Question

Human urine is mostly acidic because
A) Sodium transporter exchanges one hydrogen ion for each sodium ion, in peritubular capillaries.
B) Excreted plasma proteins are acidic.
C) Potassium and sodium exchange generates acidity.
D) Hydrogen ions are actively secreted into the filtrate.

Answer 1

Hint: The kidneys maintain natural acid-base balance mainly by sodium reabsorption and the hydrogen and ammonium ion tubular secretion.

Complete Answer:
- In humans and many other animals, urine is a liquid by-product of metabolism. Urine flows from the kidneys into the urinary bladder through the ureters.
- Urination results in the excretion of urine from the body through the urethra.
- Cellular metabolism contains many nitrogen-rich by-products that must be removed from the bloodstream, such as urea, uric acid, and creatinine.
- During urination, these by-products are expelled from the bloodstream, which is the main form of excretion from the bloodstream of water-soluble chemicals.
- Nitrogenous waste from the mammalian body can be detected by urinalysis.Urine has a part to play in the nitrogen cycle on earth.
- Urine fertilises the soil in healthy habitats, and thus helps plants grow. Urine can also be used as a fertiliser. It is used by certain animals to mark their territories. Historically, aged or fermented urine has also been used for the manufacture of gunpowder, household cleaning, leather tanning and cloth dyeing.
- Human urine and faeces are collectively referred to and handled by sanitation systems as human waste or human excreta. If the livestock population density is high, livestock urine and faeces often need correct management.
- The urine produced is a watery liquid of a light yellow colour that is mildly acidic (pH-6.0). Human urine is typically acidic since it deliberately secretes the hydrogen ions into the filtrate.

So the answer is Option D.

Note: Many species have excretory systems designed to remove soluble toxic waste. In humans, soluble wastes are mainly excreted by the urinary system, and eliminated by transpiration to a lesser degree in terms of urea.