#Pancreas

#Biology

#HumanOrgans

Introduction

• The pancreas is a vital organ located in the abdomen, playing a key role in digestion and blood sugar regulation by producing insulin and digestive enzymes.

• This glandular organ is situated behind the stomach and spans across the abdomen, with distinct sections referred to as the head, body, and tail.

• Functionally, the pancreas serves as both an endocrine gland and an exocrine gland.

• As an endocrine gland, the pancreas is part of the endocrine system. As such, it releases hormones, such as insulin, directly into the bloodstream for transport to cells throughout the body.

  
  

• As an exocrine gland, the pancreas is part of the digestive system. As such, it releases digestive enzymes into ducts that carry the enzymes to the gastrointestinal tract where they assist with digestion. In this concept, the focus is on the pancreas as an endocrine gland.

The Pancreas as an Endocrine Gland

• The tissues within the pancreas that have an endocrine role exist as clusters of cells called pancreatic islets.

• There are approximately 3 million pancreatic islets, and they are crisscrossed by a dense network of capillaries.

  
  

• The capillaries are lined by layers of islet cells that have direct contact with the blood vessels, into which they secrete their endocrine hormones.

• The capillaries are lined by layers of islet cells that have direct contact with the blood vessels, into which they secrete their endocrine hormones.

  The inset diagram shows pancreatic islet cells that produce endocrine hormones.

  
  

• The pancreatic islets consist of four main types of cells, each of which secretes a different endocrine hormone. However, all of the hormones produced by the pancreatic islets play crucial roles in glucose metabolism and the regulation of blood glucose levels, among other functions.

  1. Islet cells called alpha (α) cells secrete the hormone glucagon; low blood glucose levels stimulate its release. The function of glucagon is to increase the level of glucose in the blood. It does this by stimulating the liver to convert stored glycogen into glucose, which is released into the bloodstream.

  2. Islet cells called beta (β) cells, which make up approximately 75 percent of each islet, secrete the hormone insulin. Elevated blood glucose levels stimulate the release of insulin. The function of insulin is to decrease the level of glucose in the blood. It does this by promoting the absorption of glucose from the blood into fat, liver, and skeletal muscle cells. In these tissues, the absorbed glucose is converted into glycogen, fats (triglycerides), or both.

  3. Islet cells called delta (δ) cells secrete the hormone somatostatin. This hormone is also called the growth hormone inhibiting hormone because it inhibits the anterior lobe of the pituitary gland from producing growth hormone. Somatostatin also inhibits the secretion of the pancreatic endocrine hormones glucagon and insulin and pancreatic exocrine enzymes.

  4. Islet cells called gamma (γ) cells secrete the hormone pancreatic polypeptide. The function of pancreatic polypeptide is to help regulate the secretion of both endocrine and exocrine substances by the pancreas. It is thought to play a role in appetite, as well as in the regulation of pancreatic exocrine and endocrine secretions. Pancreatic polypeptide released following a meal may reduce further food consumption; however, it is also released in response to fasting.