Exchange and the lymphatic system Flashcards
Capillary properties
- Numerous
- Thin-walled: small diffusion barrier
- Small diameter: large surface area:volume ratio
Types of capillaries (3)
- Continuous
- Fenestrated
- Discontinuous
Continuous capillaries
No clefts or pores e.g. brain
Clefts only e.g. muscles
Fenestrated capillaries
Cleft and pores e.g. intestines
Discontinuous capillaries
Clefts and massive pores e.g. liver
Methods of exchange (2)
- Diffusion: self-regulating, non-saturable and non-polar substances through clefts/channels
- Carrier-mediated transport e.g. glucose
Blood-brain barrier function
- Highly selective impermeable border of endothelial cells to protect against circulating toxins/pathogens that could cause infection, while allowing passage of vital nutrients
Blood-brain barrier structure
Continuous capillaries with no clefts or pores and glucose-specific protein carriers
Normal clotting process
Formation of platelet plug and fibrin clot
Clotting prevention techniques in capillaries (5)
- Stops blood contacting collagen
- Prostacyclin and NO production
- TFPI production
- Thrombomodulin and heparin expression
- t-Pa secretion
- Stops blood-collagen contact
Prevents platelet aggregation
- Prostacyclin and nitric oxide production
Inhibit platelet aggregation
- Tissue factor and pathway inhibitor production
Stops thrombin production
- Thrombomodulin and heparin expression
Inactivates thrombin
- Tissue plasminogen activator secretion
Plasminogen -> plasmin and digest clot
Starling’s Forces are balance of…
- Hydrostatic pressures (20L)
2. Osmotic/oncotic pressures (17L)
Oedema
Accumulation of excess fluid
Oedema causes
- Lymphatic obstruction (filiariasis, surgery)
- Raised CVF (raised hydrostatic)
- Hypoproteinaemia (nephrosis, LF, nutrition)
- Increased capillary permeability (inflammation)
