Discussion Post
Fluid can enter the body as preformed water, ingested food and drink, and, to a lesser extent, as metabolic water that is produced as a byproduct of aerobic respiration and dehydration synthesis. A constant supply is needed to replenish the fluids lost through normal physiological activities such as respiration, sweating, and urination. Water generated from the biochemical metabolism of nutrients provides a significant proportion of the daily water requirements for some arthropods but it provides only a small fraction of a human's necessary intake. In the normal resting state the input of water through ingested fluids is approximately 2500 ml/day. Body water homeostasis is regulated mainly through ingested fluids which in turn depends on thirst. Thirst is the basic instinct or urge that drives an organism to ingest water. Thirst is a sensation created by the hypothalamus or the thirst center of the human body. Thirst is an important component of blood volume regulation which is slowly regulated by homeostasis. Fluid can leave the body in three ways. Urination, Excretion and Perspiration. The majority of fluid output occurs from urination, at approximately 1500 ml/day in a normal adult at resting state. Some fluid is lost through perspiration and as water vapor in expired air however these fluid losses are considered to be very minor. The body's homeostatic control mechanisms maintain a constant internal environment to ensure that a balance between fluid gain and fluid loss is maintained. The hormones ADH and aldosterone, which is a hormone created by the reninangiotensin system that play a major role in this balance. If the body is becoming fluid deficient, there will be an increase in the secretion of these hormones that causes water to be retained by the kidneys through increased tubular reabsorption and urine output to be reduced. Conversely if fluid levels are excessive the secretion of these hormones is suppressed and results in less retention of fluid by the kidneys and a subsequent increase in the volume of urine produced due to reduced fluid retention.
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