Blood Glucose

CNS triggers desire to eat Food consumed and glucose absorbed Plasma glucose increases Insulin release stimulated GLUT externalisation Glucose uptake by fat and muscle Glycogen synthesis Plasma glucose levels fall Production of glucagon triggered Triggers breakdown of glycogen Plasma glucose levels increase Euglycaemia restored

Live and kidney Express glycogen phosphorylase which can supple glucose to bloodstream from glycogen Liver can also convert many small molecules into glucose via gluconeogenesie

GLUT 1 Glut 2 Glut 3 GLUT 4 GLUT 5

GLUT 4

Insulin responsive glucose transporter For skeletal muscle, cardiac muscle and adipose tissue

Oscillation between catabolic and anabolic states Driven by nutrient supply (post-prandial increase in anabolic processes) Pituitary also involved (senses low glucose and triggers hormone production)

Cortisol Epinephrine (adrenaline) Growth hormone (IGF1) Glucagon

Insulin

Glucose is the main source of energy during the absorptive (fed state) Fatty acids are the main source of energy during the long fasting state Brain is the only exception which uses glucose

Beta cells

Rising blood glucose levels

Polypeptide hormone - 51 amino acids Synthesised as a precursor (preproinsulin -> proinsulin -> insulin + C-peptide)

Considered unstable if taken orally

Acts via insulin receptor Phosphorylation triggers intracellular signalling pathway

They equalise concentrations across membranes They transport down concentration gradients GLUTs are stored in intracellular granules Insulin signalling promotes externalisation of preformed GLUT

This induces a signal transduction cascade which allows the glucose transporter (GLUT 4) to transport glucose into the cell Results in gene expression and growth regulation and glucose utilisation

The blood-brain barrier excludes fatty acids from the brain High FFA can act as detergents to the brain

Brain depends on glucose Needs a constant supply of about 110g a day Older brains need more glucose to carry out the same tasks GLUT1 expressed on the BBB which facilitates blood-brain movement of glucose GLUT3 expressed on neurons

Stimulates the pancreas to release insulin Insulin stimulates the uptake of glucose and storage as glycogen in the liver and muscles Insulin also stimulates the conversion of excess glucose into fat for storage Blood levels begin to decline

This stimulates the pancreas to release glucagon into the bloodstream Glucagon stimulates liver cells to break down glycogen and release glucose into the blood Blood glucose begins to rise again

If blood glucose is too high some will spill into the urine Kidney filters glucose into tubules and then reabsorbs it (100% in normal people) If glucose concentration is too high reabsorption cannot keep up with filtration and some glucose stays in tubule and becomes part of urine Glucose in the urine will suck more water into the urine via osmosis and cause excess urine production in diabetes -> causes dehydration and thirst

Its a minor glycogen store Filtered glucose is reabsorbed by the kidney For normal concentrations it is 100% effective are reabsorption If concentration too high it will exceed capacity and will spill over which leads to glucose rich urine (glucosuria)

After meals blood glucose comes from carbohydrates in meal Between meals blood glucose comes from the liver and kidneys Liver provides 80% of blood glucose supply via - glycogenolysis - gluconeogenesis

Breakdown of liver glycogen