MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedoniuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

SECTION 4. BLOOD SYSTEM

PHYSICOCHEMICAL PROPERTIES OF BLOOD

1. OSMOTIC PRESSURE OF BLOOD

Osmotic pressure is the pressure exerted by substances dissolved in Blood Plasma and formed elements. It is primarily generated by plasma salts. Under normal conditions, it is 7.5 atm (9300 mOsm/L). Although Plasma Proteins account for 7-8% and salts for 1%, the protein-derived pressure is only 0.03-0.04 atm (25-30 mmHg). This fraction of pressure is referred to as oncotic pressure. Osmotic and oncotic pressures play a vital role in maintaining Water exchange between blood plasma and Tissues. They also regulate water balance between plasma and Blood Cells; therefore, any alteration in these constants affects not only cellular Functions but also Cell integrity.

When erythrocytes are placed in a solution with a higher osmotic pressure than that of blood (known as a hypertonic solution), they lose water and shrink. Conversely, in a solution with a lower osmotic pressure than blood (hypotonic solution), erythrocytes absorb water, swell, enlarge, and eventually rupture. In this process, Hemoglobin is released from THE RED BLOOD cells, dissolves in the plasma, and the blood turns transparent and crimson, a condition known as "lacquered blood". The destruction of erythrocytes in a hypotonic solution is called osmotic hemolysis. Hemolysis can also occur upon the Introduction of toxic substances into the blood (such as ether, gasoline, chloramine, or ammonia), which is referred to as chemical hemolysis. Exposure of erythrocytes to snake, bee, or scorpion venom leads to biological hemolysis. Furthermore, hemolysis is observed when red blood cells from an animal of one species are repeatedly injected into an animal of a different species, as well as during incompatible blood transfusions in humans. In such cases, hemolysins appear in the blood and destroy the transfused erythrocytes. Mechanical hemolysis may occur due to vigorous agitation or violation of transportation guidelines. Hemolyzed blood is unfit for transfusion.