Zoology Epithelial Tissues PDF

 prof. Ali Hassan Amin Faculty of For Sciences 1st level Biology Programs Zoology Department 2  Cells are the building blocks of all living...

 prof. Ali Hassan Amin Faculty of For Sciences 1st level Biology Programs Zoology Department 2  Cells are the building blocks of all living things Cells Tissues Organs Systems Entire body Therefore: Tissues are groups of cells that are similar in structure and function.  Epithelial tissues = covering + lining  Connective tissues = supporting + protection  Muscular tissues = movement  Nervous tissues = controlling Most organs contain all 4 types  Epithelial tissue or epithelium is composed of one or more layers of cells, arranged next to each other without any space between them.  This tissue covers the external surface of body, forming the skin, and lines cavities and tracts such as the intestines and glandular tissue.  ❑ Physical Protection by Covering external surface  Epidermis of the skin.  Cornea of the eye.  Hair and nails are epidermal structures. ❑ Lining cavities  Internal organs – intestines and blood vessels “Body cavities”. ❑ Control cell permeability (absorption) Anything entering or leaving body crosses epithelia. ❑ Form glands (glandular epithelia) that produce secretions  salivary, gastric, intestinal, mucous. ❑ Sensory: Parts of sense organs known as neuroepithelia (large sensory nerve supply)  Compact sheets of cells Tissue layer always has one exposed surface (Apical surface) The lower surface (basal surface) is bound by a basement membrane – Fibers The side surface (lateral surface) is bound to other epithelial cells. Avascular (have no blood supply) Nerve supply Regenerate easily if well nourished  1- Cell shape: squamous cells are flat cuboidal cells are cubic columnar cells are tall & thin  2- Number of cell layers: ❖ Simple (one layer): epithelia named by shapes of cells ❖ Stratified (more than one layer): epithelia named by shapes of the surface cells ❖ pseudostratified: one layer but looks like more than one layer.  3- Cilia: ❑ Non ciliated : absorptive cells (microvilli) and goblet cells (secrete mucus) ❑ Ciliated : to move substances (Ex. upper respiratory passages and fallopian tubes.) 1- Simple squamous Single layer of flat cells Usually forms membranes Lines body cavities Lines lungs and capillaries  Simple Epithelium 2- Simple cuboidal Single layer of cube-like cells Common in glands and their ducts Forms walls of kidney tubules Covers the ovaries  Simple Epithelium 3- Simple columnar Single layer of tall cells Often includes goblet cells that produce mucus Lines digestive tract for nutrients absorption. Sometimes provided by cilia  Stratified(Compound)Epithelium Two or more (usually) layers. Basal layer : rests on the basement membrane. Surface layer faces outward or faces the cavity. Named by the appearance of the surface cells.  Stratified(Compound)Epithelium 1- Stratified squamous: The basal layer is columnar followed by several layers of polygonal cells and a flatten superficial layer. Found as a protective covering where friction is common. Locations: Skin Mouth Esophagus  Stratified(Compound)Epithelium Stratified squamous: Keratinized stratified squamous Keratin deposit in apical layer and several layers below it. Non-keratinized stratified squamous No keratin  Stratified(Compound)Epithelium 2- Stratified cuboidal (rare): More than two layers of cuboidal cells Protection, secretion, absorption  Stratified(Compound)Epithelium 3- Stratified columnar (rare): ❑ Surface cells are columnar, cells underneath vary in size and shape ❑ For------Protection and secretion  Stratified(Compound)Epithelium 4- Transitional epithelium: The shapes of surface cells change with the degree of stretching. Elastic: As the cells stretch, they become flattened Lines organs of the urinary system  Not a true stratified tissue. Contains Two or more cell types: * Small: undifferentiated cells. * Tall: columnar differentiated cells. All cells touch basement membrane but not all reach the apical surface so that, Nuclei at different levels. When viewed from the side, it appears that they have several layers giving it a False stratified appearance Ciliated: cells in Trachea and other respiratory passages. Non ciliated: cells Uterine tube.  Epithelial specialized for secretion. ❑ A portion of an epithelium grows into the underlying supporting connective tissue. ❑ The down growth develops into a secretory portion and a duct. This is an exocrine gland. ❑ If the duct disappears, This is an endocrine gland. 1 3 4 2 Glands can be classified in many overlapping ways:  1- Ducts:  Exocrine (with ducts) and endocrine (ductless).  2- Type of secretion: ◦ enzymes, mucous or mixed.  3- According to its shape:  1- Unicellular glands (goblet cell).  2- Simple tubular glands.  3- Coiled tubular gland.  4- Branched tubular glands.  5- Compound tubular glands.  6- Simple alveolar glands.  7- Branched alveolar glands.  8- Compound tubulo-alveolar glands (Pancreas).  9- Reticular glands (Liver of mammals).  It is highly specialized for reception of stimuli.  The neuroepithelial cells are provided with hairlets on the free end. Its basal end is attached with fine branches of a sensory nerve.  The sensory epithelia are classified into:-  A- Gustatory or taste cells.  This type is present in the taste buds present between the epithelial cells which cover the tongue and the pharynx.  B-Olfactory cells.  It is present in the dorsal part of the nasal cavity. It is formed of pseudostratified epithelium.  C- Auditory cells:-  They are found lining the middle ear. They are elongated cells with large nucleus. The auditory cells carry sensory hairs at their free surfaces, at their base; they are connected with nerve endings to transmit sound waves.  Supporting cells are found between the auditory cells to support them.  D- Optic cells:-  They are found in the retina in the eye of higher animals. The cells are cylinderical suitable for receiving light and color.These cells named the rods and cons, the rods are more numerous and with their wall than that of the cones. The optic cells connect with nerve endings to transmit the sense of light to the optic nerve. 23 24 ‫شكرا ☺‬ ‫‪25‬‬