Presentation on theme: "Chapter 27: Fluid, electrolyte, and acid-base homeostasis"— Presentation transcript:
1 Chapter 27: Fluid, electrolyte, and acid-base homeostasis Copyright 2009, John Wiley & Sons, Inc.
2 Body fluidall the water and dissolved solutes in the body’s fluid compartmentsMechanisms regulatetotal volumedistributionconcentration of solutes and pHRegulatory mechanisms insure homeostasis of body fluids since their malfunction may seriously endanger nervous system and organ functioning.
3 Balance Between Fluid Compartments About 55%(female) or 60%(male)of total body massIntracellular fluid (ICF) –about 2/3of body fluidExtracellular fluid (ECF):-Interstitial fluid- about 80%of ECF- Plasma in blood- about 20%- Also includes lymph, CSF, synovial fluid, aqueous humor, vitreous body, endolymph, perilymph, pleural, pericardialand peritoneal fluidsVolume of fluid in each is kept constant. Since water follows electrolytes, they must be in balance as wellOnly 2 places for exchange between compartments:Cell/plasma membranes separate intracellular from interstitial fluid.only in capillaries are walls thin enough for exchange between plasma and interstitial fluidsPrinciples of Human Anatomy and Physiology, 11e
4 Copyright 2009, John Wiley & Sons, Inc. Fluid BalanceFluid balance means that the various body compartments contain the required amount of water, proportioned according to their needs.Fluid balance = water balance = electrolyte balance → inseparable.Osmosis is the primary way in which water moves in and out of body compartments. Solute concentration in the fluids is therefore a major determinant of fluid balance.Most solutes in body fluids are electrolytes, compounds that dissociate into ions.2 barriers separate ICF, interstitial fluid and plasmaPlasma membrane separates ICF from surrounding interstitial fluidBlood vessel wall divide interstitial fluid from plasmaWater- largest single component of the body≈ 45-75% of total body massInfants have low body fat, low bone mass, and are 73% or more waterTotal water content declines throughout life≈ 60%(males) & 50%(females)Difference due to > body fat & < amount of skeletal muscle in femalesIn old age, only about 45% of body weight is waterContinual exchange of water and solutes among compartments via filtration, reabsorption, diffusion, and osmosisCopyright 2009, John Wiley & Sons, Inc.
5 Sources of Body Water Gain and Loss Fluid balance related to electrolyte balanceIntake of water and electrolytes rarely proportionalKidneys excrete excess water through dilute urine or excess electrolytes through concentrated urineBody can gain water byIngestion of liquids and moist foods (2300mL/day)Metabolic synthesis of water during cellular respiration and dehydration synthesis (200mL/day)Body loses water throughKidneys (1500mL/day)Evaporation from skin (600mL/day)Exhalation from lungs (300mL/day)Feces (100mL/day)Normally loss = gainCopyright 2009, John Wiley & Sons, Inc.
6 Daily Water Gain and Loss Copyright 2009, John Wiley & Sons, Inc.
7 Regulation of body water gain Metabolic water volume depends mostly on the level of aerobic cellular respiration, which reflects the demand for ATP in body cells.The main way to regulate body water balance is by adjusting the volume of water intake.Dehydration – when water loss is greater than gainDecrease in volume, increase in osmolarity of body fluidsStimulates thirst center in hypothalamusRegulation of fluid gain is by regulation of thirstCopyright 2009, John Wiley & Sons, Inc.
8 Regulation of water and solute loss Although increased amounts of water & solutes are lost through sweating & exhalation during exercise, loss of body water or excess solutes depends mainly on regulating how much is lost in the urineMain factor that determines body fluid osmolarity is extent of urinary water loss3 hormones regulate renal Na+ and Cl- reabsorption (or not)ADH(Vasopressin) & Angiotensin II-Aldosterone promote urinary Na+ and Cl- reabsorption of (and water by osmosis) when dehydratedAtrial natriuretic peptide (ANP) promotes natriuresis, excretion of Na+ and Cl- followed by water excretion to decrease blood volumeMajor hormone regulating water loss is antidiuretic hormone (ADH)- stimulates thirst- increases permeability of principal cells of collecting ducts to assistin water reabsorption→ very concentrated urine is formed- ADH secretion shuts off after the intake of water- ADH secretion is increased when BP drops due to ↓blood volume;dehydration, vomiting, diarrhea, sweating ….Copyright 2009, John Wiley & Sons, Inc.
13 “water follows salt”Fluid imbalance between the intracellular and interstitial fluids can be caused by a change in their osmolarity.Most often a change in osmolarity is due to change in Na+ concentration:Increasing IF osmolarity draws water out of cells→cells shrinkDecreasing IF osmolarity causes cells to swellWhen water is consumed faster than the kidneys can excrete it, water intoxication may result.Repeated use of enemas can increase the risk of fluid and electrolyte imbalances.
15 ELECTROLYTES IN BODY FLUIDS Electrolytes serve four general functions in the body.Because they are more numerous than nonelectrolytes, electrolytes control the osmosis of water between body compartments.Maintain the acid-base balance required for normal cellular activities.Carry electrical current, which allows production of action potentials and graded potentials and controls secretion of some hormones and neurotransmitters. Electrical currents are also important during development.Serve cofactors needed for optimal activity of enzymes.Concentration expressed in mEq/liter or milliequivalents per liter for plasma, interstitial fluid and intracellular fluidThe chief difference between plasma and interstitial fluid is that plasmacontains quite a few protein anions→ blood colloid osmotic pressurePlasma also contains slightly more sodium ions but fewer chloride ions than the interstitial fluid.Principles of Human Anatomy and Physiology, 11e
16 ICF differs considerably from ECF ECF most abundant cation is Na+, anion is Cl-SodiumImpulse transmission, muscle contraction, fluid and electrolyte balanceChlorideRegulating osmotic pressure, forming HCl in gastric acidControlled indirectly by ADH and processes that affect renal reabsorption of sodiumICF most abundant cation is K+, anion are proteins and phosphates (HPO42-)PotassiumResting membrane potential , action potentials of nerves and musclesMaintain intracellular volumeRegulation of pHControlled by aldosteroneNa+ /K+ pumps play major role in keeping K+ high inside cells and Na+ high outside cellCopyright 2009, John Wiley & Sons, Inc.
19 Electrolyte and protein anion concentrations Copyright 2009, John Wiley & Sons, Inc.
20 Copyright 2009, John Wiley & Sons, Inc. Sodium Na+Most abundant ion in ECF - accounts for 1/2 of osmolarity of ECF90% of extracellular cationsPlays pivotal role in fluid and electrolyte balanceLevel in blood controlled byAldosternone – increases renal reabsorptionADH – if sodium too low, ADH release stopsAtrial natriuretic peptide – increases renal excretionExcess Na+ in the body can result in edema → generally due to renal failure& hyperaldosteronemiaExcess loss of Na+ causes excessive loss of water, which results in hypovolemia, an abnormally low blood volume→ generally due toinadequate secretion of aldosterone or too many diureticsCopyright 2009, John Wiley & Sons, Inc.
21 Copyright 2009, John Wiley & Sons, Inc. Chloride Cl-Most prevalent anions in ECFMoves relatively easily between ECF and ICF because most plasmamembranes contain Cl- leakage channels and transporters- Passively follows Na+Can help balance levels of anions in different fluids- ex. Chloride shift – in RBCs- plays role in HCl production in stomachRegulated byADH – governs extent of water loss in urineProcesses that increase or decrease renal reabsorption of Na+ also affect reabsorption of Cl-Copyright 2009, John Wiley & Sons, Inc.
22 Copyright 2009, John Wiley & Sons, Inc. Potassium K+Most abundant cation in ICFKey role in establishing resting membrane potential in neurons and muscle fibersAlso helps maintain normal ICF fluid volumeHelps regulate pH of body fluids when exchanged for H+Controlled by aldosterone – stimulates principal cells in renal collecting ducts to secrete excess K+Abnormal plasma K+ levels adversely affect cardiac and neuromuscular functionCopyright 2009, John Wiley & Sons, Inc.
25 Copyright 2009, John Wiley & Sons, Inc. Bicarbonate HCO3-Second most prevalent extracellular anionConcentration increases as blood flows through systemic capillaries due to CO2 released from metabolically active cellsCO2 combines with H2O to form carbonic acid which dissociatesConcentration decreases as blood flows through pulmonary capillaries and CO2 is exhaleChloride shift helps maintain correct balance of anions in ECF and ICFKidneys are main regulators of blood HCO3-intercalated cells form more HCO3- if levels are too lowexcrete excess in the urineCopyright 2009, John Wiley & Sons, Inc.
26 Copyright 2009, John Wiley & Sons, Inc. Calcium Ca2+Most abundant mineral in body99% of calcium in adults in skeleton and teeth – contributes to hardnessIn body fluids mainly an extracellular cationPlays important roles in blood clotting, neurotransmitter release, muscle tone, and excitability of nervous & muscle tissueRegulated by parathyroid hormoneStimulates osteoclasts to release calcium from bone – resorptionAlso enhances reabsorption from glomerular filtrateIncreases production of calcitriol to increase absorption for GI tractCalcitonin lowers blood calcium levelsCopyright 2009, John Wiley & Sons, Inc.
28 Copyright 2009, John Wiley & Sons, Inc. PhosphateAbout 85% in adults present as calcium phosphate salts in bone & teethRemaining 15% ionized – H2PO4-, HPO42-, and PO43- are important intracellular anionsHPO42- important buffer of H+ in body fluids and urineSame hormones governing calcium homeostasis also regulate HPO42- in bloodParathyroid hormone – stimulates resorption of bone by osteoclasts releasing calcium and phosphate but inhibits reabsorption of phosphate ions in kidneysCalcitriol promotes absorption of phosphates and calcium from GI tractCopyright 2009, John Wiley & Sons, Inc.
30 Regulation of Phosphate Ions Under normal conditions, reabsorption of phosphate occurs at maximum rate in the nephronAn increase in plasma phosphate increases amount of phosphate in nephron beyond that which can be reabsorbed; excess is lost in urine
31 Copyright 2009, John Wiley & Sons, Inc. MagnesiumSecond most common intracellular cationIn adults, about 54% of total body magnesium is part of bone as magnesium saltsRemaining 46% as Mg2+ in ICF (45%) or ECF (1%)Cofactor for certain enzymes and sodium-potassium pumpEssential for normal neuromuscular activity, synaptic transmission, and myocardial functionSecretion of parathyroid hormone depends on Mg2+Regulated in blood plasma by varying rate excreted in urineCopyright 2009, John Wiley & Sons, Inc.
35 Principles of Human Anatomy and Physiology, 11e Acid-Base BalanceThe overall acid-base balance of the body is maintained by controlling theH+ concentration of body fluids, especially extracellular fluid.Homeostasis of H+ concentration is vitalProteins’ 3-D structure sensitive to pH changesnormal plasma pH must be maintained betweendiet high in proteins tends to acidify the blood3 major mechanisms to regulate pHbuffer systemexhalation of CO2 (respiratory system)kidney excretion of H+ (urinary system)Principles of Human Anatomy and Physiology, 11e
36 3 Types of Acids in the Body Volatile acids - Can leave solution and enter the atmosphere Carbonic acid is an important volatile acid in body fluid Fixed acids - Are acids that do not leave solution. Once produced they remain in body fluids until eliminated by kidneys Sulfuric Acid and Phosphoric Acid are most important fixed acids in the body generated during catabolism of AA’s, phospholipids, & nucleic acids Organic acids : Produced by aerobic metabolism are metabolized rapidly & do not accumulate Produced by anaerobic metabolism (e.g., lactic acid) build up rapidly
37 Copyright 2009, John Wiley & Sons, Inc. Buffer systemsAct to quickly temporarily bind H+Raise pH but do not remove H+Most consist of weak acid and salt of that acid functioning as weak baseChange either strong acid or base into weaker oneWork in fractions of a secondFound in fluids of the body3 principal buffer systemsprotein buffer systemcarbonic acid-bicarbonate buffer systemphosphate buffer systemCopyright 2009, John Wiley & Sons, Inc.
42 Copyright 2009, John Wiley & Sons, Inc. Buffer systemsProtein buffer system - Most abundant buffer in ICF & blood plasmaHemoglobin in RBCs & Albumin in blood plasmaHemoglobin acts as a buffer in blood by picking up CO2 or HFree carboxyl group acts like an acid by releasing H+Free amino group acts as a base to combine with H+Side chain groups on 7 of 20 amino acids also can buffer H+Copyright 2009, John Wiley & Sons, Inc.
43 Copyright 2009, John Wiley & Sons, Inc. Buffer SystemsCarbonic acid / bicarbonate buffer systemBased on bicarbonate ion (HCO3-) acting as weak base &carbonic acid (H2CO3) acting as weak acidHCO3- is a significant anion in both ICF and ECFBecause CO2 and H2O combine to form this buffer system cannot protect against pH changes due to respiratory problems in which there is an excess or shortage of CO2Copyright 2009, John Wiley & Sons, Inc.
44 Copyright 2009, John Wiley & Sons, Inc. Buffer SystemsPhosphate buffer systemDihydrogen phosphate (H2PO4-) and monohydrogen phosphate (HPO42-)Phosphates are major anions in ICF and minor ones in ECFImportant regulator of pH in cytosol but also acts to buffer acids in urineCopyright 2009, John Wiley & Sons, Inc.
45 Exhalation of carbon dioxide The pH of body fluids may be adjusted by a change in the rate & depth of respirations, which usually takes from 1 to 3 minutesIncrease in the rate & depth of breathing = more CO2 exhaled = ↑ blood pH.Decrease in respiration rate & depth= less CO2 exhaled = ↓blood pH .The pH of body fluids, in turn, affects the rate of breathingIncrease in carbon dioxide in body fluids lowers pH of body fluidsThe kidneys excrete H+ and reabsorb HCO3- to aid in maintaining pH.Because H2CO3 can be eliminated by exhaling CO2 it is called a volatile acidCopyright 2009, John Wiley & Sons, Inc.
46 Regulation of blood pH by the respiratory system pH modified by changing rate & depth of breathing:faster breathing rate, blood pH risesslow breathing rate, blood pH dropsH+ detected by chemoreceptors in medulla oblongata, carotid & aortic bodiesRespiratory centers inhibited or stimulated by changes is pHCopyright 2009, John Wiley & Sons, Inc.
49 Kidney Excretion of H+Metabolic reactions produce 1mEq/liter of nonvolatile acid/kg BWExcretion of H+ in the urine is only way to eliminate huge excessIn the PCT, Na+/H+ antiporters secrete H+ as they reabsorb Na+Intercalated cells of collecting duct include proton pumps→ secrete H+ into tubule fluid; reabsorb K+ & HCO3-Urine can be up to 1000 times more acidic than bloodKidneys synthesize new bicarbonate and save filtered bicarbonateRenal failure can cause death rapidly due to its role in pH balance2 other buffers can combine with H+ in collecting duct:- HPO42- and NH3
51 Regulation of Acid-Base Balance Cells in the PCT and collecting ducts secrete H+ into the tubular fluid.In the PCT Na+/H+ antiporters secrete H+ and reabsorb Na+The apical surfaces of some intercalated cells include proton pumps (H+ ATPases) that secrete H+ into the tubular fluid and HCO3– antiporters in their basolateral membranes to reabsorb HCO3–Other intercalated cells have proton pumps in their basolateral membranes and Cl–/HCO3– antiporters in their apical membranes.These two types of cells help maintain body fluid pH by excreting excess H+ when pH is too low or by excreting excess HCO3– when the pH is too high.Normal pH range of arterial bloodAcidosis – blood pH below 7.35 ; Alkalosis – blood pH above 7.45Major physiological effect of :Acidosis – depression of synaptic transmission in CNSAlkalosis – overexcitability of CNS and peripheral nervesPrinciples of Human Anatomy and Physiology, 11e
53 Physiological responses to normalize arterial blood pH Changes in blood pH may be countered by compensationComplete – brought within normal rangePartial – still too low or highRespiratory compensation – hyperventilation or hypoventilationRenal compensation – secretion of H+ and reabsorption of HCO3-Respiratory acidosis / alkalosis are primary disorders of blood PCO2.Metabolic acidosis/alkalosis are primary disorders of HCO3- concentrationCopyright 2009, John Wiley & Sons, Inc.
54 Copyright 2009, John Wiley & Sons, Inc. Respiratory acidosisAbnormally high PCO2 in systemic arterial bloodInadequate exhalation of CO2Any condition that decreases movement of CO2 out – emphysema, pulmonary edema, airway obstructionKidneys can help raise blood pHGoal to increase exhalation of CO2 – ventilation therapyRespiratory Alkalosis- Abnormally low PCO2 in systemic arterial bloodCause is hyperventilation due to O2 deficiency from high altitudeor pulmonary disease, stroke, severe anxiety, aspirin overdoseRenal compensation involves decrease in excretion of H+ and increasereabsorption of bicarbonate- One simple treatment to breathe into paper bag for short timeCopyright 2009, John Wiley & Sons, Inc.
55 Copyright 2009, John Wiley & Sons, Inc. Metabolic AcidosisResults from changes in HCO3- concentrationMetabolic acidosis – abnormally low HCO3- in systemic arterial bloodLoss of HCO3- from severe diarrhea or renal dysfunctionAccumulation of acid (ketosis with dieting/diabetes)Kidney failing to remove H+ from protein metabolismRespiratory compensation by hyperventilationAdminister IV sodium bicarbonate and correct cause of acidosisMetabolic AlkalosisAbnormally high HCO3- in systemic arterial bloodNon-respiratory cause: vomiting acidic stomach contents, gastric suctioningExcessive intake of alkaline drugs (antacids) & use of certain diureticsSevere dehydrationRespiratory compensation is hypoventilationGive fluid solutions to correct Cl-, K+ and other electrolyte deficienciesand correct cause of alkalosisCopyright 2009, John Wiley & Sons, Inc.
59 Diagnosis of Acid-Base Imbalances Evaluatesystemic arterial blood pHconcentration of bicarbonate (too low or too high)PCO2 (too low or too high)Solutionsif problem is respiratory, the pCO2 will not be normalif problem is metabolic, the bicarbonate level will not be normalPrinciples of Human Anatomy and Physiology, 11e
60 Copyright 2009, John Wiley & Sons, Inc. End of Chapter 27Copyright 2009 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.Copyright 2009, John Wiley & Sons, Inc.