Every breath you take is your lungs’ function in a nutshell. Oh, it’s also a song played by The Police, which you have probably heard by now.
But what you maybe haven’t heard so far, is a nice simple presentation of the lungs anatomy. The textbooks may be too extensive and confusing when presenting this topic, and it’s easy to get lost while going through dozens of pages. For that reason, this page will introduce you to the anatomy of the lungs.
Trachea and bronchi
The trachea is the beginning of the respiratory tree. It is a musculocartilaginous tube that extends from cricoid cartilage at the C2 level, to its bifurcation at the level of T4/T5. The C-shaped cartilages that comprise the anterior and lateral walls of trachea keep its lumen constantly open and available for air conduction, while the posterior wall is muscular.
Learn everything about the trachea function and anatomy through this article and video tutorial.
The trachea bifurcates into the left and right main bronchi, with each bronchus passing through the hilum of their respective lung. The right main bronchus is wider and has a more vertical course than the left one, which is why foreign particles mostly go through the right main bronchus and reach the right lung. After entering the lung parenchyma, the main bronchus arborizes and gives the next generations of successively smaller bronchi, conducting air deep into the lungs;
- Lobar (secondary) bronchi; one for each lung lobe (three for the right lung, and two for the left lung).
- Segmental (tertiary) bronchi; one for each bronchopulmonary segment (ten bronchopulmonary segments in each lung but some of them fuse in the left lung). Bronchopulmonary segments, by definition, are the lung segments supplied by one segmental bronchi and accompanying branch of pulmonary artery. Segmental bronchi undergo multiple divisions, eventually resulting in bronchioles.
- The many conducting bronchioles; the terminology changes from bronchi to bronchiole when the narrow air passageway walls lack supporting cartilage.
- Terminal bronchioles; the smallest and final branches of the conducting airway, transition into respiratory bronchioles.
- Respiratory bronchioles; give rise to alveolar ducts.
Want to learn more about the respiratory tree? Check out this video tutorial and quiz:
Pleura is a two layered serous sac, comprised of parietal and visceral layers. Parietal pleura is in contact with the walls of the thoracic cavity and mediastinum, while the visceral pleura adheres onto the lung tissue.
The space between these two layers is called the pleural cavity. It is filled with around 20 milliliters of serous fluid which helps to reduce friction during respiration. The pleura function is also to contribute to the system of pressures that enables the lungs to expand and collapse during respiration.
You can find out everything about pleural cavity with this great article.
The lungs are our two respiratory organs. They are laterally placed within the pleural cavities of the thorax. The bronchial tree conducts air into and out of the lungs.
Each lung has a base, an apex, two surfaces (costal and mediastinal) and three borders (anterior, posterior and inferior). The base is placed on the diaphragm, while the apex projects towards the superior thoracic aperture. The medially facing mediastinal surface is of interest because it contains the lung hilum. The hilum of the lung is a passage for the pulmonary artery, two pulmonary veins and the main bronchus, as well as bronchial arteries and veins, nerves and lymphatic vessels.
The two lungs are not a mirror reflection of one another. The right lung has three lobes; inferior, superior and middle. These lobes are further divided, giving 10 bronchopulmonary segments, which are the functional units of the lung tissue. The right lung lobes are separated by two fissures; oblique and horizontal. The mediastinal surface of the right lung is in contact with the heart, superior vena cava, inferior vena cava, azygos vein and the esophagus. The impressions of these structures can be seen on the medial lung surface.
On the other hand, the left lung only has two lobes; superior and inferior, and 8 lung segments. The lobes are separated by a single oblique fissure. The mediastinal surface of the left lung shows impressions of the following structures: the heart, aortic arch, thoracic aorta and esophagus.
Curious to find out everything about the lung anatomy? Sure, we have some articles, video tutorials and quizzes for you.
The lungs and visceral pleura are supplied by the anterior pulmonary plexus and posterior pulmonary plexus which, as indicated by their names, are placed anteriorly and posteriorly to the tracheal bifurcation.
The sympathetic source for the plexus is the sympathetic trunk, while the parasympathetic source is the vagus nerve. They act in synchronization, with sympathetic stimulation leading to bronchial dilation, and parasympathetic leading to constriction of the bronchi.
Lymphatic drainage of lungs
The lymph of the lungs drains into the tracheobronchial nodes which are placed around the main and lobar bronchi, and along the sides of trachea. They extend from the inside of the lung through the hilum and posterior mediastinum. The vessels from the tracheobronchial nodes unite with vessels from the parasternal and brachiocephalic nodes, forming the left and right bronchomediastinal trunks. These trunks eventually drain either into the venous angle or thoracic duct.
Solidify your knowledge about the lymphatic drainage of the lungs by watching this awesome video tutorial and then quizzing yourself.
The lungs have two circulatory systems: functional and nutritive. The functional, or pulmonary, circulatory system is comprised of two pulmonary arteries and four pulmonary veins. Pulmonary arteries originate from the pulmonary trunk, they convey deoxygenated blood from the right ventricle to the lungs.
By dividing into smaller vessels and ultimately into pulmonary capillaries, they reach the respiratory surfaces of the lungs. On the other hand, left and right pairs of pulmonary veins carry oxygenated blood from the lungs to the left atrium of the heart.
You may think that we have made some kind of mistake by saying that the arteries carry deoxygenated blood, and veins oxygenated, but we didn't. Here is the trick; even though the widest definition of an artery is a vessel that carries oxygenated blood, and the vein is the vessel that carries deoxygenated blood; actually an artery is every vessel that carries the blood from the heart towards the periphery, and a vein is a vessel that carries blood from the periphery back to the heart. Because of this definition, we have an unique example within the pulmonary circulation where an artery carries deoxygenated blood and the vein carrying oxygenated. This part of the circulation is called functional because it is not intended for the nutritional supply of the lung tissue, but for the process of oxygen and carbon dioxide exchange within the lungs.
The nutritive circulatory system of the lungs refers to the bronchial circulation. Bronchial arteries supply oxygen to the tissue of the lungs, supporting the primary lung function of gas exchange. The 4 bronchial arteries arise from the thoracic aorta: right bronchial artery, two left bronchial arteries and superior bronchial arteries. On the other hand, bronchial veins drain the lung tissue into the right atrium via the pulmonary or azygos veins.
Fortify your knowledge about the pulmonary arteries and veins by going through this article, video and quiz. Also, don’t miss to read an interesting clinical case of pulmonary embolism.
Alveoli are the terminal units of the respiratory tree. The full alveoli definition is that they are the thin outpockets of the walls of the respiratory bronchioles specialized for the gas exchange.
Alveoli are found in clusters called the alveolar sacs. The thin wall of an alveolus is a place where gas exchange occurs. Together with capillaries, the alveoli form the respiratory membrane, whose layers are: the squamous cells of an alveolus, basement membrane of an alveolus, basement membrane of the capillary and the capillary endothelium.
We’ve got you covered with everything you need to know about alveoli and the anatomy of respiration with these articles and quiz.