Untitled Quiz

The stomach is involved in chemical and mechanical digestion, food storage and the production of chyme.
Chyme is a mixture of ingested food and stomach secretions
The stomach also produces gastric juice which is a mixture of HCl, electrolytes, mucus, water, and bicarbonate.
The pH of gastric juice is 1-3
The stomach secretes 2-3 liters of gastric juice per day
The stomach is regulated by the oesophageal sphincter and the pyloric sphincter.

The stomach is divided into 4 regions:
- The cardia: surrounds the opening of the esophagus into the stomach.
- The fundus: the area above the level of the cardial orifice.
- The body: the largest region of the stomach.
- The pyloric part: divided into the pyloric antrum and pyloric canal and is the distal end of the stomach.

The stomach wall is made up of 4 layers:
- Mucosa
- Submucosa
- Muscularis externa
- Serosa

The stomach is innervated by the autonomic nervous system, which includes the sympathetic and parasympathetic nervous systems.
The stomach also has an intrinsic nervous system called the enteric nervous system.
The enteric nervous system consists of two plexuses:
- The submucosal plexus: controls gastric secretion, blood flow, and detects the nutritional composition of food.
- The myenteric plexus: controls muscle tone and velocity of smooth muscle contractions

Gastric pits extend into the mucosa as straight and branched tubules, forming gastric glands.
Gastric glands contain 4 major types of cells:
- Parietal cells: secrete HCl and intrinsic factors.
- Neck cells: secrete bicarbonate, mucus, and water.
- Chief cells: secrete digestive enzymes.
- Endocrine cells: secrete hormones e.g., gastrin, ghrelin, somatostatin.

Parietal cells are located in the proximal 80% of the stomach also known as oxyntic gland area.
Gastrin producing cells are found in the antrum of the stomach also known as the pyloric gland area.
Parietal cells secrete:
- HCl: converts pepsinogen to pepsin, provides an optimal pH environment for digestion, and destroys bacteria.
- Intrinsic factor: a glycoprotein essential for the absorption of vitamin B12 in the terminal ileum of the small intestine.
Parietal cells have a unique structure with:
- A truncated pyramidal shape with the apex oriented towards the gastric lumen.
- Highly folded luminal membrane forming canaliculi which are lined with “proton pumps” that secrete H+.
- High mitochondrial content.
- The high mitochondrial content in parietal cells is necessary to provide energy for the proton pumps that secrete H+.

G cells are located in the antrum:
- Secrete gastrin, a hormone that stimulates the secretion of acid, pepsinogens, mucus, HCO3-, and gastric motility and inhibits gastric emptying.
D Cells are located in the antrum and body:
- Secrete somatostatin, a polypeptide hormone that inhibits the release of gastrin and acid secretion.
Enterochromaffin-like (ECL) cells are scattered throughout the gastric mucosa, close to parietal cells.
- Secret Histamine, which acts as a paracrine agent to stimulate the secretion of acid and supports the increase in metabolism associated with acid secretion.

Mucus neck cells and surface mucus cells produce mucus which protects the stomach lining from acid and digestive enzymes.
Mucus is a mixture of glycoproteins and lipopolysaccharides.
Mucus forms a gel layer over the luminal surface of the gastric mucosa.
Mucus secreting cells also secrete bicarbonate (HCO3-) to buffer the pH.
Mucus and bicarbonate contribute to the gastric mucosal barrier.

The gastric mucosal barrier protects the stomach against acid, proteolytic enzymes, and mechanical damage.
The gastric mucosal barrier includes the mucus layer, bicarbonate-rich mucus, tight junctions between epithelial cells, prostaglandins which increase mucus and bicarbonate production while inhibiting acid secretion.
Cells of the stomach lining have a high rate of cell division.
The continual renewal of the gastric mucosa protects the stomach against autodigestion.

Breaching the gastric mucosal barrier leads to gastritis an inflammation of the underlying tissue.
Persistent erosion of the gastric mucosa can lead to the formation of ulcers.
Gastric ulcers are lesions in the gastric mucosa.
Benign gastric ulcers and deep gastric ulcers are both types of gastric ulcers