Anatomy and Physiology Part 1b: Body Fluid Ions, and Water Balance Marieb’s Human Anatomy and Physiology Ninth Edition Marieb w Hoehn Chapter 26 Fluid, Electrolytes, and Acid-Base Balance Lecture 17 Part 1b: Body Fluid Ions, and Water Balance Slides 1-15; 80 min (with review of syllabus and Web sites) [Lecture 1] Slides 16 – 38; 50 min [Lecture 2] 118 min (38 slides plus review of course Web sites and syllabus)

Body Fluid Ionic Composition ECF major ions: - sodium, chloride, and bicarbonate ICF major ions: - potassium, magnesium, and phosphate (plus negatively charged proteins) Figure from: Hole’s Human A&P, 12th edition, 2010 You should know these chemical symbols and charges (valences) of ions

Movement of Fluids Between Compartments Figure from: Hole’s Human A&P, 12th edition, 2010 Water moves across mesothelial surfaces: peritoneal, pleural, and pericardial cavities as well as the synovial membranes. It also moves between the blood and CSF and through the fluids of the eye and ear Net movements of fluids between compartments result from differences in hydrostatic and osmotic pressures

Fluid (Water) Balance Figure from: Hole’s Human A&P, 12th edition, 2010 * urine production is the most important regulator of water balance (water in = water out)

Water Balance and ECF Osmolarity Regulation of water intake increase in osmotic pressure of ECF → osmoreceptors in hypothalamic thirst center → stimulates thirst and drinking (water! ) Regulation of water output Obligatory water losses (must happen) insensible water losses (lungs, skin) water loss in feces water loss in urine (min about 500 ml/day) increase in osmotic pressure of ECF → ADH is released small volume of concentrated urine is excreted more water is retained LARGE changes in blood vol/pressure → Renin and ADH release

Fluid Imbalance Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

Dehydration Dehydration (removing only H2O) osmotic pressure increases in extracellular fluids water moves out of cells osmoreceptors in hypothalamus stimulated hypothalamus signals posterior pituitary to release ADH urine output decreases Severe thirst, wrinkling of skin, fall in plasma volume and decreased blood pressure, circulatory shock, death

Overhydration Overhydration (adding only H2O) osmotic pressure decreases in extracellular fluids water moves into cells osmoreceptors inhibited in hypothalamus hypothalamus signals posterior pituitary to decrease ADH output urine output increases ‘Drunken’ behavior (water intoxication), confusion, hallucinations, convulsions, coma, death

Review There are two major forces affecting movement of fluid between compartments Hydrostatic Pressure Osmotic Pressure Fluid balance Amount of water you take in is equal to the amount of water you lose to the environment Intake of water in food/drink is the most important source of fluid Kidney regulation of water is the most important regulator of water loss