![]() ![]() If blood osmolality increases above its ideal value, the hypothalamus transmits signals that result in a conscious awareness of thirst. Osmoreceptors are sensory receptors in the thirst center in the hypothalamus that monitor the concentration of solutes (osmolality) of the blood. As the blood becomes more concentrated, the thirst response-a sequence of physiological processes-is triggered ( Figure 26.2.1). The water that leaves the body, as exhaled air, sweat, or urine, is ultimately extracted from blood plasma. So how is water intake regulated by the body? Consider someone who is experiencing dehydration, a net loss of water that results in insufficient water in blood and other tissues. A healthy body maintains plasma osmolality within a narrow range, by employing several mechanisms that regulate both water intake and output.ĭrinking water is considered voluntary. A person’s plasma osmolality value reflects his or her state of hydration. Plasma osmolality is thus the ratio of solutes to water in blood plasma. Osmolality is the ratio of solutes in a solution to a volume of solvent in a solution. This type of water loss is called insensible water loss because a person is usually unaware of it. Water is lost through the skin through evaporation from the skin surface without overt sweating and from air expelled from the lungs. The kidneys can regulate water levels in the body they conserve water if you are dehydrated, and they can make urine more dilute to expel excess water if necessary. The kidneys also can adjust blood volume though mechanisms that draw water out of the filtrate and urine. Additionally, each day about the same volume (2500 mL) of water leaves the body by different routes most of this lost water is removed as urine. Although most of the intake comes through the digestive tract, about 230 mL (8 ounces) per day is generated metabolically, in the last steps of aerobic respiration. On a typical day, the average adult will take in about 2500 mL (almost 3 quarts) of aqueous fluids. Define dehydration and identify common causes of dehydration.Describe the role of ADH and aldosterone and their effect on body water levels.Identify the main route by which water leaves the body.Explain how water levels in the body influence the thirst cycle.By the end of this section, you will be able to:
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