Microcirculation and Lymphatics Flashcards
What are considered the precapillary resistance vessels?
1) arterioles
2) metarterioles
3) precapillary sphincter
What is the primary exchange vessel?
capillaries
What are the post capillary resistance vessels?
venules
Name 5 characteristics of capillary blood flow:
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)
What are the four factors governing transcapillary fluid exchange?
1) plasma oncotic pressure
2) capillary hydrostatic pressure
3) tissue oncotic pressure
4) interstitial hydrostatic pressure
What is Plasma Oncotic Pressure caused by?
proteins in the plasma - it is an osmotic pressure exerted by the substances found in the plasma
(osmotic pressure INSIDE blood)
Conversely, what is tissue oncotic pressure?
an osmotic pressure driven by substances dissolved in the interstitium (such as extracapillary proteins)
What are the hydrostatic pressures caused by (both intracapillary and extra)?
The volume of fluid
Hydrostatic pressure forces fluid ____ while oncotic pressure pulls fluid ____
Out; In
Why is oncotic pressure able to pull fluid in?
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
What direction is the net fluid movement on the arteriole side of the capillary?
OUT of the capillary because hydrostatic forces > oncotic
filtration
What direction is the net fluid movement on the venule side of the vapillary?
IN because oncotic pressure > hydrostatic
absorption
What is responsible for holding fluid within the capillaries?
the osmotic pressure of the plasma proteins (ONCOTIC PRESSURE)
What protein is particularly important in maintaining oncotic pressure in the blood?
albumin
What noteworthy property of albumin allows it to contribute to oncotic pressure in a huge way?
the positive charge of it (attracts NaCl which increases oncotic pressure)
Arterial pressure exerts a relatively ________ (small/large) effect on capillary hydrostatic pressure because of _______ (small/large) pre-capillary resistance
small; large
COUNTER INTUITIVE because you would expect a large resistance to exert a large effect
Venous pressure exerts a relatively ________ (small/large) effect on capillary hydrostatic pressure because of _______ (small/large) post-capillary resistance
large; small
Capillary hydrostatic pressure is primarily determined by the __________________ ratio
pre/post capillary resistance ratio
What is the normal pre/post capillary resistance ratio?
4:1
If you decrease this pre/post capillary resistance ratio (in other words, decrease pre capillary resistance and increase post) what happens to hydrostatic pressure?
it INCREASES (easy for fluid to get in but hard to get out leads to pressurized pile up)
If you increase the pre/post capillary resistance ratio (increase pre cap resistance but decrease post) what happens to hydrostatic pressure?
it DECREASES (hard for fluid to get in but easy to get out leads to little volume in the tube)
Name four vasodilators
1) prostacyclins
2) EDRF
3) Nitric oxide (NO)
4) metabolites (H+, CO2, K+)
What does endothelin do?
causes vasoconstriction of the blood vessels
What is the main function of the lymphatic system?
collects and returns interstitial fluid to the circulatory system
Describe the flow mechanism of fluid through the lymphatic system back to the heart
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
What 3 factors govern lymph flow?
1) amount of capillary filtration
2) skeletal muscular activity
3) lymphatic unidirectional valves
What clinical outcome can result from reduced plasma protein concentration?
edema (weakened oncotic pressure in the blood so less fluid is pulled in. Also heightens hydrostatic pressure causing more fluid to leave the blood)
What are 3 other precipitating factors that can lead to edema?
1) increase in capillary hydrostatic pressure
2) increased permeability of capillart membrane
3) lymphatic obstruction
What are 5 potential causes of this pressure imbalance?
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)
