Microcirculation and Lymphatics

Question 1

What are considered the precapillary resistance vessels?

Answer 1

1) arterioles
2) metarterioles
3) precapillary sphincter

Question 2

What is the primary exchange vessel?

Answer 2

capillaries

Question 3

What are the post capillary resistance vessels?

Answer 3

venules

Question 4

Name 5 characteristics of capillary blood flow:

Answer 4

1) low velocity of flow (huge cross sectional area)
2) intermittent (vasomotion)
3) direction (pressure gradients)
4) not uniform
5) Rouleaux formation (RBCS go in single file and touch membrane of endothelial cell to enact gas/waste exchange)

Question 5

What are the four factors governing transcapillary fluid exchange?

Answer 5

1) plasma oncotic pressure
2) capillary hydrostatic pressure
3) tissue oncotic pressure
4) interstitial hydrostatic pressure

Question 6

What is Plasma Oncotic Pressure caused by?

Answer 6

proteins in the plasma - it is an osmotic pressure exerted by the substances found in the plasma

(osmotic pressure INSIDE blood)

Question 7

Conversely, what is tissue oncotic pressure?

Answer 7

an osmotic pressure driven by substances dissolved in the interstitium (such as extracapillary proteins)

Question 8

What are the hydrostatic pressures caused by (both intracapillary and extra)?

Answer 8

The volume of fluid

Question 9

Hydrostatic pressure forces fluid ____ while oncotic pressure pulls fluid ____

Answer 9

Out; In

Question 10

Why is oncotic pressure able to pull fluid in?

Answer 10

Because there are usually more solutes in the blood (proteins and such in plasma) than in the interstitium so that provides a driving force for water to move in

Question 11

What direction is the net fluid movement on the arteriole side of the capillary?

Answer 11

OUT of the capillary because hydrostatic forces > oncotic

filtration

Question 12

What direction is the net fluid movement on the venule side of the vapillary?

Answer 12

IN because oncotic pressure > hydrostatic

absorption

Question 13

What is responsible for holding fluid within the capillaries?

Answer 13

the osmotic pressure of the plasma proteins (ONCOTIC PRESSURE)

Question 14

What protein is particularly important in maintaining oncotic pressure in the blood?

Answer 14

albumin

Question 15

What noteworthy property of albumin allows it to contribute to oncotic pressure in a huge way?

Answer 15

the positive charge of it (attracts NaCl which increases oncotic pressure)

Question 16

Arterial pressure exerts a relatively ________ (small/large) effect on capillary hydrostatic pressure because of _______ (small/large) pre-capillary resistance

Answer 16

small; large

COUNTER INTUITIVE because you would expect a large resistance to exert a large effect

Question 17

Venous pressure exerts a relatively ________ (small/large) effect on capillary hydrostatic pressure because of _______ (small/large) post-capillary resistance

Answer 17

large; small

Question 18

Capillary hydrostatic pressure is primarily determined by the __________________ ratio

Answer 18

pre/post capillary resistance ratio

Question 19

What is the normal pre/post capillary resistance ratio?

Answer 19

4:1

Question 20

If you decrease this pre/post capillary resistance ratio (in other words, decrease pre capillary resistance and increase post) what happens to hydrostatic pressure?

Answer 20

it INCREASES (easy for fluid to get in but hard to get out leads to pressurized pile up)

Question 21

If you increase the pre/post capillary resistance ratio (increase pre cap resistance but decrease post) what happens to hydrostatic pressure?

Answer 21

it DECREASES (hard for fluid to get in but easy to get out leads to little volume in the tube)

Question 22

Name four vasodilators

Answer 22

1) prostacyclins
2) EDRF
3) Nitric oxide (NO)
4) metabolites (H+, CO2, K+)

Question 23

What does endothelin do?

Answer 23

causes vasoconstriction of the blood vessels

Question 24

What is the main function of the lymphatic system?

Answer 24

collects and returns interstitial fluid to the circulatory system

Question 25

Describe the flow mechanism of fluid through the lymphatic system back to the heart

Answer 25

unidirectional flow typically carries plasma and protein back to the heart via large collecting vessels that dump fluid into subclavian veins. The lymph ducts have non-fenestrated endothelium with little to no basal lamina and no smooth muscle. Valves also help keep flow unidirectional

Question 26

What 3 factors govern lymph flow?

Answer 26

1) amount of capillary filtration
2) skeletal muscular activity
3) lymphatic unidirectional valves

Question 27

What clinical outcome can result from reduced plasma protein concentration?

Answer 27

edema (weakened oncotic pressure in the blood so less fluid is pulled in. Also heightens hydrostatic pressure causing more fluid to leave the blood)

Question 28

What are 3 other precipitating factors that can lead to edema?

Answer 28

1) increase in capillary hydrostatic pressure
2) increased permeability of capillart membrane
3) lymphatic obstruction

Question 29

What are 5 potential causes of this pressure imbalance?

Answer 29

1) congestive heart failure
2) mechanical obstruction of venous return
3) renal disease (loss of protein)
4) liver disease (lack of protein synthesis)
5) burn (increases capillary permeability)