Bowman’s glands, which are unique to the olfactory epithelium, release fluids to protect the olfactory sensory neurons from infection as well as trap odor molecules. Once an odorant is trapped, it binds to specific receptors located on olfactory sensory neurons, which begins the process of perceiving a smell.
Sir William Bowman (1816—1892), an English surgeon, histologist, and anatomist, is best known for his research using microscopes to study human organs. Sir William was also a successful ophthalmologist. Throughout his life, many anatomical structures were named after him including Bowman’s capsule, which is a cup-like sac at the tubular portion of the nephron of the kidney and is the first step in filtering blood from urine; Bowman’s membrane, which is the anterior limiting membrane in the cornea of the eye; and Bowman’s glands, which are below the olfactory epithelium to secrete fluid that traps odorants.
Anatomy and Physiology
The nasal cavity is found between the ethmoid bone superiorly and the palate inferiorly. It is divided into two sections by the nasal septum. The nasal cavity is essential for conditioning the air that passes into the lungs as well as acting as a resonance chamber to enhance a person’s speech. Within the nasal cavity lie the nasal and olfactory epithelia. The nasal epithelium is a pseudostratified ciliated layer with goblet cells, which secrete mucous to trap small foreign particles so that they are breathed into the lungs. The olfactory epithelium is also pseudostratified but has a columnar look to it and does not contain goblet cells. Instead it contains ciliated olfactory sensory neurons. Just beneath this epithelium are the Bowman’s glands.
Also known as olfactory glands, Bowman’s glands penetrate to the surface of the olfactory epithelium. The glands consist of an acinus (cluster of cells that resembles a “berry” shape) in the lamina propria (thin layer of loose connective tissue) and a secretory duct that exits through the olfactory epithelium. Bowman’s glands are situated in the dorsal (roof of the nasal cavity) and caudal (toward the back) portions of the nasal cavity. Secretions from Bowman’s glands, including lysozyme (a type of protein or enzyme that damages bacterial cell walls to fight and/or prevent infection), amylase (an enzyme that breaks up starches), and immunoglobulin A (an antibody that is necessary for mucosal immunity), help moisten the epithelium in the nasal passages. Additionally, these secreted enzymes are essential for maintaining the immune system of the nasal cavity, and particularly the olfactory epithelium. As a person ages, Bowman’s glands are lost or disrupted in their main function. Infection can also cause Bowman’s glands to be lost or damaged, particularly if the olfactory epithelium is damaged.
For decades the main function of the Bowman’s glands was unknown. Recent research completed at the University of Oslo (Solbu & Holen, 2011) showed that in rats and mice (1) Bowman’s glands secreted mucin (a protein found in mucus), and that (2) aquaporin-5 (a water channel protein) was present at the apical face of the olfactory epithelium. Immunogold electron microscopy analysis revealed an intricate network of fine aquaporin-1-positive fibroblast processes (principal water-transporting proteins) surrounding Bowman’s glands. These results show how the olfactory mucosa could be protected from infection and dehydration as well as how neuronal function is protected against ion concentration changes. This is done by the rapid replacement of water loss through aquaporin pathways.
Renee Johnson and Jennifer L. Hellier
See also: Anosmia; Dysosmia; Olfactory Mucosa; Olfactory Sensory Neurons; Olfactory System
Ablimit, Abduxukur, Toshiyuki Matsuzaki, Yuki Tajika, Takeo Aoki, Haruo Hagiwara, & Kuniaki Takata. (2006). Immunolocalization of water channel aquaporins in the nasal olfactory mucosa. Archives of Histology and Cytology, 69, 1—12.
Jayaraman, Sujatha, Nam Soo Joo, Bruce Reitz, Jeffery J. Wine, & A. S. Verkman. (2001). Submucosal gland secretions in airways from cystic fibrosis patients have normal [Na(+)] and pH but elevated viscosity. Proceedings of the National Academy of Sciences of the United States of America, 98, 8119—8123. Retrieved from http://www.pnas.org/content/98/14/8119.abstract?ijkey=668b36099966ef706e75d33c9b2a9c6a78668cad&keytype2=tf_ipsecsha
Solbu, Tom T., & Torgeir Holen. (2011). Aquaporin pathways and mucin secretion of Bowman’s glands might protect the olfactory mucosa. Chemical Senses, 37(1), 35—46. Retrieved from http://chemse.oxfordjournals.org/content/37/1/35.full