7. Changes in blood glucose levels – hyperglycemic and hypoglycemic states.

CHANGES IN BLOOD GLUCOSE LEVELS – HYPERGLYCEMIA AND HYPOGLYCEMIA

Carbohydrates

• Breakdown of carbohydrates begins in the mouth → continues to intestines
• Amylase breaks down polysaccharides → disaccharides → monosaccharides
• Salivary amylase + pancreatic amylase breaks down poly → di
• Intramural amylase (lactase, maltase) breaks down di → mono
• A lack of enzymes → increases level of osmotic molecules (undigested carbohydrates) → attract H2O to within the intestines → bacterial fermentation in colon → diarrhoea

Glycemic index

• ⭐ Glycemic index - measures the effects of CH on blood glucose levels
• High glycemic index - carbohydrates that break down quickly → release glucose rapidly
• Low glycemic index - carbohydrates that break down slowly → release glucose slowly

Blood glucose levels

• Normal blood glucose levels = 3.9 - 6 mmol/L
• Hormones that affect blood glucose levels:
• Decrease = insulin
• Increase = glucagon, adrenaline, GH, glucocorticoids, T3/T4
• Processes that affect blood glucose levels
• Increase glycogenolysis - glucagon, catecholamines, T3/T4
• Increase gluconeogenesis - glucocorticosteroids
• Glucose is absorbed into the cells via glucose transporters:
• Glut-1 → found in endothelial cells and RBCs, insulin dependent
• Glut-2 → in pancreatic beta-cells, insulin independent
• Glut-3 → expressed mostly in neurons and in the placenta
• Glut-4 → striated muscle and adipose tissue, insulin dependent

Pancreas

• Islets of Langerhans contain 4 types of hormone-secreting cells:
• Alpha - glucagon
• Beta - insulin
• Delta - somatostatin
• F-cells - pancreatic polypeptide

Insulin

• Insulin = anabolic hormone that directly decreases blood glucose levels
• The actions of insulin are threefold:

1. Promotes glucose uptake by target cells and glycogenesis
2. Prevents fat and glycogen breakdown and inhibits gluconeogenesis
3. Increases protein synthesis and inhibits protein breakdown

• The active form of the hormone is composed of two polypeptide chains - an A chain and a B chain
• Active insulin is formed in the beta cells from a larger molecule called proinsulin
• In converting proinsulin to insulin, enzymes in the beta cell cleave proinsulin at specific sites to form two separate substances:

1. Active insulin
2. Biologically inactive connecting peptide (C-peptide) chain that joined the A and B chains before they were separated.

• Active insulin and the C-peptide chain are packaged into secretory granules and released simultaneously from the beta cell.
• The C-peptide chains can be measured clinically, and this measurement can be used to study beta cell activity

Hypoglycemia

• Blood sugar level < 3.9 mmol/L
• Causes:
• Excess of insulin dose
• Skipping meals
• Alcohol consumption
• Excessive exercise
• Can be:

1. Physiological state
2. Pathological condition

• Decrease carbohydrate uptake
• Altered carbohydrate metabolism in the liver