Peripheral Circulation (5)

Question 0

What is total peripheral resistance?

Answer 0

• Sum of the resistance of all peripheral vasculature

Question 1

What is the cardiac output equation?

Answer 1

• Cardiac output = Stroke volume x heart rate

Question 2

Why do vessels have distensible walls?

Answer 2

• Systole, allows arteries to stretch
• More blood in than out
• Arteries recoil in diastole allows flow to continue
• Allows less of a change in pressure during systole and diastole, easier for the body to deal with

Question 3

What are the values for systolic and diastolic pressure?

Answer 3

• Systolic: ~120mmHg

- Diastolic: ~80mmHg

Question 4

What factors affect systolic pressure?

Answer 4

• How the heart pumps
• Total peripheral resistance
• Stretchiness of arteries (compliance)

Question 5

What are the factors affecting diastolic pressure?

Answer 5

• Systolic pressure

- Total peripheral resistance

Question 6

What is average pressure?

Answer 6

• Diastolic pressure + ⅓ pulse pressure

Question 7

Want is pulse pressure?

Answer 7

• Difference between systolic and diastolic pressure

Question 8

What types of blood vessel are high resistance?

Answer 8

• Arterioles

- Pre-capillary sphincters

Question 9

What happens to the resistance of arteries when the smooth muscle around the blood vessel contracts and why?

Answer 9

• Contraction narrows the lumen

- High resistance due to the decrease in r^4

Question 10

What effect does vasoconstriction and vasodilatation have on resistance?

Answer 10

• Vasoconstriction: Increases resistance

- Vasodilatation: Decrease resistance

Question 11

How is the contraction of vascular smooth muscle affected?

Answer 11

• Vasomotor tone via sympathetic NS

- Tone is antagonised by vasodilator factors

Question 12

What is reactive hyperaemia?

Answer 12

• Circulation is cut off for a couple of minutes

- When blood flow is restored this leads to enormous blood flow for a short while.

Question 13

What are the vasodilator metabolites?

Answer 13

• H+/K+/Adenosine

Question 14

What is the roles of the vasodilator metabolites and what does the effect depend on?

Answer 14

• Act to relax vascular smooth muscle

- Effect depends on balance between production rate and rate at which blood flow wastes away.

Question 15

Why does an increase in metabolic activity lead to an increase in blood flow?

Answer 15

• Metabolic rate increases -> more metabolites produced -> so metabolite concentration increases -> vasodilation -> needs metabolites to be washed away -> increased blood flow.

Question 16

What is autoregulation?

Answer 16

• If supply pressure remains within certain limits: tissues will automatically take what blood they need.
• A change in metabolite concentration alters resistance of arterioles so blood flow returns to appropriate level for metabolism.
• Blood flow is the same when normal and blockage + recovery

Question 17

What is central venous pressure?

Answer 17

• Pressure in great veins which fills heart in diastole.

Question 18

What does central venous pressure depend on?

Answer 18

• Return of blood from the body
• Pumping of the heart
• Gravity and muscle pumping.