12.1 Physicochemical properties of blood
12.2 Erythrocyte system
Profile materials Control questions
Situational tasks
12.1. Physicochemical properties of blood
The concept of blood system
The blood system has four components:
1) blood-forming organs;
2) circulating blood;
3) blood cell destroying organs;
4) neurohumoral regulation apparatus providing stable connections between the system elements (G.F. Lang, 1939).
Main functions of blood ("Blood is a juice of rarest quality." I. Goethe).
Transport function: respiratory, trophic, excretory, thermoregulatory (convectional transport of heat from the "core" to the body surface).
Protective function: participating in reactions of immunity, hemostasis, re-action of blood buffers in acido-sis and alkalosis.
Regulatory function: humoral regulation implemented by the transport of biologically active substances (especially hormones).
The amount and composition of blood Absolute and relative amount of blood: in a healthy person with a weight of 70 kg ≈5.0 l, 70 ml/kg; ≈7% of body weight, which is called normovolemia; a decrease
or increase in the volume of circulating blood is called hypovolemia or hypervolemia, respectively.
Composition of blood. The blood consists of formed elements (Fig. 12.1) and plasma.
Formed elements (RBCs account for 98% of their volume) include:
• cells: WBCs;
• post-cell structures: RBCs, platelets.
The ratio of RBC volume to the volume of blood is called hematocrit: in healthy men 40-48%, in women 36-42%. A change in hematocrit characterizes the degree of hemoconcentration or dilution of blood, which is associated with a change in the amount of water and RBCs in the blood, affects blood viscosity and resistance to blood flow.