Lecture 16 - Female Reproduction Flashcards
what are the main structures in the female reproductive system (4)
- the ovaries (2) form the gametes, oocytes/eggs
- communicates with the fallopian tube where the egg can be fertilized by the sperm
- if fertilized, the zygote (fertilized egg) travels down the fallopian tube to the uterus, where it implants in the endometrial lining, beginning pregnancy. this structure has muscle around it, allowing for contractions and nourishment of the fetus.
- The cervix connects the uterus to the vagina. It produces cervical mucus, which changes consistency during the menstrual cycle to either facilitate or prevent sperm from entering the uterus. During labor, the cervix dilates to allow passage of the baby from the uterus to the vagina.
how are oocytes produced?
process of oogenesis in embryo and reproductive adult
- embryo
- puberty
- ovulation
- fertilization
Fetal life in Embryo
- during fetal life, primordial germ cells will go through mitosis several times to generate a pool of oogonia
- before birth the oogonia will enter meiosis 1, but only duplicate their DNA then STOP
- so when a female is born they have what is called primary oocytes – cells where DNA has replicated but no cell division occurs
- the baby is born with 1-2 million primary oocytes. no more oocytes can be made after the baby is born.
reproductive adult:
- when the female enters puberty only around 300k primary oocytes remain (a lot degrade overtime).
- after puberty, one primary oocyte completes meiosis I (ie. goes through meiotic division) and enters meiosis II to become a secondary oocyte (egg) every ~28 days.
- the secondary oocyte/egg is released at ovulation from the ovary
- the other primary oocyte becomes the first polar body and disintegrates (the polar body contains the genetic material whereas the egg contains the cytoplasm and sex info)
- The secondary oocyte/egg completes meiosis II (divides from diploid to haploid) ONLY if it is fertilized by a sperm (stops in metaphase 2). a second polar body with unwanted genetic material is released and disintegrates.
- Unfertilized egg dies 12-24 hours after ovulation.
- fertilized haploid egg develops into a zygote with sperm haploid.
what are the differences between oogenesis and spermatogenesis
- cell division
- duration
- supply
Cell division
- oogenesis: asymmetric cell division = formation of one large secondary oocyte and small polar bodies
- spermatogenesis: symmetric cell division = four equal-sized, viable sperm cells from each original cell.
Duration:
- oogenesis: limited = begins during fetal development, pauses at birth, and resumes at puberty. It stops entirely at menopause (around age 51), after which no more oocytes are produced.
- spermatogenesis: continuous = begins at puberty and continues throughout a man’s life, with sperm production occurring continuously without a set endpoint.
Supply:
- oogenesis: limited number of eggs = females are born with a finite number of primary oocytes (about 1–2 million), and this number decreases over time, leaving around 300,000 by puberty. Only about 400–500 will mature and be ovulated over a lifetime.
- spermatogenesis: infinite = spermatogenesis is ongoing, allowing for the production of millions of sperm daily, with no fixed reserve.
What happens to a girl’s oocytes from birth through her reproductive years, and how many follicles are typically recruited each year? what is atresia?
- A girl is born with about 0.5 million oocytes per ovary, each surrounded by a primary follicle in stasis until puberty.
- During each menstrual cycle, 5-10 follicles per ovary are recruited, but usually, only one fully matures into a secondary oocyte/egg for ovulation.
- This means around 250 follicles are recruited each year, totaling about 10,000 throughout her reproductive years.
- The remaining oocytes and follicles that are not selected for maturation undergo a process called atresia, a natural degeneration.
what are follicles and how do they relate to oocytes?
A follicle is a small, fluid-filled sac within the ovaries that surrounds and nourishes an oocyte (an immature egg cell) at different stages of development. Follicles play a crucial role in supporting the growth and maturation of oocytes.
- so the primary oocyte is within a primary follicle
- a secondary oocyte/egg is within a mature follicle
- the mature follicle is the chosen 1 follicle as only 1 follicle from 5-10 are matured
- At ovulation, the mature follicle ruptures and releases the secondary oocyte, making it available for fertilization.
what are the cells in the follicle that surround the oocyte
Granulosa cells – support oocyte development. immediately surround the oocyte.
Theca cells – secrete steroid hormone precursors. second ring around the granulosa cells.
what are the two cycles in the menstrual cycle
- ovarian cycle and uterine cycle
- occurs monthly
- cyclic changes in activity, defined by stages of hormonal fluctuations
how long is a typical menstrual cycle?
what are the two phases in the ovarian cycle?
what are the three phases in the uterine cycle?
- menstrual cycle typically 28 days (20-40 days range)
- the phases in the ovarian cycle: >1/2 follicular phase (14 day mark), <1/2 luteal phase
- phases in uterine cycle: menstrual phase (day 1-5), proliferative phase (day 5-14), secretory phase (day 14-28)
ovarian cycle: follicular phase
explain the 6 steps and the name of follicle in each step
- days 1-14
- there are 5-10 follicles/ovary
- 1 follicle matures to the dominant (Graafian) follicule that will be ovulated.
process:
1- primordial follicle: oocyte starts to develop granulosa cells around it.
2- primary follicle: granulosa cell layer thickens and theca cells are added after (theca synthesizes androgens and is converted to estrogens in granulosa cells).
3- secondary follicle: further thickening of theca cells
4- tertiary follicle: development of the antrum (fluid filled cavity with hormones and enzymes)
5- dominant (Graafian) follicle: antrum grows immensely, the theca cells are fully thickened. secondary oocyte remains the same.
6- The Graafian follicle ruptures and ovulation occurs.
what hormone and enzymes are involved in releasing the oocyte from the ovary and entering the fallopian tube.
- when the Graafian follicle ruptures, it releases the oocyte and the cumulus (surrounding area)
- this triggers LH hormone to sure so the follicular cells can release collagenase (enzyme to digest the connective tissue between the oocyte and the ovary), and progesterone (hormone that promotes the smooth muscle around the ovary to contract to expel the oocyte)
- the oocyte is then expelled into a small gap between the ovary and fallopian tube where the fimbria on the fallopian tube (finger like portions) grab the oocyte.
ovarian cycle: luteal phase
explain the remaining 3 steps of the ovarian cycle, specifically the luteal phase
- second part of the ovarian cycle after ovulation
1- Follicular cells left behind in ovary (since only the oocyte is ejected) become corpus luteum. Corpus luteum releases progesterone and estrogen.
2-3. If fertilization does NOT occur, corpus luteum degenerates. The scar tissue remaining is called the corpus albicans.
- If fertilization occurs, the corpus luteum continues to make progesterone and estrogen until the end of the first trimester to support the development of the fetus.
uterine cycle:
- why is the uterus very muscular
- what is the endometrium
- the uterus is very muscular to house the feedback and push out the fetus in childbirth
- the endometrium is a vascular tissue and has strong connections to the blood supply with continous growth of blood vessels
uterine cycle:
explain the 1. menstrual phase/menses of the uterine cycle
- days 1-5 of uterine cycle
- constriction of blood vessels supplying the endometrium
- due to dec. progesterone and estrogen when the body detects that no fertilization has occurred.
- this causes shedding of the endometrial lining –> blood in period
uterine cycle:
explain the 2. proliferative phase of the uterine cycle
- days 5-14 of uterine cycle
- note on day 14 ovulation occurs from the ovarian cycle
- Endometrium thickens as the blood supply to the tissue is re-established and cells proliferate
- due to estrogen inc. in ovaries (more follicles are formed thus more estrogen)
uterine cycle:
explain the 3. secretory phase of the uterine cycle
- days 14-28 of the uterine cycle
- inc. progesterone –> glands in endometrium secrete more viscous fluid - this secretion is rich in nutrients and is intended to support a fertilized egg if implantation occurs.
- inc. progesterone and estrogen –> Endometrial cells deposit lipid and glycogen in cytoplasm - readily avaliable energy for potential embryo.
- if no fertilization occurs then, hormone levels drop, returns back to the menstrual phase
