Acid Base Balance Flashcards
Define Acid and Base
acid - substance that releases H+ ions in a solution
base - substance that accepts H+ ions in a solution
Normal pH Range
(list values, 3 implications of deviation)
Normal: 7.35 - 7.45
Deviation:
- Cell membraine instability
- Protein structure change
- Enzyme activity change
Acid Production Mechanisms
(4)
All work by releasing H+ ions
- Protein catabolism
- Methods - sulfuric, phosphytics, and uric acids
- Example - meals
- Fat oxidation
- Methods - ketone bodies
- Example - starvation, inability to metabolize glucose
- Anaerobic glucose catabolism
- Methods - lactic acid
- Example - MI
- Intracellular metabolism
- Methods - CO2
- Example - all life processes
Acidosis
(definition, effect)
Defintion: pH < 7.35
Effect: **depressing ** CNS synaptic transmission, thus organism-wide functional depression
Alkalosis
(define, effect)
Definition: pH > 7.45
Effect: overexcited CNS synaptic transmission, increased organism activity
pH Regulatory Systems
(3, general MOA and timeline)
- Chemical buffers - instant neutralization *via *combination c offending agent
- Respiratory system - transcient change in minutes via hypoventilation/hyperventilation acid excretion and retention* *
- Renal system - **excretion and retention **balance over hours or days
Overview, Acid-Base Balance
(diagram)
see attached
Chemical Buffer Systems
(function, 2 components, general MOA)
Function: Solution designed to minimize the charge in pH when a base or acid is added to the soln. Note that independently, this soln is balanced
Components:
- Weak acid (releases H+ ions)
- Weak base (binds H+ ions)
MOA:
- If acidic soln is added to buffer, the buffer’s weak base will bind excess H+ ions to maintain the pH
- If basic soln is added to buffer, the buffer’s weak acid will release H+ ions to maintain the pH
Chemical Buffers
(list 3 c main locations)
- Sodium bicarbonate-carbonic acid
- Major Location - ECF
- Phosphate
- Major Location - ICF, urine
- Protein
- Major Location - ECF, ICF
Note - know this (as per Sandy)
Bicarbonate Buffer System
(2 components, 2 MOAs)
Components:
- Acid, carbonic acid: H2CO3
- Salt, sodium bicarbonate: NaHCO3
MOA: both rxns catalyzed by enzyme carbonic anhydrase
- Acidic Environment: H+ ions combine c biarbonate ions (HCO2-) to form carbonic acid (H2CO3), resulting in slight pH decrease
- Baisc Environment: basic ions react c carbonic acid (H2CO3) to form sodium bicarbonate (NaHCO3), resulting in slight pH increase
Phosphate Buffer System
(location, components, MOA)
Locations: action while passing thru kidneys
- ICF
- Urine
Components:
- Acid: H2PO4
- Salt/Alcaline: Na2HPO4
MOA: similar to sodium bicarb-carbonic acid system, used as its backup
- Acidic Environment: H+ ions combine c basic ions (HPO42-) to form acid (H2PO4), resulting in slight pH decrease
- Basic Environment: basic ions react c acid (H2PO4) to form a base (Na2HPO4), resulting in slight pH increase
Protein Buffer System
(location, component, MOA)
Location: ECF and ICF
Component: amino acids carboxyl/carboxylate groups and amino groups
MOA:
- Acidic Environment: H+ ions combine c carboxylate ion (-COO) or amino group (-NH2) to form carboxyl group (-COOH) or -NH3, resulting in slight pH decrease
- Basic Environment: basic ions react c carboxyl group (-COOH) to form a carboxylate ion (-COO), resulting in slight pH increase
Note - includes hemoglobin buffer system
Hemoglobin Buffer System
(category, function, MOA)
Category: part of protein buffer system
Function: prevent drastic pH changes due to pCO2 variation
MOA: Absorbs plasma CO2 and convert it to H2CO3 (carbaminohemoglobin)
Note: carbonic acid-bicarb buffers also happen in RBC’s.
Plasma CO2 Destinations
(3, c frequency)
- 70% = buffered in carbonic acid-bicarb system
- 20% = combined c hemoglobin to form carbaminohemoglobin
- 10% = dissolved in plasma
Acid-Base Balance Maintanence
(general principles)
- temporary fix - buffer systems
- permanent removal - respiratory and renal mechanisms
Respiratory Buffer System
(buffer system category, describe homeostasis)
Buffer System Category: physiological system
Equilibrium State: Balance between…
- CO2 and H2O
- H2CO3 (Carbonic acid) and H+/HCO3- (hydrogen and bicarb ions)
**CO2 + H2O ⇔H2CO3 ⇔H++ HCO3- **
Hypercapnia
(define, physiology)
Def: increased H+ in blood
Physiology: deeper and more rapid breathing expel more acidic CO2, reducing H+ ion (respiratory acidosis)
Respiratory Alkalosis
(define, physiology, tx)
Define: acid-base imbalance c too much base
Physiology: slower, shallower breathing to conserve H+ and decrease CO2 expulsion
Tx: rebreathe CO2 from brown paper bag
Renal Acid-Base Balance
(function, involved ions, general MOA)
Function: eliminate metabolic acids and prevent metabolic acidosis. The “ultimate acid-base regulatory organs.”
Eliminated acids:
- Phosphoric acid
- Uric acid
- Lactic acid
- Ketones
MOA:
- Eliminating bicarbonate ions thru excretion (less basic, therefore more acidic)
- Reabsorbing bicarbonate ions (more basic, therefore more acidic)
Renal Bicarbonate Reabsorption
- In filtrate: H2CO3 → H2O + CO2 (dissociation c help of carbonic anhydrase)
- CO2 diffucses into tubule cells
- H+ secretion to compensate for extra acid in cell from CO2
- For each H+ secreted, a Na+ and HCO3- are reabsorbed by PCT cells
- Secreted H+ ions form carbonic acid
- Na+ and HCO3- continue to recycle and the process continues
Ammonium Ion Excretion
(definition, MOA, results)
Definition: Renal excretion in the proximal convoluted tubule, characterized by glutamate metabolism.
MOA:
- Glutamate is metabolized to produce end products -
- **2 ammonium ions **(acid)
- **2 bicarbonate ions **(base)
-
Metabolites leave proximal convoluted tubule
- Ammonium secretion/excretion
- Bicarbonate reabsorption and retention
Result: reduce acidosis (increase alkylosis)
Phosphate Buffer System
(define, MOA, result)
Definition: backup renal buffering system concerning carbonic anhydrase
MOA:
- Carbonic anhydrase is always present in renal tubules
- Entering CO2 combines c preexisting H2O → H2CO3
- End product includes H+ions
- H+ secreted
- In tubules, H+ combines c HPO4 → H2PO4 (dihydrogen phosphate)
- H2PO4 excretion
Result: Decrease acidosis (increase aklylosis)
Renal Buffers
(3, summarize each)
Listed in order they appear on diagram:
- Bicarb buffer system
- Phosphate buffer system
- Protein buffers c ammonia (A-)
Hydrogen Ion Secretion
(define, MOA, result)
Definition: Renal management of excess H+ flow thru nephron
MOA:
- Excess H+ flow thru nephrons
- Kidney generates bicarb ions for reabsorption
- Bicarb moved into interstitial space actively via cotransport system
- Bicarb moved into peritubular capillary system passive diffusion
- H+ secretion in response to oppositely charged bicarb
- H+ remains in tubules after binding to buffers via phosphate buffer system
- Excretion
Result: Decreased acidosis, increased alkalosis
Bicarbonate Ion Secretion
(definition, MOA, result)
Definition: Renal defense against extreme alkalosis
MOA:
- Tubular secretion of bicarbonate ions via Cl- antiporters (dual negative charge maintains ionic balance within the cells)
- Ions reclaim H+ ions
- Blood pH decreases
Result: Increased acidosis (decreased alkalosis), opposite of bicarbonate ion reabsorption
Note: most cases of alkalosis are due to excess baking soda ingestion
Nephron Acidification Location
Collecting ducts
The reaction that is primarily responsible for H+ secretion in the proximal tubules is Na+–H+ exchange. Na is absorbed from the lumen of the tubule and H is excreted
Lowest Possible Urine pH
- 5
* Explaination - this pH corresponds with the Tm of H+ excretion transport gradient*
* Rxns involving the following work together to achieve that Tm if necessary:*
* Reactions with HCO3– to form CO2 and H2O, with HPO42– to form H2PO4–, and with NH3 to form NH4+*
