1. Salivary Glands : There are 3 Pairs of Salivary Glands :
(i) Parotid Glands
- These are the largest salivary glands. They lie on the sides of the face, just below and in front of the ears.
- Viral infection of the parotid glands causes swelling and pain, disease being called Mumps.
(ii) Sublingual Glands
These lie under the front part of the tongue.
(iii) Sub – Maxillary Glands
- These lie at die angles of the lower jaw.
- The salivary glands secrete a viscous liquid called saliva (already studied).
2. Gastric Glands
They are innumerable and have 3 types of gland cells: Peptic (Chief or Zymogen) cells that produce enzymes, large deep seated Oxyntic cells that secrete HCl and Mucous cells which add mucous.
It is bilobed, Right Lobe being the larger and Left Lobe the smaller.
Secretes Bile, which is yellowish in color. It is stored in Gall Bladder for subsequent use.
Bile helps in digestion in three ways: It emulsifies the fats, it prevents decomposition of food by checking the growth of bacteria and it neutralizes the acid coming from the stomach.
Liver is a gland which has got diverse functions:
Digestion : With the help of bile (already discussed)
Regulation of Blood Sugar: The liver separates the excess of sugar from the blood and stores it in its cells as glycogen (animal starch).
This process is called Glycogenesis and is aided by pancreatic hormone insulin.
It takes place when the animal gets plenty of food.
During the days of food shortage, the stored glycogen is changed into glucose and added to the blood stream for distribution to the body. This process is called as Glycogenolysis.
It is aided by glucagon, another pancreatic hormone.
Formation of Glycogen from Non-carbohydrate sources: Excess of amino acids/fats are also changed into glycogen.
This process is called Glyconeogenesis.
Deamination: In the liver, the amino acids coming from the alimentary canal are sorted out.
Those necessary for protein synthesis are distributed to the tissues.
The excess or unnecessary amino acids are broken down, their amino radical separating as ammonia, and carbon chain changing into a keto acid.
This process is known as Deamination. Ammonia is toxic and need removal, while keto acid takes part in metabolism.
Excretion: Liver collects haemoglobin of the worn-out red blood corpuscles and changes it into bile pigments.
The latter passes into the alimentary canal along with the bile for elimination with faeces.
Blood Clotting: Liver produces heparin, prothrombin and fibrinogen.
Heparin prevents clotting of blood inside the blood vessels.
Prothrombin and fibrinogen help in the clotting of blood at the injured surfaces.
Formation of Red Blood Corpuscles: Liver produces RBCs in the embryo. The process of formation of RBCs is called erythropoiesis.
Phagocytosis: Foreign matter, dead cells and bacteria are disposed off in the liver.
These are engulfed and digested by large, star-shaped cells called the macrophages, or Kupffer’s cells that occur in the lining of liver sinusoids.
Synthesis of Vitamin A: Liver synthesis Vitamin A from the (i-carotene, an orange yellow substance of carrots.
Storage: Besides glycogen, liver stores
- Lipids such as Fats, Fatty Acids and Cholesterol.
- Minerals like Copper and Iron.
- Vitamins, namely, A, B12, D and E.
- Bile in the Gall Bladder.
It is both an exocrine and an endocrine gland.
The endocrine part (called Islets of langerhans) secretes hormones (already studied).
The exocrine part secretes pancreatic juice. The juice is carried by the pancreatic duct into the duodenum.
The pancreatic juice contains three proenzymes (trypsinogen, chymotrypsinogen and procarboxypeptidases) and several enzymes (mentioned in the list).
5. Intestinal Glands
They are of two types: Crypts of Lieberkuhn and Brunner’s Glands. Their mixture of secretion is called Intestinal juice or Succus Entericus.
It is alkaline and is poured into the intestine.
The juice contains many enzymes (mentioned in the list of Important Digestive Enzymes).