|
The Reproductive System
1. What are the organs that are part of the male genital system?
The organs that comprise the male genital system are the testicles, the epididymides, the vas deferens, the seminal vesicles, the ejaculatory duct, the prostate, the bulbourethral glands, the urethra and the penis.
Genital System - Image Diversity: male genital system
2. Concerning reproduction what is the function of the testicles?
The testicles are the male gonads, i.e., the organs where the production of gametes takes place. In human beings the gametes are made by meiosis that occur in the testicles.
3. After passing the epididymides through which structures do sperm cells go until exteriorization?
After leaving the epididymis in the testicle sperm cells enter the vas deferens, after that they receive secretions from the seminal vesicles and gather (from right and left sides) in the ejaculatory duct that passes inside the prostate. 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 the semen. The secretions have the function of nourishing the sperm cells and serving them as a fluid means of propagation. The basic pH of the seminal fluid also neutralizes the acid secretions of the vagina allowing the survival of sperm cells in the vaginal environment after copulation.
5. What are the endocrine glands that regulate sexual activity in males? How does this regulation work and what are the involved hormones?
In males the sexual activity is regulated by the endocrine glands hypophysis (pituitary), adrenals and gonads (testicles).
The FSH (follicle-stimulating hormone) secreted by the adenohypophysis acts upon the testicles stimulating the spermatogenesis. The LH (luteinizing hormone), another adenohypophyseal hormone, stimulates the production of testosterone by the testicles too. Testosterone, whose production intensifies after the beginning of puberty, acts in several organs of the body and it is responsible for the appearing of the male secondary sex characteristics (beard, body hair, deep voice, increase of the muscle and osseous mass, maturation of genitalia, etc.) Testosterone also stimulates spermatogenesis.
Reproductive System - Image Diversity: hypophysis adrenals
6. What are the organs that are part of the female reproductive system?
The organs that constitute the female reproductive system are the ovaries, the Fallopian tubes (or uterine tubes), the uterus, the vagina and the vulva.
Reproductive System - Image Diversity: female reproductive system
7. In which period of life does the formation of gametes begin in women?
The meiosis that forms female gametes begins in the cells of the 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. The meiotic process is only concluded however if fecundation happens.
8. What is the organ that releases the female gamete under formation? How is this release triggered? What is the organ that collects the released gametes?
The organ that liberates 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 the 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 there is still intra-abdominal space.
10. What is the menstrual cycle?
The menstrual cycle is the periodic succession of interactions between hormones and the organs of the female reproductive system that, after the beginning of puberty, regulates the release of the female gametes and prepares the uterus for fecundation and pregnancy.
Reproductive System - Image Diversity: menstrual cycle
11. What are the endocrine glands involved in the menstrual cycle? What are the hormones in action?
The endocrine glands that secrete hormones involved in the menstrual cycle are the hypophysis (pituitary) and the ovaries.
The hormones from adenohypophysis are FSH (follicle-stimulating hormone) and LH (luteinizing hormone) and the hormones from the ovaries are estrogen and progesterone.
Reproductive System - Image Diversity: hormone levels during menstrual cycle
12. What event marks the beginning of the menstrual cycle? What is the blood concentration of FSH, LH, estrogen and progesterone in this phase of the cycle?
By convention the menstrual cycle begins at the day that menses begins. (Menses is the endometrial hemorrhage excreted through the vaginal canal.) At these days the hormones FSH, LH, estrogens and progesterone are in low concentration.
13. After menses what is the hormone that influences the maturation of the ovarian follicles?
The maturation of the ovarian follicles after menses is stimulated by the action of FSH (follicle-stimulating hormone).
Reproductive System - Image Diversity: ovarian follicles
14. What is the hormone secreted by the growing ovarian follicles? What is the action of that hormone upon the uterus?
The follicles that are growing after menses secrete estrogen. These hormones act upon the uterus stimulating the thickening of the endometrium (the internal mucosa of the uterus).
15. What is the relationship between the 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. In this phase LH acts together with FSH promoting the maturation of the follicle that at the 14th day ruptures releasing the female gamete (ovulation). After the release of the ovum LH acts stimulating the formation of the corpus luteum, a structure made from the remaining follicular mass. The LH concentration is at maximum at the 14th day of the cycle.
Reproductive System - Image Diversity: corpus luteum
16. What are the hormones that promote the release of the female gamete from the follicle and at 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) the 14th day of the menstrual cycle.
17. How does the female gamete move from the ovary to the uterus?
The female gamete released from 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 fecundated egg cell towards the uterus.
Reproductive System - Image Diversity: Fallopian tube
18. How long after ovulation must fecundation occur to be effective?
If fecundation does not occur approximately 24 hours after ovulation the released ovum often dies.
19. What is the structure into which the follicle is transformed after ovulation? What is the importance of that structure in the menstrual cycle?
The follicle that released the ovum suffers 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 (implantation of the zygote in the uterine wall) and embryonic development since they stimulate the thickening of the mucous tissue, increase its vascularity and make the appearing of uterine glycogen-producing glands.
20. What is the importance of the uterine glycogen-producing glands?
The uterine glands produce glycogen that can be degraded into glucose to nourish the embryo before the complete development of the placenta.
21. How does the hypophysis-corpus luteum negative feedback 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 the hypophyseal FSH and LH secretions (this happens by inhibition of GnRH, gonadotropin-releasing hormone, a hypothalamic hormone). The blood concentration of these adenohypophyseal hormones falls to basal levels 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.
Reproductive System - Image Diversity: corpus albicans
22. In hormonal terms why does menses occur?
Menses is the endometrial monthly desquamation that occurs as the estrogen and progesterone levels fall after the regression of the corpus luteum because these hormones, mainly progesterone, can no longer support and maintain the thickening of the endometrium.
Reproductive System - Image Diversity: endometrium
23. What is the explanation for the bleeding that accompanies menses?
The hemorrhage that accompanies menses occurs because the endometrium is a richly vascularized tissue. The rupture of blood vessels of the uterine mucosa during the menstrual desquamation causes the bleeding.
24. Which 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 at 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 main events and hormonal changes how can the menstrual cycle be described?
One can imagine a cycle like an analog clock at which at 0 o’clock is the beginning and the end of the menstrual cycle and that 6 o’clock corresponds to the 14h day of the cycle.
At 0 o’clock the menses and so the menstrual cycle begins and FSH blood level begins to increase. Around 2 o’clock the maturing follicles under FSH action are already secreting estrogen and the endometrium is thickening. Around 3 o’clock estrogen is intensely stimulating the increase of LH blood level. At 6 o’clock (the 14th day) LH is at its maximum concentration and FSH 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 great amount of estrogen and progesterone and the endometrium thickens even more, concomitant lowering of FSH and LH occurs 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 0 o’clock again (28th day) the endometrium desquamates and a new menstrual cycle begins.
26. In general what is the phase of the menstrual cycle when copulation may lead to fecundation?
Although this is not a rule, to be effective fecundation in general must occur within about 24 hours after ovulation (that occurs around the 14th day of the menstrual cycle). Fecundation may occur even if copulation took place up to 3 days before ovulation since the male gametes remain viable for about 72 hours within the female reproductive system.
The fertile period of the women however is considered the period from 7 days before ovulation to 7 days after ovulation.
27. What is the part of the female reproductive system where fecundation occurs?
Fecundation generally occurs in the Fallopian tubes but it can also take place within the uterus. There are cases when fecundation may occur even before the ovum enters the uterine tube, a fact that may lead to a severe medical condition known as abdominal pregnancy.
28. How does the sexual arousal mechanism in women facilitate fecundation?
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 to the uterine tubes. During copulation the uterine cervix advances inside the vagina to facilitate the entering of male gametes through the cervical canal.
29. What is nidation? In which phase of the menstrual cycle does nidation occur?
Nidation is the implantantion of the embryo in the uterus. Nidation occurs around the 7th day after fecundation, i.e., 7 to 8 days after ovulation (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.
Reproductive System - Image Diversity: nidation
30. What is tubal pregnancy?
Many times fecundation takes place in the Fallopian tubes. Generally the newly formed zygote is taken to the uterus where nidation and the embryonic development occur. In some cases however the zygote cannot go down to the uterus and the embryo implants itself in the uterine tube tissue, characterizing the tubal pregnancy. Tubal pregnancy is a severe clinical condition since often the tube ruptures during gestation causing hemorrhage and even death of the woman. The most common treatment for tubal pregnancy has been 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 thus inhibits the secretion of FSH and LH from 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 that in their 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 besides being the organ through which the exchange of substances between the mother and the fetus is done also has the function of secreting estrogen and progesterone to keep a high level of these hormones during pregnancy. (The placenta still secretes other hormones like human placental lactogen, that act similarly to the hypophyseal hormones that regulate reproduction, and HCG, human chorionic gonadotropin.)
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 the FSH and LH secretions. Since these hormones then do not reach their normal high levels during the menstrual cycle ovulation does not occur.
(Treatment with contraceptive pills must be initiated under medical supervision.)
35. What are the common contraindications of the 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 increased propensity to cardiovascular diseases (like infarction, strokes and thrombosis) and to malignant neoplasias (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 which will forbid the sperm cells to follow to the ejaculatory duct but still allowing the release of seminal fluid during ejaculation.
Surgical sterilization of women is often done by bilateral tubal ligation. With tubal ligation the ovum does not pass to the uterus so the sperm cells cannot reach it.
Reproductive System - Image Diversity: vasectomy tubal ligation
37. How does the contraceptive diaphragm work? What are the limitations of this contraceptive method?
The contraceptive diaphragm is an artifact made of latex or plastic that when placed on the vaginal fundus covers the uterine cervix forbidding the passage of sperm cells through the cervical canal. To be more effective the diaphragm needs to be used together with spermicide. This method however does not prevent sexually transmitted diseases (STDs).
Reproductive System - Image Diversity: contraceptive diaphragm
38. Why is the use of condoms not just a contraceptive method but also a health protection behavior?
The use of condoms besides being an efficient contraceptive method also helps the prevention of diseases caused by sexually transmitted agents (STDs), like syphilis, gonorrhea, HPV (human papilloma virus that may lead to genital cancers) infestation, HIV infection, etc.
Reproductive System - 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 in different cycles of 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 that intercourse should be avoided to prevent pregnancy. (This method is not exempt from failures. A doctor must always be consulted before relying on any contraceptive method.)
40. How is the ovulation date estimated with the control of the woman's body temperature?
One method to estimate the exact ovulation day is daily control of the body temperature taken always under same conditions. At the ovulation day the body temperature often increases about 0.5 degrees centigrade.
41. What is the contraceptive mechanism of the IUD?
The IUD (intrauterine device) is a piece of plastic coated with copper that is inserted within the uterus by a doctor. Copper is then gradually released (IUD may last 5 to 10 years) and since it has a spermicidal action sperm cells are destroyed before fecundation. Besides this mechanism the movement of the IUD inside the uterus causes slight endometrial inflammation that helps to prevent nidation.
Reproductive System - Image Diversity: IUD
42. Generally how does a male animal realize that the female is receptive to copulation?
In most vertebrate species with internal fecundation the 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 for territorial demarcation 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 but without fecundation by the male gamete. According to the species, individuals born by parthenogenesis may be male or female, or of any sex.
In bees the drone (the single male bee) is haploid and born by parthenogenesis while the females (queen and workers) are diploid.
|
