Back To CoursePathophysiology Textbook
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Jen has taught biology and related fields to students from Kindergarten to University. She has a Master's Degree in Physiology.
Have you ever heard someone talk about a friend or relation who has 'sugar?' It's a too sweet term for a serious condition. Diabetes mellitus, usually just called diabetes, is a condition in which the body is unable to use glucose properly. Diabetics mostly fall into one of two groups, based on what factors cause the disease. Unlike type 1 diabetes, which is caused by a lack of insulin in the body, type 2 diabetes, is a condition caused by either the body's inability to make enough insulin, or an inability to use the insulin it makes.
Before we get any further, let's review how a healthy body provides its cells with the energy it needs for metabolism. After a healthy person eats a meal, the body breaks it down into simpler parts for the cells to use. Many carbohydrates are broken down into a simple sugar called glucose, which is absorbed by the small intestine, where it enters the bloodstream to be transported to cells. But, glucose can't enter the cells without the help of the protein hormone responsible for helping get glucose into cells, insulin. Insulin is made in the beta cells of the pancreas and is released when blood glucose levels are high. So normally, when blood glucose levels go up, insulin is secreted, and glucose gets stashed away in the cells, where it's either used for energy or stored, usually in the form of starch or fat. This makes blood glucose levels go back down.
In type 2 diabetes, though, even though there is insulin present, and many times plenty of it, the body's cells stop reacting properly to insulin. This is called insulin resistance, the condition in which cells don't respond normally to insulin. Insulin resistance occurs when the body saturates cells with a lot of insulin for a long period of time - the cells become less sensitive to it. It's a little like what would happen if you were trapped in a room with a strong smell. After a while, the odor doesn't smell as strong.
What are some things in a person's life that might lead to insulin resistance? The list is long. However, well-known risk factors include:
Unhealthy lifestyle choices: Type 2 diabetes is caused by the things we know we shouldn't do, but do anyway. High fat, low fiber diets, lack of exercise, and smoking have all been implicated in the disease.
Physiological Problems: Unhealthy lifestyle choices lead to other risk factors. High blood pressure, low HDL (good) cholesterol, and high levels of triglycerides in the blood stream are all separate risk factors for type 2 diabetes.
Family Factors: Genetics plays a big role in your chances of becoming a type 2 diabetic, as do race and ethnicity. African Americans, Hispanic Americans, Asian Americans, and Native Americans all have a higher risk than Caucasians do.
Age: Insulin resistance tends to naturally increase as we age. People ages 45 or older have a greater risk for type 2 diabetes than younger people do. This factor is one reason why type 2 diabetes used to be called 'adult onset' diabetes. However, that term is no longer used, especially since type 2 diabetes in children is skyrocketing, mostly because of the childhood obesity epidemic.
Weight and Fat Distribution: Obesity is by far the most famous risk factor for type 2 diabetes. There is a clear correlation between the number of people who are clinically obese and the number of people who have type 2 diabetes. Furthermore, people who store fat around their abdomen (people who are 'apple shaped') tend to be diabetic more frequently than those who accumulate fat in other places.
Prediabetes: Prediabetes means that some of the criteria used to diagnose diabetes are met in a patient. We'll talk about what this means as we discuss symptoms of type 2 diabetes. As a risk factor, prediabetes is significant, increasing a person's likelihood of becoming type 2 diabetic by at least 25%.
Now that we know the risk factors for type 2 diabetes, let's look at how we become insulin resistant and how this insulin resistance leads to symptoms of type 2 diabetes.
The mechanism for insulin resistance is very complex. A person might not be insulin resistant in some tissues, like liver tissue, but be resistant in others, like adipose (fat) tissue. In fact, while scientists are fairly sure of the correlation between insulin resistance and obesity, they're faced with a 'chicken or the egg' problem; that is, it's not clear if insulin resistance causes obesity or the other way around.
What they do know is that when a combination of risk factors makes a person insulin resistant, the hormone loses its effectiveness, and muscle, fat, and liver cells don't take up glucose. In response, the body makes even more insulin in an effort to drop blood glucose levels - and it works...at first. Eventually, though, even this increase in insulin doesn't do anything, and so the pancreas' beta cells make even more. The cycle continues with blood glucose levels increasing and the beta cells making more insulin to compensate... until eventually, the beta cell function starts to decline, leaving just high concentrations of glucose in the blood.
This high concentration of glucose in the blood is called hyperglycemia, and it is probably the most well-known symptom of diabetes. This makes sense: if insulin isn't able to help glucose get into cells, then it's going to remain in high levels in the bloodstream. In a normal person, fasting blood glucose levels are usually around 100mg/dL. In a prediabetic person, it ranges from 100 mg/dL to about 125 mg/dL, and in a diabetic person, it's 126 mg/dL or more.
In the early stages of type 2 diabetes, hyperglycemia often appears with another 'hyper' symptom: hyperinsulinemia, a high concentration of insulin in the blood. Hyperinsulinemia starts to disappear when beta cell function declines.
Before we leave blood parameters that mark type 2 diabetes, let's talk about one more: Hba1c. This is a measure of glycosylated hemoglobin, basically, how much glucose is attached to the hemoglobin present in red blood cells. The longer a person is in a state of hyperglycemia, the higher their Hba1c. In a normal person, it's less than 5.7%. It's elevated in prediabetes, up to 6.4%, and high in diabetics, where it's over 6.5%.
Type 2 diabetes also usually appears with what medical professionals sometimes call the 'three Ps': polyphagia, a frequent feeling of being hungry; polydipsia, drinking frequently to try and quench a constant feeling of thirst, and polyuria, a frequent need to urinate. You should notice that the word 'frequently' appears in all three definitions, as does the Greek root 'poly.' 'Poly' means 'frequently.' Other symptoms include blurred vision, glucose in the urine, fatigue, and the inability to heal cuts and infections quickly. Prediabetics also experience some of these symptoms.
All of the symptoms make sense when you use an 'if/then' type of logic. If cells aren't able to use glucose, then it's going to trigger the body's hunger response and also make you feel tired and energy-deprived. If there is a high concentration of glucose in the blood, then the kidney won't be able to absorb it all, and some will spill into the urine. If there is a high concentration of glucose in the urine, then more water will move into the urine through osmosis, creating a large urine output. If a lot of water is lost through a high volume of urine, then the body will activate the thirst response. If there is an elevated level of blood glucose, then the circulatory system will react to this constant saturation by becoming compromised, leading to symptoms like poor wound healing and elevated levels of Hba1c.
Both the prognosis and treatment of type 2 diabetes are very variable and focus on managing blood sugar. Patients must monitor their blood glucose daily using a blood glucose monitor and also regularly have a doctor check their Hba1c. These two things together tell both doctors and patients how 'in control' a person is, that is, how close blood glucose is to normal.
In some cases, lifestyle changes like increasing exercise, eating a low salt/low refined sugar/high fiber diet, and quitting smoking will be enough to keep blood glucose levels within a proper range. In some cases, medication that either improves insulin sensitivity or lowers blood glucose need to be taken. In more extreme cases, insulin itself will need to be administered through injection.
Patients who don't commit to lifestyle changes that help keep their blood glucose under tight control face a number of problems, many of which end in 'pathy,' which means 'disease of.' Chronic hyperglycemia can lead to retinopathy (eye damage), nephropathy (kidney damage) and neuropathy (nerve damage). Furthermore, the damage to the cardiovascular system can lead to maladies like a compromised immune system and stroke.
In some cases, when hyperglycemia is extreme, the body, unable to use glucose, turns to breaking down fat stores, releasing ketone bodies at a high rate into the blood. This condition can be fatal if the blood becomes too acidic. This is called ketoacidosis.
Let's review what we've learned about type 2 diabetes. Type 2 diabetes is a condition caused by the body's inability to make enough insulin or to use the insulin it makes. In a healthy person, the protein hormone responsible for helping get glucose into cells, called insulin, keeps the level of glucose in the blood fairly stable. In type 2 diabetes, however, cells become insulin resistant; that is, they no longer respond to insulin properly.
There are many risk factors that increase a person's likelihood for getting type 2 diabetes, including genetics, age, and unhealthy lifestyle choices, such as a poor diet and obesity.
Insulin resistance leads to a high elevation of glucose in the blood, hyperglycemia. In an effort to counteract hyperglycemia, the pancreas makes more insulin, causing insulinemia, a high elevation of insulin in the blood.
Hyperglycemia is the root cause of most of the symptoms of type 2 diabetes, including:
- elevated Hba1c, glycosylated hemoglobin
- polyphagia, the increased need to eat
- polydipsia, the increased need to drink
- polyuria, the increased need to urinate
The prognosis and treatment of type 2 diabetes is unique to each patient, and depends, at least in part, on patient compliance. Treatments include diet and exercise, medications to increase insulin sensitivity and/or lower blood glucose, or, in some cases, administration of external insulin.
Patients who don't take care in maintaining a consistent blood glucose level face eye, kidney, and nerve damage, as well as a potentially fatal condition called ketoacidosis, the state of a high number of ketone bodies in the blood.
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Back To CoursePathophysiology Textbook
20 chapters | 274 lessons