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Chapter 27 Fluid, Electrolyte, and Acid-Base Balance

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When the amount of water you gain each day is equal to the amount you lose to the environment, you are in
fluid balance
When the production of hydrogen ions in your body is precisely offset by their loss, you are in
acid-base balance
Electrolyte balance primarily involves balancing the rates of absorption across the digestive tract with rates of loss at the
kidneys and swear glands
Nearly two-thirds of the total body water content is
intracellular fluid (ICF)
Extracellular fluids in the body consist of
interstitial fluid, blood plasma, lymph, cerebrospinal fluid, synovial fluid, serous fluids, aqueous humor, perilymph, endolymph
The principal ions in the ECF are
sodium, chloride, bicarbonate
If the ECF is hypertonic with respect to the ICF, water will move
from the cells into the ECF until osmotic equilibrium is restored
When water is lost but electrolytes are retained, the osmolarity of the ECF rises and osmosis then mvoes water
out of the ICF and into the ECF until isotonicity is reached
When pure water is consumed, the ECF becomes
hypotonic with respect to the ICF
Physiological adjustments affecting fluid and electrolyte balance are mediated primarily by
ADH, aldosterone, ANP & BNP
The two important effects of increased release of ADH are
reduction of urinary water losses and stimulation of the thirst center
Secretion of aldosterone occurs in response to
a drop in plasma volume at the juxtaglomerular apparatus, a decline in filtrate osmotic concentration at the DCT, high potassium ion concentrations
Atrial natriuretic peptide hormone
reduces thirst, blocks the release of ADH, blocks the release of aldosterone
The principal ions in the ECF are
sodium, chloride, and bicarbonate
The force that tends to push water out of the plasma and into the interstitial fluid is the
net hydrostatic pressure
The exchange between plasma and interstitial fluid is determined by the relationship between the
net hydrostatic and net colloid osmotic pressures
The concentration of potassium in the ECF is controlled by adjustments in the rate of active secretion
along the distal convoluted tubular and collecting system of the nephron
The activity that occurs in the body to maintain calcium homeostasis occurs primarily in the
bone, digestive tract, kidneys
The hemoglobin buffer system helps prevent drastic alterations in pH when
the plasma PCO2 is rising or falling
The primary role of the carbonic acid-bicarbonate buffer system is in preventing pH changes caused by
the rising and falling of the plasma PCO2
Pulmonary and renal mechanisms support the buffer systems by
secreting or generating hydrogen ions, controlling the excretion of acids and bases, generating additional buffers when necessary
The lungs contribute to pH regulation by their effects on the
carbonic acid-bicarbonate buffer system
Increasing or decreasing the rate of respiration can have a profound effect on the buffering capacity of body fluids by
lowering or raising the PCO2
The renal response to acidosis is limited to
secretion of H+ and generation or reabsorption of HCO3
When carbon dioxide concentrations rise, additional hydrogen ions are produced and the
pH goes down
Disorders that have the potential for disrupting pH balance in the body include
emphysema, renal failure, neural damage, CNS disease, heart failure, hypotension
Respiratory alkalosis develops when respiratory activity
lowers plasma PCO2 to below-normal levels
The most frequent cause of metabolic acidosis is
production of a large number of fixed or organic acids
A mismatch between carbon dioxide generation in peripheral tissues and carbon dioxide excretion at the lungs is a
respiratory acid-base disorder
The major causes of metabolic acidosis are
production of a large number of fixed or organic acids, impaired ability to excrete H+ at the kidneys, a severe bicarbonate loss
The most important factor affecting the pH in body tissues is
the PCO2
As a result of the aging process, the ability to regulate pH through renal comensation declines due to
a reduction in the number of functional nephrons
The risk of respiratory acidosis in the elderly is increased due to
a reduction in vital capacity
All of the homeostatic mechanisms that monitor and adjust the composition of body fluids respond to changes in the
extracellular fluid
Important homeostatic adjustments occur in response to changes in
plasma volume or osmolarity
All water transport across cell membranes and epithelia occur passively, in response to
osmotic gradients and hydrostatic pressure
Whenever the rate of sodium intake or output changes, there is a corresponding gain or loss of water that tends to
keep the sodium concentration constant
Angiotensin II produces a coordinated elevation in the ECF volume by
stimulating thirst, causing the release of ADH, triggering the secretion of aldosterone
The rate of tubular secretion of potassium ions changes in response to
alterations in the potassium ion concentration in the ECF, changes in pH, aldosterone levels
The most important factor affecting the pH in body tissues is
carbon dioxide concentration
The body content of water or electrolytes will rise if
intake exceeds outflow
When an individual loses body water
plasma volume decreases and electrolyte concentrations rise
The most common problems with electrolyte balance are caused by
an imbalance between sodium gains and losses
Sodium ions enter the ECF by crossing the digestive epithelium via
facilitated diffusion and active transport
Deviations outside of the normal pH range due to changes in hydrogen ion concentrations
disrupt the stability of cells membranes, alter protein structure, change the activities of important enzymes
When the PCO2 increases and additional hydrogen ions and bicarbonate ions are released into the plasma, the
pH goes down, acidity rises
Important examples of organic acids found in the body are
lactic acid and ketone bodies
In a protein buffer system, if the pH increases a carboxyl group (COOH) of an amino acid dissociates and releases
a hydrogen ion
Normal pH values are limited to the range between
7.35-7.45
The condition that results when the respiratory system cannot eliminate all the carbon dioxide generated by peripheral tissues is
respiratory acidosis
When a pulmonary response cannot reverse respiratory acidosis, the kidneys respond by
increasing the rate of hydrogen ion secretion into the filtrate
Chronic diarrhea causes a severe loss of bicarbonate ions resulting in
metabolic acidosis
Compensation for metabolic alkalosis involves
decreased pulmonary ventilation, increased loss of bicarbonates in the urine