Module 3 : Physiology

Lecture 12 : Digestive System (Part-II)

 

  1. Salivary glands: The major gland of salivation are parotid, submandibular and sublingual glands. Along with this there are many small buccal glands. A Healthy individual secretes about 0.8 to 1.5 litres of saliva daily. Saliva mainly composed two major type of proteins. A) Ptyalin (an α-amylase) - for digestion of starch, B) Mucin – for protection of surface. Parotid glands are larges salivary glands situated near ears. The parotid glands secrete mainly ptyalin, whereas submandibular and sublingual glands secrete both ptyalin and mucin. The small buccal glands secrete only mucus. The pH of saliva is between 6 to 7 which favours the digestive action of ptyalin.

    2. The esophageal glands secretes only mucous which provide lubrication for swallowing.

  2. Gastric glands: The entire surface of stomach lining contains mucus- secreting cells. The stomach mucosa has two types of tubular glands: Oxyntic glands (gastric glands) and pyloric glands. The oxyntic glands secrete hydrochloric acid pepsinogen, intrinsic factor and mucus. The pyloric gland secretes mainly mucus for protection from stomach acid. They also secrete gastrin hormone.
  3. Liver: It is larges gland of the body, mainly secrete bile normally between 0.6 to 1 litre/day. Bile serves two major function.
    1. Fat digestion and absorption: Along with the enzymes for fat digestion bile acids in bile helps to emulsify the large fat particles of food into many small particles, the surface of which attacked by lipase enzymes secreted in pancreatic juice. Bile acids aid in absorption of end product digested fat through the intestinal mucosal membrane.
    2. Excretion of waste products from blood: An important waste product bilirubin, an end product of haemoglobin digestion and excesses of cholesterol are excreted out with the help of bile.A pear shaped structure attached to the posterior surface of the liver stores 30 to 60 ml bile secreted by the liver.
  4. Pancreas: The pancreas is soft lobulated large compound gland whose internal structure is similar to salivary gland. It lies parallel to and posterior to stomach. Pancreatic acini secrete digestive enzymes whereas large amount of sodium bicarbonate solution are secreted by small ductules and larger ducts. The mixture of enzymes and sodium bicarbonates passes through a long pancreatic duct. Pancreaticduct joins with hepatic duct before it empties into duodenum through the papilla of vater.