You have had the organs of a reproductive system since birth, but they don't fully work until puberty, somewhere between ages 10 and 14. From then on they produce very special cells, the gametes, which can join to give rise to a new person. What is special about these cells, and where do they travel?
The gametes
If you scrape your knee, your skin cells divide to close the wound, but none of them can join with another to form a person. Which cells does the body need for reproduction, and how do they differ from all the others?
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Name the two types of human gametes, state in which organs each is produced, and cite one observable difference between them.
Name the two types of human gametes, state in which organs each is produced, and cite one observable difference between them.
To implant safely, the embryo needs to reach the uterus. Its muscular wall (the myometrium) is thick and stretches a great deal to hold the fetus for months. The tube, on the other hand, is a thin, barely elastic duct.
If the journey fails (for example, because the tube is damaged or partly blocked and the cilia and contractions don't push well), the embryo can implant in the tube itself. This is called a tubal ectopic pregnancy. It cannot continue: as it grows, the tube stretches and may rupture, causing severe abdominal pain and a risk to life. It requires urgent medical care.
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In the image of the female reproductive system, four structures have been marked with numbers. Write the name of the marked structures and state in which of them egg…
In the image of the female reproductive system, four structures have been marked with numbers. Write the name of the marked structures and state in which of them egg cells (ova) are formed.
Explain where fertilisation usually takes place in the female reproductive system and what path the zygote takes afterwards until it becomes implanted in the place where…
Explain where fertilisation usually takes place in the female reproductive system and what path the zygote takes afterwards until it becomes implanted in the place where it will develop.
A woman goes to the emergency department with acute abdominal pain at 7 weeks of pregnancy. The ultrasound confirms that the embryo is not in the uterus, but has…
A woman goes to the emergency department with acute abdominal pain at 7 weeks of pregnancy. The ultrasound confirms that the embryo is not in the uterus, but has implanted in the wall of one of the Fallopian tubes (tubal ectopic pregnancy).
a) Knowing that the embryo normally takes between 5 and 7 days to travel from the site of fertilization to the uterus propelled by cilia and muscular contractions, deduce what functional or anatomical failure in the tube could have caused it to become trapped there.
b) Compare the structure and distensibility of the uterine myometrium with the thin muscular layer of the Fallopian tube. Based on this comparison, justify why this pregnancy is non-viable and represents a surgical emergency due to the risk of rupture and severe hemorrhage.
In the cross-sectional image of the male reproductive system, four structures have been marked with numbers. Write the name of the marked structures and describe the…
In the cross-sectional image of the male reproductive system, four structures have been marked with numbers. Write the name of the marked structures and describe the path sperm cells travel from where they are formed in the testes until they leave the body, naming the structures they pass through.
The testes are located outside the abdominal cavity, in the scrotum, because sperm production requires a temperature slightly lower than that inside the body. Reason…
The testes are located outside the abdominal cavity, in the scrotum, because sperm production requires a temperature slightly lower than that inside the body. Reason what might happen to sperm production if the testes were always kept at internal body temperature.
Gonads, hormones, and differences between the two systems
At puberty, body hair appears, your voice or body shape changes, and at the same time gametes begin to mature. Which organs coordinate the making of gametes and the chemical signals that transform the body?
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In addition to producing gametes, the ovaries and testes produce sex hormones. Explain what type of organs ovaries and testes are, therefore, and state two changes that…
In addition to producing gametes, the ovaries and testes produce sex hormones. Explain what type of organs ovaries and testes are, therefore, and state two changes that these hormones cause during puberty.
Look at the compared characteristics of the two human gametes: Sperm cell: length of about 0.05 mm, no nutrient reserves, motile via flagellum, continuous production of…
Look at the compared characteristics of the two human gametes:
Sperm cell: length of about 0.05 mm, no nutrient reserves, motile via flagellum, continuous production of about 100 million per day.
Egg cell: diameter of about 0.15 mm (a volume hundreds of times greater), non-motile, loaded with nutrient reserves, maturation of 1 every 28 days.
a) Justify why the sperm cell requires such a light design and such a massive production, relating it to the physical obstacles and the journey it faces within the female reproductive system.
b) Explain why it would be biologically unfeasible and detrimental for a woman to mature millions of egg cells at once, taking into account the energy cost of producing reserves and the type of mammalian gestation.
Biology explains how the reproductive systems work, but the way sexuality, gender, and reproduction are understood changes from one culture to another. In Mexico many views coexist: those of Indigenous peoples, those of cities, those of each family and community.
Some beliefs and customs support health and others harm it. For example, the idea that preventing a pregnancy is "a woman's business" puts the whole burden on women. Another false idea is that a teen pregnancy "doesn't change anything." In response:
Responsibility is shared: men and women take part in decisions and in preventing pregnancy.
Starting sexual activity must always be a consensual decision: no one should pressure or be pressured.
Women and men have the same rights to information, to health care, and to decide about their life plan.
Contraception and STI prevention
Preventing a pregnancy and preventing a sexually transmitted infection (STI) are related but different goals. Some STIs cause no symptoms. STIs, how they are transmitted, and how to prevent them are studied in more detail in the chapter on sexually transmitted infections. Planning a pregnancy around your life plan (studying, working, deciding when to become a mom or dad) includes knowing the methods and their effectiveness: how well they prevent pregnancy when used in real life.
Method
Pregnancy prevention
Protection against STIs
External or internal condom
High, with correct and consistent use
Reduces the risk of most; does not eliminate it completely
Birth control pills, implant, patch, injection
High, depending on use and schedule
No
IUD (copper or hormonal)
Very high
No
Surgical methods (vasectomy, tubal ligation)
Very high; they are permanent
No
Calendar or withdrawal
Low: not very reliable
No
The calendar and withdrawal are not considered reliable methods. Long-acting methods (implant, IUD) have very few failures because they don't depend on remembering something every day.
What surgical methods do
Surgical methods cut or block the duct; they don't remove the gonad:
Vasectomy: the vas deferens are cut and closed. Sperm can no longer pass into the urethra. But the testicles remain intact: they keep producing testosterone, which reaches the blood (it doesn't need the duct), so masculine characteristics are not lost. In addition, most of the semen comes from the prostate and the seminal vesicles, which are still there; the man ejaculates semen almost the same as before, just without sperm.
Tubal ligation: the fallopian tubes are cut or closed. The egg no longer meets sperm or reaches the uterus. But the ovaries keep producing estrogen and progesterone, and the uterus keeps thickening and shedding its lining, so menstruation continues.
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A classmate holds two mistaken ideas: "After a vasectomy, a man can no longer ejaculate semen and loses his male characteristics because he has no testosterone," and "a…
A classmate holds two mistaken ideas: "After a vasectomy, a man can no longer ejaculate semen and loses his male characteristics because he has no testosterone," and "a woman with tubal ligation stops having periods because the egg does not reach the uterus."
a) Reasonably refute the statement about the man: explain where most of the volume of ejaculated semen comes from and clarify why a vasectomy does not prevent testosterone from reaching the blood or alter its effects.
b) Refute the statement about the woman: explain why she continues to have a menstrual cycle and ovulate normally despite having her fallopian tubes severed.
