Epithelial tissue Flashcards
Epithelial tissue
Consists of cells arranged in continuous sheets with little extracellular matrix
Either single or multilayered
Avascular
What does epithelial tissue form?
Epithelia and glands
Three surfaces
Apical
Lateral
Basal
Apical surface
Faces the body surface, body cavity, or lumen of a hollow organ or duct
Lateral surfaces
Face the lateral surface of adjacent cells
Basal surfaces
Located opposite the apical surface
Adheres to extracellular materials
Basement membrane
Thin layer of extracellular material underlying the epithelial cells
Provides a point of attachment and support for the overlying epithelial tissue
Components of basement membrane
Basal lamina
Lamina densa
Basal lamina
Secreted by epithelial cells and is found closes to them
Lamina densa
Found below the basal lamina and is composed of fibrous proteins produced by the underlying connective tissues
Functions of epithelia tissue
Protecting underlying structures Secretion of substances Absorption Filtration Sensation
Example of protecting underlying structures
The outer layer of skin and epithelium of the oral cavity protect underlying structures from abrasion
Example of secretion of substances
Mucous glands, sweat glands, enzyme-secreting portions of pancreas all composed of epithelial cells
Example of Absorption
Absorption of nutrients across epithelium of small intestines
Example of filtration
Kidney epithelia in glomeruli filer out wastes from blood capillaries
Example of sensation
Epithelial structures with sensory nerve endings are found in the skin, nose, ear and eyes
Major divisions of epithelia
Covering and lining epithelia
Glandular epithelia
Types of covering and lining epithelial tissue
Simple
Stratified
Pseudo-stratified
Transitional
Simple epithlia
Composed of one layer of cells which may be squamous cuboidal or columnar
Simple Squamous epithelium
One layer of flat cells
Permeable by meany substances allowing movement (absorption, secretion and gas exchange)
Involved in diffusion
Simple squamous epithelium locations
Alveoli (lungs), Glomeruli (kidneys), Endothelium (blood vessels) and serosa (gut)
Heart, blood and lymphatic vessels, air cells, body cavities and glomeruli
Simple cuboidal epithelium
One cell layer of cube shaped cells
Involved in secretion such as mucous production and absorption
Simple cuboidal epithelium locations
Found in many glands and ducts e.g thyroid, mammary and salivary glands
Also found in the liver, bronchioles (lungs) and kidney tubules
Simple columnar epithelium
Single layer of tall column shaped cells
Involved in absorption and secretion
Can be modified for function
Modifications of simple columnar epithelium
Goblet cells (secretion)
Cilia (movement)
Microvilli (Absorption)
Locations of simple columnar epithelium
Often lines hollow visceral structures e.g GI tract, uterus, kidney and uterine tubes
Stratified epithelia
Refers to several layers of cells also variable in shape
Types of stratified epithelia
Keratinised stratified squamous epithelium
Non-keratinised stratified squamous epithelium
Stratified cuboidal epithelium
Stratified columnar epithelium
Keratinised stratified squamous epithelium
Multiple layers of flat, squamous cells covered with dead cells filled with keratin (tough protein)
Slows down water loss and provides a barrier to microorganisms
Keratinised stratified squamous epithelium locations
Covers outer skin on body surface
Non-Keratinised stratified squamous epithelium
Multilayered surface epithelium forming moist, slippery layer without surface layer of dead cells
Primary function is protection
Non-keratinised stratified squamous epithelium locations
Lines mouth, tongue, esophagus, vagina and anal canal
Stratified cuboidal epithelium
Two or more cell layers; surface cells square
Secretions
Location of stratified cuboidal epithelium and role in that location
Sweat gland ducts - Secret sweat
ovarian follicles and semiiniferous tubules - Produce sperm and hormones
Stratified columnar epithelium
Multiple layers of columnar cells
Rare
Stratified columnar epithelium locations
Located in segments of male urthra and near anus
Pseudostratified
Tissues that appear to be more than one layer but are in fact just one
Pseudostratified columnar epithelium
Columnar cells of differing heights but still a single layer
All cells rest on basement membrane but may not reach the free surface above
Pseudostratified columnar epithelium locations
Line the trachea (respiratory tract) and segments of the male reproductive system
Pseudostratified columnar epithelium modifications
Motile cilla and muscus secretion
Cilia function
Cilia move surface material by undulating power strokes and alternating rest strokes
Transitional epithelium
Flexible cells that change the tissue shape as they stretch and relax
Cells change from round to flat when stretched
Protect organ walls from tearing
Stratified; often 10 or more layers thick
Transitional epithelium locations
Lining of hollow viscera subjected to stress e.g urinary bladder
Types of glandular epithelia
Endocrine glands
Exocrine glands
Glandular epithelia
Function is secretion
Helps form glands in the body
Gland
May be single or group of glandular epithelial cells that secrete substances into ducts, onto surface, or into the blood stream
Endocrine glands
Secrete substances (hormones) into the blood stream
Exocrine glands
Secretes substances into a duct that empties onto the surface of a covering and lining epithelium e.g skin surface, GI tract
