Chapter 26: Fluid, Electrolyte and Acid-Base Balance Flashcards
Water Content of the Body
influenced by age, body mass, fat content and sex; infants 73%, young male 60%, young female 50% (bc of higher fat), elderly 45%
Intracellular Fluid Compartment
fluid within cells (cytoplasm) 40% of body weight
Extracellular Fluid Compartment
fluid outside cells 20% of body weight 2 divisions- plasma (confined to blood vessels) and interstitial fluid (spaces between cells)
Electrolytes
dissociate in water to form ions (such as NaCl + h20 = Na + Cl)
Nonelectrolytes
do not dissociate in water; most are organic molecules (lipids, glucose etc)
In ECF main cation and manin anion is
Na and Cl
In ICF main cation and main anion is
K and HPO4
Fluid MOvement Among Compartments
ions move selectively between compatments via facilitated diffusion or active transport; h20 moves passively (always) between compartments to equalize ECF and ICF osmolaties (solute concentration); h20 ALWAYS follows ECF osmolaity
Increase in ECF osmolality =
h20 diffusing out of cells
Decerease in ECF osmolality =
h20 diffuses into cells
Dehydration
water loss exceeds intake; causes: homorrhage, severe burns, prolonged vomiting or diaherra, profuse sweating, water deprivation and dieuretic abuse; may lead to hypervolemic shok (not enough blood volume)
Hypotonic Hydration
water gain exceed outtake which leads to cells swelling; causes: renal insufficiency or consuming large amounts of water too quickly results hyponatremia (liw ECF na); may lead to cerebral edma and death
Edema
atypical accumulation of fluid in the interstitial fluid space which leads to tisses swelling; causes: pregnancy, increased NaCl, congestive heart failure, kidney disease; may impair diffusion of o2 and nutrients or blood circulation
Electrolyte Balance
usually refers to salt balance in the body; maintained primarily by the kidneys
Regulation of Na Balance
sodium required to maintain fluid balance, BP, nerve impulse conduction, and muscle contraction; na contraction and na body content are monitored indirectly
What is the most important hormone for regulating Na?
aldosterone
Renin-Angiotensin-Aldoesterone Mechanism
RAA; 90% of sodiu absorption is obligatory (65% from PCT and 25% from ascending limb); remaining 10% absorbed from DCT and collecting duct ONLY if aldosterone is present
What triggers the RAA mechanism?
low body na content; increased potassium in ECF; low systemic BP
Estrogens are similar too…
aldoesterone and leads to water retention
How does addisons disease affect na balance?
autoimmune disorder that attacks adrenal cortex which inhibits aldoesterone which leads to a lot of urination (polyuria) and that can lead to releaseing too much na (and water)
Atrial Natriuretic Peptide
ANP; reduces BP and volume by inhibting systemic vasoconstriction, na and h2o reabsorption
Regulation of K Balance
potassium required for proper kidney and heart function, nerve impulses and muscle contraction; as with na 90% of K reabsorption is obligatory (65% from PCT and 25% from ascending limb); HOWEVER (unlike sodium) K is secreted into DCT and Collecting duct
What two factors influence K secretion?
K concentration in ECF (most impt) (increasing K causes it to be secreted more and reverse); and Aldosterone (enhances K secretion into filtrate)
Regulation of Ca and HPO4
99% of bodys calcium found in bones as calcium phosphate salts; ECF levels regulated by PTH; decreased ca in ECF stimulates PTH release
Increased Ca reabsorption causes
decreased phosphate reabsorption in DCT; activates osteoclasts to break down bone ; stimulates kidneys to transform vit D to its active form enabling ca absorption from the small intestine
Hyper/Hyponatremia
na excess/deficit
Hyper/Hypokalemia
K excess/deficit
Hyper/Hypophosphatemia
HPO4 excess/deficit
Hyper/Hypocalemia
ca excess/deficit
Acids
release H into solution
Bases
remove H from a solution
H of blood regulated by…
1) chemical buffers (act w/n secs); 2) brain stem respiratory centers (act within 1-3mins); 3) renal mechanism(takes hours to days to change blood pH)
Chemical Buffer System
a mixture of compounds that minimize changes in pH when a strongacid or base is added; if pH drops, buffer system ties up (removes) h from solution; if pH increases buffer sys releases (adds) H to solution
Bicarbonate Buffer System
impt buffer sys in ECF; mixture of carbonic acid (weak acid) and sodium bicarbonate (weak base)
Phosphate Buffer System
impt buffer in urine and ICF; mixture of sodium dihydrogen phosphate (NaH2PO4) (weak acid) and sodium monohydrogen phosphate (Na2HPO4) (weak base)
Protein Buffer System
most imp buffer in ICF; also operates in blood plasma; most protein molecules are amphoteric: if pH rises it can act as a acid and if it drops it can act as a base
What is the most important buffer in RBCs
hemoglobin
What systems are included in the physiological buffering system?
respiratory sys and renal sys
Respiratory System H Regulation
adjusts pH by expelling or retaining co2
Respiratory System response to Acidosis
decreased pH detected by central and peripheral chemoreceptors; which stimulates medullary respiratroy center to increase respiration which leads to a decrease in blood co2 which decreases H2CO3 which increases blood pH
Respiratory System Response to Alkalosis
increased pH detected by central and peripheral chemoreceptors which inhibits the medullary respiratory center which results in decreased respiration this leads to increased blood co2 which increases blood H2CO3 which lowers pH
Hypoventilation
co2 accumulation; leads to increased blood H levels which causes respiratory acidosis
Hyperventilation
co2 elimination (a lot) leads to decreased blood H content which causes respiratory alkalosis
Renal System Regulation of H
adjusts pH by regulating blood levels of HCO3
Renal Response to Acidosis
if pH drops the kidneys conserve (reabsorb) filtered HCO3 from PCT and returns it to the peritubular capillaries
Kidneys generate new…
HCO3 in PCT cells that moves into the peritubular capillaries; new HCO3 generated via buffering of secreted H by HPO4 OR new HCO3 generated via glutamine metabolism and NH4 secretion
Renal Response to Alkalosis
if blood pH increaes kidneys excrete (secrete) HCO3 into collecting ducts to pass out in urine
Respiratory Acidosis
most common cause of acid base imbalance; results from co2 retention; if uncompensated Pco2 >45 mmhg and ph <7.35; renal mechanism tries to compensate b retaining HCO3
Respiratory Alkalosis
co2 eliminated faster than it is generated; if uncompensated Pco2 <35 mmhg and pH > 7.45; renal sys tries to compensate by eliminating HCO3
Metabolic Acidosis
occurs when nonvolatile acids (such as lactic acid and ketone bodies) accumulate in blood or HCO3 is lost from body; if uncompensated HCO3 <22 mEq/L and pH < 7.35; respiratory sys attempts to compensate by increasing rate and depth of breathing
Metabolic Alkalosis
occurs when HCO3 levels are excessive; if uncompensated HCO3 >26 mEp/L and pH >7.45; respiratory sys attempts to compensate by decreasing rate and depth of breathing
Steps to Identifying Acidosis/Alkalosis
1) determine blood pH (if it is high or low); 2) check Pco2 and HCO3 levels for cause of blood pH; 3) check for compensation; if respiratory imbalance look at HCO3 and vice versa
ADD VALUES FOR IDENTIFYNG
