1 / 36

Chapter 27 Fluid, Electrolyte and Acid-Base Homeostasis

Chapter 27 Fluid, Electrolyte and Acid-Base Homeostasis. Body fluid all the water and dissolved solutes in the body’s fluid compartments Mechanisms regulate total volume distribution concentration of solutes and pH. Balance Between Fluid Compartments.

hilda
Télécharger la présentation

Chapter 27 Fluid, Electrolyte and Acid-Base Homeostasis

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 27Fluid, Electrolyte and Acid-Base Homeostasis • Body fluid • all the water and dissolved solutes in the body’s fluid compartments • Mechanisms regulate • total volume • distribution • concentration of solutes and pH Tortora & Grabowski 9/e 2000 JWS

  2. Balance Between Fluid Compartments Volume of fluid in each is kept constant. Since water follows electrolytes, they must be in balance as well • Only 2 places for exchange between compartments: • cell membranes separate intracellular from interstitial fluid. • only in capillaries are walls thin enough for exchange between plasma and interstitial fluids Tortora & Grabowski 9/e 2000 JWS

  3. Body Water Gain and Loss • 45-75% body weight • declines with age since fat contains almost no water • Gain from ingestion and metabolic water formed during aerobic respiration & dehydration synthesis reactions (2500 mL/day) • Normally loss = gain • urine, feces, sweat, breathe Tortora & Grabowski 9/e 2000 JWS

  4. Regulation of Water Gain • Formation of metabolic water is not regulated • function of the need for ATP • Main regulator of water gain is intake regulation • Stimulators of thirst center in hypothalamus • dry mouth, osmoreceptors in hypothalamus, decreased blood volume causes drop in BP & angiotensin II • Drinking occurs • body water levels return to normal Tortora & Grabowski 9/e 2000 JWS

  5. Dehydration Stimulates Thirst • Regulation of fluid gain is by regulation of thirst. Tortora & Grabowski 9/e 2000 JWS

  6. Regulation of Water and Solute Loss • Elimination of excess water or solutes occurs through urination • Consumption of very salty meal demonstrates function of three hormones • Demonstrates how • “water follows salt” • excrete Na+ and water will follow and decrease blood volume Tortora & Grabowski 9/e 2000 JWS

  7. Hormone Effects on Solutes • Angiotensin II and aldosterone promote reabsorption of Na+ and Cl- and an increase in fluid volume • stretches atrial volume and promotes release of ANP • slows release of renin & formation of angiotensin II • increases filtration rate & reduces water & Na+ reabsorption • decreases secretion of aldosterone slowing reabsorption of Na+ and Cl- in collecting ducts • ANP promotes natriuresis or the increased excretion of Na+ and Cl- which decreases blood volume Tortora & Grabowski 9/e 2000 JWS

  8. Hormone Regulation of Water Balance • Antidiuretic hormone (ADH) from the posterior pituitary • stimulates thirst • increases permeability of principal cells of collecting ducts to assist in water reabsorption • very concentrated urine is formed • ADH secretion shuts off after the intake of water • ADH secretion is increased • large decrease in blood volume • severe dehydration and drop in blood pressure • vomiting, diarrhea, heavy sweating or burns Tortora & Grabowski 9/e 2000 JWS

  9. Movement of Water • Intracellular and interstitial fluidsnormally have the same osmolarity,so cells neither swell nor shrink • Swollen cells of water intoxicationbecause Na+ concentration of plasmafalls below normal • drink plain water faster than kidneys canexcrete it • replace water lost from diarrhea or vomitingwith plain water • may cause convulsions, coma & death unless oral rehydration includes small amount salt in water intake Tortora & Grabowski 9/e 2000 JWS

  10. Enemas and Fluid Balance • Introduction of a solution into the bowel to stimulate activity and evacuate feces • Increase risk of fluid & electrolyte imbalance unless isotonic solution is used Tortora & Grabowski 9/e 2000 JWS

  11. Concentrations of Electrolytes • Functions of electrolytes • control osmosis between fluid compartments • help maintain acid-base balance • carry electric current • cofactors needed for enzymatic activity • Concentration expressed in mEq/liter or milliequivalents per liter for plasma, interstitial fluid and intracellular fluid Tortora & Grabowski 9/e 2000 JWS

  12. Comparison Between Fluid Components • Plasma contains many proteins, but interstitial fluid does not • producing blood colloid osmotic pressure • Extracellular fluid contains Na+ and Cl- • Intracellular fluid contains K+ and phosphates (HPO4-2) Tortora & Grabowski 9/e 2000 JWS

  13. Sodium • Most abundant extracellular ion • accounts for 1/2 of osmolarity of ECF • Average daily intake exceeds normal requirements • Hormonal controls • aldosterone causes increased reabsorption Na+ • ADH release ceases if Na+ levels too low--dilute urine lost until Na+ levels rise • ANP increases Na+ and water excretion if Na+ levels too high Tortora & Grabowski 9/e 2000 JWS

  14. Edema, Hypovolemia and Na+ Imbalance • Sodium retention causes water retention • edema is abnormal accumulation of interstitial fluid • Causes of sodium retention • renal failure • hyperaldosterone • Excessive loss of sodium causes excessive loss of water (low blood volume) • due to inadequate secretion of aldosterone • too many diuretics Tortora & Grabowski 9/e 2000 JWS

  15. Chloride • Most prevalent extracellular anion • Moves easily between compartments due to Cl- leakage channels • Helps balance anions in different compartments • Regulation • passively follows Na+ so it is regulated indirectly by aldosterone levels • ADH helps regulate Cl- in body fluids because it controls water loss in urine • Chloride shift & hydrochloric acid of gastric juice Tortora & Grabowski 9/e 2000 JWS

  16. Potassium • Most abundant cation in intracellular fluid • Helps establish resting membrane potential & repolarize nerve & muscle tissue • Exchanged for H+ to help regulate pH in intracellular fluid • Control is mainly by aldosterone which stimulates principal cells to increase K+ secretion into the urine • abnormal plasma K+ levels adversely affect cardiac and neuromuscular function Tortora & Grabowski 9/e 2000 JWS

  17. Bicarbonate • Common extracellular anion • Major buffer in plasma • Concentration increases as blood flows through systemic capillaries due to CO2 released from metabolically active cells • Concentration decreases as blood flows through pulmonary capillaries and CO2 is exhaled • Kidneys are main regulator of plasma levels • intercalated cells form more if levels are too low • excrete excess in the urine Tortora & Grabowski 9/e 2000 JWS

  18. Calcium • Most abundant mineral in body (skeleton & teeth) • Abundant extracellular cation in body fluids • Important role in blood clotting, neurotransmitter release, muscle tone & nerve and muscle function • Regulated by parathyroid hormone • stimulates osteoclasts to release calcium from bone • increases production of calcitriol (Ca+2 absorption from GI tract and reabsorption from glomerular filtrate) Tortora & Grabowski 9/e 2000 JWS

  19. Phosphate • Present as calcium phosphate in bones and teeth, and in phospholipids, ATP, DNA and RNA • HPO4-2 is important intracellular anion and acts as buffer of H+ in body fluids and in urine • mono and dihydrogen phosphate act as buffers in the blood • Plasma levels are regulated by parathyroid hormone & calcitriol • resorption of bone releases phosphate • in the kidney, PTH increase phosphate excretion • calcitriol increases GI absorption of phosphate Tortora & Grabowski 9/e 2000 JWS

  20. Magnesium • Found in bone matrix and as ions in body fluids • intracellular cofactor for metabolic enzymes, heart, muscle & nerve function • Urinary excretion increased in hypercalcemia, hypermagnesemia, increased extracellular fluid volume, decreases in parathyroid hormone and acidosis Tortora & Grabowski 9/e 2000 JWS

  21. Acid-Base Balance • Homeostasis of H+ concentration is vital • proteins 3-D structure sensitive to pH changes • normal plasma pH must be maintained between 7.35 - 7.45 • diet high in proteins tends to acidify the blood • 3 major mechanisms to regulate pH • buffer system • exhalation of CO2 (respiratory system) • kidney excretion of H+ (urinary system) Tortora & Grabowski 9/e 2000 JWS

  22. Actions of Buffer Systems • Prevent rapid, drastic changes in pH • Change either strong acid or base into weaker one • Work in fractions of a second • Found in fluids of the body • 3 principal buffer systems • protein buffer system • carbonic acid-bicarbonate buffer system • phosphate buffer system Tortora & Grabowski 9/e 2000 JWS

  23. Protein Buffer System • Abundant in intracellular fluids & in plasma • hemoglobin very good at buffering H+ in RBCs • albumin is main plasma protein buffer • Amino acids contains at least one carboxyl group (-COOH) and at least one amino group (-NH2) • carboxyl group acts like an acid & releases H+ • amino group acts like a base & combines with H+ • some side chains can buffer H+ • Hemoglobin acts as a buffer in blood by picking up CO2 or H+ Tortora & Grabowski 9/e 2000 JWS

  24. Carbonic Acid-Bicarbonate Buffer System • Acts as extracellular & intracellular buffer system • bicarbonate ion (HCO3-) can act as a weak base • holds excess H+ • carbonic acid (H2CO3) can act as weak acid • dissociates into H+ ions • At a pH of 7.4, bicarbonate ion concentration is about 20 times that of carbonic acid • Can not protect against pH changes due to respiratory problems Tortora & Grabowski 9/e 2000 JWS

  25. Phosphate Buffer System • Most important intracellularly, but also acts to buffer acids in the urine • Dihydrogen phosphate ion acts as a weak acid that can buffer a strong base • Monohydrogen phosphate acts a weak base by buffering the H+ released by a strong acid Tortora & Grabowski 9/e 2000 JWS

  26. Exhalation of Carbon Dioxide • Breathing plays a role in the homeostasis of pH • pH modified by changing rate & depth of breathing • faster breathing rate, blood pH rises • slow breathing rate, blood pH drops • H+ detected by chemoreceptors in medulla oblongata, carotid & aortic bodies • Respiratory centers inhibited or stimulated by changes is pH Tortora & Grabowski 9/e 2000 JWS

  27. Kidney Excretion of H+ • Metabolic reactions produce 1mEq/liter of nonvolatile acid for every kilogram of body weight • Excretion of H+ in the urine is only way to eliminate huge excess • Kidneys synthesize new bicarbonate and save filtered bicarbonate • Renal failure can cause death rapidly due to its role in pH balance Tortora & Grabowski 9/e 2000 JWS

  28. Acid-Base Imbalances • Acidosis---blood pH below 7.35 • Alkalosis---blood pH above 7.45 • Compensation is an attempt to correct the problem • respiratory compensation • renal compensation • Acidosis causes depression of CNS---coma • Alkalosis causes excitability of nervous tissue---spasms, convulsions & death Tortora & Grabowski 9/e 2000 JWS

  29. Summary of Causes • Respiratory acidosis & alkalosis are disorders involving changes in partial pressure of CO2 in blood • Metabolic acidosis & alkalosis are disorders due to changes in bicarbonate ion concentration in blood Tortora & Grabowski 9/e 2000 JWS

  30. Respiratory Acidosis • Cause is elevation of pCO2 of blood • Due to lack of removal of CO2 from blood • emphysema, pulmonary edema, injury to the brainstem & respiratory centers • Treatment • IV administration of bicarbonate (HCO3-) • ventilation therapy to increase exhalation of CO2 Tortora & Grabowski 9/e 2000 JWS

  31. Respiratory Alkalosis • Arterial blood pCO2 is too low • Hyperventilation caused by high altitude, pulmonary disease, stroke, anxiety, aspirin overdose • Renal compensation involves decrease in excretion of H+ and increase reabsorption of bicarbonate • Treatment • breathe into a paper bag Tortora & Grabowski 9/e 2000 JWS

  32. Metabolic Acidosis • Blood bicarbonate ion concentration too low • loss of ion through diarrhea or kidney dysfunction • accumulation of acid (ketosis with dieting/diabetes) • kidney failing to remove H+ from protein metabolism • Respiratory compensation by hyperventilation • Treatment • IV administration of sodium bicarbonate • correct the cause Tortora & Grabowski 9/e 2000 JWS

  33. Metabolic Alkalosis • Blood bicarbonate levels are too high • Cause is nonrespiratory loss of acid • vomiting, gastric suctioning, use of diuretics, dehydration, excessive intake of alkaline drugs • Respiratory compensation is hypoventilation • Treatment • fluid and electrolyte therapy • correct the cause Tortora & Grabowski 9/e 2000 JWS

  34. Diagnosis of Acid-Base Imbalances • Evaluate • systemic arterial blood pH • concentration of bicarbonate (too low or too high) • PCO2 (too low or too high) • Solutions • if problem is respiratory, the pCO2 will not be normal • if problem is metabolic, the bicarbonate level will not be normal Tortora & Grabowski 9/e 2000 JWS

  35. Homeostasis in Infants • More body water in ECF so more easily disrupted • Rate of fluid intake/output is 7X higher • Higher metabolic rate produces more metabolic wastes • Kidneys can not concentrate urine nor remove excess H+ • Surface area to volume ratio is greater so lose more water through skin • Higher breathing rate increase water loss from lungs • Higher K+ and Cl- concentrations than adults Tortora & Grabowski 9/e 2000 JWS

  36. Impaired Homeostasis in the Elderly • Decreased volume of intracellular fluid • inadequate fluid intake • Decreased total body K+ due to loss of muscle tissue or potassium-depleting diuretics for treatment of hypertension or heart disease • Decreased respiratory & renal function • slowing of exhalation of CO2 • decreased blood flow & glomerular filtration rate • reduced sensitivity to ADH & impaired ability to produce dilute urine • renal tubule cells produce less ammonia to combine with H+ and excrete as NH+4 Tortora & Grabowski 9/e 2000 JWS

More Related