Department of Anatomy &Histology: Dr. Raja Ali

--------------------------------------------------------------------Digestive SYSTEM:

GENERALS TRUCTURE OF THE DIGESTIVET RACT

ORAL CAVITY LIP Tongue HARD &SOFT PALATE

Pharynx Teeth ESOPHAGUS STOMACH SMALL INTESTINE LARGE INTESTINE

2 groups of organs compose the digestive system

Gastrointenstinal (GI) tract or alimentary canal – mouth, most of pharynx, esophagus, stomach, small intestine, and large intestine

Accessory digestive organs – teeth, tongue, salivary glands, liver, gallbladder, and pancreas

Functions of the digestive system

1. Ingestion

2. Secretion of water, acid, buffers, and enzymes into lumen

3. Mixing and propulsion

4. Digestion Mechanical digestion churns food

Chemical digestion – hydrolysis

5. Absorption – passing into blood or lymph

6. Defecation – elimination of feces

Layers of the GI tract

Wall of GI tract from lower esophagus to anal canal has same basic 4 layers Fig. (1):

1. Mucosa – inner lining

Epithelium protection, secretion, absorption

Lamina propria – connective tissue with blood and lymphatic vessels and mucosa-associated lymphatic tissue (MALT)

Muscularis mucosae – thin layer of smooth muscle making folds to increase surface area.

The main functions of the digestive tract epithelial liningare to:

. Provide a selectively permeable barrier between the contents of the tract and the tissues of the body, " Facilitate the transport and digestion of food, Promote the absorption of the products of this digestion, Produce hormones that affect the activity of the digestive system, Produce mucus for lubrication and protection.

2. Submucosa

Connective tissue binding mucosa to muscularis Contains many blood and lymphatic vessels Submucosal plexus

3. Muscularis Voluntary skeletal muscle found in mouth, pharynx, upper 2/3

of esophagus, and anal sphincter Involuntary smooth muscle elsewhere Arranged in inner circular fibers and outer longitudinal fibers Myenteric plexus between muscle layers

4. Serosa Outermost covering of organs suspended in abdominopelvic

cavity Also called visceral peritoneum The first two third of Esophagus lack serosa ( has adventitia)

Fig. (1):Schematic histological section illustrate the layers of alimentary tract.

Lip: lip section showing: Fig.(2)

one side covered by typical oral mucosa the opposite side covered by skin containing hair follicles and associated glands.

Between the oral portion of the lips and normal skin is the vermilion , or the vermilion zone, where epidermis is very thin, lightly keratinized ,and transparent to blood in the rich microvasculature of the underlying connective tissue.

Because this region lacks the glands for oil and sweat, it is prone to excessive dryness and chapping in cold, dry weather.

Internally, the lips contain much-striated muscle orbicularis oris and many minor salivary glands.

Fig.(2): Schematic histological section.

ORAL CAVITY: The oral cavity (Fig. 3) is lined with stratified squamous epithelium,

keratinized or nonkeratinized, depending on the region. The keratin layer protects the oral mucosa from damage during

masticatory function and is best developed on the gingival (gum) and hard palate.

The lamina propria in these regions has many papillae and rests directly on bony tissue.

Nonkeratinized squamous epithelium covers the soft palate, lips, cheeks, and the floor of the mouth.

The lamina propria has papillae similar to those in the dermis of the skin and is continuous with a submucosa containing diffuse small salivary glands. The soft palate also has a core of skeletal muscle and lymphoid nodules.

The oral cavity consists of the mouth and its structures, which include the tongue, teeth and their supporting structures (periodontium), major and minor salivary glands, and tonsils.

The oral cavity is divided into a vestibule and the oral cavity proper. The vestibule is the space between the lips, cheeks, and teeth. The oral cavity proper lies behind the teeth and is bounded by the hard

and soft palates superiorly, the tongue and the floor of the mouth inferiorly, and the entrance to the oropharynx posteriorly.

Fig. (3): Oral cavity

Tongue:

The tongue is a muscular organ projecting into the oral cavity from its inferior surface.

The striated muscle of the tongue is arranged in bundles that generally run in three planes, with each arranged at right angles to the other two. This arrangement of muscle fibers allows enormous flexibility and precision in the movements of the tongue, which are essential to human speech as well as to its role in digestion and swallowing.

Grossly, the dorsal surface of the tongue is divided into an anterior two thirds and a posterior one third by a V-shaped depression, the sulcus terminalis (Fig. 4).

The apex of the V points posteriorly and is the location of the foramen cecum,

Papillae cover the dorsal surface of the tongue fig.(4&5). Numerous mucosal irregularities and elevations called lingual

papillae cover the dorsal surface of the tongue anterior to the sulcus terminalis. The lingual papillae and their associated taste buds constitute the specialized mucosa of the oral cavity.

Four types of papillae are described: filiform, fungiform, circumvallate, and foliate.

Fig.(4):Tongue.

Filiform papillae are the smallest and most numerous in humans. They are conical, elongated projections of connective tissue that are

covered with highly keratinized stratified squamous epithelium , does not contain taste buds.

The papillae serve only a mechanical role. Filiform papillae are distributed over the entire anterior dorsal

surface of the tongue, with their tips pointing backward. They appear to form rows that diverge to the left and right from the

midline and that parallel the arms of the sulcus terminalis.• Fungiform papillae, are :

mushroomshaped projections located on the dorsal surface of the tongue .

They project above the filiform papillae, among which they are scattered, and are just visible to the unaided eye as small spots .

They tend to be more numerous near the tip of the tongue. Taste buds are present in the stratified squamous epithelium on the

dorsal surface of these papillae.

• Circumvallate papillae Are the large, dome-shaped structures that reside in the mucosa just

anterior to the sulcus terminalis . The human tongue has 8 to 12 of these papillae. Each papilla is

surrounded by a moat like invagination lined with stratified squamous epithelium that contains numerous taste buds .

Ducts of lingual salivary (von Ebner’s) glands empty their serous secretion into the base of the moats.

• Foliate papillae Consist of parallel low ridges separated by deep mucosal clefts . They occur on the lateral edge of the tongue. In aged individuals, the foliate papillae may not be recognized; In younger individuals, they are easily found on the posterior

lateral surface of the tongue and contain many taste buds in the epithelium of the facing walls of neighboring papillae . Small serous glands empty into the clefts.

Fig.

(5):Lingual papillae