Glucose regulation Flashcards
What are the main cell types in the islets of Langerhans and their relative proportions?
β cells (65%)- beta
α cells (20%)- alpha
δ cells (10%)- delta
Other cells include F (PP/γ) cells, ε cells, and enterochromaffin cells
What does each cell type in the islets of Langerhans secrete?
β cells: insulin
α cells: glucagon
δ cells: somatostatin
F (PP) cells: pancreatic polypeptide
ε cells: Ghrelin protein
what is the role of somatostatin?
regulating hormone release
How are the islets of Langerhans perfused compared to other tissues?
They are richly perfused with blood, receiving 5 times more blood flow than the myocardium
What is the mechanism by which glucose stimulates insulin secretion in β cells?
- Glucose enters via GLUT2
- Converted to glucose-6-phosphate by glucokinase
- ATP production increases
- ATP closes KATP channels
- Cell membrane depolarizes
- Opens calcium channels
- Calcium influx triggers insulin exocytosis
How does sympathetic stimulation affect insulin secretion?
β-adrenergic increases secretion, while α-adrenergic decreases it (during exercise to prevent hypoglycaemia)
How does parasympathetic stimulation affect insulin secretion?
Parasympathetic stimulation (via vagus nerve - ACh) increases insulin release
What is the primary action of insulin on blood glucose?
Insulin decreases blood glucose concentration by increasing glucose transport into target cells through GLUT4
What is the structure of the insulin receptor?
A heterotetramer with α/β subunits and intracellular tyrosine kinase
What are the four major effects of insulin on muscle?
1) Promotes glucose uptake via GLUT4
2) Promotes glycogen synthesis
3) Promotes glycolysis
4) Promotes protein synthesis
What are the three main types of communication and control in the islets of Langerhans?
- Humoral (via blood vessels)
- Drugs
- Neural (via innervation)
Any tissue responding to insulin must have a receptor on it. Describe how insulin work via its receptor
1- Insulin binds to the α subunits on the cell surface. This triggers a conformational change
2- The receptor auto phosphorylates (adds phosphate groups to itself). This activates the tyrosine kinase domain
3- insulin receptor complex becomes internalised- comes into the cell so DOWREGULATED (not available to be bound to by further insulin)
what is glucose stored as in liver and muscle cells? what is the process called?
It is stored as glycogen through glycogenesis
*short term storage
when glycogen is replenished, what is the excess glucose converted into?
fat though the process of lipogenesis
*longer term storage
What are the three main actions of insulin on the liver?
1) Promotes glycogenesis
2) Inhibits glycogenolysis
3) Inhibits gluconeogenesis
