Trachea, Bronchi and Bronchioles | 气管、支气管与细支气管

📚 Trachea, Bronchi and Bronchioles | 气管、支气管与细支气管

The trachea, bronchi and bronchioles form the conducting airways that carry air between the external environment and the gas-exchange surfaces of the alveoli. Their structure changes progressively along the respiratory tree, balancing rigidity, flexibility, cleaning and airflow control.

气管、支气管和细支气管构成导气通道，将空气从外界输送至肺泡的气体交换表面。它们的结构沿呼吸树逐级变化，在刚性、弹性、清洁和气流控制之间取得平衡。

1. Overview of the Conducting Airways | 导气通道概述

The conducting zone includes the nasal cavity, pharynx, larynx, trachea, bronchi and bronchioles up to the terminal bronchioles. It does not carry out gas exchange; its main roles are to transport, warm, humidify and filter inspired air.

导气区包括鼻腔、咽、喉、气管、支气管以及直至终末细支气管的通道。导气区不进行气体交换，其主要功能是运输、加温、加湿并过滤吸入的空气。

As air moves deeper into the lungs, the epithelial lining becomes thinner, cartilage support decreases, and smooth muscle becomes relatively more important. This gradient reflects the changing functional demands of each airway generation.

随着空气向肺部深处流动，上皮内衬逐渐变薄，软骨支撑减少，而平滑肌变得相对更加重要。这种梯度变化反映了各级气道功能需求的改变。

2. Gross Anatomy of the Trachea | 气管的大体解剖

The trachea is a flexible tube about 10-12 cm long and approximately 2.0-2.5 cm in diameter in adults. It extends from the lower border of the larynx at the level of C6 to the sternal angle, where it divides at the carina into the left and right primary bronchi.

气管是一根柔韧的管道，成人中约长 10-12 cm，直径约 2.0-2.5 cm。它从第 6 颈椎水平喉的下缘延伸至胸骨角，在隆嵴处分为左、右初级支气管。

The trachea is located anterior to the oesophagus and is kept open by a series of C-shaped hyaline cartilage rings. These rings allow the oesophagus to expand during swallowing while preventing the trachea from collapsing during inspiration.

气管位于食管前方，由一系列 C 形透明软骨环保持开放。这些软骨环使食管在吞咽时能够扩张，同时防止气管在吸气时塌陷。

3. C-shaped Cartilage Rings and Posterior Gap | C 形软骨环与后方缺口

There are usually 16-20 C-shaped cartilage rings in the human trachea. Each ring is open posteriorly, and the gap is bridged by the trachealis muscle and fibroelastic connective tissue.

人类气管通常有 16-20 个 C 形软骨环。每个环的后方有缺口，该缺口由气管肌和纤维弹性结缔组织填补。

The C-shape provides anterior and lateral support while allowing slight changes in tracheal diameter. The posterior trachealis muscle can contract during coughing, narrowing the lumen and increasing air speed to help expel mucus.

C 形结构提供前部和侧方支撑，同时允许气管直径发生轻微变化。后方的气管肌在咳嗽时收缩，使管腔变窄并提高气流速度，有助于排出黏液。

4. Tracheal Histology: Epithelium and Glands | 气管组织学：上皮与腺体

The tracheal lumen is lined by pseudostratified ciliated columnar epithelium with goblet cells. Cilia beat in a coordinated upward direction toward the pharynx, while goblet cells secrete mucus that traps inhaled particles and pathogens.

气管腔面被覆假复层纤毛柱状上皮，内含杯状细胞。纤毛向咽部方向协调摆动，杯状细胞分泌黏液以捕获吸入的颗粒和病原体。

Beneath the epithelium lies the lamina propria and submucosa, which contain seromucous glands. These glands add watery secretions and antimicrobial substances such as lysozyme and IgA, helping to condition the air and protect the airway surface.

上皮下方为固有层和黏膜下层，其中含有浆液黏液腺。这些腺体分泌较稀的液体以及溶菌酶和 IgA 等抗菌物质，有助于调节空气并保护气道表面。

5. Mucociliary Escalator and Defence | 黏液纤毛清除系统与防御

The mucociliary escalator is a primary defence mechanism of the conducting airways. Mucus traps dust, bacteria and debris, and the coordinated beating of cilia transports this mucus upward to the pharynx, where it can be swallowed or expectorated.

黏液纤毛清除系统是导气通道的主要防御机制。黏液捕获尘埃、细菌和碎屑，纤毛的协调摆动将这些黏液向上运送至咽部，随后被吞咽或咳出。

Smoking damages this system by increasing mucus production, decreasing ciliary beat frequency, and eventually destroying ciliated cells. This explains the persistent cough and frequent respiratory infections seen in smokers.

吸烟通过增加黏液分泌、降低纤毛摆动频率并最终破坏纤毛细胞来损害该系统。这解释了吸烟者为何出现持续性咳嗽和反复呼吸道感染。

6. Primary Bronchi and Branching Pattern | 初级支气管与分支模式

The trachea divides at the carina into the right and left primary bronchi. The right primary bronchus is wider, shorter and more vertical than the left, so inhaled foreign bodies more often enter the right lung.

气管在隆嵴处分为右、左初级支气管。右初级支气管比左初级支气管更宽、更短、更垂直，因此吸入的异物更容易进入右肺。

Each primary bronchus enters the lung at the hilum and divides into secondary lobar bronchi: three on the right and two on the left, corresponding to the lobes of the lungs. These further divide into tertiary segmental bronchi supplying bronchopulmonary segments.

每个初级支气管经肺门进入肺，并分为次级叶支气管：右侧三支，左侧两支，与肺叶相对应。次级叶支气管进一步分为三级段支气管，供应支气管肺段。

7. Bronchial Wall: Cartilage Plates and Smooth Muscle | 支气管壁：软骨片与平滑肌

In the bronchi, the complete C-shaped rings of the trachea are replaced by irregular plates of hyaline cartilage. This provides support while allowing the airway to change diameter more easily during breathing.

在支气管中，气管完整的 C 形环被不规则的透明软骨片所替代。这既提供支撑，又使气道在呼吸时更容易改变直径。

A continuous layer of smooth muscle lies beneath the mucosa in the bronchi. The smooth muscle can alter bronchial diameter and therefore influence airway resistance, especially in the smaller bronchi.

支气管黏膜下方有一连续的平滑肌层。平滑肌可以改变支气管直径，因此影响气道阻力，尤其是在较小的支气管中。

8. Bronchioles: Structure and Loss of Cartilage | 细支气管：结构与软骨消失

Bronchioles are conducting airways with a diameter of less than 1 mm. They lack cartilage and submucosal glands, so their walls are supported mainly by smooth muscle, elastic fibres and surrounding lung tissue.

细支气管是直径小于 1 mm 的导气通道。它们没有软骨和黏膜下腺体，因此管壁主要由平滑肌、弹性纤维和周围肺组织支撑。

The epithelium of larger bronchioles is simple ciliated columnar epithelium, which becomes simple cuboidal epithelium in terminal bronchioles. Goblet cells are largely absent, but club cells become more numerous and secrete a protective surfactant-like substance.

较大细支气管的上皮为单层纤毛柱状上皮，至终末细支气管变为单层立方上皮。杯状细胞基本消失，但克拉拉细胞数量增多，分泌具有保护作用的类表面活性物质。

9. Smooth Muscle and Airflow Control in Bronchioles | 细支气管平滑肌与气流控制

Bronchioles have a relatively thick smooth muscle layer compared with their wall thickness. Contraction or relaxation of this smooth muscle regulates the diameter of the small airways and therefore the resistance to airflow.

细支气管的平滑肌层相对于其管壁厚度而言较厚。该平滑肌的收缩或舒张调节小气道的直径，从而调节气流阻力。

Sympathetic stimulation and adrenaline activate beta-2 adrenergic receptors, causing bronchodilation. Parasympathetic stimulation via the vagus nerve and histamine released in allergic reactions cause bronchoconstriction, which increases airway resistance.

交感神经兴奋和肾上腺素激活 β2 肾上腺素能受体，引起支气管扩张。迷走神经传递的副交感刺激以及过敏反应中释放的组胺引起支气管收缩，从而增加气道阻力。

10. Terminal and Respiratory Bronchioles | 终末细支气管与呼吸性细支气管

Terminal bronchioles are the most distal purely conducting airways. They divide into respiratory bronchioles, which are the first airways to have alveoli budding from their walls and therefore participate in some gas exchange.

终末细支气管是最末端的纯导气气道。它们分支为呼吸性细支气管，后者是最早从管壁萌出肺泡的气道，因此参与部分气体交换。

Respiratory bronchioles lead into alveolar ducts and alveolar sacs. This marks the start of the respiratory zone, where the surface area for gas exchange increases enormously.

呼吸性细支气管通向肺泡管和肺泡囊。这标志着呼吸区的开始，此处气体交换表面积急剧增大。

11. Comparison Table: Trachea vs Bronchi vs Bronchioles | 比较表：气管、支气管与细支气管

The table summarises the key structural differences between the trachea, bronchi and bronchioles. These differences are frequently examined and should be linked to function.

下表总结了气管、支气管和细支气管的关键结构差异。这些差异常被考查，应与功能联系起来理解。

Feature | 特征	Trachea | 气管	Bronchi | 支气管	Bronchioles | 细支气管
Cartilage | 软骨	16-20 C-shaped rings | 16-20 个 C 形环	Irregular plates | 不规则软骨片	Absent | 无
Smooth muscle | 平滑肌	Trachealis muscle posteriorly | 后方气管肌	Continuous layer | 连续平滑肌层	Relatively thick layer | 相对较厚
Epithelium | 上皮	Pseudostratified ciliated columnar | 假复层纤毛柱状	Pseudostratified to simple ciliated columnar | 假复层至单层纤毛柱状	Simple ciliated columnar to cuboidal | 单层纤毛柱状至立方
Goblet cells | 杯状细胞	Present | 存在	Present but fewer | 存在但减少	Absent in terminal bronchioles | 终末细支气管无
Main role | 主要功能	Air conduction, cleaning, warming | 导气、清洁、加温	Distribution of air to lung lobes | 向肺叶分配空气	Control airflow resistance | 控制气流阻力

12. Exam Focus: Common Confusions and Key Terms | 考试重点：常见混淆与关键术语

Students often confuse the trachea, bronchi and bronchioles when describing cartilage and smooth muscle. Remember that cartilage decreases from rings to plates to none, while the relative importance of smooth muscle increases as airway diameter decreases.

学生在描述软骨和平滑肌时，常混淆气管、支气管和细支气管。请记住：软骨从环状变为片状再到消失，而平滑肌的相对重要性随气道直径减小而增加。

Do not state that gas exchange occurs in bronchioles. Gas exchange begins only at the respiratory bronchioles and becomes extensive in the alveoli. Terminal bronchioles are still part of the conducting zone.

不要写气体交换发生在细支气管中。气体交换仅从呼吸性细支气管开始，并在肺泡中大量进行。终末细支气管仍属于导气区。

Be precise with the mucociliary escalator: mucus is secreted by goblet cells and submucosal glands, and cilia move mucus upward. In the small bronchioles, club cells replace goblet cells and secrete protective fluid, not mucus for the escalator.

描述黏液纤毛清除系统时要准确：黏液由杯状细胞和黏膜下腺体分泌，纤毛将黏液向上运送。在小细支气管中，克拉拉细胞取代杯状细胞，分泌保护性液体，而非参与清除系统的黏液。

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