Microcirculation

Question 1

What are metaarterioles?

Answer 1

They are thoroughfare vessels that go stratight from the arterioles to the venule, bypassing the capillary bed altogether

Question 2

What regulates flow through capillaries?

Answer 2

Neural and metabolic mechanisms that can control the precapillary sphincters

Question 3

Do capillaries have muscles?

Answer 3

No, but there are precapillary sphincters where the capillary comes off the arteriole that can close off the capillary

Question 4

If blood flows through a metarteriole and bypasses a capillary bed, is there exchange of gas/waste products?

Answer 4

No

Question 5

What is the difference between the arteriolar radius and the precapillary sphincters when it comes to regulating blood flow?

Answer 5

The arteriolar radius determines the overall blood flow to a particular capillary bed

The capillary sphincters determine which capillaries are perfsued

Question 6

What are the 3 types of capillaries?

Answer 6

Continuous

Fenestrated

Discontinuous

Question 7

What are continuous capillaries?

Answer 7

Capillaries that have tiny clefts between each endothelial cell to allow hydrophilic molecules to pass through

(Found in muscle, skin, lung, and brain)

Question 8

What are fenestrated capillaries?

Answer 8

Capillaries that have fenestrae which are like “windows” in the cell membranes of each cell to allow water and small hydrophilic molecules to pass

(Found in kidneys, intestine, endocrine glands)

Question 9

What are discontinuous capillaries?

Answer 9

Capillaries that have wide gaps between adjacent endothelial cells to allow large molecules and water to pass through

(Found in liver, bone marrow, spleen)

Question 10

How do lipophilic molecules get through the capillary cells?

Answer 10

They diffuse right through the plasma membranes

Question 11

Does albumin easily leak out the capillaries?

Answer 11

No, proteins are usually too large to diffuse through

Question 12

What is filtration?

Answer 12

Movement of fluid OUT of the capillary and into the intersitium

Question 13

What is absorption?

Answer 13

Movement of fluid INTO the capillary from the interstitial space

Question 14

What are the 4 starling forces that affect capillary fluid movement?

Answer 14

1. Capillary hydrostatic pressure
2. Interstitial fluid hydrostatic pressure
3. Plasma oncotic pressure
4. Interstitial oncotic pressure

Question 15

Does capillary hydroststic pressure favor filtration or absorption

Answer 15

Filtration

Question 16

What is the capillary hydrostatic pressure dependednt on?

Answer 16

Pre- and post- capillary resistances and pressures

Question 17

If you increase resistance in the arterioles, what will happen to the pressure inside the capillary?

Answer 17

Decrease

Question 18

If you increase the amount of venular resistance, what happens to the pressure in the capillary?

Answer 18

Increase

Question 19

What happens to the capillary pressure if you increase venous pressure?

Answer 19

Increases

Question 20

What is the reason for the plasma oncotic pressure?

Answer 20

The plasma proteins which can not leave the capillary lumen

Question 21

What is the approximate pressure measurement that is contributed by plasma oncotic pressure?

Answer 21

25-40 mmHg

Question 22

Does plasma oncotic pressure favor absorption or filtration

Answer 22

Absorption

Question 23

What produces the interstitial hydrostatic pressure?

Answer 23

The fluid located in the intermolecular spaces of the interstitial matrix

(Very small pressure)

Question 24

What produces the interstitial oncotic pressure?

Answer 24

Proteins in the oncotic pressure

Very small

Question 25

How do you calculate net filtration pressure?

Answer 25

NFP= Pc+ πi - Pi - πc NFP= (capillary hydrostatic pressure) + (interstitial Oncotic pressure) - (hydrotstatic interstitial pressure) - (capillary osmotic pressure)

Question 26

If the net filtration pressure is positive , what direction is the fluid moving

Answer 26

Filtration (moving out of capillary lumen)

Question 27

If the net filtration pressure is negative, which direction is fluid moving

Answer 27

Absorption (fluid moving into capillary from interstitial space)

Question 28

How do you calcaule the rate of fluid movement (F)?

Answer 28

F= Kf x NFP Kf is the filtration coefficient which reflects the capillary permeability (NFP=Pc+ πi-Pi-πc)

Question 29

What does Kf represent

Answer 29

Kf is the filtration coefficient and it reflects the capillary permeability

Question 30

When you calculate the NFP, you use 4 values. 3 of them stay pretty constant, but one of them is variable. Which is which?

Answer 30

Pc (capillary hydrostatic pressure) varies as you move from the arteriole end to the venule end πi, Pi, and πc tend to stay pretty constant SO what does that mean? It means that as you move from the beginning to the end of the capillary, you actually move from a positive NFP (filtration) to a negative NFP (absorption)

Question 31

If you increase capillary pressure, do you get more filtration or absorption

Answer 31

Filtration

Question 32

If you decrease capillary pressure, do you favor filtration or absorption?

Answer 32

Absorption

Question 33

If you decrease the plasma protein level, do you favor absorption or filtration?

Answer 33

Filtration

Question 34

If you were hypovolemic and needed to get more fluid back into the bloodstream, what could your body do at the capillary level to accomplish that

Answer 34

If you increase the vasoconstriction at the arteriole, it will decrease capillary hydrostatic pressure, which will favor absorption, and your capillaries will absorb fluid from the interstitial space

Question 35

Why doesn’t fluid accumulate in the interstitial spaces? I thought that the overall balance was towards filtration!

Answer 35

Becasue the lymph vessels collect interstitial fluid and return it to the bloodstream

Question 36

What kinds of things can increase capillary hydrostatic pressure and favor filtration, possibly causing edema?

Answer 36

Arteriolar dilation Venous constriction Increased venous pressure Heart failure Extra cellular fluid volume expansion

Question 37

What kinds of things would decrease capillary oncotic pressure and favor filtration, and possible cause edema?

Answer 37

Decreased plasma protein concentration Severe liver failure (failure to make protein) Protein malnutrition Nephrotic syndrome (losing protein in urine)