The Peripheral Circulation

Question 1

Describe capillaries

Answer 1

Exchange vessels
Thin walled and have small diameter
Big surface area: volume ratio

Question 2

Where are clefts in capillaries?

Answer 2

Between epithelial cells

Question 3

Where are pores in capillaries?

Answer 3

Across epithelial cells

Question 4

Explain continuous capillaries

Answer 4

No clefts or pores ex. brain
Clefts only ex. muscles and most other capillaries

Question 5

Explain fenestrated capillaries

Answer 5

Clefts and pores ex. intestine and kidney for fluid exchange

Question 6

Explain discontinuous capillaries

Answer 6

Clefts and massive pores ex. liver

Question 7

What are the benefits of diffusion?

Answer 7

Non-saturable, self-regulating, non-polar substances across phospholipid membrane and polar substances cross by pores and clefts

Question 8

What is bulk flow determined by?

Answer 8

Starling’s Forces

Question 9

What are starling’s forces?

Answer 9

Capillary hydrostatic pressure vs ISF hydrostatic pressure
Plasma osmotic pressure vs ISF osmotic pressure
Net filtration pressure = (HC-HIF0 - (πC - πIF)

Question 10

How much fluid is retained and lost per day?

Answer 10

20l lost
17l is regained
3l drains to lymphatics

Question 11

How is the 3l of fluid drained in lymphatics?

Answer 11

Drains to lymphatic system to LN then to larger lymphatic vessels and makes way back up to heart where drains to vena cava
Then returned to CVS

Question 12

What is oedema?

Answer 12

Accumulation of excess fluid

Question 13

What could oedema be caused from?

Answer 13

Raised CVP
Lymphatic obstruction
Hypoproteinaemia
Increased capillary permeability

Question 14

How does raised CVP cause oedema?

Answer 14

Raised CVP can be caused by ventricular failure
If left side not pumping blood correctly then blood can accumulate in lungs
Increase in hydrostatic pressure of capillaries leading to oedema

Question 15

How does hypoproteinaemia cause oedema?

Answer 15

Protein helps build up oncotic pressure and pull water back in so if not enough protein then lose more fluid

Question 16

What is Darcy’s Law?

Answer 16

Flow = Difference in pressure/ resistance

Question 17

What can help control flow and redirect blood?

Answer 17

Varying the radius of resistance vessels

Question 18

What can varying the radius of capillaries help control?

Answer 18

Flow and redirect blood
Control TPR and therefore regulate MAP

Question 19

What is MAP equal to?

Answer 19

MAP = CO x TPR

Question 20

What happens if MAP is too low?

Answer 20

Decreased perfusion through vascular bed so brain will notice and can lead to light headedness/ fainting

Question 21

What happens if MAP is too high?

Answer 21

Wont be any immediate effects
Hypertension if over long period, time increases the risk

Question 22

What happens if resistance of vascular bed increases?

Answer 22

Increases flow through vascular bed

Question 23

What happens if TPR is reduced?

Answer 23

Increased flow
Reduces MAP

Question 24

What are the 2 levels of control over smooth muscle surrounding arterioles?

Answer 24

Local (intrinsic) mechanisms
Central (extrinsic) mechanisms

Question 25

What are local mechanisms concerned with?

Answer 25

With meeting the selfish needs to each individual tissue

Question 26

What are the central mechanisms concerned with?

Answer 26

With ensuring the TPR and therefore MAP of whole body stays in right ball park

Question 27

Explain active hyperaemia - local control

Answer 27

Trigger is increase in local metabolite which can be caused by increase in metabolic activity Release of paracrine signal - EDFR Causes arteriolar dilation so increased flow to wash out metabolites

Question 28

Explain pressure autoregulation - local control

Answer 28

Trigger is a decrease in perfusion pressure which increases MAP and decreases flow Metabolites accumulate Triggers release of EDRF ad arterioles dilate and flow is restored

Question 29

What is the aim of active hyperaemia?

Answer 29

Match blood supply to the metabolic needs of that tissue

Question 30

What is the aim of pressure autoregulation?

Answer 30

Ensure that a tissue maintains its blood supply despite changes in MAP

Question 31

Explain reactive hyperaemia - local control

Answer 31

Same mechanism, different trigger Trigger is occlusion of blood supply which causes increase in blood flow and an extreme version of pressure autoregulation

Question 32

Explain the injury response

Answer 32

Aids delivery of blood born leukocytes etc. to injured area C fibre releases AP to trigger substance P which acts on mast cells Mast cells release histamine which causes arteriolar dilation to increase blood flow and permeability

Question 33

What is the affect of sympathetic nerves on central controls?

Answer 33

Release Noradrenaline which binds to alpha 1 receptors on smooth muscle Causes arteriolar constriction so decrease in flow through tissue that tends to increase TPR and MAP

Question 34

What is the affect of parasympathetic nerves on central controls?

Answer 34

Usually no effects as don't usually innervate blood vessels Genitalia and salivary glands are exception and increase flow

Question 35

What is the affect of adrenaline on central controls - hormonal?

Answer 35

Released from adrenal gland and binds to alpha 1 receptors Causes arteriolar constriction which increases TPR and MAP as decreased flow

Question 36

What happens when adrenaline binds to beta 2 receptors in skeletal and cardiac muscle?

Answer 36

Causes arteriolar dilation Increase in flow so decreased TPR This is significant during exercise

Question 37

Describe coronary circulation?

Answer 37

Blood supply is interrupted by systole but still has to cope with decreased demand during exercise Express many B2 receptors Shows active hyperaemia Swamp any sympathetic arteriolar constriction

Question 38

Why is blood supply interrupted by systole?

Answer 38

When heart contracts an builds up big pressure in ventricles for pushing out blood. Increases in pressure of wall of heart too, This squishes the blood vessels in heart

Question 39

What happens if adrenaline binds to B2 receptors in coronary circulation?

Answer 39

Relaxes and dilates arterioles

Question 40

Does diastole or systole have higher pressure?

Answer 40

Diastole - blood flow is higher

Question 41

Describe cerebral circulation

Answer 41

Needs to be kept stable Shows excellent pressure autoregulation so if pressure falls then arterioles dilate and main perfusion

Question 42

Explain pulmonary circulation

Answer 42

Decreased O2 causes arteriolar constriction which is opposite of other tissues Ensures blood is directed to best ventilated parts of the lung

Question 43

Explain renal circulation

Answer 43

Main job is filtration which is dependant on pressure Filtration rate kept relatively constant during normal fluctuations in MAP due to excellent pressure autoregulation Protects glomeruli from HBP as causes damage