Digestive tract
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Digestive tract

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    Digestive tract Digestive tract Presentation Transcript

    • DIGESTIVE TRACT: INTRODUCTION
    • ORAL CAVITY The oral cavity 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 gingiva (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. In the lips, there is also striated muscle and a transition from the oral nonkeratinized epithelium to the keratinized epithelium of the skin
    • Tongue  Mucosa: Stratified squamous epithelium keratinized (dorsal surface) Stratified squamous epithelium non-keratinized (ventral surface)  In the dorsal surface of the tongue are modifications called lingual papillae. There are three types of papillae present on the body of the tongue: 1. filiform – most numerous and the smallest; slender in shape; arranged in more or less distinct rows diverging to the right and left from the middle line and parallel to the V shaped region. 2. Fungiform – mushroom shaped with a short, narrow slightly constricted stalks and broad, rounded tops. 3. Circumvallate or vallate – located near the junction of the anterior and posterior parts of the tongue. They form a V-shaped row at the junction. They are the largest varieties that do not extend above the surface of the tongue but sink beneath it.
    •  (a): Drawing of a single taste bud shows the gustatory (taste) cells, the supporting cells whose function is not well-understood, and the basal stem cells.Microvilli at the ends of the gustatory cells project through an opening in the epithelium, the taste pore. Afferent sensory axons enter the basal end of taste buds and synapse with the gustatory cells. (b): In the stratified squamous epithelium of the tongue surface or oral mucusa, taste buds form as distinct clusters of cells that recognizable histologically even at low magnification. At higher power the taste pore may be visible, as well as the elongated nuclei of gustatory and supporting cells and the fewer, round nuclei of basal stem cells. 140X and 500X. H&E.
    •  The interior of the tongue consists of interlacing bundles of skeletal muscles that run in three planes and cross one another at right angles. Barrel shaped taste buds are located in the epithelium of the lateral surfaces of the papillae and are made up of two cells: 1. Neuroepithelial cells : Dark, slender cells which are thickened in the middle due to the nucleus. These cells terminate in a stiff process called the taste hair. 2. Sustentacular cells: Paler cells with rounded lightly stained nucleus.  Presence of mixed glands (serous and mucous alveoli) on the lower half of the tongue. Von ebner’s glands are tubulo-alveolar glands of vallate papillae.
    • ESOPHAGUS  It is lined by nonkeratinized stratified squamous epithelium with stem cells scattered throughout the basal layer (a): Longitudinal section of esophagus shows mucosa consisting of nonkeratinized stratified squamous epithelium (SS), lamina propria (LP), and smooth muscles of the muscularis mucosae (MM). Beneath the mucosa is the submucosa containing esophageal mucous glands (GL) which empty via ducts (D) onto the luminal surface. X40. H&E. (b): Transverse section showing the muscularis halfway along the esophagus reveals a combination of skeletal muscle (right) and smooth muscle fibers (left) in the outer layer, which are cut both longitudinally and transversely here. This transition from muscles under voluntary control to the type controlled autonomically is important in the swallowing mechanism. X200. H&E.
    • STOMACH  The stomach, like the small intestine, is a mixed exocrine- endocrine organ that digests food and secretes hormones.  the mucosa of the stomach consists of a simple columnar surface epithelium that invaginates into the lamina propria, forming gastric pits
    •  . The stomach is divided into regions: 1. cardia antrum is the opening from the esophagus into the stomach 2. fundus is located to the left of the cardia, form a dome shaped bulge above the level of the gastrointestinal junction 3. corpus is the capacious central portion 4. pylorus is the region of transition of the stomach into the duodenum.
    •  The wall of the stomach consists of the following layers: Mucosa: This is lined with Simple columnar epithelium. Several structures are observed in this layer: 1. Gastric pits or foveolae gastricae which are depressions or deep surface invaginations in the lamina propria 2. Gastric glands are tubular structures of the stomach and are found in the fundus and body of the stomach. These are made up of: a. Chief cells or Zymogenic b. Parietal cells or oxyntic cells c. Argentaffin cells d. Neck mucous cells
    • Submucosa  This consists of denser connective tissue that contains some fat cells and is rich in mast cells, lymphoid wandering cells and eosinophilic leukocytes. This layer contains the large blood vessels and lymph vessels. Serosa  This covers the outer portion of the stomach, consisting of a  mesothelium and a thin lamina propria of loose connective tissue. RUGAE are folds in the mucosa and submucosa and run parallel to the longitudinal axis of the organ.
    • SMALL INTESTINE  The small intestine is relatively long—approximately 5 m—and consists of three segments: duodenum, jejunum, and ileum.  Viewed with the naked eye, the lining of the small intestine shows a series of permanent circular or semilunar folds (plicae circulares), consisting of mucosa and submucosa which are best developed in the jejunum.  Intestinal villi are 0.5- to 1.5-mm-long mucosal outgrowths (epithelium plus lamina propria) and project into the lumen  In the duodenum they are leaf-shaped, but gradually assume fingerlike shapes moving toward the ileum.  Villi are covered by a simple columnar epithelium of absorptive cells and goblet cells.
    • Mucosa  This is lined with a Simple columnar epithelium with Goblet cell. A number of structural specializations that serves to increase the area of surface exposed the lumen. 1. Plicae cirulares (valves of kerckring): These are grossly visible concentric folds that extend half to two thirds of the way around the lumen. This is a permanent structure involving both the mucosa and the submucosa. 2. Intestinal villi: These are minute finger-like projections of the mucosa having a length of 0.5 to 1.5 mm. They cover the entire surface of the mucosa and give it a characteristic velvety appearance in fresh state. They are the most numerous in the duodenum and a proximal jejunum. Each villus is drained by a single, blind ending lymphatic capillary known as lacteal.
    • 3. Crypts of Lieberkuhn (intestinal glands): These are simple tubular glands, which extend down into the lamina propria nearly to the thin layer of smooth muscle comprising the muscularis mucosae.  Three types of cells can be distinguished in the epithelium:  Intestinal absorptive cells  Goblet cells  Basal granular cells (Argentaffin or Enterochromafin cells)  Paneth cells occuring in small groups only in the depths of the crypts of Lieberkuhn. They are pyramidal in form with a round or oval nucleus situated near the base and conspicous secretory granules in the apical cytoplasm. The cytoplasm is basophilic with large acidophilic granules. These granules contain lysozyme.
    • s  Absorptive surface of the small intestine.  (a): The mucosa and submucosa are the inner two of the gut's four concentric layers. (b): They form circular folds or plicae circulares, which increase the absorptive area. (c, d): They are lined by a dense covering of finger-like projections called villi. Internally each villus contains lamina propria connective tissue with microvasculature and lymphatics called lacteals. Villi are covered with a simple columnar epithelium composed of absorptive enterocytes and goblet cells. (e): At the apical cell membrane of each enterocyte are located dense microvilli, which serve to increase greatly the absorptive surface of the cell. Between the villi the covering epithelium invaginates to form short tubular intestinal glands or crypts, which include stem cells for the epithelium and Paneth cells which prevent intestinal flora from becoming concentrated in these glands where damage to the stem cells could occur.
    • LARGE INTESTINE  Large intestine is about 160 cm long. The surface is relatively  smooth, lacking the rugae and plicae circulares. This is divided into caecum, colon and rectum.  Mucosa : Simple columnar epithelium with Goblet cell
    • (a): Transverse section of the colon shows the muscularis externa (ME), including a taenia coli cut transversely in the lower part of the figure, the submucosa (S), the mucosa (M) filled with tubular intestinal glands. Some of these glands are cut longitudinally, but most seen here are cut transversely. X14. H&E. (b): Transversely cut glands are seen to consist of simple columnar epithelium surrounded a tubular lumen (asterisk) and embedded in lamina propria (LP) with many free lymphocytes. Lymphocytes can also be seen penetrating the epithelium (arrow). X200. H&E.
    • (c): Longitudinal section of one gland stained for glycoproteins shows mucus in the lumen and two major cell types in the epithelium: goblet cells (G) and other columnar cells specialized for water absorption. X400. PAS. (d): TEM micrograph of the absorptive cells, called colonocytes, reveals short microvilli at their apical ends, prominent Golgi complexes above the nuclei, and dilated intercellular spaces with interdigitating leaflets of cell membrane (L), a sign of active water transport. The absorption of water is passive, following the active transport of sodium from the basolateral surfaces of the epithelial cells. X3900.
    • ANUS OR CANAL  Epithelium: Stratified squamous epithelium  Lamina propria: Dense irregular connective tissue containing large veins which when abnormally distended and varicose present at the anus as hemorrhoids.  Muscularis externa: Circular muscle layer increase greatly in thickness and forms the internal anal sphincter. Below, this is replaced by external anal sphincter. Above abd external to this sphincter is the levator ani muscle (skeletal muscle).