Lecture 15: capillaries and fluid exchange

Question 1

what makes capillaries specialized for the exchange of gases, nutrients, and waste

Answer 1

they are made of a single layer of endothelial cells surrounding lumen

Question 2

what results in edema

Answer 2

when too much of the fluid components exit vessels and accumulate in the interstitial space

Question 3

what happens to most of the fluid lost in the process of capillary exchange

Answer 3

most fluid is quickly returned back to the capillary due to osmotic pressure changes and blood moves from the arterial to venous end of capillary

the rest gets returned by the lymphatic system

Question 4

why doesn’t blood flow through all capillary beds all the time??

Answer 4

b/c if that happened, TRP would dramatically drop and so would BP. If too many capillary systems are open, the pressure needed to maintain proper blood flow would not be maintained

Question 5

what are capillary sphincters and their function?

Answer 5

they are cuffs of smooth muscle that surround the root of each true capillary

they work like a tiny valve to control blood flow through the capillary

Question 6

continuous vs discontinuous capillaries

Answer 6

continuous capillaries have pores (fenestrations) that allow water and lipid soluble substances to pass

Discontinuous capillaries have intercellular gaps that allow proteins to pass easily

Question 7

Method of transport in capillaries

Answer 7

1. Pinocytosis: formation of little membrane vesicles that contain fluid
2. Vesicles cross the capillary endothelia cell from the bloodstream side into the ISF
3. exocytosis of plasma components into ISF

Question 8

capillaries in brain vs liver

Answer 8

brain capillaries
- have tight junctions so that only water and small ions can pass through

Liver capillaries
- discontinuous
- large gaps allow proteins to enter into bloodstream directly, as well as for absorbing toxins out of blood

Question 9

how does glucose get into the brain

Answer 9

brain capillaries have specialized carrier proteins that transport glucose via facilitated diffusion

Question 10

Fick’s Law of Diffusion is based on what factors

Answer 10

[gradient] of the substance
capillary SA
capillary pore size
diffusion coefficient
thickness of capillary wall

Question 11

what is oncotic pressure and where is it the highest

Answer 11

oncotic pressure = the pressure difference b/w the plasma and ISF that drives water to move from ISF into capillary blood plasma

oncotic pressure is highest in plasma

*drives reabsorption

Question 12

what is hydrostatic pressure and where is it the highest

Answer 12

hydrostatic pressure = what causes water to move by bulk flow
- higher in capillary than ISF
- higher in arteriolar end of capillary
- favors filtration

Question 13

what helps prevent fluid from accumulating in the ISF

Answer 13

lymph vessels that collect ISF fluid and return it to the bloodstream via subclavian veins

Question 14

what factors promote the filtration rate

Answer 14

1. increases the hydrostatic pressure difference
2. decreasing oncotic P difference
3. increasing the permeability of the capillary to water

Question 15

what can cause an increased hydrostatic pressure in the capillaries?

Answer 15

increased arterial pressure or decreased resistance
increased venous pressure or obstruction to venous flow

Question 16

what is ISF pressure most greatly affected by

Answer 16

the volume of fluid in the ISF

Question 17

what affects net oncotic pressure

Answer 17

the concentrations of proteins in the plasma and ISF

Question 18

what can affect ISF protein concentration?

Answer 18

inflammation - causes the capillary pores to open wide enough to let plasma proteins through

Question 19

what removes plasma proteins from the ISF?

Answer 19

lymph flow removed plasma proteins since the clefts in lymphatic vessels are big enough to let protein through

Question 20

where is there a high-drive towards filtration into the interstitial spaces and what combats this

Answer 20

in the lungs, but the lungs have a highly invasive lymphatic system that can continuously remove the fluid and prevent edema

Question 21

what are 3 safety factors the body uses to help prevent or reduce edema?

Answer 21

1. increased ISF pressure limits filtration and 2. promotes lymph flow
2. increased filtration and flow decreased ISF protein concentration and decreases ISF oncotic pressure

Question 22

what is Pi

Answer 22

hydrostatic pressure in the interstitium

Question 23

what is Pc

Answer 23

hydrostatic pressure in the capillary