Microscopic Structure of Glandular Epithelium PDF

Updated 09/09 / 2024 GLANDULAR EPITHELIUM It is a type of epithelium specialized in producing secretion as the epithelial cells form glands. The glands are classified in many ways. 1. According to presence or absence of ducts: * Endocrine or ductless...

Updated 09/09 / 2024 GLANDULAR EPITHELIUM It is a type of epithelium specialized in producing secretion as the epithelial cells form glands. The glands are classified in many ways. 1. According to presence or absence of ducts: * Endocrine or ductless glands, secreting hormones directly in the blood as these glands rich in blood capillaries e.g., Thyroid, parathyroid, pituitary, & suprarenal glands. * Exocrine glands: They have ducts to carry their secretions to the target site of action e.g., salivary glands, sweat and sebaceous glands. *Mixed glands: They possess both exocrine and endocrine parts e.g., pancreas, testis, and ovary. 2- According to number of cells form the gland: * Uni-cellular gland: a goblet cell which is formed of one cell and is considered as a gland. It is present in: Respiratory and intestinal tracts. * Multi-cellular glands (formed of many cells): as the salivary glands. 3- According to changes in the secretory cells during secretion (mode of secretion): *Merocrine gland: In these glands, there are no cellular changes in the secretory cells of the acini during secretion e.g., the salivary glands. These glands expel their secretion by exocytosis. *Apocrine gland: in which the tips (apices) of the secretory cells line the acini are detached and come out with the products of the gland e.g., mammary glands secrete milk that contains parts of the secretory cells. *Holocrine gland: the whole secretory cells are destroyed and come out with DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License  Updated 09/09 / 2024 the secretion e.g., sebaceous glands. These glands have stem cells to replace the destructed cells during secretion. 4- According to the kind of their secretion into: a- Serous glands: as parotid gland b- Mucous glands: as goblet cells. c- Mucoserous glands: as submandibular and sublingual glands. d- Fatty secretory glands (sebum): as sebaceous glands. e- Watery secretory glands: as sweat glands. f- Waxy secretory glands: as glands of external ear. g- Cellular secretory glands: as testis and ovary. 5- According to the shape and branching of the secretory part of exocrine glands: tubular, acinar (alveolar), or Tubulo-acinar (tubule-alveolar). A) Tubular Glands may be: i- Simple tubular glands: the intestinal glands ii- Simple branched tubular: gastric glands. iii- Simple coiled tubular: sweat glands. iv- Compound tubular: e.g., the kidney, testis, and liver. B) Acinar (alveolar) glands may be: i- Simple acinar: (sebaceous glands) ii- Simple branched acinar: (sebaceous glands) iii- Compound acinar: (sebaceous glands) C) Tubulo acinar glands may be: i- Simple tubulo acinar: is not present in the human body. DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License Updated 09/09 / 2024 ii- Simple branched tubulo acinar: glands of the mouth. iii- Compound tubulo acinar: (3Ps) as prostate, pancreas & parotid. Epithelial Polarity The epithelial cells show certain specialization (modification) to perform specific functions. These specializations are known as polarity. This polarity is found on the luminal (upper), on the lateral (inter-cellular) & the basal surfaces. * Apical Polarity: the upper surface of some epithelial cells shows cilia, DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License  Updated 09/09 / 2024 microvilli, stereocilia (very long microvilli) and kinocilium. Kinocilium is a true cilium but non motile. It is found in the maculae (receptors for equilibrium) found in the inner ear. microvilli *Polarity of the lateral surfaces: inter- cellular junctions: 1- Tight junction (zonula occludens): the two adjacent cell membranes are very close to each other, and they fuse completely. For 0.2 µ, the two cell membranes fuse 2- 4 times. This junction prevents the intra-luminal substances from passing in between the cells. It is present near the apices of the epithelial cells. It surrounds the epithelial cell as a belt. DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License  Updated 09/09 / 2024 2- Adherens junction: (zonula adherens): it is next to the tight junction. It forms a belt around the epithelial cells. The two cells are separated by 20-40 nanometers. This space is filled with an adhering substance of low electron density and of unknown chemical composition but rich in calcium. 3- Macula adherens (desmosome): The two adjacent cells show thickening of their cell membranes from the cytoplasmic side. This thickening is called plaque. The intermediate filaments implanted in this plaque as hair pen like structure. Desmosomes help in the stability of the cell membrane. N B: The tight junction, the adherens junction and desmosomes form junctional complex. DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License  Updated 09/09 / 2024 4- Gap junction: the two cells are separated by a space of 2- 4 nanometers. There are hydrophilic channels to allow fast passage of ions and nerve impulses from one cell to another. *Basal surface polarity 1- Basal infoldings to increase the surface area of basal surface of the cell. The mitochondria are arranged in between these infoldings. This area of the cell is DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License Updated 09/09 / 2024 concerned with ion transport e.g., cells of convoluted tubules of the kidney and cells of thyroid glands. 2- Hemidesmosomes present in the basal cells of epithelium in its basal surfaces. It is half of the desmosome present between the basal epithelial cells & the underlying C.T. Basal infoldings hemidesmosomes Clinical Relevance: iodide transport in thyroid hormone synthesis Summaries and Key Points: classification of glands specialization of epithelial cells References and Additional Resources: Basic Histology by Jane Quire Latest Edition Color Atlas of Histology by Lesie P Gartner Latest Edition NAME: Nadia Mahmoud DESIGNATION: prof. of Histology DEPARTMENT: biomedical sciences DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License