Lecture 37- Female reproductive system 2 Flashcards
What is the female germ cell?
Oogonia
What is oogenesis?
Formation and development of the oocyte (female gamete) from oogonia.
What cell division processes does oogenesis require?
Mitosis and meiosis
In females when are gametes made via oogenesis and how does this differ to males?
-Lifetime supply of gametes produced before birth
-Development then continues between puberty and menopause in a Cyclic nature (1 ovulation every 28ish
days)
-Differs from males where oogenesis continues across life
What do oocytes develop within?
- Ovarian follicles (surround the oocyte)
- These also undergo changes
- 1 oocyte exists per follicle
Once the developed oocyte exits the ovary what happens to the follicle?
Undergoes change to form the corpus luteum (major endocrine organ= Produce inhibin + estrogen+ progesterone )
What happens to the corpus luteum if fertilisation doesn’t occur?
Breaks down to become the corpus albicans
Does the oocyte move around the ovary when it develops?
No, stays in same place diagrams just set out like that to make stages clear
Does the oocyte move around the ovary when it develops?
No, stays in same place diagrams just set out like that to make stages clear
In female oogenesis what happens before birth?
- Oogonium (diploid, 2n=46) in gonad. Undergo mitosis so population increases (stops before birth)
- Oogonia differentiate to form primary oocytes (diploid, 2n=46). These are encased in primordial follicle. Many primary oocytes undergo atresia (cell death)
- Primary oocytes start meiosis. Meiosis halts at prophase I. Halts until puberty begins
In female oogenesis what happens before birth?
- Oogonium (diploid, 2n=46) in gonad. Undergo mitosis so population increases (stops before birth)
- Oogonia differentiate to form primary oocytes (diploid, 2n=46). These are encased in primordial follicle. Many primary oocytes undergo atresia (cell death)
- Primary oocytes start meiosis. Meiosis halts at prophase I. Halts until puberty begins
What happens in oogenesis from puberty to menopause?
- Under GnRH influence, small number of follicles recruited each ovarian/menstrual cycle.
- Only one oocyte will complete development and ovulate (within dominant follicle).
- Primary oocyte completes meiosis I forming a secondary oocyte and 1st polar body (both haploid, n=23).
- Secondary oocyte starts meiosis II. Halts at metaphase II and is suspended until fertilisation.
Is the number of oocytes in a female fixed before birth?
Yes, at puberty females have ~300,000 oocytes
What happens in oogenesis at fertilisation? What happens if not fertilized?
- Meiosis II resumes when the sperm penetrates plasma membrane of the ovum at fertilisation.
- If not fertilize, will degenerate (called atresia) and therefore never complete meiosis.
How do polar bodies form? When do they form?
- Happens when unequal division occurs. Although both cells produced in division are haploid all the cytoplasm and organelles have gone into oocyte.
- 2 are produced as occurs in both meiosis 1 and meiosis 2 of oogenesis
- The polar body in meiosis 1 usually dies but can undergo further division in meiosis 2 to create 2 more
- The polar bodies at end (either 1 or 3 depending on if meiosis 2 went ahead) all die
Describe the general sequence of changes in oogenesis (included chromosome numbers)…
Oogonium: 2n=46
Primary oocyte: 2n=46 :arrested at prophase 1
(present before birth)
Secondary oocyte: n=23 :halted at metaphase 2
Polar body: n=23
(change that occurs each month from puberty to menopause)
Fertilised ova (zygote): 2n=46 (metaphase 2 completes)
Ultimately one primary oocyte forms…
1 ova
What is the sequence that occurs in follicle development?
- Primordial follicle
- Primary follicle
- Secondary follicle
- Vesticular (antral) follicle
- Follicle erupts ( release oocyte)
- Corpus luteum forms
- Degrades to corpus albicans
What cells make up follicles? What are their functions?
Follicles are multilayered
- Granulosa cells= produce estradiol
- Theca cells= surround
What happens to the oocyte at ovaluation?
Oocyte and corona radiata released into peritoneal cavity (uterine tube) and guided by fimbriae to ampulla where can be fertilized
The 1 follicle that goes on to ovulate is called the…
Dominant follicle
Where is it produced and what is the role of GnHR?
- Hypothalamus
- Causes release of FSH and LH.
Where is it produced and what is the role of FSH?
- Anterior pituitary
- Stimulates the growth of ovarian follicles
Where is it produced and what is the role of LH?
-Anterior pituitary
-Surge of LH involved in ovulation, formation of corpus
luteum.
Where is it produced and what is the role of estradiol?
- Developing follicles
- Assists follicle growth (with FSH); bone and muscle growth; endometrial growth; secondary sex characteristics; feedback to anterior pituitary
Where is it produced and what is the role of inhibin?
- Granulosa cells
- Negative feedback to anterior pituitary to suppress FSH.
Where is it released and what is the role of Progesterone?
- Corpus luteum
- Negatively feeds back to suppress GnRH (therefore LH and FSH); endometrial maturation; maintains pregnant state.
What do the cyclic changes in the ovaries and uterus prepare the body for?
- Oocyte/ova for fertilisation
- Endometrium for embryo implantation
How long roughly is a menstrual cycle?
- Varies a lot between individuals
- Anywhere between 24-38 days is normal (average is 28 days)
What is menarche?
-First menstrual period
-Occurs at age 12-13 y on average
-Part of puberty: orchestrated by increase in sex steroid
production (estrogens) by the gonads
What is menopause?
- Cessation of menstruation
- Typically occurs in early 50s
- Reduction of estradiol and progesterone due to absence of or lack of response by follicles
- Anterior pituitary feedback no longer active ∴ FSH/LH high
What are the two ovarian cycles? What days in the cycle do they approximately occur?
- Follicular (preovulatory phase): Day 1 - 14
- Luteal (postovulatory phase): Day 15 - 28
Describe the follicular stage of the ovarian cycle…
-Increased FSH from the anterior pituitary stimulates follicular growth
-Growing follicles secrete estradiol and inhibin which reduces FSH from anterior pituitary (negative feedback)
Growing follicles then undergo atresia, except dominant follicle.
-Dominant follicle secretes large amounts of estradiol
-High estradiol stimulates surge of LH (positive feedback)
-Follicle ruptures and ovulation occurs. Oocyte enters peritoneal space/collected into uterine tube.
Describe the luteal stage of the ovarian cycle…
- Ovulated follicle collapses & forms corpus luteum. Secretes progesterone, estradiol & inhibin.
- These decrease FSH & LH secretion results in negative feedback on the hypothalamus and pituitary
What happens in the luteal phase of the ovarian cycle if fertilisation does not occur?
- If fertilisation and implantation does not occur, the corpus luteum involutes (luteolysis).
- Means Fall in progesterone & estradiol.
- This removes negative feedback on FSH and LH…. Cycle starts again…
What are the two phases in the menstrual (endometrial cycle)? When do they roughly occur?
- Menstrual and Proliferative: Day 1 - 14.
- Secretory (and premenstrual phase): Day 15 - 28
Describe the menstrual and proliferative phase…
- Endometrium breaks down and bleeds during menstruation
- Estradiol stimulates endometrial growth from approx days 6-14
- Rapid tissue growth, including growth of glands and vasculature
Describe the secretory phase…
- After ovulation (day 14) - corpus luteum secrets progesterone.
- Progesterone promotes endometrial maturation
- Glands become secretory
- Spiral arterioles grow and coil
What happens in the secretory phase if fertilisation and implantation does not occur?
- Corpus luteum atrophies
- Progesterone levels fall
- Spiral arteries contract
- Endometrial tissue breaks down and bleeding occurs
- Shed tissue and blood removed via cervix and vagina (menstruation /menses)
What happens in the secretory phase if fertilisation and implantation does not occur?
- Corpus luteum atrophies
- Progesterone levels fall
- Spiral arteries contract
- Endometrial tissue breaks down and bleeding occurs
- Shed tissue and blood removed via cervix and vagina (menstruation /menses)
