During sexual intercourse, semen is deposited into the vagina, where it begins its journey within the female reproductive system. So, what is the path of semen through the female reproductive organs, and how does it interact with its new environment?
Semen Components
Before exploring the journey of semen in the female reproductive system, let’s first understand its components. This helps us understand how each component plays a role in keeping the sperm alive and ensuring they reach the egg:
● Spermatozoa: These are the male reproductive cells whose mission is to fertilize the ovum. They are also known as sperm cells.
● Seminal Vesicle Fluid: This constitutes the majority of semen volume and contains fructose, which nourishes the sperm.
● Prostate Fluid: Secreted by the prostate gland, this fluid includes citric acid, enzymes, and other substances that help enhance sperm motility within the female reproductive tract.
● Bulbourethral Gland Fluid (Cowper’s Gland Fluid): The Cowper’s glands secrete an alkaline fluid that helps neutralize the harmful acids prevalent in the vaginal environment. This provides suitable conditions for the sperm to survive and advance in their new setting.
Semen’s composition also includes small amounts of minerals like zinc, potassium, and calcium, in addition to proteins and vitamins such as D, C, and B12.
The Path of Semen Inside the Female Reproductive System
Semen passes through several stations from the moment of ejaculation until its remnants exit the female body as discharge. Here are these stations in chronological order and what occurs at each:
1. The Vagina
This is the first stop in the journey, where sperm are deposited in a highly acidic and harsh environment. The vagina’s high acidity can destroy some sperm if they don’t move to the next station quickly. However, the cervix, with its mucous secretions, plays a crucial role in facilitating the forward movement of the sperm.
2. The Cervix
The cervix acts as the gateway through which semen passes towards the uterine cavity. The mucus within the cervix facilitates this passage, enabling sperm cells to move through. This transit becomes easier during ovulation when the mucus is more fluid and less viscous.
It’s worth noting that the mucus can filter out some of the semen’s components, including sperm with poor morphology (shape) and motility (movement), thereby hindering their progress.
3. The Uterine Cavity
When healthy sperm reach this area, they swim towards the fallopian tubes. Their passage is aided by uterine muscle contractions. Only a very small number manage to reach the next station. The majority of sperm do not succeed in reaching the fallopian tubes; they either adhere to the uterine wall or are stopped along the way by obstacles and the long distance.
4. The Fallopian Tubes
It can take sperm up to five hours to travel from the vagina to the fallopian tubes. Here, the surviving sperm are stored in a reservoir where they maintain their viability by interacting with the endosalpingeal epithelium (the inner lining of the tubes). They wait here before resuming their journey in their quest to reach the egg. Fertilization specifically begins when sperm interact with the ampulla, the outer third of the fallopian tube.
5. The Ovum (Egg)
This is the final destination for the sperm, guided by a combination of thermotaxis (attraction to heat) and chemotaxis (attraction to chemical signals). As the sperm approach the egg, many will attempt to penetrate it.
However, only one sperm will succeed in penetrating and fertilizing it. The remaining sperm are blocked by a mechanism that prevents multiple fertilizations, known as the cortical reaction. This process changes the chemical structure of the membrane surrounding the egg as soon as the first sperm enters.
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What Is the Fate of the Remaining Semen Components?
Surviving sperm can remain alive for up to 5 days within the female reproductive tract. After this period, the female immune system may detect them as foreign elements and initiate an immune response. The immune system eliminates these sperm through phagocytosis (being engulfed by immune cells), and they are then cleared out via vaginal secretions.
The other components of semen, such as proteins, enzymes, and sugars, are either absorbed or broken down by the tissues of the female reproductive system. In other cases, they are simply expelled from the vagina in the form of discharge.
Factors Affect Sperm Motility
Several factors can harm sperm health in the testes, which in turn affects their ability to move and survive within the female reproductive tract:
* Sperm Disorders: Conditions like oligospermia (low sperm count) reduce the number of sperm available to make the journey. Additionally, teratospermia (abnormal sperm shape) leads to an increase in malformed sperm, which weakens their speed and ability to penetrate the egg.
* Male Health Conditions and STIs: Sperm may develop in an unhealthy environment affected by disease, which impacts their growth, quality, and resilience. Examples include varicocele, chlamydia, and gonorrhea.
* Certain Medications: Some drugs prescribed for conditions like high blood pressure, heart failure, and prostate cancer can have side effects that negatively affect sperm quality, motility, and endurance.
* Environmental and Lifestyle Factors: Many negative factors can harm sperm integrity. These include habits like smoking, alcohol consumption, and drug use. Direct trauma to the testes can also damage sperm. Likewise, exposing the testes to high heat—whether by wearing tight underwear or spending long periods in saunas or hot tubs—can have the same detrimental effect.
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Test Your Sperm’s Readiness Before You Start
Before planning for conception, it’s wise to undergo medical tests to ensure your sperm are healthy and to rule out fertility problems. These tests include a semen analysis, which evaluates sperm count, morphology (shape), and motility (activity).
Furthermore, you can take steps to improve your sperm quality:
- Reduce or abstain from alcoholic beverages.
- Quit all forms of smoking.
- Follow a healthy diet rich in nutrients like zinc, selenium, and vitamins E, C, and D.
- Exercise regularly and maintain a healthy weight.
- Manage stress and practice relaxation techniques.
Conclusion
The journey of sperm within the female reproductive system is a long and intricate process involving complex interactions. Understanding its stages allows us to develop treatments for various reproductive health conditions. This includes improving methods for diagnosing and treating infertility—such as artificial insemination and in vitro fertilization (IVF)—as well as creating more effective methods of contraception.
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References
(1) Suarez, S. S., & Pacey, A. A. (2006). Sperm transport in the female reproductive tract. Human reproduction update, 12(1), 23–37.
(2) Bromfield, J. J (2024), Interaction of semen with female reproductive tract tissues: what we know, what we guess and what we need to do, SciELO
(3) Schjenken, J. E., & Robertson, S. A. (2020). The female response to seminal fluid. Physiological Reviews, 100(3), 1077–1117.
(4) Lawrentschuk, N., Ptasznik, G., & Ong, S. Benign Prostate Disorders, National Library of Medicine