Epithelial Tissue M.Sc. Sarah Ahmed انسجة عملي / د . سارة (م 1 – 3 ) ثاني اسنان موصل 8 / 12 / 2015 (م 1) Epithelial Tissue M.Sc. Sarah Ahmed

Epithelial Tissue Makes up 3% of your body weight Their cells are all touching one another Of all tissues, they are the most widely varied in structure and function

Locations of Epithelial Tissues Covers the body (epidermis) Found on the inside of hollow organs and the outside of all organs Found above a connective tissue layer (epi = above) Lines the cavities, tubes, ducts, and blood vessels inside the body

Epithelial Anatomy Apical surface – upper surface that is free or exposed to the “exterior” Basal surface – attached surface (below)

Epithelial Tissues: Covers a body surface or lines a body cavity Forms most glands Functions of epithelium Protection Absorption, secretion, and ion transport Filtration Forms slippery surfaces

Three Basic Shapes Squamous – like scales Cuboidal – looks like cubes Columnar – longer and look like columns

Simple – single layer of cells; typically found where absorption and filtration occur or a single layer of epithelial is needed simple squamous simple cuboidal simple columnar Stratified – layers of cells; common in areas where protection is needed like the skin stratified squamous stratified cuboidal stratified columnar

The shape of the nucleus is sometimes important in distinguishing different types of epithelia Nucleus is flattened Nucleus is spherical Nucleus is oblong

Squamous Epithelium Simple – one layer Nucleus is flattened Forms solid layer of cells which line blood vessels, body cavities and covers organs in body cavities Stratified – multiple layers Forms epidermis

(a) Simple squamous epithelium Description: Single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm; the simplest of the epithelia. Air sacs of lung tissue Function: Allows passage of materials by diffusion and filtration in sites where protection is not important; secretes lubricating substances in serosae. Nuclei of squamous epithelial cells Location: Kidney glomeruli; air sacs of lungs; lining of heart, blood vessels, and lymphatic vessels; lining of ventral body cavity (serosae). Photomicrograph: Simple squamous epithelium forming part of the alveolar (air sac) walls (125x).

Figure 4.3e Epithelial tissues. (e) 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. Stratified squamous epithelium Function: Protects underlying tissues in areas subjected to abrasion. Nuclei Location: Nonkeratinized type forms the moist linings of the esophagus, mouth, and vagina; keratinized variety forms the epidermis of the skin, a dry membrane. Basement membrane Connective tissue Photomicrograph: Stratified squamous epithelium lining the esophagus (285x).

Cuboidal Epithelium Simple – one layer Roughly cube shaped Cuboid Cells Simple – one layer Roughly cube shaped Nucleus is spherical Duct Line ducts in kidneys where re-absorption and secretion activities take place. Cuboid Cells Duct

Figure 4.3b Epithelial tissues. (b) Simple cuboidal epithelium Description: Single layer of cubelike cells with large, spherical central nuclei. Simple cuboidal epithelial cells Function: Secretion and absorption. Basement membrane Location: Kidney tubules; ducts and secretory portions of small glands; ovary surface. Connective tissue Photomicrograph: Simple cuboidal epithelium in kidney tubules (430x).

Columnar Epithelium Simple – one layer Column shaped (long and narrow) Lines digestive tract where re-absorption & secretion occurs.

Figure 4.3c Epithelial tissues. (c) 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). Simple columnar epithelial cell 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. Basement membrane Photomicrograph: Simple columnar epithelium of the stomach mucosa (860X).

“Pseudostratified Columnar Epithelium” Looks like it has more than one layer because of the position of the nucleus Nuclei are positioned at differing levels Cells narrow in the area without the nucleus

Figure 4.3d Epithelial tissues. (d) Pseudostratified 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. Cilia Mucus of mucous cell Pseudo- stratified epithelial layer 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 tract. Basement membrane Photomicrograph: Pseudostratified ciliated columnar epithelium lining the human trachea (570x). Trachea

Transitional Epithelium – stratified tissue ; basal cells cuboidal or columnar; surface cells dome shaped or squamous like, depending on degree of organ stretch. Shape of cells depends upon the amount of stretching (ex: bladder)

Figure 4.3f Epithelial tissues. (f) Transitional epithelium Description: Resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells dome shaped or squamouslike, depending on degree of organ stretch. Transitional epithelium Function: Stretches readily and permits distension of urinary organ by contained urine. Location: Lines the ureters, urinary bladder, and part of the urethra. Basement membrane Connective tissue 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 and become elongated when the bladder is filled with urine.

Epithelial Tissue in Review…