Pancreas: Structure, Exocrine Part, Endocrine Part, Disorder of the Pancreas, Practice Problems and FAQs

How often have you heard that someone you know has been diagnosed with diabetes? Every 1 person out of 11 in India is diabetic. Diabetes mellitus as you know is characterised with high blood sugar levels. Any idea why is it caused? One of the main reasons is less production of the insulin hormone in the body. Do you know which endocrine gland is responsible for the secretion of this hormone? It’s the pancreas. But, wait! Isn’t the pancreas an exocrine digestive gland that secretes digestive enzymes? Yes, it is, but it also has an endocrine part that secretes hormones. Hence, it is considered to be a heterocrine gland. So which part of the pancreas is responsible for its endocrine function and which part accounts for its exocrine function? Is insulin the only hormone produced by the pancreas? What are the different enzymes it releases? Know the answers to these questions and more about the pancreas through this article.

Table of Contents

• Structure of pancreas
• Exocrine Function of the Pancreas.
• Endocrine Function of the Pancreas
• Disorder of the pancreas
• Practice Problems
• FAQs

Structure of pancreas

The pancreas is a long, tapered, leaf-like organ that is situated behind the stomach between the loop of the duodenum. It is derived from the embryo's endoderm. The head, neck, body, and tail of the pancreas are the four distinct sections of the pancreas’ anatomy. The head is located in the C-shaped region of the duodenum, whereas the body and tail extend from the C-loop of the duodenum and touch the spleen.

Fig: Pancreas

As discussed above, the pancreas has an exocrine part and an endocrine part. Let us now discuss the structure of these parts individually.

Exocrine part

The exocrine component of the pancreas, which accounts for 85% of its mass, secretes water, bicarbonate, and digestive enzymes to aid in digestion. It is made up of lobules or acini which are held together in connective tissue. Each acinus is formed of a single layer of large pyramid-shaped acinous cells that are situated around intercalated ducts.

Fig: Pancreatic Acini

These cells are responsible for the synthesis and secretion of the pancreatic juice into the intercalated ducts which drain it in the intralobular ducts which in turn join the larger interlobular ducts. The interlobular ducts join to form the pancreatic duct. The pancreatic duct joins the common bile duct (carrying bile from liver and gallbladder) and forms the hepatopancreatic duct which opens into the duodenum via a dilated hepatopancreatic ampulla or Vater’s ampulla. This opening is controlled by the sphincter of Oddi. The pancreatic juice carried by the pancreatic duct is emptied into the duodenum through this opening.

Fig: Hepatopancreatic duct

Endocrine part

There are about 1 to 2 million Islets of Langerhans in a normal human pancreas representing only 1 to 2 percent of the pancreatic tissue. The endocrine part of the pancreas is represented by patches of cells, known as the islets of Langerhans, in the exocrine part. The islets of Langerhans are formed of four types of cells -

Fig: Islets of Langerhans

Exocrine Function of the Pancreas

The pancreatic acini synthesises and secrete pancreatic juice into the duodenum which plays an important role in the digestion of carbohydrates, proteins, fats and nucleic acids present in the food. The pancreatic juice is an alkaline secretion having a pH of 7.5-8.5 and is composed of sodium bicarbonate, three inactive proteinase (protein digesting) enzymes such as trypsinogen, chymotrypsinogen, procarboxypeptidase and some active enzymes such as pancreatic amylase, pancreatic lipase (steapsin), DNase and RNase.

Function of sodium bicarbonate

The sodium bicarbonate aids in neutralising the acidic pH of the chyme (partially digested food from the stomach). The chyme is acidic as it mixes with dilute hydrochloric acid in the gastric juice of the stomach. This is a crucial step in digestion since the small intestine is not designed to survive the strong stomach acids. This is so because, unlike the stomach, the small intestine does not have a substantial layer of mucous protection. Additionally, a basic pH is necessary for the pancreas' digestive enzymes to work at their best. The pancreas secretes bicarbonate, which helps to achieve this.

Function of digestive enzymes

Digestion of carbohydrates

The pancreatic amylase catalyses the hydrolysis of remaining starch present in the chyme into disaccharides such as maltose, isomaltose and α-dextrins

Fig: Digestion of starch

Digestion of proteins

Inactive trypsinogen is converted to active trypsin by the action of enterokinase enzyme released by the Brunner’s gland in the duodenal lining. Trypsin converts proteins to smaller polypeptides.

Trypsin also activates inactive chymotrypsinogen in the pancreatic juice to active chymotrypsin which also converts proteins into smaller polypeptides.

Inactive procarboxypeptidase in the pancreatic juice gets converted to active carboxypeptidase by the action of the trypsin enzyme. Carboxypeptidase acts on the free terminal carboxylic groups of peptides and removes single amino acids from the C-terminus of the polypeptide chain.

Fig: Digestion of proteins

Digestion of lipids

The pancreatic lipase or steapsin enzyme hydrolyses fats and lipids into glycerol, fatty acids, diglycerides and monoglycerides.

Fig: Digestion of lipids

Digestion of nucleic acids

The DNase enzyme breaks DNA present in the partially digested food into deoxyribonucleotides and RNase breaks down the RNA into ribonucleotides.

Fig: Digestion of nucleic acids

Endocrine Function of the Pancreas

Disorder of the pancreas

Pancreatitis

When pancreatic enzyme secretions build up and start to break down the organ itself, it results in pancreatitis, which is an inflammation of the organ. It could be a chronic disorder that worsens over years, or it might appear as acute, painful attacks that last only a few days.

Fig: Pancreatitis

Acute pancreatitis

Acute pancreatitis is a sudden attack that causes pancreatic inflammation and is usually accompanied by severe upper abdominal pain. The pain could be severe and last for several days. Nausea, vomiting, diarrhoea, bloating, and fever are also symptoms of acute pancreatitis. It may be triggered by various factors such as bacterial or viral infections, alcohol use, gallstones, etc.

Fig: Symptoms of pancreatitis

Chronic pancreatitis

Chronic pancreatitis is a progressive disorder characterised by pancreas destruction. The disease is more common in men and usually develops between the ages of 30 and 40. Because the symptoms are similar, chronic pancreatitis may be confused with acute pancreatitis at first. Upper abdominal pain and diarrhoea are the most common symptoms. As the disease progresses, patients may experience malnutrition and weight loss. Diabetes mellitus can develop if the pancreas is destroyed in the later stages of the disease.

Fig: Severe abdominal pain is one of the symptoms of chronic pancreatitis

Diabetes mellitus

Diabetes mellitus is a chronic disease that is characterised by high blood glucose level or hyperglycaemia. Some of the common symptoms of diabetes mellitus are frequent urination, urine loaded with sugar, excessive thirst. It can be of two types -

Insulin Dependent Diabetes Mellitus or Type I Diabetes

It is caused due to hyposecretion of insulin from the beta cells of the Islets of Langerhans or absence of beta cells in the pancreas.

Insulin Independent Diabetes Mellitus or Type II Diabetes

This is an autosomal recessive disorder that is heritable in nature. It appears when cells in the body are unable to utilise the insulin which can be due to defective insulin receptors on the surface of the cells.

Pancreatic cancers

Pancreatic cancers are formed due to malignant growth of cells in the pancreatic tissues. Smoking, obesity, suffering from diabetes or chronic pancreatitis, having a family history of pancreatic cancer or pancreatitis, having hereditary disorders such as multiple endocrine neoplasia type 1 (MEN1) syndrome, hereditary nonpolyposis colon cancer, etc can increase the risk factors of pancreatic cancers.

Fig: Pancreatic cancer

Practice Problems

Q1. Which of the following cells in the pancreas might be affected if a person is suffering from high blood sugar?

A. Alpha cells
B. Acinous cells
C. Beta cells
D. Delta cells

Solution: The beta cells present in the Islets of Langerhans of the pancreas are responsible for the secretion of the insulin hormone which helps in reducing blood sugar level of the body. If the beta cells are affected, hyposecretion of insulin occurs which can result in elevated blood sugar levels. Thus, the correct option is c.

Q2. Which of the following enzymes is responsible for the activation of the trypsinogen enzyme?

A. Chymotrypsinogen
B. Enterokinase
C. Procarboxypeptidase
D. Trypsin

Solution: Trypsinogen is an inactive enzyme present in the pancreatic juice which is activated by the enterokinase enzyme when it reaches the duodenum. Enterokinase is released by the cells of the Brunner’s gland in duodenum and converts inactive trypsinogen to active trypsin which helps in breaking down proteins into smaller polypeptide chains. Thus the correct option is b.

Q3. Pancreatic amylase breaks down _____ into _____.

A. Glycogen, glucose
B. Starch, maltose
C. Sucrose, glucose
D. Lactose, maltose

Solution: Pancreatic amylase is an enzyme present in the pancreatic juice that converts the remaining starch in the partially digested food, coming from the stomach, to maltose, isomaltose and alpha dextrins. Thus, the correct option is b.

Q4. Which of the following is not a function of the glucagon hormone?

A. Glycogenolysis
B. Gluconeogenesis
C. Reducing breakdown of fatty acids and proteins in the tissues
D. Both a and b

Solution: Glucagon increases blood glucose levels by glycogenolysis (breakdown of glycogen) and gluconeogenesis (synthesis of glucose from fats and amino acids). Insulin is responsible for reducing breakdown of fatty acids and proteins in the tissues. Thus, the correct option is c.

FAQs

Q1. How much pancreatic juice is secreted by the human body everyday?
Answer: The human body secretes around 500-800 mL of pancreatic juice everyday.

Q2. What is the sphincter muscle of Boyden?
Answer: The sphincter muscle of Boyden is an aggregation of muscle fibres that guards the opening of the common bile duct into the pancreatic duct.

Q3. What are zymogens?
Answer: Zymogens are inactive precursors of enzymes which have their active sites masked by an inhibiting factor. These need activators to unmask the active sites. Examples are trypsinogen, chymotrypsinogen, pepsinogen, etc.

Q4. Which hormones control the secretion of pancreatic juice?
Answer: Secretin and cholecystokinin are two hormones that regulate pancreatic juice release. Secretin hormone aids in the regulation of the pH of the duodenum. It prevents gastric acid secretion. It also stimulates pancreatic acinar cells to release water and bicarbonate into the pancreatic ducts.