Glucose Homeostasis

Glucose homeostasis

The fed state
Presentation copyright © 2007 David A Bender

The central nervous system is very largely reliant on glucose as its metabolic fuel; it cannot oxidise fatty acids
(but can metabolise ketone bodies in prolonged starvation) glycogen

Red blood cells are absolutely reliant on glucose; they have no mitochondria and form ATP only by anaerobic glycolysis

triacyglycerol

protein glucose triacylglycerol in VLDL

triacylglycerol in chylomicrons amino acids glucose The problem:

glycogen protein We eat 2 – 3 times a day; how can we maintain a constant supply of glucose for the brain and red blood cells?

amino acids

The fasting state

An overview of metabolism
GLYCOGENOLYSIS
glycogen glucose-6-phosphate GLYCOGEN SYNTHESIS

amino acids glucose triacyglycerol protein ketone bodies

glucose

lactate

pyruvate
(3 carbons)

triacylglycerols

hormone-sensitive lipase CO2
FATTY ACID SYNTHESIS acetyl CoA fatty acids
(2 carbons) FATTY ACID OXIDATION

ketones
KETOGENESIS

amino acids

glucose
( 6 carbons)

GLYCOLYSIS

GLUCONEOGENESIS

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LIPASE

glycerol oxaloacetate fatty acids glycogen fatty acids

citrate

CITRIC ACID CYCLE

CO2
CO2

Control of blood glucose by insulin and glucagon

hormones

islet of Langerhans

Fasting state: glucagon from α-cells

• In the fed state insulin is secreted by the β-cells of pancreatic islets of Langerhans
• stimulates synthesis of metabolic fuel reserves
• lowers circulating glucose

digestive enzymes

Fed state: insulin from β-cells

Control of blood glucose by insulin and glucagon

• In the fasting state glucagon is secreted by the α-cells of pancreatic islets of Langerhans
• stimulates mobilisation of metabolic fuel reserves
• raises circulating glucose

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Metabolic actions of insulin and glucagon

increased by insulin liver • fatty acid synthesis
• glycogen synthesis
•