Chapter 27: Fluid, Electrolyte and Acid-Base HomeostasisChapter ObjectivesFLUID COMPARTMENTS AND FLUID BALANCEELECTROLYTES IN BODY FLUIDACID-BASE BALANCEChapter Lecture NotesIntroductionIn lean adults body fluids comprise about 55-60% of total body weight. (Fig 27.1)Only 2 places for exchange between compartments:Fluid and Solute BalanceFluid balance primarily means water balance, but also implies electrolyte balance; the two are inseparable.Osmosis is the primary way in which water moves in and out of body compartments. The concentrations of solutes in the fluids are major determinants of fluid balanceIntracellular and interstitial fluids normally have the same osmolarity, so cells neither swell nor shrinkdrinking plain water faster than kidneys can excrete it replace water lost from diarrhea or vomiting with plain waterosmolarity of plasma and interstitial fluid falls below cells, cells may swell and burstBody Water Gain and LossBody water = 45-75% body weightdeclines with age since fat contains almost no waterNormally loss = gain (Fig 27.2)dehydration - water loss is greater than water gainRegulation of fluid gain is by regulation of thirst (Fig 27.3)One mechanism for stimulating the thirst center in the hypothalamus is the renin-angiotensin II pathwayUnder normal conditions, urine production fluid output (loss) is adjusted by (Fig 27.4& Table 27.1)antidiuretic hormone (ADH)atrial natriuretic peptide (ANP)aldosteroneElectrolytes in Body Fluids (Table 27.2)Electrolytes serve four general functions in the bodyelectrolytes control the osmosis of water between body compartments because they are more numerous than nonelectrolytesmaintain the acid-base balance required for normal cellular activitieselectrolytes can be cofactors needed for optimal activity of enzymes.Intracellular fluid, interstitial fluid and blood plasma differ considerably from each other in electrolyte concentrations. (Fig 27.6 & Table 27.2) Blood plasma contains many proteins, but interstitial fluid does notproduces blood colloid osmotic pressureInterstitial fluid and blood plasma contains Na+ and Cl-Intracellular fluid contains K+ and phosphates (HPO4 2-)Most abundant extracellular ionHormonal that control sodium levels Aldosterone ADH ANP Sodium retention causes water retentionCaused by renal failure or hyperaldosteroneEdema - abnormal accumulation of interstitial fluidExcessive loss of sodium causes excessive loss of water Due to inadequate secretion of aldosterone or too many diuretics hypovolemia=low blood volumeChloride (Cl-)Most prevalent extracellular anionMoves easily between compartments due to Cl- leakage channelsHelps balance anions in different compartmentsChloride shift across red blood cells with buffer movementIt plays a role in forming HCl in the stomach Regulationpassively follows Na+ so it is regulated indirectly by aldosterone levelsADH helps regulate Cl- in body fluids because it controls water loss in urinePotassium (K+)The most abundant cation in intracellular fluid. It is involved in maintaining fluid volume nerve impulse conductionmuscle contractionExchanged for H+ to help regulate pH in intracellular fluidThe plasma level of K+ is under the control of mineralocorticoids, mainly aldosterone.Bicarbonate (HCO3-)It is a significant plasma anion in electrolyte balance (Fig 27.8)It is a major component of the plasma acid-base buffer systemKidneys are main regulator of plasma levelsCalcium (Ca2+)The most abundant ion in the body, principally an extracellular ion It is a structural component of bones and teeth. Important role in blood clotting neurotransmitter release muscle tonenerve and muscle functionRegulated by parathyroid hormonestimulates osteoclasts to release calcium from boneincreases production of calcitriol (Ca2+ absorption from GI tract and reabsorption from glomerular filtrate)PhosphatePresent as calcium phosphate in bones and teeth, and in phospholipids, ATP, DNA and RNAHPO4 2- is important intracellular anion and acts as buffer of H+ in body fluids and in urine Plasma levels are regulated by parathyroid hormone & calcitriolMagnesium (Mg2+)Primarily an intracellular cation Activates several enzyme systems involved in the metabolism of carbohydrates and proteins Needed for operation of the sodium-potassium pump It is also important inneuromuscular activity neural transmission within the central nervous system myocardial functioningAcid-Base BalanceThe overall acid-base balance of the body is maintained by controlling the H+ concentration of body fluids, especially extracellular fluid3 major mechanisms to regulate pH (Table 27.3)buffer systemsexhalation of CO2 (respiratory system)kidney excretion of H+ (urinary system)Buffer systems prevent rapid, drastic changes in pH in body fluids3 principal buffer systemsprotein buffer systemhemoglobin very good at buffering H+ in RBCs albumin is main blood plasma protein buffercarbonic acid-bicarbonate buffer system bicarbonate ion (HCO3-) can act as a weak baseholds excess H+carbonic acid (H2CO3) can act as weak aciddissociates into H+ ionsphosphate buffer systemmost important intracellularly, but also acts to buffer acids in the urine dihydrogen phosphate ion acts as a weak acid that can buffer a strong basemonohydrogen phosphate acts a weak base by buffering the H+ released by a strong acidAcid-Base ImbalancesAcidosis - blood pH below 7.35Acidosis causes depression of CNS - comaAlkalosis - blood pH above 7.45Alkalosis causes excitability of nervous tissue - spasms, convulsions & deathRespiratory acidosis and respiratory alkalosis are primary disorders of blood PCO2 (Table 27.4)Metabolic acidosis and metabolic alkalosis are primary disorders of bicarbonate concentrationChapter 27: Fluid, Electrolyte and Acid-Base Homeostasis Chapter Objectives FLUID COMPARTMENTS AND FLUID BALANCE 1. Describe the various fluid compartments of the body and tell where fluid can move between them. 2. Discuss the effect of osmolarity on water movement between compartments. 3. Define water intoxication and describe possible causes. 4. Discuss the sources of water gain and its avenues for loss. 5. Define the processes available for fluid intake and how they are regulated. 6. Indicate how ADH, Angiotensin II, Aldosterone and ANP act on organ systems to control the rate of fluid loss. ELECTROLYTES IN BODY FLUID 7. Discuss the four general functions of electrolytes in the body. 8. Contrast the electrolyte concentrations of the three major fluid