Question

Do humans excrete ammonia?

Answer 1

Humans have to get rid of two types of wastes, the wastes from the digestive system called feces and the wastes from the metabolic activities called sweat & urine. The removal of metabolic wastes is called excretion whereas the removal of digestive wastes is called egestion.

Complete answer:
No humans do not excrete ammonia directly. In humans, ammonia is converted into urea through a process that occurs in the liver and kidney. Urea is less toxic compound as compared to ammonia because by conversion two nitrogen atoms are eliminated from it and for its excretion less water is required.
- In humans, there are four excretory organs found: the skin, the lungs, the liver, and the kidney.
- The skin excretes the sweat outside the body through numerous pores present on the surface of the skin. Sweat is a combination of water, salt, and urea.
- In the lungs, cellular respiration takes place which produces energy in the form of ATP that is needed for various cellular activities and carbon dioxide as the waste product.
- This carbon dioxide diffuses out of the cell into the bloodstream and reaches the lungs where it gets diffused into the lung tissues and later removed from the body by the process of exhalation.
- In the liver by the process of deamination the breakdown of some proteins and other nitrogenous compounds takes place into nitrogenous waste called urea.
- The liver helps in the excretion of toxic substances, drugs, and their derivatives; and bile pigments and cholesterol also.
- The kidney excretes the waste products which contain nitrogen and sulfur. They aid in the excretion of the drugs, toxic substances, and their derivatives, e.g. penicillin.

Note:
- The ammonia is very toxic and is usually excreted directly by marine animals.
- In humans and many mammals the ammonia is converted into urea because it is a light compound that is tolerable by the body even if present in higher concentrations than ammonia.
- The amphibians and mammals secret urea which they produce in their liver.
- The birds and insects excrete uric acid which is produced by them through large energy expenditure but with little water loss.