Chapter 27: WATER, ELECTROLYTES, AND ACID-BASE BALANCE I. RELATED TOPICS Integumentary system Cerebrospinal fluid Aqueous humor Digestive juices Feces Capillary dynamics Lymph circulation Edema Osmosis Metabolic water Diabetes Thermoregulation Renal dynamics Lactation Systems which control fluid balance? II. THE FLUID COMPARTMENTS A. Body Fluid Distribution (Table 27.1) Total body water (TBW) body weight Intracellular fluid body weight or TBW Extracellular fluid body weight or TBW Plasma body wt.; Interstitial fluid body wt. B. Intracellular Fluid 1. Location 2. Volume = total body water 3. Major electrolytes (charged ions or molecules) a. Cations (): -2 b. Anions (-): HPO 4 - (Phosphate) 86
87 C. Extracellular Fluid 1. Plasma a. Volume: % body weight b. Major cation: c. Major anions:, 2. Interstitial fluid a. Volume: % body weight b. Major cation c. Major anion e. Differs how from plasma? 3. Lymph III. REGULATION OF WATER CONTENT A. Water intake and loss (Table 27.3) 1. Sources of water Fluid Food Metabolic H2O 2. Water loss routes Urine Lungs Other Skin Feces Abnormal water loss Premature rupture of membranes
88 B. Thirst (Fig. 27.1) 1. Increased osmolarity of plasma affects hypothalamus --> thirst 2. Renin > > > Angiotensin II > thirst 3. Low blood pressure affects baroreceptors --> thirst C. Regulation of extracellular fluid concentration: ADH (Fig. 27.2, 27.3) Increased concentration of plasma Stimulation of hypothalamic neurons water reabsorption Release of ADH from permeability of distal tubule and collecting duct to water D. Regulation of extracellular fluid volume: 1. Renin-angiotensin system (Fig. 21.45 [21.42]; 27.5) Decreased blood pressure Renin (juxtaglomerular cells) Angiotensinogen ------->angiotensin I (inactive plasma protein) Angiotensin II --> aldosterone release ---> from adrenal cortex blood pressure blood volume water reabsorption Na reabsorption from nephrons vasoconstriction; thirst; salt appetite; ADH
89 2. Atrial natriuretic hormone (Fig. 27.6) a. Source b. Stimulus for release c. Function E. Regulation of intracellular fluid (Fig. 27.7) 1. Major extracellular ion 2. Role of Na in osmosis IV. ROLE OF ELECTROLYTES IN FLUID BALANCE A. Major electrolytes 1. Sodium ion (Na ) a. Functions b. Excretion c. Na in sweat: d. Control (Fig.27.5,27.6, p. 1010 [1011]) Aldosterone Na reabsorption Atrial natriuretic hormone Na reabsorption Hypernatremia Hyponatremia
90 2. Chloride ion (Cl - ) a. Functions b. Control 3. Potassium ion (K ) a. Function b. Control (Fig. 27.8) Hyperkalemia c. If aldosterone is greatly reduced, [K ] causes death. Why? 4. Calcium ion (Ca ) a. Functions b. Control (Fig. 27.9) PTH from blood Ca Calcitonin from blood Ca Hypercalcemia/ Hypocalcemia c. Role of vitamin D
91 5. Magnesium a. Function b. Sources c. Control (Fig. 27.9 [27.10]) Hypomagnesemia 6. Phosphate ions (HPO - 4 ) a. Function b. Control (Fig. 27.10 [27.11]) C. Causes of electrolyte imbalances: 1. Increased sweating 2. Vomiting 3. Diarrhea 4. Diuretic drugs 5. Inadequate nutrient intake 6. Renal insufficiency 7. Endocrine disorders D. Note that some of these can also cause acid-base imbalances
92 V. ACID-BASE BALANCE A. Significance: Blood ph = 7.35-7.45 a. 7.0-7.35: acidosis Effect: b. 7.45-7.8: alkalosis Effect: c. NOTE: Intracellular ph = 6.0-7.4 B. Causes of imbalances (Table 27-A) 1. Gastric vomiting 2. Diarrhea 3. Intestinal vomiting 4. Kidney dysfunction 5. Pneumonia 6. Ketosis 7. Emphysema 8. Intake of acidic or basic drugs C. Definitions (Fig. 27.11) - 1. Acid: Electrolyte dissociating (separating) into H and anion a. Strong acid --> total dissociation b. Weak acid --> partial dissociation 2. Base: Anion which can bind an H a. Weak base: weak H acceptor b. Ex.: 3. Acids bases --> salt H2O
93 4. Buffer system: Solution of two or more compounds which prevent large changes in ph whether acid or base is added a. Components: weak acid weak base b. If excess acid (excess H )? c. If excess base (too little H )? d. Only released H lower ph D. Physiology of ph maintenance 1. Buffers (Table 27.11) - a. Carbonic acid/ Bicarbonate buffer system: H2CO 3 Na HCO3 Location: weak weak b. Phosphate buffer system NaH2PO 4 Na2HPO4- Na dihydrogen phosphate Na monohydrogen phosphate Locations: weak weak c. Protein buffer system Locations: d. Hemoglobin buffer Buffers excess carbonic acid in blood
94 2. Respiratory system (Fig. 27.12 [27.14]) a. Relatively rapid (minutes, hours); more effective than buffers Why? b. CO 2 H2O H2CO 3 H HCO3 c. Decreased respiration --> in CO 2 Increased respiration --> in CO 2 d. Increased CO 2 --> [H ] --> ph Decreased CO 2 --> [H ] --> ph e. Control: decreased ph --> ventilation rate -- > Increased ph --> ventilation rate > f. Respiratory acidosis: ph Cause: ventilation or respiratory exchange Effect: g. Respiratory alkalosis: ph Cause: ventilation Effect: h. Respiratory stresses which affect acid-base balance High altitude Pneumonia, Emphysema Hyperventilation
95 ` 3. Kidneys a. Slow acting but exact b. Control: Local, by cells of distal tubule and collecting duct c. If blood ph is too low (too ), the distal tubule and collecting duct H and reabsorb. H is eliminated in the urine, buffered -- by Na H PO 4 ----> Na H 2 PO 4 - ---------> - and NH 3 Cl NH 4 Cl (Ammonium Chloride) d. If blood ph is too high (too ), H is/ is not secreted and Na HCO - 3 is/ is not reabsorbed by distal tubules and collecting duct; H in urine. e. If urine contains more acid, blood becomes acid. f. If urine contains less acid, blood becomes acid. 4. Metabolic acidosis a. Causes b. Effect 5. Metabolic alkalosis a. Causes b. Effect See also Clinical Focus: Acidosis and Alkalosis, pp. 1021 [1025]