14 Human Nutrition - part 03 - Digestive Glands

 


14 Human Nutrition - part 03 - Digestive Glands

Digestive Glands :

  • The digestive glands associated with the alimentary canal include 
  1. the salivary glands
  2. liver 
  3. pancreas.

Salivary glands : 

  • There are three pairs of salivary glands which open in buccal cavity.
  • Parotid glands are present in front of the ear. 
  • The submandibular glands are present below the lower jaw. 
  • The glands present below the tongue are called sublingual. 
  • Salivary glands are made up of two types of cells.
  1. Serous cells
  2. Mucous cells
  • Serous cells secrete a fluid containing digestive enzyme called salivary amylase. 
  • Mucous cells produce mucus that lubricates food and helps swallowing.

Liver : 


  • This dark reddish-brown coloured gland is present just below the diaphragm. 
  • It occupies the right upper portion of the abdominal cavity. 
  • It is the largest gland of the body. 
  • It weighs about 1.2 to 1.5 kg in an adult human being. 
  • Each lobe of this bilobed gland is covered by thin covering called Glisson's capsule. This capsule is made up of connective tissue. 
  • Each lobe is divided into several structural and functional units of liver called hepatic lobules.
  • Each hepatic lobule is polygonal in shape. 
  • At the junction of adjacent lobules a triangular portal area is present. In this portal area a branch of each of hepatic artery, hepatic portal vein and bile duct is present.
  • A lobule consist of cords of hepatic cells which are arranged around a central vein.
  • In between the cords of hepatic cells, spaces called sinusoids are present through which the blood flows. 
  • In the sinusoids, phagocytic cells called Kupffer cells are present.
  • These cells destroy toxic substances, dead and worn-out blood cells and microorganisms. Hepatic cells produce bile juice. 
  • It is collected and carried through bile duct and stored in sac like gall bladder. 
  • The duct of the gall bladder and hepatic duct together form common bile duct.
  •  Liver is a vital organ.
  • Bile juice secreted by liver emulsifies fats and makes food alkaline.
  • Liver stores excess of glucose in the form of glycogen. 
  • Deamination of excess amino acids to ammonia and its further conversion to urea takes place in liver. 
  • It is also involved in synthesis of vitamins A, D, K and B12. 
  • Liver also produces blood proteins like prothrombin and fibrinogen. 
  • During early development, liver acts as haemopoietic organ. Kupffer cells help in detoxification process and destruction of old RBCs.

Pancreas : 


  • Pancreas is a leaf shaped heterocrine gland present in the gap formed by bend of duodenum under the stomach. 
  • Exocrine part of pancreas is made up of acini. 
  • Acinar cells secrete alkaline pancreatic juice that contains various digestive enzymes. 
  • Pancreatic juice is collected and carried to duodenum by pancreatic duct.
  • The common bile duct joins pancreatic duct to form hepato-pancreatic duct. It opens into duodenum. 
  • Opening of hepato-pancreatic duct is guarded by sphincter of Oddi. 
  • Endocrine part of pancreas is made up of groups of cells called islets of Langerhans present between the acini. 
  • Islets contain three types of cells. 
  1. α-cells secrete glucagon
  2. β-cells secrete insulin and 
  3. somatostatin hormone is secreted by δ-cells. 
  • Glucagon and insulin together control the blood-sugar level.
  • Somatostatin hormone inhibits glucagon and insulin secretion.

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