THE DIGESTIVE SYSTEM

Dr. Samar AskerDr. Samar Asker

The oral cavity represent a common entrance for respiratory &digestive tracts

The oral cavity is bounded anterioly by lip, posterioly by pharynx, superioly by palate inferioly by tongue, and laterally by cheeks.

The lip The main bulk is formed of bundles of skeletal muscles (orbicularis oris muscle)Arranged in different directions.

THE LIPThe lip is formed of:a) Outer surface.b) Inner surface.c) Middle layer.d) Red margin.

(A) Outer surface:

Thin skinEpidermis: keratinized

stratified squamous epithelium.

Dermis: C.T. rich in hair follicles, sweat glands and sebaceous glands.

(B) Inner surface: Lined by Thick, transparent and wet mucous membrane formed of :

1- Epithelium: It is non kretanized stratified squamous & C.T. Coriumwhich contains mucous glands called labial gland which are accessory gland .

(D) Red margin: Covered by modified skin which has no hair follicles, no sweat glands & no sebaceous glands.The CT. dermis forms deep papillae that contain numerous blood capillaries & receptors. The skin is thin , transparent & highly sensitive.

Thin skin

Red margin

Skeletal ms.

Lipial glandsMucus membrane

THE TONGUE

A bag of mucous membrane full of sckletal muscle.

Macroscopic appearance: formed of dorsal surface & ventral surfaceThe dorsal surface is rough & adherent mucous membrane divided by V- shaped line called sulcus terminalis into:

1.Posterior1/3: Where lingual tonsil are present. 1.Anterior 2/3: The ventral surface: non adherent mucous membrane

(A) Skeletal muscle bundles:

• run in vertical, horizontal and longitudinal directions.

• Covered by stratified squamous epithelium & a CT corium.

• The ventral surface covered by non keratinized. The CT corium has lingual glands( mucous )

• The dorsal surface is covered by partially keratinized & rough due to lingual papillae

Lingual papillae:

Numerous projections of the mucous membrane on the dorsal surface of the tongue .Each papilla is formed of:Central core of C.T covered with stratified squamous epithelium.

Filiform papillae (conical papillae):

Site: anterior 2/3 of the dorsum of the tongueShape: conicalNumber: most numerous.Taste buds: not present

Fungiform papillae:Site: anterior2/3 particularly on the tip and lateral sides scattered between conical papillae.Shape: basal narrow neck and rounded top.Number : less numerous than conical papillae.

Taste buds: few.

Circumvallate papillaeSite: on the V- shaped line.Number: 8 -12 in number (few)

Shape: rounded with constricted base which is surrounded by a groove .Von- Ebner’s glands (serous) underneath this papillaeTaste buds: numerous

Foliate papillaeSite: lateral margin of the dorsal surface the tongue of rabbit.Shape: parallel broad projections of CT covered by epithelium.Number: well developed in rabbit tongue but not in human

Taste buds: numerous

Filiform Fungiforn Circumvillate Foliata

Site: Ant 2/3 of dorsal surface

At tip & lateral sides

On V shaped line

Lateral margin of dorsal surface of tongue of rabbit

Shape: Conical & long .(broad base & pointed tip)

Fungus shape narrow base & rounded top

Constricted base & broad top

Parallel ridges

No: Numerous Less in No 8-12 in number

Taste buds:

Abscent + ve few numerous numerous

Taste budsNeuroepithelium responsible for taste sensation.Sites: on mucous membranes of:Soft palate.Pharynx.Epiglottis.

Professor Kikunae Ikeda

• Structure:• It appears as flask

shaped bodies scattered among the stratified squamous epithelium covering some lingual papillae

• It is formed of an upper opening called gustatory pore & contain 3 types of cells:

• (1) Gustatory cells (haircells)

• Central in position.• Shape: modified

columnar.• Their free ends show

short microvilli• Their basal ends

surrounded by free nerve endings which carry the taste sensation.

• 2) Sustentacular cells:

• Peripheral in position & supporting cells

• (3) Basal cells: • Basally located &

act as stem cells.

The free red margin of the lip contains :–Hair follicles.–Sweat glands.–Sebaceous glands.–Numerous receptors.

The mucous membrane covering the inner surface of the lip :–Is formed of stratified squamous

keratinized epithelium.–Contains sebaceous glands.–Contains sweat glands.–Is thicker than the skin of the outer

surface of the lip.–Has no glands.

The lip:

a.Its inner surface is covered by mucous membrane.

b.Its outer surface is covered by thick skin.

c.Smooth muscles run in different directions.

d.Labial glands are mainly serous.

Taste buds are : 

a.Neuroepithelial structures.b.Formed of 3 types of cells.c.Situated between the cells of stratified

squamous epithelium.d.In contact with fine nerve fibres that carry

taste sensations.e.All of the above.

•  

The skin covering the outer surface of the lip :

a.Contains no hair follicles or sebaceous glands.

b.Contains no sweat glands.c.Is thicker than the inner surface of the lip.d.All of the above.e.None of the above.