Exchange and the Lymphatic System

Question 1

What are capillaries specialised for?

Answer 1

Exchanging nutrients

Question 2

Why are capillaries thin walled?

Answer 2

Presents a small diffusion barrier

Question 3

What is the advantage of capillaries having a small diameter?

Answer 3

Large surface area:volume ratio

Question 4

What does the ultrastructure of capillaries relate to?

Answer 4

Function

Question 5

What are the 3 kinds of capillaries?

Answer 5

Continuous

Fenestrated

Discontinuous

Question 6

What are the 2 different kinds of continuous capillaries?

Answer 6

No clefts or channels such as in the brain

Only clefts such as in muscle

Question 7

What is present in fenestrated capillaries?

Answer 7

Clefts and channels

Question 8

Where are fenestrated capillaries found?

Answer 8

Intestine

Question 9

Where are continuous capillaries found?

Answer 9

Brain

Muscle

Question 10

Where are discontinuous capillaries found?

Answer 10

Liver

Question 11

What is present in discontinuous capillaries?

Answer 11

Clefts and massive channels

Question 12

What is the difference between continuous and fenestrated capillaires?

Answer 12

Continuous have leaky junctions whereas fenestrated have large pores

Question 13

What causes more of a nutrient to diffuse across a capillary?

Answer 13

If the cell uses more of it, it creates a larger concentration gradient and so more diffuses across

Question 14

What are the 2 ways that nutrients can cross capillaries?

Answer 14

Diffusion

Carrier mediated transport

Question 15

What is an example of carrier mediated transport?

Answer 15

Glucose transporter

Question 16

How do polar substances diffuse across capillaries?

Answer 16

Through clefts/channels

Question 17

How to non-polar substances diffuse across capillaries?

Answer 17

Across the membrane

Question 18

What does hydrostatic pressure do?

Answer 18

Pushes fluid out of capillaries

Question 19

What pushes fluid out of capillaries?

Answer 19

Hydrostatic pressure

Question 20

What does osmotic (oncotic) pressure do?

Answer 20

Draws fluid back into capillaries

Question 21

What causes osmotic pressure?

Answer 21

Hydrostatic pressure pushing fluid out of capillaries builds up an osmotic pressure

Question 22

What is the balance between hydrostatic and osmotic pressures called?

Answer 22

Starling’s forces

Question 23

What makes up Starling’s forces?

Answer 23

Capillary hydrostatic pressure vs interstitial fluid hydrostatic pressure

Plasma osmotic pressure vs interstitial fluid osmotic pressure

Question 24

What formula describes net filtration pressure?

Answer 24

Net filreation pressure = (P_C - P_IF) - (π_P - π_IF)

Question 25

Overall how much fluid is lost and gained from capillaries each day?

Answer 25

20L is lost 17L is gained

Question 26

If 20L of fluid is lost from capillaries and 17L is gained each day, what happens to the remaining 3L?

Answer 26

Goes into the lymphatic system

Question 27

What eventually happens to fluid that is drained into the lymphatic vessels?

Answer 27

Returned to venous circulation

Question 28

What happens when the lymphatic system becomes overwhelmed?

Answer 28

Oedema

Question 29

What is an oedema?

Answer 29

Accumulation of excess fluid

Question 30

What is an accumulation of excess fluid called?

Answer 30

Oedema

Question 31

What can an oedema be caused by?

Answer 31

Lymphatic obstruction Raised hydrostatic pressure Low osmotic pressure

Question 32

What can cause a lymphatic obstruction?

Answer 32

Filariasis or surgery

Question 33

What can cause a raised hydrostatic pressure?

Answer 33

Ventricular failure

Question 34

What can cause low osmotic pressure?

Answer 34

Hypoproteinemia Increased permeability

Question 35

What can increased permeability be caused by?

Answer 35

Inflammation such as rheumatism

Question 36

What can hypoproteinemia be caused by?

Answer 36

Nephrosis Liver failure Nutrition

Question 37

What redirects blood?

Answer 37

Arterioles not capillaries

Question 38

Why do capillaries not redirect blood?

Answer 38

They do not have any smooth muscle around them

Question 39

What is varying the resistance of arterioles done by?

Answer 39

Altering the radius

Question 40

What is Darcy's Law?

Answer 40

Question 41

What is Poiseuille's Law?

Answer 41

Question 42

What equation to you get by substituting Poiseuille's Law back into Darcy's Law?

Answer 42

Question 43

What equation describes flow?

Answer 43

Question 44

Why does varying the resistance of one set of vessels not only affect the flow through that region of the body?

Answer 44

Because it changes the total peripheral resistance so affects the mean arterial pressure

Question 45

What formula describes the mean arterial pressure?

Answer 45

MAP = CO x TPR

Question 47

What does MAP stand for?

Answer 47

Mean arterial pressure

Question 48

What does TPR stand for?

Answer 48

Total peripheral resistance

Question 49

Why is mean artieral pressure very important?

Answer 49

It provides the driving force that pushes blood through useful places like the brain, so a system must monitor and regulate in by controlling the state of construction in arterioles

Question 50

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

Answer 50

Intrinsic mechanisms Extrinsic mechanisms

Question 51

What are intrinsic mechanisms concerned with?

Answer 51

Meeting the needs of each individual tissue

Question 52

What are extrinsic mechanisms concerned with?

Answer 52

Ensuring that the total peripheral resistance (and so mean arterial pressure) of the whole body stays at the right levels

Question 53

What is extrinsic control achieved by?

Answer 53

Neural Hormonal Angiotensin II Vasopressin Atrial natriuretic factor

Question 54

How is the autonomic system used for extrinsic control?

Answer 54

Sympathetic nerves release noradrenaline which binds to A₁ receptors causing arteriolar constriction and decreases flow through that tissue, increase total peripheral resistance Parasympathetic system has no effect

Question 55

What receptors does the sympathetic nervous system act on arterioles?

Answer 55

A₁

Question 56

What effect does parasympathetic nerves have on arterioles?

Answer 56

Usually no effect

Question 57

What is a hormone that achieves extrinsic control?

Answer 57

Adrenaline

Question 58

Where is adrenaline released from?

Answer 58

Adrenal medulla

Question 59

What receptor on arterioles does adrenaline act on?

Answer 59

A₁

Question 60

How do hormones achieve extrinsic control?

Answer 60

Adrenaline causes arteriolar constriction so decrease flow through that tissue and increase total peripheral resistance

Question 61

What is a complication with using adrenaline to achieve extrinsic control?

Answer 61

In some tissues (such as skeletal and cardiac muscle) as well as A₁ it also binds to B₂ receptors which cause arteriolar dilation, increasing flow and decreasing total peripheral resistance

Question 62

What is angiotensis II produced in response to?

Answer 62

Low blood pressure

Question 63

What effect does angiotensin II have?

Answer 63

Causes arteriolar constriction so increases total peripheral resistance

Question 64

What is vasopressin released in response to?

Answer 64

Low blood volume

Question 65

What effect does vasopressin have?

Answer 65

Causes arteriolar constriction so increases total peripheral resistance

Question 66

What is atrial natriuretic factor released in response to?

Answer 66

High blood volume

Question 67

What impact does atrial natriuretic factor have?

Answer 67

Causes arteriolar dilation so decreases total peripheral resistance

Question 68

What is the important effect of B₂ receptors in blood vessels?

Answer 68

Only in some places of the body so redirects blood to heart and skeletal muscles during fight or flight reaction

Question 69

What is local (intrinsic) control achieved by?

Answer 69

Active (metabolic) hyperaemia Pressure (flow) autoregulation Reactive hyperaemia The injury response

Question 70

How does active (metabolic) hyperaemia achieve intrinsic control?

Answer 70

1) Increased metabolic activity causes increase in the concentration of metabolites 2) Triggers release of EDRF/NO (paracrines) 3) Causes arteriolar dilation 4) Increased flow to wash out metabolites 5) An adaptation to match blood supply to the metabolic needs of that tissue

Question 71

How is pressure (flow) autoregulation used to achieve intrinsic control?

Answer 71

1) Decreased mean arteriolar pressure causes decrease in flow 2) Metabolites accumulate 3) Arterioles dilate and flow is restored to normal 4) An adaptation to ensure that a tissue maintains its blood supply despite changes to mean arterial pressure

Question 72

How is reactive hyperaemia used to achieve intrinsic control?

Answer 72

Occlusion (the blockage or closing of a blood vessel) of blood supply causes a subsequent increase in blood flow An extreme version of pressure autoregulation

Question 73

How is the injury response used to achieve intrinsic control?

Answer 73

1) Substance P acts on mast cells which release histamine 2) Histamine causes arteriolar dilation which increases blood flow and permeability 3) Aids delivery of blood born leukocytes to injured area

Question 74

What are areas that are 'special' (in terms of pressure)?

Answer 74

Coronary circulation Cerebral circulation Pulmonary circulation Renal circulation

Question 75

How is coronary circulation special?

Answer 75

Blood flow is interupted by systole But still has to cope with increased demand during exercise Does so by showing excellent active hyperaemia Expressed many B₂ receptors These swamp any sympathetic arteriolar constriction

Question 76

How is cerebral circulation special?

Answer 76

Needs to be kept stable whatever the circumstances Shows excellent pressure autoregulation

Question 77

How is pulmonary circulation special?

Answer 77

Decrease in O₂ causes arteriolar constriction The opposite reaction to most tissues Ensures that blood is directed to the best ventilated parts of the lungs

Question 78

How is renal circulation special?

Answer 78

Main function is filtration which depends on pressure Changes in mean arteriolar pressure would have a big effect on blood volume Shows excellent pressure autoregulation