Ever wondered how your body digests what you eat?

By Dr Modala Mallesh, Subject Expert Palem, Nakrekal, Nalgonda Ph. 9989535675 This article is the continuation of the previous one which focused on the digestive system and the absorption of food. In the previous article, we studied about the tongue and small intestines. Today, we will focus on large intestines and digestive glands. • The […]

By Dr Modala Mallesh,
Subject Expert
Palem, Nakrekal,
Nalgonda
Ph. 9989535675

This article is the continuation of the previous one which focused on the digestive system and the absorption of food. In the previous article, we studied about the tongue and small intestines. Today, we will focus on large intestines and digestive glands.

• The large intestine consists of caecum, colon and rectum.

• Caecum is a small blind sac which hosts some symbiotic micro-organisms.

• A narrow finger-like tubular projection, the vermiform appendix which is a vestigial organ, arises from the caecum.

• The caecum opens into the colon.

• The colon is divided into four parts – an ascending, a transverse, descending part and a sigmoid colon.

• The descending part opens into the rectum which opens out through the anus.

• The wall of alimentary canal from oesophagus to rectum possesses four layers namely serosa, muscularis, sub-mucosa and mucosa.

• Serosa is the outermost layer and is made up of a thin mesothelium (epithelium of visceral organs) with some connective tissues.

• Muscularis is formed by smooth muscles usually arranged into an inner circular and an outer longitudinal layer. An oblique muscle layer may be present in some regions.

• The sub-mucosal layer is formed of loose connective tissues containing nerves, blood and lymph vessels. In duodenum, glands are also present in sub-mucosa.

• The innermost layer lining the lumen of the alimentary canal is the mucosa. This layer forms irregular folds (rugae) in the stomach and small finger-like foldings called villi in the small intestine.

• The cells lining the villi produce numerous microscopic projections called microvilli giving a brush border appearance. These modifications increase the surface area enormously. Villi are supplied with a network of capillaries and a large lymph vessel called the lacteal.

• Mucosal epithelium has goblet cells which secrete mucus that help in lubrication. Mucosa also forms glands in the stomach (gastric glands) and crypts in between the bases of villi in the intestine (crypts of Lieberkuhn).

• All the four layers show modifications in different parts of the alimentary canal.

DIGESTIVE GLANDS

• The digestive glands associated with the alimentary canal include – the salivary glands, the liver and the pancreas.

• Saliva is mainly produced by three pairs of salivary glands – the parotids (cheek), the sub-maxillary/sub-mandibular (lower jaw) and the sub- linguals (below the tongue).

• These glands situated just outside the buccal cavity secrete salivary juice into the buccal cavity.

• The Liver is the largest gland of the body weighing about 1.2 to 1.5 kg in an adult human.

• It is situated in the abdominal cavity, just below the diaphragm and has two lobes.

• The hepatic lobules are the structural and functional units of liver containing hepatic cells arranged in the form of cords.

• Each lobule is covered by a thin connective tissue sheath called the Glisson’s capsule.

• 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.

• The bile duct and the pancreatic duct open together into the duodenum as the common hepato-pancreatic duct which is guarded by a sphincter called the sphincter of Oddi.

• The pancreas is a compound (both exocrine and endocrine) elongated organ situated between the limbs of the ‘C’ shaped duodenum.

• The exocrine portion secretes an alkaline pancreatic juice containing enzymes and the endocrine portion secretes hormones, insulin and glucagon.