The Structure of Alveoli and Gas Exchange Function | 肺泡的结构与气体交换功能

📚 The Structure of Alveoli and Gas Exchange Function | 肺泡的结构与气体交换功能

The alveoli are the terminal air sacs of the mammalian respiratory system, representing the fundamental functional unit where gas exchange between the atmosphere and the blood takes place. Understanding their structure-function relationship is a cornerstone of A-Level Biology, frequently examined in CIE papers as a basis for essays and data interpretation questions.

肺泡是哺乳动物呼吸系统的末端气囊，是大气与血液之间进行气体交换的基本功能单位。理解其结构与功能的关系是 A-Level 生物学的核心内容，也是 CIE 考试中论文题和数据分析题的常见考点。

1. Overview of the Alveoli | 肺泡概述

Each human lung contains approximately 300 million alveoli, providing a total surface area of around 70 to 100 m² – roughly the size of a tennis court. This enormous surface area is the first and most crucial adaptation for efficient gas exchange.

每侧人类肺脏包含约 3 亿个肺泡，总表面积约为 70 至 100 平方米，大致相当于一个网球场的大小。如此巨大的表面积是高效气体交换的第一个也是最关键的适应特征。

Alveoli are arranged in clusters at the ends of the branching bronchioles. Each alveolus is a tiny, balloon-like sac with a diameter of approximately 200 to 300 μm. Their elastic walls allow them to expand during inspiration and recoil passively during expiration.

肺泡成群排列在分支细支气管的末端。每个肺泡是一个直径约 200 至 300 微米的气球状小囊。其弹性壁允许它们在吸气时扩张，并在呼气时被动回缩。

2. The Alveolar Wall: Cells and Tissues | 肺泡壁：细胞与组织

The alveolar wall is remarkably thin, typically measuring only 0.2 to 0.5 μm. It consists primarily of two types of epithelial cells: Type I pneumocytes and Type II pneumocytes.

肺泡壁异常薄，通常仅厚 0.2 至 0.5 微米。它主要由两类上皮细胞组成：I 型肺泡细胞和 II 型肺泡细胞。

Type I pneumocytes (squamous epithelial cells) cover approximately 95% of the alveolar surface. They are extremely thin, flattened cells that provide a minimal diffusion distance for gases. These cells are not capable of cell division and are therefore vulnerable to damage.

I 型肺泡细胞（鳞状上皮细胞）覆盖约 95% 的肺泡表面。它们极薄且扁平，为气体提供了最小的扩散距离。这类细胞不具备分裂能力，因此容易受到损伤。

Type II pneumocytes (septal cells) are cuboidal cells that make up about 5

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