tonic contraction of VSMCs

Question 12

What do vasoconstriction and vasodilatation do to resistance?

Answer 12

VC - increases resistance to flow

VD - decreases resistance to flow

Question 13

What factors affect the contraction of VSMCs?

Answer 13

Sympathetic branch of ANS controls vasomotor tone

Tone is antagonised by vasodilator factors e.g. H+, K+, adenosine

Question 14

What is reactive hyperaemia?

Answer 14

Increase in blood flow to a part of the body.

Question 15

How is reactive hyperaemia brought about?

Answer 15

Regulatory process mostly e.g. blood supply cut off to arm.

Metabolically active produce vasodilator metabolites e.g. H+, K+, Adenosine which accumulate in vessels due to no blood flow.

These act to relax VSMCs to cause vasodilatation of blood vessels. This decreases the resistance of these vessels to a very low level such that upon reuturn of blood flow, flow is very high through the vessels.

Question 16

How is reactive hyperaemia resolved?

Answer 16

High flow of blood through low resistance vessels that have been dilated by metabolites washes them away causing VSMCs to contract.

Question 17

What is the relationship between metabolism and blood flow?

Answer 17

Metabolism increases, more metabolites produced
Concentration increases of metabolites, vasodilatation occurs
Washes away metabolites from increased blood flow from low resistance
More metabolism = more blood flow

Question 18

Describe autoregulation for local blood pressure and flow.

Answer 18

If supply pressure changes, blood flow to a tissue will change.
Which will change [metabolite]
Alter the resistance of arterioles so blood flow returns to an appropriate level for metabolism

Question 19

What is the relationship between the TPR and blood flow?

Answer 19

TPR is inversely proportional to the body’s need for blood flow.

Question 20

What determines the volume of blood in veins?

Answer 20

Pressure

Question 21

The pressure in veins depends on…?

Answer 21

Balance between flows in from the body and out from the heart (increase heart pumping decreases venous pressure))

Question 22

What is central venous pressure? What does it fill and what does it depends on?

Answer 22

1) Pressure in great veins
2) Fills heart in diastole
3) Depends on: return of blood from the body
pumping of the heart
gravity & muscle pumping

Question 23

What affects superficial veins?

Answer 23

Gravity