Microcirculation

Question 1

What are the 2 functions of microcirculation?

Answer 1

• Exchange of molecules from the blood to cells and vice versa, via DIFFUSION
• Regulation of blood volume by altering the distribution of fluid between the interstitial and vascular compartments, via FILTRATION from or ABSORPTION into capillaries

Question 2

Do capillaries have smooth muscle cells?

Answer 2

NO! just endothelial cells

Question 3

What controls the blood flow into capillary beds?

Answer 3

As the metarterioles give off capillaries, the junction is surrounded by precapillary sphincters that regulate the blood flow into the capillary bed and venules.

Question 4

Where are precapillary sphincters most abundant?

Answer 4

mesenteric circulation

Question 5

What molecules can cross capillaries via diffusion?

Answer 5

Oxygen and Carbon dioxide

Question 6

What molecules can diffuse through clefts?

Answer 6

water and small solutes

Question 7

How are proteins transported across capillaries?

Answer 7

1) Fenestrations (in liver)

2) taken up by endocytosis and transported across endothelial cells via exocytosis! (very low flux thorugh this system)

Question 8

Can proteins usually cross capillaries?

Answer 8

NO

Question 9

What is the equation for osmotic pressure?

Answer 9

Osmotic pressure π=RTσΔc

Question 10

What is the reflection coefficient related to?

Answer 10

σ =1 - permeability coefficient

Question 11

What is the reflection coefficient of proteins?

Answer 11

Albumin and Hemoglobin have permeability coefficient of around 0, so they are almost completely reflected (.999)! This means that they generate a significant osmotic pressure.

Question 12

What is the reflection coefficient of water?

Answer 12

Water has permeability coefficient of 1, so it is NOT reflected (0)

Question 13

What can change the refection coefficient of proteins?

Answer 13

The reflection coefficients of proteins can decrease significantly during inflammatory conditions (like burns)

Question 14

What is the Starling Equation?

Answer 14

Jv = Kf [(Pc - Pi ) – (Πc – Πi) ]

Question 15

What does Jv stand for?

Answer 15

transcapillary flow

Question 16

What does a positive Jv mean?

Answer 16

(+) when flow is outward, filtration

Question 17

What does a negative Jv mean?

Answer 17

(-) when flow is inward, reabsorption

Question 18

What does Kf stand for?

Answer 18

filtration coefficient (hydraulic conductance)- equal to inverse of resistance

Question 19

What regulates Kf?

Answer 19

• Regulated by precapillary sphincters that can block flow into capillaries and shunt blood around them
• Regulated by capillary type (fenestrated (high) v. continuous (low))
• Regulated by inflammation (which will increase capillary permeability and raise Kf)

Question 20

What is [(Pc - Pi ) – (Πc – Πi) ] ?

Answer 20

Net transcapillary pressure

Question 21

What is (Pc - Pi )?

Answer 21

capillary - interstitial hydrostatic pressure

Question 22

Is hydrostatic pressure negative or positive?

Answer 22

+ PRESSURE- forces water OUT

Question 23

What is (Πc – Πi)?

Answer 23

oncotic pressure: capillary - interstitial colloid osmotic pressure

Question 24

Is oncotic pressure negative or positive?

Answer 24

• PRESSURE- high protein content within plasma pulls water IN from interstitium

Question 25

Increasing Pc will do what to filtration?

Answer 25

INCREASE IT! (water is forced out of capillaries)

Question 26

Decreased arteriolar hydrostatic RESISTANCE will have what effect?

Answer 26

increase blood flow and increase pressure in capillary

Question 27

Increasing the venous hydrostatic pressure will have what effect on pressure in the capillary?

Answer 27

decreases blood flow and increases capillary pressure

Question 28

What is the only factor in the Starling equation that changes from the arteriole to the venous side?

Answer 28

Pc is the only variable that really changes (DECREASES), because pressure as lost with forward movement of fluid

Question 29

Is the net filtration or absorption on the arteriole side of the capillary?

Answer 29

net filtration

Question 30

Is the net filtration or absorption on the venuole side of the capillary?

Answer 30

net absorption

Question 31

What controls Pi?

Answer 31

Depends on interstitial fluid volume (fluid flowing in from the capillaries vs fluid flowing out via lymphatics ). Usually a vacuum!

Question 32

A higher Pi says what about lymph flow?

Answer 32

HIGHER

Question 33

Πc depends on what?

Answer 33

plasma protein concentration

Question 34

What decreases plasma protein concentration (and decreases Πc)?

Answer 34

liver disease, starvation, kidney disease, transient dilution (IV infusion and fluid shifts)→ increased filtration

Question 35

What increases plasma protein concentration (and increase Πc)?

Answer 35

lowering liquid component via dehydration, diarrhea, vomiting, prolonged sweating→increased absorption to replace fluid

Question 36

Πi is regulated by what?

Answer 36

input (protein entering from capillaries)- output (protein leaving via lymphatic drainage)

Question 37

Increased lymph flow does what to the interstitial protein concentration?

Answer 37

lowers it! flushes it out!

Question 38

What opens flap valves?

Answer 38

increased interstitial pressure

Question 39

What creates negative pressure (suction) that can pull fluid into the lymphatic vessel?

Answer 39

smooth muscle around lymph vessels

Question 40

What is the most simplistic way to explain edema?

Answer 40

fluid entry is greater than fluid removal

Question 41

List the edema safety factors.

Answer 41

1. increase in lymph flow as interstitial fluid pressure increases (to a certain point)

Question 42

How does increase in interstitial fluid pressure act as a safety factor to edema?

Answer 42

Negative interstitial pressure and Low compliance: flow will resist swelling until it is around 0mmHg (get about 5mm Hg of safety) increase in interstitial volume → increase in Pi (goes from negative to more positive)→ decrease in (Pc – Pi) → reduce any further increase in interstitial volume

Question 43

How does lymph flow act as a safety factor to edema?

Answer 43

Get around 7 mmHg of safety due to increasing lymph flow as interstitial fluid pressure increases

Question 44

List the causes of edema.

Answer 44

``` Capillary pressure Interstitial pressure Plasma oncotic pressure Interstitial oncotic pressure Permeability – inflammation ```

Question 45

What can increase capillary pressure?

Answer 45

heart failure; venous obstruction, inflammation (local vasodilation)

Question 46

What can change interstitial pressure and lead to edema?

Answer 46

pulmonary-- restrictive lung disease

Question 47

What can decrease plasma oncotic pressure?

Answer 47

liver disease and malnutrition (reduced production), kidney disease (loss)

Question 48

What can increase interstitial oncotic pressure?

Answer 48

lymphatic obstruction (only way for protein to get back into circulation is via lymphatics), inflammation (increased permeability)