7 - Microcirculation Flashcards
What is blood flow rate? What is the equation?
Volume of blood passing through a vessel per unit time. Flow rate (Q) = Pressure gradient(P) / Resistance(R)
What is pressure gradient? Increase in pressure gradient affects what?
Pressure A (at start of arteriole, MAP) - Pressure B (end of arteriole)
Bigger pressure gradient = increased flow rate
What is resistance and what factors affect resistance in blood vessels?
Hinderance to blood flow due to friction between moving fluid and stationary vascular walls.
Vessel Length
Vessel Radius
Blood Viscosity
How does increased blood pressure affect flow rate and pressure gradient?
Pressure gradient increases = Flow rate increases
How does arteriolar vasoconstriction affect resistance and flow rate?
Resistance increases = Flow rate decreases
How do you determine blood flow to an organ? (equation)
F(organ) = Pressure gradient (MAP) / Resistance (organ)
Pressure gradient is MAP as capillary pressure is so small its negligible.
What is vasoconstriction?
Contraction -
Radius decreases
Resistance increases
Flow rate decreases
What is vasodilation?
Relaxation -
Radius increases
Resistance decreases
Flow rate increases
What is vascular tone and why is it important?
The partial constriction which is always present in arteriolar smooth muscle.
Important as it allows both constriction and dilation to occur.
What are the 2 reasons that the radius of arterioles is adjusted?
- To match blood flow to metabolic needs of tissue (intrinsic control)
- To maintain blood pressure (extrinsic control)
Function 1: What is chemically driven change in vasodilation of arterioles? What is this also called?
e.g. during exercise a cell requires more metabolites and more oxygen. This causes vasodilation so blood flow increases.
Called active hyperaemia
What does hyperaemia mean?
Increase in blood flow to an area.
Function 1: How can vasoconstriction be physically driven?
If blood temperature drops
If blood vessels are physically stretched (due to increased bp)
What is myogenic autoregulation?
Pressure induced vasocontriction.
e.g. When blood vessels are physically stretched (due to increased bp)
Also allows blood to go where it needs to go.
What is the equation for blood pressure (MAP)
Cardiac output x Total peripheral resistance
Function 2: How is blood pressure regulated?
Neural control - cardiovascular control centre in medulla controls vasoconstriction to control blood flow to specific organs.
Function 2: What are 3 major hormonal vasoconstrictors?
Vasopressin
Angiotensin II
Adrenaline/Noradrenaline
Arterioles are the major WHAT vessels?
Resistance
What is the purpose of the capillaries?
To deliver metabolic substrates to the cells of an organism.
Why is capillary density important?
To minimise diffusion distance
To maximise surface area for diffusion
What is a pre-capillary sphincter?
Wraps around beginning of capillary to effectively shut off a capillary network if it is not needed at that time.
Why do some structures have denser capillary networks? Examples.
Because they are more metabolically active - brain and skeletal muscle (DURING EXERCISE ONLY).
Lung capillary network is massive as it is the location for gas exchange.
What are the 3 types of capillary?
Continuous
Fenestrated
Discontinuous
What is in the continuous capillary gap junction?
Water
What do the walls of fenestrated capillaries look like?
Bigger gaps between endothelial cells.
What are discontinuous capillaries?
Random gaps between cells in capillary wall. e.g. in liver
What type of capillaries are in to blood brain barrier?
Continuous BUT instead of gap junctions there are TIGHT junctions between cells.
What is a leaky blood brain barrier?
Continuous capillaries but with normal water filled gap junctions.
What is hydrostatic pressure?
The force pushing (protein-free) fluid out of the capillary into interstitial fluid. Generated by blood pressure.
What is oncotic pressure?
The force pulling fluid back into the capillary. Generated by proteins in capillary.
What is Starling’s hypothesis?
There must be a balance between hydrostatic and oncotic pressure.
What is ultrafiltration?
Pressure inside the capillary is greater than pressure in the IF.
Fluid LEAVES capillary
What is reabsorption?
Inward driving pressures are greater than the outward pressures across the capillary . Fluid ENTERS capillary.
What is the significance of ultrafiltration being more effective than reabsorption?
Net loss of fluid.
Lymphatic system solves this.
What is the role of lymphatic capillaries?
Fluid that leaves the capillary into the IF drains into the blind-eneded, single layered lymphatic capillaries which surround blood capillaries.
What is the purpose of lymph nodes?
Lymph passes through nodes. This checks for any pathogens and can trigger an immune response. Increased production of lymphocytes.
How does lymph return?
There is NO pump.
Returns via drainage at the thoracic duct and right and left subclavian veins.
How can the lymphatic system cause oedema?
When rate of production of lymph > rate of drainage of lymph.
What is elephantiasis caused by?
Parasitic blockage of lymph nodes.
