Oedema (AMI)

Question 1

Interstitial Fluid (def.)

Answer 1

Interstitial fluid is the extracellular water that bathes the body cells. It acts as a go between for blood and body cells.

Question 2

What % of body weight is water, and how much of this is extracellular/interstitial?

Answer 2

60% of body weight is water.
One third of total water is extracellular (~14L).
75% of this is interstitial (~11L).

Question 3

Capillaries are lined with…

Answer 3

a single layer of endothelial cells.

Question 4

How is Capillary lining suited to their function?

Answer 4

Capillaries are lined with a single layer of endothelial cells. This allows the rapid exchange of gases, water and solutes with interstitial fluid, to deliver nutrients and oxygen to the cells and remove metabolites.

Question 5

Blood flow in the capillaries is dependent on…

Answer 5

contractile state of arterioles.

Question 6

How is blood flow in capillaries regulated?

Answer 6

In most, terminal arterioles regulate blood flow at a regional level.
In some tissues e.g. mesentery, Precapillary Sphincters regulate blood flow.

Question 7

Why is blood flow in capillaries slow?

Answer 7

to allow adequate time for exchange to occur.

Question 8

How do hydrophilic substances move in and out of capillaries?

Answer 8

Water filled pores which exist between the endothelial cells.
E.g. Na+, K+ and glucose.

Question 9

How do Lipophilic substances move in and out of capillaries?

Answer 9

Diffuse across the endothelial cells.

Question 10

How do exchangeable proteins move out through capillary walls?

Answer 10

Vesicular Transport

Question 11

How do plasma proteins move across capillary walls?

Answer 11

Plasma proteins generally cannot cross the capillary wall.

Question 12

What regulates fluid movement and movement of gases and solutes across the capillary walls?

Answer 12

Fluid - pressure gradient/bulk flow.

Gases and solutes- Fick’s Law of Diffusion.

Question 13

Fick’s Law of Diffusion

Answer 13

Movement of gases and solutes across the capillary wall is in proportion to the concentration gradient.

Question 14

What drives transcapillary fluid flow/exchange?

Answer 14

pressure gradients across the capillary wall passively drive transcapillary flow/exchange.

Question 15

Ultra-filtration (def.)

Answer 15

The plasma exchanged across the capillary wall is essentially protein free

Question 16

Net Filtration Pressure (NFP) =

Answer 16

forces favouring filtration - forces opposing filtration.

=> (Pc - πi) - (πc - Pi)

Question 17

Kf (def.)

Answer 17

filtration coefficient that affects net fluid filtration.

Question 18

Starling Forces favouring filtration

Answer 18

Capillary hydrostatic pressure (35 –> 17 mmHg)

Interstitial fluid osmotic pressure (~1 mmHg)

Question 19

Starling Forces opposing filtration

Answer 19

Capillary osmotic pressure (35 mmHg)

Interstitial fluid hydrostatic pressure (1 mmHg, -ve in some tissues)

Question 20

In skeletal muscle capillaries, NFP…

Answer 20

varies at the arteriolar and venular ends.
E.g. @A = (35 + 1) - (25 + 1)
@V = (17 + 1) - (25 + 1)

Question 21

Starling Forces favour __ at the arteriolar end, but favour __ at the venular end

Answer 21

filtration

reabsorption

Question 22

What are the two main forces involved in SYSTEMIC transcapillary flow?

Answer 22

Pc (favouring filtration)

πc (opposing filtration)

Question 23

How is filtered fluid removed and why?

Answer 23

Efficient lymphatic draining removed filtered fluid to prevent accumulation of interstitial fluid.

Question 24

Pulmonary resistance is ___ of that of the systemic circulation.

Answer 24

around 10%

Question 25

Starling Forces in pulmonary circulation

Answer 25

Po Capillary Hydrostatic Pressure = 8-11 mmHg

Capillary osmotic pressure = 25 mmHg

Question 26

Oedema (def.)

Answer 26

accumulation of fluid in the interstitial spaces

Question 27

Effect of pulmonary oedema on gas exchange

Answer 27

Oedema increases diffusion distances, therefore compromises gas exchange

Question 28

Causes of Oedema

Answer 28

1. Raised capillary pressure
2. Reduces plasma osmotic pressure
3. Lymphatic insufficiency
4. Changes in capillary permeability

Question 29

Causes of raised capillary pressure

Answer 29

1. Arteriolar dilatation

2. Raised venous pressure - heart failure

Question 30

Oedematous effects of heart failure

Answer 30

LVF - pulmonary oedema
RVF - peripheral oedema

HF shifts frank starling curve to the right

Question 31

Causes of reduced plasma osmotic pressure

Answer 31

Malnutrition, protein malabsorption, excessive renal secretion of protein, hepatic failure.

Question 32

Normal vs. Oedematous plasma osmotic pressure

Answer 32

Normal = 65-80 g/l 
Oedema = < ~ 30 g/l

Question 33

Lymphatic insufficiency causes….

Answer 33

Lymph node damage

Filariasis - elephantiasis

Question 34

What causes changes in capillary permeability?

Answer 34

Inflammation

Histamine increases protein leakage.

Question 35

Pulmonary Oedema (def.)

Answer 35

accumulation of fluid in the interstitial and intraalveolar spaces.

Question 36

Manifestations of Pulmonary Oedema

Answer 36

Varying degrees of SOB
Clinically, crepitations in auscultation of lung bases.
CXR will appear hazy in perihilar region

Question 37

Peripheral Oedema (def.)

Answer 37

accumulation of fluid in tissues perfused by the peripheral vascular system, most commonly the lower limbs.

Question 38

Pitted Oedema (def.)

Answer 38

type of peripheral oedema with characteristic indentations.

Question 39

Common sites of peripheral (and pitted) oedema

Answer 39

ankle and sacrum