Exploring the anatomy and physiology of ageing Part 8 - the reproductive system

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In addition to a gradual age-related reduction in fertility, both men and women experience a variety of anatomical and physiological changes within their reproductive tracts. Some of these changes have far-reaching effects on organs and tissues distant from the reproductive areas. This article examines the major changes that occur within the female (Fig 1) and male
(Fig 2) reproductive tracts as a result of normal ageing and discusses treatments available for age-related symptoms.

Female reproductive system

The menopause
The menopause is a cessation of the normal menstrual cycle and is usually preceded by a perimenopausal phase of varied duration. In the UK the menopause usually occurs between the ages of 45 and 55 (Montague et al, 2005). By their mid 50s, most women have passed through the menopause, leaving their childbearing years behind. Many experience changes to their menstrual cycle in their 40s, with a gradual reduction in the frequency of ovulation.

Hormonal changes
The pituitary hormone that drives the menstrual cycle is follicle stimulating hormone (FSH). Levels of FSH in menopausal women remain high, often higher than in premenopausal women but the hormone appears unable to stimulate follicular development (Montague et al, 2005) and oestrogen production within the ovaries. Eventually follicular activity ceases altogether leading to a decline in the level of oestrogen secretion. Similarly, luteinising hormone (LH), which triggers ovulation, is secreted at normal levels and, as with FSH, levels may increase in post-menopausal women. However, in the absence of mature follicles, no ova can be released.

Consequences of reduced oestrogen
The reduction in oestrogen levels has a variety of negative consequences (Chahal and Drake, 2007) including:

• Reduction in bone density and skeletal mass, increasing the likelihood of osteoporosis. Women entering the menopause may lose up to 15% of their bone mass (Riggs and Melton, 1986), mainly from spongy bone, particularly in the vertebrae of the spine. This often leads to the curvature of the spine seen in postmenopausal women with osteoporosis (see part 10 in this series);

• Reduction in vasomotor control. As oestrogen levels fall, the thermoregulatory centre within the hypothalamus may go through a period of adaptation and fluctuation. This often results in alternating periods of vasodilation and vasoconstriction within the dermis of the skin, which are experienced as classic 'hot flushes';

• Shrinkage (atrophy) of oestrogen-dependent tissues (Chahal and Drake, 2007) including the breasts and vaginal walls. This may lead to breast sagging, which is exacerbated by age-related loss of skin elasticity (see part 11). The vaginal epithelia may thin and the vaginal walls and labia shrink. This effectively shortens the vagina. Together with a reduction in the natural lubricating secretions of the vagina, this may lead to vaginal bleeding, particularly after sex. The myometrium (muscular layer of the uterus) shrinks, with smooth muscle fibres replaced by adipose tissue (fat);

• Psychological changes. There is some evidence that reduced oestrogen levels can negatively affect memory and mood;

• A decrease in cardioprotective high-density lipoprotein (HDL 'good' cholesterol) and an increase in damaging low-density lipoprotein (LDL 'bad' cholesterol) associated with the build-up of atherosclerotic plaque (Montague et al, 2005). These changes correlate well with an increased risk of cerebrovascular accident (stroke), coronary artery disease (CAD) and myocardial infarction (MI);

• Loss of sex drive. Most women experience a drop in libido as they pass through the menopause. This is thought to be related to a reduction in circulating oestrogens and androgens (testosterone-like hormones produced by the adrenal glands).

Hormone replacement therapy
Although the age-associated changes described above cannot be prevented, some of the effects of the menopause can be reduced and alleviated by hormone replacement therapy (HRT). This is usually based around oestrogen or oestrogen and progesterone. It is reported to be effective in:

• Treating osteoporosis;

• Reducing the risk of bone fractures;

• Reducing the risk of colorectal cancer;

• Reducing vaginal dryness;

• Reducing hot flushes and night sweats;

• Improving sleep;

• Reducing headaches;

• Improving memory;

• Reducing panic attacks.

Some studies have revealed that certain forms of HRT (particularly combined oestrogen and progesterone) increase the risk of breast cancer (Bush et al, 2001), coronary artery disease, pulmonary embolism and stroke.

Male reproductive system

Men show an age-related reduction in testicular mass (Chahal and Drake, 2007). This corresponds to a reduction in spermatogenesis (sperm production) and testosterone release. A reduced sperm count is an inevitable consequence of male ageing but sperm are produced in such high numbers that even men in their 80s and 90s are capable of fathering children.

The sperm ducts (vas deferens) gradually become less elastic because of an accumulation of collagen (sclerosis). The output of the seminal vesicles and prostate gland may decrease, often reducing the volume of ejaculate.

Many men show an age-related increase in the size of the prostate gland, termed benign prostatic hypertrophy (BPH). Although this is generally harmless, it can lead to the prostate compressing the urethra, which makes micturition difficult. BPH often causes much anguish as the symptoms are similar to those of prostate cancer. In most cases, a simple blood test can rule out malignancy.

The andropause (male menopause)
Men do not experience the sudden physiological changes experienced by many women passing through the menopause.
They experience many gradual changes, collectively called the andropause (Chahal and Drake, 2007). These are thought to be caused by a gradual decline in levels of circulating testosterone. Its onset is slow and usually has a small impact on general health.

There have been few major studies on the andropause but it appears that the testosterone-secreting cells of the testes (interstitial cells) synthesise and release less testosterone. It is unclear whether this is caused by changes in the interstitial cells or in the secretions of the pituitary gland that governs testosterone output.

Reduced testosterone output may contribute to erectile dysfunction and can lead to impotency, particularly if associated with blood vessel disease. Reduced levels of testosterone are associated with some important physiological changes including:

• Increased body fat (usually central and visceral body fat);

• Reduced muscle mass;

• Reduced bone mass;

• Erectile dysfunction and reduced libido;

• Increased risk of anaemia.

There are few treatments for andropause although erectile dysfunction is often treated with drugs such as sildenafil (Viagra).

References

Bush, T.L. et al (2001) Hormone replacement therapy and breast cancer - a qualitative review. Obstetrics and Gynaecology; 98: 498-508.

Chahal, H.S., Drake, W.M. (2007) The endocrine system and ageing. Journal of Pathology; 211: 173-180.

Montague, S.E. et al (2005) Physiology for Nursing Practice (3rd ed). Oxford: Baillière Tindall.

Riggs, B.L., Melton, L.J.I. (1986) Involutional osteoporosis. New England Journal of Medicine; 314: 26, 1676-1686.

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