Water in the Body Page 373-375 Water = ~50 to 70% of body weight, depending on body fat % (higher body fat=lower water content) Major fluid compartments: Intracellular fluid: cytoplasm of cells is an aqueous (watery) solution. It is thicker than water (think egg whites) because there are lots of other molecules dissolved in it Extracellular fluid: like inside cells, the fluid bathing the outsides of cells is a watery milleau (pronounced Milyu ) extra cellular fluid consists of the fluid in between cells and the fluid that is found in the circulatory systems (blood plasma and lymph). interstitial fluid: the fluid in between cells Plasma: blood stream and lymph fluid Water travels freely between these compartments by osmosis through plasma membranes of the cells. See page 374 for a nice explanation of how osmosis works if you don t remember from chemistry. 1
Functions of Water Page 375-376 Heat capacity water tends to resist changes in temperature. It is not considered a volatile substance. And it takes quite a bit of energy to raise a gram of water 1 degree Celsius. Thermoregulation as related to heat capacity to keep temps stable, but also involved in evaporative cooling Solvent polar and ionic substances will dissolve in water helps rid the body of wastes helps carry substances around the body into and out of compartments Provides a solution for chemical rxns to occur ph can be an acid or a base (donate protons and hydroxides) go back to chemistry lecture for a recap on ph if you need it 2
Water Balance p. 376-380 Fluid input: adults need about 8 cups of water a day Beverages (~4 c./day) most beverages are mostly water (99%+) Foods(~4c./day) many foods are also mostly water (50-90%) see table on page 376 for water content of some foods even dry foods often contain SOME water (i.e. bread, cereal) Metabolism (h2o from ETC ~1.5c./day) Fluid output (excretion) Kidneys-urine (~5.5c./day) Mammary glands-milk (~20-40oz./day[3-5c.]- varies widely- depends on age of infant, health of mother, etc.) Nursing mothers need to increase water intake!!! Feces-water (~0.6c./day)- increases with malabsorption (i.e. diarrhea- must increase water intake to keep hydrated- this is how diarrhea kills!!!) Skin-sweat (~2c./day, but varies widely) Lungs-water vapor (~1.7c./day, also varies- increases if respiratory rate increases for ex. with exercise, etc.) Hormonal effects Antidiuretic hormone (ADH): released by pituitary gland- causes kidneys to conserve water and reduce urine production Aldosterone: released by the adrenal glands- causes kidneys to retain more sodium and chloride (and thus, more water) Substances that affect water balance Alcohol, caffeine, and diuretic medications cause the body to lose water. 3
Mineral Bioavailability Page 381-382 Mineral bioavailability is affected by several factors Minerals are generally only absorbed if they are needed by the body s cells at the time they pass through the GI Other minerals with similar size and elemental properties can compete for absorption Vitamins can increases or decrease mineral absorption Phytate in fiber and oxalate can limit some mineral absorption 4
Semi-Permeable Membrane H 2 O CO 2 O 2 Lipids Flow directly through phospholipid bilayer Ca + Mg 2+ H + Glucose (sugars) Cannot flow through phospholipid bilayer This slide is just here as a refresher about how substances cross phospholipid membranes. Recall that some substances cross by simple diffusion (through the membrane directly- no ATP-down their concentration gradient) -some (ions and large molecules) must cross by facilitated diffusion (through membrane protein channels- no ATP- down their concentration gradient) Also, if they need to go against their concentration gradient: -they must cross by active transport (using membrane protein PUMPS- requires ATPagainst their concentration gradients) 5
Sodium (Na+) Page 383-386 Functions Fluid balance Nerve impulse transmission Food sources and recommended intake Salt Processed and convenience foods Limit to 2,400 milligrams/day (DV) 6
Potassium (K+) Functions Muscle contraction (see sodium/potassium pump-last slide) Nerve impulse transmission (see next slide) Fluid balance Food sources Unprocessed foods: fruits, vegetables, grains 7
Action Potential Function of sodium and potassium in action potentials 8
Chloride (Cl-) Page 388 Functions of chloride Fluid balance Hydrochloric acid (stomach acid) Food sources of chloride Table salt 9
Calcium (Ca 2+ ) Page 389-399 Functions Bone structure (major storage of calcium in bones) The hard part of bone is made of hydroxyapatite - Ca 10 (PO 4 ) 6 OH 2 Blood clotting A blood clot consists of a plug of platelets enmeshed in a network of insoluble fibrin molecules. Platelet aggregation and fibrin formation both require the proteolytic enzyme thrombin. Clotting also requires: calcium ions (Ca2+)(which is why blood banks use a chelating agent to bind the calcium in donated blood so the blood will not clot in the bag). Nerve impulse transmission, muscle contraction (see next two slides for overview) Food sources Milk and dairy products Green vegetables, tofu, fortified foods 10
Muscle Contraction Overview 11
The Molecular Basis of Contraction 12
Phosphorus (P) Page 400-401 Functions Bone structure (remember hydroxyapatite - Ca 10 (PO 4 ) 6 OH 2???) Component of ATP, DNA, RNA, phospholipids Food sources Meat, milk, eggs Processed foods 13
Magnesium (Mg 2+ ) Page 401-402 Functions DNA and protein synthesis Blood clotting, muscle contraction, ATP production Food sources Whole grains, vegetables, legumes, tofu, seafood 14