L17 Circulation- Microcirculation and Lymphatics Flashcards
Explain precapillary resistors in terms of microcirculation arrangement.
Arterioles, precapillary sphincters
-Most resistance is here b/c of VSM
Explain metarterioles in terms of microcirculation arrangement.
Act as shunts between arterioles and venous sides, do not exchange gas
Explain postcapillary resistors in terms of microcirculation arrangement.
Venules, much less resistance than on arteriole side
Explain capillaries in terms of microcirculation arrangement.
Exchange vessels- O2 exchange happens here
- no VSM
- 5 micron D
Explain the characteristics of capillary blood flow in terms of precapillary sphincter control.
- Low velocity
- Pressure gradients cause forward and backward motion
Explain the characteristics of capillary blood flow in terms of vasomotion.
Intermittent motion: non-continuous flow through capillaries, some open/closed
Explain the characteristics of capillary blood flow in terms of Rouleaux formation.
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
Define transcapillary fluid exchange.
Movement of fluid and exchange of nutrients out of and into the capillary
-Starling Law of Cardiac Exchange
Explain how interstitial hydrostatic pressure determines transcapillary fluid exchange.
Hydrostatic pressure caused by the volume of fluid in the interstitium
-Synonymous with water P
Explain how interstitial oncotic pressure determines transcapillary fluid exchange.
Osmotic pressure exerted by substances dissolved in interstitium (proteins)
-Counterpart to plasma oncotic pressure
Explain how plasma hydrostatic pressure determines transcapillary fluid exchange.
Mean capillary blood pressure
-Synonymous with BP
Explain how plasma oncotic pressure determines transcapillary fluid exchange.
Osmotic pressure exerted by substances found in the plasma (plasma proteins)
-Protein solutes put pressure on capillary
Explain TCF exchange in different pathological conditions (hemorrhage, nephosis, liver damage, portal hypertension, CHF, burns
1
Define the importance of albumin in TCF exchange.
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
Define pre/post capillary resistance.
Precapillary resistance= arterial resistance (high)
Postcapillary resistance= venous resistance (low)
-Ratio is usually 4:1
How does pre/post capillary resistance determine capillary hydrostatic pressure.
- 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
Define the role of endothelial-derived mediators in regulation of resistance vessels.
- Prostacyclins, endothelium-derived relaxing factor (EDRF), NO and metabolites cause VASODILATION
- Endothelin (ET) causes VASOCONSTRICTION
Explain the structure of the lymphatic system.
- 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
Explain the function of the lymphatic system.
Fxn to collect and return interstitial fluid to circulatory system
-Large collecting vessels return fluid to subclavian veins
Define edema.
Accumulation of excess fluid within interstitial space
-Swelling of ankles, ascites, pulmonary edema
Which conditions predisopose edema?
- 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)
What is the key factor that holds fluid in capillaries?
Osmotic pressure of plasma proteins (oncotic pressure)
