CVS Fluid Movement and Oedema Flashcards
What is movement of fluid across capillary membrane into interstitial space due to?
Fluid moves across membrane into
interstitial space due to
Capillary blood pressure
How is oncotic pressure generated and what does this create?
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
What is Lp in the starling’s principle of fluid exchange equation?
Conductance of the endothelium
How leaky the endothelium is to fluid
What is A in the starling’s principle of fluid exchange equation?
Endothelium plasma membrane area
What is σ in the starling’s principle of fluid exchange equation?
Reflection coefficient – related to intercellular gaps
What is fraction(σ) of the osmotic pressure exerted by?
Fraction () of the osmotic pressure
is exerted by gaps
What is the equation for effective osmotic pressure?
Effective osmotic pressure =
σ x potential osmotic pressure
How does filtration and reabsorption generally occur along the length of capillaries?
Fluid filtration generally occurs throughout length of capillaries
Reabsorption does not occur - important for fluid replacement
What is the revised starling’s principle of fluid exchange including glycocalyx?
Plasma proteins move from lumen into interstitial space via vesicle system
Not via intercellular spaces as glycocalyx acts as a barrier
What does the revised starling principle mean in terms of filtration?
-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
Where does the fluid go, if there is constant filtration?
Lymphatic circulation
Where does lymphatic circulation return excess tissue fluid/ solutes back to?
Lymphatic circulation returns
excess tissue fluid/solutes back to
the cardio-vascular system
What do lymph vessels have?
Lymph vessels have valves and
smooth muscle
What does spontaneous contraction of smooth muscle in lymphatic circulation contribute to?
Spontaneous contractions of the
smooth muscle contributes to
lymph flow
What does skeletal muscle surrounding lymphatic circulation contribute to?
Surrounding skeletal muscle
contractions / relaxation also
contributes to lymph flow
Organisation of the lymphatic(thoracic duct) system
Slide 14. MEMORISE
What does the control of extracellular fluid balance depend on?
Capillary filtration
Capillary reabsorption
Lymphatic system
What if this balance between filtration, reabsorption,
lymphatic function is not maintained?
Results in Oedema
What is Oedema?
Excessive fluid in interstitial space
What are factors promoting excessive filtration?
Increased Pc, Decreased πp,
Increased πg, Increased Lp
What are the factors promoting reabsorption?
Decreased Pc, Increased πp
How does increased capillary pressure (Pc) increase filtration i.e. in DVT?
-Prevention of venous return
-Increases venous pressure causes ‘backup’ of pressure leading to:
-Increased PC across capillaries
Increased filtration
What are clinical scenarios where we may see increased capillary pressure (Pc)?
-Gravitational oedema – ‘standing up for long periods’
-Deep venous thrombosis
-Cardiac failure
How does decreased plasma osmotic pressure (πp) lead to Oedema?
-Reduced plasma protein concentration
-Reduced plasma oncotic pressure (πp)
Greater influence of Pc
-Excessive fluid filtration from capillaries
into the interstitial fluid
-Oedema
What are the clinical scenarios where there may be a decreased plasma osmotic pressure(πp)?
-Low protein oedema
-Malnutrition/malabsorption, hepatic failure, nephrotic syndrome
What is inflammatory mediated oedema caused by?
e.g., Insect bites/stings, infection, trauma, autoimmune disease
What is swelling triggered by in inflammatory mediated oedema?
Swelling is triggered by local chemical mediators of inflammation
What does the swelling in inflammatory mediated oedema increase?
Increase capillary permeability – they become more ‘leaky’
How is filtration enhanced in inflammatory-mediated oedema?
Inflammation = Increased Lp, (also Decreased σ , as capillary become more leaky so oncotic
pressure in reduced)
Enhanced filtration
What happens in lymphatic obstruction due to nematode infestation?
nematode infestation, larvae migrate to lymphatic system grow/mate/form nests – block lymphatic drainage
Why does continued filtration lead to oedema?
Continued filtration leads to build up of fluid in interstitial space
What can cause breakdown/dysfunctional glycocalyx in patient?
sepsis, following surgery
What will increasing fluids in conditions that involve a dysfunctional glycocalyx result in?
In these conditions increasing fluids (either crystalloids or colloids) will cause movement of plasma proteins through intercellular gaps
Reducing oncotic pressures
