📚 Organisms 2.1.1 – Structure of the Gas Exchange System: Experimental Design | 生物体 2.1.1 气体交换系统结构实验设计
Understanding the structure of the gas exchange system is essential for explaining how mammals efficiently obtain oxygen and remove carbon dioxide. Experimental investigations, from dissection to model building and spirometry, allow us to link anatomical features to their physiological roles. This article outlines core experimental designs that help students and researchers explore the trachea, bronchi, bronchioles, alveoli, and the mechanics of ventilation in a safe and systematic way.
理解气体交换系统的结构，对于解释哺乳动物如何高效地获取氧气并排出二氧化碳至关重要。从解剖操作到模型构建，再到肺活量测定，各种实验研究使我们能将解剖学特征与生理功能联系起来。本文概述了核心实验设计，帮助学生和科研人员以安全、系统的方式探索气管、支气管、细支气管、肺泡以及通气力学。
1. Mammalian Lung Dissection: Revealing Gross Anatomy | 哺乳动物肺解剖：揭示大体结构
A dissection of a mammalian lung, typically from a sheep or pig, provides direct observation of the trachea, primary bronchi, and the spongy texture of lung tissue. Before starting, ensure the specimen is obtained from a reputable supplier and all instruments are sterilised. The purpose is to identify the major airways and to see how the trachea branches into the left and right bronchi, which then subdivide into smaller bronchioles within the lobes.
对哺乳动物（通常为羊或猪）的肺进行解剖，可以直接观察气管、主支气管以及肺组织的海绵状质地。开始前，应确保标本来自可靠供应商，所有器械均已消毒。实验目的是识别主要气道，观察气管如何分支为左右支气管，并在肺叶内进一步分为更小的细支气管。
Make a midline incision along the trachea and extend it downwards. Notice the C-shaped cartilage rings that keep the trachea open. Use a seeker or blunt probe to follow the bronchi into each lung. The lungs can be inflated with a hand pump via a tube inserted into the trachea to demonstrate the elastic nature of the tissue and the lobular divisions. Record observations through labelled photographs or scientific drawings.
沿气管正中线切开并向下延伸切口。注意保持气管开放的C形软骨环。使用探针或钝性分离器沿着支气管进入每一侧肺。可将一根管子插入气管，用手泵向肺内充气，以展示组织的弹性特征和小叶划分。通过带标注的照片或科学绘图记录观察结果。
2. Examining the Conducting Airways: Trachea and Bronchi | 检查传导气道：气管与支气管
The conducting airways are more than passive tubes. The trachea and bronchi are lined with ciliated epithelium and goblet cells. To observe these under a light microscope, prepare a transverse section of trachea stained with haematoxylin and eosin. Look for pseudostratified columnar epithelium, mucus-secreting goblet cells, and the underlying hyaline cartilage. This microscopic examination connects the structural reinforcement by cartilage with the need to keep airways patent during pressure changes.
传导气道不仅仅是被动通道。气管与支气管内衬有纤毛上皮和杯状细胞。若要在光学显微镜下观察，需制作气管横切片并用苏木精-伊红染色。寻找假复层柱状上皮、分泌黏液的杯状细胞以及下方的透明软骨。这一显微观察将软骨的结构支撑与压力变化时保持气道通畅的需求联系起来。
An experimental design could involve comparing tracheal sections from different mammals or measuring the thickness of the cartilage layer using a calibrated eyepiece graticule. This allows quantification of the relationship between airway diameter and cartilage reinforcement. Always calibrate the microscope and stain consistently to ensure valid comparisons.
实验设计可以包括比较不同哺乳动物的气管切片，或使用校准的目镜测微尺测量软骨层厚度。这能够定量探讨气道直径与软骨加固之间的关系。务必始终校准显微镜并统一染色方法，以确保比较有效。
3. The Bell Jar Model: Demonstrating Ventilation Mechanics | 钟罩模型：展示通气力学
The bell jar model is a classic representation of how pressure changes drive breathing. It consists of a glass bell jar (representing the thoracic cavity), a Y-shaped tube with two small balloons (lungs), and a rubber sheet (diaphragm) stretched across the base. When the rubber sheet is pulled downwards, the volume inside the jar increases, pressure decreases, and the balloons inflate. Releasing the sheet causes the balloons to deflate.
钟罩模型是展示压力变化如何驱动呼吸的经典装置。它由一个玻璃钟罩（代表胸腔）、一个带两个小气球的Y形管（肺）以及覆盖底部的橡胶膜（膈肌）组成。向下拉橡胶膜时，罩内容积增大、压力降低，气球随之膨胀；松开橡胶膜则气球回缩。
To design a quantitative experiment, attach a pressure sensor or manometer to the bell jar and record the change in pressure as the rubber sheet is displaced by measured distances. Plot pressure difference against volume change to mimic a simple pressure-volume curve. This model reinforces the concept that lung inflation is passive and relies on negative intrapleural pressure – a key principle in gas exchange physics.
若要设计定量实验，可将压力传感器或压力计连接到钟罩上，记录橡胶膜被位移固定距离时压力的变化。绘制压力差随容积变化的曲线，模拟简单的压力-容积曲线。该模型强化了肺充气是被动过程并依赖负的胸膜腔内压的概念——这是气体交换物理学中的关键原理。
4. Measuring Lung Volumes with a Spirometer | 用肺活量计测量肺容积
A spirometer is a device used to measure the volume of air inspired and expired by the lungs. A simple water-sealed spirometer consists of a chamber floating in water, connected to a mouthpiece and a recording pen. As the subject breathes, the chamber moves, tracing a spirogram. With a modern dry spirometer or electronic spirometer, the same principles apply. Key variables include tidal volume (VT), vital capacity (VC), and inspiratory reserve volume (IRV).
肺活量计是用于测量肺吸入与呼出空气体积的装置。简单的水封式肺活量计由一个浮在水中的气室、一个接口以及一支记录笔组成。被试者呼吸时，气室上下移动，描记出呼吸图。现代干式肺活量计或电子肺活量计遵循相同原理。关键变量包括潮气量（VT）、肺活量（VC）和补吸气量（IRV）。
An experiment can be designed to compare lung volumes before and after exercise, or between athletic and non-athletic subjects. Control variables: the subject’s posture, the time of day, and the type of spirometer. Use a nose clip to prevent air leakage. After maximal inspiration, the subject forcefully exhales to determine forced vital capacity (FVC). Analyse the spirogram to calculate minute ventilation as tidal volume × breathing rate. All values must be corrected to body temperature and ambient pressure.
可以设计实验比较运动前后的肺容积，或运动员与非运动员被试者的差异。控制变量：被试者的姿势、一天中的时间、肺活量计类型。使用鼻夹防止漏气。最大限度吸气后，被试者用力呼气以测定用力肺活量（FVC）。分析呼吸图，通过潮气量 × 呼吸频率计算每分通气量。所有数值必须校正至体温与环境气压条件。
5. Microscope Investigation of Alveolar Structure | 显微镜观察肺泡结构
Alveoli are the terminal air sacs where gas exchange takes place. To visualise their structure, prepare thin sections of lung tissue stained to highlight the alveolar walls, capillaries, and elastic fibres. Under high magnification (×400), alveoli appear as thin-walled hollow spaces surrounded by extensive capillary networks. The very short diffusion distance (less than 1 µm) between alveolar air and red blood cells is the structural basis for efficient gas exchange.
肺泡是进行气体交换的末端气囊。为观察其结构，需制备肺组织薄切片并染色以突显肺泡壁、毛细血管和弹性纤维。在高倍镜下（×400），肺泡呈现为由丰富毛细血管网包围的薄壁中空腔隙。肺泡气体与红细胞之间极短的扩散距离（小于 1 µm）是高效气体交换的结构基础。
Design an experiment to measure the surface area-to-volume ratio of alveoli using image analysis software or a graticule. Count the number of alveoli per unit area and estimate the total alveolar surface area from lung volume by applying morphometric principles. Comparing lung sections from different ages or after exposure to pollutants can reveal structural changes such as emphysema, where alveolar walls break down, reducing surface area. This links directly to diffusion rates in Fick’s law.
设计实验利用图像分析软件或测微尺测量肺泡的表面积与体积比。计数单位面积内的肺泡数，并应用形态计量学原理从肺容积推估肺泡总表面积。比较不同年龄或暴露于污染物后的肺切片，可揭示诸如肺气肿等结构变化（肺泡壁破坏、表面积减小）。这直接关联到菲克定律中的扩散速率。
6. Investigating Elastic Recoil of Lung Tissue | 探究肺组织的弹性回缩
Lung elasticity is vital for passive exhalation. A simple experiment can quantify recoil using a freshly excised lung lobe. Insert a cannula into the bronchus, tie it securely, and connect it to a syringe or air pump. Gradually inject a known volume of air and then allow the lung to deflate passively. Measure the volume of air expelled. The percentage of air that is not passively expelled indicates the degree of elastic recoil and the presence of residual volume.
肺弹性对于被动呼气至关重要。使用新切除的肺叶可设计简单实验来量化回缩力。向支气管插入插管并扎紧，将其连接到注射器或气泵。逐步注入已知体积的空气，然后让肺被动放气。测量被排出的空气体积。未被动排出的空气百分比表明弹性回缩程度和残气量的存在。
Repeat the procedure after treating the lung tissue with a mild detergent to disrupt the surfactant layer; this demonstrates the contribution of alveolar surface tension to recoil. A graph of injected volume against expelled volume illustrates hysteresis, similar to a clinical pressure-volume curve. Care must be taken to handle biological tissue ethically and dispose of it according to local safety guidelines.
用温和去垢剂处理肺组织以破坏表面活性层后重复该步骤；这可以展示肺泡表面张力对回缩的贡献。注入量-排出量的关系图显示滞后现象，类似于临床压力-容积曲线。处理生物组织时须符合伦理，并按当地安全准则进行处置。
7. The Role of Surfactant: A Simple Bubble Model | 表面活性剂的作用：简易气泡模型
Pulmonary surfactant reduces surface tension in the alveoli, preventing collapse. A simple bench-top experiment uses a bubble frame and soap solution to model this. A pure water film has high surface tension and quickly ruptures. Adding a small amount of detergent (surfactant) stabilises the film. To illustrate Laplace’s law (P = 2T/r), blow two interconnected bubbles of different sizes – the smaller bubble will deflate into the larger one because of higher internal pressure. This mimics how surfactant equalises pressures across alveoli of different sizes.
肺表面活性剂能降低肺泡表面张力，防止塌陷。一个简单的台面实验可利用气泡框架和肥皂溶液来模拟此过程。纯水膜的表面张力高，会迅速破裂。加入少量去垢剂（表面活性剂）能使膜稳定。为演示拉普拉斯定律（P = 2T/r），可以吹两个大小不同但连通的气泡——小气泡会因其更高的内部压力而向大气泡排气。这模拟了表面活性剂如何平衡大小不同肺泡间的压力。
In an experimental design, measure the pressure inside bubbles using a sensitive manometer. Vary the concentration of detergent and record the maximum stable bubble size. This data can be plotted to find the critical micelle concentration. Linking this model to neonatal respiratory distress syndrome, where surfactant deficiency leads to alveolar collapse, powerfully illustrates the clinical relevance of basic gas exchange structure.
在实验设计中，使用灵敏压力计测量气泡内部压力。改变去垢剂浓度并记录最大稳定气泡尺寸。将这些数据绘图以求得临界胶束浓度。将此模型与新生儿呼吸窘迫综合征（肺表面活性物质缺乏导致肺泡塌陷）相联系，极具说服力地展示了气体交换基本结构的临床相关性。
8. Effect of Exercise on Breathing Rate – Experimental Design | 运动对呼吸频率的影响 – 实验设计
Breathing rate is a readily measurable physiological variable that reflects the demands of gas exchange. Design an experiment to investigate how different intensities of exercise affect breathing rate. Independent variable: exercise intensity (e.g., resting, walking, jogging, sprinting). Dependent variable: breathing rate (breaths per minute). Controlled variables: duration of exercise, time of measurement after exercise, fitness level of the subject, and ambient temperature.
呼吸频率是一项易于测量的生理变量，能反映气体交换的需求。设计一个实验来研究不同运动强度对呼吸频率的影响。自变量：运动强度（如静息、步行、慢跑、冲刺）。因变量：呼吸频率（每分钟呼吸次数）。控制变量：运动持续时间、运动后测量的时间点、被试者的健康水平以及环境温度。
Use a stopwatch to count the number of breaths taken in 30 seconds, then multiply by 2 to obtain breaths per minute. Ensure the subject is at complete rest for 5 minutes before taking the resting measurement. After each exercise bout, count breaths immediately and then at 1-minute intervals until recovery. Plot a graph of mean breathing rate (with standard deviation error bars) against exercise intensity. This investigation reinforces how increased metabolic CO₂ production stimulates chemoreceptors to raise ventilation, reflecting the close coupling between structure and physiological demand.
使用秒表计数 30 秒内的呼吸次数，再乘以 2 得出每分钟呼吸频率。在测量静息值前，确保被试者完全休息 5 分钟。在每次运动后立即计数呼吸，然后每隔 1 分钟计数一次直至恢复。绘制平均呼吸频率（附标准差误差线）随运动强度变化的图表。该探究强化了代谢产生的 CO₂ 增多如何刺激化学感受器以提高通气量，反映了结构与生理需求的紧密耦合。
9. Safety and Ethical Considerations in Respiratory Experiments | 呼吸实验中的安全与伦理考量
All experiments involving human subjects must follow strict ethical guidelines. Obtain informed consent and ensure subjects are aware that they can withdraw at any time. For dissection, wear gloves, safety goggles, and a lab coat. Use sharp instruments with proper technique and dispose of biological material in biohazard waste containers. Disinfect work surfaces before and after the practical.
所有涉及人体被试的实验都必须遵循严格的伦理准则。需获得知情同意，并确保被试者知晓他们可以随时退出。在解剖时，需佩戴手套、护目镜和实验服。以正确技术使用锋利器械，并将生物材料弃置于生物危险废物容器中。实验前后均对工作台面进行消毒。
When using a spirometer, check the mouthpiece for hygiene; use disposable cardboard mouthpieces or sterilise reusable ones. Subjects with respiratory conditions such as asthma should not participate in maximal breathing tests. For animal specimens, source only from ethical suppliers and never from the wild unless permitted. Respect for biological material is central to sound scientific practice.
使用肺活量计时，检查接口卫生；使用一次性纸质接口或对可重复使用的接口进行消毒。患有哮喘等呼吸系统疾病的被试者不应参与最大呼吸测试。对于动物标本，只从符合伦理的供应商处获取，除非获准，否则不得从野外采集。尊重生物材料是良好科学实践的核心。
10. Variables, Controls, and Data Analysis | 变量、控制与数据分析
Robust experimental design requires clear identification of independent, dependent, and controlled variables. In gas exchange experiments, temperature and pressure are often confounding factors; always note barometric pressure and room temperature and correct gas volumes to STPD (standard temperature and pressure, dry) or BTPS (body temperature and pressure, saturated). Use calibrated equipment and repeat measurements to calculate means and standard deviations.
严谨的实验设计要求清晰界定自变量、因变量和控制变量。在气体交换实验中，温度与气压常为混杂因素；应始终记录大气压和室温，并将气体体积校正至 STPD（标准温度与气压、干燥）或 BTPS（体温与气压、饱和水蒸气）。使用校准设备并重复测量以计算平均值和标准差。
For data presentation, use scatter plots with lines of best fit when examining relationships, and column charts for comparisons. Statistical tests such as the Student t-test or ANOVA can determine if differences are significant. Always label axes with units and include a descriptive figure caption. Linking raw data to the structure-function relationship solidifies the conclusion that thick alveolar walls or narrowed airways impair gas exchange efficiency.
在数据展示方面，检查关系时使用散点图并附最佳拟合线，进行比较时使用柱状图。可采用学生 t 检验或方差分析等统计方法判断差异是否显著。始终标注坐标轴与单位，并附上描述性的图题。将原始数据与结构—功能关系联系起来，能巩固如下结论：增厚的肺泡壁或狭窄的气道会损害气体交换效率。
11. Common Pitfalls and How to Avoid Them | 常见错误及避免方法
Air leaks in models or spirometers lead to inaccurate volume readings; always check seals and connections with leak tests before starting. In dissection, tearing the delicate bronchioles and alveoli obscures fine detail – use blunt dissection and gentle manipulation. When making microscope slides, sections that are too thick prevent light penetration and clear visualisation; aim for 5–10 µm thickness.
模型或肺活量计中的漏气会导致体积读数不准；开始前务必通过检漏测试检查密封件与连接。解剖时，撕扯脆弱的细支气管和肺泡会掩盖微细结构——应使用钝性分离和轻柔操作。制作显微玻片时，切片过厚会阻碍透光和清晰成像；目标厚度为 5–10 µm。
Measuring breathing rate immediately after strenuous exercise can be difficult due to movement artifacts; have the subject sit still while counting and use a standardised counting interval. In the bubble model, ambient vibrations can burst the film – set up away from drafts and vibrations. Addressing these pitfalls not only improves data quality but also teaches essential troubleshooting skills.
剧烈运动后立即测量呼吸频率可能因运动伪影而难以进行；应让被试者静坐并采用标准计数间隔。在气泡模型中，环境振动可能使液膜破裂——需设置在远离气流和振动的地方。排除这些失误不仅提升数据质量，还传授了重要的排查故障技能。
12. Linking Structure to Function: Conclusions | 结构功能关联：总结
The gas exchange system’s design is a masterpiece of biological engineering: a large, moist surface area, extremely thin diffusion barrier, rich blood supply, and a ventilation mechanism driven by pressure gradients. Experimental approaches – dissection, microscopy, models, and spirometry – collectively demonstrate how each structural level, from the cartilaginous trachea to the surfactant-lined alveoli, contributes to overall function. By designing and conducting careful experiments, learners gain a deep, evidence-based understanding of why the system is built the way it is.
气体交换系统的构造是生物工程的杰作：广阔潮湿的表面积、极薄的扩散屏障、丰富的血液供应，以及由压力梯度驱动的通气机制。解剖、显微观察、模型和肺活量测定等实验方法共同证明了从软骨气管到覆有表面活性剂的肺泡，每一级结构如何为整体功能做出贡献。通过设计并进行严谨的实验，学习者能够基于证据深刻理解该系统为何拥有如此精妙的构造。
Moreover, these experiments connect classroom theory to clinical reality, from asthma to emphysema. The ability to design, execute, and interpret gas exchange experiments is a core skill for A‑level biologists, preparing them for further study and an appreciation of the delicate balance that sustains life.
此外，这些实验将课堂理论与从哮喘到肺气肿的临床实际联系在一起。设计、实施和解读气体交换实验的能力是A-level 生物学家的核心技能，为他们深造和理解维持生命的精妙平衡打下基础。
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