Diabetes mellitus (DM) or simply diabetes, is a chronic health condition in which the body either fails to produce sufficient amounts of insulin or it responds abnormally to insulin. Commonly referred to as a syndrome, diabetes is classified into three types, namely, Type 1 diabetes, Type 2 diabetes, and Gestational diabetes. The ultimate outcome for all three types of diabetes is high blood glucose level. The pathophysiology of diabetes mellitus is very complex, as this ailment is characterized by different etiologies while sharing similar signs, symptoms, and complications. Diabetes Mellitus: Pathophysiology The pathophysiology of all types of diabetes is related to the hormone insulin, which is secreted by the beta cells of the pancreas. In a healthy person, insulin is produced in response to the increased level of glucose in the bloodstream, and its major role is to control glucose concentration in the blood. What insulin does is, allowing the body cells and tissues to use glucose as a main energy source. Also, this hormone is responsible for conversion of glucose to glycogen for storage in the muscles and liver cells. This way, sugar level is maintained at a near stable amount. In a diabetic person, there is an abnormal metabolism of insulin hormone. The actual reason for this malfunction differs according to the type of diabetes. Whatever the cause is, the body cells and tissues do not make use of glucose from the blood, resulting in elevated blood glucose (a typical symptom of diabetes called hyperglycemia). This condition is also exacerbated by the conversion of stored glycogen to glucose, i.e., increased hepatic glucose production. Over a period of time, high glucose level in the bloodstream can lead to severe complications, such as eye disorders, cardiovascular diseases, kidney damage, and nerve problems. In Type 1 diabetes, the pancreas cannot synthesize enough amounts of insulin as required by the body. The pathophysiology of Type 1 diabetes mellitus suggests that it is an autoimmune disease, wherein the body's own immune system generates secretion of substances that attack the beta cells of the pancreas. Consequently, the pancreas secretes little or no insulin. Type 1 diabetes is more common among children and young adults (around 20 years). Since it is common among young individuals and insulin hormone is used for treatment, Type 1 diabetes is also referred to as Juvenile Diabetes or Insulin Dependent Diabetes Mellitus (IDDM). In case of Type 2 diabetes mellitus, the insulin hormone secreted by the beta cells is normal or slightly lower than the ideal amount. However, the body cells are not responding to insulin as they do in a healthy person. Since the body cells and tissues are resistant to insulin, they do not absorb glucose, instead it remains in the bloodstream. Thus, the Type 2 diabetes is also characterized by elevated blood sugar. It is commonly manifested by middle-aged adults (above 40 years). As insulin is not necessary for treatment of Type 2 diabetes, it is known as Non-insulin Dependent Diabetes Mellitus (NIIDM) or Adult Onset Diabetes. The third type of diabetes is called Gestational diabetes. As the term clearly suggests, it is exhibited by pregnant women. Over here, high level of blood glucose is caused by hormonal fluctuations during pregnancy. Usually, the sugar concentration returns to normal after the baby is born. However, there are also instances, in which it remains high even after childbirth. This is an indication for increased risks of developing diabetes in the near future. As already mentioned, the symptoms and effects of all the three forms of diabetes are similar. The noticeable symptoms include increased thirst (polydipsia), increased urination (polyuria), and increased appetite (polyphagia). Other diabetes signs and symptoms include excessive fatigue, presence of sugar in the urine (glycosuria), body irritation, unexplained weight loss, and dehydration. Elevated blood sugar and glycosuria are interrelated; when sugar amount in the blood is abnormally high, the reabsorption by proximal convoluted tubule is reduced, thereby retaining some glucose in the urine. Diabetes Mellitus: Diagnosis and Treatment Regarding the definition of diabetes mellitus, it is often described as a fasting blood glucose level of 126 milligrams per deciliter (mg/dL) or more. As per statistics, Type 2 diabetes is the most commonly occurring type, in comparison to the other two forms of diabetes mellitus. Early and correct detection of the diabetes is necessary to prevent severe health effects. After diagnosis, the physician prescribes appropriate medication for treatment of diabetes, which may include insulin injections or oral insulin medicines, depending upon the type of diabetes mellitus. In addition to the therapeutic intervention, healthy lifestyle modifications, especially in terms of diet and exercises are recommended for effective management of diabetes symptoms and long-term effects. Since it is a global health issue, studies regarding the diabetes mellitus pathophysiology are currently in progress in order to minimize its associated health effects, and also, to treat it effectively.