Page 171 - 86 human physiology part-2

Chapter 19

attacks and a decline in DNA's mechanism of self repair. Things such as free radicals attack DNA and
other molecules causing structual changes. These changes in DNA endanger the synthesis of enzymes
and other proteins that are required for life. This damage interferes with cell division.

Most researchers believe that aging is a combination of an internal clock that ticks out the life span
of cells and the accumulation damage to DNA.

Old Age Diseases

Diabetes

Diabetes mellitus is a disease characterized by persistent hyperglycemia (high blood sugar levels),
resulting either from inadequate secretion of the hormone insulin, an inadequate response of target cells
to insulin, or a combination of these factors. Diabetes is a metabolic disease requiring medical
diagnosis, treatment and lifestyle changes

Type 1 diabetes mellitus is characterized by loss of the insulin-producing beta cells of the islets of
Langerhans of the pancreas. Sensitivity and responsiveness to insulin are usually normal, especially in
the early stages. This type comprises up to 10% of total cases in North America and Europe, though
this varies by geographical location. This type of diabetes can affect children or adults, but has
traditionally been termed "juvenile diabetes" because it represents a majority of cases of diabetes
affecting children. The most common cause of beta cell loss leading to type 1 diabetes is autoimmune
destruction, accompanied by antibodies directed against insulin and islet cell proteins. The principal
treatment of type 1 diabetes, even from the earliest stages, is replacement of insulin. Without insulin,
ketosis and diabetic ketoacidosis can develop.

Type 2 diabetes mellitus is due to a combination of defective insulin secretion and defective
responsiveness to insulin (often termed reduced insulin sensitivity). In early stages the predominant
abnormality is reduced insulin sensitivity, characterized by elevated levels of insulin in the blood. The
initial defect of insulin secretion is subtle and initially involves only the earliest phase of insulin
secretion. In the early stages, hyperglycemia can be reversed by a variety of measures and medications
that improve insulin sensitivity or reduce glucose production by the liver, but as the disease progresses
the impairment of insulin secretion worsens, and therapeutic replacement of insulin often becomes
necessary. Type 2 diabetes is quite common, comprising 90% or more of cases of diabetes in many
populations. There is a strong association with obesity and with aging, although in the last decade it has
increasingly begun to affect older children and adolescents. In the past, this type of diabetes was often
termed adult-onset diabetes or maturity-onset diabetes.

Gestational diabetes, Type III, also involve a combination of inadequate insulin secretion and
responsiveness, resembling type 2 diabetes in several respects. It develops during pregnancy and may
improve or disappear after delivery. Even though it may be transient, gestational diabetes may damage
the health of the fetus or mother, and about 40% of women with gestational diabetes develop type 2
diabetes later in life.

386 | Human Physiology