Functions of the Stomach:
- Storage of food until it can be emptied into the small intestine for digestion & meter the
rate at which it leaves
- Secretion of HCl and enzymes to begin protein (and some fat) digestion
- Pulverize and mix food with gastric secretions to produce chyme to be delivered to
duodenum
Anatomy of the Stomach:
- Cardia: Prevents the contents of the stomach from backflowing into the esophagus
- Opening between cardia and esophagus is called cardiac orifice
- Fundus: Lies above cardiac orifice and has Smooth muscle is relatively thin
- Body: Main part of the stomach
- Smooth muscle layer is thin
- Pylorus: Terminal end of the stomach
- Thick layer of smooth muscle
- Opening to duodenum is called pyloric orifice surrounded by smooth muscle
sphincter called pyloric sphincter
- Gastric folds (rugae): The longitudinal folds of the stomach mucosa
- Allow the stomach to expand when it fills with food and drink
- Lesser curvature: Smaller, concave superomedial surface
- Greater curvature: Larger, convex inferolateral surface
Histology of the Stomach:
- Mucosa: Lined by simple columnar epithelium
- Indented with numerous gastric pits
- Several gastric glands extend deep into the mucosa from the base of each gastric
pit
- Muscularis mucosae partially surround the gastric glands to help expel the gastric
secretions
- Muscularis: Composed of three layers of smooth muscle
- Outer longitudinal, Middle circular, and Inner oblique
- Assists the continual churning of the foodstuffs
- Increases in thickness as it progresses from the body to pyloris
Gastric secretions:
- Surface mucous cells: Line the stomach lumen and extend into gastric pits
- Continuously secrete a viscous, alkaline mucus
- Prevents ulceration of the stomach lining
- Mucous neck cells: Found in the neck of the gastric pit and interspersed with parietal
cells
- Produce a watery, acidic mucus
- Helps to maintain acidic conditions of stomach
, - Mucus is protective: Lubricating properties protect stomach lining from mechanical
damage
- Protects the stomach wall from self-digestion
- Inhibits pepsin activity
- Neutralizes HCl due to its alkaline nature
- Parietal cells (onxytic cells): Produce intrinsic factor
- Glycoprotein required for the absorption of Vit B12 needed for
erythropoiesis
- Produce hydrochloric acid
- Not produced as HCl, H+ and Cl- ions are secreted
- Responsible for low pH of stomach
- Functions of HCl: Does not actually digest anything
- Activates pepsinogen to pepsin and provides an optimal environment for its
activity
- Kills most microorganisms
- Aids the breakdown of connective tissue, muscle fibers, and plant cell walls
- Denatures proteins via low pH and promotes chemical digestion
- Chief cells (Most numerous): Secrete zymogenic packets containing pepsinogen
- Inactive precursor to the proteolytic enzyme pepsin
- Converted to pepsin in the stomach by HCl and other active pepsin molecules
- HCl cleaves off a small fragment activating the enzyme
- Pepsin (active form) is autocatalytic – It activates other pepsinogen to the
active form
- Cleaves specific amino acid sequences of proteins to produce smaller
peptide
- Produce gastric lipase
- Limited role in fat digestion
- G-cells (enteroendocrine cells): Secrete gastrin into bloodstream
- Paracrine hormone
- Stimulates stomach secretions and stomach motility
Gastric Motility:
- Mixing: Form of mechanical digestion that convert the bolus into chyme
- Strong peristaltic contractions mix the bolus with gastric secretions to produce
chyme
- Results in the reduction in size of the food particles
- Emptying: Movement of acidic chyme through the pyloric sphincter into the duodenum
- Thickening of muscularis results in stronger contractions
- Creates a pressure gradient to drive chyme (~3 mL) through pyloric
sphincter
- Retropulsion
- Storage of food until it can be emptied into the small intestine for digestion & meter the
rate at which it leaves
- Secretion of HCl and enzymes to begin protein (and some fat) digestion
- Pulverize and mix food with gastric secretions to produce chyme to be delivered to
duodenum
Anatomy of the Stomach:
- Cardia: Prevents the contents of the stomach from backflowing into the esophagus
- Opening between cardia and esophagus is called cardiac orifice
- Fundus: Lies above cardiac orifice and has Smooth muscle is relatively thin
- Body: Main part of the stomach
- Smooth muscle layer is thin
- Pylorus: Terminal end of the stomach
- Thick layer of smooth muscle
- Opening to duodenum is called pyloric orifice surrounded by smooth muscle
sphincter called pyloric sphincter
- Gastric folds (rugae): The longitudinal folds of the stomach mucosa
- Allow the stomach to expand when it fills with food and drink
- Lesser curvature: Smaller, concave superomedial surface
- Greater curvature: Larger, convex inferolateral surface
Histology of the Stomach:
- Mucosa: Lined by simple columnar epithelium
- Indented with numerous gastric pits
- Several gastric glands extend deep into the mucosa from the base of each gastric
pit
- Muscularis mucosae partially surround the gastric glands to help expel the gastric
secretions
- Muscularis: Composed of three layers of smooth muscle
- Outer longitudinal, Middle circular, and Inner oblique
- Assists the continual churning of the foodstuffs
- Increases in thickness as it progresses from the body to pyloris
Gastric secretions:
- Surface mucous cells: Line the stomach lumen and extend into gastric pits
- Continuously secrete a viscous, alkaline mucus
- Prevents ulceration of the stomach lining
- Mucous neck cells: Found in the neck of the gastric pit and interspersed with parietal
cells
- Produce a watery, acidic mucus
- Helps to maintain acidic conditions of stomach
, - Mucus is protective: Lubricating properties protect stomach lining from mechanical
damage
- Protects the stomach wall from self-digestion
- Inhibits pepsin activity
- Neutralizes HCl due to its alkaline nature
- Parietal cells (onxytic cells): Produce intrinsic factor
- Glycoprotein required for the absorption of Vit B12 needed for
erythropoiesis
- Produce hydrochloric acid
- Not produced as HCl, H+ and Cl- ions are secreted
- Responsible for low pH of stomach
- Functions of HCl: Does not actually digest anything
- Activates pepsinogen to pepsin and provides an optimal environment for its
activity
- Kills most microorganisms
- Aids the breakdown of connective tissue, muscle fibers, and plant cell walls
- Denatures proteins via low pH and promotes chemical digestion
- Chief cells (Most numerous): Secrete zymogenic packets containing pepsinogen
- Inactive precursor to the proteolytic enzyme pepsin
- Converted to pepsin in the stomach by HCl and other active pepsin molecules
- HCl cleaves off a small fragment activating the enzyme
- Pepsin (active form) is autocatalytic – It activates other pepsinogen to the
active form
- Cleaves specific amino acid sequences of proteins to produce smaller
peptide
- Produce gastric lipase
- Limited role in fat digestion
- G-cells (enteroendocrine cells): Secrete gastrin into bloodstream
- Paracrine hormone
- Stimulates stomach secretions and stomach motility
Gastric Motility:
- Mixing: Form of mechanical digestion that convert the bolus into chyme
- Strong peristaltic contractions mix the bolus with gastric secretions to produce
chyme
- Results in the reduction in size of the food particles
- Emptying: Movement of acidic chyme through the pyloric sphincter into the duodenum
- Thickening of muscularis results in stronger contractions
- Creates a pressure gradient to drive chyme (~3 mL) through pyloric
sphincter
- Retropulsion
