CVS Fluid Movement and Oedema

Question 1

What is movement of fluid across capillary membrane into interstitial space due to?

Answer 1

Fluid moves across membrane into
interstitial space due to
Capillary blood pressure

Question 2

How is oncotic pressure generated and what does this create?

Answer 2

Large molecules (e.g. plasma proteins)
cannot pass through membrane
So they exert osmotic pressure termed
Oncotic pressure
which creates suction force to move
fluid from interstitial space into capillary

Question 3

What is Lp in the starling’s principle of fluid exchange equation?

Answer 3

Conductance of the endothelium
How leaky the endothelium is to fluid

Question 4

What is A in the starling’s principle of fluid exchange equation?

Answer 4

Endothelium plasma membrane area

Question 5

What is σ in the starling’s principle of fluid exchange equation?

Answer 5

Reflection coefficient – related to intercellular gaps

Question 6

What is fraction(σ) of the osmotic pressure exerted by?

Answer 6

Fraction () of the osmotic pressure
is exerted by gaps

Question 7

What is the equation for effective osmotic pressure?

Answer 7

Effective osmotic pressure =
σ x potential osmotic pressure

Question 8

How does filtration and reabsorption generally occur along the length of capillaries?

Answer 8

Fluid filtration generally occurs throughout length of capillaries
Reabsorption does not occur - important for fluid replacement

Question 9

What is the revised starling’s principle of fluid exchange including glycocalyx?

Answer 9

Plasma proteins move from lumen into interstitial space via vesicle system
Not via intercellular spaces as glycocalyx acts as a barrier

Question 10

What does the revised starling principle mean in terms of filtration?

Answer 10

-Filtration occurs across length of capillaries
-Less Pc at venous end means plasma proteins diffuse into subglycocalyx region
-π i = π g
-So filtration occurs at venous end, even with low Pc

Question 11

Where does the fluid go, if there is constant filtration?

Answer 11

Lymphatic circulation

Question 12

Where does lymphatic circulation return excess tissue fluid/ solutes back to?

Answer 12

Lymphatic circulation returns
excess tissue fluid/solutes back to
the cardio-vascular system

Question 13

What do lymph vessels have?

Answer 13

Lymph vessels have valves and
smooth muscle

Question 14

What does spontaneous contraction of smooth muscle in lymphatic circulation contribute to?

Answer 14

Spontaneous contractions of the
smooth muscle contributes to
lymph flow

Question 15

What does skeletal muscle surrounding lymphatic circulation contribute to?

Answer 15

Surrounding skeletal muscle
contractions / relaxation also
contributes to lymph flow

Question 16

Organisation of the lymphatic(thoracic duct) system

Answer 16

Slide 14. MEMORISE

Question 17

What does the control of extracellular fluid balance depend on?

Answer 17

Capillary filtration
Capillary reabsorption
Lymphatic system

Question 18

What if this balance between filtration, reabsorption,
lymphatic function is not maintained?

Answer 18

Results in Oedema

Question 19

What is Oedema?

Answer 19

Excessive fluid in interstitial space

Question 20

What are factors promoting excessive filtration?

Answer 20

Increased Pc, Decreased πp,
Increased πg, Increased Lp

Question 21

What are the factors promoting reabsorption?

Answer 21

Decreased Pc, Increased πp

Question 22

How does increased capillary pressure (Pc) increase filtration i.e. in DVT?

Answer 22

-Prevention of venous return
-Increases venous pressure causes ‘backup’ of pressure leading to:
-Increased PC across capillaries
Increased filtration

Question 23

What are clinical scenarios where we may see increased capillary pressure (Pc)?

Answer 23

-Gravitational oedema – ‘standing up for long periods’
-Deep venous thrombosis
-Cardiac failure

Question 24

How does decreased plasma osmotic pressure (πp) lead to Oedema?

Answer 24

-Reduced plasma protein concentration
-Reduced plasma oncotic pressure (πp)
Greater influence of Pc
-Excessive fluid filtration from capillaries
into the interstitial fluid
-Oedema

Question 25

What are the clinical scenarios where there may be a decreased plasma osmotic pressure(πp)?

Answer 25

-Low protein oedema
-Malnutrition/malabsorption, hepatic failure, nephrotic syndrome

Question 26

What is inflammatory mediated oedema caused by?

Answer 26

e.g., Insect bites/stings, infection, trauma, autoimmune disease

Question 27

What is swelling triggered by in inflammatory mediated oedema?

Answer 27

Swelling is triggered by local chemical mediators of inflammation

Question 28

What does the swelling in inflammatory mediated oedema increase?

Answer 28

Increase capillary permeability – they become more ‘leaky’

Question 29

How is filtration enhanced in inflammatory-mediated oedema?

Answer 29

Inflammation = Increased Lp, (also Decreased σ , as capillary become more leaky so oncotic
pressure in reduced)
Enhanced filtration

Question 30

What happens in lymphatic obstruction due to nematode infestation?

Answer 30

nematode infestation, larvae migrate to lymphatic system grow/mate/form nests – block lymphatic drainage

Question 31

Why does continued filtration lead to oedema?

Answer 31

Continued filtration leads to build up of fluid in interstitial space

Question 32

What can cause breakdown/dysfunctional glycocalyx in patient?

Answer 32

sepsis, following surgery

Question 33

What will increasing fluids in conditions that involve a dysfunctional glycocalyx result in?

Answer 33

In these conditions increasing fluids (either crystalloids or colloids) will cause movement of plasma proteins through intercellular gaps
Reducing oncotic pressures