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-Endocrine Communication:
Endocrine system: a communication system using hormones
as signaling molecules
Hormones: molecules that are released by endocrine glands
directly into the blood
Target cells: cells that possess a specific receptor on their
plasma membrane which is complementary to the shape of a
hormone molecule
Types of hormones:
• Proteins and peptide hormones (adrenaline, insulin and
glucagon)
• Steroid hormones (oestrogen and testosterone)
Proteins are not soluble in the phospholipid bilayer therefore do
not enter the cell
...

However steroid hormones can pass through the phospholipid
bilayer and enter the cell and nucleus and bind to DNA
...

Exocrine gland that secrete useful molecules into a duct that
carries the molecules to where they are used
...

• The first messenger binds to the receptor and activates
the enzyme adenyl cyclase which converts ATP to cyclic
AMP which is the second messenger
...

• The steroid hormone binds with specific receptors in the
cytoplasm
• The receptor steroid hormone complex enters the nucleus
and bind to another receptor on the chromosome
• Binding stimulates the production of mRNA which code for
protein
Hormones from the adrenal cortex:
The adrenal cortex uses cholesterol to make a range of
hormones
...
g
...


Glucocorticoids e
...
cortisol: from the zona fasciculate which
helps control metabolism of carbohydrates, fats and protein in
the liver
...

Adrenaline and noradrenaline is released from the adrenal
medulla into the blood
...

Many cells have adrenaline receptors; therefore, the effects are
widespread
...

• Pancreatic juices contain enzymes which are secreted into
the small intestines (exocrine)
• Hormones which are secreted form the islets of
Langerhans into the blood (endocrine)

The fluid from the pancreatic duct contains the following
enzymes: pancreatic amylase, lipase and trypsinogen
...

• Alpha cells secrete glucagon
• Beta cells secrete insulin
How is insulin released from beta cells
1
...
When blood glucose concentration is high, glucose move
into cell
3
...
ATP closes the potassium ion channels
5
...
This then causes calcium ion channels to open
7
...

• Target cells are liver and muscle
• When insulin binds to receptor on target tissue, it activates
the enzyme tyrosine kinase which causes phosphorylation
of inactive enzyme leading to a cascade of enzyme
controlled reactions

This can lead to:
• more glucose enters cell
• more glucose converted to fats
• more glucose used in respiration
• glycogenesis à glucose converted to glycogen
If blood glucose concentration is too low
• This is detected by the alpha cells which then secrete
glucagon
• Its target tissue is liver cells
• Glucagon binds to receptors which stimulates a G protein
which activates the enzyme adenyl cyclase which
converts ATP to cAMP which activate a cascade
More fatty acids used in respiration
Gluconeogenesis amino acids + fats à additional glucose
Glycogen is converted to glucose in glycogenolysis
Diabetes mellitus
A condition in which blood glucose concentration cannot be
controlled effectively
Type 1
A person cannot store excess glucose as glycogen therefore
not removed from the blood (hyperglycaemia)
However when the blood glucose concentration falls there is no
store of glycogen that can be used to release glucose
Treatments for diabetes mellitus

• Insulin pump therapy – a small device that constantly
pumps insulin
• Islet cell transplantation – healthy beta cells from
pancreas of deceased donor are implanted
• Pancreas transplant
The source of insulin for treating diabetes
Advantages include:
• Exact copy of human insulin
• Lower risk of infection
• Cheaper to manufacture
• Less chance of rejection
• Less chance of developing tolerance
• Less likely chance that people have moral objections





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