The Microcirculation Flashcards
What is the aim of CVS?
What is blood flow rate?
How do you calculate flow rate?
What is fluid circuit/darcys law?
Aim of CVS = adequate blood flow through the capillaries
Blood flow rate - volume of blood passing through a vessel per unit time
Q (flow rate) = delta P / R
(Pressure (Resistance)
Gradient)
Fluid circuit (darcys law): delta P = Q x R
How do you calculate the pressure gradient in a capillary?
What does an increase in the pressure gradient result in?
Under what circumstances would viscosity of gas in the lungs change?
Take two the two regions eg. A and B
Pressure gradient (delta P) = pressure A - pressure B
Increases in Pressure gradient, increases flow rate
Scuba diving,
What is the effect of arterioles on resistance?
What is the relationship between force, pressure and resistance?
Why is the pressure difference in blood useful?
Arterioles are major resistance vessels -> inc resistance
F (flow of blood to an organ) = delta P (MAP) / R (of organ)
Without this pressure difference, blood wouldn’t reach tissue capillary beds
Explain what happens to radius, resistance and flow of arterioles during vasoconstriction and vasodilation
What is vascular tone?
Vasoconstriction:
Radius decreases, resistance increases, flow decreases
Vasodilation:
Radius increase, resistance decreases, flow increases
Arterial muscles displaying a state of partial constriction - vascular tone
What two functions are the radii of arterioles adjusted to do?
What are the functions regulated by respectively?
- Match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs)
- regulated by local (intrinsic) controls & independent of nervous or endocrine stimulation - Help regulate systemic arterial blood pressure
- regulated by extrinsic controls which travel via nerves or blood and are usually centrally coordinated
What is active hyperaemia?
Vasodilation of arterioles - may be chemically driven by increase of metabolites, increase of oxygen usage
Arterioles vasodilate to match blood flow to the metabolic needs of specific tissues.
What is myogenic autoregulation?
Vasoconstriction of arterioles -
In response to decreased blood temp, and increased stretch (distension) to increase blood pressure —> myogenic autoregulation
^^ in order to match blood flow to the metabolic needs of specific tissues
What are the two types of control that regulate vasoconstriction of arterioles?
What function of arterioles does this aid?
Neural control:
Cardiovascular control centre in the medulla
Hormonal control:
Vassopressin/ADH
Angiotensin II
Adrenaline/noradrenaline
^^ all lead to vasoconstriction
These help regulate arterial blood pressure
What is the Purpose of capillary exchange?
Why is capillary density important?
Describe the flow of blood through skeletal muscles at rest
Purpose of capillary exchange: delivery of metabolic substrates to the cells of the organism
Capillary density is important bc it’s suited to enhance diffusion: ficks law - specially designed to maximise the diffusion distance, maximise SA and time for diffusion
Highly metabolically active tissues have denser capillary networks
Skeletal muscle = 100 cm2/g
Myocardium/brain = 500 cm2/g
Lung = 3500 cm2/g
Skeletal muscle has a huge capacity but limited flow at rest
What is meant by bulk flow through capillaries?
A volume of protein free plasma filters out of the capillary, mixes with the surrounding interstitial fluid (IF) and is reabsorbed
There are hydrostatic ‘pushing’ forces
And oncotic ‘pulling’ forces
What is starlings hypothesis?
What must there be a balance between?
What determines transudation, what determines absorption?
There must be a balance between the hydrostatic pressure of the blood in the capillaries and osmotic attraction of the blood for the surrounding fluids
Capillary pressure determines transudation, osmotic pressure of the proteins of the serum determines absorption
Capillaries - fluid movement:
What leads to ultrafiltration?
What leads to reabsorption?
What is the significance of the fact that ultrafiltration is more effective than reabsorption?
If pressure inside the capillaries > in the IF - ultrafiltration
If inward driving pressures > outward pressures across the capillary - reabsorption
As ultrafiltration is more effective than reabsorption, there is a net loss, which is where the lymphatic system comes into play
Lymphatic system:
Describe the journey of fluid drainage in the lymphatic system
How much fluid drains into the lymphatic system each day
What causes oedema in the lymphatic system?
What is elephantiasis?
There’s no pump (heart) to induce flow
Drainage - right lymphatic duct - thoracic duct
Thoracic duct —> right and left subclavian veins
3 L per day
If the rate of production > rate of drainage, then oedema ensures
Parasitic blockage of lymph nodes - elephantiasis
