Student Question

What is made of waste, extra water, and salt in the excretory system?

Expert Answers

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Living things must operate within a delicate balance in order to maintain homeostasis. One way this is accomplished is by the process of excretion of metabolic wastes. The skin contains sweat glands and is part of the excretory system along with the kidneys which filter wastes from the circulating blood to be excreted by the process of urination.

Excess salt, water and urea (waste) are the components of urine. Urea is an organic compound which forms when excess protein (which cannot be stored by the body) is converted first to ammonia and then, to urea in the liver. It is a soluble nitrogenous waste. Urine consists mainly of water: up to 96%. Inorganic salts are also present in urine, along with hormones and other metabolic waste products.

However, perspiration or sweat also contains water, with small quantities of the waste urea along with mineral salts including sodium and potassium. The sweat glands in the skin can function as excretory organs also.

Therefore, salt, water and wastes can be found in both urine as well as sweat.

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