L6 -Capillaries

Question 1

equation for flow with area and velocity

Answer 1

Flow = cross sectional area x velocity

Question 2

If we increase the area in that equation, what happens to the flow?

Answer 2

• When blood moves from arteries to capillaries, the total cross-sectional area increases significantly—but flow DOES NOT increase. Instead, velocity decreases, maintaining a relatively steady flow rate.

Question 3

Why do arterioles decide how much blood is going through the capillaries?

Answer 3

Capillaries are unable to regulate their own flow. They cant vasoconstrict or vasodilate. so arterioles are the main regulators of the capillary blood flow.

Question 4

in some rare cases capillaries can control their blood flow? when and how?

Answer 4

Capillaries can autoregulate blood flow using pre-capillary sphincters at their proximal end.

Question 5

Where do capillaries branch off from?

Answer 5

Arterioles branch into metarterioles. These allow to shunt blood from one side to the other. shunt = shifting the direction of blood if the capillaries are closed.

Question 6

Define Bulk flow

Answer 6

-Fluid and electrolytes move together en masse through pores an intracellular clefts.
-Driven primarily by pressure differences between the capillary and the tissue.

Question 7

What are the 2 forces favouring filtration in the capillary?

Answer 7

-capillary hydrostatic pressure( Pc)
- interstitial oncotic pressure(pi i) > More of a FORCE.

Question 8

Define capillary hydrostatic pressure

Answer 8

Pressure exerted on the walls of capillary by the blood that’s in it.

Question 9

Define interstitial oncotic pressure(pi i)

Answer 9

This equates to 1.
- Its the force that is wanting the fluid to move out to go where the proteins are.

Question 10

What are the 2 forces favouring reabsorption in the capillary?

Answer 10

-interstitial hydrostatic pressure
-capillary oncotic pressure

Question 11

Define intersitiaal hydrostatic pressure and why is it low or high

Answer 11

pressure of the fluid on the other side of the blood vessel.
OR
pressure with the tissue that it exerts on the vessel.

ususllay Very LOW value - bc fluid doesn’t tend to collect in the tissue.

Question 12

Define capillary oncotic pressure

Answer 12

Quite HIGH
- 60-70% of of capillary oncotic pressure is due to the actions of the albumin.

Question 13

Describe Starling force EQUATION in words

Answer 13

Hydrostatic pressure promoting fluid movement out of the capillary MINUS oncotic pressure promoting fluid retention in the capillary.

Question 14

Draw the starling force diagram with symbols

Answer 14

Interstitial - small i
Capillary - small c

Hydrostatic pressure - P
Oncotic pressure - Big Pi

Question 15

Why does the hydrostatic pressure when moving from the arteriole end to the venule end decreases?

Answer 15

Capillary offers some resistance

Question 16

Does the oncotic pressure increase or decrease when moving from arteriole end to the venules end?

Answer 16

No, stays the same.
Because the plasma proteins cannot leave the blood vessel.

Question 17

What does a +ve value of starling force tells us at the arteriole end? OLD MODEL

Answer 17

A +ve net filtration pressure pushing fluid out of the vessel at the arteriole end.

Question 18

What does a -ve value for starling force tells us at the venule end?OLD MODEL

Answer 18

A net absorption pressure moving the fluid into the vessel.

Question 19

Simple explanation of the OLD starling force

Answer 19

Shift between the net filtration at one end to net absorption pressure at the other end.

Question 20

Define glycocalyx and use?

Answer 20

-gel like structure that sits around the capillary wall on the surface of the endothelial cell.
- acts as an additional barrier to fluid movement.

Question 21

Are capillaries permeable to protein?

Answer 21

Yes, capillaries are slightly permeable to proteins, but it’s highly regulated due to glycocalyx But they are mainly permeable to proteins.

Question 22

What are the 4 main changes to the NEW Starling force 2.0 ?

Answer 22

1. The glycocalyx is a barrier on the endothelial surface that complicates fluid exchange.
2. Capillaries are slightly permeable to proteins, but it’s highly regulated due to glycocalyx, they are still permeable to proteins though.
3. The sub-glycocalyx space is important in managing oncotic pressure across the vessel wall.
4. The lymphatics remove all superfluous tissue fluid, with no net reabsorption across the capillary at all.

Question 23

How does the fluid movement actually happens according to the NEW Starling force model?

Answer 23

1. When there is high hydrostatic pressure(Pc - Pi), there is a big pressure force driving fluid out of the vessel through the intercellular clefts.( tiny gaps between the endothelial cells).
   -high oncotic pressure gradient(Pic-Pig).
2. There are free proteins flowing around in the tissue. But bc there is a high hydrostatic pressure these proteins can’t diffuse easily. As the fast flowing fluid is washing these proteins away as they come through.
3. This favours filtration because there is a big distance between the capillary oncotic pressure and the sub-glycocalyx oncotic pressure.
4. If we reduce the capillary hydrostatic pressure, the fluid starts to flow slower.
5. now the proteins are able to move from the tissue into the space/cleft because the driving force for fluid has decreased.

6.Increases pig which decreases the oncotic pressure gradient. But his number never gets lower than the hydrostatic pressure. The hydrostatic pressure is never insufficient compared to oncotic pressure.
-Restores filtration.

Question 24

What does capillaries do when people get old like in legs and hands?

Answer 24

Oedema - swollen leg or fingers.
-Fluid leaving the capillaries and accumulating in the tissue space due to excess fluid filtration.

Question 25

4 ways of compromising(damaging or dysfunctiong) tissue within Oedema.

Answer 25

-Extramural compression of vessels > if interstitial space gets filled with fluid that can compress the blood vessel on the right hand side, narrowing it. -increased diffusion distance > moves the tissue away from the wall so longer pathway. -impaired cell trafficking > if the capillary reduces in size, its difficult to get bigger cells through. -Compression of other external structures> if blood vessels are pushing on the nerves, it can be painful.

Question 26

Conditions that reduce albumin levels.

Answer 26

liver disease malnutrition

Question 27

What are the 4 types of oedema?

Answer 27

-Hydrostatic oedema -oncotic oedema -permeability oedema -Lymphoedema

Question 28

effects of low levels of albumin in oedema.

Answer 28

if oncotic oedema, less oncotic pressure gradient. harder to keep the water in the blood vessel. there is less protein in the blood vessel keeping the water in.

Question 29

Define permeability oedema

Answer 29

makes the vascular wall leakier to cause more fluid to move out.

Question 30

Define Lymphoedema

Answer 30

caused by drainage in the lymph. effects:- - fluid to collect in the tissue. - vessel is fully constricted. - interstitial pressure👆ses.