Topic 279: Human Excretion and the Kidney | 主题279：人体排泄与肾脏

📚 Topic 279: Human Excretion and the Kidney | 主题279：人体排泄与肾脏

Excretion is essential for maintaining a stable internal environment. In this revision article, we will review the key organs and processes involved in removing metabolic waste from the human body, focusing on the structure and role of the kidney, and including renal dialysis and osmoregulation.

排泄对于维持稳定的内部环境至关重要。在本复习文章中，我们将回顾人体清除代谢废物所涉及的主要器官和过程，重点讲解肾脏的结构与功能，并包括肾透析和渗透调节。

---

1. What Is Excretion? | 什么是排泄？

Excretion is the removal of metabolic waste products from the body. These wastes are produced by reactions inside cells, such as cellular respiration, and can be toxic or change the pH of body fluids.

排泄是清除体内代谢废物的过程。这些废物由细胞内的反应（如细胞呼吸）产生，可能有毒，或会改变体液的pH值。

Important metabolic wastes include carbon dioxide, urea and excess water. They are produced in different organs and removed by different systems.

重要的代谢废物包括二氧化碳、尿素和过多的水分。它们在不同的器官中产生，并由不同的系统排出。

It is important not to confuse excretion with egestion. Egestion is the removal of undigested food from the digestive tract, and it is not a form of excretion.

注意不要将排泄与排遗混淆。排遗是清除消化道中未消化的食物，不属于排泄。

---

2. The Organs of Excretion | 排泄器官

The main excretory organs and the wastes they remove are summarised below.

主要的排泄器官及其排出的废物总结如下。

Organ	Waste produced	How it is removed
Lungs	Carbon dioxide	Exhaled air
Kidneys	Urea, excess water and salts	In urine
Skin	Water, salts and small amount of urea	In sweat

The liver produces urea by breaking down excess amino acids. This process is called deamination.

肝脏通过分解多余的氨基酸产生尿素，这个过程称为脱氨基作用。

---

3. Position and Gross Structure of the Kidney | 肾脏的位置和宏观结构

Humans have two kidneys located in the back of the abdomen. Each kidney receives blood from a renal artery, and cleaned blood leaves through a renal vein.

人体有两个肾脏，位于腹腔后部。每个肾脏通过肾动脉接收血液，净化后的血液通过肾静脉离开。

Urine leaves each kidney through a tube called the ureter and is stored in the bladder before passing down the urethra.

尿液通过输尿管从每个肾脏离开，储存在膀胱中，然后经尿道排出。

In a section of a kidney, you can identify the outer cortex, the inner medulla and the renal pelvis, which connects to the ureter.

在肾脏纵切面上，可以辨认出外侧的皮质、内侧的髓质以及与输尿管相连的肾盂。

---

4. The Nephron: The Functional Unit | 肾单位：肾脏的基本功能单位

Each kidney contains about a million microscopic tubular structures called nephrons. Each nephron has the following main parts:

每个肾脏含有约一百万个微小的管状结构，称为肾单位。每个肾单位包含以下主要部分：

• Glomerulus: a ball of capillaries where filtration occurs.
• 肾小球：一团毛细血管，发生滤过的地方。
• Bowman’s capsule: a cup-shaped structure that collects the filtered fluid.
• 肾小囊：杯状结构，收集滤出的液体。
• Proximal convoluted tubule: a twisted tube where most reabsorption happens.
• 近曲小管：弯曲的管道，大部分重吸收在此发生。
• Loop of Henle: a U-shaped tube that helps concentrate urine.
• 髓袢：帮助浓缩尿液的U形管。
• Distal convoluted tubule and collecting duct: the final parts where water and salts are adjusted.
• 远曲小管和集合管：调节水分和盐分的最终部分。

The nephron is surrounded by a network of capillaries that reabsorb useful substances from the filtrate.

肾单位周围环绕着毛细血管网，从滤液中重吸收有用的物质。

---

5. Ultrafiltration | 超滤作用

Blood enters the glomerulus through a wide afferent arteriole and leaves through a narrower efferent arteriole. This creates a high blood pressure, forcing small molecules out of the blood into Bowman’s capsule.

血液通过较粗的入球小动脉进入肾小球，从较细的出球小动脉离开。这会产生较高的血压，促使小分子从血液滤入肾小囊。

Small molecules such as water, glucose, amino acids, urea and dissolved salts pass through the capillary walls and the basement membrane. Large proteins and blood cells stay in the blood.

像水、葡萄糖、氨基酸、尿素和溶解的盐这样的小分子可以穿过毛细血管壁和基底膜。大分子蛋白质和血细胞留在血液中。

The filtered fluid is called glomerular filtrate. It contains many useful substances that the body must reclaim.

滤出的液体称为原尿。其中含有很多身体必须回收的有用物质。

---

6. Selective Reabsorption | 选择性重吸收

As the filtrate moves along the proximal convoluted tubule, useful substances are reabsorbed into the surrounding capillaries.

当原尿沿近曲小管流动时，有用的物质被重吸收回周围的毛细血管。

All glucose and amino acids are reabsorbed, along with most of the salts and a large proportion of water. For example, glucose is reabsorbed by active transport against a concentration gradient.

所有葡萄糖和氨基酸都被重吸收，同时大部分盐分和大量水分也被重吸收。例如，葡萄糖通过逆浓度梯度的主动转运被重

Published by TutorHao | IGCSE Biology Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）