A collection of cells with a similar structure and function
What is the study of tissues?
What are the 4 primary tissue types?
Where do you find epithelial tissue?
Covers the surface of the body, lines the body cavities, forms the external and internal linings of most organs and constitutes bulk of most glands
What is the function of epithelial tissue?
Protection (the skin)
Secretion (glandular secretion)
Absorption (regulates substances in and out of body)
Characteristics of epithelia?
Composed almost entirely of sheets of close packed cells and very littl extracelular material, no blood vessels (avascular), can regenerate and is strongly connected to adjacent calls via tight junctions and desmosomes
What are tight junctions?
protien complexes that completely encircle a cell and thus connect it to all its neighboring cells and makes it impossible for anything to pass between them. Common in lining of the stomach and intestines.
What are desmosomes?
A "spot weld" that holds cells together and enables a tissue to resist mehanical stress (ex: friction). Common in the epidermis and cervix
What are gap junctions?
Protein channels in cell membranes made up of two connexons that connect each cell which allows ions and small molecules to pass between adjacent cells.
What is the apical side?
The area of an epithelial cell adjacent to the exterior or to a body cavity is the apical side (top side)
What is the basal side?
The area of an epithelial cell adjacent to the interior or to a body cavity is the basal side (bottom side)
What is the basement membrane?
A layer of connective tissue that supports epithelia. It’s known as the basement membrane.
What is simple epithelium?
A single layer of cells
What is stratified epithelium?
More than one layer of cells
What are the 3 epithelial cell shapes?
Squamous - flat, scale like
Cuboidal - cube shaped
Columnar - column shaped
What are the different types of epithelial tissue?
Simple squamous, cuboidal and columnar
Stratified squamous, cuboidal and columnar
Pseudostratified columnar epithelium
What does simple squamous epithelium look like?
A single layer of flattened cells, nucleus is flattened, cytoplasm may be very thin and hard to see.
Where can you find simple squamous epithelium?
Air sacs (alveoli) of lungs
Glomerular capsules of kidneys
Some kidney tubules
Lining of heart and all blood vessels (endothelium)
External lining of visceral organs (mesothelium)
What are the functions of simple squamous epithelium?
Thinness allows material to rapidly diffuse or be transported through the epithelial layer. Ex: Gases diffuse across the thin air sac epithelium in the lungs.
Blood is filtered through the epithelium of the kidney capillaries.
Secretion of lubricating fluid by the epithelium making up the serous membranes
What does simple cuboidal epithelium look like?
Single layer of square or round cells. Centrally-placed spherical nuclei. Apical layer often has microvilli
Where can you find simple cuboidal epithelium?
Thyroid, salivary, and most other glands
Most kidney tubules
Bronchioles (small tubes within the lungs)
What are the functions of simple cuboidal epithelium?
Absorption (kidney tubules: Microvilli often present to increase the available surface area), liver
Secretion (kidney tubules, liver, pancreas, thyroid, salivary, and most other glands
What does simple columnar epithelium look like?
Single layer of tall, narrow cells. Oval nuclei usually located in the basal half of the cell. Secretory vesicles sometimes visible in apical portion of the cell, goblet cells and microvilli & cilia occasionally present.
Where can you find simple columnar epithelium?
Inner lining of stomach, intestines, and rectum
Inner lining of gallbladder
Inner lining of uterus and uterine tubes
What are the functions of simple columnar epithelium?
Absorption and secretion (cells in small intestine have microvilli to increase surface area for the absorption of nutrients)
Movement of egg and embryo in uterine tube.
Secretion of mucus (Lots of goblet cells in the large intestine to lubricate it and ease the passage of feces)
What does stratified squamous epithelium look like?
Multiple cell layers with cells becoming flatter and flatter toward surface
What is keratinized stratified squamous epithelium?
The apical layers are layers of dead cells lacking nuclei and packed with the toughprotein keratin.
What is nonkeratinized stratified squamous epithelium?
lacks the layers of dead cells at the surface
Where is Stratified Squamous epithelium located?
Location of keratinized version: Epidermis, palms and soles of feet are typically heavily keratinized
Locations of non-keratinized version: Lining of oral cavity and surface of tongue, lining of esophagus, lining of vagina and anal canal
What are the functions of stratified squamous epithelium?
Keratinized: "dry epithelium" protects against mechanical abrasion, water loss and pathogen entry. Keratin is very strong, waterproof, and is bacteriostatic (prevents bacteria from reproducing)
Non-keratinized: "wet epithelium" protects from mechanical abrasion (friction), eating food, swallowing, sexual intercourse, birth, defecation.
What does stratefied cubiodal epithelium look like?
2 or more layers of cells.
Surface layers are square or round (cuboidal)
Where is stratified cuboidal epithelium located?
Some sweat gland ducts
Ovarian follicle (cells that surround the developing egg)
What are the functions of stratified cuboidal epithelium?
Contributes to sweat secretion
Secretion of ovarian hormones. Ex: estrogens
What does stratified columnar epithelium look like?
2 or more layers of cells. Surface cells tall and narrow with basally located nuclei
Where is stratified columnar epithelium located?
Small portions of anal canal, pharynx, epiglottis, and male urethra.
Sometimes seen in large ducts of sweat and salivary glands.
What are the functions of stratified columnar epithelium?
Often seen where 2 other tissue types meet
Structural integrity of gland ducts
What does pseudostratified columnar epithelium look like?
Looks multi-layered, but it’s NOT! All cells touch the basement membrane. Cells are of varying heights which gives the appearance of stratification. Nuclei are at several levels. Often has goblet cells interspersed and cilia
What are the locations of pseudostratified columnar epithelium?
Respiratory tract from nasal cavity to bronchi(ciliated & goblet cells)
Portions of male reproductive tract (non-ciliated)
What are the functions of pseudostratified columnar epithelium?
In the respiratory tract there are lots of mucus-secreting goblet cells. The mucus traps dust and bacteria, cilia “sweep” the bacteria-laden mucus up the respiratory tract towards the pharynx where it can be swallowed.
What does transitional epithelium look like?
Resembles stratified squamous epithelium, but surface cells are rounded and often bulge above surface. 5-6 cell layers thick when relaxed and 2-3 cell layers thick when stretched. Some cells have 2 nuclei
Where is transitional epithelium located?
Predominant epithelium lining the urinary tract
Found in part of the kidney, the ureters (tubes that connect the kidney to the urinary bladder), the urinary bladder, and part of the urethra.
What are the functions of transitional epithelium?
Stretches to allow filling of the urinary tract
Originally called “transitional” because it was thought to be an intermediate between stratified squamous and stratified columnar epithelium. This isn’t true but the name has persisted.
What are exocrine glands?
Secrete material into ducts that lead to the body surface or to one of the cavities that is continuous with the body surface. Ex: digestive, reproductive, respiratory tract.