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Control, Coordination and Control, Coordination and FeedbackFeedback

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Blood glucose control

• What is glucose?• Why is glucose in the blood?• Where does it come from?• Where does it go?• What is it there for?• How much is there?• How do you measure it?• When does the concentration increase?• When does the concentration decrease?

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Blood glucose regulation

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Glucose concentration

80 to 120 mg 100 cm-3 blood

This is the ‘normal’ rangeThe concentration fluctuates Below 60 mg 100 cm-3 – comaAbove 180 mg 100 cm-3 exceeds renal

threshold and glucose appears in the urine

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Blood glucose

What goes wrong when the concentration decreases?

What goes wrong when the concentration increases?

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Blood glucose

What goes wrong when the concentration decreases too far?

HypoglycaemiaThe symptoms associated with low blood

sugar are: tiredness, confusion, dizziness,

headaches, mood swings, muscle weakness, shaking

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Blood glucose

What goes wrong when the concentration increases too far?

HyperglycaemiaThe symptoms include: Excessive thirst; frequent urination; fatigue; unexplained weight loss; vision problems, such as blurring; increased susceptibility to infections such

as thrush.

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Blood glucose concentration

• Keep within narrow limits• Corrective action if it increases• Corrective action if it decreases• Control mechanism needs to respond to

fluctuations– Negative feedback– reduces the difference between actual

and ideal / norm / set point

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Feedback system

• Input

• Receptor

• Control centre

• Effector(s)

• Communication system

• Corrective actions

• Negative feedback

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Liver cellsBinucleate cell

central vein

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Liver cell

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Liver cell

protein metabolism

lipid metabolism

carbohydrate metabolism

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Carbohydrate metabolism

• glucose absorbed across membrane by facilitated diffusion

• glucose stored as glycogen• glucose glucose 6 phosphate• glucose 6 phosphate glucose 1 phosphate • glucose units added onto end of glycogen

molecule (glycosidic links)• glycogen synthetase

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Carbohydrate metabolism

• glycogen broken down to glucose• glucose 1 phosphate molecules formed• glucose phosphorylase• glucose 1 phosphate glucose 6

phosphate• glucose 6 phosphate to glucose• glucose diffuses out of cell through

protein carriers

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Glucose storage

• glucose concentration in blood increases

• beta cells in pancreas release insulin• insulin stimulates liver cells to store

glucose as glycogen• insulin stimulates lipid synthesis• insulin stimulates protein synthesis• insulin helps to conserve resources

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Islet of Langerhans

exocrine tissue

endocrine tissue

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Alpha cells Beta cells

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Structure of insulin

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Insulin receptor

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Secondary messengers

• Glucagon and insulin are both proteins• Do not cross membranes• Signalling transduction at cell

membrane• Secondary messenger produced inside

membrane• 2o messenger transmits signal to

enzymes within cytoplasm

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Cyclic AMP

• Produced just inside cell membrane

• ATP cyclic AMP

• Catalysed by Adenylate cyclase

• Cyclic AMP combines with a protein

• Starts a ‘chain reaction’ following stimulation by glucagon

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Amplification

• Quick response required from many enzymes

• Signal is amplified• Chain reaction:

A B C D• Enzyme cascade• Final enzyme converts glycogen

glucose

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Glucagon

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Glucagon

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Insulitis

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Modern technology

Biosensor Insulin mini-pump