Circulation and Hemokdynamics II Flashcards
where are the smooth muscle locations found in the capillary bed
Arterioles will contain smooth muscle in the walls
Metarterioles will contain some smooth walls
the capillaries will contain pre-capillary sphincters which will be important in shunting the blood or increasing flow into the bed
how are substances able to cross the capillary wall
Clefts allow for passage of water soluble substances such as glucose and electrolytes
- small in brain
- large in liver and gut
Lipid soluble substances such as O2 and CO2 can pass through the cell wall
some larger molecules may pass through in vesicles
what is the starling equation
flow = kf (Pc-Pi) - (hc-hi) or flow = kf (forces moving fluid out) - (forces moving fluid in)
flow = (Pc + hi) - (Pi + hc)
net driving pressure determines rate of fluid exit from or entry into the capillary
the net exchange is a gradual leakage of fluid out of capillary and into the interstitium which must be gathered up by the lymphatic system and returned to venous circulation
what are the two pressures that play a factor in the movement of water in and out of the capillary
(-) drawing it into the capillary
(+) drawing out of the capillary
Hydrostatic pressure (blood pressure)(P)
Osmotic pressure (solute sucking pressure) (pi symbol)
both sides of the capillary wall will have a intervascular and extravascular component to each of these pressures
Pc = hydrostatic pressure pushing out of the capillary (+) hc = hydrostatic pressure pushing into the capillary (-)
pi = osmotic pressure pulling into the capillary (-) hi = osmotic pressure pulling into the intersitial space (+)
what is a net positive starling equation
net movement of fluid out of the capillary
what is a net negative starling equation
net movement of fluid into the capillary
what can elevate Pc, Pi, hc,hi?
Pc = elevated venous pressure (heart failure)
Pi = restricted lymphatic flow or increased driving force out of capillary
hc = decrease in albumin (starvatio or liver failure)
hi = restricted lymph flow or inflammation
edema!
what is the typical net pressure at the arterial end and at the venous end
arterial = positive (flow out of capillaries)
venous = negative (flow into capillaries)
how does lymph impact the flow?
excess fluid and proteins and other substances enter lymphatics via valved channels
muscle pumps push lymph through lymph node scrubbers
about 2 to 3 liters a day re enter at subclavian vein
what is the metabolic control of the capillary bed: Active hyperemia
Active hyperemia is increasing interstitial concentration of metabolites such as CO2, H+, K+, lactate and adenosine or reduction of O2 due to increasing metabolic rate
this causes smooth muscle of arterioles, metaarterioles, and pre-capillary sphinctors to relax and increase flow through the area
what is the metabolic control of the capillary bed: reactive hyperemia
reactive hyperemia is when a vascular obstruction causes build up of metabolites leading to a vasodilation
therefore if the obstruction is removed the area is flooded with blood
i.e: sitting on hand
Method of local control: Shear
if a vascular bed dilates due to metabolic demand, the flow through upstream arterioles and small arteries would increase
this would increase the shear or wall friction leading to the release of NO which would cause vasodilation and augment the downstream metabolic effect.
how does Histamine and Bradykinin affect blood flow
lead to arteriolar vasodilation
increases capillary porosity (Kf) allowing escape of large molecules
can cause edema in response to tissue damage
How does serotonin affect blood flow
can cause vasoconstriction in response to tissue damage
how does prostaglandin affect blood flow
can cause mixed signals of both vasoconstriction and vasodilation
what controls Coronary circulation
Largely under metabolic control
sympathetic innervation of vasculature but usually ignored
ventricular contraction (especially on left side) causes constriction of vasculature most notably near the endocardial surface
what controls cerebral circulation
largely metabolic control
where is the highest pressure of the pulmonary vascular system found?
in the right ventricle and pulmonary artery at about 24 to 0 mmHg
why is the pressure in the Pulmonary circulation much lower than in the systematic circulation
it is because there is a much lower resistance in the pulmonary circulation
how does the body regulate the pulmonary blood flow
Vasoconstriction to alveolar hypoxia (hypoxic vasoconstriction) to move blood to more oxygenated regions of the lung
little sympathetic influence
Arterial system in Pulmonary is much more compliant than in the systemic arteries: therefore, relatively small changes in mean pressure will significantly dilate arteries and reduce resistance and help maintain pressure low in the fact of large changes to flow
how is skeletal muscle controlled at rest and during flight response
at rest: central, baroreceptor control
- norepinephrine to alpha receptors
- when active it comes under local control via metabolic dilation buts some sympathetics to keep CO up via the potential dilation from metabolic control
During flight response: adrenal glands secret epinephrine which bind to B2 receptors and cause vasodilation
how is the skin blood flow regulated
sympathetic vasoconstriction to baroreceopter reflex
sympathetic inhibition and dilation of shunt pathways to excessive body temperature to help cool down
what are the two types of shunts
Right to left shunt: blood passing from systemetic veins to systemic arteries without passing through functional lung tissue
left to right shunt: Blood passing from systemic arteries to systemic veins without passing through a capillary bed for substance exchange
central vs local control for skin and gut, heart, brains, muscle, and pulmonary
skin: more central control than local
heart: way more local control than central
brain: way more local than central control
muscle: much more local control when active than central control when active
Pulmonary: some central control, and hypoxic vasoconstriction to alveolar gasses for local control
