Transcript Blood Sugar Regulation

Regulating blood
sugar
The Pancreas
Medline Plus
Anatomy
The pancreas is an exocrine gland
 secreting alkaline digestive juices
 into the duodenum via the pancreatic duct
The pancreas is also an endocrine gland
 the endocrine cells are in the Islets of
Langerhans
Islets of Langerhans
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An oval collection of cells scattered through
the pancreas
1 to 2 million islets in a human pancreas
1 to 2% of its mass
Islets are darker red than the surrounding
tissue having a rich blood supply
The blood from the islets drains into the
Hepatic Portal Vein going directly to the liver
Hormone secreting cells
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 cells. (20%)
secrete glucagon
 cells (75%)
secrete insulin
 cells (1 to 8%)
Insulin and Glucagon
INSULIN
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A protein made of two short
polypeptide chains linked by
disulphide bridges
Synthesised at the ribosome on
Rough ER) as a single
polypeptide (proinsulin)
It is later activated by
enzymatic cleavage into the
two chains.
GLUCAGON
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A small protein made up of 29
amino acids
It is made by the alpha cells in
the Islets.
It is also made in an inactive
form proglucagon before it is
released
Hormone action
Action of Insulin
Action of Glucagon
Increases the entry of glucose
into the body cells
Inhibits glycogen breakdown in Glucagon binds to liver cells,
liver and muscle
stimulating the breakdown of
glycogen into glucose
Inhibits lipid breakdown in liver Increases lipid breakdown
and adipose tissue
though its influence is small
Increases the uptake of amino
acids by cells and increases
the rate of protein synthesis
Stimulates the formation of
glucose from amino acids in
the liver
Hormone action
Action of Insulin
The action of insulin is very
rapid, so is its breakdown (t½ = 10
to 25 min).
 Once released into the blood
stream insulin binds with the
receptor sites on its target cells’
plasma membrane.
 This stimulates vesicles, which
carrying glucose pores, in the
cytoplasm of these cells, to fuse
with the plasma membrane.
 Insulin is broken down by
enzyme action in many tissues.
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Action of Glucagon
Glucagon is also very short lived
(t½ = 5 to 10 min).
 Glucagon is broken down
particularly by the liver tissue.
 As the hormone is secreted into
the blood flowing into the liver little
glucagon is seen circulating in the
rest of the body.
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Control
Control of Insulin Secretion
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Because it has a rapid half-life
the islet cells tend to respond
more often to stimulating rather
than inhibiting chemicals in the
plasma.
These include: Glucose, amino
acids, glucagon,
Control of Glucagon Secretion
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Glucagon levels rise between
meals as the glucose and fatty
acid levels in the blood fall
Secretion is also stimulated by
amino acids and hormones
secreted by the digestive
system
In many ways it is antagonistic
to insulin.
Summary
2
Blood glucose / g dm
-3
1.8
1.6
INSULIN
1.4
1.2
1
0.8
Normal blood glucose concentration
0.6
0.4
0.2
0
GLUCAGON
INSULIN DEFICIENCY:
Diabetes mellitus
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Symptoms
Hyperglycaemia (high blood glucose)
Glucosuria (glucose in the urine)
Polyuria (passage of copious urine)
Polydipsia (drinking large amounts)
Increased appetite
Weight loss
Acids and ketones in the blood from lipid
breakdown (toxic)
Coma if ketones build, up
Diabetes
Diabetes is sometimes described as:
“STARVATION IN THE MIDST OF PLENTY”
There is plenty of glucose circulating in the
blood but it cannot get into the cells that need it
Treatment
 Intravenous or oral doses of insulin at regular
intervals
 Strict diet and meal times
Types of diabetes
Type 1
Aka “Juvenile”
β-cells no longer make
insulin
Islet cells destroyed by
the immune system
(autoimmune disease)
Type 2
Aka “adult-onset”
Insulin made normally but
the body cells do not use
it
More insulin is secreted to
compensate
Eventually the islet cells
cannot keep up with the
demand
Types of diabetes
Type 1
Type 2
Thought to be genetic in Associated with obesity
origin
and inactivity
May be triggered by
Obseity also has a
childhood infection (e.g. genetic predisposition
mumps)
Today more and more
young people suffer from
Type 2
Gestational diabetes
Similar to Type 2
 Develops during pregnancy
 Placental hormones interact with
insulin secretion
 Women who develop it seem to have
a genetic predisposition
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Increasing numbers of
diabetics
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Life style (exercise, snacking)
Change of diet (refined sugar, saturated
fats)
Migration and change of diet
Ethnic differences
(US: Caucasians 6%, Afro/Asiatic
Americans 10%, Native Americans 20-50%)