It's the expanded part of the digestive tract where the esophagus opens. empty stomach have folds called "gastric pits" ,which accomidate the fullness and elongation of the stomach.

Structure of stomach wall:
• mucosa:
Stomach surface lined by a simple columinar epithelial cells called
"mucous cells"
gastric pits lined by mucous cells.stomach divided into 3 regions:
1-Cardiac region:
contain cardiac glands,it,s a narrow band near the esophagus.almost of mucous secreting cells which secret mucous to protect the esophagus against acid reflux.
2-Fundic region:
It constitutes the majority of the stomach.glands in this region are gastric,fundic or oxyntic glands.
Cells in fundic region:
-Mucous neck cells. -Enteroendocrine cells.
-Chief "peptic" cells. -Undifferentiated cells.
-Parietal cells.
3-Pyloric region: proximal to pyloric sphincter and contain pyloric glands.

• Submucousa: Consist of dense irregular connective tissue
• Muscularis externa:
consist of 3 layers,inner oblique ,middle circular and outer longitudinal layer. it mix chym and expel it to small intestine.
• Serosa: It's continous layer with the peritonium of the body.

Role of gastric solutions:
1- Protect the mucosa from the action of the digestive juice.
2-Begine food digestion by breakdown with low PH and enzymatic action.
• Oxyntic gland: It,s the secretary unit in the gastric secretion.
• Structure of oxyntic gland:
1-Surface epithelial cells: in the neck of pit,the whole stomach lined by them.
2-Mucous neck cell: secrete lubricating mucous and bicarbonate ions which make mucous layer alkaline.
3-Parietal cells: secrete HCL acid and the intrinsic factor.
4-Peptic cells: secrete pepsinogen.
Other Secretions:
1-Mucous: from superficial epithelial mucous cells and the neck of gastric cells.
2-Pepsinogen: It's the inactive purcursor of pepsin,converted to pepsin in PH<5 .
pepsinogen released fromgastric cells by action of acetylcholine.
3-Intrinsic factor: It's necessary for vitamin B12 absorption.
4-Gastrin: It's secreted by G-cells response to distention of the stomach wall,travells to parietal cells.stimulating acid secretion and to enterochromaffine-like cells "ECL" to stimulate histamine secretion.
5-Histamine: It's release stimulation by action of gastrin and acetylcholine on ECL. it acts on the parietal cell by histamine H2-receptors to stimulate acid production with gastrin and acetyl choline.