University:
Kentucky State University
Course:
BIO 301 | Human Anatomy
Academic year:

2019
Views:

334

Pages:

41
Author:

Hallie Randolph

Epithelium-1 General features • Epithelium is an avascular tissue composed of cells that cover the exterior body surfaces and line internal closed cavities and tubes. • It also forms the secretory portion of glands and their ducts. • Specialized epithelial cells function as receptors for the special senses. • Can be derived from all embryonic germ layers. • Epithelial cells are polarized and resting on basement membrane. • Epithelium lining skin, mouth, nose and anus: ectoderm • Epithelium lining respiratory system, digestive tract and glands of digestive tract: endoderm • Epithelium lining blood vessels: mesoderm 4 Cell polarity The epithelial cell shows two domains 1- Apical 2- Baso-lateral Each domain shows modifications to suit its functions Functions • • • • • Protection Transcellular transport Secretion Absorption (selective permeability) Involved in sensation Classifications & Naming of Epithelia • According to number of layers – Simple – one layer of cells – Stratified – more than one layer of cells Classification & Naming of Epithelia • According to shape of cells – Squamous – cells wider than tall (plate or “scale” like) – Cuboidal – cells are as wide as tall, as in cubes – Columnar – cells are taller than they are wide, like columns Naming Epithelia • Naming the epithelia includes both the layers (first) and the shape of the cells (second) – i.e. stratified cuboidal epithelium • The name may also include any accessory structures – Keratin – Goblet cells – Cilia • Special epithelial tissues (don’t follow naming convention) – Pseudostratified – Transitional Squamous Simple Cuboidal Columnar Pseudostratified Epithelium keratinized Squamous nonkeratinized Cuboidal Stratified Transitional Columnar Simple epithelium Stratified epithelium Simple Epithelia • Simple Squamous – Locations: • Vascular system (endothelium) • Body cavities (mesothelium) • Bowman’s capsule (kidney) – Major function: • Exchange Endothelium is the simple squamous epithelium that lines the lumen of the cardiovascular system Mesothelium is the simple squamous epithelium that lines serous cavities (peritoneal, pleural, and pericardial cavities) and coats many of the organs in these cavities Stratified Epithelia • • • • Contain two or more layers of cells Regenerate from below Major role is protection Are named according to the shape of cells at apical layer Mitotic activity in stratified epithelium is limited to the basal layer (under normal conditions). Stratified Squamous Epithelium • Specific types – Keratinized – contain the protective protein keratin • Surface cells are dead and full of keratin – Non-keratinized – forms moist lining of body openings • Function – Protects underlying tissues in areas subject to abrasion • Location – Keratinized – forms epidermis – Non-keratinized – forms lining of mouth, esophagus, and vagina – Goblet cells produce mucus – Cilia (larger than microvilli) sweep mucus Ciliated Pseudostratified Columnar Epithelium with goblet cells Transitional Epithelium (Urothelium) • • • Description – Basal cells usually cuboidal or columnar – Superficial cells dome-shaped or squamous Function – stretches and permits distension of urinary bladder Location – Lines ureters, urinary bladder and part of urethra Apical domain  It is the part of the cell that faces the lumen or external environment (the free surface of the cell).  It is rich in ion channels, carrier proteins and hydrolytic enzymes.  The apical modifications are: Microvilli Cilia Stereocilia Microvilli - Present mainly in absorptive cells. - 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 and the brush border in the kidney. Structure - The microvillus is 1µ in length, 0.1µ in width. - 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 and IF at the apical part of the cell. - The microvillus is covered by glycocalyx. Terminal web is a cytoskeletal feature at the apical pole in many epithelial cells Microvilli under LM and EM Cilia - Motile cytoplasmic hair like projections capable of moving fluid and particles along epithelial surfaces. - Measurements: length 5-10μ, diameter 0.2 μ. Number of cilia/cell is variable and ranges 1-300 cilium/cell. - They move rhythmically and rapidly in one direction - 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 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. -Cilia wiggle to move mucus - Found in respiratory epithelium Stereocilia -Stereocilia are long immotile microvilli present in the epididymis and inner ear. They have special functions in these places -They are longer than typical microvilli, more widely separated and branched - They contain actin filaments

Epithelium-1

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