Chapter 9 Nutrients Involved in Fluid and Electrolyte Balance Body Fluid Is the Liquid Portion of Cells and Tissues 50 70 of a healthy adult s body weight is fluid Intracellular fluid 2 3 held within the walls of cells Extracellular fluid 1 3 flows outside of the cells o Interstitial fluid flows between the cells that make up a particular tissure or organ muscle fibers of the liver o Intravascular fluid water in the bloodstream and lymph plasma Not every tissue in the body contains the same amount of fluid o Lean tissues muscle are more than 70 fluid o Fat tissues 10 20 fluid Body fluid varies according to gender and age o Males have more lean tissue o Amount of body fluid as a percentage of total weight decreases with age Body Fluid Is Composed of Water and Dissolved Substances Called Electrolytes Electrolytes mineral salts dissolve in water the two component minerals separate and form electrically charged particles called ions o Negatively charged chloride and phosphorus o Positively charged sodium and potassium o Extracellular sodium and chloride o Intracellular potassium and phosphate Fluids Serve Many Critical Functions Solvent water capable of dissolving a wide variety of substances o Amino acids glucose water soluble vitamins minerals and some medications readily transported into the bloodstream o Fats do not dissolve in water to overcome this fatty substances such as lipids and the fat soluble vitamins are either attached to or surrounded by water soluble proteins so they can be transported in the blood to the cells too Blood Volume is the amount of fluid in blood o When rises inappropriately blood pressure increases o When decreases inappropriately blood pressure decreases Kidneys play a central role in the regulation of blood volume and blood pressure o ADH antidiuretic hormone stimulate the kidneys to reabsorb water and to reduce the production of urine o Renin activates blood protein called angiotensinogen produced in the liver o Angiotensin 2 vasoconstrictor works to constrictor the diameter of blood vessels results in an increase in blood pressure o Aldosterone signals the kidneys to retain sodium and chloride Fluids are vital to the body s ability to maintain its temperature within a safe range Water has a high capacity for heat o It takes a lot of energy to raise its temperature o Body fluids are our primary coolant o The sweat glands secrete more sweat from the skin Heat is released and the skin and underlying blood are cooled This cooler blood flows back to the body s core and reduces internal body temperature Fluids protect and lubricate the tissues o Cerebrospinal fluid that surround the brain and spinal column o Fetus in a mother s womb is protected by amniotic fluid o Synovial fluid lubricates joint o Tears cleanse and lubricate eyes o Saliva moistens the food we eat Electrolytes Support Many Body Functions Cells are permeable to water water flows easily through them Cell membranes are not freely permeable to electrolytes o Osmosis electrolytes attract water towards areas where they are concentrated Continues until concentration of solutes is equal on both sides of the cell membrane o Osmotic pressure pressure that is needed to keep the particles in a solution from drawing liquid toward them across the semipermeable membrane Nerve impulses are initiated at the membrane of a nerve cell in response to a change in the degree of electrical charge across the membrane o Depolarization influx of sodium into a nerve cell causes the cell to become slightly less negatively charged o Action potential an electrical signal that is then propagated along the length of the cell Only happens when enough sodium enters the cell the change in electrical charge triggers the action potential o Repolarization the release of potassium to the outside of the cell causes the cell membrane to return to its normal electrical state Muscles are stimulated to contract in response to stimulation of nerve cells How Does the Body Maintain Fluid Balance Thirst Mechanism o Consciously desire fluids Increased concentration of salt and other dissolved substances in the blood Reduction in blood volume and blood pressure Dryness in the tissues of the mouth and throat o This mechanism is NOT always sufficient The amount of fluid consumed may not be enough to achieve fluid balance Especially when body water is rapidly lost such as during intense exercise in the heat or high humidity Obtained through 3 primary sources beverages foods and the production of metabolic water by the body o Metabolic water the water formed from the body s metabolic reactions 10 14 of the water the body needs each day Sensible water loss urine output and sweating Insensible water loss water continuously evaporated from the skin even when a person is not consciously sweating also continuously exhaled from the lungs o Illnesses that involve fever coughing vomiting diarrhea and a runny nose o Traumatic injury internal hemorrhaging blood donation and surgery o Exercise increases fluid loss o Environmental conditions o Pregnancy increases fluid loss o Breastfeeding needs and increased fluid intake o Diuretics increases fluid loss via urine Ex alcohol Essential for life o Only survive a few days without The need for water varies greatly depending on age body size healthy status physical activity level and exposure to environmental conditions Carbonated water contains carbon dioxide gas that either occurs naturally or is added to the water Drinking too much water and becoming overhydrated is very rare Dehydration results when we do not drink enough water or are unable to retain the water we Water drink Sodium Major positively charged electrolyte in the extracellular fluid Exchange with potassium cross cell membranes allows cells to maintain proper fluid balance and regulate blood pressure and acid base balance Assists with the transmission of nerve signals and aids in muscle contraction and relaxation Absorption of glucose from the small intestine Ai for sodium is 1 5g day Processed foods contain large amounts of sodium High blood pressure is more common in people who consume high sodium diets Consuming excess amounts of sodium can increase urinary excretion of calcium bone loss Hypernatremia abnormally high blood sodium concentration o Congestive heart failure or kidney disease can t excrete sodium effectively o An abnormally high blood volume leading to edema and raising blood pressure Hyponatremia abnormally low blood sodium
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