Microcirculation Flashcards
Give an equation relation flow rate, pressure gradient and resistance
Give the overall purpose of the CV system and the def of blood flow rate
Adequate blood flow through the capillaries
Volume of blood passing through a vessel per unit of time
How is blood pressure determined in a capillary and how will increased pressure gradient influence blood flow?
Increased ΔP will increase blood flow rate
What is the def of resistance in a blood vessel?
‘Hindrance to blood flow due to friction between moving fluid and stationary vascular walls’
How can you relate flow rate, vessel length,pressure, vessel radius and blood viscosity
How does raised blood pressure / arteriolar vasoconstriction influence ‘deltaP, resistance and flow rate’
How can you mathematically relate blood flow rate, pressure gradient and resistance in an organ?
Why is vascular tone important?
Vascular tone-Natural partial contraction of arteriolar muscle
-It allows the artery to undergo vasodilation or vasoconstriction at any time
How does vasoconstriction/vasodilation affect flow rate, resistance and vessel radius?
What 2 functions do arteries regulate their radii independently for and through what means are they regulated?
Function 1: Match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs)
Regulated by local (intrinsic) controls and independent of nervous or endocrine stimulation
Function 2: Help regulate systemic arterial blood pressure
Regulated by extrinsic controls which travel via nerves or blood and are usually centrally coordinated
What is arteriolar vasodilation normally driven by and what is another term for it?
Chemically driven
-Metabolites(ATP metabolites are powerful vasodilators)
-O2 usage
Active hyperaemia
What is arteriolar vasoconstriction normally driven by and what is another term for it?
Physically driven
-Drop in blood temp
-Vessel distension due to increased BP
Myogenic autoregulation
Explain these graphs
Pressure gradient across the arteriole is higher(higher perfusion pressure)
Vessel senses increased pressure, in turn constricts the vessel, increasing resistance and reducing blood pressure back to normal
How can you mathematically relate cardiac output, total peripheral resistance and blood pressure?
How is arterial blood pressure regulated neurally and hormonally?
Neural:
CV control center in the medulla sends signals through the sympathetic trunk
Hormonal:
Vasopressin/ADH from pituitary
Angiotensin II from lungs
Adrenaline/Noradrenaline from adrenal glands
Why is capillary density so important?
Minimise the diffusion distance
Maximise the surface area and time for diffusion
-Ficks law
How does capillary network density vary?
More dense capillary networks in more metabolically active tissue
What are the 3 capillary types and how are they different?
Continuous-Has regular H20 gap junctions between endothelial cells
Fenestrated-Has ~80nm wide fenestrae
Discontinuous-Has open gaps between endothelial cells
Outline hydrostatic and oncotic force in capillaries and what causes them
What is the premise of starlings’(1896) hypothesis
“…there must be a balance between the hydrostatic pressure of the blood in the capillaries and the osmotic attraction of the blood for the surrounding fluids. “
” …and whereas capillary pressure determines transudation, the osmotic pressure of the proteins of the serum determines absorption.”
What causes capillary ultrafiltration and reabsorption?
If pressure inside the capillary > in the IF - Ultrafiltration
If inward driving pressures > outward pressures across the capillary – Reabsorption
Ultrafiltration is slightly greater than reabsorption in capillaries, what is the significance of this in the capillaries?
There is a net loss of fluid, which the lymphatic system absorbs.
Outline the structure of a lymphatic vessel
Give the general structure+main ducts+drainage capacity of the lymphatic system
What is the disease called when rate of lymphatic production is greater than the rate of drainage and what is a common cause of this?
Elephantiasis
-Parasitic blockage of lymph nodes
What occurs to hydrostatic and oncotic pressures over the length of a vessel?
Hydrostatic pressure drops
Oncotic pressure remains the same
-Overall force is a reabsorption
