24.6 The Lungs

• • Each lung is cone shaped. Its apex extends superior to the attachment of the first rib to the sternum, and its base sits on the diaphragm.
• Each lung is a blunt cone with the tip, or apex, pointing superiorly
• The broad concave inferior portion, or base, of each lung rests on the superior surface of the diaphragm
• SUMMARY - Lobes and Fissures of the Lungs

  • Lobes of lungs are separated by fissures. The right lung has three lobes: superior lobe, middle lobe, inferior lobe with an oblique fissure separating superior and inferior and horizontal fissure separating superior and middle. The right lung also has three lobar or secondary, bronchi: the superior lobar, middle lobar, and inferior lobar bronchi. The left lung has two lobes: superior lobe and inferior lobe with an oblique fissure separating the lobes; and two lobar bronchi; superior lobar and inferior lobar bronchi.
• SUMMARY - Lung Surfaces

  • Costal surface of the lung follows the inner contours of the rib cage. The mediastinal surface contains a hilum, and the left lung bears the cardiac notch.
  • Connective tissues of the root of each lung extend inward as a series of trabeculae (partitions). These branches form septa that divide the lung into lobules.
• SUMMARY - The Main Bronchi

  • Left and right main bronchi are outside the lung tissue. Branches within the lung are surrounded by bands of smooth muscle.
  • Each lung is further divided into smaller units called bronchopulmonary segments. These segments are named according to the associated segmental bronchi. The right lung contains 10 and the left lung usually contains 8-9 bronchopulmonary segments.
• SUMMARY - The Bronchioles

  • Within bronchopulmonary segments, each segmental bronchus ultimately gives rise to terminal bronchioles that supply individual lobules.
• SUMMARY - Alveolar Ducts and Alveoli

  • Respiratory bronchioles open into alveolar ducts; many alveoli are interconnected at each duct
  • Blood air barrier consists of a simple squamous epithelium of type I alveolar cells; type II alveolar cells scattered in it produce an oily secretion (surfactant) that keeps the alveoli from collapsing. Alveolar macrophages patrol the epithelium and engulf foreign particles.
• SUMMARY - The Blood Supply to the Lungs

  • The respiratory exchange surfaces are extensively connected to the circulatory system via the vessels of the pulmonary circuit
• Why are there almost no cilia or mucous glands in the respiratory bronchiole?

  Filtration and humidification are complete by the time air reaches this point, so the need for cilia and mucous glands is eliminated.
• What is the function of the surfactant produced by the type II alveolar cells?

  The surfactant coats the inner surface of each alveolus and helps to reduce surface tension and avoid the collapse of the alveoli.