The Aetiology Of Diabetes Mellitus Biology Essay

Published: Last Edited:

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.


Diabetes mellitus is a common metabolic disease associated with abnormally high levels of blood sugar (glucose), which results from absence or insufficient production of insulin, or resistance to insulin. Most patients excrete sweet urine due to high levels of glucose circulating in the bloodstream and feel great thirst. They are also characterized by abnormalities in fat and protein metabolism, inflammation, and immune system, especially regarding vascular and cardiac disease.

Insulin is a hormone made up of 51 amino acids. It is synthesized within the beta cells of the islets of Langerhans in the pancreas. It is regulating energy and glucose metabolism in the body. Insulin enables glucose to be used by the body cells and then stored it as glycogen in the liver and muscles. It can prevent the body from using fat or body protein as an energy source. Normally, insulin is released into the bloodstream after a meal and allows the glucose obtained from food to cells in the nerves and brain. When the insulin is absent or insufficient, the glucose cannot be taken up by the body cells and become excessive in the bloodstream and then excrete into the urine. If high level of glucose circulates in the blood consistently, it may damage organs, tissues, and blood vessels in the body, leading to serious complications such as heart disease, kidney failure, nerve damage, gangrene and blindness.


From the guidelines of the American Diabetes Association (ADA) in 1997, there are four types of diabetes: Type I insulin-dependent diabetes (IDDM), type II non-insulin-dependent diabetes (NIDDM), gestational diabetes and other specific types of diabetes mellitus due to genetic defects, exocrine disorder, drug or chemical induced causes. In 2003, the diagnosis of impaired fasting glucose is regarded as prediabetes. (Diabetes Care, 2009)

The aetiology of diabetes mellitus

Type I diabetics is also known as 'juvenile onset diabetes' that usually occurs in childhood or early adolescence, but it occasionally occurs in adult as latent autoimmune diabetes. Type I accounts for only 5-10% of all cases of diabetes. It is unable to produce any insulin due to autoimmune mediated destruction of insulin-producing cells (Beta-cell) in the pancreas. It is considered as an autoimmune disease that means the body's own immune system attacks and destroys healthy beta-cells in the pancreas by the production of autoantibodies. This abnormal immune response may be triggered by environmental factors such as virus, diet, or stress. During the insulin reaction of those people with Type I diabetes, there is not enough insulin to allow glucose into the cells, so the body will break down fat as a source of energy and waste products called acetone or ketones are produced. The ketones travel through the blood and excrete in the urine. It may lead to 'diabetic ketoacidosis'. By the way, those with a first degree relative (sibling or parents) with type I diabetes is a high risk group connecting to heredity with genetic component called HLA complex. (Daneman, D., 2006, 847-58)

Type II diabetes is also known as 'maturity onset diabetes'. It usually occurs in patients over 30 years old and overweight and affects 90% of the total diabetes population. Patients with Type II diabetes usually continue to produce insulin but they cannot rapidly increase the amounts of insulin secretion for the body's need after a meal. Sometimes mostly the cells of muscle and fat tissue lack the sensitivity to insulin and the insulin cannot work effectively, leading to hyperglycemia and diabetes. It is known as insulin resistance that is caused by defective insulin receptors. There are some risk factors for Type II diabetes: hypertension, dyslipidaemia, age greater than 45 years, overweight, high body mass index, high waist:hip ratio, and family history of diabetes. (Albache et al., 2010, p.85-91) Patients often have a lifestyle risk that involves in a high fat diet and low level of physical activities.

Gestational diabetes is most likely occurred in the last trimester of pregnant women. The pregnant women associated with insulin resistance cannot keep extra insulin to control blood sugar levels in balance in respond to pregnancy hormones. It will increase the risk of developing type II diabetes later. The excess glucose circulating in the mother's blood crosses the placenta to the foetus. The result of excessive in glucose and insulin can make the baby fat, and once the baby is born the blood sugar usually become normal. However, the baby may suffer from hypoglycaemia. Nevertheless, blood sugars usually return to normal once the baby is born. It is important to maintain the normal weight and good control of blood sugars during pregnancy. (Milchovich, S. K. & Dunn-Lung, B., 2007, p.4-6)

Other types of diabetes mellitus can be caused by another factor such as genetic defects of beta cell in pancreas, genetic defects in the action of insulin, endocrine disorder, drug or chemical induced, infection and genetic syndrome associated diabetes mellitus. (American Diabetes Association, 2008)

Prediabetes is also known as impaired glucose or impaired glucose tolerance. It is formerly called borderline diabetes. Those with prediabetes are usually overweight and have insulin resistance. (Milchovich, S. K. & Dunn-Lung, B., 2007, p.4-6) They have high risk to develop diabetes and cardiovascular disease. (Nathan et al, 2007, 753-759)


The symptoms of diabetes can affect anyone at any age. People with untreated diabetes can cause high sugar levels in blood and easy to loss glucose in the urine. The urine output is increased and leads to dehydration. So, the patient always feels great thirst and needs to drink much more water. They always feel tired, nausea and vomiting. The weight loss is very obvious in type I diabetes patient but it is not noticeable for gradual insulin resistance in type II. Patients associated with type I are always very thin but those with type I are always overweight. Patient associated with chronic hyperglycaemia causes pathological and functional changes. If glucose in blood is consistently high, it damages various organs (e.g. nervous system, cardiovascular system and renal system). Blurred vision, itchy or dry skin, frequent infection and taking a long time for wound healing are also signs for diabetes. The long term effects of diabetes develop the complications of retinopathy with potential blindness, cardiovascular disease, peripheral vascular and cerebrovascular disease, stroke, neuropathy with risk of foot ulcers, lower limb amputation and periodontitis. (Behl et al., 2008, 1411-1418) In the severe stage, ketoacidosis may develop and lead to coma or death. If the above signals appear, we should consult our doctor immediately.

Diagnosis of Diabetes Mellitus

Diagnostic criteria are mainly according to ADA in 1997. There are several laboratory tests for diabetes such as fasting plasma glucose (FPG), oral glucose tolerance test (OGTT), random plasma glucose test.

The fasting plasma glucose (FPG) test measures the amount of glucose in blood after a person has fasted for 8 to 12 hours. It is very easy to perform and convenient. The cost is low. Normal fasting plasma glucose levels are less than 100 milligrams per deciliter (mg/dl). People with a fasting glucose level of 100 to 125 mg/dl have a form of pre-diabetes called impaired fasting glucose (IFG) that leads to a high risk factor for diabetes. A fasting plasma glucose level is more than 126 mg/dl and is confirmed by repeating the test on different days that indicates diabetes.

The oral glucose tolerance test (OGTT) is a good for making the diagnosis of type II diabetes. It is commonly used for diagnosing gestational diabetes and in conditions of pre-diabetes. A person should have high carbohydrate diet for three days before the test. An OGTT measures blood glucose after the person fasts at least 8 hours but not more than 16 hours. The fasting plasma glucose is measured immediately before and two hours after a person drinks a liquid containing 75grams of glucose in water (100 grams for pregnant women). In a normal person without diabetes, the glucose levels rise and then fall quickly. In a person with diabetes, the glucose levels rise higher than normal and fail to come down rapidly. Normal range of OGTT is 139 mg/dl or below. If the blood glucose level is between 140 and 199 mg/dl in two hours after drinking the liquid, it leads to a form of pre-diabetes called impaired glucose tolerance (IGT). A person with IGT or IFG has increased cardiovascular risks and high risks for development of diabetes mellitus. (American Diabetes Association, 2007) If two hour glucose level of 200 mg/dl or above, it is confirmed by repeating the test on different days and this person indicates diabetes. For those with prediabetes and asymptomatic type 2 diabetes, age, obese and abnormal BMI have close relationships and regular examination for FPG or the 2-hour OGTT is needed for prevention of type II diabetes.

A random plasma glucose test is used to diagnosis diabetes by measuring blood glucose with an assessment of symptoms, but it is not good for pre-diabetes. It is confirmed by repeating the test on a different day. A blood glucose level of 200 mg/dl or higher, with the symptoms such as increased urination, great thirst, weight loss, tired, blurred vision, increased hunger, and longer time for wound healing, all indicate diabetes. The blood glucose level of patient should be confirmed by FPG and OGTT.

The hemoglobin A1c (HbA1c) measurement is used for measuring the percentage of hemoglobin that is sugar coated or glycosylated and reflects the average level of blood sugar over the preceding 3 months. (Gallagher, Roith & Bloomgarden, 2009) It should be used as an indicator for blood glucose control and as a marker for complications of type 2 diabetes. (Manley, S., 2003, 1182-90) The American Diabetes Association recommends HbA1c levels of less than 7.0%. The normal value can vary from different laboratory. Generally it will be about 4-6%.

In each clinic visit, blood glucose, blood pressure, serum lipid profiles (cholesterol or triglyceride), urinalysis (ketones or albumin) and body weight should be measured for clinical assessment of diabetes.


Diabetes is a chronic metabolic and lifelong disorder. Short term complications are very common. Hypoglycaemia affects patient who have to inject insulin or take glucose-lowering drugs to control their disease. Too much insulin circulates in the blood and it causes lower blood sugar levels. Hyperglycemia means too much sugar circulating in blood due to lack of insulin or insufficient of insulin and is main signal of out of control of diabetes. Diabetic ketoacidosis is caused by using fat as energy source when there is not enough sugar in the blood during an insulin reaction or there is not enough insulin to allow glucose into the cells and then fat is broke down into waste product called ketones. Moreover, ketones travel through the blood and pass out of body in the urine. The symptoms of diabetic ketoacidosis include nausea, vomiting, dehydration, abdominal pain, drowsiness and rapid breathing, leading to diabetic coma. Blurry vision may be result of high glucose level affecting the lens of the eye. Periodontal disease is associated with diabetes in adolescents due to poor metabolic control and bad oral hygiene. (Orlando, et al., 2010) If the patients are without proper treatment for these chronic complications, they can result from long term effects on microvascular or macrovascular complications. The microvascular disease may damage small blood vessels and always associates with eye problems, kidney damage, nerve damage and sexual problems. The macrovascular disease may damage large blood vessels and cause heart disease, arterioslerosis, high blood pressure and Sy Diabetic vascular complications are often asymptomatic during early stages.

ndrome X. (Moore, Gregory, Kumah-Crystal & Simmons, 2009)

Diabetic nephropathy

Diabetic nephropathy can lead to end stage of renal disease requiring dialysis or transplantation. It is caused when small blood vessels in the kidney become thickened. Initially, the protein may leak in urine and waste products cannot be filtered out of blood to urine. Patients may suffer from microalbuminuria that can develop into gross proteinuria. As it worsens, they also have high blood pressure and decreased function in glomerular filtration that may eventually lead to renal failure.

Diabetic Retinopathy

Diabetic retinopathy mostly occurs in patient who has long periods of uncontrolled diabetes. High glucose levels can form blockages in the small vessels in the retina. It results from macrovascular occlusion and microvascular leakage into retina. Abnormal new blood vessels grow on the surface of the retina and leak blood into the center of the eye. This is proliferative retinopathy. By the way, the fluid can leak into the center of macula leading to macular edema. Then, vision can become blurred or lost completely.


Diabetic neuropathy is mainly due to uncontrolled blood glucose that damages the nerve system. Peripheral neuropathy generally affects the feet, legs, arms and hands. The common symptoms are tingling, numbness and pain in the affected areas. It can result in gangrene and amputation. Autonomic neuropathy is the damage to nerves serving the heart and blood vessels, nerves in the eyes and lung, and the internal organs that can affect blood pressure. Proximal neuropathy affects thigh, hips, buttocks or legs. Focal neuropathy causes weakness of one nerve or a group of nerves in the body suddenly.

Cardiovascular disease

Male diabetics and pre-menopausal diabetic women have high risk of developing cardiovascular disease. The macrovascular disease can cause damage to large blood vessel. It may develop heart diseases, harden the arteries and high blood pressure.


Patients with type I diabetes are prescribed insulin therapy in order to restore insulin level to normal, prevent diabetic ketoacidosis, maintain glycemic control and reduce the risk of long-term complications. Instance, the change in lifestyle by taking up more exercise and balancing food can manage the diabetes well.

Treatment for type II diabetes is mainly by oral anti-hyperglycemic agents to lower blood glucose levels or drugs to stimulate insulin production. Insulin will be prescribed for type II diabetes if there are persistent symptoms such as weight loss, lack of energy, ketone found in the urine. Islet cell transplantation and pancreas transplantation are under developed in Britain and America for last resort treatment for diabetes.

Balancing diet, performing regular exercise and weight control are very important for reducing the risk of diabetes

From the investigations of the Diabetes Control and complications Trial (DCCT) in type 1 the UK Prospective Diabetes Study (UKPDS) in type 2 diabetes

Diabetic care plan:

The diabetic care plan is mainly a self management technique to suit the patient's age, social status and cultural level. Firstly, a patient has a medical check up for initial assessment of diabetes and its chronic complications. Secondly, patient should achieve an evaluation of glycemic control by periodical glycated haemoglobin (HbA1c) testing and self-monitoring of blood glucose. The stable value of HbA1c is under 7% and normal blood glucose concentrations can prevent the development of microvascular and macrovascular complications. Thirdly, a medical nutrition therapy is given to diabetic patient by dietician who will design suitable diet to fit for personal requirement, such as the appropriate intake of carbohydrate, low fat, low salt, high fibre, limit protein intake. A regular exercise plan is recommended to improve glycemic control, body weight control and prevent heart disease. Finally, stress management can help the patient with positive attitude towards the diabetes and diabetes-related complications, economic, social and psychological problems. (Micheli, A. D., 2008, 107-127). In facts, different countries have different treatment standards for diabetes mellitus according to their lifestyle, age, sex, diet, social and medical situation. A well cooperation between multidisciplinary professional and the general practitioner can provide a good diabetes care.