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19-400: Examples include: As ducts travel from the acinus which generates the fluid to the target, the ducts become larger and the epithelium becomes thicker. The parts of the system are classified as follows: Some sources consider "lobar" ducts to be the same as "interlobar ducts", while others consider lobar ducts to be larger and more distal from the acinus. For sources that make the distinction,

38-406: A many-lobed " berry ," such as a raspberry ( acinus is Latin for "berry"). The berry-shaped termination of an exocrine gland , where the secretion is produced, is acinar in form, as is the alveolar sac containing multiple alveoli in the lungs . Acinar exocrine glands are found in many organs, including: The thyroid follicles can also be considered of acinar formation but in this case

57-593: A part of the glandular system that resides within the lobules. Lobules contain clusters of ducts whose secretory alveolies are drained by the intralobular duct. The intralobular ducts are usually lined with simple cuboidal epithelial cells that are lined by myoepithelial cells as well. The intralobular ducts of the lobules drain into the interlobular ducts between lobules. They can be seen in: Acinus An acinus ( / ˈ æ s ɪ n ə s / ; pl. : acini ; adjective, acinar / ˈ æ s ɪ n ər / or acinous ) refers to any cluster of cells that resembles

76-439: A small number of alveoli. Terminal bronchioles are lined with simple ciliated cuboidal epithelium containing club cells . Club cells are non-ciliated, rounded protein-secreting cells. Their secretions are a non-sticky, proteinaceous compound to maintain the airway in the smallest bronchioles. The secretion, called pulmonary surfactant , reduces surface tension , allowing for bronchioles to expand during inspiration and keeping

95-400: Is a stub . You can help Misplaced Pages by expanding it . Respiratory bronchioles The bronchioles ( / ˈ b r ɑː ŋ k i oʊ l s / BRONG -kee-ohls ) are the smaller branches of the bronchial airways in the lower respiratory tract . They include the terminal bronchioles, and finally the respiratory bronchioles that mark the start of the respiratory zone delivering air to

114-532: Is called bronchoconstriction , which is the tightening of the smooth muscle surrounding the bronchi and bronchioles due to and stimulated by histamine , parasympathetic nerves , cold air, chemical irritants, excess mucus production, viral infections, and other factors to decrease air flow. Bronchoconstriction can result in clinical symptoms such as wheezing, chest tightness, and dyspnea, which are common features of asthma, chronic obstructive pulmonary disease (COPD), and chronic bronchitis. The trachea divides into

133-639: The gas exchanging units of the alveoli . The bronchioles no longer contain the cartilage that is found in the bronchi, or glands in their submucosa . The pulmonary lobule is the portion of the lung ventilated by one bronchiole. Bronchioles are approximately 1 mm or less in diameter and their walls consist of ciliated cuboidal epithelium and a layer of smooth muscle . Bronchioles divide into even smaller bronchioles, called terminal , which are 0.5 mm or less in diameter. Terminal bronchioles in turn divide into smaller respiratory bronchioles which divide into alveolar ducts . Terminal bronchioles mark

152-401: The parotid gland , but are more developed in the parotid gland. They are not present in pancreas . An intralobular duct is the portion of an exocrine gland inside a lobule , leading directly from acinus to an interlobular duct (between lobules). It is composed of two subdivisions, the intercalated duct and the striated duct . In the human mammary gland, the intralobular duct is

171-421: The bronchioles from collapsing during expiration. Club cells are a stem cell of the respiratory system , and also produce enzymes that detoxify substances dissolved in the respiratory fluid. The respiratory bronchioles are the narrowest airways of the lungs, 0.5 mm across. The bronchi divide many times before evolving into the bronchioles. The respiratory bronchioles deliver air to the exchange surfaces of

190-631: The bronchioles. The bronchioles are histologically distinct from the bronchi in that their walls do not have hyaline cartilage and they have club cells in their epithelial lining. The epithelium of the bronchioles starts as a simple ciliated columnar epithelium and changes to simple ciliated cuboidal epithelium as the bronchioles decreases in size. The diameter of the bronchioles is often said to be less than 1 mm, though this value can range from 5 mm to 0.3 mm. As stated, these bronchioles do not have hyaline cartilage to maintain their patency. Instead, they rely on elastic fibers attached to

209-489: The end of the conducting division of air flow in the respiratory system while respiratory bronchioles are the beginning of the respiratory division where gas exchange takes place. The diameter of the bronchioles plays an important role in air flow. The bronchioles change diameter to either increase or reduce air flow. An increase in diameter is called bronchodilation and is stimulated by either epinephrine or sympathetic nerves to increase air flow. A decrease in diameter

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228-412: The follicles, being part of an endocrine gland, act as a hormonal deposit rather than to facilitate secretion. Mucous acini usually stain pale, while serous acini usually stain dark. The end of the terminal bronchioles in the lungs mark the beginning of a pulmonary acinus that includes the respiratory bronchioles , alveolar ducts, alveolar sacs, and alveoli . This anatomy article

247-418: The interlobar ducts are more likely to classified with simple columnar epithelium (or pseudostratified epithelium ), reserving the stratified columnar for the lobar ducts. The intercalated duct , also called intercalary duct (ducts of Boll), is the portion of an exocrine gland leading directly from the acinus to a striated duct . The intercalated duct forms part of the intralobular duct . This duct has

266-519: The left main bronchus which supplies the left lung, and the right main bronchus which supplies the right lung. As they enter the lungs these primary bronchi branch into secondary bronchi known as lobar bronchi which supply each lobe of the lung. These in turn give rise to tertiary bronchi ( tertiary meaning "third"), known as segmental bronchi which supply each bronchopulmonary segment . The segmentary bronchi subdivide into fourth order, fifth order and sixth order segmental bronchi before dividing into

285-472: The lungs. They are interrupted by alveoli which are thin walled evaginations . Alveolar ducts are side branches of the respiratory bronchioles. The respiratory bronchioles are lined by ciliated cuboidal epithelium along with some non-ciliated cells called club cells . Bronchospasm , a potentially life-threatening situation, occurs when the smooth muscular tissue of the bronchioles constricts, severely narrowing their diameter. The most common cause of this

304-518: The numerous mitochondria. Along with the intercalated ducts, they function to modify salivary fluid by secreting HCO 3 and K and reabsorbing Na and Cl using the Na-K pump and the Cl-HCO 3 pump, making the saliva hypotonic. Their epithelium can be simple cuboidal or simple columnar . Striated ducts are part of the intralobular ducts . They are found in the submandibular gland , sublingual duct , and

323-413: The sixteenth division of the respiratory tract . Alveoli only become present when the conducting zone changes to the respiratory zone , from the sixteenth through the twenty-third division of the tract. The terminal bronchioles are the most distal segment of the conducting zone. They branch off the lesser bronchioles. Each of the terminal bronchioles divides to form respiratory bronchioles which contain

342-419: The surrounding lung tissue for support. The inner lining ( lamina propria ) of these bronchioles is thin with no glands present, and is surrounded by a layer of smooth muscle . As the bronchioles get smaller they divide into terminal bronchioles. Each bronchiole divides into between 50 and 80 terminal bronchioles. These bronchioles mark the end of the conducting zone , which covers the first division through

361-421: The thinnest epithelium of any part of the duct system, and the epithelium is usually classified as "low" simple cuboidal . They are found in both the pancreas and in salivary glands . A striated duct ( Pflüger's ducts ) is a gland duct which connects an intercalated duct to an interlobular duct. It is characterized by the basal infoldings of its plasma membrane, characteristic of ion-pumping activity by

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