tissue fluid

• Blood is the liquid in blood vessels made of blood cells in plasma
• Plasma contains many dissolving substances like oxygen, CO2, salts, glucose, fatty acids, amino acids, hormones, and plasma proteins
• Tissue fluid is similar to blood but doesn’t contain most of the cells found in blood, nor plasma proteins
• Tissue fluid's role is to carry oxygen and nutrients from the blood into the cells and to carry CO2 and wastes back to the blood
• Tissue fluid is formed when blood flows from an organ or tissue and is contained within the capillaries
• Pressure is higher at the start of capillary beds due to arteries being under pressure from the heart (hydrostatic pressure)
• Fluid is forced out of the capillaries into the surrounding tissue, forming tissue fluid
• Tissue fluid mainly contains water, oxygen, ions, amino acids, fatty acids, and glucose
• Tissue fluid does not contain red blood cells and blood proteins because they are too big to leave
• Fluid returns to the blood due to hydrostatic pressure pushing it back into the capillaries
• Blood and fluid contain solutes giving them negative water potential
• The water potential of tissue fluid is less negative than that of the blood, causing water to move back to the blood by osmosis down the potential gradient
• At the venous end of the capillary, the blood has lost its hydrostatic pressure
• The combined effect of hydrostatic pressure in the tissue fluid and the osmotic force of the plasma proteins pushes the fluid back to the capillary
• Not all tissue fluid returns to capillaries; some is drained into the lymphatic system
• The lymphatic system consists of vessels like capillaries that start in the tissues and drain excess fluid into larger vessels re-joining the blood system in the chest cavity
• Lymph fluid is similar to tissue fluid and contains the same solutes
• Lymph has less oxygen and fewer nutrients, more CO2, wastes from body cells, and fatty material absorbed from the intestines
• The main difference between tissue fluid and lymph is that lymph contains lymphocytes, made in the lymph nodes
• Lymph nodes filter bacteria and foreign material from lymph fluid, and lymphocytes engulf and destroy these bacteria and particles