Human sweat consists primarily of water and:

Correct Option

The correct option is Lactic acid, NaCl, and urea.

Explanation

Sweat is a hypotonic fluid secreted by the sweat glands (primarily eccrine glands) in the skin. Its primary physiological function is thermoregulation through evaporative cooling, though it also plays a minor role in the excretion of metabolic wastes.

Detailed Analysis

• Composition of Sweat: Human sweat is composed of approximately 99% water. The remaining 1% consists of dissolved solutes.
• Key Solutes:
  • Sodium Chloride (NaCl): This is the primary electrolyte lost in sweat, responsible for its salty taste.
  • Urea: Small amounts of urea, a nitrogenous waste product, are excreted through sweat.
  • Lactic Acid: Produced during metabolism, lactic acid is also present in sweat and contributes to the skin's acid mantle (pH 4-6), which inhibits microbial growth.
• Incorrect Options:
  • Hemoglobin: This is the iron-containing oxygen-transport metalloprotein in red blood cells, not found in normal sweat.
  • Pepsin: This is a digestive enzyme found in the stomach that breaks down proteins into peptides.
  • Bilirubin: This is a yellowish pigment formed in the liver by the breakdown of hemoglobin and excreted in bile and urine.

Key Takeaway: Human sweat is an aqueous solution primarily consisting of water, sodium chloride (NaCl), urea, and lactic acid.