Epithelial Tissue Types and Characteristics

• There are 6 types of Epithelial Tissue.
• Epithelial Tissue exists in several forms: Simple squamous, Simple cuboidal, Simple columnar with microvilli, Stratified squamous, Transitional, and Pseudostratified columnar with cilia and microvilli.

Characteristics of Epithelial Tissue

• Cells exhibit polarity, featuring apical (upper, free) and basal (lower, attached) surfaces.
• Apical surfaces may have microvilli, such as the brush border of the intestinal lining, or cilia, like those lining the trachea.
• Epithelial tissues consist of closely packed cells.
• Continuous sheets are maintained by tight junctions and desmosomes.
• Connective tissue reticular lamina supports the basal lamina
• Epithelial tissues are avascular yet innervated.
• They possess a high rate of regeneration.

Classification of Epithelia

• Two key questions to classify epithelia are how many layers are present and what shape the cells are?
• If there's one layer, it's considered a simple epithelium; more than one layer classifies it as stratified and named according to how many layers of cells there are
• There many types of epithelia cells to look at : Squamous, Cuboidal, and Columnar
• In stratified epithelia with multiple layers, the tissue is named according to the apical layer of cells.

Overview of Epithelial Tissues

• Focusing on descriptions, functions, and locations facilitates preparation for exams regarding epithelia.

Simple Squamous Epithelium

• Consists of a single layer of flattened cells with disc-shaped central nuclei and scarce cytoplasm.
• Its primary function is to facilitate the passage of materials through diffusion and filtration in areas where protection isn't crucial and it also secretes lubricating serosae.
• It can be located in Kidney glomeruli, air sacs of lungs, lining of heart, blood vessels, and lymphatic vessels.

Simple Squamous Locations - Endothelium

• It lines of Lymphatic vessels, blood vessels, and the heart

Simple Squamous Locations - Mesothelium

• It is the epithelium of serous membranes in the ventral body cavity

Simple Cuboidal Epithelium

• It is composed of a single layer of cubelike cells with large, spherical central nuclei.
• Its function includes absorption and secretion.
• It can be found in Kidney tubules, ducts and secretory portions of small glands, and the ovary surface.

Simple Columnar Epithelium

• Exhibits a single layer of tall cells with round to oval nuclei.
• Some cells feature cilia, and the layer may include unicellular mucus-secreting glands, known as goblet cells.
• Nonciliated types line the digestive tract from stomach to anal canal, gallbladder, and excretory ducts of some glands.
• Ciliated types propel mucus or reproductive cells by ciliary action.
• Ciliated varieties line small bronchi, uterine tubes, and certain areas of the uterus.

Pseudostratified Columnar Epithelium

• It contains a single layer of cells varying in height, with some not reaching the surface.
• Nuclei appear at different levels, and the tissue may contain mucus-secreting cells and bear cilia.
• Functions in secretion, particularly mucus, and the propulsion of mucus through ciliary action.
• Nonciliated types are found in male's sperm-carrying ducts and ducts of large glands.
• Ciliated varieties line the trachea and most of the upper respiratory tract.

Stratified Squamous Epithelium

• It's a thick membrane composed of several cell layers.
• Basal cells are cuboidal or columnar and metabolically active, while surface cells are flattened (squamous).
• They are found in nonkeratinized and keratinized forms.
• The primary function is to protect underlying tissues in areas prone to abrasion.
• The nonkeratinized type forms the linings of the esophagus, mouth, and vagina.
• Keratinized varieties create the epidermis of the skin, acting as a dry membrane.

Transitional Epithelium

• Transition epithelium resembles both stratified squamous and stratified cuboidal.
• Basal cells can be cuboidal or columnar, while surface cells appear dome-shaped or squamous-like, based on organ stretch.
• It stretches easily and permits distension to fill the bladder
• It lines the ureters, urinary bladder, and sections of the urethra.