Stomach Histology PDF

Histology of the Stomach Dr. Heba Fathy Ibrahim Assistant professor of Histology & cell Biology  THE STOMACH The most dilated segment of the tube. Functions: - Adds acidic fluid to the ingested food. - Transforms food into a viscid mass (chyme)....

Histology of the Stomach Dr. Heba Fathy Ibrahim Assistant professor of Histology & cell Biology  THE STOMACH The most dilated segment of the tube. Functions: - Adds acidic fluid to the ingested food. - Transforms food into a viscid mass (chyme). - Secrets proteolytic enzymes to continue digestion.  Histologically, the stomach is divided into three regions: The cardiac region surrounds the entrance of the oesophagus. The fundic region and body. The pyloric region.  The mucosa and the submucosa of empty stomach show longitudinal folds called Rugae (WHY?) They permit expansion of the stomach & allow volume changes after food intake. These disappear when distended with food not permanent.  I- THE FUNDUS AND THE BODY OF THE STOMACH o THE MUCOSA: 1-The surface epithelium: Type : Simple columnar. Type of surface cells: surface mucous cells.  The lining epithelium invaginates into the mucosa forming gastric pits WHY? to increase the surface of gastric mucosa.  The surface mucous cell L.M: Tall columnar cells with oval basal nuclei. Upper pale vacuolated region (stored mucinogen granules), and basal basophilic region (rER). Function:- Manufacture thick, insoluble mucus with neutral pH or slightly alkaline & a cloudy appearance (visible mucous) WHY? Protection of epithelium from acidic gastric secretion & abrasion(trauma) by food.  Mucosa 2- The lamina propria Formed of loose highly vascular CT. 1 Occupied mostly by gastric glands (simple branched tubular). Gastric glands open at the base of the pits. 2  3-The muscularis mucosa Formed of smooth muscle fibers arranged in an inner circular and an outer longitudinal layers.  The fundic gland or gastric gland of the stomach Simple branched tubular gl. Arranged perpendicular to muscularis mucosa & parallel to each other. Closely packed with minimal CT corium in between. The fundic gland or gastric gland of the stomach Fundic glands are lined by five types of cells: 1.Mucous neck cells. 2.Peptic (chief) cells. 3.Oxyntic cells. 4.Entero-endocrine cells. 5.Stem cells.  Cells lining the fundic glands 1- The mucous neck cells: In the upper part of the glands. Columnar in shape. Function: soluble mucus to lubricate the gastric content.  2- The Oxyntic cells ( Parietal cells) Responsible for the HCl formation & secretion in the stomach and production of Intrinsic Factor. Present mainly in the middle of the gland. HCl provides acidic PH needed for activation of digestive enzymes.  By LM:  Appear as rounded or pyramidal cells One or two central, rounded nuclei. Intensely eosinophilic cytoplasm. (WHY??) Ultrastructurally : ⦿ They show extensive invagination of the apical plasma membrane forming intracellular canaliculus (WHY?) communicating with the lumen of the gland. ⦿ Numerous microvilli project from the surface of the canaliculus. ⦿ Active ionic transport occurs across these membranes and is important for HCl formation. ⦿ Abundant rounded and tubular vesicles, tubulovesicular system, is present adjacent to the canaliculi. ⦿ Their membranes are inserted in the plasma membrane of the canaliculi to increase the surface area of canaliculi by forming microvilli-like projections. WHY? to increase surface area of the active ionic transport that occurs during HCl formation. ⦿ Inbetween canaliculi: - Abundant scattered mitochondria (deep eosinophilia) to provide energy for ionic transport. - Cytoskeleton; actin & myosin. (WHY??) To pull tubulovesicular structures towards canalicular membrane. ⦿ A Golgi complex, few rER but no secretory granules. EM of a Parietal Cell  3-The Peptic Cells ( Chief cells; Zymogen cells) Localized mainly in the lower third of the glands. Function: They produce & secrete digestive enzymes (pepsin& lipase). LM: Pyramidal shaped cells Basal basophilic cytoplasm. Apical acidophilic (zymogen granules) Ultrastructurally: Numerous parallel cisternae of rER occupying the basal part of the cell. Large number of ribosomes. Prominent supranuclear Golgi complex. Numerous apical sec gr filled with pepsinogen (precursor of pepsin). 4-Enteroendocrine Cells: Group of cells located at the bases of the gastric glands, between the peptic cells. They belong to (APUD or DNES) and show their common features.  Enteroendocrine Cells: Entero= gastrointestinal Endocrine=secrete peptide like hormones into blood capillaries directly. Pyramidal in shape basal sec granules Infranuclear Golgi complex. Ex; EC-cells: serotonin G-cell: gastrin D-cell: somatostatin Their secretion: regulates gastric motility and secretion.  5- Undifferentiated Cells (Stem cells) They are located in the upper part of the gland. LM: low columnar cells with oval basal nuclei (usually in mitosis).  II - THE CARDIAC REGION OF THE STOMACH A narrow zone at the transition between the oesophagus and the stomach. Mucosa contains branched coiled tubular cardiac glands. Lined mainly by mucus-secreting cells.  III-THE PYLORUS OF THE STOMACH THE MUCOSA: Gastric pits ; Wide, deep occupying more than half the lengths of the mucosa. Pyloric glands: Branched, coiled tubular glands with wide lumina. Secretory portion tortuous and coiled (cut transversely or obliquely).  Glands are lined mainly by: Mucus Secreting Cells and Some Enteroendocrine cells: particularly G-cells.  THE SUBMUCOSA Moderately thick layer of dense CT  THE MUSCULOSA o Thick, formed of spirally oriented smooth muscle fibers. o Arranged in 3 layers; an inner oblique, middle circular & outer Longitudinal layers. o Arrangement in three layers in such orientation allows good mixing of chyme for more contact of gastric juice (digestive enzymes with food).  Musculosa in Pylorus Thick inner circular smooth muscle layer constituting the pyloric sphincter. THE SEROSA: Narrow layer of loose CT covered by the visceral layer of peritoneum (the mesothelium).  Cardiac Fundus Pylorus region Gastric oShallow o Short & narrow. oWide & pits deep(1/2 mucosa) Gastric oSimple o Simple branched oSimple glands branched coiled tubular branched coiled tubular oLined By 5 cells tubular o lined mainly 1- mucous neck cells oLined by 3 cells by mucous 2- stem cells 1- mucous secreting cells 3- oxyntic cells secreting cells. and Stem cells 4- peptic cells 2- 5-enteroendocrine enteroendocrine (G-cells) 3- stem cells