Presentation on theme: "Water, Electrolyte and Acid-Base Balance"— Presentation transcript:
1 Water, Electrolyte and Acid-Base Balance Chapter 21
2 Balance – a state of equilibrium – substances are maintained in the right amounts and in the right place in the body
3 Water BalanceOsmosis is the primary method of water movement into and out of body fluid compartments.Osmosis is the net movement of water molecules through a selectively permeable membrane from an area of high water concentration to an area of lower water concentration.
4 The concentration of solutes determines the direction of water movement. Most solutes in the body are electrolytes – inorganic compounds which dissociate into ions in solution.“Where sodium goes, water follows.”
5 About 40 Liters (10.56 gallons) of body water Babies – 75% waterMen – 63 %Women – 52%
7 Fluid compartments Separated by selectively permeable membranes Intracellular – 2/3 (63%) of total body waterExtracellular – 1/3 (37%)Interstitial fluid – 80 % of extracellular waterBlood plasma – 20 % of extracellular water
9 Composition of compartments Extracellular fluids:High in Na+, Cl-, Ca++, HCO3-Blood plasma has more protein than interstitial fluid and lymphIntracellular fluids:High in K+, phosphate, Mg++, and more protein than plasma
11 Movement of water Hydrostatic pressure – pressure of fluids Osmotic pressure – solute concentration (often Na+)In blood referred to as colloid osmotic pressure (COP)
12 Water intake = Water loss Average adult takes in about 2,500 ml/daySources of water:Preformed water: 2,300 mlDrinking water: 1,500 ml (60%)Moist food : ml (30%)Water of metabolism: 250 ml (10%)Cellular respirationDehydration synthesis
14 Regulation of water intake Main regulator is thirst.Dehydration (output>intake) as little as 1% decrease in body water causes:Decreased production of salivaIncreased blood osmotic pressure – stimulates osmoreceptors in the hypothalamusDecreased blood volume – renin is produced
15 The thirst center in hypothalamus is stimulated ( or mistakenly, the hunger center) and person feels thirstyWetting of the mouth and stretching of stomach or intestines decrease thirst before we take in too much water.Water is absorbed, and blood osmotic pressure decreases.
16 Sources of water loss Through kidneys in urine – 1500 ml (60%) Through intestines ml (6%)Can be significant in vomiting and diarhheaFrom skin (sweat) ml (6%)From lungs and skin ml (28%)Last is called insensible loss(menstruation)
18 Regulation of Water Output Through regulating urine formationADH – production stimulated by ↑ blood tonicity of decrease in volume.Acts on distal convoluted tubules and collecting ducts of kidney – permits reabsorption of water
19 Aldosterone – production is stimulated by angiotensin II through renin production Causes sodium ( and water) to be reabsorbedANP – causes sodium (and water) loss when pressure in right atrium is too high
20 Water imbalances Dehydration is the imbalance seen most often. Prolonged diarrhea or vomitingExcessive sweating
22 Water toxicity If lose water by sweating, we also lose sodium. Rapidly drinking large quantities of water decreases plasma sodium concentration initially, then see decrease in ISF as well.Water is drawn into cellsThis increases ISF tonicity, and water is drawn from bloodAdd salt when replacing fluids like this!
24 OverhydrationCan occur if I.V. fluids are given too rapidly or in too large amounts.Extra fluid puts strain on heart
25 Decrease in blood proteins caused by: Dietary deficiency in proteins Water that moves back into capillaries depends on concentration of plasma proteins.Decrease in blood proteins caused by:Dietary deficiency in proteinsLiver failureBlockage of lymphatic systemIncreased capillary permeabilityBurns, infection
31 Edema Can be caused by: Decrease in plasma proteins Retention of electrolytes, esp. Na+Increase in capillary blood pressure
32 Electrolyte Balance Cations – positively charged ions Anions – negatively charged ionsBody fluids also contain charged organic moleculesOnly a small percentage of molecules in fluids are non-electrolytes: glucose, urea, creatinine
33 Functions of electrolytes Certain ions control the osmosis of water between body compartmentsIons help maintain the acid-base balance necessary for cellular activityIons carry electric current, which allows for action potentials and secretion of neurotransmittersSeveral ions are cofactors needed for the optimal activity of enzymes
34 Electrolyte intakeFood and waterProduced by metabolismSalt craving
37 OsmolarityThe total concentration of dissolved particles determines osmolarity.Glucose – one dissolved particleNaCl – dissolves into two particlesOne mole of NaCl = 2 osmolesOsmoles/L = osmolarity of solution
38 Sodium (Na+)90 % of extracellular cations and half the osmolarity of extracellular solutionsNecessary for action potentials in nerve & muscle cellsAldosterone increases reabsorption from DCT and collecting ducts↓ blood volume, ↓ extracellular Na+ ,↑ extracellular K+ANP causes loss of Na+
39 Potassium (K+) Most numerous intracellular cation Membrane potential and repolarizationControlled by aldosterone – causes loss of K+ in urine
41 Calcium (Ca++)Part of bone, most abundant mineral in body. 98% of Ca is in boneExtracellular cationNeeded for blood clotting, nerve and muscle functionPTH causes reabsorption of bone and increases reabsorption from G.I tract and glomerular filtrateCalcitonin inhibits osteoclasts and stimulates osteoblast, so calcium is removed from blood
42 Chloride (Cl-) Most common extracellular anions Cl- diffuses easily between compartments – can help balance charges (RBC’s)Parietal cells in stomach secrete Cl- & H+Aldosterone indirectly adjusts Cl- when it increases the reabsorption of Na+ - Cl- follows the Na+
43 Bicarbonate (HCO3-)Part of the body’s chief buffer and transports CO2 in blood stream.CO2 + H2O ↔H2CO3 ↔ H HCO3-The kidneys are the main regulators of bicarbonate: they form bicarb when levels are low and excrete it when levels are high.
44 Phosphate (HPO42-)Like calcium, most of the phosphate is found in the bones.15% is ionizedFound in combination with lipids, proteins, carbohydrates, nucleic acids and ATP.Three different formsPart of the phosphate buffer systemPTH causes phosphate to be released from bones and to be excreted by the kidneys. Calcitonin removes phosphate by encouraging bone formation.
45 Acid-Base Balance pH – negative log of H+ concentration Affects functioning of proteins (enzymes)Can affect concentrations of other ionsModify hormone actions (proteins)
49 Strengths of Acids and Bases Acids and bases that ionize (break apart) completely are strong acids and bases. (HCl; NaOH)Acids and bases that do not completely dissociate in solution are weak acids and bases. (lactic acid, carbonic acid)
50 Remember, blood needs to stay between 7. 35 and 7 Remember, blood needs to stay between 7.35 and 7.45 for the body to function properly.Since more acids than bases are formed, pH balance is mainly a matter of controlling excess H+.
51 Control of Acid-Base Balance Buffer systemsExhalation of carbon dioxideKidney excretion
52 BuffersAre pairs of chemical substances that prevent a sharp change in the pH of a solution.Buffers exchange strong acids for weaker acids that do not release as much H+ and thus change the pH less.
53 Bicarbonate Buffer System NaHCO H2CO3sodium bicarbonate carbonic acidAddition of a strong acid:HCl + NaHCO3 → H2CO3 + NaClCarbonic acid does not dissociate completely, and pH is changed much less.
54 Addition of a strong base: NaOH + H2CO3 → NaHCO3 + H2OWater dissociates very little, and pH remains nearly the same.
55 Usually the body is called upon to buffer weaker organic acids, such as lactic acid. Carbonic acid is formed, and amount of bicarbonate ion decreases.Blood needs to maintain a 20:1 ratio of bicarbonate ion : carbonic acid.H+ concentration increases slightlypH drops slightly
56 Carbonic acid is the most abundant acid in the body because it is constantly being formed by buffering fixed acids and by:H2O + CO2 ↔ H2CO3 ↔ H+ + HCO3-
57 Phosphate Buffer System Is present in extracellular and intracellular fluids, most important in intracellular fluids and renal tubules.H+ + HPO42- → H2PO4-monohydrogen dihydrogenphosphate phosphateOH- + H2PO4- → H2O + HPO42-
58 Protein Buffer System The most abundant in body cells and plasma. Carboxyl group -COOH ↔ -COO- + H+Amino group –NH2 ↔ -NH3+
59 Respiratory Mechanisms – Exhalation of CO2 Because carbonic acid can be eliminated by breathing out CO2 it is called a volatile acid.Body pH can be adjusted this way in about 1-3 minutespH also affects breathing ratePowerful eliminator of acid, but can only deal with carbonic acid.
61 Kidney excretion of H+Metabolic reactions produce large amounts of fixed acids.Kidneys can eliminate larger amounts of acids than the lungsCan also excrete basesCan excrete acids while conserving bicarbonate ionCan produce more bicarbonate ionKidneys are the most effective regulators of pH; if kidneys fail, pH balance fails
63 The regulators work at different rates Buffers are the first line of defense because they work almost instantaneously.Secondary defenses take longer to work:Respiratory mechanisms take several minutes to hoursRenal mechanisms may take several days
65 pH imbalances The normal blood pH range is 7.35 – 7.45 Any pH below this range is considered to be a condition of acidosisAny pH above this range is considered to be a condition of alkalosisThe body response to acid-base imbalance is called compensation: Compensation may be complete if the blood pH is brought back to normal, or partial if it is still outside the norms.
67 Respiratory problemsRespiratory acidosis is a carbonic acid excess (blood CO2 is too high)Respiratory alkalosis is a carbonic acid deficit (blood CO2 is too low)Compensation would occur through the kidneys