Flashcards in Cardio L10 Tissue Fluid and Oedema Deck (25):
Types of capillary:
3. Discontinuous (sinusoidal)
Metabolite Exchange across the Capillary Wall:
1. Passive diffusion down concentration gradients (Fick’s First Law of diffusion)
2. Convective transport in trans capillary fluid “solvent drug” (minor importance).
Fluid exchange across the Capillary Wall:
1. Fluid flows across the capillary wall due to a pressure gradient.
2. Water also diffuses across the capillary wall but this is bi-directional and no net transfer occurs.
1. Extracellular fluid (ECF).
2. Isotonic to intracellular fluid (ICF).
Tissue fluid produced by
a. Ultrafiltration across the capillary wall.
Tissue fluid drained into
a. The lymphatic system and eventually returned to the vascular system.
Flow through pores in the membrane (e.g. capillary endothelium)
Ultrafiltration: Driven by
A pressure gradient
Ultrafiltration: Pore size permits
Selective passage of molecules according to their size
Ultrafiltration: Example of molecules
Glucose and ions
Reflection Coefficient: definition
This is an index of the membranes molecular selectivity.
Reflection Coefficient =0
If the solute passes freely through the membrane and it exerts no osmotic pressure across the membrane.
Reflection Coefficient =1
If the solute is totally reflected by the membrane and it exerts its full osmotic effect across the membrane.
Hydraulic Conductance (Lp):
1. This describes the permeability of the membrane to fluid.
2. Increased during inflammation.
rate of production of tissue fluid = filtration pressure x surface area.
Filtration Pressure (I):
1. There is a hydraulic pressure gradient across the capillary wall.
2. Pressure gradient= capillary hydrostatic pressure (Pc) – interstitial pressure (Pi).
3. Net effect is to “drive” ultrafiltration.
Filtration Pressure (II):
1. There is an osmotic pressure gradient
2. Pressure gradient = colloid osmotic pressure of plasma – colloid osmotic pressure of interstitial fluid.
3. Net effect is to retain within the vascular system.
Landis Model →
→ Transient capillary reabsorption probably only occurs under conditions such as haemorrhage.
Functions of the Lymphatic System:
1. Fluid balance
1. An excess of tissue fluid.
2. May be localised or generalised.
3. Occurs when production of tissue fluid exceeds its drainage.
Raised Capillary Pressure:
1. Heart failure
2. Fluid overload
3. Venous thrombosis
4. Venous valve incompetence
Decreased Plasma COP: due to
3. Protein losing enteropathy
4. Nephrotic syndrome
5. Hepatic failure
Increased Capillary Permeability: