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 Langerhans
o 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
o 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
o
o
o
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
o 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
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•
•
•
•
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
o Joins Central Bile Duct at the ampulla of Vater
o 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
o 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 enzymes
o 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
o
o
o
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
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
o only digestive enzyme secreted by pancreas in active form
o hydrolyzes starch and glycogen to glucose, maltose, maltotriose,
and dextrins
• Lipase
o emulsify and hydrolyze fat in the presence of bile salts
• Proteases
o
o
o
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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 selfregulate 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 inhibitors
o 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 circulation
o
o
o
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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
o Amino acids, Cholinergic fibers, β-Sympathetic fibers
• Major inhibitors
o 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 effect
o Inhibits the release of growth hormone
o Inhibits the release of almost all peptide hormones
o 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
o 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 Duct
o In adults, the most common cause is alcoholic pancreatitis
o 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
o Represents up to 30% of all cases of pancreatic carcinoma
Diseases and Disorders
• Endocrine Tumors – Rare with an incidence of five
per one million
o Insulinoma: Most common endocrine tumor of the pancreas
• Gastrinoma (Zollinger-Ellison Syndrome)
o Identification of a islet cell tumor of the pancreas
o Patient management is through control of gastric acid
hypersecretion
• Pancreatic Lymphoma
o Involvement of pancreas with non-Hodgkin’s lymphoma is an
unusual neoplasm
• Pancreatic Trauma
o Pancreas is injured in less than 2% of patients with abdominal
trauma
Diseases and Disorders
• Diabetes Mellitus
o 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 dependence
o commonly detected before age 30
• Type 2 Diabetes (non-insulin-dependent diabetes)
o blood glucose levels rise due to
1) Lack of insulin production
2) Insufficient insulin action (resistant cells)
o commonly detected after age 40
o effects > 90% of persons with diabetes
o 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 gland
o Has exocrine and endocrine functions
• Plays major role in digestion and
glucose homeostasis