What is the normal pH range of the human body?

Normal pH Range of the Human Body

The normal pH range of human blood is between 7.35 and 7.45, with a tight regulation that is essential for proper physiological function. 1

Blood pH Regulation

• The body maintains blood pH within the narrow range of 7.35-7.45, which is slightly alkaline 1
• This tight regulation is critical as deviations outside this range can lead to life-threatening conditions such as acidosis (pH < 7.35) or alkalosis (pH > 7.45) 1
• The regulation of pH is essential for proper metabolism and cellular function throughout the human body 2

Physiological Significance of Blood pH

• The alpha-stat theory suggests that the normal arterial pH of 7.40 is derived from intracellular pH, which is close to neutrality 2
• This pH level offers evolutionary advantages by affecting the ionization of intermediates in biosynthetic pathways, decreasing their membrane penetration and benefiting cellular economy 2
• Blood pH is one of the most tightly regulated parameters in human physiology due to its critical importance for enzyme function and cellular processes 1

pH in Different Body Compartments

• While blood pH is maintained between 7.35-7.45, other body compartments have different normal pH ranges:
  • Skin (stratum corneum): 4.1-5.8 3
  • Urine: typically around 6.0, with variations between men (average 5.88-6.07) and women (average 5.79-6.74) 4, 5
• These variations serve specific physiological functions, such as antimicrobial protection in the skin 3

Acid-Base Disorders

• Acidosis is defined as a pH < 7.35 (hydrogen ion concentration > 45 nmol/L) 1
• Alkalosis is defined as a pH > 7.45 (hydrogen ion concentration < 35 nmol/L) 1
• Respiratory acidosis occurs when carbon dioxide accumulates, combining with water to form carbonic acid, which dissociates to bicarbonate and hydrogen ions 1
• Metabolic acidosis can result from failure to excrete acids, increased acid production, or loss of bicarbonate 1

Clinical Implications

• pH disturbances can indicate serious underlying conditions requiring prompt intervention 1
• In diabetic ketoacidosis, bicarbonate therapy may be beneficial in patients with pH < 6.9, but is not necessary if pH is > 7.0 1
• In respiratory failure, pH values help determine treatment approaches, with pH < 7.25 suggesting consideration for mechanical ventilation 1
• Chronic latent acidosis (subclinical condition with normal blood pH but low urine pH) has been associated with osteoporosis, diabetes mellitus, hyperuricemia, gout, and restricted renal function 4

Monitoring and Assessment

• Arterial blood gas analysis is the gold standard for assessing blood pH 1
• Venous pH is typically about 0.03 units lower than arterial pH and can be used to monitor resolution of acidosis in many clinical scenarios 1
• When monitoring acid-base status during treatment of conditions like diabetic ketoacidosis, regular assessment of pH is essential 1

Human pH regulation represents a remarkable example of physiological homeostasis, with multiple buffer systems working in concert to maintain this critical parameter within its narrow normal range.