Sperm formation - Frequent Ejaculations

Question

I have visited various authenticated websites and other materials and learnt that a complete sperm development takes approximately 64 days.

My doubts :

1. If sperm truly takes 64 days to develop, how can a man ejaculate multiple times (e.g., 4-5) in a day and still have sperm come out each time? Why don't all the sperm come out at once? And each time he ejaculates, the sperm are complete (i.e., the "head" and "tail" portions are always included), right?

2. Does frequent ejaculation, then, reduce the sperm count of each subsequent ejaculation? If so, do the sperms remain depleted for extended periods (i.e., 64 days), or are they replaced more regularly? At what rate are they replaced?

Answer 1

The arithmetic of human sperm

A young, healthy man produces about 1000 sperms every second, which comes to about 90 million per day [1]. These sperms are stored in the epididymis and ductus deferens until ejaculation. With several days of storage, the number can easily become big enough to allow for multiple ejaculations on the same day.

The maturation period of 64 days does not matter here, because sperms form and mature asynchronously [1]. While one spermatogonium is on day 1 of its life, another is on day 2, another on day 3 and so on. Only those sperms that are mature are released from the testes (NOT directly in semen, but into the epididymis for storage).

Does semen normally contain sperm with abnormal morphology?

Yes. Even men in whom 96% of the ejaculated sperms have abnormal morphology can successfully conceive [2].

What happens on ejaculating repeatedly?

This has already been assessed in several studies [3–5]. Overall, the results have been that with repeated ejaculation in quick succession,

1. Semen volume decreases.
2. Sperm count decreases (pointing to sperm depletion) but not to zero.
3. The percentage of sperms with abnormal morphology remains unchanged.

Hope that answers your questions.

References

1. Mesiano S, Jones EE. The male reproductive system. In: Boron WF, Boulpaep EF, editors. Medical physiology. 3rd ed. Philadelphia: Elsevier; c2017. p 1092–1107.
2. Cooper TG, Noonan E, von Eckardstein S, et al. World Health Organization reference values for human semen characteristics. Human Reproduction Update. 2010 May–Jun;16(3):231–45. doi: 10.1093/humupd/dmp048
3. Oldereid NB, Gordeladze JO, Kirkhus B, Purvis K. Human sperm characteristics during frequent ejaculation. J Reprod Fertil. 1984 May;71(1):135–140. doi: 10.1530/jrf.0.0710135
4. Zvĕrina J, Pondĕlícková J. Changes in seminal parameters of ejaculates after repeated ejaculation. Andrologia. 1988 Jan–Feb;20(1):52–4. doi: 10.1111/j.1439-0272.1988.tb02363.x
5. Mayorga-Torres JM, Agarwal A, Roychoudhury S, et al. Can a short term of repeated ejaculations affect seminal parameters? J Reprod Infertil. 2016 Jul-Sep;17(3):177-83. http://www.jri.ir/article/674

Answer 2

Spermatogenesis begins in the seminiferous tubules. In this process, sperm are formed from the processes of mitosis and meiosis from germline cells called spermatagonia. Given continuous signaling from Sertoli cells, although the meiosis cycling takes about 64 days, all cell lineages are on their own schedule depending on unique signaling pathways they synergize. Thus, there is no problem ejaculating 80-300 million sperm per ejaculation, several times per day, if the proper levels of testosterone and temperature are present to regulate the process.

This may seem like a lot of cells, but note one sperm is about 85000 times smaller than an oocyte (cell in an ovary). A certain fraction of spermatogonium is always reserved no matter how much a healthy male ejaculates, thanks to Sertoli cell signaling. Leydig cells that regulate spermatogenesis through testosterone production are also critical for spermatid maturation from the seminiferous valves to the epididymis. Further understanding the signaling pathways and genetic traits allowing the spermatogonia to be retained and replenished to form semen could have huge implications for regenerative medicine from a genetic engineering stand-point (aside from reproductive physiology).

Information pertaining to the rate of sperm production is highly dependent on individualized omic data. The 64-day cycle you mention is analogous to the circadian rhythm which repeats every 24 hours. With a super healthy metabolism because you ejaculate three times in one day does not mean it will be impossible to ejaculate once or twice the next day, like if you run thrice in one day it doesn't mean you can't run twice again the next day. Thanks for the interesting question!