151 The Pancreas
Pancreas
The pancreas is a gland organ in the digestive and endocrine systems.
Learning Objectives
Describe the function of the pancreas
Key Takeaways
Key Points
- The pancreas is a gland organ in the digestive and endocrine systems.
- As an endocrine gland, the pancreas produces several important hormones that include insulin, glucagon, somatostatin, and pancreatic polypeptide.
- As a digestive organ, the pancreas secretes pancreatic juice that contains digestive enzymes that assist the absorption of nutrients and digestion in the small intestine.
- These enzymes help to further break down the carbohydrates, proteins, and lipids in the chyme.
Key Terms
- pancreas: A gland near the stomach that secretes a fluid into the duodenum to help with food digestion.
Anatomy of the Pancreas
The pancreas is a gland organ in the digestive and endocrine systems. As an endocrine gland, the pancreas produces several important hormones that include insulin, glucagon, somatostatin, and pancreatic polypeptide.
As a digestive organ, the pancreas secretes pancreatic juice that contains digestive enzymes that assist the absorption of nutrients and digestion in the small intestine. These enzymes help to further break down the carbohydrates, proteins, and lipids in the chyme.
Location
The pancreas is located posterior to the stomach and next to the duodenum. The pancreas functions as both an exocrine and endocrine gland. The exocrine function of the pancreas is essential for digestion as it produces many of the enzymes that break down the protein, carbohydrates, and fats in digestible foods.
Composition
The pancreas is composed of pancreatic exocrine cells, whose ducts are arranged in clusters called acini. The cells are filled with secretory granules containing the inactivated digestive enzymes, mainly trypsinogen, chymotrypsinogen, pancreatic lipase, and amylase, that are secreted into the lumen of the acini.
Glandular Function of the Pancreas
The pancreas is a dual-function gland, having features of both endocrine and exocrine glands.
Exocrine Function
The pancreas synthesizes its enzymes in the inactive form, known as zymogens, to avoid digesting itself. The enzymes are activated once they reach the small intestine. The pancreas also secretes bicarbonate ions from the ductal cells to neutralize the acidic chyme that the stomach churns out.
The exocrine function of the pancreas is controlled by the hormones gastrin, cholecystokinin, and secretin, which are hormones secreted by cells in the stomach and duodenum in response to food.
The two major proteases that the pancreas synthesizes are trypsinogen and chymotrypsinogen. These zymogens are inactivated forms of trypsin and chymotrypsin.
Once released in the intestine, the enzyme enterokinase, which is produced by the intestinal mucosa, activates trypsinogen by cleaving it to form trypsin. The free trypsin then cleaves the rest of the trypsinogen and chymotrypsinogen to their active forms. Pancreatic secretions accumulate in small ducts that drain to the main pancreatic duct that drains directly into the duodenum.
Endocrine Function
The part of the pancreas with endocrine function is made up of approximately a million cell clusters called the islets of Langerhans. Four main cell types exist in the islets. They are relatively difficult to distinguish using standard staining techniques, but they can be classified by their secretions:
- α cells secrete glucagon (increase glucose in blood ).
- β cells secrete insulin (decrease glucose in blood).
- Delta cells secrete somatostatin (regulates/stops α and β cells).
- PP cells or gamma cells, secrete pancreatic polypeptide.
The Islets of Langerhans
The islets are a compact collection of endocrine cells arranged in clusters and cords that are crisscrossed by a dense network of capillaries. The capillaries of the islets are lined by layers of endocrine cells that are in direct contact with blood vessels, either by cytoplasmic processes or by direct apposition.
Pancreas: This image shows the location of the pancreas relative to other organs. The pancreas is seen positioned with the duodenum slightly on top of it and next to the right kidney. The pancreas crosses above the left kidney.
Anatomy of the Pancreas
The pancreas lies in the epigastrium or upper central region of the abdomen and can vary in shape.
Learning Objectives
Outline the anatomy of the pancreas
Key Takeaways
Key Points
- The pancreas lies in the epigastrium or upper central region of the abdomen.
- The pancreas is composed of a head, uncinate process, neck, body, and tail.
- A number of blood vessels connect the pancreas to the duodenum, spleen, and liver.
Key Terms
- epigastrium: The upper middle region of the abdomen, between the umbilical and hypochondriac regions.
Variation
Pancreatic tissue is present in all vertebrate species, but its precise form and arrangement varies widely. There may be up to three separate pancreases, two of which arise from ventral buds, and the other dorsally. In most species (including humans), these fuse in the adult, but there are several exceptions.
Even when a single pancreas is present, two or three pancreatic ducts may persist, each draining separately into the duodenum (or an equivalent part of the foregut). Birds, for example, typically have three such ducts.
In teleosts, and a few other species (such as rabbits), there is no discrete pancreas at all, with pancreatic tissue being distributed diffusely across the mesentery and even within other nearby organs, such as the liver or spleen.
Anatomy of the Pancreas
The pancreas lies in the epigastrium or upper central region of the abdomen. It is composed of several parts.
- The head lies within the concavity of the duodenum.
- The uncinate process emerges from the lower part of head, and lies deep to superior mesenteric vessels.
- The neck is the constricted part between the head and the body.
- The body lies behind the stomach.
- The tail is the left end of the pancreas. It lies in contact with the spleen.
The superior pancreaticoduodenal artery from the gastroduodenal artery and the inferior pancreaticoduodenal artery from the superior mesenteric artery run in the groove between the pancreas and the duodenum and supply the head of pancreas.
The pancreatic branches of the splenic artery also supply the neck, body, and tail of the pancreas. The body and neck of the pancreas drain into the splenic vein; the head drains into the superior mesenteric and portal veins. Lymph is drained via the splenic, celiac, and superior mesenteric lymph nodes.
Parts of a pancreas: 1: Head of pancreas 2: Uncinate process of pancreas 3: Pancreatic notch 4: Body of the pancreas 5: Anterior surface of the pancreas 6: Inferior surface of the pancreas 7: Superior margin of the pancreas 8: Anterior margin of the pancreas 9: Inferior margin of the pancreas 10: Omental tuber 11: Tail of the pancreas 12: Duodenum.
Histology of the Pancreas
The pancreas serves digestive and endocrine functions, and it is composed of two types of tissue: islets of Langerhans and acini.
Learning Objectives
Describe the histology of the pancreas
Key Takeaways
Key Points
- Under a microscope, the stained sections of the pancreas reveal two different types of parenchymal tissue.
- The light-stained clusters of cells are called islets of Langerhans. These produce hormones that underlie the endocrine functions of the pancreas.
- The dark-stained cells form acini that are connected to ducts. Acinar cells belong to the exocrine pancreas and secrete digestive enzymes into the gut via a system of ducts.
Key Terms
- islets of Langerhans: Regions in the pancreas that contain its endocrine cells.
- acini: An acinus (adjective: acinar; plural: acini) refers to any cluster of cells that resembles a many-lobed berry, such as a raspberry (acinus is Latin for berry).
The pancreas is a glandular organ in the digestive system and endocrine system of vertebrates. It is both an endocrine gland that produces several important hormones—including insulin, glucagon, somatostatin, and pancreatic polypeptide—as well as a digestive organ that secretes pancreatic juice that contain digestive enzymes to assist the absorption of nutrients and digestion in the small intestine. These enzymes also help to further break down the carbohydrates, proteins, and lipids in the chyme.
Anatomy of the Pancreas
Under a microscope, stained sections of the pancreas reveal two different types of parenchymal tissue. Light-stained clusters of cells are called islets of Langerhans. These produce hormones that underlie the endocrine functions of the pancreas.
The dark-stained cells form acini that are connected to ducts. Acinar cells belong to the exocrine pancreas and secrete digestive enzymes into the gut via a system of ducts.
The pancreas is a dual-function gland that has the features of endocrine and exocrine glands.
The part of the pancreas with endocrine function is made up of approximately a million cell clusters called islets of Langerhans. Four main cell types exist in the islets. They are relatively difficult to distinguish using standard staining techniques, but they can be classified by their secretion
- α cells secrete glucagon (increase glucose in blood ).
- β cells secrete insulin (decrease glucose in blood).
- Delta cells secrete somatostatin (regulates/stops α and β cells).
- PP cells or gamma cells, secrete pancreatic polypeptide.
The islets are a compact collection of endocrine cells arranged in clusters and cords and are crisscrossed by a dense network of capillaries. The capillaries of the islets are lined by layers of endocrine cells in direct contact with vessels, and most endocrine cells are in direct contact with blood vessels, either by cytoplasmic processes or by direct apposition.
Pancreatic Juice
Pancreatic fluid contains digestive enzymes that help to further break down the carbohydrates, proteins, and lipids in the chyme.
Learning Objectives
Describe the nature and function of pancreatic juice
Key Takeaways
Key Points
- Pancreatic fluid or juice contains digestive enzymes that pass to the small intestine where they help to further break down the carbohydrates, proteins, and lipids (fats) in the chyme.
- Pancreatic fluid is alkaline in nature due to its high concentration of bicarbonate ions that neutralize the gastric acid and allow effective enzymic action.
- Pancreatic juice secretion is regulated by the hormones secretin and cholecystokinin. It is produced by the walls of the duodenum upon detection of acid food, proteins, fats, and vitamins.
Key Terms
- pancreatic fluid: A liquid secreted by the pancreas that contains a variety of enzymes, including trypsinogen, chymotrypsinogen, elastase, carboxypeptidase, pancreatic lipase, and amylase.
The pancreas is a glandular organ in the digestive system and endocrine system of vertebrates. It is both an endocrine gland that produces several important hormones—including insulin, glucagon, somatostatin, and pancreatic polypeptide—and a digestive organ that secretes pancreatic juice that has digestive enzymes that assist the absorption of nutrients and digestion in the small intestine. These enzymes help to further break down the carbohydrates, proteins, and lipids in the chyme.
Pancreatic Juice
Pancreatic juice is a liquid secreted by the pancreas that contains a variety of enzymes, including trypsinogen, chymotrypsinogen, elastase, carboxypeptidase, pancreatic lipase, nucleases, and amylase.
Pancreatic fluid: A schematic diagram that shows pancreatic acini and the ducts where fluid is created and released.
Pancreatic juice is alkaline in nature due to its high concentration of bicarbonate ions that neutralize the gastric acid and allow effective enzymic action.
Pancreatic juice secretion is regulated by the hormones secretin and cholecystokinin. It is produced by the walls of the duodenum upon detection of acid food, proteins, fats, and vitamins. Pancreatic secretion consists of an aqueous bicarbonate component from the duct cells and an enzymatic component from the acinar cells.
Because the pancreas is a sort of storage depot for digestive enzymes, injury to the pancreas is potentially fatal. A puncture of the pancreas generally requires prompt and experienced medical intervention.
A variety of factors cause a high pressure within pancreatic ducts. Pancreatic duct rupture and pancreatic juice leakage cause pancreatic self-digestion.
