The Song of the Cell: An Exploration of Medicine and the New Human

by Siddhartha Mukherjee

Back, then, to the sodium that you consumed. The excess sodium causes a hormonal system, regulated by the kidney and the adrenal gland, which sits just above the kidney, to decrease its signal. The cells in the tubule respond to these changes by excreting the excess sodium into urine, thereby discarding the salt and returning the sodium level to normal. The salt is also detected by specialized cells in the brain that monitor the overall concentration of salts in the blood, a property called osmolality. These cells, sensing a high osmolality, send out another hormone to cause the cells in the kidney to retain more water. As more water is absorbed into the body, the sodium level in the blood is diluted, and the concentration is reset—albeit at the cost of retaining more water overall. You might find your feet swollen the next morning—but you might well argue that the baccala was worth the shoes that don’t fit.