University:
Kentucky State University
Course:
BIO 408 | Cell Biology
Academic year:

2019
Views:

334

Pages:

34
Author:

Turfmorrybk9

THE BASAL DOMAIN AND ITS SPECIALIZATIONS 1 The basal domain of epithelial cells is characterized by several features: ▪The basement membrane is a specialized structure located next to the basal domain of epithelial cells and the underlying connective tissue stroma. •Cell-to-extracellular matrix junctions anchor the cell to the extracellular matrix; they are represented by focal adhesions and hemidesmosomes. •Basal cell membrane infoldings increase the cell surface area and facilitate morphologic interactions between adjacent cells and extracellular matrix proteins. 2 Basement Membrane Structure and Function The term basement membrane ➢It is a dense layer of variable thickness at the basal surfaces of epithelia. ➢Can bee seen as a prominent structure referred to as basement membrane using hematoxylin and eosin (H&E) stain in a few locations such as the trachea and, occasionally, the urinary bladder and ureters 3 ➢In contrast to H&E. The periodic acid–Schiff (PAS) staining technique results in a positive reaction at the site of the basement membrane. ➢It appears as a thin, well-defined magenta layer between the epithelium and the connective tissue. The stain reacts with the sugar of proteoglycans, accumulating in sufficient amounts and density to make the basement membrane visible in the light microscope. Stained by H&E, the basement membrane is not seen Stained by the periodic acid–Schiff (PAS), 4 Arrows showing the basement membrane 5 Layers of Basal Lamina consisting of a network of fine fibrils that comprise 1- Lamina lucida it is a relatively clear or electron-lucent area, between the basal lamina and the cell 2- THE BASAL LAMINA or (lamina densa) 3- RETICULAR LAMINA With the development of new EM preparation techniques, the lamina lucida appears to be an artifact of fixation;in the living state, the basal lamina is composed of a single layer of the lamina densa This layer is made of 7 The basal lamina characteristically include the following: 1- laminins 2- Type IV collagen 3-various associated proteoglycans and glycoproteins These proteins are synthesized and secreted by the epithelial 8 9 Functions of Basal lamina Filtration: The movement of substances to and from the connective tissue is regulated in part by the basal lamina, largely through ionic charges and integral spaces Tissue scaffolding: the basal lamina serves as a guide or scaffold during regeneration. Newly formed cells or growing processes of a cell use the basal lamina that remains after cell loss, thus helping to maintain the original tissue architecture basal laminae also allow cells to migrate under physiologic conditions but act as barriers against tumor cell invasion Regulation and signaling: Many molecules that reside in the basal lamina interact with cell surface receptors, influencing epithelial cell behavior during morphogenesi 10 11 The basal lamina in nonepithelial cells is referred to as the external lamina Muscle cells, adipocytes, and peripheral nerve supporting cells exhibit an extracellular electron-dense material that resembles the basal lamina of epithelium. This material also corresponds to a PAS-positive staining reaction, as described earlier Smooth muscle external lamina. This photomicrograph is stained by the PAS method and counterstained with hematoxylin (pale nuclei) 12 Morphologic Modifications of the Basal Cell Surface Read only The orientation of the mitochondria, combined with the basal membrane infoldings, results in a striated appearance along the basal aspect of the cell when observed in the light microscope. Because of this phenomenon, the salivary gland ducts that possess these cells are referred to as striated ducts. •Basal infoldings. Electron micrograph of the basal portion of a kidney tubule cell showing the infolding of the plasma membrane. Note the aligned mitochondria. The infoldings of adjoining cells result in the interdigitations of 13 cytoplasm between the two cells. 25,000. 3 Features of Apical surface of Epithelium 14 15 Apical Domain It is the part of the cell that faces the lumen (the free surface of the cell). It is rich in ion channels, carrier proteins and hydrolytic enzymes. The apical modifications are: • • • • Microvilli. Cilia. Stereocilia. Flagella. Microvilli ▪ Finger-like extensions of plasma membrane of apical epithelial cell. ▪ Present mainly in absorptive cells. ▪ Main function is the absorption of nutrients from intestines and glomerular filtrate. ▪ Increase surface area for absorption. 17 18 Structure of the Microvillus The microvillus is 1- 2µ in length. Contains a core of 25-30 actin filaments. Actin filaments are cross-linked with villin. The actin filaments are inserted into the terminal web. The terminal web is a network of actin and spectrin supported by myosin, IF, and camodulin in the apical part of the cell. The microvillus is covered by glcocalyx. Microvilli contain a conspicuous core of about 20 to 30 ACTIN FILAMENTS The actin bundle extends down into the apical cytoplasm where it interacts with a horizontal network of actin filaments, THE TERMINAL WEB 20 Microvilli • Their number and size vary according to the degree of activity of the cell. • They are usually crowded on the cell apex forming the : • Striated border in the intestine. • Bruch border in the kidney. 21 Striated border in the intestine. 23 Stereocilia are long immotile microvilli present in the epididymis and inner ear. They have special functions in these places. Stereocilia • They are similar to microvilli except that they are longer. • Branched. • In epididimus and ductus deferens they have an absorptive function. • In the internal ear they have a sensory function. 25 Cilia Motile cytoplasmic hair like projections capable of moving fluid and particles along epithelial surfaces. Measurements: length 7-10μ, diameter 0.2 μ. Number of cilia/cell is variable and ranges 1-300 cilium/cell. They move rhythmically and rapidly in one direction. Cilia • Motile cytoplasmic hair like projections capable of moving fluid and particles along epithelial surfaces. • Line cells in the respiratory organs, uterine tubes, and efferent ducts in testes. • They move rhythmically and rapidly in one direction. 27 The core of the cilium is called axoneme. The axoneme consists of longitudinal microtubules arranged as 9 (doublets) peripheral surrounding 2 (singlets) central (9+2). The singlets are separated by 13 protofilaments. The doublets are composed of 2 subunits A & B. Subunit A is formed of 13 protofilaments. Subunit B is formed of 10 protofilaments. Neighboring doublets are connected by nexin. Doublets are connected to the singlets by radial spokes. Dynein radiates form subunit A to subunit B. Dynein has ATPase activity. Cilia are attached to basal bodies similar in structure to centrioles. 30 Cilia 31 Cilia 32 33 34

The Basal Domain and Its Specializations

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