Acid-base Balance #1 Flashcards Preview

Genitourinary System > Acid-base Balance #1 > Flashcards

Flashcards in Acid-base Balance #1 Deck (19)

What is pH  and why is it so tightly regulated?

Measure of [H+] in solution.

Tightly regulated so the proteins/moleules can function.


Acidosis (acidemia) and Alkalosis (alkalemia) ranges


**Acidosis and alkalosis are processes that cause abnormal pH

pH 7.4 = normal (7.35-7.45)

if pH <7.35 = acidosis
<7.2 = severe acidosis
<6.9 = incompatible with life

If pH >7.45 = alkalosis
>7.6 = severe alkalosis
>7.9 = incompatible with life


Purpose of a Buffer? Equation

A weak acid/base solution that minimises pH change due to +/- of H

Only removes H+ temporarily

pH = pK + log ([base] / [acid])


pK of a buffer is?

pH at which the concentrations of A- (base) and HA (buffer) are equal


What are the 2 main buffers in blood?

  1. Bicarbonate
    H+ (40nmol/L)   +   HCO3- (24mmol/L)    ⇔   H20      +     CO2​​
  2. Proteins: albumi, haemoglobin
    H+    +     A-    ⇔     HA


Why do we have so much H+ to remove?

Body metabolism produces large amounts of CO2 every day (>1500mmol/day), that drives 


REspiratory control over pCO2?

Increased pCO2 → acidosis

decreased pCO2 → alkalosis


Increased pCO2 → acidosis/ low pH → stimulated increase in ventilation → more expired CO2


What does a blood gas analyser measure?

pH, pO2, pCO2

bicarbonate and base excess


Types of Respiratory Disturbances

CO2 retention (eg; acute asthma) → respiratory acidosis
Low pH and High pCO2


CO2 Expiration (eg; hyperventilation) → Respiratory alkalosis
High pH and low CO2


Types of Metabolic Disturbances

Metabolic Acidosis:  Low pH and low HCO3-

Increased acid production → leads to a low HCO3- as the buffer has been 'used up' → eventually renal buffers can also be used up.


Metabolic Alkalosis: High pH and high HCO3-

Either due to an increase of HCO3- injestion or Loss of acid (vomiting)


Main causes of Metabolic Acidosis (low pH and HCO3-)

  1. Increased Acid Production
    - Lactic Acidosis: hypoxia, poor tissue perfusion (car accident, MI)
    - Diabetic Ketoacidosis (DKA): increased betahydroxybutyric acids
  2. Decreased Acid Excretion
    -Renal Failure
    -Renal Tubular Acidosis


Role of Kidney Buffers in acid-base balance?

Can excrete H+ via Renal buffers (just like bicarbonate). These are generally PO43- and NH3


Maintain urinary pH between 5-8


List a few rarer causes of metabolic acidosis

Methanol and ethylene glycol poisoning

Glue/paint sniffing

Alcoholic Ketoacidosis


What is Respiratory compensation in metabolic acidosis

Normally M. acidosis is a low pH and low HCO3- .  
This low pH stimulates ventilation, "acidotic breathing", lowering pCO2 and balancing the low bicarbonate change. 


3 Roles of Kidney in Acid-base balance?

  1. Bicarbonate Reabsorbtion (Proximal Tub.)
  2. New Bicarbonate Generation (Proximal Tub., via carbonic Anhydrase)
  3. H+ secretion (distal Tubule) 


  1. Proximal Tubule: Bicarbonate Reabsorbtion

Filtered HCO3- is reabsorbed across BL membrane similar to Na+


2. Proximal Tubule: New Bicarbonate generation

Acetazolamide= carbonic anhydrase inhibitor that causes metabolic acidosis. 


Hypervent. → resp. alkalosis →(acetazolamide) → decreased Carbonic anhydrase activity → decreased HCO3- generation→ metabolic acidosis


3.  H+ excretion in the distal Tubule

ENaC (Na+ epithelial channel) creates a difference across the membrane by driving Na+ reabsorbtion. THis drives K+ and H+ into the distal lumen for excretion


how does renal Compensation counteract Resp. acidosis

By increasing HCO3- generation in the proximal tubule, restoring the ratio.