Reproductive Physiology Flashcards
1
Q
Give an overview of the events before and during puberty.
A
- Repro system quiescent during early childhood.
- Increased activity of repro system during adolescence.
- When inihibition is withdrawn or overcome at puberty, phenotypic and behavioural changes occur.
- Increases in GnRH (gonadotrophin-releasing hormone) lead to increases in LH and FSH secretion (both females and males).
- Age of onset varies (according to various factors e.g. sex, nutritional state, race.
2
Q
Describe adrenarche.
A
- 6-8 years of age (adrenal gland secretes androgens (e.g. dehydroepiandrosterone, DEHA) - similar to male puberty).
- Trigger not known - “pre-programmed”?
- Androgens eventually cause growth spurt
- Pubic hair growth starts
- Breast development starts
3
Q
Describe menarche.
A
- Onset of menstrual cycle at 10-16 years old.
- Ability to produce mature ova and an endometrium that could support a zygote.
- Increased FSH and LH from pituitary (triggered by GnRH).
- Ovaries respond to FSH and LH by producing steroids.
- Oestrogen induces ovulation.
- Onset related to critical level of body fat - triggers GnRH release.
4
Q
Describe the phenotypic changes associated with female puberty.
A
-
Secondary sexual characteristics induced by ovarian oestrogens.
- Pubic hair
- Growth / maturation of reproductive tract (including uterus) and external genitalia.
- Fat deposition - breasts, buttocks, thighs.
- Closure of epiphyseal plates (stops growing) (at end of puberty).
-
Somatic growth
- Begins ~2 years earlier in girls compared with boys.
- Growth induced by gonadal sex steroids, growth hormone and insulin-like growth factor (as for males).
5
Q
Describe the endocrinology of male puberty.
A
- Bursts of GnRH release begin at 8-12 years (initially at night) to initiate puberty.
- Exact trigger for GnRH production is not clear.
- “Pre-programmed”? Critical body weight? Inhibition of melatonin secretion?
- GnRH triggers bursts of FSH and LH release (as for females).
- This triggers testes to produce androgens and sperm.
- Frequency of bursts increases until levels of GnRH, LH, FSH and testosterone are the same as in the adult.
- Rising levels of testosterone produce secondary sexual features.
6
Q
Describe the phenotypic changes associated with male puberty.
A
-
Secondary sexual characteristics appear (caused by testosterone and metabolites).
- Testicular enlargement
- Pubic hair growth
- Growth of larynx
- Deepening of voice
- Increased bone mass
- Increased mass and strength of skeletal muscle
- Thickened skin
- Increased and thickened har on trunk, arms, legs, face
-
Somatic growth
- Induced by gonadal sex steroids, growth hormone and insulin-like growth factor.
- Puberty lasts many years - facial hair pattern may not mature until 20-25 years of age.
7
Q
Describe the female monthly sexual cycle.
A
- Ovarian cycle - production and release of ova.
- Cycle lasts for 28 days (average).
- Has 2 phases:
-
Follicular phase
- 1st half of cycle.
- Maturation of egg, ready for ovulation at midcycle - ovulation signals end of follicular phase.
-
Luteal phase
- 2nd half of cycle.
- Development of corpus luteum (yellow body).
- Induces preparation of reproductive tract for pregnancy (if fertilisation occurs).
-
Follicular phase
- Menstrual cycle - signified by blood loss via vagina due to sloughing of uterine endometrial lining - if it is not required to maintain a pregnancy.
8
Q
What effect does LH have during the menstrual cycle?
A
Triggers ovulation at ~ day 14.
9
Q
What happens to oestrogen concentration in response to ovulation?
A
It falls.
10
Q
Describe the concentrations of oestrogen, FSH and LH during the menstrual cycle?
How do these concentrations correlate to follicular development?
A
11
Q
What effect does progesterone have on FSH and LH?
A
Inhibitory
12
Q
Describe the female menopause.
A
- Menopause - determined retrospectively: begins at 12 months after the end of last menstrual bleed.
- Cessation of menstruation - commonly occurs between approximately 45 and 55 years.
- Menopause manifests physically but isn’t a disease - it is a normal part of ageing.
13
Q
What are the potential triggers of the female menopause?
A
- Precise trigger still not known.
- Oocyte depletion? Post-menopause there may still be some healthy oocytes so this can’t be the full picture.
- Remaining follicles might not be as sensitive to LH and FSH? In the reproductive cycle, these gonadotrophins trigger ovaries to produce a follicle (containing the oocyte).
- Age-related changes in CNS alter GnRH secretion?
14
Q
Describe the physiological changes associated with menopause.
A
-
Before menopause (menopause transition):
- Menstrual cycle may be irregular- may be shorter due to lack of complete follicular development, sometimes no ovulation occurs.
-
Progressively:
- Ovaries atrophy - there are few or no healthy follicles.
- Decrease in oestrogen secretion with concomitant increase in LH and FSH.
- Increased LH stimulates ovaries to produce androstane-dione.
- Androstene-dione is androgen precursor → hirsuteness and precursor for estrone.
- Estrone becomes the dominant oestrogen post-menopause, beta-oestradiol was dominant pre-menopause.
- Overall decrease in oestrogens → breast and reproductive tract atrophy, vaginal dryness.
- LH pulses coincide with hot flushes but are not responsible for flushes. More likely to be due to temporary disturbances of hypothalamus thermoregulatory centres (linked somehow to GnRH pulse generator).
- Increased bone mineral loss → decreased density.
- Increased CV disease risk due to lack of protection due to oestrogen concentration falling.
15
Q
Describe the male andropause.
A
- There is no distinct andropause in males.
- However, as men age:
- Gonadal sensitivity to LH decreases.
- Androgen production decreases.
- Serum LH and FSH increase.
- Sperm production typically declines after age ~50.
- Many men maintain reproductive function and spermatogenesis throughout life.
16
Q
What are the essential female reproductive functions?
What are the roles of the different parts of the female reproductive tract which carry out these functions?
A
- Production of ova
- Reception of sperm
- Capacitation
- Transport of sperm and ova to site of fertilisation
- Gestation
- Parturition
- Nourishment of the infant by lactation
18
Q
What are the essential male reproductive functions?
What are the roles of the different parts of the male reproductive tract which carry out these functions?
A
- Production of sperm (spermatogenesis).
- Delivery of sperm to female.
- Route of sperm: testes → epididymus → vas deferens → ejaculatory duct → urethra.
20
Q
What are the 4 stages of sexual arousal?
A
- Excitement
- Plateau
- Orgasm
- Resolution
22
Q
Describe the erection reflex.
A
25
Q
Describe the ejaculation reflex.
A
26
Q
Describe the structure of a spermatozoon.
A
Plural = spermatozoa
29
Q
Describe the journey of sperm after ejaculation.
A
- Most sperm stay in the vagina (millions) and eventually leak out.
- Some sperm found in the cervix (minutes).
- If mucous is thin and watery and cervix is soft, some sperm can get into uterus.
- Some sperm get to site of fertilisation (typically hours) (a few hundred).
32
Q
Describe the stages in the first phase of implantation.
A
- Initial contact with epithelium of uterus - blastocyst sticky.
- Proteases released from trophoblast.
- Pathways created allowing trophoblast cells to grow into endometrium.
- Trophoblast releases nutrients for embryo.
33
Q
Describe the stages in the second phase of implantation.
A
- Trophoblast cells tunnel into the endometrial lining.
- Boundaries between trophoblast cells disintegrate - “syncytiotrophoblast” will become fetal placenta.
- Trophoblast induces “decidualisation” of endometrium - increased local vascularisation and nutrient storage.
- Blastocyst becomes buried in uterine lining by day 12.
34
Q
Describe the development of the placenta.
A
- Placenta derived from both trophoblast and decidual tissue.
- Trophoblast cells (chorion) differentiate into multinucleate “syncytiotrophoblasts” which invade decidua and break down capillaries to form cavities filled with maternal blood.
- Developing embryo sends capillaries into the syncytiotrophoblast projections to form placental villi.
- Each villus contains fetal capillaries separated from maternal blood by a thin layer of tissue - no direct contact between fetal and maternal blood.
- 2 way exchange of respiratory gases, nutrients, metabloites etc. between mother and fetus, largely down diffusion gradient.
- Placenta (and fetal heart) are functional by the 5th week of pregnancy.
35
Q
What does HCG do?
A
- hCG is responsible for maintenance of pregnancy.
- In the first trimester.
- Human chorionic gonadotrophin (hCG).
- Produced by the blastocyst.
- Prolongs life of corpus luteum (now called corpus luteum of pregnancy).
- For further 10 weeks, corpus luteum of pregnancy grows and produces increasing concentrations of progesterone and oestrogen (first trimester).
- After 10 weeks, the placents produces these hormones.
- THEREFORE, the uterine lining is maintained during pregnancy.
- Pregnancy test = hCG detected in urine.
- Morning sickness = hCG may trigger vomiting centre.
- At the end of the first trimester, hCG stimulates male fetal gonads to produce steroid hormones → genitalia differentiation.
- Second and third trimester, oestrogen and progesterone take over.
