4. Most dilated part
Bag like organ
Lies in epigastric, umblical &
left hypogastric regions of the
abdomen
5. Functions of stomach
• Temporary storage of food
• Grinding & mixing of food
• Secretion of HCl
• Secretion of intrinsic factor (IF)
• Secretion of pepsinogen
• Absorption of water and lipid soluble substances
• Performs its own controlled emptying
6.
7.
8. • Surface/Neck mucous cells-
secrete protective bicarbonate
ions
• Parietal Cells- most numerous in
the isthmus of the glands, secrete
gastric acid (HCL) + intrinsic
factor.
Structure of Glands
• Chief/peptic/zymogenic cells- located towards the bases of
the gastric glands. Secrete gastric lipase and pepsinogen.
9. • Neuroendocrine cells- part of
the diffuse neuroendocrine
system, secrete serotonin and
other hormones
• Stem cells- divide continuously
to replace all other types of cell
in the glands.
10. Synthesize and secrete the HCl acid
responsible for the acidic pH in the
gastric lumen.
Synthesize and secrete the protease
precursor known as pepsinogen.
Produce alkaline mucus that covers
mucosa layer
11. Contents of Normal Gastric Juice
•Volume: 1 -1.5 liters
• Nature: acidic pH 0.7 to 4
Constituents: Water (99.5%); solids (0.5%)
Inorganic constituents: anions ( Cl-
, PO4
3-, SO4
2- & HCO3
- and
cations (H+, Na+, K+, Ca++, Mg ++)
Organic constituents: pepsinogen, IF, mucin, renin, gastric
lipase, gelatinase, carbonic anhydrase and lysozyme.
12. Structure of parietal cell: resting and stimulated
•H+ - K+ ATPase in inactive form
•When activated , fuse to cell membrane & microvilli project to increase surface
area for secretion
13. Mechanism of HCl Secretion
• Water dissociated into H+ & OH-
• Pumping of H+ out of cell by H+K+ATPase; permits OH- to accumulate & form
HCO3
- from CO2
• Water passes into canaliculus by osmosis making gastric juice isotonic to
plasma
28. Pepsinogen secretion
• Secreted by chief cells in gastric
glands, & mucous cells
• Pepsinogen : aspartic proteinases,
endopeptidases
• Two types: Group I ( chief cells of
corpus)
• group II ( chief cells +
mucous neck cells in all
parts)
• Zymogen granule compound
exocytosis pepsinogen
29. • Agonist acting through Ca++
M3 muscarinic receptors for Ach
Gastrin/CCk family peptides’ receptors
Stimulated by:
The stomach is a J-shaped, baglike organ that expands to store food (Figure 1). Typical of that of the entire digestive tract, the wall of the stomach contains four layers. However, the inner layer, the mucosa, is modified for the specialized functions of the stomach. In particular, the innermost layer of the mucosa (facing the lumen) contains a layer of simple columnar epithelium consisting of goblet cells. Gastric pits on the surface penetrate deep into the layer, forming ducts whose walls are lined with various gastric glands.
Not easily but become very prominent with plentiful mitotic figures after damage to the mucosa has occurred, e.g. after an episode of gastritis.
ie. important histopathology feature
Max concn can reach upto 150 meq/L.pepsinogen is secreted from peptic cells and acts best at 2-4 PH. Mucin are of two types insoluble mucin and soluble mucin.
Gastric secretion is a colorless, watery, acidic, digestive fluid produced in the stomach .
Physical properties;
It is a watery fluid, that has a pale yellow colour , pH is 1-3 , the volume secreted per day is 2-3 L .
The stomach is famous for its secretion of acid, but acid is only one of four major secretory products of the gastric epithelium, all of which are important either to the digestive process or to control of gastric function.
Chemical composition; It is 97-99% water , it contains inorganic salts ,and organic components that include ,mucin, digestive enzymes , hormones ….
The resting parietal cell has intracellular canaliculi opening in the apicla membrane. And many hace h+ k+ atpase in inactive form
Postprandial Alkaline Tide
The resting parietal cell has intracellular canaliculi opening in the apicla membrane. And many hace h+ k+ atpase in inactive form
Agents inhibiting the parietal cells
Acid
Somatostatin
Food
Agonist acting through cAMP
Chief cells have receptors for secretin/VIP
β2 adrenergic receptors
EP2 receptors for PGE2
Lubricating and Protective Properties of Mucus, and Importance of Mucus in the Gastrointestinal Tract Mucus is a thick secretion composed mainly of water, electrolytes, and a mixture of several glycoproteins, which themselves are composed of large polysaccharides bound with much smaller quantities of protein. Mucus is slightly different in different parts of the gastrointestinal tract, but everywhere it has several important characteristics that make it both an excellent lubricant and a protectant for the wall of the gut. First, mucus has adherent qualities that make it adhere tightly to the food or other particles and to spread as a thin film over the surfaces. Second, it has sufficient body that it coats the wall of the gut and prevents actual contact of most food particles with the mucosa. Third, mucus has a low resistance for slippage, so the particles can slide along the epithelium with great ease. Fourth, mucus causes fecal particles to adhere to one another to form the feces that are expelled during a bowel movement. Fifth, mucus is strongly resistant to digestion by the gastrointestinal enzymes. And sixth, the glycoproteins of mucus have amphoteric properties, which means that they are capable of buffering small amounts of either acids or alkalies; also, mucus often contains moderate quantities of bicarbonate ions, which specifically neutralize acids. In summary, mucus has the ability to allow easy slippage of food along the gastrointestinal tract and to prevent excoriative or chemical damage to the epithelium. A person becomes acutely aware of the lubricating qualities of mucus when the salivary glands fail to secrete saliva, because then it is difficult to swallow solid food even when it is eaten along with large amounts of water.
