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