L17 Circulation- Microcirculation and Lymphatics

Question 1

Explain precapillary resistors in terms of microcirculation arrangement.

Answer 1

Arterioles, precapillary sphincters

-Most resistance is here b/c of VSM

Question 2

Explain metarterioles in terms of microcirculation arrangement.

Answer 2

Act as shunts between arterioles and venous sides, do not exchange gas

Question 3

Explain postcapillary resistors in terms of microcirculation arrangement.

Answer 3

Venules, much less resistance than on arteriole side

Question 4

Explain capillaries in terms of microcirculation arrangement.

Answer 4

Exchange vessels- O2 exchange happens here

• no VSM
• 5 micron D

Question 5

Explain the characteristics of capillary blood flow in terms of precapillary sphincter control.

Answer 5

• Low velocity

- Pressure gradients cause forward and backward motion

Question 6

Explain the characteristics of capillary blood flow in terms of vasomotion.

Answer 6

Intermittent motion: non-continuous flow through capillaries, some open/closed

Question 7

Explain the characteristics of capillary blood flow in terms of Rouleaux formation.

Answer 7

RBC= 8 micron, caps= 5 micron
RBCs squeeze through caps at angle, membranes touching allows for enhanced O2 exchange
-Problem in sickle cell b/c RBC get stuck

Question 8

Define transcapillary fluid exchange.

Answer 8

Movement of fluid and exchange of nutrients out of and into the capillary
-Starling Law of Cardiac Exchange

Question 9

Explain how interstitial hydrostatic pressure determines transcapillary fluid exchange.

Answer 9

Hydrostatic pressure caused by the volume of fluid in the interstitium
-Synonymous with water P

Question 10

Explain how interstitial oncotic pressure determines transcapillary fluid exchange.

Answer 10

Osmotic pressure exerted by substances dissolved in interstitium (proteins)
-Counterpart to plasma oncotic pressure

Question 11

Explain how plasma hydrostatic pressure determines transcapillary fluid exchange.

Answer 11

Mean capillary blood pressure

-Synonymous with BP

Question 12

Explain how plasma oncotic pressure determines transcapillary fluid exchange.

Answer 12

Osmotic pressure exerted by substances found in the plasma (plasma proteins)
-Protein solutes put pressure on capillary

Question 13

Explain TCF exchange in different pathological conditions (hemorrhage, nephosis, liver damage, portal hypertension, CHF, burns

Answer 13

1

Question 14

Define the importance of albumin in TCF exchange.

Answer 14

Most abundant protein in plasma
-Exerts more force than expected by concentration b/c positive surface charges attract Cl-, which brings Na+, and NaCl solid exerts pressure

Question 15

Define pre/post capillary resistance.

Answer 15

Precapillary resistance= arterial resistance (high)
Postcapillary resistance= venous resistance (low)
-Ratio is usually 4:1

Question 16

How does pre/post capillary resistance determine capillary hydrostatic pressure.

Answer 16

• High precap resistance keeps arterial P from affecting cap hydrostatic P
• Low postcap resistance means venous P affects cap hydrostatic P more
• Decrease in pre:post resistance= increase in cap hydrostatic P
• Increase in pre:post resistance= decrease in cap hydrostatic P

Question 17

Define the role of endothelial-derived mediators in regulation of resistance vessels.

Answer 17

• Prostacyclins, endothelium-derived relaxing factor (EDRF), NO and metabolites cause VASODILATION
• Endothelin (ET) causes VASOCONSTRICTION

Question 18

Explain the structure of the lymphatic system.

Answer 18

• Valves cause unidirectional flow of tissue fluid (plasma) and protein back to heart
• Thinner wall structure
• Non-fenestrated endothelium, little/no basal lamina, no VSM

Question 19

Explain the function of the lymphatic system.

Answer 19

Fxn to collect and return interstitial fluid to circulatory system
-Large collecting vessels return fluid to subclavian veins

Question 20

Define edema.

Answer 20

Accumulation of excess fluid within interstitial space

-Swelling of ankles, ascites, pulmonary edema

Question 21

Which conditions predisopose edema?

Answer 21

• Reduction in plasma protein conc. (lose albumin= decrease oncotic P= increased filtration of fluid out of cap)
• Increase in cap. hydrostatic P (increased venous P)
• Increased permeability of cap. membrane (burns)
• Lymphatic obstruction/destruction (surgery)

Question 22

What is the key factor that holds fluid in capillaries?

Answer 22

Osmotic pressure of plasma proteins (oncotic pressure)