Digestive Glands: Definition, Structure, Location, Functions

Digestive Glands: The digestive system, also known as the alimentary canal, and the Digestive Glands are two parts of the human digestive system. Food digestion is a complicated process in the human body. Ingestion, propulsion, mechanical or physical digestion, chemical digestion, absorption, and faeces are only a few of the activities involved. Salivary glands, liver, gastric glands, and other digestive glands are examples. To digest food, they release enzymes to surrounding target organs. Let us learn more about the many Digestive Glands that exist in the human body and their activities.

Digestive Glands Definition

Digestive glands refer to the exocrine glands which can produce digestive enzymes to digest different biomolecules of the food into their simpler forms so that they can easily be absorbed by the body.

Digestive Glands Examples

Digestive glands secrete their secretions into the nearby target organ through ducts. So, these glands are called exocrine glands.
1. Salivary Glands
a. Parotid glands
b. Sublingual glands
c. Submandibular glands
2. Gastric Glands
a. Chief cells
b. Oxyntic cells
c. Goblet cells
d. Endocrine cells
i. Gastrin cells
ii. Argentaffin cells
e. Stem cells
3. Liver
4. Pancreas
5. Intestinal glands
a. Crypts of Lieberkuhn
i. Paneth cells
ii. Argentaffin cells
b. Brunner’s gland

Digestive Glands Structure, Location and Functions

1. Salivary Glands- These are exocrine glands. There are three pairs of major salivary glands that secretes their secretions in the oral cavity. Following are the three pairs:-
a. Parotid glands
i. Largest salivary glands.
ii. Present near ears.
iii. Its duct, called Stenson’s duct, opens in the oral cavity.
b. Sublingual glands
i. Smallest salivary glands.
ii. Present beneath the tongue.
iii. Its duct called sublingual ducts or ducts of Rivinus open in the floor of the oral cavity.
c. Submandibular glands
i. Medium-sized glands.
ii. Present below the jaw.
iii. Its duct, called Wharton’s duct, opens in the oral cavity near the lower central incisor.

Functions of Salivary Gland

Salivary glands secrete saliva, which contains salivary amylase or ptyalin, lysozyme, water, electrolyte and mucus. Parotid glands secrete saliva in more quantity.
Salivary amylase is the digestive enzyme that breaks down carbohydrates into its simpler form. While lysozyme is the antibacterial agent.
Mumps is a viral disease in which one or both the parotid glands swell. It is a painful swelling.

Fig: Salivary Gland

2. Gastric Glands- There are many tubular glands present in the mucosa of the stomach.
It is of three types- cardiac glands, pyloric glands and fundic glands.
Fundic glands have three different types of cells, namely-
a. Chief Cells or peptic cells- It secretes digestive enzymes in their inactive forms called proenzymes like pepsinogen and prorennin. Gastric amylase and lipase are also secreted.
Pepsinogen is activated to pepsin which helps in the digestion of proteins. Rennin helps in milk coagulation.
Gastric amylase helps in the digestion of carbohydrate, while gastric lipase contributes in the digestion of fats.
b. Oxyntic cells or parietal cells– These cells secrete HCl and intrinsic factor of Castle.
It helps in the absorption of \(B12\) in the ileum. HCl makes the medium of the stomach acidic. These cells are numerous in the sidewalls of the gastric gland.
c. Goblet Cells– These secrete mucus and are present throughout the epithelium.
d. Endocrine cells- These are present at the base of the gastric glands.
i. Gastrin Cells– These secrete and store the gastrin hormone, which stimulates the gastric glands to secrete gastric juice.
ii. Argentaffin Cells– These produce the hormone serotonin, somatostatin and histamine. The Serotonin hormone is a vasoconstrictor. Somatostatin suppresses gastric secretion. Histamine helps in the dilation of walls of blood vessels.
e. Stem cells– These increase its number when it has to repair the damaged gastric epithelium like during ulcer or gastritis.

Cardiac glands, pyloric glands secrete mucus only.

Functions of Gastric Glands

1. It secretes gastric juice, which contains proteolytic enzymes, HCl and mucus.
2. Proteolytic enzymes like pepsin digests protein into its simpler forms.
3. HCl makes the environment of the stomach acidic which helps in killing the germs of the stomach coming along with food.
4. HCl also activates the inactive enzymes.

Fig: Gastric Glands

3. Liver- Largest gland of the body is the liver. It is present in the right side of the abdominal cavity below the diaphragm.
It has two lobes, i.e. right and left lobes. The Hepatic lobule can be called the structural and functional unit of the liver. Lobules contain hepatic cells or hepatocytes. Each lobule is surrounded by a sheath of connective tissue called Glisson’s capsule. Kupffer cells are present in the liver of mammals. These cells are phagocytic and eat worn-out cells.
Just below the liver, the gall bladder is present.
Hepatocytes secrete bile juice and transfer it to the gall bladder, through hepatic ducts, where it is stored and concentrated. Hepatic ducts from the left and right lobes join to form a common bile duct.The common hepatic duct from right and left lobes of liver and cystic duct from gallbladder joins to form a common bile duct which runs posteriorly to join the main pancreatic duct.
The pancreatic duct and bile duct open through a common hepatio-pancreatic duct into the duodenum. Its opening is guarded by a sphincter of Oddi.
Blood in the liver comes from the hepatic artery and hepatic portal vein. The hepatic artery receives oxygenated blood while the hepatic portal vein receives deoxygenated blood. Liver can regenerate.

Functions of Liver

a. Daily \(600-1200 ml\) of bile is secreted from the liver.
b. Bile helps in the emulsification of fats and makes the acidic chyme basic.
c. Liver is involved in the process of deamination, in which an amino group is removed from amino acids resulting in the formation of ammonia and ultimately urea.
d. Liver changes haemoglobin of dead RBCs into bile pigments like biliverdin and bilirubin.
e. Heparin, an anticoagulant, is produced by the liver.
f. It helps in the production of RBCs in embryos.
g. Kupffer cells of the liver act as phagocytes.

Fig: Liver, Gall Bladder and Pancreas

4. Pancreas- It is a heterocrine gland.
It is present in the loop of duodenum. It is the second-largest gland of the body, which is yellow coloured.
Its exocrine part secretes digestive enzymes while the endocrine part secretes hormones insulin and glucagon, which regulates blood sugar level.
Pancreatic juice is alkaline in nature and is carried to the duodenum through the pancreatic duct.
Pancreatic juice contains trypsinogen, chymotrypsinogen, procarboxypeptidase, which are in the inactive form. Some more enzymes like pancreatic lipase, DNAse, RNAse are also secreted.

Functions of Pancreas

a. The exocrine part of the pancreas produces chymotrypsin and trypsin to digest proteins, amylase for the digestion of carbohydrates and lipase to break down fats. Pancreatic enzymes also help in the digestion of nucleic acids.
b. The endocrine part of the pancreas releases insulin and glucagon directly into the bloodstream and helps in regulating the blood sugar levels of the body.

5. Intestinal Glands- There are several minute glands present in the mucosa of the small intestine. These are of two types:-
a. Crypts of Lieberkuhn- These are tubular, multicellular structures present throughout the small intestine between villi. These secrete digestive enzymes and mucus. Some different types of cells are found here, like paneth cells and argentaffin cells. Paneth cells are present at the bottom of the crypts of Lieberkuhn and found mostly in the duodenum. They may secrete lysozyme and are phagocytic in nature. Argentaffin cells secrete secretin hormone.
b. Only in the submucosa of the duodenum Brunner’s gland is present. It secretes mucus which protects the wall of the intestine from the acidic chyme coming from the stomach to the duodenum. The secretions of the intestine are collectively called succus entericus or intestinal juices.

Functions of Intestinal Glands

a. It secretes intestinal juice or succus entericus, which contains various enzymes such as peptidase, sucrase, maltase, lactase and intestinal lipase that helps in complete digestion of food.
b. Brunner’s gland secretes mucus lubricates the food and digestive tract and, protects the mucosa of the stomach from damage.

Summary

Digestive glands are exocrine glands and secrete their secretions through ducts to the target organs. Its examples are salivary glands, gastric glands, liver, pancreas and intestinal glands. Salivary glands secrete saliva. Gastric glands secrete HCl, pepsin, rennin and other enzymes and mucus. The liver secretes bile. The pancreas secretes pancreatic juice in the duodenum. Intestinal glands present in the small intestine secretes succus entericus or intestinal juice. These all secretions help in the digestion of complex food into its simpler form.

1. The digestive system’s two major activities are digestion and absorption.
2. Digestion is required for the breakdown of food particles into nutrients that the body uses for energy, cell repair, and development.
3. Before food and drink can be absorbed by the circulation and delivered to the cells throughout the body, they must first be transformed into smaller nutritional molecules. The nutrients in liquids and meals are broken down into carbs, vitamins, lipids, and proteins by the body.

Frequently Asked Questions (FAQs) on Digestive Glands

Q.1. Explain Digestive Glands with examples?
Ans: a. Salivary glands secrete saliva that digests carbohydrates. Saliva contains salivary amylase.
b. Gastric glands secrete pepsin to digest protein, amylase to digest sugar, lipase to digest fats and mucus to protect the lining of the stomach from the attack of HCl. HCl is also secreted by the gastric gland. Collectively the secretion of this gland is called gastric juice.
c. Liver secretes bile which helps in the emulsification of fat.
d. Pancreas secretes pancreatic juice which contains different enzymes to digest the semi -digested chyme coming from the stomach to the duodenum.
e. Intestinal glands secrete enzymes that finally digest all the semi-digested food. Or simply can be said that complete digestion of food is done by the intestinal juice.

Q.2. How many digestive glands are in the human body?
Ans: Following digestive glands are present in the body:-
a. Salivary glands
b. Gastric glands
c. Liver
d. Pancreas
e. Intestinal glands

Q.3. What is the major function of Digestive Glands?
Ans: The function of digestive glands is to digest food into its simpler form so that it can be easily absorbed by the body.

Q.4. What does the gastric glands secrete?
Ans: Gastric glands secrete gastric juices, which contain various enzymes to digest protein (pepsin), fats (lipase) and carbohydrates (amylase). Gastric juice also contains HCl, which makes the environment acidic. It also secretes mucus which protects the stomach lining from the acid attack.

Q.5. Which is the largest gland in the human body?
Ans: Liver is the largest gland in the human body.

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