Prolonged exposure to extreme sun results in a rise in body temperature beyond the normal range resulting in a condition known as sunstroke. The body loses a lot of water in attempting to cool itself, causing inadequacy of the body water concentration and dehydration. This affects the body fluid and electrolyte balance (Maidment & Tipton, 2016). If not restored, imbalance results in complications and even death. The kidney attempts to restore the fluid and electrolyte homeostasis through the action of pituitary and adrenal hormones. Dehydration stimulates hypothalamus to signal the posterior pituitary to release antidiuretic hormone (ADH). ADH cause more aquaporin proteins to move to the surface of the renal tubules thereby increasing the permeability of collecting tubules to water, resulting in the reabsorption of water into the bloodstream. The kidney’s renin-angiotensin hormonal system through the active angiotensin II stimulates the thirst center of the hypothalamus. Aldosterone hormone secretion by the adrenal glands is stimulated by Angiotensin II. Aldosterone increases the reabsorption of sodium at the distal tubules. Reabsorption of sodium has a direct effect of increasing the reabsorption of water from the tubules into the bloodstream (Hall, 2015). The overall effect of these processes is the restoration of the fluid and electrolyte balance.
Water forms an important component of blood. Changes in fluid balance have a direct effect on blood osmolality and pressure. The kidneys are responsible for regulation of fluid balance and blood purification. Increased water loss e.g. through excessive release by the kidneys causes a decrease in blood pressure which is detected by the aortic baroreceptors. The heart is stimulated to increase its contractions to compensate for the low pressure, thereby increasing the cardiac output. The reverse happens when there is an increase in cellular fluid (Hall, 2015). The kidney relies on blood supply from the heart to perform its filtration and tubular functions properly. According to Damman and Testani (2015), the renal blood flow (RBF) affects the glomerular filtration rate (GFR), which is one of the main determinants of kidney function. RBF is dependent on the cardiac output, constituting approximately 20% of the cardiac output. Inadequate blood supply resulting from low cardiac output may cause kidney congestion.
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References
Damman, K., & Testani, J. M. (2015). The kidney in heart failure: an update. European heart journal , 36 (23), 1437-1444.
Hall, J. E. (2015). Guyton and Hall textbook of medical physiology e-Book . Elsevier Health Sciences.
Maidment, G., & Tipton, M. (2016). Human physiology in the thermal environment. Ernsting's Aviation and Space Medicine 5E , 189.
