# A nurse is assessing a patient's respiratory system. Which of the following best describes the primary function of the alveoli? > source: MyMerci (mymerci.kr) > url: https://mymerci.kr/pages/nclex_q.php?qn_id=541247 > language: ko > subject: Adult Health ## 문제 A nurse is assessing a patient's respiratory system. Which of the following best describes the primary function of the alveoli? ## 보기 1. Transport oxygen-rich blood to body tissues 2. Filter and warm incoming air before it reaches the lungs 3. Facilitate gas exchange between air and blood **✔ 정답** 4. Produce surfactant to maintain lung expansion **정답: 3** ## 해설 The alveoli are the primary site for gas exchange between air and blood in the lungs. Other options describe functions of the cardiovascular system, upper airways, or secondary alveolar roles. ## 심화 해설 Understanding the Core Question This question asks you to identify the primary function of the alveoli. While some of the options describe real physiological processes, only one captures the essential, defining role of these microscopic air sacs. To answer correctly, you must connect the anatomical structure directly to its main physiological purpose. Analysis of Options Let's break down why option 3 is correct and the others are not, using the provided physiological context. Option 1: Transport oxygen-rich blood to body tissues. This is the primary function of the systemic circulatory system, specifically the left heart, arteries, and hemoglobin within red blood cells. The alveoli are not involved in the transport of blood; they are the site where blood receives* its oxygen. * Option 2: Filter and warm incoming air before it reaches the lungs. This describes the function of the upper airways, including the nasal cavity, turbinates, and trachea. These structures are lined with mucus and cilia to trap particles and have a rich blood supply to warm and humidify the air, a process called air conditioning. By the time air reaches the alveoli, it has already been conditioned. * Option 3: Facilitate gas exchange between air and blood. This is the correct answer. The alveoli are the terminal ends of the respiratory tree, structured to create an enormous surface area with an extremely thin tissue barrier. This unique anatomy exists for one critical purpose: the passive diffusion of oxygen (O₂) from the inhaled air into the pulmonary capillary blood and carbon dioxide (CO₂) from the blood into the alveolar air to be exhaled. The provided source emphasizes that the entire physiological organization of the heart and lungs is coupled to ensure this "efficient gas exchange" at the alveolar level [1]. Option 4: Produce surfactant to maintain lung expansion. This is a vital secondary function of a specific cell type within* the alveoli, the type II alveolar epithelial cells. Surfactant reduces surface tension, preventing alveolar collapse (atelectasis) and easing the work of breathing. However, this is a supportive role that enables the primary function. The primary function of the organelle (alveolus) itself is gas exchange, not the production of a single substance by one of its cell types. Deep Dive into Alveolar Gas Exchange The process of gas exchange at the alveolar-capillary membrane is not an active one but relies on a diffusion-perfusion interaction based on physical principles, as highlighted in the source material [1]. Understanding this interaction is key to grasping the pathophysiology of respiratory failure. The efficiency of gas exchange hinges on a delicate balance, which can be modeled quantitatively. For optimal function, two processes must be matched: 1. Ventilation (V): The flow of fresh air into the alveoli. 2. Perfusion (Q): The flow of blood through the pulmonary capillaries surrounding the alveoli. The ideal V/Q ratio is approximately 0.8. A mismatch is a common cause of hypoxemia. The source material points out that a "frequently overlooked contributor to impaired gas exchange" is a perturbation in lung fluid balance [1]. This is a direct application of the diffusion principle. The respiratory membrane across which gases must diffuse consists of the alveolar epithelium, a fused basement membrane, and the capillary endothelium. When fluid accumulates in the interstitial space (pulmonary edema) or within the alveoli themselves, the diffusion distance for oxygen increases dramatically. Because CO₂ is more soluble and diffuses about 20 times faster than O₂, an increased diffusion barrier from fluid will impair oxygenation first and more severely. This explains why a patient with early pulmonary edema will be hypoxemic but may have a normal or even low CO₂ level as they hyperventilate. The source also discusses the lung's "intrinsic mechanisms to resist edema formation" [1]. These protective factors are crucial for maintaining the thinness of the alveolar-capillary membrane and, therefore, efficient gas exchange. They include: * Tight junctions between alveolar epithelial cells, which are far less permeable than the capillary endothelium. * Active sodium transport by type II alveolar cells, which creates an osmotic gradient that pulls fluid out of the alveoli and back into the interstitium. * The lymphatic system's capacity to drain interstitial fluid. When these protective mechanisms are overwhelmed by high capillary pressure (hydrostatic edema, as in heart failure) or increased capillary permeability (permeability edema, as in ARDS), the primary function of the alveolus—gas exchange—fails. This clinical correlation demonstrates why option 3 is the most fundamental and accurate description: the entire structural and physiological design of the alveolus is centered on creating a space where air and blood can come into near-direct contact for diffusion, and the most critical pathologies are those that disrupt this core function [1].References (research sources) - [1]Heart-Lung Interactions in Gas Exchange: From Physiology to Pathophysiology.Research articleMiserocchi G, Beretta E. (2026) · DOI: 10.1002/cph4.70149 ## 임상 시나리오 Alveolar Gas Exchange: Core FunctionThe primary role of the respiratory unit The alveoli are the terminal air sacs where the respiratory system meets the circulatory system. Their primary function is gas exchange, specifically the diffusion of O₂ into the blood and CO₂ out of the blood. This process relies on an extremely thin alveolar-capillary membrane. While Type II alveolar cells secrete surfactant to lower surface tension and prevent alveolar collapse, this is a supportive function. The defining purpose of the structure is the exchange of respiratory gases. CautionDo not confuse the role of the alveoli with that of the upper airways (filtration, warming) or the circulatory system (oxygen transport). Impaired gas exchange at the alveolar level indicates a severe ventilation-perfusion (V/Q) mismatch. ## 핵심 개념 - **Alveoli** — Microscopic air sacs at the end of the respiratory tree where gas exchange occurs between air and pulmonary capillary blood. - **Gas Exchange** — The diffusion of oxygen from inhaled air into the blood and carbon dioxide from the blood into the alveoli to be exhaled. - **Type II Alveolar Cells** — Cuboidal epithelial cells in the alveoli responsible for producing pulmonary surfactant to reduce surface tension and prevent collapse. ## 같은 주제 문제 - [A nurse is evaluating a 65-year-old patient with chronic obstructive pulmonary disease (CO…](https://mymerci.kr/pages/nclex_q.php?qn_id=541248) --- More free questions: [기출문제](https://mymerci.kr/) _학습 참고용입니다. 실제 임상은 최신 지침과 소속 기관 프로토콜을 따르세요._