F - Microcirculation and Special Circulations - Ballam Flashcards
What does the Starling equation calculate?
The flow of water either out of the capillary (+) or drawing it into the capillary (-)
What is the Starling equation?
J = (Pc - Pi) - (pc-pi) J = (forces moving fluid out) - (forces moving fluid in)
What does it mean if the Starling equation is positive?
This would predict a net movement of fluid out of the capillary
How are Starling values changed in edema?
Pc - elevated venous pressure (heart failure)
Pi - restricted lymphatic flow
pc - decrease in albumin (starvation, liver failure)
pi - restricted lymph flow or inflammation
3 Types of local control?
Metabolic - active or reactive hyperemia
Myogenic control
Shear
Active hyperemia
Increasing interstitial concentration of CO2, H+, K+, lactate, adenosine, or reduction in O2
-causes relaxation of smooth muscle increasing flow through area
Reactive hyperemia
Vascular obstruction causes build up of metabolites leading to vasodilation
-if obstruction is removed, area flooded with blood
Myogenic control
If BP elevated arterial walls become stretched and that causes vasoconstriction
Shear
Local control
If vascular bed dilates due to metabolic demand the flow through upstream arterioles and small arteries would increase.
This increases shear friction = release of NO
What areas of the body have the most local control?
Heart, brain, skeletal muscle
Histamine and bradykinin
Arteriolar vasodilation
Increases cap porosity allowing escape of large molecules
Causes edema in response to tissue damage
Serotonin
Vasoconstriction in response to tissue damage
Coronary circulation
Largely under metabolic control
Skin and circulation
Symp vasoconstriction to baroreceptor reflex
Symp inhibition and dilation of shunt pathway to excessive body temp
The highest pressures of pulmonary vascular system?
RV (24 to 0) and pulmonary a. (24 to 10)
Distribution of blood flow in lung zones?
zone 1 - collapses
zone 2 - cap open part of cardiac cycle
zone 3 - cap always open
Is arterial system more compliant than systemic arteries?
Yes
Small changes in mean pressure will significantly dilate arteries, reduce resistance and help maintain pressure low in face of large changes in flow
Right to left shunt
Systemic v to systemic a without passing through functional lung tissue
Foramen ovale - RA to LA
Ductus arteriosis - pulmonar a to aorta
Left to right shunt
blood from systemic a to systemic v without passing through a cap bed for substance exchange
Umbilical v.
O2 blood from placenta to fetus
Connects fetal IVC in the liver
Post-parturition changes
Umbilical a and v clamped = increased fetal total peripheral resistance.
Ductus venosus closes
Lungs expand and pulmonary resistance falls
Ductus arterioles after birth
Left pressure greater than right, flow reverses through ductus arterioles and passes from aorta into pulmonary a generating a left to right shunt
Hormonal changes will close it
What 2 major factors cause a change in blood flow pattern following birth?
Systemic vascular resistance is increased due to removal of placental circulation
Decreased resistance of the pulmonary circulation due to expansion and oxygenation
