Page 168 - 86 human physiology part-2

Development: Birth Through Death

Technically, menopause refers to the cessation of menses; whereas the gradual process through
which this occurs, which typically takes a year but may last as little as six months or more than five
years, is known as climacteric. Popular use, however, replaces climacteric with menopause. A natural
or physiological menopause is that which occurs as a part of a woman's normal aging process.
However, menopause can be surgically induced by such procedures as hysterectomy (when this
procedure includes oophorectomy, removal of the ovaries).

The average onset of menopause is 50.5 years, but some women enter menopause at a younger
age, especially if they have suffered from cancer or another serious illness and undergone
chemotherapy. Premature menopause (or premature ovarian failure) is defined as menopause occurring
before the age of 40, and occurs in one percent of women. Other causes of premature menopause
include autoimmune disorders, thyroid disease, and diabetes mellitus. Premature menopause is
diagnosed by measuring the levels of follicle stimulating hormone (FSH) and luteinizing hormone
(LH); the levels of these hormones will be higher if menopause has occurred. Rates of premature
menopause have been found to be significantly higher in both fraternal and identical twins;
approximately five percent of twins reach menopause before the age of 40. The reasons for this are not
completely understood. Transplants of ovarian tissue between identical twins have been successful in
restoring fertility.

Post-menopausal women, especially Caucasian women of European descent, are at increased risk
of osteoporosis.

Animals other than human beings rarely experience menopause, possibly because they simply do
not live long enough to reach it. However, recent studies have shown menopause in gorillas, with an
average age of 44 at onset.

Perimenopause refers to the time preceding menopause, during which the production of hormones
such as estrogen and progesterone diminishes and becomes more irregular. During this period fertility
diminishes. Menopause is arbitrarily defined as a minimum of twelve months without menstruation.
Perimenopause can begin as early as age 35, although it usually begins much later. It can last for a few
months or for several years. The duration of perimenopause cannot be predicted in advance.

Grandmother Hypothesis

Human females have the unique distinction of being one of the only species to stop reproduction
well before the end of their life span. This evolutionary distinction is odd because most other species
continue to reproduce until death, thus maximizing the number of offspring they produce. The
grandmother hypothesis essentially states that the presence of a grandmother has beneficial effect on
the survival of an infant. Humans are one of the slowest developing species in the animal kingdom, and
unlike many species infants, toddlers and children must be continuously cared for to ensure their
survival. (Compare that to the salmon that swims up stream, spawns and dies)

Etiology

The cessation of menses is the result of the eventual atresia of almost all oocytes in the ovaries.
This causes an increase in circulating FSH and LH levels as there are a decreased number of oocytes
responding to these hormones and producing estrogen. This decrease in the production of estrogen

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