Pancreas

The endocrine part of the pancreas consists of specialized groups of
cells known as Islets of Langerhans. These cells synthesize, store and
secrete two hormones namely insulin and glucagon. There are two kinds of
cells namely, alpha and beta cells. The alpha cells produce glucagon while the beta cells secrete insulin. In addition to alpha and beta cells another type
of cells called delta cells are present in human pancreas. According to some
investigators the delta cells represent the transitional forms of the two cell
types alpha and beta.

Insulin (Pancreas)

Insulin is a protein hormone or a polypeptide hormone with 51 amino
acid residues. Human insulin has a molecular weight of 5,734 daltons. It
consists of two chains A and B, which are linked together by disulphide bridges
formed between two cystine residues.

Physiological effects of Insulin

It decreases glucose level in the blood in three ways:
a. It increases conversion of glucose into glycogen and deposition of it in
liver and muscles.
b. It increases the rate of oxidation of glucose in the tissues.
c. It increases the rate of conversion of glucose into fat and facilitates its
storage in adipose tissue.
d. It also regulates the rate at which amino acids are catabolised into water
and CO2.
e. Moderately, it also regulates the gluconeogenesis in the liver.

Thus, insulin reduces the glucose level in the blood (Hypoglycemia).
If the insulin is not secreted sufficiently, the liver and the muscles are unable
to convert the glucose into glycogen. As a result more glucose enters into the
bloodstream raising the blood sugar level. This condition is called
Hyperglycemia. The excess of glucose is eliminated along with the urine
resulting in a disease called diabetes mellitus. A diabetic patient excretes
large amount of urine (polyurea) and consumes excessive fluid
(polydipsia). He always feels hungry and eats excessively (polyphagia).
When insulin levels are low, fat catabolism is increased and fats are
converted into glucose. This further increases blood glucose levels and
results in the accumulation of ketone bodies (Ketosis). (Pancreas)

Hyperglycemia

The normal fasting blood glucose level is 70 to 110 mg/dl
(dl = deciliter). This range is maintained under varying conditions of food
intake, fasting or body exercise. After a carbohydrate meal the blood sugar
may reach a peak level of about 140mg/dl. If such a high level is maintained
for a prolonged time, the condition may be termed as hyperglycemia.
Hyperglycemia over a long period may cause degenerative changes in several
organs and systems leading to malfunctions and mortality. Elevated blood
sugar level of 400 mg/dl or more, in a few days causes dehydration leading
to coma and death. (Pancreas)

Hypoglycemia

It means a low plasma glucose concentration. This concentration can
drop to very low values during fasting. It is termed as fasting hypoglycemia.
It may result due to excess of insulin or other physiological factors. There is
no fixed level of blood sugar at which hypoglycemia occurs.
Fasting hypoglycemia may show symptoms such as hunger, increased
heart rate, tremulousness, weakness, nervousness and sweating. These are
caused due to activities of the sympathetic nervous system. Other symptoms
such as headache, confusion, uncoordination and slurred speech are due to
availability of too little glucans to the brain. Serious brain defects such as
convulsions (epilepsy) and coma can occur if the plasma glucose
concentration goes low. (Pancreas)

Diabetes Mellitus

The name ‘diabetes’ in Greek means ‘syphon’ or ‘running through’.
This term describes the enormity of urinary volume excreted by people suffering
from this disease. A persistant hyperglycemia leads to
diabetes mellitus. This disease can be due to a deficiency of insulin or to a
hypo responsiveness to insulin.
In type I (insulin dependent) diabetes, the hormone is completely
or almost completely absent from the islets of Langerhans and the plasma. In
type II (insulin-independent) diabetes, the hormone is often present in plasma
at near normal or even above normal levels. (Pancreas)

The type I is less common. It is due to the total or near total destruction
of the pancreatic b cells.

The type II is due to insulin resistance. The insulin target cells do not
respond normally to the circulating insulin. This may result due to obesity,
over-eating and lack of exercise. The insulin hyporesponsiveness can be
corrected if the person reduces his or her caloric intake. Thus dietary control
without any other therapy is frequently sufficient to eliminate the elevated
blood glucose level of type II diabetics. An exercise programme is also
useful, since it will help to increase the number of insulin receptors.

Glucagon

Glucagon, secreted by the alpha cells of the pancreas is a polypeptide
hormone with 29 amino acids residues.

Physiological actions of glucagon

The major function of glucagon in the body is to elevate the blood
glucose level by glycogenolysis in the liver. As it raises the blood sugar level
it is also called as Hyperglycemic hormone. A second important function of
glucagon is the gluconeogenesis in the liver in which amino acids are used as
substrates. It promotes lipolysis and the release of fatty acids in the adipose
tissues. The increased fatty acid oxidation leads to ketogenesis. Glucagon
also stimulates the myocardial contractility. Glucagon exerts a direct effect
upon the kidneys and accelerates the renal plasma flow and glomerular
filtration rate. A proper balance between insulin and glucagon production is
necessary to maintain proper blood glucose level. (Pancreas)