Reproductive Physiology Flashcards
(41 cards)
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- When inihibition is withdrawn or overcome at puberty, phenotypic and behavioural changes occur.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
17
Q
What are the basic phases of oogenesis?
A
- Identical meiotic and mitotic divisions to male sperm production - but:
- Oogenesis takes many years to complete (spermatogenesis takes 60-68 days).
- Begins in utero.
- Suspended for many years.
- Begins again at puberty.
- Completed at fertilisation.
- Oogenesis ceases at menopause.
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.
19
Q
How do the male accessory organs aid fertilisation?
A
-
Epididymus and vas deferens
- Exit route from testes to urethra.
- Concentrattion and storage of sperm.
- Site for sperm maturation.
-
Seminal vesicles
- Produce semen into ejaculatory duct.
- Supply fructose.
- Secrete prostaglandins (stimulates motility).
- Secrete fibrinogen (clot precursor).
-
Prostate gland
- Produces alkaline fluid (neutralises vaginal acidity).
- Produces clotting enzymes to clot semen within female.
-
Bulbourethral glands
- Secrete mucus to act as a lubricant.
20
Q
What are the 4 stages of sexual arousal?
A
- Excitement
- Plateau
- Orgasm
- Resolution
21
Q
Describe the excitement phase of sexual arousal in males and in females.
A
-
Males
- Heightened sexual awareness.
- Testicular vasocongestion.
- Engorgement of penis → erection.
-
Female
- Heightened sexual awareness.
- Vasodilation of vagina and external genitalia → swelling of labia.
- Erection of clitoris.
- Lubrication of vagina.
- Enlargement of breasts.
- Flush to skin.
22
Q
Describe the erection reflex.
A
23
Q
Describe the plateau phase of sexual arousal in males and in females.
A
-
Male
- Intensification of excitement.
- Increased HR, BP, RR, muscle tension.
-
Female
- As male.
- Also vasodilation of lower 1/3 of vagina causes tightening around penis.
-
“Tenting effect”
- Uterus raises
- Lifts cervix
- Enlarges upper 1/2 of vagina (makes room for ejaculate)
24
Q
Describe the orgasm phase of sexual arousal in males and in females.
A
-
Males
- Intense physical pleasure.
- Ejaculation.
- Rhythmic contractions of pelvic muscles every 0.8 seconds.
- Increased HR, BP, RR, muscle tension.
-
Females
- Intense physical pleasure.
- Rhythmic contractions of pelvic muscles every 0.8 seconds, especially in lower 1/3 of vagina (“orgasmic platform”).
- Increased HR, BP, RR, muscle tension.
- No ejaculation.
- No refractory period → can have another orgasm immediately.
25
Describe the ejaculation reflex.
26
Describe the structure of a spermatozoon.
Plural = spermatozoa
27
Describe the resolution phase of sexual arousal in males and in females.
* **Male**
* Temporal refractory period - men cannot have orgasms in quick succession.
* Relaxation.
* Return of body to pre-excitement state.
* Slowing of blood flow to penis.
* **Female**
* No refractory period.
* Relaxation.
* Return of the body to pre-excitement state.
28
Describe the pre-fertilisation stage of oocytes and spermatozoa.
* Oocyte is viable approximately 6-24 hours after ovulation.
* Spermatozoa is viable approximately 24-48 hours in the female reproductive tract.
* Freshly ejaculated spermatozoa are incapable of fertilisation. They must undergo capacitation (in female reproductive tract - can be induced in vitro under correct conditions).
* Surface of sperm altered by removal of glycoprotein coat.
* Tail movements become whip-like.
* Increased calcium sensitivity and cAMP levels rise to promote acrosomal reaction.
* **Allurin** released by mature ovum to attract sperm.
* Sperm "smell" this chemical using an olfactory receptor. Detection induced directed tail movements and swimming in direction of the signal. They have a long journey.
29
Describe the journey of sperm after ejaculation.
* 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).
30
Describe the binding and penetration of sperm.
* **Fertilin** (protein on sperm) binds to **integrin** (adhesion molecule on secondary oocyte).
* **Then, acrosomal reaction.**
* ****Enzymes in the acrosomal tip allow sperm to 'burrow' through the outer layers of ovum and enter cytoplasm.
* Tail of sperm probably lost.
* 'Block to polyspermy' membrane changes triggered.
31
Describe the fusion of sperm and egg membranes.
* Fusion of sperm and egg membranes triggers 3 events:
* **Block to polyspermy:**
1. **Primary block**
* ****Egg membrane depolarises, preventing other sperm fusing.
2. **Secondary block**
* Changes to zona pelucida making sperm binding difficult (known as **cortical reaction**).
3. **Second meiotic division of the egg**
* Second polar body formed and extruded from the egg, ensuring femal pronucleus is haploid.
* Result = usually one sperm / one egg ratio (both haploid) → diploid conceptus.
* Mostly "triploid" embryos are not viable.
32
Describe the stages in the first phase of implantation.
1. Initial contact with epithelium of uterus - blastocyst sticky.
2. Proteases released from trophoblast.
3. Pathways created allowing trophoblast cells to grow into endometrium.
4. Trophoblast releases nutrients for embryo.
33
Describe the stages in the second phase of implantation.
1. Trophoblast cells tunnel into the endometrial lining.
2. Boundaries between trophoblast cells disintegrate - "syncytiotrophoblast" will become fetal placenta.
3. Trophoblast induces "decidualisation" of endometrium - increased local vascularisation and nutrient storage.
4. Blastocyst becomes buried in uterine lining by day 12.
34
Describe the development of the placenta.
* 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
What does HCG do?
* **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.
36
Describe the roles of oestrogens and progesterones during pregnancy.
* Secreted by the corpus luteum of pregnancy in the 1st trimester and placenta in 2nd and 3rd trimesters.
* **Oestrogens**
* ****Stimulates growth of myometrium musculature - to expel fetus during labour.
* Stimulates development of mammary gland ducts.
* **Progesterone**
* ****Suppresses contractions of uterine myometrium.
* Promotes formation of mucous plug.
* Stimulted development of mammary milk glands.
37
What is the role of human chorionic somatomammotrophin (hCS) during pregnancy?
* Decreased maternal glucose utilisation, increased plasma FA, increased glucose and FA availibility for fetus.
* Prepares breast glands for lactation
38
What is the role of parathyroid hormone-related peptide (PTHrp) during pregnancy?
* Mobilises maternal Ca2+ for calcification of fetal bones (if mother's diet does not contain enough Ca2+).
39
What is the role of relaxin during pregnancy?
* Softens cervix
* Loosens pelvic connective tissue
40
What is the role of placental corticotrophin releasing hormone (CRH) during pregnancy?
* Stimulates DEHA (dehydroepiandrosterone) production by fetal adrenal cortex - important in initiation of parturition.
41
Describe the interruption to menstruation associated with pregnancy.
* Typically, pregnancy "full-term" (singleton) lasts for 40 weeks (counted from the first day of the woman's last menstrual bleed).
* Usually, menstrual cycle stops during pregnancy.
* Usually, menstruation begins again after about 4-6 weeks post partum, if not breastfeeding.
* If breastfeeding, menstruation begins again after about 4-6 weeks weaning.
* Some mothers will menstruate throughout.
* Pregnancy can still occur post-partum, even if menstruation has not yet begun.
