2. Concerning reproduction, what is the function of the testicles?
The testicles are the male gonads; that is, the organs where the production of gametes takes place. In human beings, gametes are produced by meiosis that occurs in the testicles.
3. After passing the epididymis, through which structures do sperm cells travel until exteriorization?
After leaving the epididymis in the testicle, sperm cells enter the vas deferens. After that, they receive secretions from seminal vesicles and gather (from the right and left sides) in the ejaculatory duct. They also get secretions from the prostate and the bulbourethral glands and then go through the urethra, inside the penis, to the exterior.
4. What is the function of the secretions of the prostate, seminal vesicle and bulbourethral glands in reproduction?
These secretions, along with sperm cells from the testicles, form semen. These secretions have the function of nourishing the sperm cells and serving as a fluid means of propagation for them. The alkaline pH of seminal fluid also neutralizes the acidic secretions of the vagina, allowing the survival of sperm cells in the vaginal environment after copulation.
5. What endocrine glands regulate sexual activity in males? How does this regulation work and what hormones are involved ?
In males, sexual activity is regulated by the endocrine glands: the hypophysis (the pituitary), the adrenal glands and the gonads (testicles).
FSH (follicle-stimulating hormone) secreted by the adenohypophysis acts on the testicles, stimulating spermatogenesis. LH (luteinizing hormone), another adenohypophyseal hormone, also stimulates the production of testosterone by the testicles. Testosterone, the production of which intensifies after the beginning of puberty, acts on several organs of the body and is responsible for the appearance of secondary male sex characteristics (beard, body hair, deep voice, increase in the muscle and bone mass, maturation of genitalia, etc.). Testosterone also stimulates spermatogenesis.
The Female Reproductive System
6. What organs are a part of the female reproductive system?
The organs that make up the female reproductive system are the ovaries, the Fallopian tubes (or uterine tubes), the uterus, the vagina and the vulva.
7. During which period of life does the formation of gametes begin in women?
The meiosis that forms female gametes begins in the cells of ovarian follicles before birth. After the beginning of puberty, under hormonal stimuli, during each menstrual cycle, one of the cells is released on the surface of the ovary and meiosis resumes. However, the meiotic process is only concluded if fertilization occurs.
8. What organ releases the female gamete under formation? How is this release triggered? What organ collects the released gametes?
The organ that releases the female gamete is the ovary, the female gonad. The releasing of the oocyte is a response to hormonal stimuli. The immature egg cell (still an oocyte) falls into the abdominal cavity and is picked up by the Fallopian tube (uterine tube, or oviduct), a tubular structure that connects the ovary with the uterus.
9. What are the anatomical relationships between the organs of the female reproductive system, from the external vulva to the ovaries?
The external female genitalia is called the vulva. The vulva is the external opening of the vaginal canal, or vagina. The vagina is the copulation organ of females and its posterior extremity communicates with the uterus through the uterine cervix. The uterus is divided into two portions: the cervix and the uterine cavity. The lateral walls of the uterine fundus communicate with the Fallopian tubes. The other extremity of each Fallopian tube ends in fimbria, forming fringes in the abdominal cavity. Between the uterine tube and the ovary is intra-abdominal space.
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The Menstrual Cycle
10. What is the menstrual cycle?
The menstrual cycle is the periodic succession of interactions between the hormones and organs of the female reproductive system that, after the beginning of puberty, regulates the release of female gametes and prepares the uterus for fertilization and pregnancy.
11. What endocrine glands are involved in the menstrual cycle? What hormones are in involved?
The endocrine glands that secrete hormones involved in the menstrual cycle are the hypophysis (the pituitary gland) and the ovaries.
The hormones from the adenohypophysis are FSH (follicle-stimulating hormone) and LH (luteinizing hormone) and the hormones from the ovaries are estrogen and progesterone.
12. What event marks the beginning of the menstrual cycle? What is the blood concentration of FSH, LH, estrogen and progesterone during this phase of the cycle?
By convention, the menstrual cycle begins on the day that menses begins. (Menses is the endometrial hemorrhage excreted through the vaginal canal.) During these days, the hormones FSH, LH, estrogen and progesterone have low concentration.
13. After menses, what hormone influences the maturation of ovarian follicles?
The maturation of ovarian follicles after menses is stimulated by the action of FSH (follicle-stimulating hormone).
14. What hormone is secreted by the growing ovarian follicles? What is the action of that hormone on the uterus?
The follicles growing after menses secrete estrogen. These hormones act on the uterus, stimulating the thickening of the endometrium (the internal mucosa of the uterus).
15. What is the relationship between estrogen level and the LH level in the menstrual cycle? What is the function of LH in the menstrual cycle and when does its blood concentration reach a peak?
The increase in the blood concentration of estrogen with the growing of the ovarian follicle causes the hypophysis to secrete LH. During this phase, LH acts along with FSH to promote the maturation of the follicle, which on the 14th day, ruptures, releasing the female gamete (ovulation). After the release of the ovum, LH stimulates the formation of the corpus luteum, a structure made from the remaining follicular mass. LH concentration is at its maximum on the 14th day of the cycle.
16. What hormones promote the release of the female gamete from the follicle and on which day of the menstrual cycle does this phenomenon happen? What is this event called?
The hormones that promote the release of the ovum from the follicle are FSH and LH, hormones found in maximum blood concentration around the 14th day of the cycle. The release of the female gamete from the ovary is called ovulation. Ovulation happens at (around) on 14th day of the menstrual cycle.
17. How does the female gamete move from the ovary to the uterus?
The female gamete released by the ovary falls into the surrounding abdominal cavity and is collected by the Fallopian tube. The internal epithelium of the uterine tubes has ciliated cells that move the ovum or the fertilized egg cell towards the uterus.
18. How long after ovulation must fertilization occur to be effective?
If fertilization does not occur approximately 24 hours after ovulation, the released ovum often dies.
19. Into what structure is the follicle transformed after ovulation? What is the importance of that structure in the menstrual cycle?
The follicle that released the ovum undergoes the action of LH and is transformed into the corpus luteum. The corpus luteum is very important because it secretes estrogen and progesterone.
These hormones prepare the uterine mucosa, also known as endometrium, for nidation (the implantation of the zygote in the uterine wall) and embryonic development, since they stimulate the thickening of the mucous tissue, increase its vascularity and cause the appearance of uterine glycogen-producing glands.
20. What is the importance of uterine glycogen-producing glands?
Uterine glands produce glycogen that can be broken down into glucose to nourish the embryo before the complete development of the placenta.
21. How does negative feedback between the hypophysis and corpus luteum work? What is the name given to the atrophied corpus luteum after this feedback process?
After ovulation, the estrogen and progesterone secretions from the corpus luteum inhibit hypophyseal FSH and LH secretions (this happens through the inhibition of GnRH, gonadotropin-releasing hormone, a hypothalamic hormone). The blood concentration of these adenohypophyseal hormones falls to basal levels once again. As LH lowers, the corpus luteum (luteum means “yellow”) becomes atrophic and turns into the corpus albicans (“white”). With the regression of the corpus luteum, the production of estrogen and progesterone ceases.
22. In hormonal terms, why does menses occur?
Menses is the monthly endometrial desquamation that occurs as the estrogen and progesterone levels fall after the regression of the corpus luteum. This is because these hormones, mainly progesterone, can no longer support and maintain the thickening of the endometrium.
23. What is the explanation for the bleeding that accompanies menses?
The hemorrhage that accompanies menses occurs because the endometrium is a highly vascularized tissue. The rupture of the blood vessels of the uterine mucosa during menstrual desquamation causes the bleeding.
24. What are the phases of the menstrual cycle?
The menstrual cycle is divided into two main phases: the follicular (or menstrual) phase and the luteal (or secretory) phase.
The menstrual phase begins on the first day of menses and lasts until ovulation (around the 14th day). The luteal phase begins after ovulation and ends when menses begins (around the 28th day).
25. Including the main events and hormonal changes, how can the menstrual cycle be described?
The cycle can be described like an analog clock on which 12 o’clock is the beginning and the end of the menstrual cycle and 6 o’clock corresponds to the 14th day of the cycle.
At 12 o’clock, menses and therefore the menstrual cycle begin and FSH blood levels begins to increase. Around 2 o’clock, the follicles maturing under the effect of FSH are already secreting estrogen and the endometrium is thickening. Around 3 o’clock, estrogen is intensely stimulating the increase of LH blood levels. At 6 o’clock (the 14th day), LH is at its maximum concentration and FSH is also at high levels to promote ovulation. LH then stimulates the formation of the corpus luteum. Around 7 o’clock, the corpus luteum is already secreting a large amount of estrogen and progesterone and the endometrium thickens even more; levels of FSH and LH decrease with the increasing of the ovarian hormones. Around 11 o’clock, the reduced LH and FSH levels make the corpus luteum turn into the corpus albicans; the production of estrogen and progesterone ceases and the endometrium regresses. At 12 o’clock again (the 28th day), the endometrium desquamates and a new menstrual cycle begins.
26. In general, during what phase of the menstrual cycle can copulation lead to fertilization?
Although this is not a rule, to be effective, fertilization must occur within 24 hours after ovulation (which occurs around the 14th day of the menstrual cycle). Fertilization may occur even if copulation took place up to 3 days before ovulation, since male gametes remain viable for about 72 hours within the female reproductive system.
However, the fertile period of the women is considered to be the period from 7 days before ovulation to 7 days after ovulation.
27. In what part of the female reproductive system does fertilization occur?
Fertilization generally occurs in the Fallopian tubes, but it can also take place in the uterus. There are cases when fertilization may occur even before the ovum enters the uterine tube, which may lead to a severe medical condition known as abdominal pregnancy.
28. How does the sexual arousal mechanism in women facilitate fertilization?
During sexual arousal in women, the vagina secretes substances to neutralize its acidity, thus allowing the survival of sperm cells within it. During the female fertile period, hormones make the mucus that covers the internal surface of the uterus less viscous to help the passage of sperm cells into the uterine tubes. During copulation, the uterine cervix advances inside the vagina to facilitate the entrance of male gametes through the cervical canal.
Nidation and Pregnancy
29. What is nidation? During which phase of the menstrual cycle does nidation occur?
Nidation is the implantation of the embryo into the uterus. Nidation occurs around the 7th day after fecundation, that is, 7 to 8 days after fertilization (obviously, it occurs only if fecundation also occurs). Since it occurs in the luteal phase ,the progesterone level is high and the endometrium is in its best condition to receive the embryo.
- The Reproductive System Review - Image Diversity: nidation
30. What is tubal pregnancy?
Often fertilization takes place in the Fallopian tubes. Generally, the newly formed zygote is moved to the uterus, where nidation and embryonic development occur. However, in some cases, the zygote cannot descend into the uterus and the embryo implants itself in the uterine tube tissue, which is the characteristic of tubal pregnancy. Tubal pregnancy is a severe clinical condition since the tube often ruptures during gestation, causing a hemorrhage and even the death of the woman. The most common treatment for tubal pregnancy is surgery.
31. How do hormonal tests to detect pregnancy work?
Laboratory tests to detect pregnancy commonly test for human chorionic gonadotropin (HCG) concentration in blood or urine samples. If the level of this hormone is abnormally high, pregnancy is likely.
32. Does the hypophysis-ovaries endocrine axis work in the same way during pregnancy as in non-pregnant women? If pregnancy does not occur how does another menstrual cycle begin?
The functioning of the hypophysis is altered during pregnancy. Since estrogen and progesterone levels remain elevated during the gestational period, the production of GnRH (gonadotropin-releasing hormone) from the hypothalamus is inhibited. The lack of GnRH therefore inhibits the secretion of FSH and LH by the hypophysis and a new menstrual cycle does not begin.
If pregnancy does not occur, the lowering of estrogen and progesterone levels stimulates the production of GnRH by the hypothalamus. This hormone then hastens the adenohypophyseal secretion of FHS and LH, which in turn stimulate the maturation of follicles and the beginning of a new menstrual cycle.
33. What is the endocrine function of the placenta?
The placenta, in addition to being the organ through which the exchange of substances between the mother and the fetus is carried out, also has the function of secreting estrogen and progesterone to maintain a high level of these hormones during pregnancy. (The placenta still secretes other hormones such as human placental lactogen, which acts in a way similar to that of the hypophyseal hormones that regulate reproduction, and HCG, human chorionic gonadotropin.)
Reproductive Planning Methods
34. How do contraceptive pills generally work?
Contraceptive pills generally contain the hormones estrogen and progesterone. If taken daily from the 4th day after menses, the abnormal elevation of these hormones acts upon the hypophysis-hypothalamus endocrine axis, inhibiting FSH and LH secretions. Since these hormones do not reach their normal high levels during the menstrual cycle, ovulation does not occur.
(Treatment with contraceptive pills must be started under medical supervision.)
35. What are the common contraindications of contraceptive pills?
There are medical reports associating the use of contraceptive pills with vomiting, nausea, vertigo, headaches, hypertension and other pathological conditions. Some research has attempted to relate the medical ingestion of estrogen and progesterone with an increased propensity for cardiovascular diseases (such as heart attacks, strokes and thrombosis) and malignant neoplasms (cancers). Doctors must always be asked about the risks and benefits of the contraceptive pill prior to use.
36. What are the most common methods of male and female surgical sterilization?
Vasectomy is the most common method of surgical sterilization in men. In vasectomy, the vas deferens inside the scrotum are sectioned and closed at a section, forbidding the sperm cells from entering the ejaculatory duct but still allowing the release of seminal fluid during ejaculation.
The surgical sterilization of women is often done by bilateral tubal ligation. With tubal ligation, the ovum does not enter the uterus and, as a result, sperm cells cannot reach it.
37. How does a contraceptive diaphragm work? What are the limitations of this contraceptive method?
A contraceptive diaphragm is a device made of latex or plastic that, when placed on the vaginal fundus, covers the uterine cervix, preventing the passage of sperm cells through the cervical canal. To be more effective, the diaphragm needs to be used with spermicide. However, this method does not prevent sexually transmitted infections (STIs).
38. Why is the use of condoms not just a contraceptive method but also a health protection behavior?
The use of condoms, in addition to being an efficient contraceptive method, also helps the prevention of diseases caused by sexually transmitted agents (STIs), such as syphilis, gonorrhea, HPV (the human papilloma virus, which may lead to genital cancers) infection, HIV infection, etc.
- The Reproductive System Review - Image Diversity: condom
39. What is the normal duration of the menstrual cycle? How does the calendar contraceptive method work?
The normal duration of the menstrual cycle is 28 days, but it can vary among different women or different cycles in the same woman.
In the calendar contraceptive method, the date n-14 (n minus 14) is taken, considering n the number of days of the normal menstrual cycle of the woman (generally n=28). The safety margin +3 or –3 refers to the days around n-14 during which intercourse should be avoided to prevent pregnancy. (This method is not completely free of failures. A doctor must always be consulted before relying on any contraceptive method.)
40. How is the ovulation date estimated via the measurement of a woman's body temperature?
One method to estimate the exact ovulation date is daily measurement of body temperature always done under same conditions. On the date of ovulation, body temperature often increases about 0.5 degrees centigrade.
41. What is the contraceptive mechanism of an IUD?
An IUD (intrauterine device) is a piece of plastic coated with copper that is inserted into the uterus by a doctor. Copper is then gradually released (an IUD can last from 5 to 10 years) and since it has a spermicidal effect, sperm cells are destroyed before fertilization. in addition to this mechanism, the movement of the IUD inside the uterus causes slight endometrial inflammation, which helps to prevent nidation.
- The Reproductive System Review - Image Diversity: IUD
Reproduction in Other Animals
(See zoology subjects for a comprehensive review.)
42. Generally, how does a male animal realize that the female is receptive to copulation?
In most vertebrate species with internal fertilization, females have reproductive cycles with fertile periods. During this period, the female secretes pheromones (odoriferous substances that attract the male of the species) from the skin and mucosae. The presence of the male individual and his pheromones also stimulates the release of pheromones by the female. (Many animals also use pheromones to mark their territories and for signal transmission between individuals about the location of dangers and food.)
43. What is parthenogenesis?
Parthenogenesis is the reproduction or formation of a new individual from the egg cell without fertilization by the male gamete. Depending on the species, individuals born via parthenogenesis may be male or female, or of any sex.
In bees, the drone (the single male bee) is haploid and born via parthenogenesis while the females (queen and workers) are diploid.