This document summarizes acid-base homeostasis and disorders. It discusses how the body maintains pH between 7.35-7.45 through three main systems: buffers, respiration, and the kidneys. Buffers act quickly to reduce free hydrogen ions while respiration and the kidneys provide longer-term regulation. Disorders occur when pH falls outside the normal range due to low or high blood bicarbonate levels or carbon dioxide levels. The document outlines the causes, signs, and treatments of various acid-base imbalances.

1. ACID BASE
HOMEOSTASIS
DR. FARHANA ATIA
Associate Professor
Department of Biochemistry
Nilphamari Medical College, Nilphamari

2. Acid-Base Balance
• Normal pH: 7.4 [ H⁺ : 40 nmol/L]
• Body fluids maintained pH between 7.35-7.45
• Clinically safe: 7.3-7.5
• Compatible to life: 6.8-7.8
• Recovery unusual: <6.8 & >7.8
• Low pH: Acidic
• High pH: Alkaline

3. Origin of acid
Volatile acid [H₂CO₃]
• Aerobic metabolism of carbohydrate & lipid
Non volatile acid [all except H₂CO₃]
• Anaerobic metabolism of carbohydrate: lactic acid
• Insulin lack: Ketoacids
• Diet (protein)
HCl
Phosphoric acid- arginine, histidine
Sulfuric acid- cystine, methionine

4. Origin of base
Base originates by metabolism of some food stuff
• Vegetables
• Fruits
• Vegetarian: ↑ base production
• Non-vegetarian: ↑ acid production

5. Our body is net acid producer
• Volatile acid
Basal CO₂ production 12000-15000
mmoles/day
Disposed by respiratory system
• Net production of non-volatile/ fixed production
70-100 mmoles of H⁺/day
Non volatile acids are disposed by kidney

6. 3 Systems that maintain pH
First line defense: Buffers
Moves or release hydrogen ions
Act within seconds
Second line defense: Respiratory system
Regulate volatile acid by eliminating or retaining CO2
Act within minutes
Third line defense: Renal system
Long term regulation of acid-base in body
Act within hours to days

7. Buffers
• Very rapid but temporary
• Can not remove H⁺ from body
• Act as shock absorbent to reduce free H⁺ ion
• Blood buffers are-
1. Bicarbonate buffer: Most predominant buffer
2. Phosphate buffer: Mainly intracellular
3. Protein buffer: Buffer capacity is only 2% of total

8. Bicarbonate Buffer System
• Serve an index to
understand acid base
disorder in body
• At blood pH 7.4, the ratio of
HCO₃⁻ to H₂CO₃ is 20:1
• According to Henderson
Hasselbalch Equation,
pH = pK + log
HCO₃⁻
H₂CO₃

9. Compensation & Correction of ABD
• How this ratio is maintained?
1.By increasing/decreasing
plasma [HCO₃⁻]
2.By reducing/increasing PCO₂
• Normal [HCO₃⁻]:[H₂CO₃] =
20:1
• Compensation:
Maintaining the ratio of
[HCO₃⁻]:[H₂CO₃] towards
normal, so pH become
normal
• Correction: Concentration
of [HCO₃⁻] & [H₂CO₃]
become normal.

10. Respiratory Mechanism for pH Regulation
• Rapid but short term regulation
• Regulate [H₂CO₃] concentration in blood
H₂CO₃ CO₂ + H₂O
• All CO₂ is eliminated via the lungs
Carbonic Anhydrase

11. Renal Mechanism for pH Regulation
• Permanent solution of ABD
• Kidney is the only route to eliminate H⁺
ions from the body
• By two mechanisms
1. HCO₃⁻ reabsorption mechanism -
PCT (90%)
2. HCO₃⁻ generation mechanism -
DCT (where there is no filtered
HCO₃⁻)

12. Lumen PCT cell Capillary
HCO₃⁻ reabsorption mechanism

13. HCO₃⁻ Generation Mechanism

14. Acid Base Disorders
Arterial blood pH is closely regulated to 7.4 ±0.05
Simple ABD: pH change occurs due to change of either PCO₂
or HCO₃⁻
• Respiratory acidosis: ↑ PCO₂
• Metabolic acidosis: ↓ HCO₃⁻
• Respiratory alkalosis: ↓ PCO₂
• Metabolic alkalosis: ↑ HCO₃⁻
Complex ABD
• Combination of 2-3 simple type
• Both HCO₃⁻ & CO₂ get abnormal value

15. Simple Method to Diagnose ABD
Look at the pH
• pH <7.35 (acidosis); pH >7.45 (alkalosis)
Is the CO₂ abnormal?
• CO₂ is an acidic gas; raised with acidosis, lowered with
alkalosis  Respiratory problem
• No change; or an opposite one ↑↑↓↓  compensatory change
Is the HCO₃⁻ abnormal? [Normal: 22-28mmol/L]
• Is the change in keeping with pH?
• HCO₃⁻ is alkaline; raised with alkalosis, lowered with
acidosis Metabolic problem

16. State of
ABD
Primary
defect
Consequ
ence
Compensation by Correction by
Metabolic
acidosis
↓ HCO₃⁻ ↓ pH Hyperventilation
(↓PCO₂)
Kidney
Treatment of cause
(↑ HCO₃)
Metabolic
alkalosis
↑ HCO₃⁻ ↑ pH Hypoventilation
(↑PCO₂)
Kidney
Treatment of cause
(↓ HCO₃)
Respiratory
acidosis
↑ PCO₂ ↓ pH Renal HCO₃⁻
retention (↑HCO₃⁻)
Hyperventilation
Treatment of cause
Respiratory
alkalosis
↓ PCO₂ ↑ pH Renal HCO₃⁻
excretion (↓ HCO₃⁻)
Hypoventilation
Treatment of cause

17. Causes of ABD
Metabolic acidosis
[↑ production /↓ removal of
fixed or organic acid]
Metabolic alkalosis
[Accumulation of base/ loss of
acid other than H₂CO₃]
• Diabetic ketoacidosis
• Acute MI
• Lactic acidosis
• CRF
• Renal tubular acidosis
• Watery diarrhea
• Intestinal fistula
• Vomiting
• K depletion (diuretics)
• Burns
• Ingestion of base
• Excessive infusion of NaHCO₃

18. Causes of ABD
Respiratory acidosis
[Impaired excretion of CO₂]
Respiratory alkalosis
[excessive ventilation]
• COPD
• Chronic bronchitis
• Pulmonary fibrosis
• Acute bronchial asthma
• Narcotic overdose
• Anesthesia
• Stroke
• SAH
• Meningitis
• High altitude
• Hysteria
• Fever
• Pulmonary emboli
• Salicylate poisoning
• Pregnancy

19. Acid base parameters
Blood gas analysis of
arterial blood
• pH: 7.35-7.45
• HCO₃⁻: 24-30 meq/L
• PCO₂ : 40 mm of Hg
Additional parameters
• Actual HCO₃⁻: HHE from pH &
PCO₂.
• Standard HCO₃⁻: 24 meq/L
Measured under standard
condition
T: 37-38⁰ c
Hb: full saturated
PCO₂: 40 mm of Hg
• Base excess: ±2
• Total CO₂: 24-30 mmol/L

20. • Buffer base: Anti acid component of buffer pair
HCO₃⁻, pr⁻, H₂PO₄⁻, Hb⁻, HbO₂⁻
• Base excess: Changes in the concentration of buffer
base from its normal value. It refers to the HCO₃⁻
BE = Measured HCO₃⁻- Standard HCO₃⁻
Metabolic acidosis <-2
Metabolic alkalosis >+2
• Alkali reserve: Sum of all buffer base present in blood
 48 mEq/L.

21. The anion gap
• Estimates unmeasured plasma anions (fixed or organic
acids such as phosphate, ketone and lactate- hard to
measure directly)
• Importance:
1. Determine the cause of metabolic acidosis
2. Reflect those anion actually present but routinely
unmeasured

22. The anion gap
• Difference between plasma anion
& cation. In Plasma,
Cation = Anion
Na⁺+ K ⁺ = HCO₃⁻+ Cl
Na⁺+K⁺ = HCO₃⁻+Cl⁻
136+4 = 100+25
• This difference is anion gap
• 12±4meq/L= 8-16meq/L

23. Causes of Metabolic Acidosis
 MA with high AG (HCO₃⁻ & unmeasured anions
associated with the acids accumulates)
• Urate (RF)
• Lactic acid (shock, infection, tissue ischemia)
• Ketone (DM, alcohol)
• Drugs, toxins (Salisylate poisoning)

24. Causes of Metabolic Acidosis
 MA with normal AG (loss of HCO₃⁻/ ingestion of H⁺)
• Diarrhea
• Pancreatic fistula
• Renal tubular acidosis
• Addison’s disease
• NH₄Cl ingestion