Glucose Metabolism and Regulation

Study Notes

Glucose Metabolism

Glucose is the major source of energy in all living organisms.
Too little glucose can lead to brain problems, while too much glucose can cause osmotic water loss and damage blood vessels.

Sources of Glucose

Food is a direct source of glucose.
Glucose can be stored as glycogen in the liver and as fat in adipose tissue.
Glucose can be synthesized from fat and protein through gluconeogenesis.

Pancreas Functions

The pancreas produces digestive enzymes for digestion.
The pancreas produces primary messengers (hormones) such as insulin and glucagon.

Insulin

Insulin is produced by beta cells in the pancreas.
Insulin structure consists of 51 amino acids, 2 chains linked by disulfide bonds, and a molecular weight of 5800 dalton.
Insulin increases glucose uptake in nearly all cells (80%), primarily affecting the liver and muscle, but not the brain.
Insulin receptor is a tyrosine kinase receptor.
Insulin secretion is stimulated by increased blood glucose, free fatty acids, amino acids, and certain hormones.
Insulin secretion is inhibited by fasting, somatostatin, and sympathetic stimulation.

Action of Insulin

In muscle cells, insulin promotes glucose uptake and storage as glycogen, and inhibits glucose synthesis.
In liver cells, insulin promotes glucose uptake and storage as glycogen, inhibits glycogen phosphorylase, activates glycogen synthase, inhibits glucose synthesis, and promotes excess glucose conversion to fatty acids.
In adipose tissue, insulin promotes glucose uptake and conversion to glycerol for fat production.

Glucose Disorders

Type I diabetes: lack of insulin production, characterized by increased fasting blood glucose, increased blood fatty acids and cholesterol, and protein depletion.
Type II diabetes: insulin receptor insensitivity, characterized by elevated insulin levels and associated with obesity.
Hyperglycemia: excessive glucose in the blood, leading to polyphagia, polydipsia, polyuria, and slowly damaging blood vessels.

Glucagon

Glucagon is produced by alpha cells in the pancreas.
Glucagon structure consists of 29 amino acids and a molecular weight of 3485 dalton.
Glucagon prevents hypoglycemia by stimulating glycogenolysis and glucose synthesis from amino acids and fat.
Glucagon exerts its effects through cAMP.
Glucagon secretion is stimulated by decreased blood glucose, sympathetic stimulation, and stress exercise.

Other Hormones

Glucocorticoids (adrenal cortex): stimulate gluconeogenesis, inhibit glucose uptake in muscle and adipose tissue, and stimulate fat breakdown in adipose tissue.
Sympathetic activity and epinephrine: stimulate glucagon secretion and lipolysis.

Description

Learn about the importance of glucose as a source of energy, its regulation, and the consequences of too little or too much glucose. Discover the sources of glucose, including food, storage, and new synthesis, and the role of the pancreas in digestion and hormone production.