PANCREAS

  PANCREAS:

·         It is a composite gland that acts as both exocrine as well as endocrine gland. The exocrine function of the pancreas involves the synthesis and secretion of pancreatic juices. The endocrine function resides in the islets of langerhans of the pancreatic beta cells which secrete insulin that helps in controlling the metabolism of carbohydrates. Alpha cells secrete glucagon that counters the action of insulin.

·         Around 95% of the pancreas has exocrine tissue. It produces pancreatic enzymes to aid digestion.

          ·         A healthy person makes about 2.2 litres of these enzymes every day. The remaining 5% comprises of 100s of 1000s of endocrine cells called islets of langerhans. The grape like cell-clusters produces important hormones that regulate pancreatic secretions and control blood sugar.

·         It originates from the endoderm of the embryo.

·         The exocrine tissue secretes a clear, watery, alkaline juice that contains several enzymes. This breakdown food into small molecules that can be absorbed by the intestines. The enzymes includes:

                     i.            Trypsin and Chymotrypsin to digest proteins

                   ii.            Amylase for the breakdown of carbohydrates

                  iii.            Lipase, to breakdown fats into fatty acids and cholesterol

·         The endocrine portion is islets of langerhans which secrete insulin and other hormones. There are bout 1-2 million islets of langerhans in a normal human pancreas representing only 1-2 % of the pancreatic tissue.

 

Location:

It lies below the stomach; in the loop of duodenum.

Structure:

·         Pancreas is about 6-8 inches long gland which extends horizontally across the duodenum.

·         The largest part lays on the right side of the abdomen where the stomach attaches to the first part of the small intestine, the duodenum. At this point, the partially digested food passes from the stomach into the small intestine and it mixes with the secretion from the pancreas.

·          It is elongated yellowish gland that that consists of large number of acini and ducts.

·         A duct runs the length of the pancreas and it is joined by several small branches from the glandular tissue. The end of this duct is connected to a similar duct that comes from the liver which delivers bile to the duodenum.

·         Besides these, pancreas consists of 1-2 millions of small group of specialized cells called islets of langerhans. This is so called after the name of their discoverer Paul Langerhans in 1969.

                           

·         In normal human pancreas, these cells represent only 1-2% of the pancreatic tissue.

·         Each islet consists of major two types of cells as-

         i.            Alpha cells: It comprises of about 25%; secretes a peptide hormone called Glucagon.

       ii.            Beta cells: It comprises of about 60%, secretes another peptide hormone called insulin.

                        

Hormones:

Glucagon and insulin have antagonistic affect on blood glucose level. They can be explained as follows:

         i.            Glucagon:

·         Glucagon is a hormone produced by the alpha cells of the pancreas known as islets of langerhans.

          Glucagon is known as hyperglycemic hormone because it reduces the cellular glucose uptake and utilization.

·         This peptide hormone plays an important role in maintaining the normal blood glucose levels.

·          It brings about change of liver glycogen to blood glucose. When blood sugar falls, pancreatic alpha cells release hormone glucagon. 

·         Glucagon causes glycogen to be breakdown into glucose in the liver. Glucose then enters bloodstream restoring blood sugar levels to normal.

·         Glucagon plays an active role in allowing the body to regulate the utilization of glucose and fats.

·         Glucagon is released in response to low blood glucose levels and to create whereby the body needs additional glucose such as in response to vigorous exercise.

Function of Glucagon:

a)      It acts mainly on liver cells (hepatocytes) and stimulates glycogenolysis, which results in an increased blood sugar known as hyperglycaemia.

b)      It also stimulates the process of gluconeogenesis (conversion of amino acid into glucose) which also contributes to hyperglycaemic glucagon known as hyperglycaemic hormone because it reduces cellular glucose uptake and utilization.

c)       It reduces glycogenesis and also enhances lipolysis.

d)      Glucagon also stimulates the secretion of insulin from beta cells by the paracrine effect.

e)      It helps in the breakdown of triglycerides (stored fat) into fatty acid for use as fuel by the cells.

f)       Glucagon serves to keep blood glucose levels high enough for the body to function well.

                                            

      ii.            Insulin:

·         Insulin is a hormone or chemical messenger made by pancreas that allows our body to use sugar (glucose) from carbohydrate in the food that we eat for energy or to store glucose for future use.

·          Insulin helps keep our blood sugar level from getting too high (hyperglycaemia) or too low (hypoglycaemia).

·         The pancreatic beta cells release insulin, when the blood sugar tends to increase. The beta cells of the pancreas are stimulated by the glucose. As glucose levels rise in the plasma of the blood, uptake and metabolism by the pancreas beta cells are enhanced leading to insulin secretion.

·         This peptide hormone plays an important role in the regulation of glucose level in the blood. It mainly acts on hepatocytes (liver cells) and adipocytes (cells of adipose tissue), increasing the cellular glucose uptake and utilization. As a result, the movement of glucose takes place rapidly from blood liver cells of adipose tissues by decreasing the blood glucose level (hypoglycaemia).

·         Insulin acts as a powerful anabolic hormone.

·         Insulin has two modes of actions on the body, an excitatory and inhibitory one.

Function of Insulin:

a)      Insulin moves glucose from the blood into muscles and other tissues for use as energy.

b)      It helps the liver to absorb glucose and storing it as glycogen in case the body needs energy during stress or exercise.

c)       Insulin stimulates glucose uptake and lipid synthesis.

d)      Insulin inhibits the breakdown of lipids, proteins and glycogen.

e)      It also inhibits the glucose pathway (gluconeogenesis) and production of ketone bodies (ketogenesis). 

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