Epithelial Tissue PDF

TISSUES AND ITS TYPES Prepared by Dr. Asif Ali Lecturer College of Pharmacy LUMHS  Introduction  Cells combine to form tissues, and tissues...

TISSUES AND ITS TYPES Prepared by Dr. Asif Ali Lecturer College of Pharmacy LUMHS  Introduction  Cells combine to form tissues, and tissues combine to form organs.  A tissue is a collection of cells specialized for some particular function.  Cells work together in functionally related groups called tissues  Types of Tissues  The human tissue are classified into the following four types. a)Epithelial tissue or Epithelium b)Connective tissue c)Muscular tissue d)Nervous tissue Types of Tissues Types of Tissues  EPITHELIAL TISSUE  One or more layers of cells that covers the outer surface of the body or line the luminal surface of the tubular structures and cavities of the body are called epithelia.  Interconnected by cell junctions and lie on basement membrane  Derived from ectoderm, mesoderm or endoderm EPITHELIAL TISSUE  The epithelial component of skin is derived from ectoderm  Epithelial lining and glands of digestive tract are derived from endoderm  Epithelial lining of peritoneal, pericardial cavities and inner lining of blood vessels is derived from mesoderm  Special Characteristics of Epithelia  Cellularity: cells are in close contact with each other with little or no intercellular space between them  Specialized contacts: may have junctions for both attachment and communication.  Polarity: epithelial tissues always have an apical and basal surface.  Apical surfaces: (Superior) Cilia, microvilli  Special Characteristics of Epithelia  Basal surfaces: (Inferior) basement membrane  Intracellular surfaces: (lateral) cell junctions of different types  Support by connective tissue : At the basal surface, both the epithelial tissue and the connective tissue contribute to the basement membrane  Regeneration: epithelial tissues have a high capacity for regeneration.  Avascular: Epithelium is itself avascular (ie.without blood vessels) Special Characteristics of Epithelia  Function/Activities of Epithelia  Protection  Secretion  Excretion  Diffusion  Absorption  Physical protection  Digestion  Sensory Reception  Types of Epithelial Tissues Two types  – Membranous epithelia form the coverings or linings of organs  Glandular epithelia form exocrine and endocrine glands  Surface Epithelia OR Membranous Epithelia  Classified according to the cell layering , cell shape and Presence of surface specializations  Terms referring to the layers  Simple = one layer  Stratified = more than one layer  Pseudo stratified = false layered (appears to be more than one layer, but only one); ciliated = with cilia  Surface Epithelia OR Membranous Epithelia  Terms referring to the cell shapes  Squamous = flat  Cuboidal = cube  Columnar = rectangular (column)  Transitional = ability to change shape Classification based on number of cell layers. Basal Simple Apical surface surface Basal Stratified surface  Classification based on cell shape.  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  The following types of epithelial tissues  1. Simple squamous epithelial tissue (lungs)  2. Simple cuboidal epithelial tissue (kidneys)  3. Simple columnar epithelial tissue (small intestine)  4. Pseudostratified (ciliated) columnar epithelial tissue (trachea lining)  5. Stratified squamous epithelial tissue (mouth lining)  6. Stratified cuboidal epithelial tissue (salivary glands, sweat glands)  7. Stratified columnar epithelial tissue (male reproductive tract)  8. Transitional epithelial tissue (bladder)  a. The tissue may show a full bladder  b. The tissue may show an empty bladder Epithelial Tissue  Simple Squamous  Description: Single layer of flattened cells with disc- shaped central nuclei and sparse cytoplasm; the simplest of the epithelia.  Function: Allows passage of materials by diffusion and filtration in sites where protection is not Important.  Location: Kidney glomeruli; air sacs of lungs  Simple Cuboidal epithelium Description: Single layer of Cube like cells with large, spherical central nuclei. Function: Secretion And absorption. Location: Kidney tubules; ducts and secretary portions of small glands. Photomicrograph: Simple cuboid epithelium in kidney tubules (43  Simple columnar epithelium  Description: Single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucus secreting unicellular glands (goblet cells).  Function: Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action.  Location: Nonciliated type lines most of the digestive tract (stomach to anal canal), gallbladder, and excretory ducts of some glands; ciliated variety lines small bronchi, uterine tubes, and some regions of the uterus. Photomicrograph: Simple columnar epithelium  Pseudo stratified columnar epithelium  Description: Single layer of cells of differing heights, some not reaching the free surface; nuclei seen at different levels; may contain mucus secreting cells and bear cilia.  Function: Secretion, particularly of mucus; propulsion of mucus by ciliary action.  Location: Nonciliated type in male’s sperm-carrying ducts and ducts of large glands; ciliated variety lines the trachea, most of the upper respiratory Photomicrograph: Pseudostratified tract. ciliated columnar epithelium lining the human  Stratified Squamous epithelium  Description: Thick membrane composed of several cell layers; basal cells are Cuboidal or columnar and metabolically active; surface cells are flattened (Squamous); in the keratinized type, the surface cells Are full of keratin and dead; basal cells are active in mitosis and produce the cells of the more superficial layers.  Function: Protects underlying tissues in areas subjected to abrasion.  Location: Non-keratinized type forms the moist linings of the esophagus, mouth, and vagina; keratinized variety forms the epidermis of the skin, a dry Photomicrograph: Stratified membrane. Squamous epithelium lining the esophagus (285x). Stratified Columnar epithelium  Transitional epithelium  Description: Resembles both stratified Squamous and stratified Cuboidal; basal cells Cuboidal or columnar; surface cells dome shaped or Squamous like, depending on degree of organ stretch.  Function: Stretches readily and permits distension of urinary organ by contained urine  Location: Lines the ureters, urinary bladder, and part of the urethra. Photomicrograph: Transitional epithelium lining the urinary bladder, relaxed state (360X); note the bulbous, or rounded, appearance of the cells at the surface; these cells flatten Summary of Surface Epithelia  Glandular Epithelia  Some epithelial cells of the body are specialized to produce substances. These substances, which are generally fluid in nature, are not used by the cell itself but are expelled to the extracellular compartment.  These products are either secretions or excretions.  The secretions are utilized somewhere else in the body and excretions are discarded from the body.  The process of secretion is usually accompanied by the intracellular(located or occurring within cell or cells) synthesis of macromolecules. The synthesized materials are stored in the cell as small membrane bound vesicles called secretory granules  Example of secretary: Sebaceous gland, suprarenal gland & salivary gland  The glandular cells may synthesize lipids, proteins or complexes of proteins and carbohydrates.  The excretory process does not involve intracellular synthesis of macromolecule but consist of a transfer of substance (needed to be eliminated from the body).  Examples of excretory glands are kidney and sweat glands.  Classification  Exocrine glands: Connected to epithelium by branching system of ducts. Pass secretions through a duct system to a body surface  Example: Salivary glands  Endocrine glands: Pass secretion directly into blood or lymph (internal secretion) Secretions are normally hormone  Example: Thyroid gland  Types of Exocrine glands a. According to the number of secreting cells  Unicellular glands – a single cell is a complete gland. Good example is a Goblet cell (mucous cell).  Multicellular glands – each gland is formed by more than one cell, examples are Parotid (salivary) glands and Pancreas. b. According to the mode of secretion  Holocrine. whole cell dies, the discharges go together with the cellular contents eg. sebaceous and tarsal gland cells.  Apocrine. (membrane budding) Products accumulate at the apical part of the cell then discharges its apical cytoplasm eg mammary gland cells.  Merocrine. Only cell products are discharged eg sweat gland. cells C. Histological classification according to duct system:  a- Simple (the ducts are not branched);  b- Compound (with a branching duct system) D. Histological classification according to secretory portion:  a- Tubular (shaped like a tube); e.g. glands of intestine, stomach  b- Acinar or alveolar (flask-shaped with narrow centrally placed lumen); e.g. pancreas, parotid salivary gland  c- Tubuloacinar (combination of the tube ends with a sac-like dilatation); e.g. submandibular and sublingual salivary glands C. Histological classification according to duct system:  a- Simple (the ducts are not branched);  b- Compound (with a branching duct system) D. Histological classification according to secretory portion:  a- Tubular (shaped like a tube); e.g. glands of intestine, stomach  b- Acinar or alveolar (flask-shaped with narrow centrally placed lumen); e.g. pancreas, parotid salivary gland  c- Tubuloacinar (combination of the tube ends with a sac-like dilatation); e.g. submandibular and sublingual salivary glands E. According to the nature of secretions: Serous glands. Watery secretions example serous cells of the salivary glands Mucous glands. Mucous or mucin secretions esophageal glands, stomach surface, pyloric glands Seromucous glands. Mixed serous and mucous secretions Examples –sublingual gland, submandibular gland,glands of the nasal cavity, nasopharynx, larynx, trachea, and bronchi. Prepared by Dr. Asif Ali