urinary 4 Flashcards
acid-base balance
internal amount of a substance = Pool
Input : external environment/ produced in body (metabolism)
output : excreted/ used up in body
-to remain stable must balance (central to homeostasis, in this case blood H+ homeostasis)
three states of total-body balance are possible
- negative balance (loss>gain)
- positive balance (gain >loss)
- stable balance (gain=loss)
sources of hydrogen gain
- hypoventilation
- produced in metabolism
- loss of bicarbonate in diarrhea, urine
sources of hydrogen loss
- hyperventilation
- used in metabolism
- loss in vomit, urine
acid-base balance
-Normal pH arterial blood 7.35 to 7.45
Alkalosis > 7.45 →increased pH/ decreased H+
Acidosis <7.35 → decreased pH/increased H+
pH limit for sustaining life :
-<6.8 : nervous system depression; can lead to coma/death
→7.8 nervous system overexcited; can lead to convulsion/respiratory arrest
Buffering - 1st line defense
(immediate response)
chemical buffer : can reversibly bind hydrogen
reaction : buffer + H+ ←→ HBuffer
- -does not eliminate hydrogen from body or add it to body*
- try to stabilize hydrogen concentration against changes in either direction
Bicarbonate buffer
(major extracellular buffer)
H2CO3 ←→H+ + HCO3-
carbonic acid ←→hydrogen ion + Bicarbonate ion
- plasma H+ concentration decreases (alkalosis) → carbonic acid releases hydrogen and bicarbonate (reaction to right)
- plasma H+ concentration increases (acidosis) - hydrogen combines with bicarbonate to form carbonic acid (reaction to left)
Alkaline reserve = amount of bicarbonate in body
Phosphate buffer
(one of major intracellular buffers)
H2PO-4 ←→ H+ + HPO2-4
Dihydrogen phosphate ←→ Hydrogen Ion + Monohydrogen phosphate
-Plasma H+ concentration decreases (alkalosis) - dihydrogen phosphate releases hydrogen (reaction to right)
-Plasma H+ concentration increases (acidosis) - monohydrogen phosphate binds hydrogen (reaction to the left)
Protein buffer (one of major intracellular buffers)
Hb-H←→ H+ + Hb
Deoxyhemoglobin ←→ Hydrogen Ion + Hemoglobin
- plasma H+ concentration decreases (alkalosis) -carboxyl end of protein releases hydrogen (reaction to right)
- plasma H+ concentration increases (acidosis) - amino end of protein binds hydrogen (reaction to left)
Respiratory mechanism - 2nd line of defense (minutes)
-lungs react via ventilation (“breathing buffer”) and CO2 changes
CO2 + H2O ←→ H2CO3←→ H+ + HCO3-
Carbon dioxide + water ←→ carbonic acid ←→ hydrogen ion + bicarbonate ion
- plasma H+ concentration decreases (alkalosis), lungs response by hypoventilation to increase blood Co2 to increase H+ (reaction to right)
- Plasma H+ concentration increases (acidosis), lungs response by hyperventilation to decrease blood CO2 to decrease H+ (reaction to left)
Renal mechanism -3rd line of defense (hours/days)
- kidneys react to hydrogen and/or bicarbonate changes (urinary buffer)
- plasma H+ concentration decreases (alkalosis), kidneys’ response to excrete large quantities HCO3- to increase plasma H+ concentration
- plasma H+ concentration increases (acidosis), kidneys’ response to not excrete HCO3- in urine and produce new HCO3- to add to plasma to decrease plasma H+ concentration
renal mechanism - 3rd line of defense
bicarbonate = HCO3
- Considered filtered bicarbonate being reabsorbed even though not the actual same molecule (moving into interstitial fluid )
- Hydrogen is secreted (moved to tubular lumen)
renal mechanisms -3rd line of defense (hours/days)
-considered new bicarbonate as it does not involve filtered bicarbonate
mechanisms :
- involving filtered monohydrogen phosphate
- involving glutamate
- in either case bicarbonate is generated and reabsorbed while hydrogen is secreted
Responses to acidosis
renal mechanisms -3rd line of defense (hours/days)
responses to acidosis
- sufficient H+ secreted to reabsorb all filtered HCO3-
- More H+ secreted contributing new HCO3- as H+ is excreted bound to nonbicarbonate urinary buffers such as HPO42-
- glutamine metabolism, ammonium excretion contributing new HCO3-.
Net result : more new and reabsorbed bicarbonate than usual is added to blood, increasing plasma HCO3- and compensating for acidosis. Urine is highly acidic
Responses to alkalosis
renal mechanisms -3rd line of defense (hours/days)
- H+ secretion is inadequate to reabsorb all filtered HCO3-, so significant amounts of HCO3- are excreted in urine
- little or no excretion of H+ on nonbicarbonate urinary buffers (phosphate) so little or no new HCO3-
- glutamine metabolism, ammonium excretion decreased so little or no new HCO3-
Net result : plasma HCO3- is decreased, compensating for alkalosis. Urine is Alkaline
