Emmanuel E.Siddig University of Khartoum- FMLS

TISSUES Tissue is group of cells working together for a specific function Types of tissue : 1. Epithelial Tissue 2. Connective Tissue 3. Muscle Tissue 4. Nervous Tissue

Epithelial Tissue Characteristics -free surface -densely packed cells -avascular (no blood vessels) -highly regenerative

Functions of Epithelial tissue: - Barrier/protection - Absorption - Excretion - Diffusion

Classification of epithelial tissues 1) Cell shape(at the free surface) 2) Cell layers/arrangement

Classification of epithelial tissues Arrangement of layers Cell shape

Simple Squamous epithelial: Description Single layer of flat cells that resembles a tiled floor when viewed from apical surface; centrally located nucleus that is flattened and oval or spherical in shapes. Location - lines the cardiovascular and lymphatic system (heart, blood vessels, lymphatic vessel linings), where it is known as endothelium - forms the epithelial layer of serous membranes (peritoneum, pleura, pericardium), where it is called mesothelium - (Bowman’s) capsule of kidneys.

Simple cuboidal: Description: Single layer of cube-shaped cells; round, centrally located nucleus. Cuboidal cell shape is obvious when tissue is sectioned and viewed from the side. Location: Covers surface of ovary; lines anterior surface of capsule of lens of the eye; lines kidney tubules and small Function: Secretion and absorption.er ducts of many glands.

Simple columnar epithelial: Ciliated or not ciliated Sites: - Found on absorptive surfaces such as small intestine. - Lining of the excretory surface such as stomach. - Ciliated found in the fallopian tube

Stratified squamous epithelium: Keratinized stratified squamous epithelium develops tough layer of keratin in apical layer of cells and several layers deep to it. Keratin is a tough, fibrous intracellular protein that helps protect skin and underlying tissues from heat, microbes, and chemicals.) Nonkeratinized stratified squamous epithelium does not contain large amounts of keratin in apical layer and several layers deep and is constantly moistened by mucus from salivary and mucous glands; organelles are not replaced.

Location Keratinized variety forms superficial layer of skin; nonkeratinized variety lines wet surfaces (lining of mouth, esophagus, part of epiglottis, part of pharynx, and vagina) and covers tongue. Function Protection against abrasion, water loss, ultraviolet radiation, and foreign invasion. Both types form first line of defense against microbes.

Stratified Cuboidal epithelial is a type of epithelial tissue composed of cuboidal shaped cells arranged in multiple layers. Only the most superficial layer is made up of cuboidal cells, and the other layers can be cells of other types. This is because, conventionally, naming of stratified epithelium is based on the type of cell in the most superficial layer. They protect areas such as the ducts of sweat gland, mammary gland and salivary gland, esophageal gland.

Stratified columnar epithelia is a rare type of epithelial tissue composed of column shaped cells arranged in multiple layers. Stratified columnar epithelia are found in the ocular conjunctiva of the eye, in parts of the Pharynx and anus. Also found in interlobular duct of salivary gland. The cells function in secretion and protection.

Special Types of Epithelia: Transitional Epithelium: - only in urinary tract i.e. bladder, urethra, ureter. - So called urothelial - It assume like stratified squamous in the stretch bladder or filled stage….. and on other hand stratified cuboidal in non distending state or relax state(Empty).

Pseudostratified Columnar: Appears to have several layers because cell nuclei are at various levels. All cells are attached to basement membrane in a single layer, but some cells do not extend to apical surface. When viewed from side, these features give false impression of a multilayered tissue (thus the name pseudostratified; pseudo = false).

Location Ciliated variety lines airways of most of upper respiratory tract; non ciliated variety lines larger ducts of many glands, epididymis, and part of male urethra. Function Ciliated variety secretes mucus that traps foreign particles, and cilia sweep away mucus for elimination from body; non ciliated variety functions in absorption and protection.

Glandular Epithelial: - Primary involved in the secretion - Invagination of epithelial surfaces - Two types - Exocrine glands (Salivary ) - Endocrine gland (Thyroid)

Exocrine gland: - Can be divided into the secretory component and the duct. - The duct system may be branched or unbranched - The secretory component may be tubular or acinar - Coiled or branched

Endocrine gland - They secrete hormones directly to blood stream - Pancreases, thyroid, adrenal and anterior pituitary gland

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References: Books - Wheather’s Functional histology Fifth edition. - DiFiore's Atlas of Histology with Functional Correlations Online links: - Pathpedia.com

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