Lecture 3 - Histology of Epithelium PDF

VPP 3214(VETERINARY HISTOLOGY AND DEVELOPMENTAL ANATOMY) HISTOLOGY OF EPITHELIUM CELLULAR MORPHOLOGY Apex (Apical) Width Supra Peri Height Lateral Para Infra Base (Basal) Basolateral  EPITHELIAL TI...

VPP 3214(VETERINARY HISTOLOGY AND DEVELOPMENTAL ANATOMY) HISTOLOGY OF EPITHELIUM CELLULAR MORPHOLOGY Apex (Apical) Width Supra Peri Height Lateral Para Infra Base (Basal) Basolateral  EPITHELIAL TISSUE Layer of contiguous cells which lines internal and external body surface Derived from three embryonic germ layers (endoderm, mesoderm and ectoderm) Serves as protection, transcellular transportation, secretion, absorption, sensation and gametes maturation Classification – surface epithelium, glandular epithelium and neuroepithelium Interchangeably termed as tunica mucosa  BASIC CHARACTERISTICS Tightly bound by junctional complexes Lack of extracellular space and extracellular matrix Possesses basement membrane (basal lamina and lamina reticularis) Avascular type of tissue Supported by underlying connective tissue Basement Membrane Connective Tissue MORPHOLOGICAL CLASSIFICATION OF EPITHELIAL TISSUE Epithelium 1 2 Simple Epithelium Stratified Epithelium a a Non-Keratinized, Stratified Squamous Epithelium Squamous Epithelium d Transitional b Cuboidal Epithelium b Keratinized, Stratified Epithelium Squamous Epithelium c Columnar Epithelium c Cuboidal or Columnar d Stratified Epithelium Pseudostratified Columnar Epithelium  1(a) Squamous Epithelium Tightly apposed, flatted, low-profile polygonal epithelium Apical view – mosaic-like layer and centrally located, bulging nucleus Lateral view – protruding nucleus to the apical surface and sometime anuclear Facilitates in transepithelial passive diffusion for fluids and gases Endothelium – blood-lining epithelium Mesothelium – body cavities-lining epithelium Loop of Henle, pulmonary alveoli and tunica intima of blood vessels 1(a) Squamous Epithelium Loop of Henle Venule Pneumocytes  1(b) Cuboidal Epithelium Square cellular profile with the width and height is approximately equivalent Centrally located nucleus in the cytoplasm Some apical cytoplasmic modified to microvilli Mainly found in lining tubules, ducts and glands In glands appear like pyramidal type of cells Important for secretion, absorption and protection Proximal & distal convoluted tubule, thyroid follicle, ovary and bile canaliculi 1(b) Cuboidal Epithelium Thyroid Follicles Distal Convoluted Tubules  1(c) Columnar Epithelium Rectangular cell with greater height and narrow width Oval nucleus basally located (half bottom of the cell) Apical surface might be modified to microvilli, stereocilia and cilia Crucial in transportation, secretion, absorption and protection Microvilli – digestive tract and gallbladder Stereocilia – cochlear hair cell Cilia – uterine tube and bronchiole 1(c) Columnar Epithelium Duodenal Mucosa Uterine Mucosa  1(d) Pseudostratified Columnar Epithelium Single layer of columnar cells Multilevel nuclei arrangement (2-3 rows) All cells have direct contact with the basement membrane Some cells not extended to the epithelial surface (basal reserve cells) Basal reserve cells – undifferentiated replacement cells Apical modifications such as cilia and stereocilia Cilia (trachea and bronchus) and stereocilia (epididymal ducts)  1(d) Pseudostratified Columnar Epithelium Trachea Epididymis  2(a) Non-Keratinized, Stratified Squamous Epithelium Only bottom cells layer (stratum basal) has contacted with basement membrane Stratum basale composed of cuboidal epithelium (actively proliferating layer) Middle, thick layers consist of stratum spinosum multilayer Top layer (stratum superficiale) is flat cells layer with nucleus and some keratin Moistened by glandular secretion from the underlying tissue (submucosa) Influenced by species and diet to modify Oral cavity, esophagus,pharynx and vagina 2(a) Non-Keratinized, Stratified Squamous Epithelium Esophagus Vagina  2(b) Keratinized, Stratified Squamous Epithelium Consist of up to five different strata (basal, spinosum, granulosum, lucidum and corneum) Germinal layer (basal) proliferating to superficial surface to modify a keratinized layer (corneum) Stratum basal – basophilic, cuboidal to columnar cells, progenitor layer, also present melanocytes, Langerhans cells and Merkel cells Stratum spinosum – polygonal (cuboidal to spindle) cells in lattice arrangement, high distribution of intracytoplasmic tonofilaments and crucial layer for tension prevailing  2(b) Keratinized, Stratified Squamous Epithelium Stratum granulosum – 3-5 layer of flattened cells, keratohyalin granules, and commencement layer for keratinization (degradation of nucleus and organelles) Stratum lucidum – thickened, non-stained, refractive layer, compacted bundles of cytokeratin filaments, and to protect underlying layers and prevent dehydration and body fluid loss Stratum corneum – completely keratin cells, thickened plasma membrane, dissolution nucleus and other organelles, and undergo desquamation Skin and paws (carpal, metacarpal and digital pad)  2(b) Keratinized, Stratified Squamous Epithelium Thin Skin Thick Skin  2(c) Stratified Cuboidal or Columnar Epithelium Relatively few locations in the animal body lining by this epithelium Only deep layer contacts with basement membrane Restricted to 2-3 layers only Stratified cuboidal – entire layers composed of cuboidal epithelium Stratified columnar – only superficial layer composed of columnar epithelium Papillary duct, sweat glands and major salivary gland (parotid & mandibular) 2(c) Stratified Cuboidal or Columnar Epithelium Papillary Duct Salivary Duct of Parotid Gland  2(d) Transitional Epithelium Specialized form of stratified epithelium in the urinary passage (urothelium) Basal layer – cuboidal to columnar epithelium Middle layer – polygonal cells Superficial layer – rounded cells that tightly apposed by zonulae occludentes Subjected to constant changes in pressure and distension Undergo rapid modulation of cellular height Renal pelvis, ureter, bladder and urethra 2(d) Transitional Epithelium Ureter Urinary Bladder  GLANDULAR EPITHELIUM Invagination of the epithelial tissue into a deeper connective tissue Involved in synthesis and secretion of specific substance Stored in secretory granules Divided into parenchyma (secretory unit) and stroma (surrounding connective tissue) Two major types of glands: 1. Exocrine glands 2. Endocrine glands  Histogenesis of Glandular Epithelium 1. Primitive Epithelial Ingrowth 3. Ductal Branching 2. Ductal Elongation  Histogenesis of Glandular Epithelium 4. Acinar Proliferation 6. Acinar Survival 5. Acinar Differentiation  1. Exocrine Glands (Types) a. Unicellular Exocrine Glands Goblet cell - the simplest form exocrine gland Distributed along digestive and part of respiratory tract To protect and lubricating the epithelial lining (chemical and/or parasympathetic) Two cytological regions – stem and theca i. Stem – narrow and short basal region, contained nucleus, close contact with basement membrane ii. Theca – facing lumen, apical microvilli, expended cytoplasm with membrane-bound secretory droplet (mucinogen), Golgi apparatus located in between the droplets  Microvilli 1. Exocrine Glands Theca Mucin Nucleus Stem Goblet Cells  1. Exocrine Glands (Types) b. Multicellular Exocrine Glands Composed of cluster of secretory cells (acinar) to form a secretory unit (gland) Secretory units are dependently functioning to form a ‘secretory organ’ Collagenous capsule encapsulated large multicellular exocrine gland Septa – extension of collagenous connective tissue to form lobes and lobules Myoepithelial cells – modified epithelium with small nucleus and sparse actin filaments (radiating from the nucleus) partly smooth muscle cells and have contractility features Sweat glands, major salivary glands and mammary glands 1. Exocrine Glands Sweat Glands Mammary Glands  1. Exocrine Glands (Secretion) a. Serous Glands Protein-rich watery secretion Spherical nuclei and located in the middle or toward basal membrane Dense secretory granules Narrow secretory lumen Basal infolding plasma membrane Apical microvilli with acidophilic cytosol Parotid gland, lacrimal gland and pancreatic exocrine 1. Exocrine Glands Parotid Glands Exocrine Pancreatic Glands  1. Exocrine Glands (Secretion) b. Mucous Glands Mucin-rich secretion with oligosaccharides side chains Pyramidal cellular morphology with blunt apical surface Well demarcated plasma membrane and wide secretory lumen Dense basophilic, flattened nuclei at the basal Transparent, foamy, vacuolated cytosol (mucinogen) Esophageal glands and pyloric glands  1. Exocrine Glands Esophageal Glands Pyloric Glands  1. Exocrine Glands (Secretion) c. Seromucous Glands Serous demilunes or mixed glands Produces both serous and mucous secretion Mucous gland lies on top of serous gland Serous gland appears half-moon-shaped cap of acinar Homocrine – produces only one type of secretion (equine parotid gland) Heterocrine – produces mixture of serous and mucous secretion (bovine sublingual gland) 1. Exocrine Glands Parotid Glands  Exocrine Gland Classification Simple Compound Acinar Tubular Tubular Branched Acinar Coiled Branched Tubular Acinar Tubuloacinar  2. Endocrine Glands Ductless glands and release the hormones into blood vessels Cellular arrangement i. Cords (adrenal gland) – most common ii. Follicle (thyroid gland) Classification: i. Autocrine – stimulating own cells (hematopoietic cells) ii. Paracrine – targeting adjacent and vicinity cells (stomach, duodenum) iii. Endocrine – stimulating different organ and far from signaling cells (pituitary gland) 2. Endocrine Glands Endocrine Paracrine Autocrine  Mode of Secretion 1. Merocrine Membrane-bound secretory granules via exocytosis Cellular morphology remains intact Continuous secretion (pancreatic exocrine and endocrine glands) 2. Apocrine Disintegration of apical cytoplasm Sweat glands, mammary gland and prostate gland 3. Holocrine Fatty degeneration of the cell with fat droplets accumulation and necrotic nucleus E.g. sebaceous gland  Mode of Secretion Merocrine Apocrine Holocrine Thank You!