Pathophysiology of Diabetes MellitusType 1

Insulin is essential to process carbohydrates, fat, and protein. Insulin reduces blood glucose levels by allowing glucose to enter muscle cells and by stimulating the conversion of glucose to glycogen (glycogenesis) as a carbohydrate store. Insulin also inhibits the release of stored glucose from liver glycogen (glycogenolysis) and slows the breakdown of fat to triglycerides, free fatty acids, and ketones. It also stimulates fat storage. Additionally, insulin inhibits the breakdown of protein and fat for glucose production (gluconeogenesis) in both liver and kidneys.

Hyperglycemia (ie, random blood glucose concentration more than 200 mg/dL or 11 mmol/L) results when insulin deficiency leads to uninhibited gluconeogenesis and prevents the use and storage of circulating glucose. The kidneys cannot reabsorb the excess glucose load, causing glycosuria, osmotic diuresis, thirst, and dehydration. Increased fat and protein breakdown leads to ketone production and weight loss. Without insulin, a child with type 1 diabetes mellitus wastes away and eventually dies due to diabetic ketoacidosis (DKA).

The effects of insulin deficiency are shown in the image below.

 
The effects of insulin deficiency. 

An excess of insulin prevents the release of glucose into the circulation and results in hypoglycemia (blood glucose concentrations of < 60 mg/dL or 3.5 mmol/L). Glucose is the sole energy source for erythrocytes, kidney medulla, and the brain. Source : emedicine.medscape.com