DS: Stomach

Question 1

What are the general functions of the stomach?

Answer 1

1. Temporary storage of ingested food in the fundus
2. Mechanical digestion of food boluses
3. Chemical digestion by acids and enzymes
4. Production of IF for the uptake of vitamin B12

Question 2

How is vitamin B12 obtained from food? What is the role of IF?

Answer 2

Parietal cells produce HCL and IF. Animal protein is broken down, chemically and physically, to release vitamin B12 which binds to IF in the duodenum for transport to the ileum. In the ileum, in moves across the enterocytes and is taken up into the blood for delivery around the body.

Question 3

Describe the epithelial structure of the cardia and explain the transition in epithelia between the oesophagus

Answer 3

Cardia of the stomach consists of simple columnar epithelium which protects against stomach acid. Transitions from stratified squamous epithelium.

Question 4

What is the role of the cardia?

Answer 4

Layer of mucous secreting cells protects the cardia and oesophagus from gastric acid and gastric enzymes. The acids and enzymes referred to as the gastric juices are manufactured in the cardia.

Question 5

What is the role of the fundus?

Answer 5

Stores undigested food and gases that are released during the process of chemical digestion.

Question 6

What is the main function of the stomach?

Answer 6

Chemical breakdown of proteins and the conversion of the food bolus into a highly-acidic partially digested form called chyme.

Question 7

What is the role of the corpus?

Answer 7

Main body of the stomach that is largely responsible for mechanical digestion and churning of food boluses due to physiological adaptations. Acts as a mixing tank for food boluses and stomach secretions.

Question 8

How is the corpus adapted to its role as a mixing tank?

Answer 8

3 muscle layers that allow the stomach to generate powerful muscle contractions to breakdown food through churning, propulsion and grinding.

Question 9

What are the 3 musclaris externae layers in the corpus of the stomach?

Answer 9

1. Longitudinal layer
2. Circular layer
3. Oblique layer

Question 10

What are the foods and ridges formed by the internal wall of the stomach, and what are there functions?

Answer 10

Rugae- longitudinal folds of the (sub)mucosa of the stomach that allow for the expansion of the gastric lumen during digestive periods due to distension.

Question 11

What is the role of the pyloric antrum?

Answer 11

The pylorus is divided into the pyloric antrum nearer the corpus and the pyloric canal. The corpus narrows to form the pyloric canal which empties into the duodenum of the small intestine. The pyloric sphincter regulates the emptying of the chyme into the duodenum.

Question 12

What is GORD?

Answer 12

GORD: Gastric-Oesophageal Reflux Disease

Acid reflux occurs when the LOS relaxes at the wrong time and allows stomach acid to rise up the oesophagus.

Question 13

How is GORD treated?

Answer 13

Antacids which neutralise the stomach acid.

Question 14

Describe the composition of the stomach wall

Answer 14

The stomach wall consists of multiple layers of connective tissue and muscle. The mucosa layer, the most internal layer, contains the gastric glands that secrete mucus and gastric juice. The next layer, the sub mucosa is where the nerve bundles lie. Moving outward there are three layers of smooth muscle tissue that form the muscularis externa which is responsible for the movements of the stomach and finally the outermost layer is the serosa which encloses the stomach organ and is connected to the lining of the abdominal cavity.

Question 15

What are the 3 layers of the mucosa of the gut wall?

Answer 15

1. Epithelium
2. Lamina Propria
3. Muscularis Mucosae

Question 16

Describe the epithelial structure of the stomach

Answer 16

Simple columnar epithelium that has many goblet cells that secrete hydrogen carbonate ions and alkaline mucous. Gastric pits in the surface epithelium lead to gastric glands that extend deep into the lamina propria of the mucosa.

Question 17

What cell types do the gastric glands contain?

Answer 17

1. mucous neck cells
2. Parietal (oxyntic) cells
3. Chief (peptic) cells
4. Enteroendocrine cells

Question 18

What is gastric juice?

Answer 18

Combined secretions of parietal cells (HCL) and chief cells (enzymes) are

Question 19

What are parietal cells and what do they secrete?

Answer 19

Parietal cells are large triangular shaped secretory cells located in the proximal region of each gland. They secrete copious amounts of HCL and IF.

Question 20

What is the role of HCL?

Answer 20

HCL is reponsible for creating the acidic environment of the stomach which is needed to activate the protein-digesting enzyme, pepsin, from its inactive form (pepsinogen). Acidic environment also helps to kill much of the bacteria ingested with food and begins the denaturing and breakdown of proteins to make them more susceptible to enzymatic degradation.

Question 21

How are parietal cells innervated?

Answer 21

By the dorsomotor nuclei of the vagus nerves

Question 22

What are chief cells and what do they secrete?

Answer 22

Chief cells are located close to the base of each gastric gland. Chief cells secrete the zymogen (inactive enzyme) pepsinogen, which is converted to pepsin.

Question 23

What are mucous neck cells and what do they secrete?

Answer 23

Gastric glands in the upper part of the stomach contain mucous neck cells that secrete thin, acidic mucus. The role of this mucus is not currently known.

Question 24

What are enteroendocrine cells and what do they secrete?

Answer 24

Found in the gastric glands secrete various hormones into the interstitial fluid of the lamina propria. These include gastrin, which is released mainly by enteroendocrine G cells.

Question 25

What are the 2 types of enteroendocrine cells?

Answer 25

1. Histamine secreting enterochromaffin- like (ECL) cells: stimulate parietal cells to increase HCL secretion.
2. Somatostatin secreting enteroendocrine cells (D cells)

Question 26

What do G cells secrete? What is its function?

Answer 26

G cells secrete the hormone gastrin which stimulates acid secretion by stimulating the release of histamine from ECL cells which in turn stimulate the parietal cells to increase HCL production. G cells also promote mucosal growth in the corpus, SI and LI.

Question 27

What do D cells secrete? What is its function?

Answer 27

D cells secrete somatostatin, a peptide hormone that inhibits Gastrin secretion and blocks acid secretion from the parietal cells; ultimately results in the reduction of gastric acid production.

Question 28

Describe the gastric gland cell type composition in the pyloric glands

Answer 28

Lack parietal cells and chief cells so do not produce HCL, IF or pepsin; this is a safety mechanism to protec the SI from erosion by stomach acid.

Question 29

How is the gastric lumen protected?

Answer 29

The mucous barrier protects the gastric mucosa as it is relatively impermeable to the diffusion of hydrogen ions from the lumen to the epithelial cells. If, however, hydrogen ions do enter the mucous barrier, it is combined with the hydrogen-carbonate ions and neutralised. If pepsin enters the mucosa barrier, it will become deactivated by the high pH.

The mucous gel layer also lubricates the gastric mucosa to protect it from potentially abrasive food.

Question 30

Describe the composition of the MGL at the cell surface epithelium of the gastric lumen?

Answer 30

Mucosal gel layer (MGL) is composed of mucin, phospholipids, electrolytes, and water. Hydrogen carbonate ions, secreted by the surface epithelial cells in the corpus and antrum, are trapped within the mucosal barrier, and they help to maintain a local pH of 7 in the vicinity of the epithelial cells.

Question 31

What is mucin?

Answer 31

Mucin is a tetrameric protein that consists of 4 identical peptides linked by strong disulphides bonds.

Question 32

How is HCL formed by parietal cells?

Answer 32

1. Carbonic anhydrase converts carbon dioxide and water to carbonic acid.
2. Carbonic acid dissociates to hydrogen carbonate ions and hydrogen ions.
3. Hydrogen carbonate ions are released into the ECF by an antiporter that exchanges hydrogen carbonate ions for extracellular chloride ions.
4. Chloride ions diffuse passively across the cell through open chloride channels in the apical membrane of the parietal cells and out into the lumen of the gastric glands.
5. Hydrogen ions are actively transported into the lumen of the gastric glands by hydrogen-potassium ATPase pumps, in exchange for extracellular potassium ions.