Blood Tissue Fluid and Lymph

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  • Created on: 09-01-13 19:42
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Blood, Tissue Fluid and Lymph
Blood consists of a watery fluid called plasma. The plasma contains dissolves substances such as oxygen,
carbon dioxide, salt, glucose, fatty acids, amino acids, hormones and plasma proteins as well as cells such
as erythrocytes, leucocytes and platelets.
Tissue fluid is similar to blood but does not contain most of the cells or the plasma proteins. The role of the
tissue fluid is to transport oxygen and nutrients (e.g. glucose) from the blood to the
cells and then carry carbon dioxide and other waste products (e.g. urea) back to the
blood.
Tissue fluid is formed when an artery branches into smaller arterioles then further
into a network of capillaries. These eventually link up with the venules which link up
to a vein. The blood flowing into an organ is contained in capillaries. At the arterial
end of a capillary the blood is under high pressure due to the contraction of the
heart muscle known as hydrostatic pressure. This pressure pushes the blood out of
the capillaries through tiny gaps in the capillary wall. The fluid that leaves the
capillary is known as the tissue fluid and consists of plasma with dissolved nutrients
and oxygen. All the red blood cells, platelets, most of the white blood cells and
plasma proteins remain in the blood as too big to be pushed out of the gaps. The
fluid surrounds the body cells so exchange of gases and nutrients can occur
through diffusion/facilitated diffusion. Oxygen and nutrients enter cell carbon
dioxide and waste products leave cell.
The hydrostatic pressure of blood and of the tissue fluid (tends to try and push the fluid back into the
capillary) is not the only force. Both the blood and tissue fluid has dissolved solute leaving them with
negative water potential (as pure water has 0 ). The water potential of blood is more negative than the
tissue fluid so water will move from the high concentration in the tissue fluid to the low concentration of
water in the blood by osmosis. At the venous (vein) end of the capillary, the blood has lost hydrostatic
pressure. The effect of loss of hydrostatic pressure in the tissue fluid and the osmotic force of the plasma
proteins is enough to move the fluid back into the capillary bringing the dissolved waste substances if the
cells with it.

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Not all the tissue fluid returns to the blood capillaries. Some is drained away by the lymphatic system which
consists of a number of vessels (tubes) which are similar to capillaries. They start in the tissues and drain
excess fluid into larger vessels, which eventually rejoins the blood system in the chest cavity.
Lymph fluid contains similar solutes to tissue fluid.…read more

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