There are two sources of digestive enzymes: (i) the glandular cells of the lining of stomach and intestine, which directly pour their secretion into the lumen of the gut or the alimentary canal. (ii) Special glands such as the salivary glands, the liver and the pancreas which pour their secretions into the gut through their ducts.
Saliva is mainly produced by three pairs of salivary glands, the parotids (cheek), the sub-maxillary/sub-mandibular (lower jaw) and the sublingual (below the tongue). These glands situated just outside the buccal cavity secrete salivary juice into the buccal cavity.
Chemical digestion: breaks down starch by the function of salivary amylase.
Helps chewing and swallowing,
Lubricating effect: moisturizes the inside of the mouth and creates smoother speech,
Solvent effect: dissolves food and allows the tongue to taste food,
Cleaning effect: washes away food debris and bacteria remaining in the mouth,
Antibacterial effect: Lysozyme, peroxidase and lactoferrin fight against pathogenic microorganisms,
Saliva helps in the digestion of food as it contains an enzyme salivary amylase which digests starch converting it into sucrose. That is why starch when chewed leaves a sweet taste in the mouth.
Liver is the largest gland in the human body and weight about 1.5kg in an adult human being. It is located in the upper right side of the abdominal cavity. The liver is divided into right and leaf lobes, and is enclosed by a fibrous capsule. It secretes bile, which gets collected in gall bladder and is finally poured into the duodenum through the common bile duct. The bile secreted by the hepatic cells passes through the hepatic ducts and is stored and concentrated in a thin muscular sac called the gall bladder. The duct of gall bladder (cystic duct) along with the hepatic duct from the liver forms the common bile duct.
Pancreas is a reddish brown gland located in the bend of the duodenum. Pancreas has an exocrine function of producing pancreatic juice that aids in digestion. Pancreas is closely associated with the small intestine.