Peripheral circulation

Question 1

Describe the structure of the capillaries

Answer 1

Lots of them
-every tissue within 100m of one

Thin-walled
-presents a small diffusion barrier

Small diameter
-big surface area:volume ratio

Question 2

What is a continuous capillary?

Answer 2

no clefts or pores eg brain

clefts only eg muscle

Question 3

What is a fenestrated capillary?

Answer 3

clefts and pores eg intestine

Question 4

What is a discontinuous

Answer 4

clefts and massive pores eg liver

Question 5

Describe 4 factors that defines diffusion?

Answer 5

self-regulating

non-saturable

non-polar substances across membrane

polar substances through clefts/channels

Question 6

What is an example of carrier mediated transport?

Answer 6

glucose transporter

Question 7

Describe bulk flow?

Answer 7

Pressure inside the arteriole is higher than the venule. High hydrostatic pressure which pushes the water out and cant take the solutes out. Therefore the concentration of solutes increases and goes down a different gradient which makes up the osmotic pressure

Question 8

What 2 factors determine the hydrostatic pressure?

Answer 8

Capillary hydrostatic pressure vs ISF hydrostatic pressure

Question 9

How many litres lost on average everyday and regained?

Answer 9

20L lost and 17 Regained

Question 10

Where is the extra 3L regained from?

Answer 10

Lymph system

Question 11

Define Oedema

Answer 11

accumulation of excess fluid

Question 12

What are causes of oedema?

Answer 12

Lymphatic obstruction
eg due to filariasis, surgery

Raised CVP
eg due to ventricular failure

Hypoproteinemia
eg due to nephrosis, liver failure, nutrition

Increased capillary permeability
inflammation, eg rheumatism

Question 13

Which factors in poseuilles law can affect peripheral blood flow?

Answer 13

viscosity and length and radius

Question 14

What can be used to control the TPR and therefore regulate MAP?

Answer 14

Varying the radius of resistance vessels

MAP = CO x TPR ( total preipheral ressitance)

Question 15

What does arteriolar radius affect?

Answer 15

Flow through the vascular beds and the mean arterial pressure

Question 16

What are the two levels of control over smooth muscle surrounding arterioles that help keep mean arterial pressure in right range and blood flow sufficient?

Answer 16

Intrinsic mechanisms and extrinsic mechanisms

Question 17

Describe the control aim behind intrinsic mechanisms

Answer 17

concerned with meeting the selfish needs of each individual tissue

Question 18

Describe the control aim behind extrinsic mechanisms

Answer 18

concerned with ensuring that the total peripheral resistance (and therefore MAP) of the whole body stays in the right ball park

Question 19

What does extrinsic control involve in neural?

Answer 19

Sympathetic nerves
release noradrenaline
binds to alpha-1-receptors
causes arteriolar constriction
therefore decrease flow through that tissue, and tends to increase TPR

Parasympathetic nerves
usually no effect on smooth muscle surrounding the peripheral arterioles

Question 20

What does extrinsic control involve in hormonal?

Answer 20

Adrenaline
released from adrenal medulla
binds to alpha-1-receptors
causes arteriolar constriction
therefore decerases flow through that tissue, and tends to increases TPR 

but in some tissues, eg skeletal and cardiac muscle, it also activates beta2-receptors

• causes arteriolar dilation
• therefore increase flow through that tissue, and tends to decrease TPR

Other hormones include:
Angiotensin II
Vasopressin (= antidiuretic hormone)
Atrial natriuretic factor

Question 21

What does the local intrinsic control of active hyperaemia involve?

Answer 21

increase metabolic activity causes increase conc of metabolites

triggers release of EDRF/NO (?) (= paracrines)
causes arteriolar dilation

increases flow to wash out metabolites
an adaptation to match blood supply to the metabolic needs of that tissue

Question 22

What does the local intrinsic control of pressure autoregulation involve?

Answer 22

Same mechanisms as the active hyperaemia
but different initial cause

decrease MAP causes decrease flow

metabolites accumulate

triggers release of EDRF/NO (?)

arterioles dilate and flow is restored to normal

(or it could be myogenic)

an adaptation to ensure that a tissue maintains its blood supply despite changes in MAP

Question 23

What does the local intrinsic control of reactive hyperaemia involve?

Answer 23

• occlusion of blood supply causes a subsequent increase in blood flow
• an extreme version of pressure autoregulation

Question 24

What does the local intrinsic control of injury response involve?

Answer 24

When you scratch – you get a small red mark which represents increase in blood flow

C- fibres respond to damage
Reach a terminal to cause release of P and then that activates mast cells to release histamine

Arteriolar dilation allow increasing blood flow and permeability
- aids delivery of blood born leucocytes etc to injured area

Question 25

What happens in the cornoary circulation?

Answer 25

Cuts off blood supply everytime it contracts due to high pressure build up

blood supply is interrupted by systole
but still has to cope with increased demand during exercise
shows excellent active hyperaemia
expresses many beta2-receptors
these swamp any sympathetic arteriolar constriction

Question 26

Whats involved in cerebral circulation?

Answer 26

needs to be kept stable, whatever

shows excellent pressure autoregulation

Question 27

What occurs when O2 decreases in pulmonary circulation?

Answer 27

decrease O2 causes arteriolar constriction
ie the opposite response to most tissues
ensures that blood is directed to the best ventilated parts of the lung

Question 28

What is the main function of renal circulation?

Answer 28

main function is filtration which depends on pressure

Question 29

What is the effect of changing MAP in renal circulation?

Answer 29

changes in MAP would have big effects on blood volume

Question 30

Does renal circulation have good or bad pressure autoregulation?

Answer 30

Good!