Microcirculation

Question 1

In microcirculation, substances are transferred between??? How?

Answer 1

Between plasma and interstitial fluid by diffusion

Question 2

What can diffuse directly through cell membrane of capillaries?

Answer 2

Lipid soluble substances (CO2, O2)

Question 3

How does water soluble substances cross capillary walls? Give examples

Answer 3

Water-filled intercellular clefts (pores). H20, sodium, chloride.

Question 4

Describe width of capillary intercellular slit pores in a typical muscle capillary.

Answer 4

VERY SMALL

Question 5

Permeability of capillary pores for different substances varies according…

Answer 5

According to their molecular diameters

Question 6

T/F Capillaries in different tissues have similar permeabilities.

Answer 6

FALSE.
There are extreme differences. Brain has tight junctions with pores very close together (blood brain barrier) to prevent substances from getting into brain. Liver has large gaps/pores because liver metabolizes a lot of substances.

Question 7

Factors for diffusion

Answer 7

1-concentration gradient
2-Size of molecule
3-Size of pore

Question 8

Kidneys have how many microcirculation systems

Answer 8

2

Question 9

General net fluid movement across capillaries

Answer 9

1-Absorb at arterial end
2-Reabsorb at venous end (but not everything is absorbed)
3-Whatever is not absorbed, lymphatics pick up.

Edema occurs if there is low reabsorbtion and lymphatic don’t pick up.

Question 10

What are the primary forces that determine fluid movement through capillary membrane. All move fluid in what direction?

Answer 10

• Capillary pressure
• Plasma colloid osmotic pressure
• Interstitial fluid pressure
• Interstitial fluid colloid osmotic pressure

Move in ONE direction

Question 11

Explain capillary hydrostatic pressure

Answer 11

Pushes fluid OUT of capillary pores “holes in hose”

Pushes water into interstitial fluid

Question 12

Explain interstitial fluid hydrostatic pressure

Answer 12

Can have (-) or (+) pressure

+)Pushing fluid INTO capillary
(-)Vacuuming fluid OUT of capillary (most cases is (-)

Question 13

Explain colloid osmotic pressure

Answer 13

Proteins in plasma in capillaries oppose filtration to keep water in capillaries.

Opposes filtration causing osmosis of water inward through the membrane.

Question 14

Explain Interstitial fluid colloid osmotic pressure

Answer 14

Proteins in plasma in interstitiual fluid try to PULL H20 out of caps.

Question 15

Capillary filtration coefficien (Kf) measures. Describe using kidney, liver, and brain.

Answer 15

Measure of the capacity of the capillary membrane to filter water given net filtration pressure.

Capillary bed with more/or wider pumps have higher Kf

So, Liver Kf >Brain Kf
Kidney Kf> Brain Kf

Question 16

Explain hydrostatic pressure from arterial end to venous end

Answer 16

As blood goes from arterial end to venous end the hydrostatic pressure decreases.

So arterial side, water trying to be pushed out of capillary
Venous side, water trying to be pushed into capillary.

Question 17

What causes the majority of colloid osmotic pressure of plasma?

Answer 17

Albumin (75%)

Globulins (25%)

Question 18

Interstitial fluid colloid osmotic pressure

Answer 18

Small amounts of proteins leak through capillary membranes into interstitial space based on pores in tissue.

The more protein the higher osmotic pressure.

Question 19

Excess fluid that is not reabsorbed into venous end of capillaries goes…

Answer 19

Into lymph vessels and dumped back into circulation via subclavian vein.

Question 20

What happens if lymph vessels are blocked?

Answer 20

You’ll get fluid build up-edema

Question 21

Explain what would happen in microcirculation with a dog that had heart worms

Answer 21

Due to increase in atrial pressure, there’s an increase in venous pressure. There is an increase in filtration of capillaries (interstitial fluid coming out of capillaries) at atrial end and not much absorbing of interstitial fluid at venous end.

If lymphatic system doesn’t drain excess interstitual fluid, and there’s heart failure on the right side, edema forms in peripheral system (legs, abdomen, etc)

If lymphatic system doesn’t drain excess interstitual fluid, and there’s heart failure on the left side, edema forms in pulmonary system (llungs).

Question 22

Benefits of lymphatic system

Answer 22

• Prevents edema
• Returns proteins and high molecular weight substances that can’t be reabsorbed into blood
• Major route for absorption of nutrients from the GI tract
• Plays important role in the immune system- picks up bacteria.

Question 23

Factors that increase interstitial fluid pressure and lymph flow

Answer 23

• elevated capillary pressure
• decreased plasma colloid osmotic pressure
• Increased interstitial fluid colloid osmotic pressure
• Increased permeability of capillaries

Question 24

Three scenarios where capillary pressure is increased or plasma colloid interstitial fluid pressure is increased

Answer 24

1-Nephrotic syndrome= decrease in plasma proteins