Histology of GIT 1

GI Tract
Anatomy-Histology Correlate

-The digestive system allows us to ingest and digest food, effectively adsorbing the nutrients required for the normal functioning of all body systems and expelling the undigested waste products.

- The digestive tract is essentially a long tube that begins from the oral cavity and continues on to the esophagus, the stomach, the small and large intestines, and finally the anus. The pancreas, liver, and gallbladder help with the digestion and absorption of nutrients.

- Beginning with the oral cavity, we will first look at the lips. There is a transition from skin to oral mucosa at the vermillion border (v.b.). The lip gets its red color from the capillaries in the high dermal papillae which are separated from the lip surface by a thin layer of epidermis, as indicated by the bracket.

- The vermillion border lacks sweat glands or sebaceous glands, making it susceptible to chapping.

- The labial vestibule of the oral cavity is lined by non-keratinized stratified squamousepithelium. The glands found in the underlying tissue are mostly mucus-secreting with some mixed muco-serous glands. The inner surface of the cheek is essentially the same.

-The oral mucosa is composed of various types of epithelia. Non-keratinized stratifiedsquamous epithelium (blue) is present where flexibility is required, as is the case of the lip and cheeks aforementioned.

- Keratinized stratified squamousepithelium (red) is required where abrasion occurs frequently and the lining epithelium needs to be more rigid. This is the case of thehard palate (bottom left) and the gingiva (next slide). The keratinized epithelium, labeled as stratum corneum, is firmly attached to the underlying bone.

- The soft palate (bottom right) is flexible and thus covered by non-keratinized stratifiedsquamous epithelium. There are numerous mucus-secreting glands amongst the skeletal muscle within the underlying tissue.

- The remainder of the oral vestibule and the ventral surface of the tongue are also covered by non-keratinized stratified squamous epithelium.

- The tongue, discussed later, contains specialized mucosa (orange) for the special sense of taste.

-Top left panel: As the non-keratinized stratifiedsquamous epithelium (B) of the oral vestibule approaches the teeth, a transition occurs at themuco-gingival junction(C) into keratinizedstratified squamousepithelium (A) of thegingiva.

- The gingiva (bottom left) is very tightly attached to the tooth by thedentogingival fibers. Free gingiva surrounds theenamel, which was removed during slide preparation (decalcification) leaving thedentin.

- The periodontal ligament is anchored within the toothcementum and inserts into the alveolar bone. These insertions, indicated in the bottom right with an arrow, are known asSharpey’s fibers. The periodontal ligament serves to attach the tooth to the bone and to absorb shock.

-The enamel , which is 96% mineral, covers the crown of the tooth. However, the dentin (80% mineral)is much thicker and forms the majority of the tooth. The black lines (top left) that run from the pulp cavity to the dento-enamel junction are dentinal tubules that were filled with odontoblasts during tooth growth.

- At the root of the tooth, the surface is covered by cementum, which has a composition similar to bone. The bottom left panel shows the cemento-enamel junction (CEJ), where the enamel ends and cementum begins. The granular dentin is also a good marker for this junction.

- Note the acellular cementum near that CEJ and compare it to the cellularcementum (bottom right) near the root of the tooth.