The Peripheral Circulation

Question 1

Features of capillaries

Answer 1

Specialise for exchange
Abundant
Thin walled
Small diameter (big SA to volume ratio)

Question 2

Continuous capillaries

Answer 2

Muscle

Question 3

Fenestrated capillaries

Answer 3

Intestines or kidneys

Question 4

Discontinuous capillaries

Answer 4

Liver

Question 5

Features of diffusion (4)

Answer 5

Self-regulating
No-saturable
Non-polar substances across membrane
Polar substances through channels

Question 6

Example of carrier-mediated transport

Answer 6

Glucose transporter

Question 7

Where can glucose transporters be found

Answer 7

Capillaries of the brain

Question 8

What does capillary hydrostatic pressure do

Answer 8

Pushes water out through leaky capillaries

Question 9

What is the effect of the water being pushed out the capillaries

Answer 9

Mainly proteins remain in the capillary and fluid moves back through osmotic pressure

Question 10

Net filtration pressure =

Answer 10

(Capillary hydrostatic pressure - tissue interstitial hydrostatic pressure) - (Plasma colloid osmotic pressure - interstitial fluid colloid osmotic pressure)

Question 11

Overall how much is lost and regained each day

Answer 11

20L lost

17 L regained

Question 12

What happens to the remaining 3L

Answer 12

Picked up by lymphatic system and fed back through the CV system

Question 13

What can happen if the lymphatic system becomes overwhelmed

Answer 13

Oedema

Question 14

What is Oedema

Answer 14

Accumulation of excess fluid

Question 15

What causes Oedema (4)

Answer 15

Lymphatic obstruction
Raised CVP
Hypoproteinaemia
Increased capillary permeability- inflammation

Question 16

Darcy’s Law

Answer 16

Flow = Pressure/ Resistance

Question 17

MAP - CVP (usually low or 0) =

Answer 17

CO X TPR

Question 18

Poiseuille’s (4)

Answer 18

Flow rate is dependent on:
Pressure 
Radius
Fluid viscosity
Length of tube

Question 19

Why is resistance juggling important

Answer 19

Balance between blood flow to individual vascular beds and MAP need to be kept

Question 20

How is resistance juggling achieved

Answer 20

Intrinsic and Extrinsic mechanisms

Question 21

What is Intrinsic mechanism

Answer 21

Concerned with meeting the selfish needs of each individual tissue to meet its metabolic needs

Question 22

Mechanisms of Intrinsic response (3)

Answer 22

Active (metabolic) hyperaemia
Pressure flow autoregulation
Reactive hyperaemia

Question 23

Active (metabolic) hyperaemia (3)

Answer 23

Increase in metabolic activity causes increase in metabolites
Triggers release of EDRF/NO
This causes arteriolar dilation
Increased flow washes out metabolites

Question 24

Pressure Flow Autoregulation (4)

Answer 24

Decrease in MAP causes decrease in flow
Metabolites accumulate
Triggers release of EDRF/NO
Arterioles dilate

Question 25

Reactive Hyperaemia (7)

Answer 25

``` 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 ```

Question 26

What is extrinsic mechanism

Answer 26

Concerned with ensuring that the total peripheral resistance (therefore MAP) of the whole body stays regulated and comes from outside (hormonal/neural)

Question 27

Neural Extrinsic (4)

Answer 27

Sympathetic nerve release noradrenaline Binds to alpha 1 receptors Causes arteriolar constriction Decreases flow and increases TPR

Question 28

Hormonal Extrinsic (4)

Answer 28

Adrenaline released from adrenal medulla Binds to alpha1 receptors Causes arteriolar constriction Decreases blood flow and increases TPR

Question 29

What receptors does the hormones activate and what does that cause (3)

Answer 29

B2 in skeletal and cardiac Causes arteriolar dilation Increased flow and decreases TPR

Question 30

Coronary Circulation (3)

Answer 30

Blood supply of heart is interrupted during systole Expresses many B2 receptors which swamp any sympathetic arteriolar constriction Hyperaemia

Question 31

Cerebral Circulation (2)

Answer 31

Needs to be kept stable | Shows excellent pressure autoregulation

Question 32

Pulmonary Circulation

Answer 32

Decrease in O2 causes arteriolar constriction- shunt

Question 33

What is the purpose of a shunt

Answer 33

To ensure blood is directed to the best ventilated part of the lung

Question 34

Renal circulation

Answer 34

Main function is filtration which depends on pressure

Question 35

Decrease in renal circulation (extreme)

Answer 35

Swelling

Question 36

Increase in renal circulation (extreme)

Answer 36

Shrinkage