H 2 O, Electrolytes and Acid-Base Balance

H 2 O, Electrolytes and Acid-Base Balance

Body Fluids Intracellular Fluid Compartment All fluid inside the cells 40% of body weight Extracellular Fluid Compartment All fluid outside of cells 20% of body weight Divide into many subcompartments synovial fluid, cerebrospinal fluid, interstitial fluid, plasma, and lymph

Regulation of Water Content Total volume of water in the body is constant Thirst Habit, social settings Baroreceptors Renin-angiotensin pathway stimulates thirst Increased osmolarity of extracellular fluids

Water Loss Urine Evaporation skin, respiratory, perspiration Feces Respiratory Water Loss Depends on temperature and air humidity, body temperature and volume of air expired Insensible perspiration water lost through skin Sensible perspiration SWEAT contains solutes secreted by sweat glands

Regulation of Extracellular Fluid Osmolarity Osmolarity Increases Thirst ADH secretion (no urine production Osmolarity Decreases Inhibits thirst Inhibits ADH

Regulation of Extracellular Fluid Volume 1. Neural Mechanisms Blood pressure increases, afferent arterioles dilate (less sympathetic stimulation), GFR increases, filtrate increases, urine increases 2. Renin-Angiotensin-Aldosterone Mechanism Increased bp from increased blood volume, decrease renin secretion, reducing angiotensin and eventually aldosterone, reduced aldosterone causes sodium to remain in the filtrate of distil convoluted tubule and collecting duct, osmolarity of filtrate increases, water remains in filtrate, urine production increases

Regulation of Extracellular Fluid Volume 2. Renin-Angiotensin-Aldosterone Mechanism (Cont.) Decreased blood volume causes decreased blood pressure, renin secretion increases, angiotensin pathway increases causing increased aldosterone secretion, increasing sodium reabsorption, increased water reabsorption, decreasing urine output the extra water increases blood pressure

Regulation of Extracellular Fluid Volume 3. Atrial Natriuretic Hormone (ANH) Increase in blood volume stimulates ANH, sodium is excreted with water 4. Antidiuretic Hormone (ADH) Large increase in blood pressure, decrease in ADH, less water reabsorbed in distil convoluted tubule and collecting duct, greater urine output Decrease in blood pressure, increase ADH secretion, more water retained, less urine output

Regulation of Sodium Ions Kidneys maintain sodium ion balance Control occurs in distil convoluted tubule and collecting ducts Aldosterone functions to keep sodium ions Extracellular fluid osmolarity Osmolarity too high, not enough water, ADH secretion (no urine) and thirst Osmolarity too low, too much water, ADH shut off (urine produced) and not thirsty Increased bp causes sodium and water excretion, decrease bp causes sodium and water to remain in body ANH produced when bp rises causing sodium excretion and greater urine output Hypernatremia elevated plasma sodium Hyponatremia reduced plasma sodium

Chloride Regulation of Ions Mechanisms used to control cation concentrations regulate chloride levels; anions are attracted to cations Potassium Tightly maintained because of membrane potentials Hyperkalemia high extracellular potassium levels Hypokalemia low extracellular potassium levels Potassium is actively secreted in distil convoluted tubule and collecting ducts highly controlled Aldosterone promotes potassium secretion and sodium and water reabsorption

Regulation of Calcium Ions Hypocalcemia below normal extracellular level of calcium ions Hypercalcemia higher extracellular level of calcium ions Kidneys, bones, and intestinal tract maintain calcium levels Parathyroid Hormone (PTH) increases calcium ion levels and decreases phosphate levels Greater osteoclast activity Converts vitamin D to active vitamin D to increase calcium absorption in the intestines Calcitonin decreases calcium ion levels Increases osteoblast activity and decreases osteoclast activity Not as important as PTH in calcium regulation

Magnesium Regulation of Ions Hypomagnesemia below normal levels of blood Mg Hypermagnesemia above normal levels of blood Mg Phosphate Found in phospholipids, protein, DNA, RNA, ATP and carbohydrates Kidneys regulate excretion and absorption PTH causes phosphate to be excreted in urine Hypophosphatemia below normal levels of phosphate Hyperphosphatemia above normal levels of phosphate

Acid Base Balance Regulation Buffers are almost instant in working to prevent ph changes Respiratory regulation Renal regulation Kidneys regulate H + secretion and HCO 3- reabsorption Low ph of body fluids causes H + secretion and HCO 3 - reabsorption H + is antiported with sodium as sodium is reabsorbed from the filtrate Sodium and HCO 3- are symported through the basal membrane of the tubule and eventually pass into the blood H + combines with buffers, HCO 3-, HPO 4 2-, and NH 3 within the filtrate High ph of body fluids causes H + secretion to decrease and HCO 3- reabsorption decreases