The pH of human blood is a measure of its acidity or alkalinity. Normal blood pH is maintained between 7.35 and 7.45, making it slightly alkaline. Even a small change in blood pH can have serious effects on body functions, because enzymes and biochemical reactions in the body work optimally only within this narrow range.
Normal blood pH: 7.35 to 7.45 (slightly alkaline).
pH below 7.35 = Acidosis; pH above 7.45 = Alkalosis.
Arterial blood pH is slightly higher than venous blood pH.
Blood pH is maintained by bicarbonate buffer, lungs, and kidneys.
pH below 6.8 or above 7.8 is life-threatening.
Pure water has pH 7.0; blood is slightly more alkaline.
• Normal blood pH range: 7.35 to 7.45 • Arterial blood pH: 7.35–7.45 • Venous blood pH: slightly lower (~7.32–7.42, due to more CO₂) • Pure water pH = 7.0 (neutral) • Blood is slightly alkaline (above 7)
The slight alkalinity is maintained by buffer systems in the blood — mainly the bicarbonate buffer system (H₂CO₃ / HCO₃⁻).
Acidosis (pH below 7.35): • Blood becomes too acidic • Causes: Respiratory failure (CO₂ buildup), kidney disease, diabetes (ketoacidosis), severe diarrhea • Symptoms: Fatigue, confusion, rapid breathing, nausea
Alkalosis (pH above 7.45): • Blood becomes too alkaline • Causes: Hyperventilation, vomiting (loss of stomach acid), excess antacid intake, altitude sickness • Symptoms: Muscle twitching, tingling, dizziness
Critical levels: • pH below 6.8 or above 7.8 = life-threatening
Blood pH is regulated by three systems:
Buffer system (fastest): • Bicarbonate buffer: H₂CO₃ ⇌ H⁺ + HCO₃⁻ • Haemoglobin acts as a buffer • Phosphate buffer in cells
Respiratory system (minutes): • Faster breathing expels CO₂ → raises pH • Slower breathing retains CO₂ → lowers pH
Renal (kidney) system (hours to days): • Kidneys excrete or retain H⁺ and HCO₃⁻ to adjust pH
The normal pH of human blood is 7.35 to 7.45. This is slightly alkaline. Any value below 7.35 is called acidosis and any value above 7.45 is called alkalosis.
Blood is slightly alkaline (pH 7.35–7.45) because of the presence of bicarbonate ions (HCO₃⁻), which act as a buffer. The bicarbonate buffer system neutralizes excess acids or bases to maintain the narrow pH range required for normal enzymatic and metabolic functions.
Acidosis: blood pH falls below 7.35, making blood too acidic. Caused by respiratory failure, kidney disease, or diabetic ketoacidosis. Alkalosis: blood pH rises above 7.45, making blood too alkaline. Caused by hyperventilation, vomiting, or excess antacid use.
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