Release and Reuptake of Tissue Fluid in Capillaries
Definition
Tissue fluid
Fluid found in the spaces around cells
- Tissue fluid, also known as interstitial fluid, is the fluid that surrounds cells in tissues.
- It is essential for nutrient and gas exchange between the blood and tissues.
- Misconception: Tissue fluid is identical to blood plasma.
- Correction: Tissue fluid is derived from plasma but lacks large proteins and blood cells, which cannot pass through the capillary walls.
Tissue Fluid Formation: Pressure Filtration
High Blood Pressure in Arterioles
- Blood from the arterioles (small arteries) enters the capillaries under high pressure.
- The pressure is higher than the surrounding tissue pressure.
- This pressure forces plasma (the liquid portion of blood) out of the capillaries and into the surrounding tissues.
- This process is called pressure filtration.
Definition
Plasma
The liquid component of blood, consisting mostly of water, proteins, and other substances.
Movement of Substances
- As plasma moves out, it loses most of its proteins due to their large size, leaving a liquid that is similar to interstitial fluid.
- Nutrients (like glucose) and oxygen diffuse into the tissue fluid to nourish the cells.
- Waste products from the cells (like carbon dioxide) are also carried into the tissue fluid for removal.
- Picture a garden hose with tiny holes along its length.
- When water flows through the hose under high pressure, it leaks out through these holes, just like plasma leaks out of capillaries at the arterial end.
Reuptake of Tissue Fluid: Osmotic Pressure
Lower Blood Pressure in Venules
- After the exchange of gases and nutrients, the blood moves from the capillaries into the venules (small veins).
- The blood pressure in venules is much lower compared to the pressure in arterioles.
- As a result, the tissue fluid that surrounds the cells is drawn back into the capillaries due to the lower pressure in the venules.
