From its site of production in the testes, the sperm must travel through the sperm tract to reach the outside of the body. As it does so, the various components that make up the seminal fluid are added to the sperm. The sperm tract, illustrated in figure 3.7, consists of a number of ducts including the epididymis, the vas deferens, the ejaculatory duct, and the urethra. In addition, a number of glands that secrete various fluids join the sperm tract through a series of small ducts.

After being produced in the seminiferous tubules, the sperm are stored in the epididymis, which is a highly coiled, interconnected network of seminiferous tubules lying in the upper part of the testes. As the sperm mature in the epididymis, they become capable of movement as the neck of each sperm becomes flexible.

The vas deferens carries the sperm from the epididymis to the ejacu-latory duct. At this point, the ducts of the seminal vesicles join the sperm tract and provide a viscous, alkaline secretion containing fructose and prostaglandins. The fructose, a sugar, is a source of energy for the sperm; the prostaglandins stimulate uterine contractions and help the sperm move to the female's fallopian tubes where fertilization takes place. The prostate gland surrounds the ejaculatory duct at the place where it becomes the urethra. It secretes a milky fluid that aids in sperm motility. The fluid contains, among other things, a large concentration of bicarbonate ions that gives the semen its alkaline pH. The alkaline nature of the seminal vesicle fluid and the prostate gland fluid reduces the acidity present in the urinary system, which is joined to the sperm tract at the urethra. This is particularly important since sperm motility is adversely affected by an acidic environment. Finally, the bulbourethral glands (Cowper's glands) secrete a mucuslike substance that provides lubrication for the urethra.

The secretions just described are called seminal fluid, and the combination of sperm and seminal fluid is called semen. Since there frequently is confusion as to the distinction between sperm and semen, it is worthwhile to point out that while sperm are under the careful hormonal control previously described, the seminal fluid is produced by the body as needed and is not affected by hormonal levels. Also important is the fact that the semen contains an antibiotic substance called seminalplasmin. Were it not for seminalplasmin, seminal bacteria would almost always infect women's vaginas, making sexual intercourse a routine health hazard.


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Calcium in the diet is required not only for strong bones and the prevention of osteoporosis, but also for normal blood coagulation, nerve transmission processes, and both heart and muscle action.

In early childhood the body retains 150 mg of calcium from the diet each day. In adolescence, when bone growth is at its peak, 275-500 mg of calcium is deposited in bone each day. Later in adult life bone maintenance takes over from bone growth and less calcium is needed; nevertheless, an average of 180 g is required yearly.

Calcium is absorbed mainly in the duodenum and the jejunal (first) part of the small intestine, stored in bone during the day, and released for use during the night when its normal source, food, is not available. (Women experiencing the menopause lose calcium during the night; they should have a milky bedtime drink to counteract this.)

The required daily allowance of dietary calcium has been revised. International consensus is that the recommended daily allowance (RDA) of calcium is:

1000 mg/day for pre-menopausal women

1200 mg/day for peri-menopausal women

1400 mg/day for post-menopausal women

However, the RDA is under review and these figures may change.

A post-menopausal woman absorbs calcium less efficiently from the intestine and reabsorbs it more poorly in the kidneys. Higher levels of dietary calcium are therefore required. For women receiving HRT the daily intake of calcium may be lowered to 1200 mg, because oestrogen improves the absorption/reabsorption process.

Calcium is absorbed only in the 'elemental form' and several surveys indicate that only a small percentage of women take in sufficient dietary calcium on a daily basis.

Research has shown that, contrary to common belief, calcium is absorbed just as well from supplements as from calcium-rich food sources such as dairy products. An adequate supply of calcium is more important than its source. There has been a national decline in calcium uptake since the consumption of dairy foods dropped as a result of concern about their fat content.

Dietary sources of calcium

Rich sources of calcium include dairy products, bread, green vegetables, hard water, dried figs and the bones of canned sardines and salmon. Skimmed milk powder can be added to puddings and milky drinks to boost calcium intake without adding fat. Listed below is the calcium content of various foods.

There are other preparations, both single and combined. A doctor or pharmacist will help determine which product is the most desirable and cost-effective for you.

Because calcium is absorbed in the small intestine, it is important that any supplement should dissolve quite rapidly. This can be checked by placing a tablet in white vinegar. It should dissolve within 30 minutes. Calcium carbonate is best taken with a meal, as less gas and wind may be produced this way.

Evidence was presented at the 1990 International Conference on Calcium Regulating Hormones (held in Montreal) to the effect that calcium, whether tablets or liquid, was absorbed better from the intestine when in the citrate or malate form rather than as the carbonate. In the USA calcium is available combined with citric and malic acids in tablets and as an orange juice preparation.

Factors affecting calcium absorption

As described earlier, phytic acid and dietary oxalate (such as is found in spinach and rhubarb) reduce calcium absorption. Other dietary factors can lead to a lack of calcium. These are:

Lactase enzyme deficiency Milk intolerance is not unusual. The sufferer is unable to digest milk products because of a lack of the lactase enzyme, and this results in poor calcium absorption from the bowel, abdominal pain and diarrhoea. This deficiency of lactase, and poor lactose intake, can be overcome by eating yoghurt. This fermented product contains friendly bacteria which produce the lactase enzyme, and in turn lactose is able to be absorbed along with calcium.

Low dietary fat Vitamin D is manufactured, in part, in the skin following exposure to sunlight. In its active form (D3-calcitrol) it assists in calcium absorption. Absorption of vitamin D from the bowel is dependent upon normal fat levels in the food. In the elderly this may be defective, giving rise indirectly to poor calcium absorption and the risk of worsening osteoporosis. Some nutritionists advise a supplement of 400 iu (international units) vitamin D daily. In Britain this can be obtained from one calcium and vitamin D tablet daily.

Excessive salt intake Dietary salt, in excess, is known to increase the level of the parathyroid hormone, with a resulting increased loss of sodium from the kidneys; calcium is also lost in large quantities with it. This increased loss takes place when salt intake reaches one teaspoonful (approx 5 g) or more daily (2000 mg sodium).

Daily requirement is approximately 500 mg sodium (1.25 g salt). (A diet high in vegetables and fruit contains a lot of potassium, which may counteract the effect of sodium.) Suggestions for reducing dietary salt are:

read food labels before purchase and try to use products with as low a salt content as possible. Remember that sodium on the label may be shown as Na, the abbreviated chemical name

wash frozen, canned and smoked seafood well in cold water

wash cottage cheese in a fine-mesh sieve

do not add salt to food

avoid convenience foods and meals from fast-food outlets, which usually have a high sodium content

avoid monosodium glutamate (MSG), sodium sulphate, sodium chloride and sodium nitrite, which are present in many foods

avoid baked goods containing baking powder (sodium bicarbonate).