The bronchial circulation, via bronchial arteries that branch from the aorta, supplies all of the lung tissue other than the alveoli (i.e., the walls of the bronchi and bronchioles and the connective tissue of the lung other than that of the alveolar septum). The finest branches of the bronchial arterial tree also open into the pulmonary capillaries. Therefore, the bronchial and pulmonary circulations anastomose at about the level of the junction between the conducting and respiratory passages. Bronchial veins drain only the connective tissue of the hilar region of the lungs. Most of the blood reaching the lungs via the bronchial arteries leaves the lungs via the pulmonary veins.
A dual lymphatic drainage of the lungs parallels the dual blood supply. One set of lymphatic vessels drains the parenchyma of the lung and follows the air passages to the hilum. Lymph nodes are found along the route of the larger lymphatic vessels. A second set of lymphatic vessels drains the surface of the lung and travels in the connective tissue of the visceral pleura, a serous membrane consisting of a surface mesothelium and the underlying connective tissue.
Most of the nerves that serve the lung are not visible at the level of the light microscope. They are components of the sympathetic and parasympathetic divisions of the autonomic nervous system and mediate reflexes that modify the dimensions of the air passages (and blood vessels) by contraction of the smooth muscle in their walls.
Olfactory mucosa is located in the roof and part of the walls of the nasal cavity. Its pseudostratified epithelium is thicker than that of nonsen-sory epithelium, and it serves as the receptor for smell. Olfactory epithelium consists of olfactory cells, supporting (sustentacular) cells, basal cells, and brush cells. Olfactory cells are bipolar neurons. The apex of the cell is expanded into the olfactory vesicle from which nonmotile cilia, the actual recep-tors, extend into surface secretions. The base of the cell tapers into an axonal process that enters the lamina propria and joins axons from other receptor cells to form the olfactory nerve. Large, cuboidal Schwann cells are a prominent feature of these axons, giving the nerve an un-usual appearance. Supporting cells are columnar cells with apical microvilli. They attach to the receptor cells through adhering junctions and provide me-chanical and metabolic support to the olfactory cells. Basal cells are stem cells from which olfactory and supporting cells differentiate. Brush cells are the same cell type that occurs in nonsensory respiratory epithelium. The lamina propria is directly contiguous with periosteum. It contains numerous blood and lymphatic vessels, unmyelinated and myelinated nerves, and olfactory (Bowman’s) glands. These are tubuloalveolar serous glands whose watery secretion serves as a trap and solvent for odorant substances and continuously washes the olfactory surface.
Olfactory mucosa, nasal cavity, human, Azan ×75.
This low-magnification orientation micrograph shows part of the wall of the nasal cavity. The olfactory mucosa (OM ) and adjacent ethmoid bone (EB ) are indicated. The olfactory mucosa is directly attached to the bone tissue; no submucosa is present. In this specimen, however, the mucosa is separated from the bone tissue because of shrinkage, a frequently encountered artifact.
The olfactory epithelium (OEp) is pseudostratified, like respiratory epithelium; however, it is typically thicker. Note the respiratory epithelium (REp) included in the lower right of the micrograph. The feature that is most useful in identifying olfactory mucosa is the presence of numerous large, unmyelinated nerves (N ) and extensive olfactory (Bowman’s) glands (BG) in the connective tissue of the mucosa. Note that the adjacent respiratory mucosa lacks the nerves and exhibits a relative paucity of glands.