Microcirculation and Nutrient Exchange

Question 1

Structure of microcirculation

Answer 1

Artery branches to arterioles

Smooth muscle precapillary sphincter encircles the capillary

Venules larger than arterioles and weaker muscular coat

Question 2

Precap sphincters

Answer 2

Close contact with tissues they serve so the local conditions of the tissues can cause direct effects on the vessels

Question 3

Structure of cap wall

Answer 3

Unicellular layer of endothelial cells with a basement membrane

Intercellular cleft

THis is where change between blood and interstitial fluid occurs

Question 4

Exchange across capillaries

Answer 4

Area available for exhcnage is greatest

Greatest surface to volume ratio

Velocity is slowest - this is due to expanded cross sectional area

Question 5

Interstitium and interstital fluid

Answer 5

This is between cells

COllagen fibers and proteoglycan filaments

Question 6

3 processes of exchange of things bt blood and IS fluid

Answer 6

Lipid soluble - directly through cell mmb (O2 and CO2)

Water soluble, non-lipid sobule subs - intercellular pores in capillary membrane - water, Na, Cl, glucose

Vesicular transport - whole proteins across capillary ednothelium

Question 7

Exchangeb y diffusion equaition

Answer 7

Qx = Pxa(Cpx-Cifx)

A - diffusion area
Px - permeabiltiy

Question 8

Area abailable for exchange

Answer 8

Highly lipid soluble - whole endothelial surgace for diffusion

Water-soluble restricted to pore within capillaries

Therefore lipid is much fast

For both lipid and water soluble, SA is controlled by adjusting # of caps through which blood is flowing

Question 9

Permability of substance

Answer 9

Measure of ease with whic hvascular endothelium permits passage of substance

Due to interactive ffect of capillary endothelium and diffusing substance

Question 10

Brain and Liver caps

Answer 10

Brain - tught junctions only allows extremely small

Liver - opposite

Question 11

Lipid vs. water when it comes to capillary permeability

Answer 11

Lipid - penetrate quick easily vs. water soluble

Also dependso nsize

Question 12

Flow-lmimited exhcange

Answer 12

SOlute transfer rate proportional to flow

If permability high, solute corsses so quickly that plasma equilibrates iwht pericap IS fluid before the end of the capillary

Things like O2 and CO2

Question 13

O2 transport in exercising muscle

Answer 13

Oxygen consumption increases so you must also increase blood flow

Question 14

IN diffusion-limited exchange, flow has little effect onsolute transfer…why and whay??

Answer 14

Solute has NOT equilibrated with space by end of cap

Limited by endothelial permeability rather than by flow

Inulin, vitamin B12…Urea and glucose when transit shortened by hgih blood flows

Question 15

Glucose transport in exercising muscle

Answer 15

Cap recuritment - reduces raidus of cylinder and diffusion enhances difusional SA …inc flow may also inc endothelial perm

Fall in tissue gluocse- steeper concn gradients raises fractional extraction and AV concentration diff

inc blood blood - prevents mahor fall in mean intracap plasma concentration