Microcirculation Flashcards
What is microcirculation?
Specific to organs; 1st order arterioles, covered in smooth muscle, branch off to capillaries via terminal arterioles, entering tissues; precapillary sphincters control blood flow to capillary bed; venules leave tissue to collect blood and deliver to heart
How is flow rate in a capillary calculated?
Flow rate = pressure gradient / resistance
What is the pressure gradient?
Difference in pressure between arteriole and capillary
What is the equation for organ flow?
Organ flow = pressure change / resistance of an organ
(if no pressure difference, blood doesn’t reach capillary bed.
What are arterioles?
Major resistance vessels, and increased pressure gradient increases flow rate
Describe the normal state of arteriolar smooth muscle?
Normally partially constricted to allow for both vasoconstriction and vasodilation
What is active hyperaemia?
Increased [metabolites] and oxygen usage by active tissue leads to arteriolar vasodilation to increase flow
What is myogenic autoregulation?
Decreased blood temperature or increased distention leads to arteriolar vasoconstriction to decrease flow to capillaries
What is Fick’s law?
Minimised diffusion distance, maximised surface area and time for diffusion allows for maximal exchange
What are pre-capillary sphincters?
Allow some capillaries to be almost completely closed off - allowing skeletal muscle bed flow to be reduced at rest and larger during exercise
What is the permeability of continuous capillaries?
Junctions between endothelial cells are filled with water - water soluble and small molecules diffuse over gap junctions, large and water soluble molecules require transport proteins, small and lipid soluble molecules can diffuse straight across
What is the permeability of Fenestrated capillaries?
Many fenestration make walls leaky
e.g. Glomerulus
What are discontinuous capillaries?
Large gaps between cells e.g. Bone marrow and Liver
Describe the capillaries that form the blood-brain barrier:
Continuous capillaries with tight rather than gap junctions and many transporter proteins
