Pancreas

The pancreas (Latin: pancreas) is an organ that is a part of two different systems – the digestive system and the endocrine system. The pancreas is an internal and external secretion gland. The pancreas has two parts – exocrine and endocrine parts. Both of these parts secrete hormones and enzymes that help digestion. Pancreas exocrine function helps digestion, while the endocrine function is responsible for regulating blood sugar. The pancreas is located in the abdomen behind the stomach. It is positioned slantwise at the back wall of the abdomen.

Pancreas anatomy 

The pancreas weighs approximately 60-100 grams; the length is 12-15 cm, thickness 2-3 cm. The longitudinal axis of the pancreas goes from the right side to the left side, from the bottom to the top. It is surrounded by other abdominal organs like the small intestine, spleen, and liver. The pancreas is situated in the epigastric region and the hypochondriac region

The peritoneum covers the pancreas only from the anterior aspect, meaning that the pancreas is located retroperitoneally. The pancreas is shaped like a flat pear or a fish. The pancreas has two main ducts – the pancreatic duct and the accessory pancreatic duct. The pancreatic duct goes through the pancreas parallel to the gland's longitudinal axis. It connects to the common bile duct in the posterior wall of the descending part of the duodenum. This connection creates an extension the ampulla of Vater, which has a small opening - major duodenal papilla - that opens in the duodenum. Oddi sphincter, which is made of m. sphincter ampullae hepatopancreaticae surrounds the small opening. 

The muscles relax after the food enters the duodenum and through this space, bile and pancreatic juice flows into the duodenum. The opposite happens when there is no food in the duodenum, then the muscle contracts, and the opening closes. In the same region where the pancreatic duct opens there is an opening of the accessory pancreatic duct - the minor duodenal papilla - in the back wall of the duodenum; this duct releases pancreatic juice from the head of the pancreas. 

Parts of the pancreas 

The pancreas has four parts: headneck, body, and tail

The head of the pancreas 

The head of the pancreas is the widest part of the pancreas. The head is located within the curvature of the duodenum. The location is significant as this is also where the stomach comes into contact with the first part of the small intestine, meaning that this is where digestive enzymes are released from the pancreas through the major and the minor duodenal papillae.  The head of the pancreas is flat, so it has only two surfaces: the anterior surface and posterior surface. The head is situated at the level of the second lumbar vertebrae. The head has an uncinate process that is a projection from the inferior part of the head. 

In front of the head are the peritoneum and the transverse colon, and the transverse mesocolon that is a meso-fold of the peritoneum. Behind the head sits the inferior vena cava, portal vein, and the common bile duct. To the right, the left, and below the head of the pancreas is surrounded by the duodenum. 

The neck of the pancreas

The neck of the pancreas continues from the right upper part of the front of the head. It is directed upwards and forwards. Then again upwards and changes into the body to the left. In front of the neck lies pylorus of the stomach. Posteriorly to the neck are the superior mesenteric vessels, also posteriorly the superior mesenteric vein and the splenic vein connect to form the portal vein. 

The body of the pancreas

The body of the pancreas is the largest part of the pancreas. It lies behind the stomach. The body of the pancreas crosses the vertebral column. It has a triangular form with three surfaces and three margins:

  • Anterosuperior surface
  • Posterior surface
  • Anteroinferior surface
  • Superior margin
  • Inferior margin
  • Anterior margin

The body of the pancreas crosses the spine from the right to the left side at the level of the first lumbar vertebrae. In front of the body lies the stomach and the transverse colon. Posteriorly to the body are the abdominal aorta, the coeliac plexus, the splenic vein, and the left kidney with the left renal artery, as well as the beginning of the superior mesenteric artery. Below the body of the pancreas sits the duodenojejunal flexure, the jejunal loops, and the left colic flexure. On the top of the superior margin goes the splenic artery, while next to the anterior margin lies the transverse mesocolon.

The tail of the pancreas 

The body of the pancreas without any particular border changes into the tail of the pancreas. The same as the body, also the tail of the pancreas has a triangular form with the same three surfaces and three margins. The tail ends at the level of the tenth rib. The tail of the pancreas lies between the layers of the splenorenal ligament. The organs surrounding the tail are the same as for the body of the pancreas. 

From the frontal side, there are the stomach and the transverse mesocolon. Behind the tail of the pancreas lies the abdominal aorta, the coeliac plexus, the splenic vein, and the left kidney. Below it sits the duodenojejunal flexure, the jejunum loops, the left colic flexure. The splenic artery passes its superior margin, and next to the anterior margin lies the transverse mesocolon. Laterally to the tail lies the hilum of the spleen.

Vasculature and innervation of the pancreas 

The pancreas is an organ rich in blood supply. As the pancreas is both an endocrine and exocrine organ, the innervation for both functional parts differs.

Arterial supply 

The vessels in the pancreas originate from the coeliac artery and superior mesenteric arteryThe splenic artery and its branches supply the pancreas. The splenic artery branches from the coeliac artery and runs along the top of the pancreas. The splenic artery supplies the left part of the body and the tail of the pancreas via its pancreatic branches. The biggest branch is called the grater pancreatic artery. 

The head of the pancreas is supplied by the superior and inferior pancreaticoduodenal arteries that run along the posterior and anterior surfaces of the head of the pancreas. These two arteries are branches of the gastroduodenal artery (from the coeliac trunk) and superior mesenteric arteries, accordingly. The pancreaticoduodenal arteries join to form an anastomosis in the middle.

Venous drainage 

Venous drainage of the body and the tail of the pancreas is provided by the splenic vein. The head of the pancreas drains into the pancreaticoduodenal veins that change into the superior mesenteric and portal veins.

Innervation 

The pancreas receives its involuntary innervation from the autonomic nervous systemThe sympathetic innervation rises from the greater and lesser splanchnic nerves originating from the T5-T12 level of the spinal cord. Its parasympathetic innervation comes from the vagus nerve, the tenth cranial nerve. Both parasympathetic and sympathetic fibers continue to the celiac ganglion and superior mesenteric plexus

The acinar cells and the pancreatic islets inside of the pancreas also receive nerve signaling. The parasympathetic system incites secretion of pancreatic juice, insulin, and glucagon from acinar cells, while the sympathetic system is responsible for inhibition of pancreatic juice, exocrine secretion. At the same time, sympathetic fibers inhibit the release of insulin while stimulating the release of glucagon. 

Lymphatic drainage 

Lymph from the body and tail of the pancreas is drained into splenic lymph nodes and then to the lymph nodes in front of the aorta. From the head, lymph is drained into pyloric lymph nodes and eventually also in the same lymph nodes in front of the aorta. From these lymph nodes, lymph travels to the superior mesenteric or celiac lymph nodes.

Microanatomy of the pancreas 

As the pancreas has both endocrine and exocrine functions, the cells of this organ can be divided based on their roles.

Exocrine cells 

The majority of the cells are responsible for the digestive, exocrine function. These cells are called acinar cells because they form clusters (acinus) around small ducts. The clusters form lobes that have fibrous walls. Acinar cells secrete digestive enzymes like trypsin and chymotrypsin to digest proteins, amylase to digest proteins, and lipase to digest fats. 

The enzymes are secreted in the small ducts surrounding the acinar cells. The acinar cells have a pyramid form and are located around the intercalated ducts. The intercalated ducts eventually change into intralobular ducts that drain into interlobular ducts. After draining through the system of ducts, the pancreatic juices end up in the pancreatic duct. In the ducts, cells are no longer pyramid-shaped; they are column-shaped and can be seen in more than one layer of cells.

Endocrine cells 

The endocrine function is done by pancreatic cells that form pancreatic islets, also known as islets of Langerhans. Cells are divided into alpha cells, beta cells, delta cells, gamma cells, and epsilon cells. Each cell group is responsible for its hormone. Based on their hormone, their location in the islet is also different. 

Alpha cells secrete glucagon and are located in the islets' periphery, around 15-20% of all cells in the islets. Beta cells secrete insulin and are located throughout the islets; they are also increased in numbers compared to alpha cells, around 65-80%.  Delta cells are responsible for the release of somatostatin and are also located in the islets periphery and form only 3-10% of all the cells in the islets. Only 3-5% of the cells in the islets are gamma cells. These cells produce pancreatic polypeptide, which regulates both endocrine and exocrine functions. 

The least represented cells in the islets are epsilon cells, less than 1% of all cells in the islets that secrete ghrelin. Apart from other released hormones, ghrelin is a protein that stimulates hunger. Pancreatic islets have many small arterioles to receive blood supply for efficient secretion and venules for the hormones to drain into the circulation. The signaling way in the pancreatic islets is paracrine

The feedback system in the islets depends on the other islet cells and their produced hormones. After release, insulin activates other beta cells but inhibits alpha cells. Glucagon activates other alpha cells, then that process leads to the activation of beta cells and delta cells. Somatostatin inhibits other cells. 

Functions of the pancreas

The pancreas has two main functions: endocrine or blood sugar control and exocrine or digestive. 

Pancreas function in the digestive system 

The pancreas' function in the digestive system is to help to break down food components. Acinar cells secrete enzymes that aid digestion. As mentioned above, these enzymes are trypsin and chymotrypsin for digesting proteins, amylase for digesting carbohydrates, and lipase to break down fats. Pancreas enzymes are secreted into intercalated ducts then into intralobular and interlobular ducts, ending in the pancreatic duct

Pancreas enzymes are secreted as proenzymes that are inactive and are activated by enterokinase present in the duodenum. The pancreatic duct joins with the common bile duct and forms the ampulla of Vater that opens in the duodenum. The pancreatic juices, enzymes, are mixed with bile from the common bile duct, and this mix is released in the duodenum to help digest fats, proteins, and carbohydrates. 1.5-3 liters of secrete is produced every day.Even though the pancreatic islets secrete ghrelin and pancreatic polypeptide, they take part in the digestive function. In contrast, somatostatin, also secreted by the pancreatic islets, takes part in both processes. 

Ghrelin, apart from other hormones stimulated from the islets, is a protein that stimulates hunger. The stomach mostly secretes ghrelin, but as mentioned before also small amounts are secreted by the pancreatic islets. Ghrelin stimulates appetite leading to an increased food intake and fat storage. Ghrelin levels are increased before eating and during fasting. After eating, ghrelin levels decrease. Somatostatin and other hormones released in the digestive tract inhibit ghrelins release.

The release of pancreatic polypeptide is stimulated by eating, exercising, and fasting. It inhibits the secretion of pancreatic enzymes while stimulating the secretion of gastric juice. 

The role of the somatostatin in the digestive system is to decrease gastric emptying rate by reducing smooth muscle contractions and blood flow within the intestine. The hormone also inhibits the secretion of pancreas enzymes. 

Pancreas function in the endocrine system 

The function of the pancreas within the endocrine system is to release hormones into the bloodstream. Insulin and glucagon are the main hormones released from the islets. These hormones are responsible for maintaining normal blood glucose levels. Blood glucose level is the initiator of these hormones. 

When the blood glucose levels are low, it sends a signal to alpha cells in the islets to produce their hormone, glucagon, and elevate the blood glucose level. Additionally, also low insulin levels and exercise can initiate the release of glucagon. Glucagon acts on the liver receptors and stimulates the liver to convert glycogen, from the liver, into glucose and release glucose into the bloodstream, thus elevating the blood glucose level. This process is called glycogenolysis, as glycogen is being broken down. 

When the liver's storage of glucose slowly empties, glucagon stimulates the liver and kidneys to make more glucose in a process called gluconeogenesis. At the same time, glucagon can shut off glycolysis in the liver and can induce lipolysis, which is glucose production from fat. Also, glucagon decreases the uptake of glucose in fat and muscle to elevate the blood glucose level. 

In opposite, when the blood glucose levels are high, beta cells get activated, and they start to release their hormone, insulin, to decrease the blood glucose level. Insulin's primary function is to change blood glucose into glycogen through a process called glycogenesis happening in the liver and muscle cells. Beta cells hormone works by making cells to uptake glucose, especially skeletal muscle cells, to decrease the blood glucose level. Insulin also works as an inhibitory hormone to stop gluconeogenesis and promote the storage of glucose in fay by inhibiting lipolysis. 

Not only blood glucose levels, insulin levels, and exercise affect the release of these hormones. Amino acids also can stimulate the release of insulin and glucagon. Somatostatin, which is secreted by delta cells in the islets, inhibits insulin and glucagon release. The sympathetic nervous system can also stimulate secretion of insulin and glucagon through activation of beta-2 receptors by catecholamines, while activation of alpha-1 receptors inhibits insulin and glucagon secretion from the islets. Stimulation of muscarinic acetylcholine receptors (M3) from the vagus nerve's parasympathetic nervous system stimulates insulin release from beta cells in the islets. 

Somatostatin can affect the endocrine and exocrine parts. Its endocrine function is to inhibit the release of hormones, insulin, and glucagon. Somatostatin release is stimulated by the beta cells of the islets. 

Most common pancreatic diseases 

The pancreas can have various problems, but the most common ones are diabetes, pancreatitis, and pancreatic cancer. Less common are islet cell tumors, cystic fibrosis, pancreatic cysts. Pancreatic problems may be difficult to notice early, as cancer and tumors may not have specific symptoms in the early stages. 

Some diseases of the pancreas can be noticed early and treated or controlled relatively easily, but those can lead to life-threatening conditions if left untreated. Pancreatic cancer is known to be aggressive, diagnosed mostly in late stages, and with a low survival rate. As symptoms for many pancreatic diseases are general and unspecific, problems with the pancreas are diagnosed late. 

Pancreatitis 

Pancreatitis can be acute, chronic, or hereditary. Acute pancreatitis has a sudden attack of pain in the upper abdomen. The pain usually is severe and can last for several days. The pain usually radiates to the back and can be described as belt-type pain. Commonly, the pain worsens after eating. People can also have fever, nausea, vomiting, and tenderness when touching the abdomen. 

Chronic pancreatitis is a progressive disease. The most commons signs of chronic pancreatitis are a pain in the upper abdomen and diarrhea. As the disease progresses, malnutrition and weight loss can be seen. If lead to late stages, pancreatitis can initiate the development of diabetes

Risk factors and causes of pancreatitis:

  • Alcoholism
  • Smoking
  • Obesity
  • Family history
  • Injury to the abdomen
  • Gallstones
  • Pancreatic cancer
  • Abdominal surgery.

Diabetes 

Diabetes is a disease that affects blood glucose levels. The most common types of diabetes are type 1, type 2, and gestational diabetes. The reason for type 1 diabetes is unknown but believed to be triggered by the body's own immune system, which attacking and destroying beta cells that are producing the hormone insulin. What triggers the immune system is still unknown, but it might be genes and the environment. In type 1 diabetes, there are no beta cells that could produce insulin, which the difference from type 2 diabetes. 

Type 2 diabetes is the most seen type of diabetes. It can be caused by lifestyle, genes, a polycystic ovarian syndrome in women. Risk factors for type 2 diabetes are weight, inactivity, family history, age, high blood pressure, too high cholesterol, and triglyceride levels. In this type of diabetes, the beta cells are not destroyed; they are still producing the hormone insulin, but the cells become insulin resistant, meaning that liver, muscle, and fats cells do not take up insulin efficiently enough, so the body needs help with that as with time pancreas cannot make enough insulin. 

Gestational diabetes is a type of diabetes that develops during pregnancy. It is connected to family history and insulin resistance that may happen due to weight gain during pregnancy. Many other diseases and medication can cause diabetes. 

Symptoms of diabetes:

  • Increased appetite
  • Increased thirst
  • Increased urination
  • Fatigue
  • Blurred vision
  • Weight loss for no reason
  • Sores that do not heal well
  • Numbness in the palms or feet

Pancreatic cancer 

Pancreatic cancer develops when malignant cells form in the tissues of the pancreas. Pancreas cancer is tricky as it may not have early signs. The most common symptoms are jaundice, dark urine, light-colored stools, pain in the upper or middle part of the abdomen and back, weight loss for no reason, loss of appetite, tiredness.

Due to no early symptoms, pancreatic cancer is difficult to detect. Pancreatic cancer is rarely found early. If so, pancreatic cancer can be cured by surgical resection. If pancreatic cancer is found in late stages, the treatment is only palliative to improve the quality of life and treat symptoms. 

Risk factors for pancreatic cancer:

  • Obesity
  • Smoking
  • Lack of physical activities
  • Diabetes or chronic pancreatitis in history
  • Family history of pancreatic cancer or pancreatitis
  • Certain hereditary disease:
    • von Hippel-Lindau syndrome
    • hereditary breast and ovarian cancer syndrome
    • Lynch syndrome
    • multiple endocrine neoplasia type 1 syndrome

Summary on the pancreas 

What is the function of the pancreas in the body? 

The pancreas has an endocrine and an exocrine function. The endocrine function is to control blood glucose levels with the help of insulin and glucagon. The exocrine function is to secrete pancreatic enzymes that break down fats, proteins, and carbohydrates. 

What is the anatomy of the pancreas? 

The pancreas is a flat, pear-shaped organ behind the stomach. It is situated retroperitoneally. The pancreas is surrounded by other abdominal organs like the small intestine, spleen, and liver.

What types of cells are in the pancreas? 

The pancreas has acinar cells forming clusters, and the pancreatic islets with alpha, beta, gamma, delta, and epsilon cells. 

What do pancreatic cells do?

Acinar cells secrete pancreatic enzymes: trypsin and chymotrypsin for digesting proteins, amylase for digesting carbohydrates, and lipase to break down fats. Alpha cells secrete the hormone glucagon, beta cells secrete the hormone insulin, delta cells secrete the hormone somatostatin, gamma cells secrete a pancreatic polypeptide, and epsilon cells secrete ghrelin.

Does the pancreas produce bile?

The liver produces bile. Bile is drained through the common bile duct and forms an ampulla of Vater with the pancreatic duct. Here the bile and the pancreatic enzymes mix and are released in the duodenum. 

Where in pancreatic polypeptide secreted from?

Pancreatic polypeptide is secreted by gamma cells in the islets of Langerhans.

What is the function of glucagon?

Glucagon is a hormone that is secreted as a response to low blood glucose levels. Glucagon stimulates the liver to change glycogen into glucose, thus elevating the blood glucose levels. This process is known as glycogenolysis. Glucagon can also stimulate the liver and kidneys to make more glucose when glycogenolysis is not enough. Furthermore, glucagon can initiate lipolysis so that glucose is produced from fat. 

What is the function of insulin?

Insulin is a hormone that is secreted when the blood glucose levels are high. Insulin stimulates cells to uptake more glucose from the blood so that the blood glucose level can decrease. Insulin stimulates glucose change into glycogen through glycogenesis in the liver and muscles. Insulin can also increase glucose storage in fat. 

What is the function of somatostatin?

Somatostatin is a hormone that takes part in the endocrine and exocrine functions. As the endocrine hormone, it inhibits the secretion of other hormones, insulin, and glucagon. As the exocrine hormone somatostatin decreases gastric emptying rate by reducing smooth muscle contractions and blood flow within the intestine.

What is the function of ghrelin?

Ghrelin stimulates appetite leading to an increased food intake. 

What is PP in the human body?

PP is a pancreatic polypeptide that inhibits the secretion of the pancreatic enzymes. 

What triggers ghrelin?

Ghrelin levels are increased before eating and during fasting. After eating, ghrelin levels decrease.

How do you lower ghrelin?

Avoid food with high sugar levels and eating protein at every meal. 

How do you know if something is wrong with the pancreas?

There is a sudden and constant pain in the upper part of the abdomen that can radiate to the back, nausea, unknown weight loss, dark urine, vomiting, and jaundice. 

What is the leading cause of pancreatitis?

The leading cause is gallstones. Other common causes are excessive alcohol usage, obesity, smoking.

Is pancreatitis serious?

It depends on the severity of pancreatitis and its cause. Mild pancreatitis can go away without treatment, while severe pancreatitis can lead to life-threatening conditions. 

Can pancreatitis be cured?

The more severe, the more difficult it could be to treat pancreatitis. Acute pancreatitis can be treated by pain medications or removing gallstones. Chronic pancreatitis may need pain medications, treating diabetes, improving food absorption, or surgery. 

What are the warning signs of pancreatitis? 

The warning signs of pancreatitis are sudden attacks of pain in the upper abdomen. The pain usually is severe and can last for several days. The pain usually radiates to the back and can be described as belt-type pain. Commonly, the pain worsens after eating. People can also have fever, nausea, vomiting, and tenderness when touching the abdomen.

What is the most common cause of pancreatic cancer? 

The exact cause is not known, but there are risk factors that can lead to pancreatic cancer. Those are obesity, smoking, lack of physical activities, diabetes or chronic pancreatitis in history, certain hereditary diseases (von Hippel-Lindau syndrome, hereditary breast and ovarian cancer syndrome, Lynch syndrome, multiple endocrine neoplasia type 1 syndrome).

What are the early signs of pancreatic cancer? 

There no specific signs of pancreatic cancer, so it makes it hard to diagnose. The symptoms may be jaundice, dark urine, light-colored stools, pain in the upper or middle part of the abdomen and back, weight loss for no reason, loss of appetite, and tiredness.

Can you survive pancreatic cancer? 

It depends on the stage and the location of pancreatic cancer. Early stages can be treated with surgery, radiation, and chemotherapy. Late stages usually have palliative care to improve the quality of life and control symptoms. 

Can the pancreas heal itself from diabetes? 

The pancreas cannot heal itself. Type 1 cannot be treated because the immune system keeps attacking beta cells. For type 2 diabetes, it is possible to catch a pre-diabetic state, and by changing diet and lifestyle, it can be possible to stop the development of type 2 diabetes.

Can you live without a pancreas? 

Yes, you can, but at this moment, studies have shown that the survival rate is around seven years. However, you need to substitute hormones and enzymes produced by the pancreas.