Module 2 Section 3 (Female Reproductive Physiology) Flashcards
Describe the process of gametogenesis in females.
1) The undifferentiated primordial germ cells in the ovaries -> mitotic division during fetal life.
- By the 5th month of gestation, the oogonia have divided to give rise to 6-7 million primary oocytes. This process ceases with the primary oocytes arrested just prior to their first meiotic division.
- Each of these primary oocytes is surrounded by a single layer of granulosa cells and this structure = primordial follicle.
- Immediately, the number of primary oocytes starts to decay such that by birth, only 2 million primordial follicles remain. This = the entire complement of potential ova a woman will have throughout her entire life
2) The primordial follicles give rise to an ongoing trickle of developing follicles.
- Once the follicles
begin development, the entire structure = a primary follicle.
- The developing primary follicle either -> release of an ova OR -> undergo atresia and decay.
- Prior to puberty, all primary follicles that develop undergo atresia.
- After puberty, only about 400 primary follicles will mature and release ova.
- By menopause, the
pool of primary follicles is exhausted and a woman’s reproductive capacity ceases.
3) From puberty -menopause, a small fraction of the primary follicles will develop into secondary
follicles on a cyclic basis.
- Primary follicles get larger (over 1000-fold) due to buildup of cytoplasmic materials that would be necessary for early embryonic development.
- Just prior to ovulation, the primary oocyte undergoes its first meiotic division -> produce 2 daughter cells, each w/ 23 pairs of chromosomes.
• During this division the majority of the
cytoplasm goes to one of these daughter cells, which is called the secondary oocyte.
• The other daughter cell forms the first polar body, which will eventually degenerate.
4) The secondary oocyte is released during ovulation.
- If it is fertilized by a sperm, it will undergo the second meiotic division in which 23 single stranded chromosomes form the second polar body,
while the remaining 23 single stranded chromosomes combine with the 23 single stranded chromosomes from the sperm.
Review chart on slide 3
Describe both the ovarian and uterine cycles with an emphasis on how they are related.
** Look at graph on slide 5 **
Ovarian cycle: occurs in the ovaries and prepares an ova for release
- At the onset of puberty the ovarian cycle alternates b/w 2 phases, the follicular phase (prepares a mature egg), and the luteal phase (prepares the reproductive tract for potential implantation). This cycle on average = 28 days.
Uterine cycle: prepares the uterus for implantation.
- Also lasts about 28 days
- During this cycle, the
uterus is prepared for the possible implantation of a fertilized ovum.
- If this does not occur, the uterus is stripped clean to prepare for the next cycle.
Together:
1) The menstrual phase coincides with the end of the luteal and beginning of a new follicular phase.
- Thus, the ovarian and uterine cycles begin at the same time.
2) The proliferative phase coincides with the later stages of the ovarian follicular phase.
3) The secretory phase coincides with the beginning of the luteal phase and the formation of the corpus luteum.
Describe the hormonal control of the ovarian and uterine cycles.
Ovarian Cycle
Hormonal control of the luteal phase:
- During the luteal phase, LH continues to maintain the corpus luteum.
- The corpus luteum begins secreting large amounts of progesterone in preparation of a potential pregnancy.
- Progesterone -> changes in the uterine lining to prepare for potential implantation of an embryo to establish a pregnancy.
- If no implantation occurs -> rapid degradation of the corpus luteum results in a rapid drop in circulating progesterone.
Uterine Cycle 1) The Myometrium: an outer layer comprised of smooth muscle. 2) The Endometrium: the inner lining that is highly vascularized and also has many glands. - Estrogen stimulates the growth of both the endometrium and the myometrium. - Estrogen can also causes the expression of progesterone receptors in the endometrium. • Progesterone can then act on the endometrium to transform it into a lining suitable for implantation of a fertilized ovum. • Progesterone also reduces the contractility of the uterus to further enhance implantation and development of the embryo.
Females undergo complex monthly cycling in which an egg (ova) matures and is released. This is accompanied by a cyclical secretion of the female sex hormones, estrogen and progesterone. What is the purpose of this?
The purpose of this cycling is to prepare for the female body for a potential pregnancy.
- Each month, hormones influence an ova to mature and be released.
- At the same time, hormones also influence the uterine lining in preparation for the implantation of a
fertilized egg.
What happens if the released ova is not fertilized?
If the released ova is not fertilized, the ova decays and the uterine lining is shed during the menstrual phase.
What are granulosa cells?
The layer of cells immediately surrounding a developing oocyte within an ovarian follicle.
Using what you have just learned about gametogenesis, indicate whether the cell at each step is haploid or diploid, and whether they are single or double stranded.
1) Oogonium
2) Primary oocytes
3) Secondary oocyte
4) Second polar body
5) Mature ovum
1) Oogonium
- Diploid
- Single
2) Primary oocytes
- Diploid
- Double
3) Primary oocyte
- Diploid
- Double
4) Secondary oocyte
- Haploid
- Double
5) Mature ovum
- Haploid
- Single
The follicular phase lasts for the first 14 days of the ovarian cycle. What are the 6 stages of this phase?
1) The follicular phase begins with the proliferation of granulosa cells in a primary follicle. The
granulosa cells divide -> forms several layers around the oocyte.
2) The granulosa cells secrete glycoproteins that form a thick extracellular matrix that surrounds the oocyte and separates it from the granulosa cells. This membrane = the zona pellucida.
- While the granulosa cells are proliferating, specialized ovarian connective tissue cells differentiate and surround the granulosa cells with a layer of thecal cells.
- Together, the thecal and granulosa cells = follicular cells.
- The development of this primary follicle is due to the influence
of FSH and estrogen.
3) As the follicle enlarges -> becomes a secondary follicle, which is now capable of secreting estrogens (primarily estradiol).
- The formation of the secondary follicle is mainly due to FSH and
estrogen.
4) Also during this stage, a fluid filled cavity (antrum) is formed within the granulosa cells.
- Expansion of the antrum incr the size of the follicle as it matures.
- Estrogen secretion
also incr.
5) Each cycle, one of the follicles develops faster than the others to develop into a mature follicle by around 14 days of the follicular cycle.
- In the mature follicle, the oocyte has undergone its 1st
meiotic division to become a secondary oocyte.
- Also at this time, the location of the oocyte is not central in the follicle, but rather to the side of the growing follicle.
6) Under the influence of LH and FSH, ovulation occurs around day 14.
- The ovarian follicle ruptures to release the ovum into the abdominal cavity.
- The leaking antral fluid helps push the ovum into
the oviduct. The release of the ovum represents the end of the follicular phase.
The luteal phase occurs during the last 14 days of the ovarian cycle. What are the 2 stages of this phase?
1) Once the ovum has been released, the remaining follicular cells undergo a process called
luteinisation to form the corpus luteum.
- The corpus luteum becomes highly vascularized and it
becomes very active in secreting hormones, mainly progesterone with some estrogens.
2) If within around 14 days the ovum is not fertilized and implanted, the corpus luteum rapidly degenerates to form the corpus albicans (a fibrous scar tissue).
- This signifies the end of one ovarian cycle and the follicular phase begins again.
The ovarian cycle is under control of FSH, LH, and estrogen. What is the importance of these hormones?
FSH and estrogen are important for stimulating early follicular development and formation of the
secondary follicle.
LH is also important in the production of estrogen, which is secreted in increasing quantities by the secondary follicle.
During the follicular phase, the anterior pituitary preferentially releases LH as the circulating estrogen inhibits the actions of GnRH on FSH-secreting cells of the anterior pituitary.
- As estrogen levels continue to rise, estrogen then exerts a positive feedback action on the anterior pituitary to cause a surge in LH secretion.
What are the actions of LH surge? (4)
1) It stops estrogen synthesis by follicular cells
2) It reinitiates meiosis in the oocyte
3) It triggers release of local factors that incr the swelling of the follicle and weaken the wall
4) It differentiates the follicular cells into luteal cells
Using what you know about hormonal regulation in females, match the hormone to its function in females:
- Estrogen
- FSH
- Inhibin
- LH
- Progesterone
1) Causes changes in the uterine lining to prepare for potential implantation of an embryo to establish a pregnancy
2) Important in the production of estrogen which is secreted in increasing quantities
by the secondary follicles
3) Exerts a positive feedback action to cause a surge in LH secretion
4) Important for stimulating early follicular development and formation of the
secondary follicle
5) Inhibit the production of LH and FSH by the pituitary gland
1) Causes changes in the uterine lining to prepare for potential implantation of an embryo to establish a pregnancy
- Progesterone
2) Important in the production of estrogen which is secreted in increasing quantities by the secondary follicles
- LH
3) Exerts a positive feedback action to cause a surge in LH secretion
- Estrogen
4) Important for stimulating early follicular development and formation of the
secondary follicle
- FSH
5) Inhibit the production of LH and FSH by the pituitary gland
- Inhibin
What are the 3 phases of the uterine cycle?
** Check graph on slide 10 **
1) The Menstrual Phase
- With decr estrogen at the end of the luteal phase, the endometrial growth ceases.
- The decr in estrogen and progesterone = the local release of prostaglandins (constricts the blood supply to the endometrium, and cause the myometrium to
rhythmically contract).
- The endometrial lining then sloughs off and is expelled out through the vagina.
- Menstruation = 5-7 days. During this time, the newly developing follicles are secreting enough estrogen to begin repair of the endometrium.
2) The Proliferative Phase
- Begins when the menstrual flow ceases and it coincides with the later stages of the ovarian
follicular phase.
- At the end of the menstrual phase, the endometrium consists only of a few layers of cells less than 1mm in thickness.
- Under the influence of estrogen, these cells proliferate and there is an ingrowth of glands and blood vessels until the lining is 3-5 mm in thickness.
- Ovulation occurs during this phase, in which the ovum leaves the ovary and begins travelling through
the oviduct towards the uterus.
3) The Secretory Phase
- With the formation of the corpus luteum and the beginning of the ovarian luteal phase, the secretory phase begins.
- The large amounts of progesterone and estrogen convert the endometrium -> a richly vascularized
and glycogen-filled tissue necessary to support an early embryo.
- By this phase, the ovum has made its way to the uterus.
- W/o implantation, the corpus luteum degrades and triggers the next menstrual phase.
What is endometriosis?
It’s a disorder in which the endometrium grows outside of the uterus.
It’s an often
debilitating disease affecting more than 176 million women worldwide.
In cases of endometriosis the endometrial tissue commonly grows on the ovaries, fallopian tubes, connective tissues (such as the ligaments stabilizing the uterus and ovaries), and other tissues lining the pelvis.
- Less commonly it can spread to tissues beyond the pelvic region, such as to the large and small bowel or the abdomen
Just as the endometrial tissue in the uterus thickens, breaks down and bleeds with each menstrual cycle, so does the endometrial tissue outside of the uterus.
What do you think would be the result of this ectopic tissue? Can you predict any long term consequences of this disease?
The tissue has no way to exit the body and it becomes trapped. B/c of this entrapment, the surrounding tissue may become irritated, eventually developing -> scar tissye and adhesions.
- When endometriosis specifically involves the ovaries, this tissue can lead to the formation of cysts (endometriomas).
Endometriosis incr the risk of developing ovarian cancer. It can also leads to fertility problems since the lesions that form from the outer uterine tissue can prevent the sperm from penetrating and fertilizing the egg.
