Excretion in Humans: Kidney Function and Osmoregulation | 人体排泄：肾脏功能与渗透调节

📚 Excretion in Humans: Kidney Function and Osmoregulation | 人体排泄：肾脏功能与渗透调节

Excretion is the removal of metabolic waste products from the body. These wastes are produced by chemical reactions inside cells, and many are toxic if they accumulate. In humans, excretion is carried out mainly by the lungs, liver, skin and kidneys; the kidneys play the central role in removing nitrogenous waste and regulating water and ion balance.

排泄是指将代谢废物从体内清除的过程。这些废物由细胞内的化学反应产生，许多废物若在体内积累会产生毒性。在人体中，排泄主要由肺、肝脏、皮肤和肾脏完成；肾脏在清除含氮废物以及调节水和离子平衡方面发挥核心作用。

1. What is Excretion? | 什么是排泄？

Excretion is the removal of waste products of metabolism from the body. These wastes are produced by cells and include carbon dioxide from aerobic respiration, urea from excess amino acids, and water and ions taken in excess of the body’s requirements.

排泄是指将代谢产生的废物从体内清除。这些废物由细胞产生，包括有氧呼吸产生的二氧化碳、过量氨基酸代谢产生的尿素，以及超过身体需求的水和离子。

Excretion is different from egestion. Egestion is the removal of undigested food material from the gut, which has never entered the body’s cells. Excretion removes substances that have been produced inside cells by metabolism.

排泄与排遗不同。排遗是指将消化道中未被消化的食物残渣排出体外，这些物质从未进入体内细胞。排泄清除的是在细胞内由代谢产生的物质。

2. Nitrogenous Waste Products | 含氮废物

Amino acids from digested protein are used to build body proteins. However, excess amino acids cannot be stored. In the liver they are deaminated: the amino group (-NH₂) is removed, producing ammonia (NH₃) and a keto acid. Ammonia is very toxic and highly soluble in water, so it must be excreted or converted rapidly.

来自消化蛋白质的氨基酸用于构建人体蛋白质。然而，过量的氨基酸不能被储存。在肝脏中它们会脱氨基：

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