What are Digestive Glands?
o Complete digestion of food is completed with different parts of alimentary canal contributing to the process.
o The glands here secrete the digestive juices along with enzymes that helps in the chemical breakdown of food along with the physical digestion eliminating the non-digestible food.
Types and Function of Digestive Glands
o The different glands that are responsible for the secretion of enzymes and other digestive juices that assists in the process of digestion has been discussed below.
Digram Representing Digestive System and Digestive Glands
I. Salivary Glands
o There are three salivary glands present in the buccal cavity.
o It is the parotid (located one each side of the face below and in front of the ears), sublingual (located between the muscles of the oral cavity) and the submandibular (found under the tongue) glands situated.
a) Parotid Glands
o Parotid glands helps in mastication of food with saliva secreted via parotid gland and helps in swallowing.
b) Sublingual Glands
o It helps in swallowing as its secrets thick mucinous fluid moistens the oral cavity and initiate the digestion.
o It lacks striated ducts so the saliva is secreted out of rivinus ducts.
c) Submandibular Glands
o Submandibular glands are found under the tongue but the ducts open into the sublingual glands.
o The secretion consists of serous fluid and mucus.
o Around 70% of the saliva is produced by the gland.
o Saliva consists of several enzymes like amylase, lipase, urease etc. that initiates the process of digestion from mouth.
o Amylase breakdown the starch into sugar and lysozyme helps in hydrolysis.
o The pH value lies from 5.6 to 7.6.
II. Gastric Glands
o Gastric glands are located on the walls of stomach in the simple or branched tubular form.
o Gastric glands secrets about 2 to 3 litres of juice.
o As salivary glands there are three types of gastric glands namely, parietal cells provide the hydrochloric acid, chief cells help with the supply of pepsin along with rennin gastric lipase and mucous cells releases mucin.
o These are present in gastric mucosa.
o The presence of hydrochloric acid makes the pH of stomach low to 2.
o The pepsin helps in the break down of proteins into protease and peptones.
o Rennin helps in digestion of milk proteins in infants.
o There is presence of two other gland cells called argentaffin cells secrets serotonin and endocrine cells triggers the secretion of enzymes.
III. Liver
o It is known as the largest gland of the body situated on right side of the upper abdominal cavity.
o There is a pear-shaped structure present in the liver called gall bladder.
o Gall bladder stores the bile secreted from liver and acts as reservoir.
o Hepatic duct of the liver with gall bladder forms the bile duct.
o Bile duct with the pancreatic duct open together at the duodenum of the small intestine.
o Bile is responsible to turn chyme turn alkaline so that pancreatic juice can act upon it. Also, bile helps in the emulsification of fats.
o Other functions of bile are as follows;
a) Regulation of Blood Sugars
The process of glycogenesis takes place in the liver that is the conversion of glycogen into glucose with the help of glucagon.
o It also helps in process of gluconeogenesis.
o The process of lipogenesis takes place here that is the conversion of excess glucose and amino acids into fats.
b) Maintenance of Body Temperature
o Liver is responsible for high metabolic activity due to which high levels of heat is released hence helps maintaining the body temperature.
c) Immunological Functions
o Kupffer cells of liver works as phagocytes. Through the phagocytosis process they feed upon dead cells and bacteria.
d) Vitamin Synthesis
o Liver is responsible for the synthesis of vitamin A from beta carotene.
o It also helps in the storage of vitamin A, D, E, K, iron and copper along with glycogen, fats and water.
IV. Pancreas
o Pancreas is located behind the stomach lying horizontally in the curve of duodenum with the length of 12 – 15cm long and 2.5cm wide.
o Pancreas is both exocrine as well as endocrine in nature.
o The pancreatic juice rises the pH to 8.8. and releases 800mL of pancreatic juice every day.
o The juice consists of three different proenzymes called chymotrypsinogen, procarboxypeptidase, trypsinogen and other enzymes like pancreatic amylase, lipase, nuclease.
o The endocrine tissue of pancreatic has group of cells, islets of Langerhans that has following cells;
a) Alpha Cells
o Alpha cells produce glucagon that helps liver with the conversion of glycogen to glucose. Alpha cells form the 25% of the islets of Langerhans.
b) Beta Cells
o Insulin is supplied by the beta cells that helps in conversion of glucose into glycogen in liver and muscles.
o They constitute the 60% of cells and deficiency of insulin causes diabetes mellitus.
c) Delta Cells
o Delta cells forms the 10% of islets of Langerhans and produces the somatostatin hormone that controls the secretion of glucagon from alpha and insulin from beta cells.
d) Pancreatic Polypeptide Cells
o Pancreatic polypeptide cells inhibit the secretion of pancreatic juice when needed.
V. Intestinal Glands
o There is presence of microscopic glands present in the mucosa of small intestine but the major glands are crypts of lieberkuhn and Brunner’s gland.
a) Crypts of Lieberkuhn
o Crypts of lieberkuhn is a finger like projection called villi are the location for these glands and releases the digestive enzymes and mucus with alkaline in nature with pH of 7.5 to 8.0.
o These juices have enzymes like aminopeptidase, maltase, nucleotidases, enterokinases, lactase, sucrase, intestinal lipase and many others that helps in the digestion of all kinds of food molecule.
b) Brunner’s Gland
o Brunner’s glands are responsible for the secretion of mucus that helps to adhere the food together and lubrication.
o Mucus helps in the protection of mucosa from all the enzymes. Brunner’s glands are branched tubular gland restricted to the duodenum.
You may like to read;
Krebs Cycle: Definition, Diagram, Steps, and Mechanism
Human Digestive System: Diagram, Parts and Function
Alimentary Canal: Diagram, Parts and Function
Mitochondria: Function, Definition, Significance, and Facts
Digestive Glands Citations
- The secretion, components, and properties of saliva. Annu Rev Food Sci Technol . 2013;4:267-76.
- Structure, development and evolution of the digestive system. Cell Tissue Res . 2019 Sep;377(3):289-292.
