ENDOCRINOLOGY - Glucose Homeostasis Flashcards
What is the key factor of blood glucose regulation?
The ratio between insulin and glucagon secretion
What are the Islets of Langerhans?
Islets of langerhans are groups of pancreatic cells which secrete glucose regulating hormones
Which structure allows islet of langerhans hormone secretion into the systemic circulation?
The network of fenestrated capillaries
List the four main pancreatic cells contained within the islets of langerhans? What do each of these cells secrete?
Alpha cells: Secrete glucagon
Beta cells: Secrete insulin
Delta cells: Secrete somatostatin
F-cells: Secrete pancreatic polypeptides
What type of hormones are insulin and glucagon?
Insulin and glucagon are peptide hormones
Where are the beta cells mainly located in the islets of langerhans?
In the centre
Where are the alpha cells mainly located in the islets of langerhans?
In the periphery
What is the main physiological stimulus for insulin secretion?
Hyperglycaemia stimulates insulin secretion
Which hormone inhibits insulin secretion?
Somatostatin
Which molecule stimulates insulin secretion from the beta cells?
Calcium stimulates insulin secretion
Describe the process of insulin secretion due to extracellular calcium stimulation
- Excess glucose enters the beta cells via GLUT 2 proteins
- Glucose enters the citric acid cycle to produce ATP
- ATP stimulates ATPase K+ channels allowing K+ to enter the cell, altering the membrane potential
- Altered membrane potential opens voltage gated Ca2+ channels, moving Ca2+ into the beta cells to stimulate insulin release from secretory vesicles
Describe the process of insulin secretion due to intracellular calcium stimulation
- Excess glucose binds to G-protein coupled receptors on the beta cell surface causing a conformational change
- Conformational change alters cAMP and IP3 levels within the cells stimulating Ca2+ release
- Ca2+ stimulates insulin release from secretory vesicles
Describe the two phases of insulin secretion (biphasic response)
Initial acute phase: release of stored insulin in the beta cells
Chronic phase: insulin is now being actively produced and secreted
What is the function of the insulin hormone?
Lower blood glucose levels through stimulating anabolic reactions reactions which store energy and to inhibit catabolic reactions which break down energy stores
What are the three anabolic reactions stimulated by insulin?
Glycogenesis
Protein synthesis
Triacylglycerol (TAG) synthesis
What are the four catabolic reactions inhibited by insulin?
Glycogenolysis
Gluconeogenesis
Lipolysis
Protein degradation
What are the three cell types targeted by insulin?
Hepatocytes
Skeletal muscle cells
Adipose cells
How long is the half life of insulin?
10 minutes
What is the main physiological stimulus for glucagon secretion?
Hypoglycaemia stimulates glucagon secretion
Which hormone inhibits glucagon secretion?
Somatostatin
What is the function of glucagon?
Glucagon raises blood glucose levels by stimulating catabolic reactions which break down energy stores and inhibits anabolic reactions
What are the three catabolic reactions stimulated by glucagon?
Glycogenolysis
Gluconeogenesis
Lipolysis
Which anabolic reaction is inhibited by glucagon?
Glycogenesis
What are the two cell types targeted by glucagon?
Hepatocytes
Adipose cells
Where in the body is glucagon produced other than in alpha cells?
Glucagon is also produced in the stomach
What is the half life of glucagon?
5 minutes
Where are insulin and glucagon metabolised?
Liver and kidneys
What are two glucose homeostasis disorders?
Hypoglycaemia
Hyperglycaemia
List two causes of hypoglycaemia
Excessive insulin administration
Insulinoma (pancreatic tumour secreting excess insulin)
List seven clinical signs of hypoglycaemia
Tachycardia
Sweating
Pallor
Tremors
Seizures
Unconsciousness
Death
What is the most common cause of hyperglycaemia?
Diabetes
If left untreated, what serious condition can be caused secondary to hyperglycaemia?
Secondary ketoacidosis
How can ketoacidosis secondary to hyperglycaemia lead to death?
Ketoacidosis causes dehydration, nausea, vomiting and anorexia leading to hypovolaemia. Stress hormones in response to hypovolaemia cause further hyperglycaemia, eventually leading to death
