Reproductive System
Questions Received:
Why are the testes kept in the scrotum at a cooler temperature?
What happens to the sperm that are left in the body after ejaculation?
How long do sperm live outside of the body? Can sperm live in water?
Responses:
Why are the testes kept in the scrotum at a cooler temperature?
Modified 15th July 1998
To facilitate sperm production. A slight but sustained rise in temperature can affect fertility by reducing the sperm count and increasing the proportion of abnormal sperm being produced (Mieusset et al, 1991). As to which sperm-producing processes within the testis are directly affected by a rise of a few degrees it is too early to say, but it seems likely that a temperature-sensitive protein might be involved. Testicular cells exposed to a temperature rise of 4 - 5° C respond by producing heat-shock factor, which is a protein that regulates the expression of genes coding for heat-shock proteins (Sarge, Bray, and Goodson, 1995). Heat-shock proteins have a protective role in cells experiencing heat stress (see previous answer). This heat-shock response by testicular cells is probably triggered by the breakdown of unstable proteins that play a key role in sperm production.
The testes begin their development within the abdomen of the fetal male, and then usually descend into the scrotum at around the time of birth. If a testis fails to descend, and thus remains in a 37° C environment (cryptorchidism), there is an increased risk of cancer in that testis later in life.
References
Mieusset, R, Bujan, L, Mansat, A, Grandjean, H, and Pontonnier, F (1991) Heat induced inhibition of spermatogenesis in man. In: Temperature and environmental effects on the testis, edited by AW Zorgniotti, New York: Plenum Press, pp 233-237.
Sarge, K.D., Bray, A.E, and Goodson, M.L. (1995) Altered stress response in testis. Nature, 374, 126.
What happens to the sperm that are left in the body after ejaculation?
24th March 1999
The spermatozoa have a limited lifespan and any that remain within the body will die within 24 hrs and be removed by the internal body defences (the immune system) of the female.
How long do sperm live outside of the body? Can sperm live in water?
27th April 1999
Living sperm (spermatozoa) - like other cells - require suitable conditions for survival outside the body. The chemical make-up of the fluid medium in which they are suspended and the temperature at which it is maintained are two key variables. The technique of in vitro fertilisation (IVF) requires that sperm are kept in optimal condition for variable amounts of time before they are placed in contact with eggs for fertilisation. This can be done either by freezing and then re-thawing when required, or by incubation at normal body temperature for up to several hours in a suitable fluid medium (Liu, Clarke, and Baker, 1986). The fluid has to be isotonic for the sperm and contain nutrients and other materials for the sperms’ survival. One of the difficulties in keeping sperm alive in a culture dish is that they produce oxygen free radicals. These are highly reactive molecules which at lower levels are thought to control normal sperm function, but which can become damaging at higher levels (Aitken, 1995; Gomez and Aitken, 1996).
Sperm would not survive for long in plain water - although the seminal fluid would provide some protection initially, the water is very hypotonic to the sperm cells and would soon cause them to swell and disintegrate.
References
Aitken, R.J. (1995) Free radicals, lipid peroxidation and sperm function. Reproduction Fertility and Development, 7(4):659-668.
Gomez, E., and Aitken, J. (1996) Impact of in vitro fertilization culture media on peroxidative damage to human spermatozoa. Fertility and Sterility, 65(4), 880-882 (Apr).
Liu, D.Y., Clarke, G.N., and Baker, H.W. (1986) The effect of serum on motility of human spermatozoa in culture. International Journal of Andrology, 9(2), 109-117 (Apr).
Can you get someone pregnant with one testicle? And what other problems with only having one testicle?
24th June 2000
Assuming that the single testicle (testis) is functioning normally, then normal fertility can be expected. The consequences of having one testicle are more to do with the fate of the other testicle - has it been removed or is it undescended (still within the abdomen or inguinal canal)? If it is undescended, there is an increased risk of a malignancy developing in it later, so operative intervention will need to be considered.