The Peripheral Circulation Flashcards
Features of capillaries
Specialise for exchange
Abundant
Thin walled
Small diameter (big SA to volume ratio)
Continuous capillaries
Muscle
Fenestrated capillaries
Intestines or kidneys
Discontinuous capillaries
Liver
Features of diffusion (4)
Self-regulating
No-saturable
Non-polar substances across membrane
Polar substances through channels
Example of carrier-mediated transport
Glucose transporter
Where can glucose transporters be found
Capillaries of the brain
What does capillary hydrostatic pressure do
Pushes water out through leaky capillaries
What is the effect of the water being pushed out the capillaries
Mainly proteins remain in the capillary and fluid moves back through osmotic pressure
Net filtration pressure =
(Capillary hydrostatic pressure - tissue interstitial hydrostatic pressure) - (Plasma colloid osmotic pressure - interstitial fluid colloid osmotic pressure)
Overall how much is lost and regained each day
20L lost
17 L regained
What happens to the remaining 3L
Picked up by lymphatic system and fed back through the CV system
What can happen if the lymphatic system becomes overwhelmed
Oedema
What is Oedema
Accumulation of excess fluid
What causes Oedema (4)
Lymphatic obstruction
Raised CVP
Hypoproteinaemia
Increased capillary permeability- inflammation
Darcy’s Law
Flow = Pressure/ Resistance
MAP - CVP (usually low or 0) =
CO X TPR
Poiseuille’s (4)
Flow rate is dependent on: Pressure Radius Fluid viscosity Length of tube
Why is resistance juggling important
Balance between blood flow to individual vascular beds and MAP need to be kept
How is resistance juggling achieved
Intrinsic and Extrinsic mechanisms
What is Intrinsic mechanism
Concerned with meeting the selfish needs of each individual tissue to meet its metabolic needs
Mechanisms of Intrinsic response (3)
Active (metabolic) hyperaemia
Pressure flow autoregulation
Reactive hyperaemia
Active (metabolic) hyperaemia (3)
Increase in metabolic activity causes increase in metabolites
Triggers release of EDRF/NO
This causes arteriolar dilation
Increased flow washes out metabolites
Pressure Flow Autoregulation (4)
Decrease in MAP causes decrease in flow
Metabolites accumulate
Triggers release of EDRF/NO
Arterioles dilate
Reactive Hyperaemia (7)
Injury Release of substance P Mast cell and Histamine release Arteriolar dilation Increase in blood supply Increase in permeability Aids delivery of blood borne leukocytes to injured area
What is extrinsic mechanism
Concerned with ensuring that the total peripheral resistance (therefore MAP) of the whole body stays regulated and comes from outside (hormonal/neural)
Neural Extrinsic (4)
Sympathetic nerve release noradrenaline
Binds to alpha 1 receptors
Causes arteriolar constriction
Decreases flow and increases TPR
Hormonal Extrinsic (4)
Adrenaline released from adrenal medulla
Binds to alpha1 receptors
Causes arteriolar constriction
Decreases blood flow and increases TPR
What receptors does the hormones activate and what does that cause (3)
B2 in skeletal and cardiac
Causes arteriolar dilation
Increased flow and decreases TPR
Coronary Circulation (3)
Blood supply of heart is interrupted during systole
Expresses many B2 receptors which swamp any sympathetic arteriolar constriction
Hyperaemia
Cerebral Circulation (2)
Needs to be kept stable
Shows excellent pressure autoregulation
Pulmonary Circulation
Decrease in O2 causes arteriolar constriction- shunt
What is the purpose of a shunt
To ensure blood is directed to the best ventilated part of the lung
Renal circulation
Main function is filtration which depends on pressure
Decrease in renal circulation (extreme)
Swelling
Increase in renal circulation (extreme)
Shrinkage
