Exchange in, and control of, the Peripheral Circulation

Question 1

What is the point where one endothelial cell meets another known as?

Answer 1

Junction

Question 2

What is a tight junction?

Answer 2

Endothelial cells are pressed very tightly together and this stops anything moving across.

Question 3

Give an example of a tight junction.

Answer 3

Blood brain barrier.

Question 4

In the vast majority of capillaries, there is a gap between the endothelial cells. What is this gap known as?

Answer 4

A cleft

Question 5

What can be diffused over clefts?

Answer 5

Water and some dissolved solutes.

Question 6

What cannot diffuse across a cleft?

Answer 6

Macromolecules, like proteins

Question 7

How do macromolecules get transported across endothelial cells?

Answer 7

Via transcytosis.

Question 8

What are the structures which carry macromolecules across during transcytosis known as?

Answer 8

Pores

Question 9

What is between endothelial cells?
What is across endothelial cells?

Answer 9

Between= clefts
Across= pores

Question 10

Name the three types of capillaries.

Answer 10

Continuous
Fenestrated
Discontinuous

Question 11

Describe continuous capillaires.

Answer 11

No clefts or pores e.g. brain (hence the blood-brain barrier)

or

May only have clefts, like in muscle

Question 12

Why is the blood brain barrier important?

Answer 12

Prevents things getting into the brain.
Protects brain from changes in potassium ion conc. which could alter the activity of the brain.

Question 13

Describe fenestrated capillaries.

Answer 13

Clefts and pores
Specialised for fluid exchange

Question 14

Give an example of fenestrated capillaries.

Answer 14

Intestine and kidneys

Question 15

Describe discontinuous capillaries.

Answer 15

Has clefts and massive pores

Question 16

Give an example of where you might find a discontinuous capillary.

Answer 16

Liver

Question 17

Why are there discontinuous capillaries in the liver?

Answer 17

Massive pores which allow protein into the liver

Question 18

Most exchange in capillaries happens via which process?

Answer 18

Diffusion

Question 19

Describe the diffusion process of oxygen from capillaries to cells.

Answer 19

Oxygen moves down it’s conc. gradient into the extracellular fluid.
Oxygen moves from ECF to the cells, again going down it’s conc. gradient.

Question 20

List the reasons why diffusion is suitable for capillaries.

Answer 20

Self-regulating
Non-saturable
Non-polar substances across the phospholipid membrane
Polar substances through clefts/pores

Question 21

Describe what is meant by diffusion being a self-regulating process.

Answer 21

If oxygen levels are low, like during exercise, the conc. gradient will increase and more oxygen will flow from the capillary->ECF->cells

Question 22

List some non-polar substances.

Answer 22

Oxygen and carbon dioxide

Question 23

Give an example of a polar substance.

Answer 23

Water

Question 24

How will carbon dioxide and oxygen get across?

Answer 24

Via dissuion.

Question 25

How will water get across the membrane?

Answer 25

Via clefts and pores.

Question 26

Give an example of a glucose mediated transporter.

Answer 26

Glucose transporter. ->brain required glucose but cannot diffuse across because of the blood brain barrier.

Question 27

The majority of exchange happens via diffusion but how else can exchange occur?

Answer 27

In bulk flow

Question 28

What is bulk flow determined by?

Answer 28

Starling's forces

Question 29

Which type of pressure can push water out of the clefts and pores of the endothelial cells in a capillary?

Answer 29

Hydrostatic pressure

Question 30

Which type of pressure brings water back into the capillary via clefts and pores of the endothelial cell when concentration gets too high?

Answer 30

Osmotic pressure

Question 31

How can we work out the balance between hydrostatic pressure and osmotic pressure?

Answer 31

By working out net filtration pressure (Difference in hydrostatic pressure between capillaries and ISF) - (Difference in osmotic pressure between the capillaries and ISF)

Question 32

On average, how much fluid is lost per day due to hydrostatic pressure?

Answer 32

20L

Question 32

On average, how much fluid is regained per day due to osmotic pressure?

Answer 32

17L

Question 33

What happens to the remaining 3L of fluid that was lost due to hydrostatic pressure?

Answer 33

It drains into the lymphatic system

Question 34

Describe the journey taken by the fluid drained into the lymphatic system.

Answer 34

Fluid in lymphatic capillaries -> Drains to lymph nodes -> Drains to larger lymphatic vessels -> Makes it's way back to the heart via vena cava and fluid is returned to the CVS

Question 35

What happens if the lymphatic system isn't working?

Answer 35

The extra fluid will form an oedema.

Question 36

Define oedema.

Answer 36

Build up of excess fluid.

Question 37

List the ways an oedema may form.

Answer 37

Raised CVP Lymphatic obstruction Hypoproteinaemia Increased capillary permeability

Question 38

Discuss how raised central venous pressure can cause an oedema.

Answer 38

Say the left ventricle isn't pumping out blood but the right side of the heart is okay, there will be blood in the lungs. This leads to an increased hydrostatic pressure in the capillaries and can lead to pulmonary oedema.

Question 39

When may there by lymphatic obstruction?

Answer 39

Due to filariasis* or surgery *parasitic disease caused by worms

Question 40

What can cause hypoproteinaemia which can ultimately lead to oedema?

Answer 40

Nephrotic syndrome*, liver failure, malnutrition *kidneys leaking protein in the urine

Question 41

Why do we need protein to prevent oedema?

Answer 41

We need protein in capillaries to build up oncotic pressure to get water back in. If there's not enough, more fluid will end up in the lymphatic system as they don't have osmotic pressure.

Question 42

When may increased capillary permeability occur?

Answer 42

In those with rheumatoid arthritis.

Question 43

RECAP- state Darcy's Law.

Answer 43

Flow= change in pressure --------------------------------------- Resistance

Question 44

When may the viscosity of your blood increase?

Answer 44

If you were dehydrated

Question 45

What happens to the resistance of a tube if you half the radius?

Answer 45

Resistance increases by 2 to the power of 4 = 16 fold

Question 46

Substituting Poiseuille’s Law into Darcy's Law gives us the following equation- Flow= (Change in pressure) x (radius to the power of 4) x pi -------------------------------------------------------------------------------------- Viscosity x (length of capillary) x 8 We do not need to get hung up over the details of this equation and you don't need to learn it. However, what is the key takeaway message?

Answer 46

Changing to radius has a large impact on flow.

Question 47

How can we calculate mean arterial pressure?

Answer 47

MAP= CO X TPR (reminder -> CO= cardiac output, TPR= total periphery resistance).

Question 48

What happens if MAP is too low?

Answer 48

Decreased perfusion through vascular beds, brain will notice this and can cause dizziness.

Question 49

What happens if MAP is too high?

Answer 49

No immediate effects but high BP over time increases risk of hypertension and risk of a stroke (h.e. knowledge coming in clutch here hehe).

Question 50

Varying the radius of resistance vessels can control which things?

Answer 50

1. Regional redirection of blood flow 2. Total periphery distance, regulating MAP

Question 51

Define active hyperaemia.

Answer 51

Increased blood flow

Question 52

What is the cause of active hyperaemia?

Answer 52

Increased metabolic activity.

Question 53

Describe what happens when metabolite production is increased in the blood.

Answer 53

Increase in metabolic activity causes an increase of metabolites produced. Triggers release of paracrine signal (e.g. EDRF/NO), causing arterial dilation to make sure the blood flow matches the rate of metabolites and i able to wash them away.

Question 54

Name four types of local/intrinsic controls for blood flow.

Answer 54

1. Active hyperaemia 2. Pressure/flow autoregulation 3. Reactive hyperaemia 4. Injury response

Question 55

What is the trigger for pressure/flow autoregaultion?

Answer 55

Decrease in perfusion pressure.

Question 56

What is the trigger for active hyperaemia?

Answer 56

Increase in local metabolism.

Question 57

Describe what happens in pressure autoregulation when there is an increase in MAP.

Answer 57

Increases causes decrease of blood flow. Metabolites accumulate. Triggers release of paracrine signal (e.g. EDRF/NO) Arterioles dilate and flow is restored to normal

Question 58

What is the trigger for reactive hyperaemia?

Answer 58

Occlusion of blood supply.

Question 59

What does an occlusion of blood supply do to blood flow?

Answer 59

Increases blood flow

Question 60

Discuss what happens in the injury repsonse.

Answer 60

Response to stubbing your toe, for example. 1. C-fibres are activated- will send active potential via spinal cord to brain 2. Action potential fired down collateral branches causing activation of substance P 3. Substance P acts on mast cells and causes them to release histamine 4. Histamine causes smooth muscle to relax causes arterioles to dilate, increasing blood flow. 5. Injury site goes red 6. Increased blood flow can help to get leukocytes to site of injury to attack any invading pathogens. Please read through this and write it out :)

Question 61

In fight or flight, what is released from sympathetic nerves?

Answer 61

Noradrenaline

Question 62

What does noradrenaline bind to and what does this cause?

Answer 62

Binds to α1 receptors Causes arteriolar constriction, decreasing blood flow

Question 63

What does a decrease in blood flow do to TPR and MAP?

Answer 63

Increases both

Question 64

What is the effect of parasympathetic nerves on blood flow?

Answer 64

Usually no effect as don't innervate blood vessels

Question 65

Where in the body is there an effect based on parasympathetic nerves?

Answer 65

Genitalia and salivary glands (↑ flow)

Question 66

What is released for the central hormonal control of blood flow?

Answer 66

Adrenaline

Question 67

Where is adrenaline released from?

Answer 67

Adrenal medulla

Question 68

Where does adrenaline bind and what is the effect on blood flow?

Answer 68

Binds to α1 receptors Causes arteriolar constriction Therefore ↓ flow through that tissue and tends to ↑ TPR and ↑ MAP

Question 69

What would happen in some tissues like skeletal or cardiac when adrenaline is released?

Answer 69

Also binds and activates B2 receptors. Causes arteriolar dilation Therefore ↑ flow through that tissue and tends to ↓ TPR

Question 70

What happens to the coronary circulation during systole?

Answer 70

Very low blood flow, almost cut off as heart contracts.

Question 71

What happens to coronary blood flow during diastole?

Answer 71

Blood flow greatly increased

Question 72

How can the heart deal with the demand of oxygen during exercise despite the blood supply being interrupted during systole?

Answer 72

->Good active hyperaemia and is sensitive to small changes in metabolites -> Expresses many Beta 2 receptors which allow adrenaline to bind, allowing smooth muscle relaxation and arteriole dilation.

Question 73

What type of local/intrinsic control is the cerebral circulation very good at?

Answer 73

Pressure autoregulation

Question 74

In the pulmonary circulation, what will a decrease in oxygen do?

Answer 74

Causes arteriolar constriction (opposite to most tissues)

Question 75

Why does a decrease in oxygen lead to arteriolar constriction in the pulmonary circulation?

Answer 75

It ensures the blood is directed to the best ventilated parts of the lungs (ventilation-perfusion matching discussed in resp. lectures!)

Question 76

What is the main job of the renal circulation?

Answer 76

Filtration

Question 77

What is filtration dependant on?

Answer 77

Pressure

Question 78

Filtration rate in the renal circulation can be kept pretty constant despite change in MAP. Why?

Answer 78

Excellent pressure autoregulation.