Pancreas Hormones: Location and Function

Pancreas produce very important hormones in our body which are required for routine normal functioning of our body at cellular level. Pancreas has 2 parts- the endocrine and exocrine part. The hormones are produced mainly by the endocrine part of the pancreas. The endocrine part of the pancreas contains numerous rounded collections of cells known as pancreatic islets or the islets of Langerhans. These are embedded within the exocrine part. There are approximately 1 million islets in the pancreas, mostly in the tail which makes up to 1-1.5% of the human pancreatic mass.

Endocrine Pancreas

Cellular structures in the Islets of Langerhans contains four types of cells which take part in the release of hormones.

• Beta cells or B cells make up the 60-70% of the total cells and make up the central core of the islet. These cells secrete insulin.
• Alpha cells or A cells form 20% of the total cells and constitute the outer rim of the islet. These cells secrete glucagon.
• Delta cells or D cells form 10% of total cells and are a source of somatostatin.
• PP cells are peripherally located and scattered amongst the alpha cells. These are a source of pancreatic peptide.

The Hormones are:

1. Insulin- It is a polypeptide hormone secreted by the beta cells of Langerhans of pancreas. Insulin is  a protien made up of 51 amino acids and there are two chains which are connected by interchain disulphide linkages. The steps of synthesis are:
   • The insulin gene directs the synthesis of pre-proinsulin , an insulin precursor.
   • Preproinsulin is cleaved to form proinsulin.
   • As the proinsulin molecule containing the A and B chain of insulin connecting peptide ( C-peptide) is guided to the golgi apparatus, disulfide linkages are formed which yield the folded proinsulin.
   • Proinsulin is cleaved in the golgi apparatus to form the active hormone insulin and a C-peptide.
   • Insulin becomes associated with zinc as the secretory granules mature.
   • The insulin molecule along with the C-peptide molecule is retained in the granule and released by exocytosis.

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Function of Insulin

• Metabolic effects of Insulin
  • On Carbohydrate metabolism, it decreases blood glucose concentration by increasing the uptake of glucose in the target cells, by increasing the glycolysis in muscle and liver and by glycogen formation. It decreases glucose production by inhibiting gluconeogenesis and glycogenolysis.
  • On lipid metabolism, it increases lipogenesis. It decreases lipolysis and reduces ketogenesis. Insulin activity promotes deposition of circulating fat into adipose tissue by activating the enzyme lipoprotien lipase in the adipose tissue.
  • Insulin decreases lipolysis by inhibiting hormone sensitive lipase activity which diminishes the delivery of the fatty acids and glycerol to the liver and peripheral tissues.
  • On Protien synthesis, It stimulates the protien synthesis by increasing the transport of amino acids into cells by increasing membrane permeability and increasing translation of messenger RNA on the ribosomes forming new protiens. Insulin also inhibits  the protien metabolism.
  • Insulin increases growth and development.

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2. Glucagon- It is secreted by A cells of islets of Langerhans and L cells of lower intestinal tract.

Functions of Glucagon-

Actions of glucagon are opposite to those of insulin. It promotes mobilization of stored nutrients such as glucose, fatty acids and keto acids and thus is a hormone of energy release.

• Metabolic effects of Glucagon:
  • Effects on Carbohydrate metabolism include increase in glycogenolysis and increased gluconeogenesis.
  • Effects on Lipid metabolism include Lipolysis ( by stimulating lipase in adipose tissue) and Ketogenesis.
  • Effects on protien metabolism include increase in the amino acid uptake of liver which promotes the gluconeogenesis.
  • Glucagon has calorigenic effect.
  • Natriuresis
  • Stimulation of secretion of growth hormone, insulin and pancretic somatostatin.

Also Read: Body Fluid Compartments and its Measurement

Exocrine Pancreas

• Exocrine pancreas contain pancreatic acini which secrete the pancreatic digestive enzyme and sodium bicarbonate which flows through a long pancreatic duct that joins the hepatic duct immediately before it empties into the duodenum.
• Pancreatic juice contains proteolytic enzymes like trypsin, chemotrypsin, carboxy polypeptidase which splits some peptides into individual amino acids.
• It secretes Pancreatic amylase which hydrolyses starch, glycogen and other carbohydrates to disaccharides and trisaccharides.
• It secretes pancreatic lipase, cholesterol esterase, phospholipase which hydrolyzes neutral fat into fatty acids and monoglycerides.
• Also secretes Large quantities of bicarbonate ions which neutralizes the acidity of the chyme emptied from the stomach into the duodenum. 

Also Read: Membrane Potentials & Resting Membrane Potential

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