tailieunhanh - Saladin Anatomy and Physiology The Unity of Form and Function Episode 11

Tham khảo tài liệu 'saladin anatomy and physiology the unity of form and function episode 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Saladin Anatomy Physiology The Unity of Form and Function Third Edition 18. The Circulatory System Text Blood The McGraw-Hill Companies 2003 You might wonder why human hemoglobin must be contained in RBCs. The main reason is osmotic. Remember that the osmolarity of blood depends on the number of particles in solution. A particle for this purpose can be a sodium ion an albumin molecule or a whole cell. If all the hemoglobin contained in the RBCs were free in the plasma it would drastically increase blood osmolarity since each RBC contains about 280 million molecules of hemoglobin. The circulatory system would become enormously congested with fluid and circulation would be severely impaired. The blood simply could not contain that much free hemoglobin and support life. On the other hand if it contained a safe level of free hemoglobin it could not transport enough oxygen to support the high metabolic demand of the human body. By having our hemoglobin packaged in RBCs we are able to have much more of it and hence to have more efficient gas transport and more active metabolism. Chapter 18 The Circulatory System Blood 691 Erythrocyte Death and Disposal Circulating erythrocytes live for about 120 days. The life of an RBC is summarized in figure . As an RBC ages and its membrane proteins especially spectrin deteriorate the membrane grows increasingly fragile. Without a nucleus or ribosomes an RBC cannot synthesize new spectrin. Many RBCs die in the spleen which has been called the erythrocyte graveyard. The spleen has channels as narrow as 3 m that severely test the ability of old fragile RBCs to squeeze through the organ. Old cells become trapped broken up and destroyed. An enlarged and tender spleen may indicate diseases in which RBCs are rapidly breaking down. Quantities of Erythrocytes and Hemoglobin The RBC count and hemoglobin concentration are important clinical data because they determine the amount of oxygen the blood can carry. Three of the most common .