microcirculation Flashcards
(16 cards)
define resistance
hindrance to blood flow due to friction between fluid and stationary vascular walls
poiseuille’s equation
r = 8Ln / (pi x r^4) n= blood viscosity r= vessel radius L = vessel length
effects of increasing BP on
P, R and F
delta P increases
R no change
F increases
effects of increasing arteriolar vasoconstriction on
P, R and F
delta P no change
R increases
F decreases
how does blood reach the tissue capillary beds?
difference in MAP and organ
Forgan = deltaP(MAP) / Rorgan
As the blood goes through the capillary bed you want it to pass relatively slowly to allow exchange of nutrients - so this system allows the blood to slow down
As pressure A is always mean arterial pressure and the pressure at the end of the capillaries is usually venous blood pressure which is more or less 0 mmHg, the blood flow rate equation can be rearranged to:
the major determinant of the blood flow in the body is
mainly the resistance of the arterioles in the organ
Active Hyperemia =
an increase in organ blood flow that is associated with increased metabolic activity of an organ or tissue
leads to vasodilation
what is myogenic autoregulation
stretch due to change in BP
leads to vasoconstriction
hormonal control of the heart
The brain can mimic the sympathetic nervous system to control the heart - by stimulating production of adrenaline and noradrenaline
The brain can control blood pressure by action on arterioles - by stimulating production of Vasopressin and Angiotensin II
design/ size of the capillary
Capillaries are perfectly designed for exchange of substrate:
Very narrow walls - 1 micrometre thick
and 7 micrometre lumen diameter
Extensive branching - no capillary is more than a few micrometres away from a tissue cell
They are ideally suited to enhance diffusion (via Fick’s law)
You want to:
Minimise diffusion distance
Maximise surface area
Maximise diffusion time
what shuts off the arterioles/capillaries
It is the PRECAPILLARY SPHINCTER which shuts off the arterioles/capillaries
Skeletal muscle has a high capillary density but a large number of these capillaries are SHUT OFF at rest
Bulk Flow =
Bulk Flow = a volume of protein-free plasma filters out of the capillary, mixes with the surrounding interstitial fluid (IF) and is reabsorbed
oedema
rate of production > rate of drainage
parasitic blockage of lymph nodes
elephantiasis
how is excess interstitial fluid drained?
skeletal and respiratory pumps direct lymph flow- vessels coalesce to lower neck
