Lecture 12: Body fluid, electrolytes, and acid-base homeostasis Flashcards
What does body fluid consist of? 
Consist of liquids (H2O) and body plus dissolved solutes 
What is the body water content of an infant? 
~73% of total body mass
What is the body water content of females?
55%
What is the body water content of males?
60%
What percent does body water content decline to an old age?
Approximately 45%
What are the two main body fluid compartments?
- Intracellular fluid (ICF) compartment: fluid inside cells
- Extracellular fluid (ECF) compartment: fluid outside cells; which has two compartments:
i) Plasma: 20% (3 L)
ii) Interstitial fluid (ISF): 80% (12 L) in spaces btw cells
what is the composition of body fluids
-Water is the universal solvent
-Substances dissolved in water – solutes
-Solutes are classified as nonelectrolytes and electrolytes
what is the nonelectryolytes composition of body fluids
Nonelectrolytes – most are organic molecules
-Do not dissociate in water
-Examples: glucose, lipids, creatinine, and urea
-No charged particles are created
what is the electrolytes composition of body fluids
-Dissociate into ions in H2O; Ex: inorganic salts, all acids and bases, some proteins
-ions conduct electrical current
-Greater osmotic power than nonelectrolytes
-Greater ability to cause fluid shifts due to ability to dissociate into two or
more ions
-NaCl → Na+ + Cl- (electrolyte; 2 particles)
-MgCl2 → Mg2+ + 2Cl- (electrolyte; 3 particles)
-Glucose → Glucose (nonelectrolyte; 1 particle)
-Conc expressed in milliequivalents per liter (mEq/L) – measure of electrical
charges per liter of solution
what are the two barries seperating body fluids
plasma membrane & blood vessel walls
what body fluids does the plasma membrane seperate
seperates ICF from ISF
what body fluids do blood vessel walls seperate
seperates ISF from blood plasma
describe fluid balance
-Exists when right amt of H2O and solutes are present in the diff compartments
-H2O – largest body component; Amt depends on age, gender and fat content
-H2O and solutes exchange with the compartments – osmosis, diffusion, filtration, reabsorption
-Solute conc. determines direction of H2O flow btw ICF and ISF
-Electrolyte balance is essential to fluid balance
describe body water gain and loss
-H2O Gain = H2O Loss → body fluid vol. constant
-H2O Gain – ingestion and metabolic synthesis
-H2O Loss – urination, perspiration, exhalation, and in feces
describe the regulation of water gain
-Vol. of metabolic H2O formed is determined by aerobic respiration
-Amt of H2O formed is directly proportional to amt of ATP produced
-When H2O loss > H2O gain → dehydration → decrease bld vol → increase fluid osmolarity → activate osmoreceptors → stimulate thirst center → thirst response → increase thirst
describe the regulation of water loss
-Excess body H2O elimination occurs through urine production
-Two main solutes in urine – Na+ and Cl-; Amt of urinary salt (NaCl) loss is the first factor determining body fluid vol
-Wherever solutes go, water follows – osmosis
-The major hormone that regulates H2O loss is antidiuretic hormone (ADH)
describe aldoesterone’s role in regulation of water and solute loss
-descreased bp & Na+ deficiency in plasma->
-increased release of renin from kidneys->
-increased aldosterone formation->
-increases Na+ reabsorption in late distal tubules and collecting ducts of kidneys. water reabsorption accompanies Na+ reabsorption via osmosis because antidiuretic hormone (ADH) is also released when there is a decrease in bp->
-the increased Na+ reabsorption relieves the Na+ deficiency in plasma; the accompanying water reabsorption increases blood volume and blood pressure
describe atrial natrdiurdetic peptide (ANP)s role in regulation of water and solute loss
increased bllod volume-> increased stretch of atria-> release of atrial natriuretic pepetide (ANP)-> inncreaszes excretion of Na+ ions into urine natriuresis). water excretion into urine also increases due to osmosis-> the increase in water excretion causes a decrease in blood volume and blood pressure
what factors maintain body water balance
thirst center in hypothalamus, ADH, aldosterone, atrial natruiretic peptibe
what is the mechanism and effect of the thirst center in the hypothalamus in maintaining body water balance
mechanism: stimulates desire to drink fluids
effect: water gained if thirst is quenched
what is the mechanism and effect of antidiuretic hormone (ADH) in maintaining body water balance
mechanism: promotes insertion of water-channel proteins (aquaporin-2) into apical membranes of principal cells in collecting ducts of kidneys, as a result water permeability of these cells increases and more water is reabsorbed
effect: reduces loss of water in urine
what is the mechanism and effect of aldosterone in maintaining body water balance
mechanism: by promoting urinary reabsorption of Na+ it increases water reabsorption via osmosis
effect: reduces loss of water in urine
what is the mechanism and effect of atrial natriuretic peptide (ANP) in maintaining body water balance
mechanism: promotes natriuresis, elevated urinary excretion of Na+, accompanied by water
effect: increases loss of water in urine
describe the regulation of anions
-Cl– is major anion accompanying Na+ in ECF:
~Helps maintain osmotic pressure of blood
~99% of Cl– is reabsorbed under normal pH
~Passively follows Na+ in PCT and is coupled to active transport of Na+ in other tubule segments
-When acidosis occurs, fewer chloride ions are reabsorbed in lieu of HCO3–
-Other anions have transport maximums, and excesses are excreted in urine. Examples: sulfates and nitrates
what is water intoxication
occurs when excess body H2O causes cells to swell, may occur when a person consumes H2O faster than the kidneys can excrete it
-Normally, ECF is isotonic to cells of the body → cells do not shrink or swell
-Changes in osmolarity of ECF (dehydration or over- hydration) cause cells of the body to shrink or swell
describe the process of water intoxication
excessive blood loss, sweating, vomiting, or diarrhea coupled with intake of plain water-> decreasee Na+ concentration (hyponatremia) of extracellular fluid (interstitial fluid and plasma)-> decreased osmolarity of water from extracellular fluid into intracellular fluid-> water intoxication (cells swell)-> mental confusion, seizures, coma, and possible death
what are the functionsof electrolytes that dissocaite and dissolve to form ions
- Control osmosis of H2O btw fluid compartments
- Help maintain the acid-base balance
- Transfer electrical current
- Serve as cofactors
-Blood plasma, ISF, and ICF have diff conc of electrolytes and protein ions
-Blood plasma contains many protein ions; ISF contains only a few
describe the sodium ion in the body
most abundant cation in ECF
-Used for impulse transmission, muscle contraction, fluid, and electrolyte balance
-its level is controlled by aldosterone, ADH, and ANP
describe the chloride ion in the body
major extracellular anion
-Helps regulate osmotic pressure btw compartments
-Forms HCl in the stomach
-Cl- balance is regulated by aldosterone
describe the potassium ion in the body
most abundant cation in ICF
-Involved in fluid volume, impulse conduction, muscle contraction, and regulating pH
-Mineralocorticoids (mainly aldosterone) regulate the plasma level
describe the bicarbonate ion in the body
important plasma ion
-Major member of the plasma acid-base buffer system
-Kidneys reabsorb or secrete it for final acid-base balance
describe the calcium mineral in the body
most abundant mineral in the body
-Structural component of bones and teeth
-Used for blood coagulation, neurotransmitter release, muscle tone, excitability of nerves and muscles
-Level in plasma regulated by parathyroid hormone
describe phosphate in the body
occurs as calcium phosphate salt
-Used in the buffer system
-Regulated by parathyroid hormone and calcitriol
describe magnesium in the body
an intracellular cation
-Activates enzymes involved in carbohydrate and protein metabolism
-Used in myocardial function, transmission in the CNS, and operation of the sodium pump
describe pH around the body
-pH affects all functional proteins and biochemical reactions, So closely regulated by the body
-Normal pH of Body Fluids:
~Arterial blood – pH 7.4
~Venous blood and interstitial fluid – pH 7.35
~ICF – pH 7.0
-Metabolic reactions release a large amt of H+
-Needs to be removed to maintain homeostasis
what three sequential mechanisms regulate H+ concentration
- Chemical Buffer systems – binds and remove highly reactive excess H+
- Respiratory centers in Brainstem (exhalation of CO2) – reduces carbonic acid (H2CO3) → increase pH
- Renal mechanisms (Kidney excretion of H+) – remove other acids through urine
explain the chemical buffer system
-strong acids dissociate completely in H2O; can dramatically affect pH
-Weak acids dissociate partially in H2O; are efficient at preventing pH changes
-Strong bases dissociate easily in H2O; quickly tie up H+
-Weak bases accept H+ more slowly
what is a chemical buffer
a system of one or more compounds that act to resist pH changes when strong acid or base is added
-will bind H+ if pH drops or release H+ if pH rises
what are the three major buffering systems
- protein buffer system
- bicarbonate buffer system
- phosphate buffer system
describe the protein buffer system
-Most abundant in ICF and blood plasma
-Protein molecules are amphoteric – can function as both weak acid and weak base
-When pH rises, organic acids or carboxyl (COOH) groups behave like acid to release H+
-When pH falls, NH2 groups behave like a base to bind H+
-Therefore, proteins buffer both acids and bases
describe the carbonic acid-bicarbonate buffer system
-Based on the bicarbonate ion (HCO3-) – acts as a weak base, and carbonic acid (H2CO3) – acts as a weak acid
-Buffers both ICF and ECF, but is only important ECF buffer
-If pH falls, HCO3- binds excess H+ and forms H2CO3
-If pH rises, H2CO3 dissociate to provide H+
describe the phospahte buffer system
-Acts similarly to the bicarbonate buffer system
-Components are sodium salts of:
*A weak acid – Dihydrogen phosphate (H2PO4-)
*A weak base – Monohydrogen phosphate (HPO42-)
-H+ released by strong acids is tied up with a weak base:
-Strong bases are converted to weak bases – HPO42- act as a weak base
overview of buffer system
most consist of a weak acid and its salt, which functions as a weak base. they orveent drastic changes in body fluid pH
overview of proteins in pH balance
the most abundant buffers in the body cells and blood. hemoglobin inside red blood cells is a good buffer
overview of carbonic acid-bicarbonate in pH balance
important regulator of blood pH. the most abundant buffers in extracellular fluid
overview of phosphates in pH balance
important buffers in intracellular fluid and urine
overview of exhalation of CO2 in pH balance
with increased exhalation of CO2, pH rise (fewer H+). with decreased exhalation of CO2, pH falls (more H+)
overview of kidneys in pH balance
renal tubules secrete H+ into urine and reabsorb HCO3- so it is not lost in urine
blood pH of acidosis
<7.35
blood pH of alkalosis
> 7.45
what is respiratory acidosis
blood pH drops due to excessive retention of CO2 leading to excess H2CO3
what is respiratory alkalosis
blood pH rises due to excessive loss of CO2 as in hyperventilation
what is metabolin acidosis
arterial blood levels of HCO3- falls
what is metabolic alkalosis
arterial blood levels of HCO3- rises
define, list common causes, and compensatory mechanism of respiratory acidosis
-definition: increased Pco2 (above 45 mmHg) and decreased pH (below 7.35) if no compensation
-common causes: hypoventilation due to emphysema, pulmonary edema, trauma to respiratory center, airway obstructions, or dysfunction of muscles of respiration
-compensatory mechanism: renal: increased excretion of H+; increased reabsorption of HCO3-. in compensation is complete, pH will be within normal range but Pco2 will be high
define, list common causes, and compensatory mechanism ofrespiratory alkalosis
-definition: decreased Pco2 (below 35mm Hg) and decreased pH (below 7.35) if no compensation
-common causes: hyperventilation due to oxygen deficiency, pulmonary disease, cerebrovascular accident (CVA), or severe anxiety
-compensatory mechanism: renal: decreased excretion of H+; decreased reabsorption of HCO3-. if compensation is complete, pH will be within normal range but Pco2 will be low
define, list common causes, and compensatory mechanism of metabolic acidosis
-definition: decreased HCO3- (below 22 mEq/liter) and decreased pH (below 7.35) if no compensation
-common causes: loss of bicarbonate ions due to diarrhea, accumulation of acid (ketosis), renal dysfunction
-compensatory mechanism: respiratory: hyperventilation, which increases loss of CO2. if compensation is complete, pH will be within notmal range but HCO3- will be low
define, list common causes, and compensatory mechanism of metabolic alkalosis
-definition: increased HCO3- (above 26 mEq/liter) and decreased pH (above 7.45) if no compensation
-common causes: loss of acid due to vomiting, gastric suctioning, or use of certain diuretics; excessive intake of alkaline drugs
-compensatory mechanism: respiratory: hypoventilation, which slows loss of CO2. if no compensation is complete, pH will be within normal range but HCO3- will be high
