Classification

Epitheliums can be classified on appearance or on function

Classification based on appearance

- Simple - one layer of cells

- Pseudostratified - looks like more than one layer but is not

- Stratified - more than one layer of cells

Simple epitheliums

Simple squamous epithelium

 Cells are flat with bulging or flat nuclei.  Lines the insides of lung alveoli and certain ducts in the kidney

 Forms serous membranes called mesothelium that line cavities like: pericardial ,  peritoneal,  plural

 Lines blood vessels - known as endothelium

Simple cuboidal epithelium

It appears square in cross section,  Found in: - Ducts of salivary glands,  Follicles of the thyroid gland,  Pigment layer in the eye,  Collecting ducts of the kidney, In the middle ear is ciliated type.

Simple columnar

• Lines the gastrointestinal tract from the stomach to the anal canal,  Some columnar cells have a  secretory function – stomach, peg cells in the oviduct,  Some columnar cells have microvilli on their free border (striated border) – gall bladder, duodenum
• Microvilli increase the surface area for absorption
• Some columnar cells have cilia – oviduct, smaller bronchi
• Cilia transport particles

Pseudostratified

Appears as stratified epithelium but all cells are in contact with the basement membrane.  Has a thick basement membrane. Different cell types make up this epithelium,  Cells that can be found in this type of epithelium are:

• Columnar cells with cilia or microvilli.
• Basal cells that do not reach the surface.
• Goblet cells that secrete mucous.
• Found in the trachea, epididymus, ductus deferens and female urethra

Stratified epithelium

Classified according to the shape of the surface cells

Stratified squamous epithelium

Has a basal layer that varies from cuboidal to columnar cells that divide to form new cells. Two types are found:

Keratinized:  Mostly forms a dry covering, The middle layers consists of cells that are forming- and filling up with keratin. The superficial cells form a tough non living layer of keratin,  Keratin is a type of protein,  The skin is of this type has  thick skin - found on the hand palms and soles of the feet,  thin skin - found on the rest of the body

Non-keratinized:  Top layer of cells are living cells with nuclei  Forms a wet covering,  The middle layers are polyhedral,  The surface layer consists of flat squamous cells

• Is found in:  mouth,  oesophagus,  vagina

Stratified cuboidal epithelium

Found: - in the ducts of sweat glands

Stratified columnar epithelium

Found at the back of the eyelid (conjunctiva)

Transitional epithelium

- Sometimes the surface cells are squamous, sometimes cuboidal and sometimes columnar

- The superficial cells are called umbrella cells because they can open and close like umbrellas, when the epithelium stretch and shrink

- Umbrella cells can have 2 nuclei

- Found in the bladder and ureter

The Salivary Glands

• There are three large, paired salivary glands: the parotid, submandibular, and sublingual glands.
• In addition to the main salivary glands, there are numerous small accessory salivary glands scattered over the palate, lips, cheeks, tonsils, and tongue.

The External Nose

• Noses vary considerably in size and shape, mainly as a result of the differences in the nasal cartilages and the depth of the glabella.

• The inferior surface of the nose is pierced by two apertures, called the anterior nares (L. nostrils).
• These are separated from each other by the nasal septum (septum nasi).
• Each naris is bounded laterally by an ala (L. wing), i.e., the side of the nose.

• The posterior nares apertures or choanae open into the nasopharynx.

The Temporalis Muscle

• This is an extensive fan-shaped muscle that covers the temporal region.
• It is a powerful masticatory muscle that can easily be seen and felt during closure of the mandible.

• Origin: floor of temporal fossa and deep surface of temporal fascia.
• Insertion: tip and medial surface of coronoid process and anterior border of ramus of mandible.
• Innervation: deep temporal branches of mandibular nerve (CN V³).

• The temporalis elevates the mandible, closing the jaws; and its posterior fibres retrude the mandible after protrusion.

Mylohyoid Muscle

• Origin: Mylohyoid line of the mandible.
• Insertion: Median raphe and body of the hyoid bone.
• Nerve Supply: Nerve to mylohyoid (branch of the trigeminal nerve, CN V3).
• Arterial Supply: Sublingual branch of the lingual artery and submental branch of the facial artery.
• Action: Elevates the hyoid bone, base of the tongue, and floor of the mouth; depresses the mandible.

Structure of the Nasal Septum

• This part bony, part cartilaginous septum divides the chamber of the nose into two narrow nasal cavities.
• The bony part of the septum is usually located in the median plane until age 7; thereafter, it often deviates to one side, usually the right.

• The nasal septum has three main components: (1) the perpendicular plate of the ethmoid bone; (2) the vomer, and (3) the septal cartilage.

• The perpendicular plate, which forms the superior part of the septum, is very thin and descends from the cribiform plate of the ethmoid bone.
• The vomer, which forms the posteroinferior part of the septum, is a thin, flat bone. It articulates with the sphenoid, maxilla and palatine bones.