5-microcirculation Flashcards
Describe the arrangement of the mocrocirculTion from the arterioles to the veunles
1st order arterioles, terminal arteriole, capillary, pericytic venule, venule
How is blood flow rate determined
Flow rate= pressure gradient/ vascular resistance
F= dP/ R
What determines vascular resistance
Vessel length
Blood viscosity
Radius (r = x/ r^4)
What is the mean arteriole pressure and the pressure in the capillaries (delta P)
93 and 37mmHg
How is the flow rate through an organ determined
F organ= dP(MAP)/ R organ
dP is similar across most organs
What is arteriole smooth muscle at normal state and why
Partially constricted, so can change blood flow to tissue
What is active hyperemia
Active Hyperemia = an increase in organ blood flow that is associated with
increased metabolic activity of an organ or tissue
How is arteriole BP regulated
Regulated by the cardiovascular control centre in the MEDULLA
• To increase blood pressure, vasoconstriction will take place thus reducing the
blood flow to organs
• There are ADRENORECEPTORS which facilitate constriction and dilation
• Alpha = CONSTRICTION
• Beta = Dilation
What is myogenic vasoconstriction
When arterioles react to an increase in BP by constricting to maintain constant BP
How can cardiac output be calculated
CO= MAP / TPR
How do hormones control BP
The brain can stimulate the release of various hormones that have an effect on blood pressure
• 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
Describe capillary density in different tissues
Skeletal muscle, myocardium/brain and lungs have a HIGH CAPILLARY DENSITY
• The myocardium and brain need a high capillary density because they are particularly vulnerable to hypoxia
• Adipose tissue, on the other hand, is poorly perfused because there is nothing that the adipose tissue does that needs a rapid response
• Skeletal muscle has a high capillary density but a large number of these capillaries are SHUT OFF at rest
Decreased the 3 types of capillaries
Continuous: A vast number of capillaries have a CONTINUOUS structure
• There are small water-filled gap junctions between the endothelial cells whichallows the passage of electrolytes and other small molecules
• MOST substances move through the endothelial cells
fenestrated: These are leakier capillaries
• They have slightly bigger holes called FENESTRAE which allow larger
substances to pass through
Discontinuous: There are LARGE holes in the capillary
• This is particularly important in the bone marrow where white cells have to get into the blood
Decreased the structure of the BBB
In the brain you DO NOT have water-filled gap junctions between the endothelial cells
• Instead you have really TIGHT gap junctions
• This means that the access of substances to the brain is tightly regulated
• Anything that wants to get to the brain has to diffuse across the endothelial
cells so the brain is far more protected from certain substances than other parts of the body
• There are some areas of the brain where you have a discontinuous blood-brain barrier - in these areas it returns to having water-filled gap junctions
What is 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
