Reproductive physiology Flashcards
Adrenarche (6-8 years) changes
Adrenal glands secretes androgens - similar to male puberty e.g. DHEA
Trigger not known
Androgens eventually cause growth spurt
Pubic hair growth starts and breast development starts
Menarche (10-16 tears old) changes
Onset of menstruation
Ability to produce mature ova and an endometrium that could support a zygote
FSH and LH increase from pituitary
Ovaries respond to FSH and LH by producing steroids
Oestrogen induces ovulation
Onset related to critical level of body fat - triggers GnRH release
Phenotypic changes in female at puberty
Secondary sexual characteristics induced by ovarian oestrogens - pubic hair, growth/maturation of retro tract e.g uterus and external genitalia, fat deposition in breasts, buttocks, thighs, closure of epiphyseal plates (stops growing) at end of puberty
Somatic growth - begins about 2 years earlier in girls compared to boys- growth induced by gonadal sex steroids, growth hormone and insulin like growth factor
male puberty endocrinology
Bursts of GnRH at 8-12 years initially at night to initiate puberty
Exact trigger for GnRH production not clear - critical body weight, inhibition of melatonin secretion links
This triggers increase in bursts of FSH and LH release
This triggers testes to produce androgens and sperm
Frequency of bursts until levels same as adult male
Phenotype of make puberty
Caused by testosterone and metabolites
Testicular enlargement, pubic hair growth, larynx growth, deepening gof voice, increased bone mass, increased mass and strength of skeletal muscle, thickened skin, increased and thickened hair on trunk, arms, legs, face
Somatic growth induced by gonadal sex steroids, growth hormone and insulin-like growth factor
Puberty lasts many years
Female monthly sexual cycle - ovarian and menstrual cycle
Lasts for 28 days and has 2 phases
Follicular phase - first half, maturation of egg, ready for ovulation at mid cycle - ovulation signals end of follicular phase
Luteal phase - second half, development of corpus lute, induces preparation of reproductive tract for pregnancy (if fertilisation occurs)
Menstrual cycle - signified by blood loss via vagina due to sloughing of uterine endometrial lining - if it is not required to maintain a pregnancy
Menopause
Determined retrospectively - begins 12 months after the end of last menstrual bleed
Cessation of menstruation commonly occurs between 45-55 years
Manifests physically but isn’t a disease - normal part of ageing
Lower levels of dominant oestrogen, physical manifestations vary - hot flushes, sweats, decreased libido, vaginal dryness, breast tissue atrophy, external genitalis atrophy, skin changes
Female menopause triggers
Not known but some ideas:
- 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 reproductive cycle these gonatrophins trigger ovaries to produce a follicle (containing the oocyte)
- Age related changes in CNS after GnRH secretion
Female menopause physiological changes
Before menopause - cycle may be irregular - may be shorter due to lack of complete follicular development, sometimes no ovulation occurs
Progressively, ovaries atrophy (few/no healthy follicles), decrease in oestrogen secretion with concomitant increase in LH and FSH, increased LH stimulates ovaries to produce androstenedione (androgen precursor) - estrange becomes the dominant oestrogen post-menopause
Overall decrease in oestrogen give post-menopausal symptoms
LH pulses coincide with hot flushes but not caused by them - more likely temp disturbances of hypothalamus thermoregulatory centres
Increased bone mineral loss - decreased density
Increase CVD due to lack of protection due to oestrogen conc falling
Andropause in males
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 through life
Essential female reproductive function
More complex roles than men Production of ova Reception of sperm Capacitation Transport of sperm and ova to site of fertilisation Gestation Parturition Nourishment by lactation
What do the different components of the female reproductive tract do?
Ovaries - maturation and release of ova
Oviducts (fallopian tubes) - site of fertilisation
Uterus - maintains foetus during gestation, expels foetus at end of gestation
Cervix - has small opening to allow sperm through to uterus, expands greatly during birth
Vagina - receptacle for sperm, birth canal - uterus to outside
Vaginal opening - allows penis in/baby out
Oogenesis
Identical meiotic and mitotic divisions to male sperm production but…
- Oogenesis takes many years ti complete
- begins in utero
- Suspended for many years
- Begins again at puberty
- Completed at fertilisation
- Oogenesis ceases at menopause
Male essential reproductive function
Production of serum and delivery to female
Testes - produce sperm
Scrotum - sac of skin where testes suspended
Accessory glands - seminal vesicles, prostate gland, bulbourethral gland) secrete sperm to suspend and sustain sperm
penis - transfer to female
How accessory organs in males aid fertilisation?
Epidydimis and vas deferens - exit route from testes to urethra, concentrate and store sperm, site for sperm maturation
Seminal vesicles - produce sperm into ejaculatory duct, supply fructose, secrete PGs (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 mucous to act as lubricant
