Acid base physiology Flashcards
What is normal blood plasma pH
7.35-7.45
how is blood plasma maintained
lungs: through CO2 excretion
kidneys: varying rate of H+ excretion and HCO3- production
What is a normal PCO2 level and HCO3 concentration
40mmHG (PCO2)
24mmol/L
-to maintain pH
what pH range is compatible with life but if it is maintained chronically can cause kidney failure
6.8-7.8
Respiratory acidosis/alkalosis is measured by what
Metabolic acidosis/alkalosis is measured by what
CO2
HCO3-
Normal defense against a pH disturbance occurs in what order
1st line of defense is buffers
2nd line of defense is ventilation
3rd is the renal system
Buffers as a normal defense against pH disturbance
immediate limitation on pH change
-henderson-hasselbalch equation is used to mathematically calculate the ability of a buffer to change pH
-chemical reactions
ventilation changes as a normal defense against pH disturbance
-CO2 excretion can adjust within seconds to minutes
-henry’s law: concentration of a gas in solution is directly proportional to partial pressure of the gas
-CO2 + H2O –> H2CO3 –> H+ +HCO3-
-as CO2 increases so does the concentration of H2CO3 and H+
Renal system as a normal defense against pH disturbance
-finally line of defense
-regulates plasma HCO3- (buffer in plasma)
-excretes fixed metabolic acids (NH4+ and H2PO4-)
what makes someone go into metabolic acidosis or metabolic alkalosis
-vomiting = metabolic alkalosis
-diarrhea = more bicarb
Respiratory role in acid base balance
-balance CO2 excretion with metabolic CO2 production
-arterial PCO2 is monitored by central chemoreceptors
-increase in pulmonary ventilation (hyperventilation)
~decrease CO2 and H+
~increase pH (more basic)
-decrease in pulmonary ventilation (hypoventilation)
~increases CO2 and H+
~decrease pH (more acidic)
-alkalosis causes a less severe acidosis
what is the kidney’s role in acid base balance
-regulation of plasma HCO3-
~most is reabsorbed in proximal tubule
~in tubule bicarbonate binds with H+ to form carbonic acid and then carbonic anhydrase in the membrane converts the carbonic acid to CO2
-excretion of fixed metabolic acids
~ammonium ions - accounts for approx. 75% of H+ excretion
~phosphoric acid - 25%
urine concentration: -renal system has much to do with body maintaining fluid osmolarity within narrow limits by
-adequate glomerular filtration (kidney failure = GFR decreases)
-Na+ reabsorption without H2O reabsorption in the ascending limb of the loop of hence
-H2O permeability in the collecting ducts is variable and controlled by ADH
Clearance
-volume of plasma (going through at a time) rendered fee of a given substance in 1 minute
What is used to estimate GFR
-inulin
-creatinine
can also be used to estimate the renal blood flow
Inulin
a low-molecule weight polysaccharide but must be infused intravenously
-small enough to be filtered through glomerulus
-not reabsorbed nor secreted through glomerulus
-see how long it goes through
creatinine
product of muscle metabolism (kidney function)
-constant function of muscle mass
- slightly overestimate GFR because some is secreted in PCT
-good diet index of GFR
-low GFR results in increased plasma creatinine
-defines stages of renal failure
Na+
-65% reabsorbed in PCT
-active transport (Cl- is passive but coupled to movement of Na+)
-distal tubule and collecting duct has variable reabsorption of the 10% that it receives (water reabsorption is coupled to NaCl via osmosis)
Mg++
balance between intestinal uptake and urinary excretion
-regulation occurs in thick ascending limb and DCT
-essential cofactor in enzymatic reactions
Urea
normal 8mg/dL-25mG/dL
-end product of nitrogen metabolism
-bun not subjected to homeostatic regulation
-ADH stimulates urea reabsorption in the collecting duct
Ca++
normal 4.0-5.2 mg/dL
-balance between GI system, renal system, and extracellular fluid and bone matrix
-PTH and vitamine D control
-handling is similar to Na+
PO4
-normal 2.5 - 4,5 mG/dL
-intestinal uptake, renal excretion and exchange in bone
-almost exclusively reabsorbed in PCT
K+
-normal 3.5-5.5mEq/L
-majority reabsorbed in PCT
-essential to maintain resting membrane potential
-aldosterone control K balance intra and extracellularly
-reciprocal relationship between secretion of H+ and K+ in collecting duct
Respiratory acidosis
-decreased excretion of CO2
-increased arterial PCO2 and H+
-PCO2>45mmHg
-renal compensation
~increase H+ excretion and HCO3 production
~secondary metabolic alkalosis
respiratory alkalosis
-decrease arterial PCO2 and H+
-PCO2 < 35mmHG
-renal compensation
~decrease H+ excretion and HCO3 production
~secondary metabolic acidosis
metabolic acidosis
-deceased kidney elimination of H+ and increased production of acidic substances
-plasma HCO3 < 22meq/L
-respiratory compensation
~hyperventilation
~secondary respiratory alkalosis
metabolic alkalosis
-plasmas HCO3- >28meq/L
-respiratory compensation
~hypoventilation
~secondary respiratory acidosis
What happens to pH during exercise
pH drops
-production of CO2 and carbonic acid in working skeletal muscle
-production of lactic acid
-ATP breakdown in woking skeletal muscles
-effects of increased acidity in skeletal muscle
-inhibits enzymes that imitate ATP production in glycolysis and aerobic respiration
-inhibites contractile process because H+ competes with calcium ions for binding on troponin (needed for contraction)
effects of exercise on pH depend on
-exercise intensity
-amount of muscle mass involved
-duration of exercise
Lactate threshold
around the shift of low intensity to moderate intensity exercise
-HCO3 drops and pH drops
intracellular buffer systems
-4 in the cytosine of muscle fiber
-sarcolemma hydrogen ion transporters
-influence of muscle fiber types
what are the 4 cytosine muscle fiber buffers system
-bicarbonate: converts strong acid to weak
-phosphates: converts strong acid to weak
-cellular proteins: accepts H+
-histidine-dipeptides (carnosine): accepts H+
Sacrolemma hydrogen ion transporters
-protect muscle tissue
-NA-H exchange 1:1
-monocarboxlate transporters (MCTs) - 1:1 of lactate;H+ ARE MOVED ACROSS
influence of muscle fiber types on intracellular buffer systems
-type 2 muscle fibers higher buffering capacity
-HITT improves buffering capacity
extracellular (blood) buffer systems
-proteins
hemoglobin
bicarbonate
proteins as an extracellular buffer syste
-similar to function in intracellular compartment
-usefullness during exercise is limited
hemoglobin
important buffer (6x more than proteins)
-especially during gest
-deoxygenated>oxygenated
bicarbonate as an extracellular buffer
-pobablly most important
-henderson-hasselbach equation is used to describe the ability of bicarbonate and carbonic acid to act as a buffer system
