Water Chapter 8 PDF

# Water Dr Hadeel Alsufiani ## Chapter outline - Introduction - Water balance and recommended intake - Fluid and electrolyte balance ## Introduction - Water is an essential nutrient, more important to life than any of the others. - Water constitutes about 60% of an adult's body weight and a hig...

# Water Dr Hadeel Alsufiani ## Chapter outline - Introduction - Water balance and recommended intake - Fluid and electrolyte balance ## Introduction - Water is an essential nutrient, more important to life than any of the others. - Water constitutes about 60% of an adult's body weight and a higher percentage of a child's. - The body maintains an appropriate balance and distribution of fluids with the help of another class of nutrients - the minerals. - In the body, water is the fluid in which all life processes occur. The water in the body fluids: - Carries nutrients and waste products throughout the body - Participate in metabolic reactions - Maintains blood volume - Aids in the regulation of body temperature - Serve as the solvent for minerals, vitamins, amino acids, glucose and many other molecules so they can participate in metabolic reactions - Act as a lubricant and cushion around joints and inside the eyes, the spinal cord, and, in pregnancy, the amniotic sac surrounding the fetus in the womb. ## Water balance and recommended intakes - Fluid inside cells is called intracellular fluid, whereas fluid outside cells is called extracellular fluid. - Every cell contains fluid of the exact composition that is best for that cell. - The composition of intracellular and extracellular fluids differ from each other. - They continuously lose and replace their components, yet the composition in each compartment remains remarkably constant under normal conditions. - Because imbalances can be devastating, the body quickly responds by adjusting both water intake and excretion as needed. - Consequently, the entire system of cells and fluids remains in a delicate, but controlled, state of homeostasis. ## Water intake Thirst and satiety influence water intake in response to changes sensed by the mouth, hypothalamus, and nerves. | Water sources | Amount (ml) | |---|---| | Beverages | 550 to 1500 | | Foods | 700 to 1000 | | Metabolism | 200 to 300 | | Total | 1450 to 2800 | ## Water losses | Water losses | Amount (ml) | |---|---| | Kidneys (urine) | 500 to 1400 | | Skin (Sweat) | 450 to 900 | | Lungs (breath) | 350 | | GI tract (feces) | 150 | | Total | 1450 to 2800 | ## Dehydration and Water intoxication - **Dehydration:** The condition in which body water output exceeds water input. - Symptoms include thirst, dry skin and mucous membranes, rapid heartbeat, low blood pressure, and weakness. - **Water intoxication:** The rare condition in which the body water contents are too high in all body fluid compartments. ## Water recommendations - The recommended water intake for a person who expends 2000 kcalories a day, then, is 2 to 3 liters of water (about 8 to 12 cups). - This recommendation is in line with the adequate intake (AI) for total water set by the DRI. ## Fluid and electrolyte balance Maintaining a balance of about two-thirds of the body fluids inside the cells and one-third outside is vital to the life of the cells. - As the figure shows, some electrolytes reside primarily outside the cells. - Whereas others reside predominantly inside the cells. - Cell membranes are selectively permeable, meaning that they allow the passage of some molecules, but not others. - If too much water to enter the cells, they might rupture; if too much water to leave, they would collapse. - To control the movement of water, the cells direct the movement of the major minerals - sodium, chloride, potassium, calcium, phosphorus, magnesium and sulfur. - Whenever electrolytes move across the membrane, water follows. # The End