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1800-102-2727The moment you hear of, see or even think of noodles, manchurian, cakes, chocolates, or anything delicious, your mouth starts watering. Have you ever wondered where this water comes from and what it actually is? This watery substance in our mouth is known as saliva. This comes from the salivary glands that are situated in different locations in the mouth. Similarly, there are various types of glands present in the digestive system that aid in the process of digestion. Digestion is the process by which large food molecules are broken down into smaller ones. These smaller molecules are absorbed by the various tissues. The digestive system of humans is composed of two parts: alimentary canal and digestive glands. In this topic, we will discuss various types of digestive glands.
Digestive glands are the specialised structures that secrete digestive juices that help in the process of digestion.
There are two types of digestive glands:
The accessory glands are associated with the alimentary canal but are not a part of the alimentary canal. They are exocrine glands and have ducts to carry out their secretions. There are three types of accessory digestive glands:
Salivary glands secrete saliva into the buccal cavity. Three pairs of salivary glands are present at different locations.These are:
‘Par’ means near and ‘-otid’ means ear. They are located just in front of each ear. These are the largest salivary glands and contribute around 10% of the saliva. The duct of the parotid gland is known as the Stenson’s duct.
These glands are located at the angles of the lower jaw. These glands are considered as the second largest salivary gland and contribute 70% to the saliva. The duct of the submandibular gland is known as the Wharton’s duct.
‘Sub’ means below and ‘lingual’ means tongue. These are located below the tongue and are considered as the smallest salivary glands. These glands contribute 5% to the saliva. The ducts of sublingual glands are known as the ducts of rivinus.
Saliva is a watery substance produced in the mouth. Around 1-1.5 L of saliva is secreted per day. It is slightly acidic (6.8 pH). Components of saliva are as follows:
There is a disease known as Sjögren's Syndrome that affects some people. The major symptoms of Sjögren's syndrome include dryness of mouth and eyes. People affected by this also suffer from a decreased sense of taste and sometimes they cannot sense any taste. This is probably due to the dryness of the mouth. Dryness of the mouth reduces the amount of saliva that is very important for the sensation of taste.
Liver is considered as the largest gland of the human body (weight: 1.2-1.5 kg in adults). It plays a crucial role in digestion. It is located in the upper right side of the abdominal cavity. It has two lobes- right and left. These lobes are separated by a falciform ligament.
Each lobe of the liver is divided into lobules. Lobules are the structural and functional units of the liver. Lobules are covered with a thin connective tissue called Glisson’s capsule. Glisson’s capsule is a characteristic feature of the mammalian liver. Cells of the liver are known as hepatocytes.
Hepatocytes are arranged in the form of cords known as hepatic cords. The space present between the adjacent hepatic lobules is known as hepatic sinusoid. Blood flows through these spaces. Sinusoids are lined by endothelial cells. In some places, macrophages are present called Kupffer cells.
Bile is secreted by the liver cells or hepatocytes. It is stored in the gallbladder. Gallbladder is a pear-shaped organ attached to the posterior surface of the liver by the connective tissues. It acts as a concentrating reservoir for bile.
The liver performs various functions that are enlisted below:
Pancreas secretes enzymes as well as hormones. Externally, the pancreas is divided into four parts: Head, Neck, Body and Tail. Head is present in the curve of duodenum.
The exocrine part of the pancreas which is the internal part consists of rounded lobules known as acini. The acinar cells secrete an alkaline pancreatic juice which helps in digestion. The pancreatic juice has a pH: 8.4. Around 500-800 mL of pancreatic juice is secreted per day.
The pancreatic juice is composed of sodium bicarbonate and enzymes such as trypsinogen, chymotrypsinogen, procarboxypeptidase, pancreatic lipase, DNase and RNase.
The pancreatic juice and the bile are transported to the duodenum of the small intestine through various ducts:
The bile is stored in the gallbladder which is then transported into the common bile duct. Common bile duct is formed by the joining of the hepatic duct (duct of the liver) and the cystic duct (duct of the gallbladder). The bile is reached to the hepato-pancreatic duct from the common bile duct. Hepato-pancreatic duct is formed by joining the common bile duct and the pancreatic duct. The bile flows through the hepato-pancreatic duct and reaches the duodenum.
There are two types of digestive glands that are present within the alimentary glands:
Ever had a burning sensation in the chest after gobbling down lots of spicy food? Do you know why spicy food causes such heartburn? It is caused due to the acids released by one of the major organs of the digestive system, the stomach. The gastric glands of the stomach are responsible for this.
The gastric glands are tubular glands formed by the epithelium of the stomach. These glands secrete enzymes necessary for digestion.
There are several cells that make up the gastric glands:
These cells secrete enzymes in their inactive form. Inactive precursor of an enzyme is known as zymogen. Secretions of chief cells help in the breakdown of proteins. The opening of this gastric gland is known as the gastric pit.
These cells secrete hydrochloric acid. HCl provides an acidic medium for the activation of pepsinogen. These cells also secrete the castle's intrinsic factor. The intrinsic factor helps in the absorption of vitamin B12.
These cells are present throughout the medium and secrete mucus. Mucus protects the lining of the stomach from strong acids.
These cells are situated at the basal part. They are of two types:
In the small intestine, epithelial cells are modified into glands. There are two types of glands present in the small intestine:
Brunner’s glands are located in the submucosal layer of the duodenum. They synthesise and secrete non enzymatic and alkaline secretion of intestinal juice. They also secrete mucus which protects the duodenal wall from getting digested. They open into the crypts of Lieberkuhn.
These are simple and tubular structures which are located throughout the small intestine between the villi. Several types of cells are found in the lining:
Q1. Which of these glands is located in front of the ear?
Solution: ‘Par’ means near and ‘-otid’ means ear. The parotid glands are salivary glands located just in front of the ear. It is the largest salivary gland. It contributes 10% of the saliva produced. Hence, the correct option is a.
Q2. Match the following:
Column I |
Column II |
A. Parietal cells |
1. Secretes serotonin |
B. Argentaffin cells |
2. Secretes mucus |
C. Goblet cells |
3. Secretes HCl |
Solution: Parietal cells secrete hydrochloric acid which provides an acidic medium for the activation of pepsinogen. These cells also secrete the castle's intrinsic factor which helps in the absorption of vitamin B12.
The argentaffin cells in the stomach secrete the vasoconstrictor serotonin.
The goblet cells secrete mucus that protects the stomach lining from the HCl.
Hence, the correct option is b.
Q3. Common bile duct and pancreatic duct are joined to form which of the following ducts?
Solution: Hepato-pancreatic duct is formed by joining the common bile duct and the pancreatic duct. The bile flows through the hepato-pancreatic duct and reaches the duodenum. Hence, the correct option is c.
Q4. Which of the following is not one of the functions of the liver?
Solution: The G cells of the stomach release the hormone gastrin which promotes the release of HCl from the oxyntic or parietal cells of the stomach.
Thus, the correct option is c.
Question 1. How many types of accessory digestive glands are there?
Answer. There are three types of accessory digestive glands present in the human body. These are enlisted below:
Question 2. How many types of salivary glands are present in the human body?
Answer. There are three types of salivary glands present in the human body. These are present in different locations that are enlisted below;
Question 3. How many types of cells make up the gastric glands?
Answer. There are four types of cells that collectively make up the gastric glands. These are:
Question 4. What is the composition of pancreatic juice?
Answer. The composition of pancreatic juice is: