Movement Through The Capillary Wall Notes

Movement Through The Capillary Wall

Three Main Processes

• The movement through the capillary wall involves three main processes:
  • Diffusion
  • Filtration
  • Reabsorption

Diffusion

• Diffusion is a key process for gas exchange.
• Oxygen ($O_2$) diffuses from the alveoli to the capillary.
• Carbon dioxide ($CO_2$) diffuses from the capillary to the alveoli.

Filtration

• Filtration is driven by hydrostatic pressure.
• Hydrostatic pressure involves two components:
  • Interstitial Fluid Hydrostatic Pressure (IHP)
  • Colloid Hydrostatic Pressure (CHP)
• Net Hydrostatic Pressure (NHP) is calculated as:
  • $NHP = CHP - IFHP$
• Filtration occurs from the capillary into the interstitial fluid.

Reabsorption

• Reabsorption is driven by osmotic pressure.
• Osmotic pressure "sucks" water across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration.
• Osmotic pressure consists of:
  • Interstitial Fluid Osmotic Pressure (IFOP)
  • Blood Colloid Osmotic Pressure (BCOP)
• Net Colloid Osmotic Pressure (NCOP) is calculated as:
  • $NCOP = BCOP - IFOP$
• Reabsorption moves fluid from the interstitial fluid back into the capillary.

Net Filtration Pressure

• Net Filtration Pressure (NFP) determines the overall movement of fluid across the capillary wall.
• It is calculated as:
  • $NFP = NHP - NCOP$
  • Where:
    • NFP: Net Filtration Pressure
    • NHP: Net Hydrostatic Pressure
    • NCOP: Net Colloid Osmotic Pressure