Page 573 - Concise Pathology for Exam Preparation ( PDFDrive )

558 SECTION II Diseases of Organ Systems

10. Gestational diabetes
Normal glucose homoeostasis regulation involves three steps:
• Glucose production by liver
• Uptake and utilization by peripheral tissue
• Secretion of insulin and counter-regulatory hormones-like glucagon
Insulin:
1. Synthesis and release (Flowchart 20.13)

Induction of insulin gene on β cells of pancreatic islets

Synthesis of insulin mRNA

Synthesis of preproinsulin in the rough endoplasmic reticulum

Delivery to Golgi apparatus

Proteolytic cleavage
C peptide
Mature insulin

Storage in secretory granules
Physiologic stimuli, eg, rise in blood
glucose facilitated by an insulin-independent
glucose transporter unit, GLUT-2

Release of insulin
β cells express an ATP sensitive K+ channel on their membrane, which comprises two subunits
a) An ATP-sensitive K+ channel.
b) The sulphonyl urea receptor (binds to this class of hypoglycaemic drugs)
Intake of food and metabolism of glucose

Generation of ATP

Inhibition of activity of ATP sensitive K+ channel
Early phase to insulin release
Membrane depolarization and influx of calcium ions

Increased intracellular calcium

Secretion of insulin from storage granules of β cells

Persistence of secretory stimulus

Active synthesis of insulin release
Delayed phase of insulin release

Delayed and protracted release
FLOWCHART 20.13. Synthesis and release of insulin.

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