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Flashcards in 5-microcirculation Deck (16):

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
• 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



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


How is lymph returned to the blood

Thoracic Duct
Right Lymphatic
Duct Right Subclavian
Vein Left Subclavian Vein