Skin excretes a variety of substances, playing a crucial role in the body's detoxification process. The primary materials excreted include sweat containing water, urea, and salts. Beyond sweat, the skin also eliminates other substances like ammonia (in small amounts), and certain heavy metals, such as lead, mercury, arsenic, and cadmium, though the kidneys handle the majority of these. Sebum, an oily substance, is also secreted by sebaceous glands to prevent skin dryness; however, its primary function isn't excretion in the same way sweat is. Some drugs can also be metabolized and excreted via the skin.
Sweat and its Composition:
Sweat, produced by sweat glands, is primarily composed of water. However, it also contains significant amounts of urea and salts, contributing to the body's overall excretion process. The quantity of substances eliminated through sweat is generally less than that eliminated by the kidneys.
- Water: The major component of sweat, responsible for cooling the body.
- Urea: A nitrogenous waste product, typically handled more extensively by the kidneys.
- Salts: Various electrolytes vital for bodily functions.
- Ammonia: Excreted in smaller quantities compared to urea.
- Heavy Metals: A notable portion of certain heavy metals can be excreted through sweat, although the extent varies by metal and individual factors. Chelating agents can enhance heavy metal excretion through both urine and sweat.
Other Excreted Substances:
Beyond sweat, other substances excreted through the skin include:
- Sebum: While not a primary excretory product, sebum helps maintain skin integrity and is secreted by sebaceous glands.
- Certain Drugs: Some medications undergo metabolism in the skin and are subsequently excreted.
- 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD): Studies have shown this toxin can be excreted through the skin, though this is a specific case related to severe intoxication.
In summary, while the kidneys are the primary organs of excretion, the skin plays a significant supplementary role, eliminating water, urea, salts, smaller amounts of ammonia, certain heavy metals, and some drugs via sweat, and sebum for skin protection.
