Columnar epithelium

Local host defenses of both the upper and lower respiratory tract, along with the anatomy of the airways, are important in preventing infection. Upper respiratory defenses include the mucodliary apparatus of the nasopharynx, nasal hair, normal bacterial flora, IgA antibodies, and complement. Local host defenses of the lower respiratory tract include cough, mucodliary apparatus of the trachea and bronchi, antibodies (IgA, IgM, and IgG), complement, and alveolar macrophages. Mucus lines the cells of the respiratory tract, forming a protective barrier for the cells. This minimizes the ability of organisms to attach to the cells and initiate the infectious process. The squamous epithelial cells of the upper respiratory tract are not ciliated, but those of the columnar epithelium of the lower tract are. The cilia beat in a uniform fashion upward, moving particles up and out of the lower respiratory tract. 

Figure 10.1 Typical tracheo-bronchial and bronchiolar epithelia showing the major cell types. The tracheo-bronchial epithelium showing the pseudostratified nature of the columnar epithelium, principally composed of ciliated cells (C), interspersed with goblet cells (G), brush cells (Br), serous cells (S), Kulchitsky s cells (K) and basal cells (B). The bronchiolar epithelium showing the cuboidal nature of the epithelium, principally composed of ciliated cells (C), Clara cells (Cl) and infrequent basal cells. Muc = mucus Ci = cilia N = nucleus Sec = secretory granules.

Bile acids are recycled via the enterohepatic circulation, with less than 5% of the total bile acid pool entering the colon.Bile adds are reabsorbed by ileum columnar epithelium cells and are transported back to the liver by the portal vein where they are extracted by hepatocytes. Approximately 6-12 enterohepatic circulations occur daily. Free bile acids, like DCA, are partly absorbed into the colon and enter the enterohepatic circulation, where they are... 

Nasal epithelium. The nasal cavity superior to the nostrils (vestibule) is covered by skin containing hair follicles and sebaceous and sweat glands. The skin is continuous with the inner nasal mucosa. Posteriorly, the epithelium is a pseudostratified ciliated columnar epithelium that covers the respiratory regions (formed by the maxilloturbinates).45,107,110 The superior turbinate (also called the ethmoturbinate) is lined by a thicker mucosa consisting of olfactory receptors and supporting cells.45,110... 

The pharynx, larynx, trachea and bronchi are lined with pseudostratified, ciliated columnar epithelium that contain at least eight cell types, including mucous secretory goblet and Clara cells, which produce a protective mucus layer of 5-10 jum thickness (see Table 9.2). Subepithelial secretory glands, present in the bronchial submucosa, also contribute to the mucus blanket [9]. Through coordinated ciliary movement a propulsive wave is created, which continuously moves the mucus layer up towards the larynx. Consequently, the mucosal surface of trachea and bronchi is constantly swept to remove inhaled materials. As the bronchi divide into bronchioli, the ciliated columnar respiratory epithelium is much thinner and changes to a simpler non-ciliated cuboidal epithelium. The epithelium in the terminal and respiratory bronchioles consists of ciliated, cuboidal cells and a small number of Clara cells. However, Clara cells become the most predominant type in the most distal part of the respiratory bronchioles [10]. 

The mucosa of the small intestine is lined by a simple columnar epithelium, which evaginates into villi and invaginates into crypts, as shown schematically in Fig. 10.11. The lamina propria of the small intestine forms the core of villi... 

The initial penetration of the oncosphere in H. diminuta appears to be largely mechanical as a result of the destruction of the columnar epithelium of the insect gut by hook movements (888), but as indicated above, lysis may also be involved. The same pattern is likely to be followed by other species in other invertebrate and vertebrate hosts. 

Uterus Columnar epithelium Protects internal surfaces... 

Columnar epithelium Bowman s membrane Supports epithelium... 

Endometrium Columnar epithelium Fibroblasts and glandular cells Basal epithelium Endothelium Basement membrane Loose connective tissue Blood vessel walls Secretes substances... 

The bronchus is a tubular structure that brings air into the alveoli. It is lined with pseudostratified columnar epithelium surrounded by a thin lamina propria containing fine collagen and elastic fibers. A thin layer of smooth muscle surrounds the lamina propria. Glands are found in the submucosa and hyaline cartilage and the pulmonary arteries are found in the outer layer (adventitia). 

Figure 3.11. Structure of uterus. The uterus contains two layers the endometrium and the myometrium. Endometrium contains columnar epithelium, lamina propria, uterine glands, and arteries. Myometrium contains smooth muscle fibers, interstitial collagen, and arteries.

Mucosa Columnar epithelium Basement membrane Food transport... 

Food is propelled through the stomach by wall contraction in a similar manner to the way blood is pushed through blood vessels. The stomach and intestines contain several layers including the mucosa, submucosa, muscu-laris, and serosa. In the stomach the inner lining is made up of a mucous layer with columnar epithelium that extend into the gastric pits about 1/4 of the thickness of the wall (Figure 3.14). Below the epithelium is the lamina... 

Figure 3.14. Structure of the stomach. Stomach contains four layers, including the mucosa, submucosa, muscularis, and serosa. The inner infolded mucous layer is made up of columnar epithelium, and gastric pits are found within the infoldings. Submucosa contains connective tissue and vessels, and the muscularis contains muscle fibers. The serosa is on the outside of the stomach and is continuous with the peritoneum.

Absorptive this is found in the entire small intestine (Figure 6.2). The intestinal villi are lined by a simple, columnar epithelium which is continuous with that of the crypts. The cells of this epithelium are of two main types ... 

What happens at the instant when an odor-active molecule comes in touch with our nasal cavity 205 The first interaction of odorant molecules takes place in the olfactory receptor neurons, which are embedded in the pseudostratified columnar epithelium (or simply, olfactory epithelium), which is located in the posterior nasal cavity in the case of mammals. Olfactory sensory neurons express receptor proteins on the surface membrane of the cilia, which gain access to the extracellular region covered with mucus. The airborne odorants are dissolved into the mucus, bind with the receptors, and then the receptor protein triggers a signal transduction cascade. This results in the opening of the cation channel that would depolarize the sensory neuron and eventually elicit a train of action potentials in the axon. The olfactory axon leads to the olfactory bulb through basal lamina and lamina propria. 

Q2 Unlike the small intestinal mucosa, the colonic mucosa does not contain any villi. There are columnar epithelial cells and mucus-secreting goblet cells in the mucosa the columnar epithelium reabsorbs fluid and electrolytes. 

In man and in other mammalian species, the major mass of the prostate, usually consisting of the right and left lateral and the middle lobes, is composed of alveoli lined with columnar epithelium embedded in a thick fibromuscular stroma. These alveoli constantly secrete a fluid which is drained off by a system of branching ducts that empty into the floor and lateral surfaces of the posterior urethra. The normal secretion is dependent upon the degree of androgenic stimulation and amounts to about 0.5-2 ml per day. The prostatic secretion, which is characterized by very high acid phosphatase activity, is a milky fluid which contains citric acid, choline, cephalin, cholesterol, proteins, and electrolytes similar to those found in the plasma. 

Mucous Surface. The mucosa of the small intestine consists of three layers (Fig. 2) an absorptive layer, a continuous single sheet of columnar epithelium the lamina propria, a layer heterogeneous in composition and cell type and the muscularis mucosa, a muscular layer separating the mucosa and submucosa. 

Emonard, H. and Grimaud, J-A. (1990). Matrix metal-loproteinases a review. Cell Mol. Biol. 4, 195-203. Estreicher, A., Muhlhauser, J., Carpentier, J-L., Orci, L. and Vassalli, J-D. (1990). The receptor for urokinase plasminogen activator polarizes expression of the protease to the leading edge of migrating monocytes and promotes d radation of enzyme-inhibitor complexes. J. Cell Biol. Ill, 783-792. Evans, M.J. and Plopper, C.G. (1988). The role of basal cells in adhesion of columnar epithelium to airvray basement membrane. Am. Rev. Respir. Dis. 138, 481—483. 

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