Water, Electrolytes, and Chapter 27 Water, Electrolytes, and Acid-Base Balance

Regulation of Water Content Sources of water Ingestion Cellular metabolism Routes of water loss Urine Evaporation Perspiration Respiratory passages Feces Content regulated so total volume of water in body remains constant Kidneys are primary regulators of water excretion Regulation processes Osmosis Osmolality Baroreceptors Learned behavior

Extracellular Fluid Osmolality Measure of water vs. solute concentration; the higher the solute concentration, the higher the osmolality Adding or removing water from a solution changes osmolality Increased osmolality: triggers thirst and ADH secretion Decreased osmolality: inhibits thirst and ADH secretion

Hormonal Regulation of Blood Osmolality

Regulation of ECF Volume ECF can increase or decrease even if osmolality of extracellular fluid is maintained Carotid sinus and aortic arch baroreceptors monitor blood pressure, juxtaglomerular apparatuses monitor pressure changes, receptors in walls of atria and large vessels respond to small changes in BP These receptors activate these mechanisms Neural: increase in BP recognized by baroreceptors. Decreased sympathetic stimulation leads to increased pressure in glomerulus leading to increased filtration and increased urine output. Renin-angiotensin-aldosterone Atrial natriuretic hormone (ANH) Antidiuretic hormone (ADH)

Increase in Blood Volume

Decrease in Blood Volume

Regulation of ECF Volume

Regulation of Electrolytes in ECF Regulation of Na+ ions Kidneys major route of excretion Small quantities lost in sweat {sweat = (in decreasing amounts) water, Na+, urea, Cl-K+, NH3}. Insensible perspiration is water evaporating from skin. Sensible perspiration is secreted by the sweat glands. Contains solutes Terms Hypernatremia: elevated plasma Na+ Hyponatremia: decreased Na+ Electrolytes Molecules or ions with an electrical charge Ingestion adds electrolytes to body Kidneys, liver, skin, remove from body Concentration changes only when growing, gaining or losing weight Na+ Ions Dominant ECF cations Responsible for 90-95% of osmotic pressure

Regulation of Chloride, Potassium, Magnesium Ions Potassium ions Maintained in narrow range Affect resting membrane potentials Aldosterone increases amount secreted Terms Hyperkalemia: abnormally high levels of potassium in extracellular fluid Hypokalemia: abnormally low levels of potassium in extracellular fluid. Chloride ions Predominant anions in ECF Magnesium ions Capacity of kidney to reabsorb is limited Excess lost in urine Decreased extracellular magnesium results in greater degree of reabsorption

Potassium Ion Regulation in ECF

Regulation of Calcium Ions PTH increases Ca2+ extracellular levels and decreases extracellular phosphate levels Vitamin D stimulates Ca2+ uptake in intestines Calcitonin decreases extracellular Ca2+ levels Regulated within narrow range Elevated extracellular levels prevent membrane depolarization Decreased levels lead to spontaneous action potential generation Terms Hypocalcemia Hypercalcemia

Regulation of Calcium Ions

Regulation of Blood Magnesium

Acids and Bases and Buffers Buffers: Resist changes in pH When H+ added, buffer removes it When H+ removed, buffer replaces it Types of buffer systems Carbonic acid/bicarbonate Protein Phosphate Acids Release H+ into solution Bases Remove H+ from solution Acids and bases Grouped as strong or weak

Comparison of Strong and Weak Acids

Regulation of Acid/Base Balance Buffers: if pH rises, buffers bind H+; if pH falls, buffers release H+ Protein buffer: Intracellular and plasma proteins absorb H+. Provide ¾ of buffering in body. E.g., hemoglobin. Bicarbonate buffering system: Important in plasma Phosphate buffer system: important as an intracellular buffer Respiratory center: if pH rises, respiratory rate decreases; if pH falls, respiratory rate increases Kidneys: if pH rises, distal tubule decreases H+ secretion into the urine; if pH falls, distal tubule increases H+ secretion into the urine

Increase in Blood pH

Decrease in Blood pH

Respiratory Regulation of Acid-Base Balance Achieved through carbonic acid/bicarbonate buffer system As carbon dioxide levels increase, pH decreases As carbon dioxide levels decrease, pH increases Carbon dioxide levels and pH affect respiratory centers Hypoventilation increases blood carbon dioxide levels Hyperventilation decreases blood carbon dioxide levels

Respiratory Regulation of Acid-Base Balance

Kidney Regulation of Acid-Base Balance

Acidosis and Alkalosis Acidosis: pH body fluids below 7.35 Respiratory: Caused by inadequate ventilation- reduced elimination of CO2, asthma, damage to respiratory center in brain, emphysema. Metabolic: Results from all conditions other than respiratory that decrease pH- diarrhea, vomiting, ingesting overdose of aspirin, untreated diabetes mellitus, anaerobic respiration Alkalosis: pH body fluids above 7.45 Respiratory: Caused by hyperventilation, high altitude (reduced partial pressure of O2 Metabolic: Results from all conditions other than respiratory that increase pH- severe vomiting, too much aldosterone, ingestion of substances like bicarbonate of soda.