Objectives
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Explain how hormones work
Outline the role of the pancreas as an
endocrinegland
Explain how blood glucose concentration is
regulated with reference to insulin, glucagon
and adrenaline
Hormone Regulation
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Hormones are
regulated by
negative feedback.
Regulation of blood
sugar is a good
example of this.
How do hormones work?
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Hormones are proteins
that are produced in
(endocrine) glands and
secreted into the blood
Carried in the blood
plasma to target cells
These cells have
complementary receptors
to the specific hormone
Adrenaline and glucagon
follow the second
messenger model of
action
The pancreas
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Is both an endocrine
and exocrine gland
Exocrine function secretes digestive
enzymes into the
pancreatic duct
Endocrine function secretes hormones
(insulin and glucagon)
directly into the
blood
Secretion of enzymes (exocrine
function)
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Pancreatic cells
surround small tubules
which drain into the
pancreatic duct
Pancreatic cells produce
pancreatic juice which is
made up of;
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Amylase (a carbohydrase)
Trypsinogen (an inactive
protease)
Lipase
Secretion of hormones (endocrine
function)
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Hormones are
secreted from the
cells in the islets of
Langerhans
α cells manufacture
and secrete the
hormone glucagon
βcells manufacture and
secrete the hormone
insulin
These are released
directly into the blood
Control of blood glucose
The natural sources of blood glucose are:
1. Directly from the diet – glucose enters
blood when carbohydrates are broken down
2. Breakdown of glycogen (Glycogenolysis )
3. Gluconeogenesis – production of new glucose
from sources other than carbohydrates
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Control of blood glucose
Is a negative feedback
process
The normal blood glucose
level is 90mg per 100ml of
blood
If the blood glucose levels
get too high or too low,
then the changes are
detected by the α and
βcells in the islets of
Langerhans
Insulin and the β cells of the pancreas
*Act as Receptors that detect rise in blood glucose level
*When rise is detected they secrete insulin into the blood
plasma
*Insulin binds to glycoprotein receptors on cell surface of most
body cells (notably excluding Red Blood Cells)
http://www.medbio.info/horn/time%2034/insulin's%20mechanism%20of%20action.htm
When bound the following can happen:
1) Modifies the tertiary structure of glucose carrier
protein channels so that they allow more glucose into
cells
2) Increase number of glucose carrier proteins in cell surface membrane
3) Activate enzymes that convert glucose to glycogen
and fat
This results in:
1) More glucose absorbed into cells
2) Increases respiratory rate of cells so more glucose is
used up so more glucose is absorbed
3) Increasing rate of conversion of glucose to glycogen
(glycogenesis) in the liver and muscles
4) Increasing conversion of
glucose to fat
http://www.youtube.com/watch?v=X0ezy1t6N08
Glucagon and the α cells of the pancreas
*Act as Receptors that detect fall in blood glucose level
*When fall is detected they secrete hormone glucagon into the
blood plasma
*glucagon binds to glycoprotein receptors on
only
LIVER cells
When bound the following happens:
a) An enzyme is activated that converts glycogen to
glucose
b) There is an increase in the conversion of amino acids
and glycerol into glucose GLUCONEOGENESIS)
This results in:
An increase in blood glucose levels
The role of adrenaline
There are a number of other hormones that increase blood
sugar levels. The most well known is adrenaline
• Produced in adrenal glands (above kidneys)
•It raises blood glucose by:
Activating an enzyme that causes breakdown of
glycogen to glucose in the liver
Inactivating an enzyme that synthesises glycogen from
glucose
Hormone interaction in regulating blood glucose
Uses negative feedback as both hormones work to keep blood
glucose at around 90mg per 100ml of blood.
They are said to work antagonistically
Task
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The exam questions