7 - Microcirculation Flashcards
What are the features of the pressure in the circulation?
- mostly stays the same in arteries
- only changes when reaches arterioles
- arterioles: major resistance vessels of circulation (drop of BP greatest)
What is elephantiasis?
parasitic blockage of lymph nodes
What are the labels of the lymphatic system?
- blood capillary
- arteriole
- lymphatic endothelium
- anchoring filament
- interstitial fluid
- opening
- tissue cell
- lymphatic capillary
What is the difference between vasodilation and vasoconstriction?
- vasoconstriction: decreased radius and flow, increased resistance (contraction)
- vasodilation: increased radius and flow, decreased resistance (relaxation)
What is the pressure gradient?
- pressure a - pressure b
- difference in pressures arriving and leaving capillaries
- generally MAP as venous pressure so low its negligible
What is blood flow rate?
- volume of blood passing through vessel per unit time
- flow rate (Q) = pressure gradient (P) / resistance (R)
- increased pressure gradient increases resistance
What are the 3 types of capillaries and their features?
- continuous: small water-soluble molecules diffuse through, lipid soluble molecules diffuse across cells
- fenestrated: allow for larger molecules to diffuse through
- discontinuous: allow for alot of space for wasy access
What is the blood brain barrier?
- continuous structure with tight junctions (not gap junctions so no space between capillary cells)
- gives brain tighter controls over substances entering
What is capillary exchange?
delivery of metabolic substrates to cells of organism
What are the general features of capillaries?
- single endothelial cell
- diameter big enough for one cell (7μm)
- extensive branching
- 1μm cell width
- pre-capillary sphincters allow for certain capillaries to be shut down
- highly metabolically active tissues have denser capillary networks
What is Fick’s law in relation to capillary density?
- minimises diffusion distance
- maximises surface area and time for diffusion
Under what conditions does ultrafiltration and reabsorption occur?
- ultrafiltration: pressure inside capillary > in interstital fluid
- reabsorption: inward driving pressures > outward pressures across capillary
How does fluid move in the capillary network?
- bulk flow: volume of protein-free plasma filters out of capillary, mixes with surruonding interstitial fluid and is reabsorbed
- hydrostatic (pushing) force: higher at arterial end - fluids leave blood vessels
- oncotic (pulling) force: constant throughout length - counteracts hydrostatic force
How do the radii of arterioles vary?
- local intrinsic control: match blood flow to metabolic needs of specific tissues
- extrinsic control: help regulate arterial BP
How does matching blood flow to metabolic needs of tissue operate in adjusting arterial radii?
- chemically driven (active hyperaemia): increased metabolites/O2 usage leads to vasodilation (skeletal muscle arterioles)
- physically driven (autoregulation): decreased blood temperature/increased stretch leads to vasoconstriction (small intestine arterioles)
