Pancreas: Anatomy & Physiology Source : http://www.mercysurgery.com/resources/presentations/Pancreas.ppt http://www.auburn.edu/academic/classes/labt/4250/west/pancreas_endocrine.pdf http://www.the-ainet.com/rom-med/files/physiology/Endocrine_Pancreas.pdf

Pancreas- Brief History Pancreas – derived from the Greek pan, “all”, and kreas, “flesh”, probably referring to the organ’s homogenous appearance Herophilus, Greek anatomist and Surgeon, first identified the pancreas in 335 – 280 BC Ruphos, another Greek anatomist, gave pancreas its name after few hundred years Wirsung discovered the pancreatic duct in 1642. Pancreas as a secretory gland was investigated by Graaf in 1671.

Pancreas Gland with both exocrine and endocrine functions 6-10 inch in length (15-25 cm) 60-100 gram in weight Location: retro-peritoneum, 2nd lumbar vertebral level Extends in an oblique, transverse position Parts of pancreas: head, neck, body and tail

Histology There are two distinct organ systems within the pancreas The endocrine portion of the pancreas is served by structures called the islet of Langerhans The islet of Langerhans have several distinct cell types Alpha cells-produce glucagon and constitute approximate 25% of the total islet cell number Beta cells-the insulin producing cells (majority of the cells) Delta cells-produce somatostatin (smallest number) The exocrine portion of the pancreas is made up of acini and ductal systems Acinar cells contain zymogen

Anatomy Is a retroperitoneal structure found posterior to the stomach and lesser omentum It has a distinctive yellow/tan/pink color and is multilobulated The gland is divided into four portions The head The neck The body The tail The pancreas has an extensive arterial system arising from multiple sources The venous drainage parallels arterial anatomy The veins terminate in the portal vein Multiple lymph nodes drain the pancreas Neural function is controlled by duel sympathetic and parasympathetic innervation

Pancreas

Head of Pancreas Broadest part Includes uncinate process: Lower part of the posterior surface of the head that wraps behind the superior mesenteric artery and superior mesenteric vein Flattened structure, 2 – 3 cm thick Attached to the 2nd and 3rd portions of duodenum on the right Emerges into neck on the left Border b/w head & neck is determined by GDA insertion SPDA and IPDA anastamose b/w the duodenum and the rt. lateral border Broadest part Moulded into the C shaped concavity of duodenum Lies over the inferior venacava, the right and left renal veins at the level of L2 Posterior surface is indented by the terminal part of the bile duct

Neck of Pancreas 2.5 cm in length Lies in front of the superior mesenteric and portal veins Posteriorly, mostly no branches to pancreas

Body of Pancreas Elongated structure Anterior surface, separated from stomach by lesser sac Posterior surface, related to aorta, lt. adrenal gland, lt. renal vessels and upper 1/3rd of lt. kidney Splenic vein runs embedded in the post. Surface Inferior surface is covered by tran. Mesocolon Body passes across the left renal vein and aorta, left crus of diaphragm, left psoas muscle, lower pole of left suprarenal gland to the hilum of left kidney Upper border crosses the aorta at the origin of the celiac trunk Splenic artery passes to the left along the upper border Lower border crosses the origin of the superior mesenteric artery

Pancreas

Tail of Pancreas Narrow, short segment Lies at the level of the 12th thoracic vertebra Lies in the lienorenal ligament along with splenic artery, vein, lymphatics End of tail of pancreas touches the hilum of spleen Anteriorly, close to splenic flexure of colon May be injured during splenectomy (fistula) Passes forward from the anterior surface of the left kidney at the level of hilum

Pancreatic Duct Main duct (Duct of Wirsung) runs the entire length of pancreas Joins Central Bile Duct at the ampulla of Vater 2 – 4 mm in diameter, 20 secondary branches Lesser duct (Duct of Santorini) drains superior portion of head and empties separately into 2nd portion of duodenum Drains the uncinate process and lower part of head

Pancreatic Physiology Exocrine pancreas 85% of the volume of the gland Extracellular matrix – 10% Blood vessels and ducts - 4% Endocrine pancreas – 1%

Histology-Exocrine Pancreas 2 major components Acinar cells which secrete primarily digestive enzymes Centroacinar or ductal cells which secrete fluids and electrolytes Constitute 80% to 90% of the pancreatic mass Acinar cells secrete the digestive enzymes 20 to 40 acinar cells coalesce into a unit called the acinus Centroacinar cell (2nd cell type in the acinus) is responsible for fluid and electrolyte secretion by the pancreas Duct system - network of conduits that carry the exocrine secretions into the duodenum

Histology-Endocrine Pancreas Accounts for only 2% of the pancreatic mass Nests of cells - islets of Langerhans Four major cell types Alpha (A) cells secrete glucagon Beta (B) cells secrete insulin Delta (D) cells secrete somatostatin F cells secrete pancreatic polypeptide

Histology-Endocrine Pancreas B cells are centrally located within the islet and constitute 70% of the islet mass PP, A, and D cells are located at the periphery of the islet

Physiology – Exocrine Pancreas Secretion of water and electrolytes originates in the centroacinar and intercalated duct cells Pancreatic enzymes originate in the acinar cells Final product is a colorless, odorless, and isosmotic alkaline fluid that contains digestive enzymes (amylase, lipase, and trypsinogen) Alkaline pH results from secreted bicarbonate which serves to neutralize gastric acid and regulate the pH of the intestine Enzymes digest carbohydrates, proteins, and fats

Exocrine The bulk of the pancreas is an exocrine gland secreting pancreatic fluid into the duodenum after a meal. The principal stimulant of pancreatic water and electrolyte secretion – Secretin Secretin is synthesized in the S cells of the crypts of Liberkuhn Released into the blood stream in the presence of luminal acid and bile http://faculty.smu.edu/jbuynak/images/Diabetes MellitusBuynak.ppt

Bicarbonate Secretion Bicarbonate is formed from carbonic acid by the enzyme carbonic anhydrase Major stimulants Secretin, Cholecystokinin, Gastrin, Acetylcholine Major inhibitors Atropine, Somatostatin, Pancreatic polypeptide and Glucagon Secretin - released from the duodenal mucosa in response to a duodenal luminal pH < 3

Enzymes: Types and Secretion Amylase only digestive enzyme secreted by pancreas in active form hydrolyzes starch and glycogen to glucose, maltose, maltotriose, and dextrins Lipase emulsify and hydrolyze fat in the presence of bile salts Proteases essential for protein digestion secreted as proenzymes; require activation for proteolytic activity duodenal enzyme, enterokinase, converts trypsinogen to trypsin Trypsin, in turn, activates chymotrypsin, elastase, carboxypeptidase, and phospholipase Released from the acinar cells into the lumen of the acinus and then transported into the duodenal lumen, where the enzymes are activated. Ultimate result of all these actions is food digestion and absorption

Physiology – Endocrine Pancreas Principal function is to maintain glucose homeostasis Insulin and glucagon play a major role in glucose homeostasis In addition endocrine pancreas secrete somatostatin, pancreatic polypeptide, c peptide, & amylin pancreatic polypeptide – released internally to self-regulate pancreas activities amylin – released with insulin; contributes to glycemic control http://www.answers.com/topic/pancreatic-polypeptide http://en.wikipedia.org/wiki/Amylin

Insulin Synthesized in the beta cells of the islets of Langerhans 80% of the islet cell mass must be surgically removed before diabetes becomes clinically apparent Insulin and C peptide are packaged into secretory granules and released together into the cytoplasm 95% belong to reserve pool and 5% stored in readily releasable pool Thus small amount of insulin is released under maximum stimulatory conditions

Insulin Major stimulants Major inhibitors Glucose, amino acids, glucagon, GIP, CCK, sulfonylurea compounds, β-Sympathetic fibers Major inhibitors somatostatin, amylin, pancreastatin, α-sympathetic fibers Stimulation of Beta cells results in exocytosis of the secretory granules Equal amount of insulin and c peptide are released into circulation Insulin circulates in free form and has half life of 4-8 minutes Liver predominantly degrades insulin C peptide is not readily degraded in the liver Half life of c peptide averages 35 minutes

Glucagon Secreted by the alpha cells of the islets of Langerhans Major stimulants Amino acids, Cholinergic fibers, β-Sympathetic fibers Major inhibitors Glucose, insulin, somatostatin, α-sympathetic fibers Main physiological role increase blood glucose level through stimulation of glycogenolysis and gluconeogenesis Antagonistic effect on insulin action Release is inhibited by hyperglycemia and stimulated by hypoglycemia

Somatostatin Secreted by the delta cells of the islets of Langerhans Major Stimulants High fat, protein rich , high carbohydrate meal Generalized inhibitory effect Inhibits the release of growth hormone Inhibits the release of almost all peptide hormones Inhibits gastric, pancreatic, and biliary secretion Used to treat both endocrine and exocrine disorders

Diseases and Disorders Acute Pancreatitis – Includes a broad spectrum of pancreatic disease Varies from mild parenchymal edema to severe hemorrhagic pancreatitis associated with gangrene and necrosis Chronic Pancreatitis Is associated with alcohol abuse (most common), cystic fibrosis, congenital anomalies of pancreatic duct and trauma to the pancreas Disruptions of the Pancreatic Duct In adults, the most common cause is alcoholic pancreatitis In children the most common cause is neoplasms. (tumors) The fifth most common cause of cancer death 90% of patients die within the first year after diagnosis Adenocarcinoma of the Body and Tail of Pancreas Represents up to 30% of all cases of pancreatic carcinoma

Diseases and Disorders Endocrine Tumors – Rare with an incidence of five per one million Insulinoma: Most common endocrine tumor of the pancreas Gastrinoma (Zollinger-Ellison Syndrome) Identification of a islet cell tumor of the pancreas Patient management is through control of gastric acid hypersecretion Pancreatic Lymphoma Involvement of pancreas with non-Hodgkin’s lymphoma is an unusual neoplasm Pancreatic Trauma Pancreas is injured in less than 2% of patients with abdominal trauma

Diseases and Disorders Diabetes Mellitus Group of diseases characterized by high levels of blood glucose resulting from defects in insulin production, insulin action, or both Leads to Hyperglycemia, or high blood glucose (sugar) Estimated 20.8 million in US ( 7% of population) Estimated 14.6 million diagnosed (only 2/3) Consists of 3 types: 1) Type 1 diabetes 2) Type 2 diabetes 3) Gestational diabetes http://faculty.smu.edu/jbuynak/images/Diabetes MellitusBuynak.ppt http://faculty.smu.edu/jbuynak/images/Diabetes MellitusBuynak.ppt

Diabetes Mellitus Type 1 Diabetes (insulin-dependent diabetes) cells that produce insulin are destroyed results in insulin dependence commonly detected before age 30 Type 2 Diabetes (non-insulin-dependent diabetes) blood glucose levels rise due to 1) Lack of insulin production 2) Insufficient insulin action (resistant cells) commonly detected after age 40 effects > 90% of persons with diabetes eventually leads to beta cell failure (resulting in insulin dependence) Gestational Diabetes 3-5% of pregnant women in the US develop gestational diabetes http://faculty.smu.edu/jbuynak/images/Diabetes MellitusBuynak.ppt http://faculty.smu.edu/jbuynak/images/Diabetes MellitusBuynak.ppt

Conclusions Pancreas is a composite gland Has exocrine and endocrine functions Plays major role in digestion and glucose homeostasis http://faculty.smu.edu/jbuynak/images/Diabetes MellitusBuynak.ppt