Figure 44

Polymerization of sickle cell hemoglobin. This polymerization occurs in three stages: 1) nucleation, 2) fiber growth, and 3) fiber alignment. The end stage is a complicated structure for a helical fiber: four inner fibers surrounded by 10 outer filaments. Sickling, the process of polymerization, occurs under three different circumstances: 1) deoxygenation, 2) acidosis, and 3) extracellular hyperosmolality. These circumstances produce shrinking of the erythro-cytes that causes elevation of the intracellular hemoglobin concentration. This mechanism occurs in the inner medulla of the kidney and renal papillae as a result of countercurrent multiplication. Extracellular osmolality increases with the results previously mentioned [8].

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