Reproductive system (basic anatomy and physiology) Flashcards
Where is GnRH released from?
-hypothalamus
What does GnRH do?
-stimulates anterior pituitary to release LH and FSH
What do FSH and LH do?
-stimulate the development of follicles in the ovaries which in turn then release oestrogen
What cells secrete oestrogen?
-the theca granulosa cells around the follicles in ovaries
What effect does oestrogen have on the hypothalamus and pituitary gland?
-oestrogen has negative feedback on the hypothalamus and anterior pituitary to suppress release of GnRH, LH and FSH
What is oestrogen?
-a steroid sex hormone produced by the ovaries in response to LH and FSH
What is the most prevalent and active form of oestrogen?
17-beta oestradiol
What does oestrogen act on?
-tissues with oestrogen receptors to promote female secondary characteristics
What does oestrogen stimulate?
- breast tissue development
- growth and development of female sex organs (vagina, vulva and uterus) at puberty
- blood vessel development in the uterus
- development of the endometrium
What is progesterone?
-a steroid sex hormone produced by the corpus luteum after ovulation
Where is progesterone produced during pregnancy?
-mainly by the placenta from 10 weeks gestation onwards
What does progesterone act on?
-tissues that have previously been stimulated by oestrogen
What does progesterone do?
- thickens and maintains the endometrium
- thickens the cervical mucus
- increases body temp
What happens to these sex hormones during puberty?
-they start to increase which leads to development of female secondary sexual characteristics and onset of menstrual cycle
What age does puberty usually begin in women?
-8-14 years
How long does puberty usually last?
-about 4 years
Why might there be delayed puberty in girls with low weight/eating disorders?
- aromatase is an enzyme found in adipose tissue
- it is important in the creation of oestrogen
- low weight means less adipose tissue so less aromatase for oestrogen production
Describe the puberty stages in order in women
breast bud development–> pubic hair—> menstrual periods
Describe the hormonal changes in puberty
- GH increases intially causing growth spurt
- GnRH is released during sleep at first then throught the day later in puberty
- GnRH stimulates release of FSH and LH whihc then stimulate release of oestrogen and progesterone from ovaries
- FSH levels plateau about a year before menarche while LH levels spike just before menarche
What are the 2 phases of the menstrual cycle?
- follicular phase
- luteal phase
When does follicular phase start?
-follicular phase is from the start of menstruation to moment of ovulation (first 14 days in 28 day cycle)
When does luteal phase start?
-luteal phase is from ovulation to the start of menstruation (last 14 days of cycle)
What are oocytes?
in the ovaries a finite number of cells that have potential to develop into eggs
What are follicles formed from?
-granulosa cells surrounding oocytes
What are the four stages of development that follicles go through in the ovaries?
- primordial follicles
- primary follicles
- secondary follicles
- antral follicles (Graafian)
Describe the process of primordial follicles maturing into primary and secondary follicles during follicular phase
- it is always occurring independent of the menstrual cycle
- once the follicles reach secondary follicle stage, they develop receptors for FSH
- further development for secondary follicles requires stimulation from FSH
Describe the effect of FSH on secondary follicles during follicular phase
- at start of menstrual cycle, FSH stimulates development of secondary follicles
- they grow and the granulosa cells surrounding them secrete increasing amounts of oestradiol(oestrogen)
- oestrogen has negative feedback on FSH and LH and also causes cervical mucus to become more permeable-> allows spem to penetrate the cervix around time of ovulation
- one of the follicles will develop further than others to become the dominant follicle
Describe the effect of LH on the dominant follicle during follicular phase
-LH spikes just before ovulation causing dominant follicle to release the ovum (unfertilised egg) from the ovary
When does ovulation happen?
14 days before end of menstrual cycle, e.g day 14 of 28 day cycle or day 16 of 30 day cycle
Describe what happens during the luteal phase after the dominant follicle has release ovum after ovulation
- the follicle that release the ovum collapses and becomes the corpus luteum
- the corpus luteum secretes high levels of progesterone which maintains the endometrial lining
- progesterone also causes cervical mucus to become thick and no longer penetrable
- the corpus luteum also secretes small amounts of oestrogen
Describe what happens during the luteal phase when fertilisation occurs
- the syncytiotrophoblast of the embryo secretes hCG
- hCG maintains the corpus luteum–> without it, it degenerates
- pregnancy tests check for hCG
Describe what happens during the luteal phase when no fertilisation occurs
- no fertilisation of ovum –> no production of hCG –> corpus luteum degenerates and stops producing oestrogen and progesterone
- this fall in oestrogen and progesterone causes the endometrium to break down and menstruation occurs
What additional substance promotes the break down of endometrium during menstruation?
-stromal cells of endometrium release prostaglandins which encourage break down of endometrium and uterus contraction
What does menstruation involve?
- it involves the superficial and middle layers of the endometrium seperating from the basal layer
- the broken down tissue in the uterus is released via the cervix and vagina resulting in a release of fluid containing blood
- this lasts 1-8 days
