let's learn about fluids and electrolytes water balance the average adult human body is about 60% water the water is located in two distinct areas or compartments in the body the majority of water is located in the cells this is known as the intracellular compartment and holds about 65% of the total water in the body water located outside of the cells occupies the extracellular compartment which holds the remaining 35% the extracellular compartment consists of several subcompartments these include the tissue fluid blood plasma and lymph and transcellular fluid transcellular fluid includes the cerebrospinal sovial peronal plural and pericardial fluids as well as the vitous and aquous humors of the eye digestive fluids in bile and fluids in the urinary and respiratory tracts water moves between these compartments through semi-permeable membranes for water to be in balance in the body the gains and losses must be equal the body gains fluids in several ways metabolism such as aerobic respiration produces a about 200 mL of water each day water is also gained by food about 700 Ms and drink about 1,600 Ms fluid is lost via feces 200 M respiration 300 M evaporation 400 m sweat 100 m and the majority via urine 1500 Ms the body gains and loses about 2500 mL of water each day water balance is regulated by several mechanisms for example when we exercise osmo receptors in the hypothalamus sensing changes in blood concentration part of the extracellular compartment send messages to the posterior pituitary gland to secrete antidiuretic hormone or ADH ADH targets the kidneys to promote retention of water the hypothalamus also sends messages to the cerebral cortex to produce the sensation of thirst only a 2 to 3% increase in osmolarity can produce thirst a 10 to 15% loss of blood can also produce thirst satiation occurs when the blood osmolarity decreases along with Cooling and moistening of the mouth and distension of the stomach a disorder of water balance is hypovolemia or dehydration this occurs when the output of water exceeds the input the concentration or osmolarity of the extracellular fluid increases drawing water out of the cells by osmosis severe dehydration can affect many cells of the body including the neurons and lead to shock in water intoxication the gain of water exceeds the loss the extracellular compartment becomes hypotonic causing water to move into the cells by osmosis water intoxication can lead to pulmonary and brain edema I hope you've learned something about water balance and see you next time time