Question

1.(a)Strong acids can dissolve or chemically burn living matter. Why is the stomach tissue not damaged by stomach acid? Describe the mechanism by which the stomach lining is protected from the very acidic gastric juice.

(b)What is the function of the gallbladder? What might be the consequences of having your gallbladder removed?

Answer 1

1.a
Gastric juice is made up of digestive enzymes, hydrochloric acid and other substances that are important for absorbing nutrients about 3 to 4 liters of gastric juice are produced per day. The hydrochloric acid in the gastric juice breaks down the food and the digestive enzymes split up the proteins. The acidic gastric juice also kills bacteria.Mucus is a mucoprotein, secreted by mucus neck cells of the gastric glands and surface mucus cells in fundus,body and other parts of stomach. It protects the gastric wall by the following ways:
Mucus:
i. Protects the stomach wall from irritation or mechanical injury, by virtue of its high viscosity.
ii. Prevents the digestive action of pepsin on the wall of the stomach, particularly gastric mucosa.
iii. Protects the gastric mucosa from hydrochloric acid of gastric juice because of its alkaline nature and its acid­combining power.
The mucus covers the stomach wall with a protective coating. Together with the bicarbonate, this ensures that the stomach wall itself is not damaged by the hydrochloric acid.

*In the stomach several mucosal defence mechanisms protect the stomach against hydrochloric acid and noxious agents. The pre-epithelial protection is made up by the mucus-bicarbonate barrier. Mucus and bicarbonate, secreted by mucus cells, create a pH gradient maintaining the epithelial cell surface at near neutral pH. In humans, secretion of bicarbonate is an active process and is activated by vagal stimulation and fundic distension. Several mechanisms at the epithelial cell level contribute to an intact mucosal barrier. Surfactants in apical cell membranes prevent water-soluble agents in the gastric lumen from reaching and damaging the epithelium. Nonprotein sulphydryls in the epithelium are capable of binding reactive free radicals. Rapid cell turn-over and the process of restitution contribute to an intact epithelial lining. In subepithelial protection, mucosal blood flow is essential in supplying the epithelium with nutrients and oxygen and for disposal of hydrogen ions and noxious agents permeating the mucosa. Prostaglandins may maintain blood flow and prevent vascular endothelial injury caused by ethanol. Several agents have been established as protective for the gastric mucosa. Prostaglandins possess direct cytoprotective actions, whilst sucralfate, aluminium containing antacids, carbenoxolone and bismuth are mild irritants that induce liberation of endogenous prostaglandins of the mucosa.

1.b
Biliary system or extrahepatic biliary apparatus is formed by gallbladder and extrahepatic bile ducts (bile ducts outside the liver).
GALLBLADDER:
Bile secreted from liver is stored in gallbladder. The capacity of gallbladder is approximately 50 mL.Gallbladder is not essential for life and it is removed (cholecystectomy) in patients suffering from gallbladder dysfunction. After cholecystectomy, patients do not suffer from any major disadvantage. In some species, gallbladder is absent.
FUNCTIONS OF GALLBLADDER
Major functions of gallbladder are the storage and concentration of bile.
1.Storage of Bile:
Bile is continuously secreted from liver. But it is released into intestine only intermittently and most of the bile is stored in gallbladder till it is required.
2.Concentration of Bile:
Bile is concentrated while it is stored in gallbladder.The mucosa of gallbladder rapidly reabsorbs water and electrolytes, except calcium and potassium. But the
bile salts, bile pigments, cholesterol and lecithin are not reabsorbed. So, the concentration of these substances
in bile increases 5 to 10 times.
3.Alteration of pH of Bile:
The pH of bile decreases from 8 – 8.6 to 7 – 7.6 and it becomes less alkaline when it is stored in gallbladder.
4. Secretion of Mucin:Gallbladder secretes mucin and adds it to bile.When bile is released into the intestine, mucin acts as a lubricant for movement of chyme in the intestine.
5. Maintenance of Pressure in Biliary System: Due to the concentrating capacity, gallbladder maintains a pressure of about 7 cm H2O in biliary system. This
pressure in the biliary system is essential for the release of bile into the intestine.