lecture 7: microcirculation Flashcards
what is the arterial flow of blood ?
first order arterioles
terminal arterioles
capillaries
what is the venous flow of blood?
post capillary venues
venues
veins
hat is the blood flow rate?
how much blood is passing through a vessel at any given time?
what is the equation of flow?
flow = change in pressure / resistance
what is change in pressure?
Mean Arterial Pressure
what is resistance of blood dependent on?
- blood viscosity
- vessel length
- vessel radius - MOST IMPORTANT
what is the major determinant of the blood flow?
- resistance of the arterioles in the organ
how is blood flow affected diagram ?
INSERT DIAGRAM
what is the mean arterial pressure entering the arteries?
93 mmHg
what is the mean arterial pressure of the blood leaving arterioles?
37 mmHg
what is vascular tone?
– the state of partial vasoconstriction that arteriolar
smooth muscle displays to allow constriction AND dilation if needs be.
what is a pressure gradient ?
pressure A (blood entering ) - pressure B (blood leaving)
without the pressure difference the blood would not reach tissue capillary beds
what is poiseulles law?
R is proportional to 1/r^4
r radius
R resistance
what are the functions of the adjusting of the radius of arterioles?
- matching the blood flow to the metabolic needs of the tissue (regulated intrinsically by the tissue)
- to help regulate the arterial blood pressure
how is the blood flow matched to the metabolic needs of the tissue?
a. chemical responses
- >the muscle becomes more metabolically active
- > the o2 usage increases
- > vasodilation happens
- > this is active hyperaemia
b. physical environment - > the tissue responds to local changes in temp
- > vasoconstriction happens so less heat is lost in the blood flow \
- > this is auto regulation
what is active hyperaemia?
an increase in organ blood flow that is associated with increased metabolic
activity of an organ or tissue.
what is auto regulation?
raised BP increases stretch on cells which stimulates myogenic vasoconstriction.
what is an equation linking cardiac output, blood pressure and total resistance
cardiac output = blood pressure / total resistance
what are the two ways that arterial blood pressure is regulated extrinsically?
neural - regulated by cardiovascular control centre in the medulla
hormonal
how does neural regulation work?
- regulated by cardiovascular control centre in the medulla
1. to increase BP, vasoconstriction happens
2. the adrenoreceptors facilitate constriction and dilation
how does hormonal regulation work?
- the brain mimics Sympathetic nervous system
1. different hormones like vasopressin , angiotensin ii and noradrenaline help regulate arterial BP
how wide are capilleries ?
how thick are capillaries ?
7 micrometers
1 micrometer
why is capillary density important?
every cell in the body needs to be close to a capillary to deliver O2, glucose ect.
what is ficks law
emphasising minimising diffusion distance and time and maximising surface area
which tissues have the greatest capillary density?
- skeletal muscle
- myocardium muscle
- brain
- lungs
they need a lot of oxygen
what does the skeletal muscle do in absence of exercise?
the skeletal muscle shuts off the majority of its capillaries via the pre capillary sphincters in absence of exercise
what are the three types of capillaries?
- continous
small water filled gap junctions to allow passage of electrolytes - fenestrated
have holes called fenestrae - discontinuous
- large holes with passage for bigger cells like
leukocytes in the bone marrow
also in the liver
what is the blood brain barrier an example of?
continuous
- there are very very tight gap junctions
(there are some parts of the brain with a leaky good brain barrier which is just normal continuous capillary walls)
what is bulk flow?
a volume of protein-free plasma filters out of
the capillary, mixes with surrounding interstitial fluid (IF)
and is then reabsorbed
what forces the plasma out?
- hydrostatic pressure (from the heart)
- oncotic pressure
(from the osmotic pressure)
what is ultrafiltration?
- at the arteriolar end the pressure inside the capillary is bigger than the pressure in the interstitial space
what is reabsorption?
at the venous end the pressure in the interstitial fluid is more than the hydrostatic pressure in the capillary
what is the significance of the fact that ultra filtration is more effective than reabsorption?
- this means some fluid is NOT reabsorbed so the extra fluid goes to the lymphatic fluid
we are always losing fluid
what are lymphatic vessels like?
they are blind ended not a closed loop like blood vessels
what does the lymphatic system have?
one way valves to prevent back flow
what drives the lymphatic system?
- muscle pressures
- thoracic cavity pressures
what are key roles of lymphatic system
- to get excess fluid, which was not reabsorbed, back into the blood
- immunity
what does the lymph drain into?
- thoracic duct
- right lymphatic duct
- right subclavian vein
- left subclavian vein
what is oedema?
- if the amount of lymph produced is greater than the rate of removal of the fluid
what might cause oedema?
- this is caused by parasitic blockage of the lymph nodes
elephantiasis
