Table 17-1— Main Components 

 of Human Blood 



A. Corpuscles 



1. Red corpuscles, or erythrocytes 



2. White corpuscles, or leucocytes 



3. Platelets, or thrombocytes 



B. Plasma 



1. Water (90 percent, by weight) 



2. Inorganic salts (1 percent) 



3. Major proteins, 7 percent: serum al- 

 bumin (4 percent), serum globulin 

 (2.7 percent), fibrinogen (0.3 percent) 



4. Other substances, 2 percent 



a. Absorbed foods (glucose, amino 

 acids, glycerol, fatty acids, neu- 

 tral fats, other lipids, and vita- 

 mins) 



b. Collected wastes (urea, uric 

 acid, and other compounds) 



c. Hormones, enzymes, and anti- 

 bodies 



d. Respiratory gases (oxygen and 

 carbon dioxide) 



The chief function of the erythrocytes is to 

 augment the oxygen-carrying capacity of the 

 blood. About 50 percent of the weight of an 

 erythrocyte represents hemoglobin, an iron- 

 containing protein compound. The hemo- 

 globin molecule is a fairly large one, having 

 a molecular weight of 68,000 and consisting 

 of a complex of four heme units (p. 364). 

 Each heme unit possesses a single centrally 

 localized iron (Fe) atom and can combine 

 chemically with one molecule of oxygen 

 (O-,). Thus the whole hemoglobin molecule 

 when fully saturated (at high partial pres- 

 sure of Oo) can carry four molecules of oxy- 

 gen. For the sake of simplicity, however, the 

 equilibrium between oxygen and hemoglobin 

 is often written: hemoglobin -4- oxygen «=± 

 oxyhemoglobin, or: Hb -4- 2 ?± Hb0 2 . 



In any event, hemoglobin greatly aug- 

 ments the oxygen-carrying capacity of the 

 blood. In addition to a small quantity of 

 oxygen carried in solution in the plasma 

 there is always the much larger quantity that 



The Circulatory System - 321 



is chemically united with hemoglobin in the 

 erythrocytes. 



A majority of vertebrates (fish, amphibians, 

 reptiles, and birds) possess erythrocytes with 

 typical nuclei. But in man and other mam- 

 mals, the nuclei are lost by the cells before 

 the erythrocytes are launched into the blood 

 stream. Mammalian erythrocytes survive in 

 the circulation for an average of only 125 

 days, whereupon the aging corpuscles are 

 phagocytized by certain tissues, particularly 

 in the spleen (p. 335). Accordingly a con- 

 stant replacement of red cells must go on, if 

 anemia is to be avoided, and, in fact, several 

 million new red cells are launched into the 

 circulation during every second of man's 

 life. In adult man the formation of new red 

 cells occurs in the hemopoietic tissues of red 

 bone marrow; but in the embryo — and in 

 lower vertebrates generally — erythrocytes are 

 formed in the liver, spleen, and lymph nodes 

 (p. 334). A lowered content of hemoglobin in 

 the blood — whether due to an abnormally 

 rapid loss of erythrocytes, or to a defective 

 formation of the red cells — is called anemia. 

 The anemia may be due to a variety of causes, 

 such as hemorrhage, metal poisoning, 

 hereditary fragility of the corpuscles, or in- 

 adequate iron in the diet. Inadequate dietary 

 iron does not reduce the number of erythro- 

 cytes; but the individual red cells are small 

 and pale, due to a paucity of hemoglobin. 



In pernicious anemia, the body lacks a 

 specific compound that is closely related to 

 (perhaps identical with) vitamin B ]2 , the 

 antipernicious anemia factor (APA). Nor- 

 mally this bone-marrow stimulant is stored 

 in the liver, and the feeding or injecting of 

 beef liver concentrates (or of the purified 

 vitamin) brings most cases of pernicious ane- 

 mia under control (see p. 353). 



Leucocytes. The white cells of the blood 

 (Fig. 17-3) are far less numerous than the 

 reds, and they normally total to only about 

 6000 to 10,000 per cubic millimeter. All leu- 

 cocytes have a colorless cytoplasm and defi- 

 nite nuclei. Leucocytes are of various kinds, 

 as is shown in Table 17-2, and some kinds are 



