Reproductive system Flashcards
What hormones control production of follicle by ovary?
FSH and LH
What steroids are produced by the ovary?
oestradiol and progesterone
When does ovulation occur?
Day 14
What steroids are released during the proliferative phase?
oestrogen
also released during the follicular phase
Which hormone does the corpus luteum release?
It makes progesterone
How does the combined oral contraceptive pill work?
- combination of oestrogen and progesterone
- Negative feedback, inhibits FSH and LH release
- This prevents follicular development, egg maturation, ovulation, egg transport in fallopian tube
- This causes unreceptive endometrium, cervical mucus is hostile to sperm
What happens during ovulation?
Egg comes down tube with scilia, turns into corpus lutem goes into uterus and implants
What is the role of trophoblasts?
- They form first around early blastocysts
- Trophoblasts form the placenta and form interface between mother and baby
What does hCG do?
- hCG produces fast quantities bc this is the maternal recognition signal that stops egg from being rejected and early miscarriage
- hormone secreted during pregnancy by the trophoblasts which stimulates continued production of progesterone by the ovaries
What is placenta previa caused by?
When the placenta is over the cervix, and during pregnancy it ruptures causing massive bleeding and death
Which hormone stimulates uterine contractions?
Oxytocin induces uterine contractions in two ways. Oxytocin stimulates the release of PGE2 and prostaglandin F2α in fetal membranes by activation of phospholipase C.
What does corticotrophin releasing hormone do and where is it released?
- regulates cortisol in adrenal gland of fetus
- released by the placenta as an indication of maturity
Late CRH release= late pregnancy
Early CRH release= early birth
Where is estrogen synthesised and what triggers it?
Adrenal gland synthesises estrogen from progesterone
Stimulated by adrenocorticotrophin (ACTH) released by pituitary
What role does estrogen play in labor?
- stimulates prostaglandin E2 (for cervix dilation)
- PGF2a secretion (stimulates uterine contractions)
Describe the sequence of events for labor initation (how CRH leads to prostoglandin production)
- Placental CRH matures the fetal HPA axis
- The now mature fetal adrenal gland makes 17α-hydroxylase enzyme (which kicks off estrogen synthesis)
- Placental trophoblasts make aromatase (which synthesises estrogen) so they secrete estrogen
- Estrogen makes myometrium sensitive (stimulates expression of prostaglandin E and F receptors)
- Estrogen stimulates prostaglandin E2 and PGF2α secretion
How do testes produce sperm?
- SSCs and sertoli cells support meoisis of spermatocytes
- Produced/Released from semineferous tubules
- Sperm production is limited by number of sertoli cells and how active SSCs are
Sperm will continue to be produced until sertoli cells or spermatogonial cells are removed
What are sertoli cells?
Referred to as nurse cells bc every germ cell are completely dependent on contact to sertoli cells for survival
Somatic cells
What are leydig cells?
Surround spermatocytes and make androgens in MALES
somatic cells
What are peritubular myoid cells?
aka PTM cells
- They comprise the basemement membrane of se
- They push the sperm through the lumen out to be released
How many spermatids are made from one spermatocyte after meiosis?
Four round spermatids are made after two meiotic divisions
Do spermatagonial stem cells (SSC) undergo mitosis or meiosis?
Mitosis
What are thecal cells?
Make up basal membrane of ovarian follicle
Release androgens (female equivalent of Leydig cells)
What are granulosa cells?
Support/nurse single oocyte
Produce estrogen converted from androgens
Female equiv of sertoli cells
What are primordial follicles?
Formed when oocytes stop undergoing mitosis and enter meoisis (occurs mid pregnancy)
There fore once primordial follicles formation has stopped the females total possible germ cell number is FIXED. From them on it will only decline, as follicles are lost
Flattened granulosa cells surround primordial follicles
How many germ cells are produced after oocyte undergoes meiosis?
After one meiotic division; one germ cell and one polar body
After two meiotic divisions; one germ cell and two polar bodies
What things occur during estrous cycles that lets males know females are ovulating?
- Pheremonal cues
- Flehmen response: male response to female
□ male sniffing pheromones to know female in oestrous
□ Lions currl upper lip back to sniff odours (pheromones) - Lordosis: female response to males (Female mice arch their backs)
- Will allow mounting often adopting different posture in presence of males
How does the HPA axis control ovulation?
GnRH stimulates pituitary-> pituitary secretes FSH and LH-> stimulates ovary to grow follicles (dominant follicles selected to grow) -> Mature follicle goes onto ovulate
How are follicles ‘selected’ to mature?
The ones that secrete the most estrogen are the ones that become dominant
Estrogen has negative feedback effect on FSH, so when a follicle becomes big enough to secrete enough estrogen that it reduces FSH secretion, this would have a negative impact on the rest of the smaller follicles inhibiting their growth
When the mature follicle(s) are approaching pre-ovulatory stage, what happens to estrogen, FSH, and LH levels?
Estrogen levels are VERY high, which induce a release of GnRH which induces a surge of LH and a small surge in FSH
What are the different phases of oestrus?
Proestrus (follicular phase): follicles grow, are selected, estrogen rises
Oestrus: mating behavior to signal ovulation, dominant follicles ovulate
Metoestrus: early luteal, CL forms
Dioestrus: mid-late luteal, CL at max size, if NO PREGNANCY CL regresses, progesterone output maximal
Anestrus: cycling stops due to change in day length (only in seasonal breeders)
CL=corpus luteum
Luteal phase: process of somatic cells from a follicle developing into a cell within a corpus luteum after ovulation
What is the difference between spontaneous and induced ovulators?
Spontaneous: Ovulate each oestrus cycle no matter what happens, ovulation set in motion by HPA (Eg sheep)
Induced: Follicles growing to full size but wont ovulate unless female mates at that time (eg cats or ferrets or rabbits)
What are some differences between menstrual and oestrus cycle?
Menstrual cycle has…
- No oestrus behavioor
- No pheremones
- No outward event revealing cyclicity
- Sexual receptivity throughout
Humans have menstrual cycle
What are the differences in sexual dimorphism in animals with oestrus vs menstrual cycles?
- Oestrus: competition for ovulating females is intense (eg male gorillas much bigger than females bc of this)
- Menstrual: more monogamous pairing= less competition= less sexual dimorphism
Seasonal breeding ensures that…
Babies are born during seasons with prime environmental conditioons (spring/summer)
How does the HPG axis and pineal gland regulate ovulation/pregnancy?
- HPG axis detects changes in melatonin secretion from pineal gland
- In seasonal breeders, this causes GnRH decrease, which decreases FSH and LH, which shuts down gonad (ovary or testes)
- Short day breeders: change from short day-> long day triggers HPG
- Long day: change from long day-> short day triggers HPG
Pineal gland gets input from the eyes, so during winter; more dark= more melatonin secretion
short day breeders only breed during winter (aka short days)
Long day breeders only breed during summer (aka long days)
Why do some species exhibit embryonic diapause?
Obligate diapause:
- Eg polar bears: mate in spring but embryos stay in diapause until autumn then born in the following spring
- Eg roe deer: mating around july/aug, but birth around May
Facultative diapause:
- Eg rodents: (regulated by lactation) Implantation of embryo is delayed to ensure that lactation of current offspring is done by the time that the next offspring is born
Embryonic diapause:
Embryos develop to the point at which they are ready to implant but then enter a suspended state, delaying implantation, and hence delaying the timing of the birth
How does the HPA axis control puberty?
GnRH is released by the hypothalamus
GnRH stimulates anterior pituitary to secrete LH and FSH
LH and FSH acts on gonads which secrete hormones that have negative feedback on hypothalamus
- LH tells leydig to secrete tesosterone, inhibin B, & estrogen
- LH/FSH tells ovary to secrete estrogen, inhibin, progesterone
What does Anti-Mullerian hormone do? What cells is it secreted by
- If men don’t express this hormone they are born with a uterus, high AMH in men leads to wolffan duct development instead of mullerian
- If women express this hormone they are born without fallopian tubes, uterus, or cervix
- Secreted by sertoli cells and granulosa cells
- High AMH in women is directly correlated to high antral follicle count
What is Kallmanns syndrome?
- Lack of GnRH so puberty never happens
- Need exogenous GnRH to drive puberty
What time of day is LH secreted during puberty?
During the night
night pulses turn on gonadal hormone production
