Water Homeostasis PDF

# Disturbances of Water Homeostasis - Gain or loss of extracellular fluid volume - Gain or loss of solute ## Four specific examples of water homeostasis: - Hypervolemia - Overhydration - Hypovolemia - Dehydration ## Water homeostasis - **Hypervolemia**: Occurs when too much water and solute at t...

# Disturbances of Water Homeostasis - Gain or loss of extracellular fluid volume - Gain or loss of solute ## Four specific examples of water homeostasis: - Hypervolemia - Overhydration - Hypovolemia - Dehydration ## Water homeostasis - **Hypervolemia**: Occurs when too much water and solute at the same time. Although extracellular fluid volume increases, plasma osmolarity may remain normal. - **Hypovolemia**: Occurs when water and solutes are lost at the same time. This condition primarily involves a loss of plasma volume. Plasma osmolarity usually remains normal, even though the volume is low. Too much IV fluids can increase plasma volume dramatically, but with an isotonic solution, the plasma osmolarity would remain normal and result in hypervolemia. - **Overhydration**: Occurs when too much water is taken by drinking without solute. Volume increases, but because solute is not present, plasma osmolarity decreases. - **Dehydration**: When water, but not solute, is lost, dehydration occurs. Dehydration involves a loss of volume but, because solutes are not lost in the same proportion, plasma osmolarity increases. ## Mechanisms of Fluid Balance The body has mechanisms that regulate fluid levels within a narrow range, the body fluids remain within certain physiological limits, an important aspect of homeostasis. Four primary mechanisms regulate fluid homeostasis: - Antidiuretic hormone or ADH - Thirst mechanism - Aldosterone - Sympathetic nervous system ## Water Intake and Water Output - **Water Intake**: Water is supplied to the body by the following processes: - Dietary liquids - Solid foods - Oxidation of foodstuffs: It is obtained from the combustion of fats, proteins and carbohydrates. The oxidation of fats yields 107 ml/100 gm, proteins 41 ml/100 gm, and carbohydrates 56 ml/100 gm. - **Water output**: Water is lost from the body by the following routes: - Urine - Respiration - Lactation - Feces - Evaporation from skin and lungs - Eyes (tears) | Water Intake | | Water Loss | |---|---|---| | **Drinks** | 48% | 1350 ml | | **Solid** | 40% | 900 ml | | **Oxidation of food** | 12% | 450 ml | | **Total** | **100%** | **2700 ml** | | **Lungs** | 12% | 500 ml | | **Skin** | 24% | 700 ml | | **Urine** | 56% | 1400 ml | | **Faeces** | 8% | 100 ml | | **Total** | **100%** | **2700 ml** | ## Functions of Water - **Solvent** - **Catalytic action** - **Lubricating actions** - **Heat regulation** ## Introduction - Water is an essential body constituent, and homeostatic processes are important to ensure that the total water balance is maintained within narrow limits, and the distribution of water among the vascular, interstitial, and intracellular compartments is maintained. - The body maintains a balance of water intake and output by a series of negative feedback loops involving the endocrine system and autonomic nervous system. ## Distribution of Water The Total Body Water (TBW) contributes about 60 percent of the total body. Two-thirds of the water are in the Intra Cellular Fluid (ICF), and one-third is in the Extra Cellular Fluid (ECF). Because the plasma membrane of most cells is highly permeable to water, ICF and ECF are in osmotic equilibrium. The ECF is divided into a vascular compartment (plasma) and an interstitial fluid compartment. - Total body water = 0.6 × (body weight) - ICF = 0.4 × (body weight) - ECF = 0.2 × (body weight)