Pancreas: Anatomy & Physiology

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 Langerhanso 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 systemso 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

o The heado The necko The bodyo The tail

• The pancreas has an extensive arterial system arising from multiple sources

• The venous drainage parallels arterial anatomyo 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• 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 pancreaso Joins Central Bile Duct at the ampulla of Vatero 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 duodenumo 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 o Acinar cells which secrete primarily digestive enzymeso 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

o Alpha (A) cells secrete glucagono Beta (B) cells secrete insulino Delta (D) cells secrete somatostatino 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

Bicarbonate Secretion• Bicarbonate is formed from carbonic acid by the

enzyme carbonic anhydrase• Major stimulants

Secretin, Cholecystokinin, Gastrin, Acetylcholine

• Major inhibitorsAtropine, Somatostatin, Pancreatic polypeptide and

Glucagon

• Secretin - released from the duodenal mucosa in response to a duodenal luminal pH < 3

Enzymes: Types and Secretion

• Amylaseo only digestive enzyme secreted by pancreas in active formo hydrolyzes starch and glycogen to glucose, maltose, maltotriose, and

dextrins

• Lipaseo emulsify and hydrolyze fat in the presence of bile salts

• Proteaseso essential for protein digestiono secreted as proenzymes; require activation for proteolytic activityo duodenal enzyme, enterokinase, converts trypsinogen to trypsino 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

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

o Glucose, amino acids, glucagon, GIP, CCK, sulfonylurea compounds, β-Sympathetic fibers

• Major inhibitorso somatostatin, amylin, pancreastatin, α-sympathetic

fibers

• Stimulation of Beta cells results in exocytosis of the secretory granules o Equal amount of insulin and c peptide are released into circulationo Insulin circulates in free form and has half life of 4-8

minuteso Liver predominantly degrades insulino C peptide is not readily degraded in the livero Half life of c peptide averages 35 minutes

Glucagon• Secreted by the alpha cells of the islets of

Langerhans• Major stimulants

o Amino acids, Cholinergic fibers, β-Sympathetic fibers

• Major inhibitorso Glucose, insulin, somatostatin, α-sympathetic fibers

• Main physiological role o 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

o High fat, protein rich , high carbohydrate meal

• Generalized inhibitory effecto Inhibits the release of growth hormoneo Inhibits the release of almost all peptide hormoneso 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 diseaseo Varies from mild parenchymal edema to severe hemorrhagic

pancreatitis associated with gangrene and necrosis

• Chronic Pancreatitis o Is associated with alcohol abuse (most common), cystic fibrosis,

congenital anomalies of pancreatic duct and trauma to the pancreas

• Disruptions of the Pancreatic Ducto In adults, the most common cause is alcoholic pancreatitiso 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 Pancreaso Represents up to 30% of all cases of pancreatic carcinoma

Diseases and Disorders

• Endocrine Tumors – Rare with an incidence of five per one milliono Insulinoma: Most common endocrine tumor of the pancreas

• Gastrinoma (Zollinger-Ellison Syndrome)o Identification of a islet cell tumor of the pancreaso Patient management is through control of gastric acid

hypersecretion

• Pancreatic Lymphomao Involvement of pancreas with non-Hodgkin’s lymphoma is an

unusual neoplasm

• Pancreatic Traumao Pancreas is injured in less than 2% of patients with abdominal

trauma

Diseases and Disorders

• Diabetes Mellituso Group of diseases characterized by high levels of blood glucose

resulting from defects in insulin production, insulin action, or both

o 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

Diabetes Mellitus• Type 1 Diabetes (insulin-dependent diabetes)

o cells that produce insulin are destroyed o results in insulin dependenceo commonly detected before age 30

• Type 2 Diabetes (non-insulin-dependent diabetes)o blood glucose levels rise due to

1) Lack of insulin production2) Insufficient insulin action (resistant cells)

o commonly detected after age 40o effects > 90% of persons with diabeteso eventually leads to beta cell failure (resulting in insulin

dependence)

• Gestational Diabetes o 3-5% of pregnant women in the US develop gestational

diabetes

http://faculty.smu.edu/jbuynak/images/Diabetes MellitusBuynak.ppt

Conclusions

• Pancreas is a composite glando Has exocrine and endocrine functions

• Plays major role in digestion and glucose homeostasis