What Is the Pathogenesis of Types I and II Diabetes Mellitus?

Medically Reviewed on 6/3/2022
What Is the Pathogenesis of Types I and II Diabetes Mellitus
Learn about what causes type I vs. type II diabetes

Diabetes mellitus is a group of metabolic illnesses characterized by persistent hyperglycemia caused by abnormalities in insulin production, insulin action, or both. 

  • Type I diabetes mellitus is caused by an autoimmune reaction to proteins in the pancreatic islets cells.
  • Type II diabetes mellitus is caused by a combination of genetic factors related to impaired insulin secretion, insulin resistance and environmental factors such as obesity, genetics, lack of exercise, stress and aging

In diabetes, the body is unable to appropriately use and store glucose. Glucose then builds up in your system, leading to excessively high levels that can cause damage if not treated and managed.

Learn about what causes type I vs. type II diabetes.

What causes type I vs. type II diabetes?

Types I and II diabetes mellitus have different fundamental causes, but the outcomes are ultimately the same. Problems with insulin cause glucose levels in the blood to increase, potentially leading to consequences such as nerve and eye damage if left untreated.

Type I diabetes mellitus pathogenesis

  • The immune system begins fighting itself, notably its own beta cells. 
  • When there are fewer beta cells, less insulin is produced in the body. 
  • Less insulin means that glucose remains in the bloodstream, which starves the cells.
  • Beta cells are assumed to be entirely eliminated when type I diabetes mellitus advances (although some early research suggests there may still be some faint activity of beta cells in some people with type I diabetes mellitus).
  • The majority of people with type I diabetes must begin injecting insulin as soon as they are diagnosed. 
  • They must be cautious about what they consume to minimize blood sugar spikes, but type I diabetes mellitus cannot be treated purely by nutrition
  • Type I diabetes mellitus is defined as insulin-dependent due to the need for insulin therapy.

Type II diabetes mellitus pathogenesis

  • The main problem is insulin resistance.
  • In type II diabetes mellitus, there is hyperinsulinemia (increased insulin secretion). However, insulin cannot enter the muscle cells because the cells develop resistance to insulin.
  • Genetics and obesity are key factors that affect insulin resistance and susceptibility. The higher your body mass index, the more difficult it is for your body to use insulin effectively.
  • Type II diabetes mellitus can be controlled with diet and exercise in the early stages. 
  • However, as type II diabetes mellitus progresses, the body's ability to produce enough insulin to force its way into the cells declines. When this occurs, people with type II diabetes mellitus must begin insulin injections.

What are common symptoms of types I and II diabetes?

Types I and II diabetes mellitus have symptoms that are comparable in both men and women. There are several early warning signs, including itchy skin and delayed healing of wounds or cuts. However, some signs may appear gradually.

Common diabetes symptoms include:

Diabetes symptoms in men include:

Diabetes symptoms in women include:

What are risk factors for types I and II diabetes?

The appearance of types I and II diabetes mellitus symptoms differs. 

  • Type I diabetes mellitus can strike swiftly, which makes it difficult to disregard. This is significant because ignoring symptoms might result in diabetic ketoacidosis.
  • Type II diabetes mellitus can be more difficult to detect because it develops more slowly, particularly in the early stages. Hence, it is critical to understand your risk of type II diabetes mellitus. Some people have diabetes and are unaware of it. 

The American Diabetes Association advises getting a diabetes screening every 3 years beginning at the age of 45. If you are more likely to develop diabetes, your doctor may encourage you to get tested sooner or more regularly.

Risk factors for diabetes include:

Because people with prediabetes may not always show symptoms, it is critical to be aware of these risk factors and to share any concerns you have with your doctor. 


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What are early warning signs of diabetes?

Type II diabetes mellitus presents a wide spectrum of symptoms in its early stages:

  • Urinating frequently
  • Feeling very thirsty 
  • Feeling very hungry even when you’ve had plenty to eat
  • Slow-healing wounds
  • Tingling or numbness in the hands and feet caused by poor blood circulation
  • Dark, velvety patches of skin (acanthosis nigricans)
  • Extreme fatigue 
  • Blurred vision 

Type I diabetes mellitus can cause the symptoms indicated above, as well as sudden weight loss, fruity-smelling breath, and stupor. In the case of type I diabetes mellitus, however, the necessity for urgent medical intervention is typically obvious. 

Early warning signs of type II diabetes mellitus may not be obvious for many years after the illness has begun. If you are at a higher risk of type II diabetes mellitus, do not wait until you start experiencing the symptoms described above to contact a doctor. Diabetes is a chronic disease that requires an active approach to treatment.

What are treatment options for type I diabetes mellitus?

The majority of people with type I diabetes mellitus are diagnosed as children or young adults, and insulin therapy is required for survival. Anyone on insulin must routinely monitor their blood glucose levels to match the insulin requirement of their body.

Types of insulin therapies for people with type 1 diabetes mellitus include:

  • Insulin injections:
    • Most people with type I diabetes inject insulin into fatty tissues beneath their skin with a syringe or prefilled injection pen. 
    • Varied types of insulin have different half-lives. 
    • Short-acting insulin begins working in 15 minutes and lasts 2-4 hours. 
    • Other types of insulin work slowly over a period of 6, 12, or 24 hours or even longer.
    • There are several choices for matching your insulin dose to your eating patterns, blood glucose levels and degree of physical activity throughout the day.
  • Insulin pump:
    • Insulin pumps are small, wearable, computerized, battery-powered devices that supply a consistent amount of insulin throughout the day through a little plastic tube (catheter) that is placed beneath the skin. 
    • You can use the pump to administer an insulin boost as needed. 
    • Newer pump systems connect an insulin pump to a continuous blood glucose monitor through software and wireless technologies, automating insulin administration in response to blood glucose readings.
  • Inhaled insulin:
    • Although uncommon, another approach to acquire insulin is to use an apparatus to breathe it into your lungs.
    • The insulin accessible in the inhalation device acts quickly (within 12 minutes) but only lasts a few hours. 
    • People with respiratory diseases such as asthma, chronic bronchitis, or emphysema should not use inhaled insulin.

What are complications of type 1 diabetes mellitus?

If a person with type I diabetes mellitus does not get appropriate insulin for an extended period of time, they may develop a potentially fatal condition known as diabetic ketoacidosis (DKA). 

Symptoms of DKA include:

DKA must be treated at the hospital as an emergency. Even if there is no emergency, elevated blood glucose levels can cause a variety of health concerns in the long run. High blood glucose levels can damage blood vessels and neurons.

Complications of type I diabetes mellitus apart from DKA include:

  • Eye damage, leading to blindness
  • Kidney damage, leading to kidney failure
  • Neuropathy (nerve damage), leading to pain and numbness in the hands and feet
  • Increased (doubled) risk of heart disease and death from heart problems
  • Increased risk of strokes (and disability from strokes) and death

Keeping your blood glucose levels as close to normal as possible will help you avoid these issues. 

What are treatment options for type II diabetes mellitus?

Adults are more likely to develop type II diabetes mellitus. Children and adolescents who are overweight are at a risk of type 2 diabetes mellitus. Eating well, being physically active and maintaining a healthy body weight are the key to successfully treating type II diabetes mellitus.

Treatment options for type II diabetes mellitus include

  • Nutrition: Consume a diet rich in fruits and vegetables, whole grains, fat-free or low-fat dairy products, and lean protein. Watch your portion sizes and avoid “empty” calories.
  • Physical activity: Since your muscles need glucose for fuel, staying active throughout the day will reduce your blood glucose levels.  Aim for 150 minutes of physical activity every week or 30 minutes at least 5 days a week.
  • Weight loss: Eating better and moving more will put you on the right track to shedding extra weight, which will help reduce blood glucose levels and slow the progression of type II diabetes mellitus.
  • Medications and injections: In addition to adopting healthy lifestyle habits, many people with type II diabetes use drugs to control their blood glucose levels. The most popular types of diabetic medicines include:
    • Metformin (pill)
    • Sulfonylureas (pill)
    • GLP-1 agonists (injections)
    • DPP-4 inhibitors (pill)
    • SGLT2 inhibitors (pill)
    • Insulin (injections)

Metformin is the first-line therapy for the majority of people with type II diabetes mellitus. Other drugs might be used in addition to metformin if necessary.

What are complications of type II diabetes mellitus?

Hyperosmolar hyperglycemia (HHS) is a potentially fatal disease that occurs in people with type II diabetes mellitus when blood glucose levels are extremely high. It is identical to diabetic ketoacidosis. 

Common symptoms HHS include:

HHS is frequently caused by an infection (such as pneumonia) or another sickness (such as a heart attack or stroke). HHS requires emergency hospital treatment in the hospital.

Type II diabetes mellitus, like type I diabetes mellitus, has all of the same long-term consequences. 

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Medically Reviewed on 6/3/2022
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Diagnosis, epidemiology and pathogenesis of diabetes mellitus: An update for psychiatrists: https://www.cambridge.org/core/journals/the-british-journal-of-psychiatry/article/diagnosis-epidemiology-and-pathogenesis-of-diabetes-mellitus-an-update-for-psychiatrists/6EBD0907F86D671090BF890A70E02CD6

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