Diabetes Symptoms, Diagnosis & Treatment - DiabetesCarePlan.org
What is Diabetes?
Elevation of blood glucose level, due to defect in insulin secretion and/or action is a characteristic feature of diabetes.
Where does the glucose in the blood come from? How is it maintained within normal limits in a normal person? Why is it elevated in diabetics?
To answer these questions, one should understand the normal mechanism of control of blood glucose level.
Food
Food supplies fuel for various activities, repairs wear and tear of the body and provides nutrients essential for growth. The food consists of carbohydrates, proteins, fats, vitamins, minerals and water etc. (See Chapter 6 for a detailed discussion of normal nutrition). Food is digested by the digestive juices produced by the stomach, small intestine, and pancreas into simple substances suitable for absorption, carbohydrates are broken down into glucose, proteins into amino acids, and fats into fatty acids and glycerol. These substances are absorbed into the blood through the small intestine.
Blood glucose
The popular notion that sugar is present only in the blood of a diabetic and not in that of a normal person is unfounded. Sugar is present in the blood of a normal person too. The type of sugar that is present in the blood is glucose or grape sugar. The blood glucose level of a normal person in fasting state is between 70 and 11Omg/dl (dl=one hundredth part of a liter). After a meal it does increase even in a normal person, but remains within narrow limits because the production and consumption of glucose are balanced by each other
Glands in the body
There are two types of glands in the body. Some of them have a tube or a duct which carries their secretion to a particular place. For example, saliva, the secretion of salivary glands is carried by means of ducts to the mouth. On the other hand, there are some glands which do not have a duct or a tube. Their secretions enter the blood directly and exercise control over various functions of the body. Such glands are called endocrine glands and their secretions are called hormones. Examples of endocrine glands are the pituitary situated at the base of the skull, the thyroid and the parathyroids situated in the neck, the adrenals situated above the kidney and the gonads. (see Fig.l)
What is insulin?
Pancreas or sweet bread weighing 70 g is situated in the abdomen behind the stomach. Its head is enclosed by the duodenum, a "C" shaped tube-like structure. The duodenum connects the stomach at its upper end to the small intestine at the lower end (Fig. 2). A major portion of the pancreas (97-98 per cent of the gland mass) produces digestive juice. Within the vast number of cells producing digestive juice, there are islands of cells called the islets of Langerhans (2-3 per cent of the gland mass). The islets of Langerhans contain several types of cells. The beta cells of the islets of Langerhans produce insulin, the alpha cells produce glucagon while the delta cells secrete somatostatin. The digestive juice of the pancreas is carried to the duodenum by a duct or a tube. Insulin, glucagon and somatostatin are not carried by the pancreatic duct but are released directly into the blood stream. Hence, insulin, glucagon and somatostatin are hormones of the pancreas.
Fuels of the body
the products of digested food, namely glucose, amino acids, fatty acids, serve fuel to the body. These fuels, when in plenty as after a meal, are stored in the liver, muscles and fat depots. Glucose is not stored in the liver as such but in the form of a complex substance called glycogen.
A steady supply of glucose is essential for the proper functioning of ihe brain. In the fasting state, glycogen in the liver is broken down into glucose for supplying glucose to the brain. Thus in the fasting state, the fuel is mobilised from the storage depots to the blood, while after a meal the fuel is mobilised from the blood to the storage depots.
What does insulin do?
Insulin is a powerful hormone which enables the liver to store glucose in the form of glycogen. It enables the muscles and fat depots to take up glucose and store it in the form of glycogen and fat respectively. Through insulin, the muscle proteins get replenished by amino acids derived from food. Thus, insulin is essential for the utilization and storage of body fuels. Insulin suppresses the output of glucose, from glycogen and other sources by liver. It also checks the breakdown of body proteins and fats. The net action of insulin is to reduce blood glucose level.
Before insulin acts, it has to get itself attached to the binding sites or receptors on the surface of the cells. Insulin fits into the receptors, just as a key fits into a lock. After insulin fits into the receptors, signals are sent to the cell to carry out the action of insulin.
Other hormones
Glucagon produced by the alpha cells of the islets of Langerhans, increases the output of glucose by liver from glycogen and other sources. Somatostatin produced by the delta cells of the islets of Langerhans, inhibits action of both insulin and glucagon. Some hormones secreted by adrenal glands and the growth hormone produced by the front part of the pituitary gland increase the output of glucose by liver and reduce the uptake of glucose by the tissues. These hermones promote the breakdown of fats and proteins. Thus they oppose the action of insulin and increase the blood glucose level.
In the fasting state, the production of insulin is at a low level. Therefore, the fuels are mobilized from the depots into the blood stream. When the person is "fed", the production of insulin is increased. Insulin thus released, enables the fuels to be used and stored in depots, as explained earlier.
In a normal person, there is a fine adjustment between insulin and other hormones, with the result that the blood glucose level neither falls to a very low level while fasting nor does it rise excessively after meals.
What happens in diabetes?
Diabetes is produced by defective insulin action to a greater or lesser extent. The defective insulin action may be due to diminished production and/or resistance to its action. The body fuels are neither used up nor stored. The blood glucose level therefore rises. When diabetes is mild, the rise in blood glucose level occurs only after meals but the fasting blood glucose is normal or near normal. When insulin shortage is severe, blood glucose level is high even when the person is fasting.
When diabetes develops at a young age, the production of insulin is very deficient. But in overweight middle-aged diabetics, the absolute amount of insulin produced may be more than normal. Yet diabetes develops due to resistance to insulin.
In some persons with diabetes, the amount of insulin and the number of insulin receptors are adequate but the signals to the cells do not come through even though insulin gets attached to the receptors.
In normal persons, glucose does not appear in the urine unless the blood glucose level exceeds a certain limit. This limit is called renal (of kidney) threshold for glucose and is around 180 mg/dl (see Ch. 4) and varies in different individuals. The kidneys act as a dam that prevents flow of glucose from the blood into the urine. An elevated blood glucose level is the primary development in diabetes and spilling of glucose in the urine is a secondary effect.