Anatomy of Lungs
Lungs are the essential organs of respiration and are attached to the heart and trachea by their roots and the pulmonary ligaments.
■ Contain nonrespiratory tissues, which are nourished by the bronchial arteries and drained by the bronchial veins for the larger subdivisions of the bronchi and by the pulmonary veins for the smaller subdivisions of the bronchial tree.
■ Have bases that rest on the convex surface of the diaphragm, descend during inspiration, and ascend during expiration.
■ Receive parasympathetic fi bers that innervate the smooth muscle and glands of the bronchial tree and probably are excitatory to these structures (bronchoconstrictor and secretomotor).
■ Receive sympathetic fibers that innervate blood vessels, smooth muscle, and glands of the bronchial tree and probably are inhibitory to these structures (bronchodilator and vasoconstrictor).
■ Have some sensory endings of vagal origin, which are stimulated by the stretching of the lung during inspiration and are concerned in the refl ex control of respiration.
■ Has an apex that projects into the neck and a concave base that sits on the diaphragm.
■ Is larger and heavier than the left lung, but is shorter and wider because of the higher right
dome of the diaphragm and the inclination of the heart to the left.
■ Is divided into upper, middle, and lower lobes by the oblique and horizontal (accessory) fissures, but usually receives a single bronchial artery. The oblique fi ssure usually begins at the head of the fi fth rib and follows roughly the line of the sixth rib. The horizontal fi ssure runs from the oblique fi ssure in the midaxillary line at the sixth rib level and extends forward to the fourth costal cartilage level.
■ Has 3 lobar (secondary) bronchi and 10 segmental (tertiary) bronchi.
■ Has grooves for various structures (e.g., SVC, arch of azygos vein, esophagus).
■ Is divided into upper and lower lobes by an oblique fi ssure that follows the line of the sixth rib, is usually more vertical in the left lung than in the right lung, and usually receives two bronchial arteries.
■ Contains the lingula, a tongue-shaped portion of the upper lobe that corresponds to the
middle lobe of the right lung.
■ Contains a cardiac impression, a cardiac notch (a deep indentation of the anterior border of the superior lobe of the left lung), and grooves for various structures (e.g., aortic arch, descending aorta, left subclavian artery).
■ Has 2 lobar (secondary) bronchi and 8 to 10 segmental bronchi.
■ Is the anatomic, functional, and surgical unit (subdivision) of the lungs.
■ Consists of a segmental (tertiary or lobular) bronchus, a segmental branch of the pulmonary artery, and a segment of the lung tissue, surrounded by a delicate connective tissue septum (intersegmental septum). It is drained by the intersegmental part of the pulmonary vein.
■ Refers to the portion of the lung supplied by each segmental bronchus and segmental artery. The pulmonary veins are said to be intersegmental.
■ Is clinically important because the intersegmental pulmonary veins form surgical landmarks; thus, a surgeon can remove a bronchopulmonary segment without seriously disrupting the surrounding lung tissue and major blood vessels.
Conducting Portion (Airway)
■ Includes the nasal cavity, nasopharynx, larynx, trachea, bronchi, bronchioles (possess no cartilage), and terminal bronchioles, whereas the respiratory portion includes the respiratory bronchioles, alveolar ducts, atria, and alveolar sacs. Oxygen and carbon dioxide exchange takes place across the wall (blood–air barrier) of lung alveoli and pulmonary capillaries.