Epithelial Tissue PDF

Epithelia Tissue Dr. A. Ibrahim. Department of Anatomy Faculty of Basic Medical Sciences University of Ilorin  Lecture expectations At the end of the lecture, students will be able to: 1. States common characteristics of all epithelia 2. Recognize and fully classify epithelia tissue based...

Epithelia Tissue Dr. A. Ibrahim. Department of Anatomy Faculty of Basic Medical Sciences University of Ilorin  Lecture expectations At the end of the lecture, students will be able to: 1. States common characteristics of all epithelia 2. Recognize and fully classify epithelia tissue based on number and shape 3. Mention the various location of epithelia tissues in relation to functions 4. Differentiate morphologically the types of epithelia tissue 5. State the functions and types of epithelia glands (i.e. exocrine glands) 6. Describe the function and importance of surface specialization of epithelia cell. 7. Classify and differentiate cellular surface specialization based on morphology and functions Epithelia: What are they and what do they do? Cover and line surfaces Protection Secretion Absorption Filtration Excretion Diffusion Sensory reception Contractile  Epi = “on” or “around”: Thele = “nipple” free surface open to the outside or an open internal space basement membrane anchors epithelium to underlying connective tissue lack blood vessels (avascular) but richly innervated. readily divide (ex. skin healing) tightly packed with little extracellular space Epithelia: They have specialized cell-cell junctions that binds adjacent cells to each other and contain communication junctions (gap junctions) Characteristics The shape is related to the amount of contained cytoplasm and organelles. In turn related to metabolic activities Some contain pigments. Present in skin, retina and iris Epithelia in the secretory portions of glands show specializations of structure that depend on the nature of secretion produced by them Epithelia cells in which transport of ions is important function (e.g., renal tubules) are marked by the presence of basolateral folds and presence of large numbers of mitochondria. Epithelia: Two types Epithelia: layers of cells covering internal or external surfaces Glands or glandular epithelia: structures that produce secretions Epithelia: Simple squamous a single layer of thin, flattened cells look like a fried egg easily damaged Sparse cytoplasm common at sites of filtration, diffusion, osmosis; cover surfaces air sacs of the lungs, walls of capillaries, linings of blood and lymph vessels Epithelia: Simple squamous Epithelia: Simple cuboidal single layer of cube- shaped cells centrally located nucleus secretion and absorption surface of ovaries, linings of kidney tubules, and linings of ducts of certain glands Epithelia: Simple columnar single layer of cells that are longer than they are wide nucleus located near basement mem. ciliated or nonciliated some have microvilli goblet cells = secrete mucus absorption, secretion, protection linings of the uterus, stomach, and intestine  Epithelia: Pseudostratified columnar appear stratified because nuclei are at 2 or more levels NOT stratified because all cells touch basement mem. ciliated goblet cells protection, secretion, movement of mucus Present in the male sperm-carrying ducts (non-ciliated) and trachea (ciliated) Epithelia: Stratified squamous Many layers of flattened cells Named based on appearance of top layer of cells Functions in protection of underlying areas subjected to abrasion Forms the external part of the skin’s epidermis (keratinized cells), and linings of the esophagus, mouth, and vagina (nonkeratinized cells) Epithelia: Stratified cuboidal Quite rare in the body Typically, two cell layers thick Only top layer is cuboidal Protection, secretion, absorption linings of larger ducts of mammary glands, sweat glands, salivary glands, and pancreas  Epithelium: Stratified columnar Limited distribution in the body Found in the pharynx, male urethra, and lining some glandular ducts Also occurs at transition areas between two other types of epithelia  Epithelia: Transitional Several cell layers, basal cells are cuboidal, surface cells are dome shaped (or flat) Stretches to permit the distension of the urinary bladder Lines the urinary bladder, ureters, and part of the urethra  Glands or Glandular epithelia  A gland is one or more cells that makes and secretes an aqueous fluid into ducts or into body fluids Gland = 1 or more cuboidal or columnar cell Relative number of Glands cells forming the gland: unicellular or multicellular Classified by: Site of product release: endocrine or exocrine Exocrine vs. Endocrine Endocrine Exocrine Secrete substances into tissue fluid More numerous than endocrine or blood glands Ductless glands that produce Secrete their products onto body hormones surfaces (skin) or into body cavities Secretions include amino acids, via ducts proteins, glycoproteins, and Examples include mucous, sweat, steroids oil, digestive, and salivary glands The only important unicellular gland is the goblet cell  Glands: Classification of exocrine glands 1. Duct Structure Simple – single unbranched duct (glands of intestine) Compound – branched duct (salivary glands) 2. Shape of Secretory Units Tubular (alveolar) – (sweat glands) Acinous (acinar) – shaped like a grape (salivary glands) 3. Mechanism of Secretion Merocrine = release watery, protein-rich fluid by exocytosis salivary glands, sweat glands Apocrine = lose small portions of their cell body during secretion mammary glands, ear wax Holocrine = entire cell lysis (breaks apart) during secretion sebaceous glands of the skin NOTE: The glands can either have serous, mucous or mixed serous and mucous secretion. Exocrine glands: Duct structural classification Exocrine glands: Classification based on Shape of Secretory Units Exocrine glands: Classification based on Mechanism of Secretion Surface specialization of epithelia cells Surface Specializations: Microvilli, Cilia, Flagella, Stereocilia The surface of the most cells have extensions They are used in cell movement, phagocytosis, absorption. Most of these extensions are based on actin filaments.  Surface Specialization: Microvilli Finger-like extensions derived from the cell surface. Finger-like prolongations 1µm in length 0.1µm diameter Contains a bundle of straight parallel filaments (20-30 Actin filaments) Actin filaments extend 0.5µm down into the apical cytoplasm. Enclosed in an extension of the plasma membrane. Glycocalix is thicker around the microvilli. Localizations (cells specialized for absorbtion): Intestinal epithelium (Striated border) Proximal tubule of the kidney (Brush border) Gall bladder epithelium Function: increase the surface area for absorption, cell movement and phagocytosis  Surface Specialization: Cilia Cilia have eyelash or hair like structures Motile Larger than microvilli (5-10µm long , 0.2µm in diameter) Have a complex internal structure (E.M ) 250 or more cilia (in each cell) arranged in parallel rows Have a complex internal structure A characteristic arrangement of microtubules called “ Axoneme’’ =9+2 microtubule complex Localization 1. Epithelial cells of the upper respiratory tract 2. Epithelial cells of the uterine tubes (oviducts ) 3. Epithelial cells of the Ductus efferentes Function 1. to move mucus and particles over epithelial surfaces (in respiratory epithelium) 2. to transport the ovum toward the uterus (in uterine tubes) 3. to drive the spermatozoa toward the epididymis (in ductus efferentes) Surface Specialization: Cilia Each cilium is covered by an extension of plasmalemma Tapering tip Cylindrical shaft Basal body (located in the apical cytoplasm) Ciliary movement is constant in direction In living cells, cilia beat in a rhythmical wave –like manner Ciliary movement requires ATP, Ca ions, Mg ions and also Dynein (a protein) Abnormality of Cilia: Kartagener’s syndrome Flagella Longer than cilia (100-200 μm), and usually occur as single appendage. Different type of movement (undulating wave type of movement) Less in number (one or two in a single cell) Mammalian sperm contains 9 additional dense fibers around the axoneme (9+9+2) (protective function) Move the cell, movement also requires Dynein Stereocilia Long and irregular microvilli 8μ (EM) Have no internal structure Microfilaments are poorly developed No motility No basal body Function: Hearing and balance Localization: Cochlear and vestibule in the inner ear In the Clinic: Cancer: Adenocarcinoma and papillary thyroid carcinoma Other conditions Asthma Conditions Adenocarcinoma: cancers that affect the glandular Celiac disease that affect epithelia tissue Almost all prostate Human papillomavirus (HPV) epithelial cancers Most breast cancers Vertigo tissue? About 96% of colorectal cancers Approximately 95% of pancreatic cancers Papillary thyroid carcinoma: Represents up to 80% of all thyroid cancers In the clinic: Epithelial cell tests? Urinalysis Pap smear Certain biopsy tests Certain cytology tests QUESTIONS?