Blood, Tissue Fluid and Lymph 2 PDF

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Notes on Blood, Tissue Fluid and Lymph Biology A Level OCR A...

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Blood, Tissue Fluid and Lymph Erythrocytes Structure  Erythrocytes have a diameter of 7μm  This is small – the average cell is 40μm in diameter  Therefore, the hemoglobin is very close to the plasma membrane – as a result oxygen is loaded and unloaded very quickly in and out of the cell  Capillaries are 8μm wide – only allowing 1 Erythrocyte through at a time

Plasma proteins and blood pressure  About 8% of blood plasma consists of plasma proteins, of which about half may be albumins.  These are a group of small proteins involved in the transport of other substances (e.g fatty acids, hormones) and which help regulate the osmotic pressure of blood.  The balance between the hydrostatic pressure of blood (‘blood pressure’) and the osmotic pressure of blood is important in the formation of tissue fluid.

Blood Water Potential  Substances dissolved in the blood plasma can move in and out of the capillaries  Some large proteins, such as albumin, have an osmotic effect  They cause the blood to have a relatively low water potential  As a result, water tends move into the blood from surrounding tissues by osmosis  This is called oncotic pressure = -3.3 kPa

Permeability of capillaries  In the formation of tissue fluid blood plasma and the dissolved substances moves out into the body’s cells  The table shows the relative permeability of the substances in blood...