Chapter 27: Fluid, Electrolyte, PH Balance
Hypocalcemia
MEq/L: < 4.3 Cause: Poor diet; lack of vitamin D; renal failure; hypoparathyroidism; hypomagnesemia Symptoms: Muscle spasms, convulsions, intestinal cramps, weak heartbeats, cardiac arrhythmias, osteoporosis Treatment: Calcium supplements; administration of vitamin D
Hyponatremia
MEq/L: <135 Cause: Infusion or ingestion of large volumes of hypotonic solution (water) Symptoms: Disturbed CNS function (water intoxication): confusion, hallucinations, convulsions, coma; death in severe cases Treatment: Diuretic use and infusion of hypertonic salt solution
Hypercloremia
MEq/L: > 108 Cause: Dietary excess; increased chloride retention Symptoms: Acidosis, hyperkalemia Treatment: Infusion of hypotonic solution to lower plasma concentration
Hypernatremia
MEq/L: > 145 Cause: Dehydration; loss of hypotonic fluid Symptoms: Thirst, dryness and wrinkling of skin, reduced blood volume and pressure, eventual circulatory collapse Treatment: Ingestion of water or intravenous infusion of hypotonic solution
Hypermagnesemia
MEq/L: > 2.0 Cause: Overdose of magnesium supplements or antacids (rare) Symptoms: Confusion, lethargy, respiratory depression, hypotension Treatment: Infusion of hypotonic solution to lower plasma concentration
Hyperphosphatemia
MEq/L: > 3.0 Cause: high dietary phosphate intake; hypoparathyroidism Symptoms: No immediate symptoms; chronic elevation leads to calcification of soft tissues Treatment: dietary reduction; PTH supplementation
Hyperkalemia
MEq/L: > 5.0 Cause: Renal failure; use of diuretics; chronic acidosis Symptoms: Severe cardiac arrhythmias; muscle spasms Treatment: Infusion of hypotonic solution; selection of different diuretics; infusion of buffers; dietary restrictions
Hypercalcemia
MEq/L: > 5.3 Cause: Hyperparathyroidism; cancer; vitamin D toxicity; calcium supplement overdose Symptoms: Confusion, muscle pain, cardiac arrhythmias, kidney stones, calcification of soft tissues Treatment: Infusion of hypotonic fluid to lower Ca2 1 levels; surgery to remove parathyroid gland; administration of calcitonin
buffer system
body fluids generally consists of a combination of a weak acid and the anion released by its dissociation
Mechanisms of pH control
body must balance gains and losses of H+ Hydrogen ions are gained at the digestive tract and through metabolic activities within cells Your kidneys eliminate H+ by secreting them into urine. The lungs eliminate H+ by forming water and CO2 from H+ and HCO3 -
phosphate buffer system
buffers pH of ICF and urine consists of the weak acid dihydrogen phosphate H2PO4 -2 and the released anion monohydrogen phosphate HPO4-2 form of the weak base sodium monohydrogen phosphate (Na2HPO4).
insensible perspiration
evaporation of water across the epithelia of the skin and lungs fever can also increase water losses each degree that body temperature rises above normal, daily insensible water losses increase by 200 mL
hypercapnia
excessive carbon dioxide in the blood
ketoacidosis
excessive production of ketones, making the blood acidic
water intoxication
hyperhydration effecting the CNS can rapidly progress from confusion to hallucinations, convulsions, coma, and then death treatment involves diuretics and salt solution
hypocapnia
insufficient carbon dioxide
Electrolytes
ions released when inorganic compounds dissociate
respiratory acid-base disorders
result from a mismatch between CO2 generation in peripheral tissues and CO2 excretion by the lungs when a respiratory acid-base disorder is present, the CO2 level of the ECF is abnormal
bodily response to acidosis
see chart Together these mechanisms can generally control pH very precisely, so the pH of the ECF seldom varies more than 0.1 pH unit, from 7.35 to 7.45
bodily response to alkalosis
see chart Together these mechanisms can generally control pH very precisely, so the pH of the ECF seldom varies more than 0.1 pH unit, from 7.35 to 7.45
amino acid buffers
If pH increases (becomes more basic), the carboxyl group (¬COOH) of the amino acid can dissociate, acting as a weak acid and releasing an H+ In a neutral solution, an amino acid carries both positive and negative charges If pH decreases (becomes more acidic), the carboxylate ion and the amino group (¬NH2) can act as weak bases and accept additional H+, forming a carboxyl group (¬COOH) and an amino ion (¬NH3 +), respectively
severe acidosis
1. CNS function deteriorates, comatose 2. cardiac contractions are weak, heart failure 3. dramatic decrease in blood pressure
limitation of carbonic-bicarbonate buffer system
1. It cannot protect the ECF from changes in pH that result from an increased or decreased level of CO2. 2. It can function only when the respiratory system and the respiratory control centers are working normally 3. The ability to buffer acids is limited by the availability of bicarbonate ions
Three types of acids
1. fixed 2. metabolic 3. volatile
three buffer system
1. phosphate 2. protein 3. carbonic-acid - bicarbonate
Normal pH of ECF
7.35-7.45
Potassium Balance
98 percent of the body's potassium is in the ICF Cells expend energy to recover K+ as they diffuse across their plasma membranes and into the ECF Urinary K+ losses are usually limited to the amount gained by absorption across the digestive epithelium, typically 50-150 mEq (1.9-5.8 g) per day. rates of K+ into urine varies - Changes in the K+ Concentration of the ECF - Changes in pH - The Level of Aldosterone
What effect would a decrease in the pH of body fluids have on the respiratory rate?
A decrease in the pH of body fluids accompanies an increase in the partial pressure of carbon dioxide. Chemoreceptors sensitive to PCO2 would stimulate the respiratory centers of the medulla oblongata, resulting in an increase in the respiratory rate.
Sodium Balance
A person in sodium balance typically gains and loses 48-144 mEq each day a change in the Na+ content of the ECF does not produce a change in the Na+ concentration if you eat a very salty meal, the osmotic concentration of the ECF will not increase Additional water enters the ECF from the digestive tract, increasing the blood volume and blood pressure
hyperhydration
A temporary excess of water; beyond the normal state of hydration. After the fluid shift, the ECF and ICF have slightly larger volumes and slightly lower osmotic concentrations than they did originally problems will develop as water shifts into the ICF, distorting cells, changing the solute concentrations around enzymes, and disrupting normal cell functions caused by 1. drinking large amount of water 2. excessive production ADH (endocrine disorder) 3. inability to eliminate excess water (renal disorder) most obvious is Na concentration is abnormally low
buffers
dissolved compounds that stabilize the pH of a solution by adding or removing H+
Name three hormones that play a major role in adjusting fluid and electrolyte balance in the body.
Aldosterone response to osmotic activity (higher concentration = more ADH) increase sodium reabsorption stimulates thirst ADH response to increasing K+ levels or RAAS increase water reabsorption Natriuretic peptides (ANP and BNP) response to stretching vessels inhibits ADH and Aldosterone to allow more water to be lost in urine
Fluid and Electrolyte Balance
All the homeostatic mechanisms that monitor and adjust the composition of body fluids respond to changes in the ECF, not in the ICF No receptors directly monitor fluid or electrolyte balance receptors can monitor plasma volume and osmotic concentration Cells cannot move water molecules by active transport "wherever salt goes, water follows" The body's content of water or electrolytes will increase if dietary gains exceed losses to the environment, and will decrease if losses exceed gains
What effect would being in the desert without water for a day have on the osmotic concentration of your blood plasma?
Being in the desert without water, you would lose fluid through perspiration, urination, and breathing. As a result, the osmotic concentration of your blood plasma (and other body fluids) would increase
Sodium Content Homeostatic Mechanism
If you consume large amounts of salt without adequate fluid, as when you eat salty potato chips without taking a drink, the plasma Na+ concentration increases temporarily When sodium ion losses exceed gains, the volume of the ECF decreases
What effect might drinking a half-gallon of distilled water (water without minerals) have on the ADH level?
Dilutes the concentration in ECF ADH would not be stimulated
Results of acid-base inbalance
Disorders affecting circulating buffers, respiratory performance, or renal function. Several conditions, including emphysema and renal failure Conditions such as heart failure or hypotension can affect the pH of internal fluids by causing fluid shifts and by changing the glomerular filtration rate and respiratory efficiency Conditions Affecting the Central Nervous System. Neural damage or disease that affects the CNS can affect the respiratory and cardiovascular reflexes that are essential to normal pH regulation
List the components of extracellular fluid (ECF) and intracellular fluid (ICF).
ECF Components: interstitial fluid, plasma, and other body fluids ICF Components: cytosol of a cell
fluid compartments
ECF and ICF contain different ionic concentrations and behave as separate sections
How would a prolonged fast affect the body's pH?
In a prolonged fast, fatty acids are catabolized, producing large numbers of ketone bodies, which are metabolic acids that decrease the blood pH. The decreased pH would eventually lead to ketoacidosis
alkaline tide
In gastric parietal cell, HCO3- leaves the cell in exchange for Cl- going in the cell. temporarily increases the HCO3 - concentration in the ECF during meals
ICF Ions
K+, PO43- , Mg + -charged proteins
Hypomagnesemia
MEq/L: < 1.4 Cause: Poor diet; alcoholism; severe diarrhea; kidney disease; malabsorption syndrome; ketoacidosis Symptoms: Hypocalcemia, muscle weakness, cramps, cardiac arrhythmias, hypertension Treatment: Intravenous infusion of solution high in Mg2+
Hypophosphatemia
MEq/L: < 1.8 Cause: poor diet; kidney disease; malabsorption syndrome; hyperparathyroidism; vitamin D deficiency Symptoms: Anorexia, dizziness, muscle weakness, cardiomyopathy, osteoporosis Treatment: Dietary improvement; vitamin D and/or calcitriol supplementation
Hypochloremia
MEq/L: < 100 Cause: Vomiting; hypokalemia Symptoms: Alkalosis, anorexia, muscle cramps, apathy Treatment: Diuretic use and infusion of hypertonic salt solution
Hypokalemia
MEq/L: < 3.0 Cause: Low-potassium diet; diuretics; hypersecretion of aldosterone; chronic alkalosis Symptoms: Muscular weakness and paralysis Treatment: Increase in dietary K+ content; ingestion of K+ tablets or solutions; infusion of potassium solution
Identify four physiologically important cations and two important anions in the ECF.
Na K Ca Mg Cl PO4 -3
ECF Ions
Na+, Ca+, Cl-, HCO3-
main cation in ICF
Potassium (K+) 160mEq
Which is more dangerous, disturbances of Na + balance or disturbances of K + balance? Explain your answer.
Potassium ion imbalances are more dangerous than sodium ion imbalances because they can lead to extensive muscle weakness or even paralysis when blood concentrations are too low, and to cardiac arrhythmias when the levels are too high. Disturbances in sodium balance, by contrast, produce dehydration or tissue edema.
main cation in ECF
Sodium (Na+) 140mEq
Why does prolonged sweating increase the plasma Na + level?
Sweat is a hypotonic solution with lower sodium ion concentration than the ECF. Sweating causes a greater loss of water than of sodium, increasing the blood plasma sodium ion level.
composition of the body
The body composition (by weight, averaged for both sexes) and major body fluid compartments of a 70-kg (154-lb) person males have greater muscle mass (75% water) male have larger blood volume (more ECF) female have greater adipose mass (10% water)
Identify the body's three major buffer systems.
The body's three major buffer systems are the phosphate buffer system, protein buffer systems, carbonic acid-bicarbonate buffer system
Na and K Balance
The most common problems with electrolyte balance are caused by an imbalance between gains and losses of Na+. Problems with K+ balance are less common but significantly more dangerous than problems related to Na+ balance.
pH regulation by tubule cells
The three major buffers involved: carbonic acid-bicarbonate buffer system and phosphate buffer system ammonia buffer system Glomerular filtration puts components of the carbonic acid- bicarbonate buffer system and the phosphate buffer system into the filtrate. Tubule cells (mainly those of the PCT) generate ammonia As tubule cells use the enzyme glutaminase to break down the amino acid glutamine, amino groups are released as either ammonium ions (NH4 +) or ammonia (NH3). The NH4 + are transported into the lumen in exchange for Na+ in the tubular fluid. The NH3, which is highly volatile and also toxic to cells, diffuses rapidly into the tubular fluid. There it reacts with an H+, forming NH4 +
Why must tubular fluid in nephrons be buffered?
Tubular fluid in nephrons must be buffered to avoid decreasing the pH below approximately 4.5, at which point H+ secretion cannot continue because the H+ concentration gradient becomes too steep. The hydrogen ions would leak out of the tubule as fast as they are pumped in
water gains and losses
Water content of food 1000mL Water consumed as liquid 1200mL Metabolic water produced during catabolism 300Ml Total: 2500mL Urination 1200 Evaporation at skin 750 Evaporation at lungs 400 Loss in feces 150 Total: 2500mL 2500 mL/day is required to balance your average water losses. This value amounts to about 40 mL/kg of body weight.
Why can prolonged vomiting produce metabolic alkalosis?
When a person has prolonged vomiting, large amounts of stomach hydrochloric acid (HCl) are lost from the body. More H+ and Cl- are then formed by the parietal cells of the stomach. The H+ that are released were produced by the dissociation of carbonic acid and exchange of bicarbonate ions with chloride ions from the blood. The alkaline tide of released bicarbonate ions increases the blood pH, leading to metabolic alkalosis
renal response to alkalosis
When alkalosis (high blood pH) develops, (1) the rate of H+ secretion by the kidneys declines (2) tubule cells do not reclaim the HCO3 - in tubular fluid (3) the collecting system transports HCO3 - into tubular fluid while releasing H+ and Cl- into the peritubular fluid The concentration of HCO3 - in blood decreases, promoting the dissociation of H2CO3 and the release of H+. The additional H+ generated by the kidneys help return the pH to a normal level
Renal Compensation
a change in the rates of H+ and HCO3 - secretion or reabsorption by the kidneys in response to changes in plasma pH secretion of H+ can continue only until the pH of the tubular fluid reaches 4.0-4.5. (At that point, the H+ concentration gradient is so great that H+ leak out of the tubule as fast as they are pumped in.) buffers in tubular fluid are extremely important, because they keep the pH high enough for H+ secretion to continue without buffering mechanisms, the kidneys could not maintain homeostasis
Dehydration
a decrease in the water content of the body that develops when water losses outpace water gains, and this threatens homeostasis both the ECF and ICF are somewhat more concentrated than normal if the fluid imbalance continues unchecked, the loss of body water will produce severe thirst, dryness, and wrinkling of the skin, cell crenation severe water losses such as excessive perspiration, inadequate water consumption, repeated vomiting, and diarrhea, water losses occur far in excess of electrolyte losses clinical therapies for acute dehydration include administering hypotonic fluids by mouth or intravenous infusion
amphoteric
a substance that can act as both an acid and a base
edema
abnormal amounts of water from plasma into interstitial fluid pulmonary edema: increase in BP pulmonary capillaries general edema: decrease in BCOP due to decrease in plasma proteins localized: damage, constriction or blockage of capillary walls,
metabolic acids
acid participants in, or by-products of, cellular metabolism pyruvic acid, lactic acid, and ketone bodies (synthesized from acetyl-CoA). Under normal conditions, most metabolic acids are metabolized rapidly, so significant accumulations do not occur
fixed acids
acids that do not leave solution, they remain in body fluids until they are eliminated by the kidneys sulfuric acid and phosphoric acid are the most important fixed acids in the body. catabolism of amino acids and compounds that contain phosphate groups
The partial pressure of _______ _______ is the most important factor affecting blood pH.
carbon dioxide when the CO2 level increases, additional H+ and bicarbonate ions are released, so the pH decreases as CO2 leaves the bloodstream and diffuses into the alveoli, the number of H+ and bicarbonate ions in the alveolar capillaries decreases, and blood pH increases
metabolic acid-base disorders
caused by the generation of metabolic acids or fixed acids or by conditions affecting the concentration of HCO3 - in the ECF
Why is acidosis more common?
cellular activates release acids
Electrolyte Balance
condition when the quantities of electrolytes entering the body equal those leaving it if you lose 500 mg of Na+ in urine and sweat, you need to gain 500 mg of Na+ from food and drink to remain in sodium ion balance
respiratory acidosis
develops when the respiratory system cannot eliminate all the CO2 generated by peripheral tissues the rate of pulmonary exchange is inadequate to keep the arterial PCO2 within normal limits
hypoventilation
decreased rate or depth of air movement into the lungs
protein buffer system
depend on the ability of amino acids to respond to pH changes by accepting or releasing H+ very important in both the ECF and the ICF buffering prevents destructive changes in pH when cellular metabolism produces metabolic acids, such as lactic acid or pyruvic acid when the pH of the ECF decreases, cells pump H+ out of the ECF and into the ICF, where intracellular proteins can buffer them when the pH of the ECF increases, pumps in plasma membranes move H+ out of the ICF and into the ECF
lactic acidosis
develops after strenuous exercise or prolonged tissue hypoxia (oxygen starvation) as cells rely on anaerobic metabolism
respiratory alkalosis
develops when respiratory activity lowers the blood PCO2 to a below-normal level problems with respiratory alkalosis are rare and involve primarily (1) persons adapting to high altitudes, where the low PO2 promotes hyperventilation; (2) patients on mechanical respirators (3) persons whose brainstem injuries render them incapable of responding to shifts in the plasma CO2 concentration
Identify the three interrelated processes essential to stabilizing body fluid volumes
fluid balance electrolyte balance acid-base balance
intracellular fluid (ICF)
fluid within cells (cytosol)
hemoglobin buffer system
have a significant effect on the pH of the ECF, because they absorb CO2 from the plasma and convert it to carbonic acid as the carbonic acid dissociates within an RBC, the bicarbonate ions diffuse into the plasma in exchange for chloride ions, a swap known as the chloride shift
volatile acids
leave the body by entering the atmosphere at the lungs carbonic acid (H2 CO3 ) is a volatile acid that forms through the interaction of water and carbon dioxide (faster with carbonic anhydrase) *mostly effects body pH
extracellular fluid (ECF)
mostly interstitial fluid of tissues and plasma
acidemia/acidosis
pH < 7.35
alkalemia/alkalosis
pH > 7.45
renal response to acidosis
plasma buffer mechanisms are stressed by excessive hydrogen ions Tubule cells bolster the capabilities of the carbonic acid-bicarbonate ion buffer system In a starving person, tubule cells break down amino acids, yielding ammonium ions that are pumped into the tubular fluid, bicarbonate ions to help buffer ketone bodies in the blood, and carbon chains for catabolism
carbonic-bicarbonate buffer system
primary role of this buffer system is to prevent changes in pH caused by metabolic acids and fixed acids in the ECF
metabolic acidosis
production of a large number of fixed acids or metabolic acids. the H+ released by these acids overload the carbonic acid-bicarbonate ion buffer system, so the pH begins to decrease compensation for metabolic acidosis generally involves a combination of respiratory and renal mechanism hydrogen ions interacting with bicarbonate ions form CO2 molecules that are eliminated by the lungs kidneys excrete additional H+ into the urine and generate HCO3 - that are released into the ECF
Metabolic generation
production of water within cells, primarily as a result of oxidative phosphorylation in mitochondria during aerobic metabolism
fluid shift
rapid water movements between ECF and ICF due to osmosis (more water in one compartment than another) If the osmotic concentration of the ECF increases, that fluid will become hypertonic compared to the ICF. Lose water but retain electrolytes If the osmotic concentration of the ECF decreases, that fluid will become hypotonic compared to the ICF. Gain water but but no gain of electrolytes
Cations and Anions in Bodily Fluids
represented in milliequivalents per liter (mEq/L) reflects total number of positive and negative charges in a solution
Respiratory Compensation
takes place whenever body pH strays outside normal limits Increasing or decreasing the rate of respiration alters pH by decreasing or increasing the PCO2 PCO2 increases, the pH decreases, because the addition of CO2 drives the carbonic acid-bicarbonate buffer system to the right When the PCO2 falls, the pH increases because the removal of CO2 drives that buffer system to the left A rise in PCO2 stimulates the chemoreceptors, leading to an increase in the respiratory rate. As the rate of respiration increases, more CO2 is lost at the lungs, so the PCO2 returns to a normal level. Conversely, when the PCO2 of the blood or CSF decreases, the chemoreceptors are inhibited. Respiratory activity becomes depressed and the breathing rate decreases, causing an elevation of the PCO2 in the ECF
equivalents
the amount of a positive or negative ion that supplies 1 mole of electrical charge 1 equivalent = 1000 milliequivalents K+ = 1000mEq Ca2+ = 2000mEq
fluid balance
the amount of water you gain each day is equal to the amount you lose to the environment involves regulating the content and distribution of body water in the ECF and the ICF digestive system is main source of water gain urinary and perspiration is main of water loss
acute respiratory acidosis
the chemoreceptors do not respond, if the breathing rate cannot be increased, or if the circulatory supply to the lungs is inadequate, the pH will continue to decrease
hyperventilation
the condition of taking abnormally fast, deep breaths continued hyperventilation can increase the pH to a level as high as 8.0 condition generally corrects itself, because the reduction in PCO2 halts the stimulation of the chemoreceptors, so the urge to breathe fades until the CO2 level has returned to normal
osmolarity
total concentration of all solute particles in a solution osmotic concentrations of the ICF and ECF are identical because ions and proteins each count as one particle in solution, despite their number of electrical charges osmosis balances out concentration because cell membranes are permeable to water
sensible perspiration
water excreted by sweat glands
ECF and Blood Volume
when ECF volume changes, so does plasma volume and, in turn, blood volume If the ECF volume is inadequate, both blood volume and blood pressure decrease, and the renin-angiotensin-aldosterone system is activated. In response, losses of water and Na+ are decreased, and gains of water and Na+ are increased. The net result is that ECF volume increases. If the plasma volume becomes abnormally large, venous return increases, stretching the atrial and ventricular walls and stimulating the release of natriuretic peptides (ANP and BNP). This in turn decreases thirst and blocks the secretion of ADH and aldosterone, which together promote water or salt conservation. As a result, salt and water loss by the kidneys increases and the volume of the ECF decreases
metabolic alkalosis
when the HCO3 - concentration is elevated HCO3 - then interact with H+ in solution, forming H2CO3. The resulting decrease in H+ concentration causes signs of alkalosis compensation for metabolic alkalosis involves a decrease in the breathing rate, coupled with an increased loss of HCO3 - in urine
Acid-Base Balance
when the production of hydrogen ions in your body is precisely offset by their loss pH is withing normal limits prevent decrease is pH is difficult, metabolic process produce generate acids DCT and collecting tube buffers blood pH and lungs release bicarbonate into circulation