Microcirculation

Question 1

Aim of cardiovascular system

Answer 1

Adequate blood flow through the capillaries

Question 2

What is blood flow rate defined as

Answer 2

Volume of blood passing through a vessel per unit time

Question 3

Flow rate

Answer 3

Flow rate=pressure gradient/resistance

Question 4

State the law that is linked with the fluid circuit and state the equation of this law?

Answer 4

Darcy’s Law

Delta P = Q x R
Where q is flow rate

Question 5

What would increasing the pressure gradient do?

Answer 5

Increases flow rate- we would increase pressure A by vasodilation and therefore increased blood flow rather than vasoconstriction (because although constriction would technically increase pressure, less blood would flow through it so less pressure)

Question 6

Pressure difference importance

Answer 6

Without it blood wouldn’t reach tissue capillary bed

Question 7

Define resistance in terms of blood flow

Answer 7

Hindrance to blood flow due to friction between moving fluid and stationary walls.

Question 8

Equation for resistance

Answer 8

Resistance =8Ln/pir^4
Where l is length r is radius and n is blood viscosity

Question 9

What does increasing BP do to pressure gradient, resistance of the vessel and flow to capillaries?

Answer 9

• Increases pressure gradient
• No change to resistance of the vessel
• Increases flow to capillaries

Question 10

• What does arteriolar vasoconstriction do to pressure gradient, resistance of the vessel and flow to capillaries?
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Answer 10

• No change to pressure gradient
• Increase in resistance of the vessel
• Decrease in flow to capillaries

Question 11

How do work out flow rate of blood

Answer 11

F=mean arterial pressure/change in pressure gradient/resistance

Question 12

Vascular tone

Answer 12

Partial constriction enables alterations to blood flow through constriction and dilation (room to accommodate movements)

Question 13

What is an increase in blood in response to local need called?

Answer 13

Active hyperaemia
Happens via vasodilation
Increased by o2 usage

Question 14

• When would vasoconstriction of arterioles happen?

Answer 14

If blood temp dropped or stretch increased (distension) due to increased bp- called myogenic autoregulation

Small intestine arterioles undergo myogenic vasoconstriction

Question 15

• Help regulate systemic arterial blood pressure e.g. maintain bp at 120/80- what is this regulated by?

Answer 15

Extrinsic controls which travel via nerves or blood and are usually centrally coordinated

Such as avp angiotensin I

Question 16

• What equation links mean arterial blood pressure, cardiac output and total peripheral resistance

Answer 16

Blood pressure (MAP)=cardiac output times total peripheral resistance

Question 17

Capillary size

Answer 17

7 micrometers diameter
1 micrometer cell width

Question 18

Why is capillary density important?

Answer 18

So that they are ideally suited to enhance diffusion through Fick’s law

This is through minimising diffusion distance and maximising SA and time for diffusion

Question 19

Which tissues have denser capillary networks?

Answer 19

Highly metabolically active tissues have denser capillary networks

Question 20

• What is the structure of capillaries (diagram)?

Answer 20

Cells have small H2O-filled gap junction between them but vessel still called continuous

Cells are covered with basement membrane which is continuous

Some cells have holes called fenestrae which allow >80nM things to pass through- these still have continuous basement membrane though which the things will have to deal with

Question 21

What are discontinuous capillaries like?

Answer 21

They have fenestrae but also breaks in basement membrane

Common in liver- liver also has sinusoids (sinusoidal capillaries) which are discontinuous structures

Question 22

What type of capillary is blood brain barrier

Answer 22

Continuous- protects brain as it only allows things to enter which we want

Neonates and premature babies have much leakier BBB so more susceptible to CNS infections secondary to infection in blood

Question 23

Bulk flow

Answer 23

A volume of protein-free plasma filters out of capillary by hydrostatic pushing force, mixes with surrounding interstitial fluid (IF) and is reabsorbed by capillaries by oncotic pulling force due to higher conc of plasma proteins in vessels

Question 24

• What are the hydrostatic and oncotic pressure like at the arteriole and venule ends of capillaries?
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Answer 24

Ultrafiltration occurs when pressure inside the capillary is greater in interstitial fluid and reabsorption occurs when there is a negative hydrostatic pressure

Question 25

Lymph vessels

Answer 25

Are discontinuous
Lymph drains into thoracic duct and right and left subclavian veins
3L travels per day