Epithelial Tissue PDF - University of Medicine and Pharmacy

University of Medicine and Pharmacy Department of histology, cytology and embryology Epithelial Tissue  Definition Tissues - groups of cells organised to perform one or more functions. Note!!(but do not write) Cell is the basic structural unit of the body. But in...

University of Medicine and Pharmacy Department of histology, cytology and embryology Epithelial Tissue  Definition Tissues - groups of cells organised to perform one or more functions. Note!!(but do not write) Cell is the basic structural unit of the body. But in the multicellular organism there are tissues that are responsible for maintaining body functions due to collaborative efforts of their individual cells. Four basic types of tissues in the body Epithelium (90% of tumors) Connective tissue Muscular tissue Nervous tissue  Epithelial Tissue - covers body surfaces, - - lines body cavities, and - - - forms glands. There are 2 main types of ET: Covering and lining (covers outer body surfaces (skin) and inner body surfaces (lumen of hollow organs (intestine) and cavities (peritoneal, pericardial, pleural), blood vessels, ducts, tubules). They separate the underlying connective tissue from the external environment or environment of internal cavities Glandular - forms glands  Origin and Distribution of Epithelium Ectoderm - epidermis of skin and epithelium of cornea together covers the entire surface of the body and oral cavity; sebaceous and mammary glands: anterior pituitary ECTODERM Endoderm - alimentary tract, liver, pancreas, gastric glands, intestinal glands Endocrine glands - lose connection with surface MESODERM Mesoderm Endothelium - lining of blood vessels Mesothelium - lining serous cavities ENDODERM  Epithelia are Specialized for Functions Absorption - intestine Secretion – pancreas Transport - eye, endothelium in vessels Excretion – kidney Protection – against mechanical damage and dehydration Sensory reception –pain to avoid injury, taste buds, olfactory, etc. Contraction – myoepithelium  Surface Specializations of Epithelia 1. Microvilli - intestine absorptive cell 2. Cilia - respiratory epithelium 3. Basal lamina - all epithelium 4. Intercellular canaliculus - hepatocyte 5. Secretory (intracellular) canaliculus - gastric parietal cell 6. Flagella Surface Specializations of Epithelia  Characteristics 1. There is no extracellular substance between the cells, cells are tightly apposed in sheets and strongly attached to one other by means of special junctions.  Characteristics 2. Their basal surface is attached to an underlying basement membrane – extracellular protein-polysaccharide-rich layer. 3. polarity - cells have 2 surfaces : the apical or free side (surface) - is the side towards the lumen or outside medium the basal side (surface) - is the side closest to the basement membrane The Polarity of Epithelial Cells Epithelial Tissues and Their Basement Membrane  Characteristics. 4. Epithelia are avascular : epithelium does not contain blood vessels but is nourished by diffusion of substances from capillaries of underlying connective tissue. 5. It is frequently mitotically active  Morphological classification of Epithelial Tissues is based on combination of the number of cell layers (first name) and the shape of surface cell (second name). Epithelium may be simple, when it is one cell layer thick and stratified when it is two or more cell layer thick.  The second name describes the shape of the cells: Squamous, where the width of the cell is greater than its height. Cuboidal, where the width, depth and height are approximately the same. Columnar, where the height appreciably exceeded the width. !!! In case of stratified epithelia the second name describes the shape of the top layer of cells. Classification of Epithelia Number of layers Simple - one layer Stratified - more than one layer Shape of superficial cells Squamous - flat Cuboidal - cube Columnar – column Other Pseudostratified - not truly stratified Transitional - urinary tract Epithelia: Histological Identification Simple squamous – single layers of flat cells (blood vessels, covering of organs) Simple cuboidal – single layer of square cells (kidney tubules, liver cells, many others) Simple columnar – single layer of tall, thin cells (intestinal epithelium) Stratified squamous – multiple layers of cells with flat ones at the surface (skin, gums)  Simple Squamous Epithelium Single layer of flat cells (very thin) – lines blood vessels (endothelium), closed body cavities (mesothelium), alveoli in the lungs – Function: controls diffusion, osmosis and filtration Mesothelium Endothelium – forms the vascular lining Blood vessels Simple squamous  Simple Cuboidal Epithelium Single layer of cube-shaped cells, lines tubules and ducts Simple Cuboidal Epithelium - it covers renal tubes and thyroid gland folicles  Simple Columnar Lines stomach, intestine. Usuallly has microvilli = finger-like projections of the cell membrane Function – absorption.  Columnar epithelium The epitheium of the small intestine contains: - Goblet - border cells. Pseudostratified Columnar Single cell layer All cells attach to basement membrane but not all reach free surface Nuclei at varying depths  Stratified squamous Epithelium Several cell layers thick, Surface cells are flat 2 types: Keratinized = surface cells are dead and filled with keratin – Example - Skin Nonkeratinized = no keratin in moist, living cells at apical surface – Example - Cornea  Stratified squamous Keratinized Epithelium  Stratified squamous NonKeratinized Epithelium Stratified Cuboidal Epithelium Surface cells cuboidal Lines sweat gland ducts  Stratified Columnar Epithelium Surface cells are columnar Lines very large ducts of gland  Transitional Epithelium Multilayered Surface cells vary in shape from round to flat if stretched Lines hollow organs of the urinary tract that expand from within !! The morphology of an epithelium correlates with its function: - Epithelia involved in secretion or absorption are typically simple. -- Stratification of the epithelium usually correlates with impermeability and protection --- The height of the cell often reflects the level of secretory or absorptive activity.  GLANDULAR EPITHELIA Secretion is the main function of the glandular epithelia. Secretion – cyclic process. 4 phases: 1. diffusion of metabolites into the cell 2. synthesis proper 3. releasing of substances from the cell 4. cell restoration Mechanisms of Glandular Secretion 2 portions of gland: Parenchyma and Stroma Parenchyma - the epithelial, secreting cells of the gland which perform the gland's essential function. Stroma - supporting cellular framework of connective tissue which contains blood vessels and nerves and gives structure to the gland.  There are two types of glands in the body: exocrine and endocrine. Exocrine glands secrete Endocrine secrete through ducts or directly onto the surface (skin or hormones into the cavity of inner organs). bloodstream. Without ducts - surface mucous cells of the stomach; With ducts - most exocrine glands; Ex.: salivary glands.  Classification of glands by cell number Unicellular gland Ex.: Goblet cell secrete mucus and lubricate small and large intestine, respiratory tract Multicellular gland  Classification of Exocrine Glands by type of secretion 1. Mucous - viscous, slimy mucus Ex.: glands of esophagus, Brunner's glands of duodenum 2. Serous - watery serum Produce wide variety of proteins (enzymes). Ex.: exocrine pancreas, parotid salivary glands, uterine glands.  Classification of Exocrine Glands by type of secretion 3. Mixed (Sero-mucous) Ex.: Submandibular and sublingual salivary glands; mixed glands of the nasal cavity, paranasal sinuses, nasopharynx, larynx, trachea and bronchi.  Secretion mechanism – 3 types Merocrine (= eccrine) Apocrine Holocrine  Apocrine (ex.: lactating mammary gland (fat droplets)) - secretion of product plus a small portion of pinched off apical cytoplasm, enclosed by a membrane derived from the plasma membrane. Apocrine  Holocrine - ex: Sebaceous glands of the skin the cell get filled with its secretory product while the nucleus becomes smaller. maturing cells filled with lipid move to the center, then toward the opening of the acinus. the cell dies and the entire cell is released and disintegrates, releasing its product. A Structural Classification of Exocrine Glands  A Structural Classification of Exocrine Glands By branching of the duct exocrine glands may be: simple or compound By the shape of secretory ends – tubular or alveolar (acinar) By branching of secretory ends exocrine glands may be: branched or non-branched