Digestive System
- Oral cavity: Lips and Tongue. - Digestive tract: Esophagus, stomach, small intestine, large intestine, rectum, appendex. - Accessory glands of digestive system: salivar y glands, pancreas, and liver.
Tongue: is a muscular organ, covered covered by St. Sq. Ep. resting on basement membrane; membrane; and lamina propria (binds epithelium to underlying muscle) that contains serous glands . Tongue papillae ( 4 types)
- Foliform (leaf-like); along side of tongue; has taste buds on posterior face. - Filiform: short bristles; covered by keratinized epi - Fungiform: red, globular; thin, non-keratinized epi - Circumvallate: row immediately anterior to sulcus terminals; contain most of taste buds and serous glands (von Ebners Ebners glands).
Tongue papillae 1
Taste buds
Digestive canal
The wall of digestive canal is formed of : 1- Mucosa : is the innermost layer, surrounding the lumen, and is formed of 3 layers. — Epithelium (wet surface epithelia or mucous membrane ): stratified squamous epithelium or simple columnar epithelium. — Lamina propria: underlying loose CT; contains glands. — Muscularis mucosa: thin layer of smooth muscle may run up into villi. 2- Submucosa: regular/irregular fibro-elastic CT.; contains glands (in some regions); submucosal (Meissner) nervous plexuses (pre- and post-ganglionic parasympathetic fibers; nonmyelinated preganglionic fibers from vagus nerve). 3- Muscularis externa : two or more muscle layers (inner circular; outer longitudinal); mesenteric (Auerbach) plexuses between muscle layers; and has independent peristaltic movements. 4- Serosa (Adventitia): irregular dense CT. surrounded by mesothelium (serosa) or bound to body wall (adventitia).
2
Structure of the wall of digestive canal
Structure of the esophageal wall
3
Cells of gastric glands
- Simple columnar epithelium: surface epithelia cells, mucous secreting cells (mucocytes or epitheliocytes); and absorptive cells. - Chief cells (zymogene cells) produces pepsin, rennin, and lipase. - Parietal (oxyntic) cells: secret hydrochloric acid (secretion stimulated by alcohol and caffeine) and intrinsic factor (glycoprotein binds vitamine B12). - Gastric endocrinocytes or enteroendocrin cells; diffuse neuroendocrine system. - APUD cells (secrete gastrin, somatostatin, secretin, and cholecystokinin) - Stem cells.
Cells of gastric glands
4
Intestine Mucosa forms villi as in small intestine or crypts as in large intestine; their epithelium is simple columnar (absorptive) cells with goblet cells that increased in large intestine. Submucosa contains mucous glands (Brunner`s glands) as in the duodenum; patches of lymphatic nodules on one side as in the ileum; or along the wall as in large intestine. Small intestine mucosal cells
-
Surface simple columnar absorptive cells with microvilli forming brush (striated) border.
-
Goblet cells (oligomucous) cells (produce mucinogen > mucus)
-
Paneth (exocrinocytes ) cells with apical eosinophilic granules; probably secrete lysozymes.
-
APUD cells (endocrinocytes; clear cytoplasm; vesicular basal nuclei): amine-secreting cells of gastrointestinal tract and other endocrine organs.
-
Stem cells.
Intestinal villi
Structure of the duodenum
5
Structure of the ileum
Structure of the large intestine
Accessory glands
- Salivary glands: mucous, serous, or muco-serous. -
Pancreas.
-
Liver.
Salivary glands
- Major salivary glands: outside wall of digestive tract; attached to lumen by duct; respond to parasympathetic activity. - Minor or accessory glands: secrete continuously; ducts directly to surface (no large collecting ducts). Saliva: hypotonic (serous glands secrete solution isotonic with plasma) watery secretion containing variable amounts of mucus, enzymes (salivary amylase) and antibacterial enzyme lysozyme, lactoferrin, and IgA (antibodies) and inorganic ions.
Major salivary glands: outside wall of digestive tract; attached to lumen by duct; respond to parasympathetic activity. 6
Mucoserous (mixed) salivary gland
Parotid (Serous) gland
7
Structure:
- Parenchyma: acinar secretory cells and ducts system. - Stroma (trabeculae) subdivide gland into lobules and lobules. interlobular s epta radiate between lobules from outer capsule; convey blood vessels, nerve and lg excretory ducts. Secretory unit: tubulo-acinar structure embraced by myoepithelial cells.
Acinar cells are of 3 types:- Mucous cells: contain mucigen granules poorly stained; nuclei condensed and flattened against basement membrane. - Serous cells: contain zymogen granules basophilic; nuclei rounded with dispersed chromatin; usually occupy more central position within cell. - Mixed units (serous demilunes) surround terminal part of mucous acini. Ducts of stratified cuboidal epithelia. Intercalated ducts are formed from merged secretor y units; lined by secretory cells; drain into striated duct. Parotid: almost serous secretory gland; thin, water y secretion rich in enzymes and antibodies; rounded nuclei toward base of serous cells; granular cytoplasm; lateral membranes and lumen indistinct; intercalated ducts. Submandibular (submaxillary): capsule gives rise to septa; subdivides gland into lobes and lobules. It is compound tubulo-alveolar gland, contains both serous (predominant) and mucous secretory acini with serous demilunes; myoepithelial (basket) cells embrace acini. Produces secretion of intermediate consistency; duct cells with pale, eosinophilic cytoplasm and large lumen. Sublingual: capsule gives rise to septa; subdivides gland into lobes and lobules. It is compound tubuloalveolar gland (mixed) gland; predominantly mucous secretory cells (flattened dark nuclei against basement membrane; frothy cytoplasm; intercellular borders and lumen apparent) with serous demilunes (vesicular nuclei, granular, basophilic cytoplasm, no intercellular borders); viscid secretion; myoepithelial (basket) cells
Liver
— Liver is the largest gland of the body; receives both venous blood (through the portal vein) and arterial blood (through the hepatic artery). — It is surrounded by a well defined thin capsule of connective tissue. The connective tissue extends into the liver parenchyma and divides it into the basic structural units of the liver, the "classical" liver lobules. 8
— It acts as an exocrine gland because it secretes bile. — The portal vein, hepatic artery and bile duct enter the liver through the porta-hepatis. — The groups of three tubes - a branch of the portal vein, a branch of the hepatic artery and a branch of the bile duct; are called collectively portal triads.
9
Hepatocytes are separated from the bloodstream by a thin disc ontinuous simple squamous epithelium, which lines the sinusoids. Between the hepatocytes and the epithelial cells is a narrow perisinusoidal space (of Disse). Contents of the blood plasma can freely enter the perisinusoidal space through the openings in the epithelium lining the sinusoids. Fixed macrophages, Kupffer cells, are attached to the epithelium Adjoining liver cells form the walls of the bile canaliculi , which form a three dimensional network within the sheets of hepatocytes. Bile canaliculi connect via very short canals (of Hering; formed by both hepatocytes and cells similar to those in the epithelium of bile ducts) to terminal bile ducts (cholangioles) which empty into the interlobular bile ducts found in the portal triads. The liver lobule is drained by the central vein, which open into the inter calated or sublobular veins of the liver. These in turn coalesce to form the hepatic veins. They run alone through the tissue, are usually covered by connective tissue and eventually empty into the inferior vena cava.
Pancreas
Pancreas: is formed of compound or mixed gland (endocrine and exocrine); releases enzymes as proenzymes (chymotrypsin, trypsin, elastase, carboxypeptidase) and active enzymes (DNase, RNase, pancreatic lipase, pancreatic amylase). 10
Exocrine pancreas: is formed of compound tubuloalveolar gland; has capsule that gives rise to septa separating the gland into lobules; acinar cells (basally basophilic with apical eosinophilic zymogen granules) coupled to centro-acinar cells (with pale, vesicular nuclei) and intercalated ducts release alkaline secretion rich in digestive enzymes. It also, contain interlobular and main duct Endocrine pancreas: pancreatic islets (islets of Langerhans) scattered among serous acini; contains 5 cell types distinguished histochemically: - α (A) cells: generally peripheral secret glucagon. - β (B) cells: most populas; located centrally secret insulin. - δ (Delta) cells: least numerous, secret somatostatin hormone - G cells; secret gastrin. - P.P- cells (F- cells); secret somatostatin; PP cells secret pancreatic polypeptide .
11
