Human Anatomy, Larry M. Frolich, Ph.D. Tissues: groups of cells closely associated that have a similar structure and perform a similar function Four types of tissue : Epithelial = covering Connective = support Muscle = movement Nervous = control Most organs contain all 4 types Connective tissue has non-living extra- cellular material (matrix) between its cells

Epithelial tissue Is composed of closely aggregated cells with very little intercellular substance which may represent the fused glycocalyces of adjacent cells. Adhesion between these cells is strong

GENERAL CHARACTERISTICS OF EPITHELIAL TISSUES 1- The epithelial tissues cover all body surfaces (skin) or line all body cavities and tubes. 2- Epithelium is derived from all three embryonic germ layers (ectoderm, endoderm and mesoderm). 3- The epithelial cells are closely packed. 4- The basal cell layer rests on basal lamina or basement membrane 5- With rare exception, blood vessels & lymphatics do not penetrate the epithelium (Avascular). 6- Most epithelial tissues receive nerve endings. 7- Minimal intercellular substance between the epithelial cells.

Features of the Basal Surface of Epithelium Basal lamina: supportive sheet between epithelium and underlying connective tissue as a selective filter Basement membrane = basal lamina plus underlying reticular fiber layer Attaches epithelium to connective tissue below. Sometimes the two are used interchangeably

Features of Apical Surface of Epithelium  Microvilli : (ex) small intestine  Finger-like extensions of the plasma membrane of apical epithelial cell Increase surface area for absorption  Cilia : (ex) respiratory tubes Whip-like, motile extensions Moves mucus, etc. over epithelial surface 1-way  Flagella : (ex) spermatoza Extra long cilia Moves cell

SPECIALIZATION OF THE LATERAL SURFACE The cell junctions (Junctional complex) The cell junctions are: 1- Impermeable Junction Zonula Occludens (Tight Junctions) 2- Adherring Junction Zonula Adherences Desmosome Hemidesmosome 3-Comunicating Junction (Gap Junction)

Classification of Epithelial tissue: I. According to number of cell layers : 1 - Simple : made of only one cell layer 2- Stratified : made of more than one cell layer ll. According to function : 1- Surface (covering or lining ) 2- Glandular 3- Myoepihlium 4- Neuroepithelium

1- According to number of cell layers 1- Simple epithelium : One cell layer a. Squamous. b. Cuboidal. c. Columnal, ciliated and non ciliated. d. Pseudostratified columnar, ciliated and non ciliated. 2- Stratified epithelium : more than one cell layer a. Squamous, keratinized and nonkeratinized. b. Cuboidal. c. Columnar, ciliated and non ciliated. d. Transitional.

Simple Squamous Epithelium

Simple Squamous Epithelium (endothelium)

Simple Cuboidal Epithelium Function: Absorption or Secretion Sample Locations: Kidney, Endocrine Glands

Simple Columnar Epithelium Function: Absorption (or Secretion) Sample Location: Digestive Tract Microvilli

Simple columnar epithelium

Pseudostratified Columnar Epithelium

II. Stratified Epithelium : more than one cell layer This type of epithelium is consists of several layers of epithelial cells. A. Stratified squamous Epithelium : keratinized or non keratinized 1. Stratified squamous non-cornified epithelium: (non keratinized): It consists of three layers: a. The layer lying on the basement membrane is composed of columnar cells with an oval nucleus. b. In the middle layers, the cells are polyhedral with a spherical nucleus. c. The superficial layers are flattened cells and contain a flat nucleus

Stratified squamous epithelium (non-keratinized)

II. Classification of Epithelia according to the function Epithelial tissue are classified according to the function into the following : 1- Surface (covering or lining ) 2- Glandular (glandular epithelium). 3- Neuroepithelium 4- Myoepihlium

SIMPLE GLANDS COMPOUND GLANDS alveolar tubular tubulo-alveolar DUCT tubular alveolar / acinar Classification by shape & duct complexity straight/coiled

3. Classification of the glands according to the nature of secretion: 1. Mucous glands : which secrete only mucous, e.g. goblet cells and Brunner ’ s glands. 2. Serous glands : which secrete only serous secretion, e.g. salivary parotid glands. 3. Muco-serous glands or mixed glands : which have a portion that secretes mucous and another portion secretes serous secretion, e.g. sublingual and submandibular glands.

4. Classification of the glands according to the mode of secretion : a. Merocrine glands. b. Apocrine glands. c. Holocrine glands. a. Merocrine glands: - In this type, the secretory products are passed through the free surface of the cell membrane without lost of any parts of the cell, e.g. salivary glands, pancreas and sweat glands (merocrine type).

Neuroepithelium It is specialized type of epithelium responsible for sensory perception of smell (olfactory epithelium ) and taste ( taste buds ) The taste buds in the tongue papillae have three types of cells : supporting, basal and sensory cells.