NEET MDS Lessons
Anatomy
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
Veins of the Face
The Supratrochlear Vein
- This vessel begins on the forehead from a network of veins connected to the frontal tributaries of the superficial temporal vein.
- It descends near the medial plane with its fellow on the other side.
- These veins diverge near the orbits, each joining a supraorbital vein to form the facial vein near the medial canthus (angle of the eye).
The Supraorbital Vein
- This vessel begins near the zygomatic process of the temporal bone.
- It joins the tributaries of the superficial and middle temporal veins.
- It passes medially and joins the supratrochlear vein to form the facial vein near the medial canthus.
The Facial Vein
- This vein provides the major venous drainage of the face.
- It begins at the medial canthus of the eye by the union of the supraorbital and supratrochlear veins.
- It runs inferoposteriorly through the face, posterior to the facial artery, but takes a more superficial and straighter course than the artery.
- Inferior to the margin of the mandible, the facial vein is joined by the anterior branch of the retromandibular vein.
- The facial veins ends by draining into the internal jugular vein.
The Superficial Temporal Vein
- This vein drains the forehead and scalp and receives tributaries from the veins of the temple and face.
- In the region of the temporomandibular joint, this vein enters the parotid gland.
The Retromandibular Vein
- The union of the superficial temporal and maxillary veins forms this vessel, posterior to the neck of the mandible.
- It descends within the parotid gland, superficial to the external carotid artery but deep to the facial nerve.
- It divides into an anterior branch that unites with the facial vein, and a posterior branch that joins the posterior auricular vein to form the external jugular vein.
The Orbital Vessels
- The orbital contents are supplied chiefly by the ophthalmic artery.
- The infraorbital artery, the continuation of the maxillary, also contributes blood to this region.
- Venous drainage is through the superior orbital fissure to enter the cavernous sinus.
The Ophthalmic Artery
- This artery arises from the internal carotid artery as it emerges from the cavernous sinus.
- It passes through the optic foramen within the dural sheath of the optic nerve and runs anteriorly, close to the superomedial wall of the orbit.
The Central Artery of the Retina
- This is the one of the smallest but most important branches of the ophthalmic artery.
- It arises inferior to the optic nerve until it approaches the eyeball.
- It then pierces the optic nerve and runs within it to emerge through the optic disc.
- The central artery of the retina spreads over the internal surface of the retina and supplies it.
The Ophthalmic Veins
The Superior Ophthalmic Vein
- The superior ophthalmic vein anastomoses with the facial vein.
- It has no valves and blood can flow in either direction.
- It crosses superior to the optic nerve, passes through the superior orbital fissure and ends in the cavernous sinus.
The Inferior Ophthalmic Vein
- This begins as a plexus on the floor of the orbit.
- It communicates with the inferior orbital fissure with the pterygoid plexus, crosses inferior to the optic nerve, and ends in either the superior ophthalmic vein or the cavernous sinus.
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First pouch |
Auditory tube, which comes in contact with epithelial line of first pharyngeal cleft, where future external acoustic meatus will form. Distal portion will form tympanic cavity (lining will become eardrum) Proximal portion will become auditory tube |
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Second pouch |
Forms buds that penetrate surrounding mesenchyme, which together form the palatine tonsils |
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Third pouch |
Forms thymus and inferior parathyroid glands |
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Fourth pouch |
Forms superior parathyroid glands |
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Fifth pouch |
Forms utlimobranchial body |
The Walls of the Orbit
- Each orbit has four walls: superior (roof), medial, inferior (floor) and lateral.
- The medial walls of the orbit are almost parallel with each other and with the superior part of the nasal cavities separating them.
- The lateral walls are approximately at right angles to each other
The Inferior Wall of the Orbit
- The thin inferior wall of the orbit or the floor is formed mainly by the orbital surface of the maxilla and partly by the zygomatic bone, and orbital process of the palatine bone.
- The floor of the orbit forms the roof of the maxillary sinus.
- The floor is partly separated from the lateral wall of the orbit by the inferior orbital fissure.
The Cheeks
- The cheeks (L. buccae) form the lateral wall of the vestibule of the oral cavity.
- They have essentially the same structure as the lips with which they are continuous.
- The principal muscular component of the cheeks is the buccinator muscle.
- Superficial to the fascia covering this muscle is the buccal fatpad that gives cheeks their rounded contour, especially in infants.
- The lips and cheeks act as a functional unit (e.g. during sucking, blowing, eating, etc.).
- They act as an oral sphincter in pushing food from the vestibule to the oral cavity proper.
- The tongue and buccinator muscle keep the food between the molar teeth during chewing.
Sensory Nerves of the Cheeks
- These are branches of the maxillary and mandibular nerves.
- They supply the skin of the cheeks and the mucous membrane lining the cheeks.