Microcirculation and lymphatics Flashcards
What is vasomotion?
Intermittency of blood flow through the capillaries
How is blood flow through the capillaries regulated?
Contraction and relaxation of the arterioles and precapillary sphincters
What are factors the affect the rate of diffusion through a cell membrane?
Lipid solubility
Molecular size
Concentration gradient
Membrane surface area
Composition of lipid layer
What is microcirculation?
Transport across the capillary wall
What is Pc?
Capillary hydrostatic pressure
What is Pi?
Interstitial hydrostatic pressure
What is pi-c?
Capillary oncotic pressure
What is pi-i?
Interstitial oncotic pressure
What is the starling equation?
Fluid movement(Jv) = Kf x A [(Pc-Pi) - sigma(pi-c - pi-i)]
What factors in the starling equation increase capillary filtration?
Increased Pc
Decreased Pi
Decreased pi-c
Increased pi-i
What can increase pi-i?
Inadequate lymph filtration
What can decrease pi-c?
Decreased protein concentration in blood
What can increase Pc?
Increased arterial and venous pressure
Arteriolar dilation
Venous constriction
What determines Kf?
Physical properties of the barrier
What is sigma represent in the Starling equation?
Reflection coefficient
What does is mean when the reflection coefficient is equal to 1? When it is equal to 0?
If sigma=1 the capillary is impermeable to protein
If sigma=0 the capillary is freely permeable to protein
What is the net movement of fluid at the arterial end of the capillary?
Net outward force of 13 mmHg
What is the net movement of fluid at the venous end of the capillary?
Net inward force of 7 mmHg
What occurs when net filtration exceeds the capacity of the lymphatics?
Edema
What factors prevent interstitial pulmonary edema?
Decreased RV force of contraction compared to LV
Increased lymph flow
Decreased interstitial oncotic pressure
High interstitial compliance
What vasoconstrictors act on Gq receptors?
Norepinephrine/epinephrine
Vasopressin/ADH
Angiotensin II
Endothelin-1
What are the steps in Gq mediated vasoconstriction?
Activation of Gq protein
G protein coupled activation of PLC
Phosphatidylinositol hydrolysis and formation of IP3 and DAG
IP3 mobilizes Ca++ from SR –> increased free Ca++
Ca++ binds to calmodulin which activates MLCK
Active myosin cross-bridges along actin
What vasodilators act on Gs receptors?
Epinephrine
Adenosine
Prostaglandin I2 and Prostacyclin
What vasodilators act via NO release?
Bradykinin
ACH
Histamine
Substance-P
Where is autoregulation of blood flow well-developed?
Kidney
Brain
Heart
Skeletal muscle
Mesentery
What is blood flow autoregulation?
Blood flow to an organ remains constant over a wide range of perfusion pressure
What factors determine autoregulation in the heart?
Local metabolites
What factors determine autoregulation of the brain?
Local metabolites - CO2
What factors determine autoregulation in the kidneys?
Myogenic
Tubuloglomerular feedback
What factors determine autoregulation in the lungs?
Hypoxia causes vasoconstriction
What factors determine autoregulation in the skeletal muscle?
Local metabolites produced during exercise
Sympathetic tone at rest
What factors determine autoregulation of the skin?
SyNS –> temperature control
About how much fluid is returned to the vascular system form lymphatics a day?
About 3 L/day
What is the relationship between lymph flow and interstitial fluid pressure?
An increase in interstitial fluid pressure will increase lymph flow
At what interstitial fluid pressure with lymph flow plateau?
2 mmHg
