Endocrine Physiology
PANCREAS
Dr. Meg-angela Christi M. Amores
Pancreas
• Digestive function
• Secretes two important hormones
– Insulin
– Glucagon
* important in regulation of glucose
• amylin, somatostatin, and pancreatic
polypeptide
Physiologic Anatomy
• Two major types of tissues:
a. Acini- secrete digestive juices into the duodenum
b. Islets of Langerhans -secrete insulin and glucagon
directly into the blood
• Islet of Langerhans
– 1 to 2 million islets
– alpha, beta, and delta cells
Physiologic Anatomy
• Beta cells
– constituting about 60% of all the cells of the islets
– secrete insulin and amylin
• Alpha cells
– about 25% of the total cells
– secrete glucagon
• Delta cells
– about 10% of the total cells
– secrete somatostatin
Insulin and Its Metabolic Effects
• Insulin is a hormone associated with energy
abundance
– insulin is secreted in great quantity when there is
great abundance of energy-giving foods in the diet
(carbohydrates)
– stored as glycogen mainly in the liver and muscles
– converted into fats and stored in the adipose
tissue
– promoting amino acid uptake by cells and
conversion of these amino acid into protein
Effect of Insulin on
Carbohydrate Metabolism
Insulin Promotes Muscle Glucose
Uptake and Metabolism
• muscle tissue depends not on glucose for its
energy but on fatty acids
• normal resting muscle membrane is only
slightly permeable to glucose except when the
muscle fiber is stimulated by insulin
Insulin Promotes Muscle Glucose
Uptake and Metabolism
• two conditions the muscles do use large
amounts of glucose
• Heavy exercise – more permeable to glucose
• Few hours after meal - pancreas is secreting large
quantities of insulin
Storage of Glycogen in Muscle
• stored in the form of muscle glycogen instead
of being used for energy
• can later be used for energy by the muscle
• useful for short periods of extreme energy use
by the muscles and even to provide spurts of
anaerobic energy
Quantitative Effect of Insulin to Facilitate
Glucose Transport Through the Muscle Cell
Membrane
• lower curve labeled "control" shows the
concentration of free glucose
demonstrating that the glucose
concentration remained almost zero
despite increased extracellular glucose
• the curve labeled "insulin" demonstrates
that the intracellular glucose
concentration rose to as high as 400
mg/100 ml when insulin was added
Insulin Promotes Liver Uptake,
Storage, and Use of Glucose
• cause most of the glucose absorbed after a
meal to be stored almost immediately in the
liver in the form of glycogen
• when food is not available, insulin secretion
decreases rapidly and the liver glycogen is split
back into glucose, which is released back into
the blood
Insulin Promotes Conversion of Excess Glucose
into Fatty Acids and Inhibits Gluconeogenesis in
the Liver
• insulin promotes the conversion of all this
excess glucose into fatty acids
• fatty acids are subsequently packaged as
triglycerides in very-low-density lipoproteins
and transported in this form to the adipose
tissue and deposited as fat.
• Insulin also inhibits gluconeogenesis
Lack of Effect of Insulin on Glucose
Uptake and Usage by the Brain
• Brain does not need insulin for glucose uptake
• Brain cells are permeable to glucose
• Glucose is the main form of energy of the
brain cells
• Have difficulty in using other substrates such
as fats
Effect of Insulin on Fat Metabolism
Insulin Promotes Fat Synthesis and
Storage
• insulin increases the utilization of glucose
which automatically decreases the utilization
of fat, thus functioning as a fat sparer
• insulin promotes fatty acid synthesis
– when more carbohydrates are ingested than can
be used for immediate energy
• Insulin promotes storage of fat in the adipose
cells
Effect of Insulin on Protein Metabolism
and on Growth
• Insulin promotes protein synthesis and
storage
• Lack of insulin causes protein depletion and
increased plasma amino acids
• Insulin and Growth Hormone interact
synergistically to promote growth
Mechanism of Insulin Secretion
Control of Insulin Secretion
• Increased Blood Glucose Stimulates Insulin
Secretion
– At the normal fasting level of blood glucose of 80
to 90 mg/100 ml, the rate of insulin secretion is
minimal-on the order of 25 ng/min/kg of body
weight
– If the blood glucose concentration is suddenly
increased to a level two to three times normal and
kept at this high level thereafter, insulin secretion
increases markedly
Glucagon and Its Functions
• hormone secreted by the alpha cells when the
blood glucose concentration falls
• functions is to increase the blood glucose
concentration, an effect that is exactly the
opposite that of insulin.
Effects of Glucagon on Glucose
Metabolism
• Glucagon causes glycogenolysis and increased
blood glucose
• glucagon increases gluconeogenesis
• activates adipose cell lipase, making increased
quantities of fatty acids available for energy
• inhibits the storage of triglycerides in the liver
Regulation of Glucagon Secretion
• Increased blood glucose inhibits glucagon
secretion
• Increased blood amino acids stimulate
glucagon secretion
• exercise stimulates glucagon secretion
Somatostatin and its Function
• Secreted by the delta cells
• all factors related to the ingestion of food
stimulate somatostatin secretion
– increased blood glucose
– increased amino acids
– increased fatty acids
– increased concentrations of several of the
gastrointestinal hormones
Somatostatin and its Function
• depress the secretion of both insulin and
glucagon
• decreases the motility of the stomach,
duodenum, and gallbladder.
• decreases both secretion and absorption in
the gastrointestinal tract
Summary of Blood Glucose Regulation
1. The liver functions as an important blood glucose buffer
system
2. Both insulin and glucagon function as important feedback
control systems for maintaining a normal blood glucose
concentration
3. In severe hypoglycemia, a direct effect of low blood glucose
on the hypothalamus stimulates the sympathetic nervous
system
4. Over a period of hours and days, both growth hormone and
cortisol are secreted in response to prolonged hypoglycemia,
and they both decrease the rate of glucose utilization by
most cells of the body, converting instead to greater amounts
of fat utilization
Diabetes Mellitus
• Is a syndrome of impaired carbohydrate, fat,
and protein metabolism caused by either lack
of insulin secretion or decreased sensitivity of
the tissues to insulin
• Type I diabetes, also called insulin-dependent
diabetes mellitus (IDDM)
• Type II diabetes, also called non-insulindependent diabetes mellitus (NIDDM)
Diabetes Mellitus