Structure of the pancreatic
islet
1. Elongated
gland, weighing approximately 100 grams, 12 to 15 cm long, and its head lies in
the duodenum, extends horizontally behind the stomach and then touches the
spleen.
2. It is composed
of endocrine and exocrine tissues
a. Pancreatic
islets or Islets of Langerhans – endocrine portion
b. Acini –
exocrine portion
The Pancreatic Islets
Each islet contains four primary types
of endocrine glands joined by a gap junction. Each of these secretes hormones
which work as team to maintain homeostasis of food molecules.
1.
Alpha cells – secretes glucagon
which has the following:
a. Increases
blood glucose level
b. Stimulate
gluconeogenesis
c. Increases
lipolysis in adipose tissue
2.
Beta cells – secretes
insulin and account for up to 75% of all pancreatic islet cells.
a. Increases
glucose uptake by skeletal muscle and its utilization for oxidation and
glycogen synthesis
b. Increase
glucose uptake by adipose tissues and triglyceride synthesis.
c. Inhibits
lipolysis in adipose tissue
d. Increases
utilization of glucose in the liver, stimulating oxidation, glycogen synthesis
and conversion to fatty acids.
e. Reduces
production of glucose in the liver by inhibiting gluconeogenesis and
glycogenolysis.
3.
Delta cells – secretes
somatostatin
a. Regulates
other endocrine cells of the pancreatic islet.
4.
Pancreatic polypeptide cells
a. Influences the
digestion and distribution of food molecules to some degree.
The Acinar cells
1. Resembles
clusters of grapes consists of a roughly spherical arrangement of
enzyme–secreting cells arranged around a system of ductules. These networks of
ductules coalesce and eventually drain into the main pancreatic duct, which in
turn opens into the duodenum.
2. The acinar
cells secrete a fluid rich in proteins, the majority of which are digestive
enzymes. The non–digestive proteins present in pancreatic juice include trypsin
inhibitor, a cofactor for lipase, a trace of plasma proteins and lactoferrin, which
is present in almost all exocrine secretions.
3. Cells within
the ductules and centroacinar cells produce water secretions rich in
bicarbonate and enzymes precursors or zymogens. Once secreted into the
duodenum, enterokinase, an enzyme secreted by the duodenal mucosa, hydrolyzes
the zymogen trypsinogen to form catalytically active trypsin. Trypsin in turn
can activate the remaining pancreatic enzyme.
4. Activation of
these enzymes within the duodenum, instead of within the pancreas, ensures that
proteolytic autodigestion of the pancreas does not occur.
Pancreatic
enzymes and preferred substrate
Enzyme Substrate
Amylase Polysaccharide
Carboxypeptidase A & B Proteins
Chymotrypsin Proteins
Elastase elastin
Lipase Triglycerides &
Diglycerides
Phospholipase Phospholipids
Trypsin Proteins
PANCREATITIS
Pancreatitis is an inflammatory
disorder of the pancreas that is almost always associated with acinar cell
injury. It is classified into chronic and acute. The distinction between
chronic and acute disease is based on the recovery of the gland of its structural
and functional integrity after a bout of disease.
1. Acute
pancreatitis
a. Characterize
by abdominal pain, epigastric tenderness, nausea and vomiting.
b. Inflammation
and necrosis of the gland result in release of pancreatic enzymes into the
blood. Leakage of activated pancreatic enzymes may lead to extensive
destruction of the pancreas and surrounding organs, loss of vascular integrity,
hypotension and shock.
2. Chronic
pancreatitis
a. Characterize
by destruction of endocrine and exocrine parenchymal cells, which may lead to
insufficiency in the form of maldigestion and diabetes.
Causes of pancreatitis
1. 75 – 85% is
cause by chronic alcoholism and biliary tract diseases.
2. 10% - unknown
cause
3. 5% cause by
surgery, hypercalcemia, drugs and hyperlipidemia
Laboratory diagnosis
1. Pancreatic
amylase isoenzyme
2. Serum lipase –
more accurate
3. Immunoreactive
trypsin
4. Carboxypeptidase
A
5. Phospholipase
A
6. Elastase
Laboratory tests indicative of
organ injury secondary to pancreatitis:
1. Electrolytes:
Na+, K+, Cl–, HCO3–, pH,
pCO2, pO2
2. Creatinine
3. Urea
4. Calcium
5. Magnesium
6. Triglycerides
7. Liver enzymes
8. Bilirubin
9. Coagulation
factors
10. Hemoglobin and
hematocrit
11. WBC count
Treatment:
2. Peritoneal
lavage
3. Fluid
replacement therapy
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