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PANCREAS

BY Dr.Apeksha Panwar Department of Kriya Sharir

INTRODUCTION

Pancreas is an organ located in the abdomenIt is a dual organ having both exocrine and endocrine function.As an exocrine part it secreates pancreatic juices into the duodenum through thr pancreatic duct. This juice contains bicrbonates which neutralizes acid entering the duodenum from the stomach and digestive enzymes which break down carbohydrates , proteins and fats in food entering the duodenum from the stomach.

As an endocrine part it functions mostly to regulate blood sugar levels,

secreating

the hormone Insulin, Glucagon, Somatostatin and Polypeptide.

EXOCRINE FUNCTION OF PANCREAS

Pancreas plays a vital role in the digestive system.It does this by secreating a fluid that contain digestive enzymes into the duodenum, the first part of the small intestine that receives food from the stomach.The cells that do this are arranged in clusters called Acini.Secreations into the middle of the acinus accumulate in intralobular ducts which drain to main pancreatic duct which drain directly to duodenum.

The cells in each acinus are filled with granules containing the digestive enzymes , these are

secreated

in inactive form called zymogens.

ENDOCRINE FUNCTION OF PANCREASThe endocrine functions of pancreas is performed by Islets of Langerhans.Human pancreas contain about 1-2 million islets.Islets of Langerhans consist of four types of cells:1-Alpha cells- which secreate glucagon

2-Beta cells- which

secreate

Insulin.3-Delta cells- which

secreate

somatostatin.

4-PP cells –which

secreate

Pancreatic Polypeptide

PANCREATIC JUICE

Volume: 500-800 ml/dayReaction: Highly alkaline due to high concentration of bicarbonates.Specific gravity: 1.010-1.018Composition: It contains 99.5% water ,0.05% solidsOrganic compounds: mainly enzymes, amylase,lipase , protease and trypsin inhibitor.

Inorganic compounds: Sodium, potassium, calcium, magnesium, zinc and bicarbonates.

MECHANISM OF PANCREATIC BICARBONATE

SECREATION

FUNCTIONS OF PANCREATIC JUICE

Its main role is in digestion of proteins and lipids.It has mild digestive action on carbohydrates.Digestion of proteins is carried out by proteolytic enzymes Trypsin and chymotrypsin.Trypsin also helps in digestion of milk and in blood clotting.

STRUCTURE OF INSULIN

Insulin is a small protein, and has a molecular weight of 5808.It is composed of two amino acids connected to each other by disulphide linkages.When the two amino acids are split apart the functional activity of the insulin molecule is lost.

Insulin is synthesized in the beta cells by the usual cell machinery for protein synthesis, beginning with translation of the RNA by ribosomes attached to the endoplasmic reticulum to form

Preproinsulin

.

These

preproinsulin

is then cleaved in the endoplasmic reticulum to form a

Proinsulin

and consisting of three chains of peptides A,B,C .

Most of the proinsulin is further cleaved in the

golgi

apparatus to form insulin, composed of the A and B chain

connectedby

disulphide

linkages and the C chain peptide called connecting peptide.

The insulin and C peptide are packaged in the

secreatory

granules and

secreated

in the

secreatory

granules and

secreated

in equimolar amounts.

When insulin is

secreated

into the blood it circulates almost entirely in an unbound form, it has a plasma life that averages about 6 minutes, so it is mainly cleared from the circulation within 10 to 15 minutes.

ACTIONS OF INSULIN

On carbohydrate metabolismInsulin is the only antidiabetic hormone secreated in the body. It reduces blood sugar levels by following mechanisms:1- Increasing transport and uptake of glucose by the cells.2-Promotes peripheral utilization of glucose.3-promoting storage of glucose- Glycogenesis,4-Inhibiting Glycogenolysis.

5- Inhibiting gluconeogenesis.

On protein metabolism

Insulin facilitatesthe synthesis and storage of proteins and

inbits

cellular utilization of proteins.

On Fat metabolism

Insulin stimulates the synthesis of fats and storage in adipose tissue.

GLUCAGON

It is a hormone secreated by the alpha cells of the islets of Langerhans, when the blood glucose concentration falls.It is a large polypeptide and has a molecular weight of 3485 and is composed of a chain of 29 amino acids.

Actions of glucagon

It increases the blood sugar level .

It increases peripheral utilization of lipids.It facilitates conversion of proteins into glucose.

It inhibits

secreation

of gastric juice.

It increases

secreation

of bile from liver

Functions of Glucagon

1-On Carbohydrate metabolismIt increases Glycogenolysis in liver. It promotes gluconeogenesis in liver.2-On Protein MetabolismIt increases transport of amino acids to liver which are essential for gluconeogenesis.3-On Fat MetabolismIt has lipolytic and ketogenic effect on fat molecules.

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