Reproductive Endocrinology I Flashcards
Development of male reproductive tract
- progression of Wolffian ducts
- degeneration of Mullerian ducts
- testosterone stimulated by hCG, secreted from the placenta
- mullarian inhibiting factor (MIF) needs to be present
- without stimulus of male testicular homeones, Wolffian ducts regress, Mullerian ducts devevlop and foetus develops female characteristics
- begins in early development and seizes until puberty
Development of female reproductive tract
- wolffian ducts degenerate
- progression of mullerian ducts
SRY gene
- encodes for production of testes determining factor
- direct differentiation of gonads to testes
- not present in females
Gonadal sex is determined by
presence or absence of SRY gene
Role of testosterone
- converted to dihydrotestosterone to promote development of external male genitalia
- transports wolffian ducts into male reproductive tract (e.g. epididymis, ductus deferens, ejaculatory duct, seminal vesicles)
Phenotypic sex is determined by
presence or absene of masculinising hormones
When does genitalia differentiation begin
10 weeks
Seminiferous tubules
- where sperm is formed
- stored within epididymis and ductus deferens
Role of prostate and bulbourethral glands
provide ejaculate fluid
Function of testes
- produce sperm and secrete testosterone
- Leydig cells lie in the connective tissue of the seminiferous tubules
- in utero, develop in abdominal cavity of foetus
- drop into scrotal sac before birth
Testosterone effects on events before birth
- masculinises the reproductive tract and external genitalia
- promotes decent of the testes into the scrotum
Testosterone effects on sex-specific tissues
- Leydig cells secrete testosterone again at puberty
- promotes growth and maturation of repro system at puberty
- causes tests to enlarge and become capable of spermatogenesis
- maintains repro tract throughout adulthood
Other reproductive effects of testosterone
- develops libido at puberty and can maintain it for life
- controls gonadotrophin hormone secretion (negative feedback - controls spermatogenesis)
Testosterone effects on secondary sexual characteristics
- inducers characteristic male patterns of hair growth
- enlarges larynx and thickens vocal chords
- thickens skin
- causes male body shape
- eunuch -> male castrated before puberty
Nonreproductive effects of testosterone
- anabolic - promotes protein and bone growth / development
- induces oil secretion by sebaceous glands
- aggressive behavior
Why is it important that testes descend
- lower temp outside body to facilitate spermatogenesis
- nervous reflexes trigger muscle movement in scrotal sac to lower or raise testes according to external temp
What is cryptorchidism
individual has reached adulthood and testes have not descended
Effects of androgen secretion from the adre- nal cortex in males
- testicular enlargement and public hair growth
- trigger for not certain - programmed within adrenal cortex independent of ACTH
What triggers testes maturation and androgen/sperm production
FSH and LH due to GnRH release from hypothalamus
What sexual characteristics of males appear during puberty
- growth of larynx
- deepening of voice
- increased bone mass
- increased mass and strength of skeletal muscle
- thickened skin
- increased and thickened hair on trunk, arms, legs, face
What induces somatic growth
gonadal sex steroids, growth hormone, and insulin-like growth factor
What is spermatogenesis
- conversion of germ cells into motile sperm
- supported by sertoli cells
Development of male gamete
- differentiation takes 64 days
- multiply by mitosis and generates more spermatogonia
- give rise to primary spermatocytes
- Sertoli cells support sperm development and prevent infections
Mitotic proliferation stage of spermatogenesis
spermatogonia (46 chromosomes) divide - one daughter cell remains undifferentiated, the other divides twice more to form primary spermatocytes
Meiotic division stage of spermatogenesis
- 1st meiotic division - each primary spermatocyte divides into 2 haploid secondary spermatocytes
- 2nd meiotic division - secondary spermatocytes divide to form 2 single-stranded spermatids
- testosterone is required for mitosis and meiosis stages
Spermiogenesis (3rd stage of spermatogenesis)
- packaging - spermatids converted to spermatozoa, removal of unnecessary cellular components and rebuilding into specialised, motile spermatozoa
- FSH required
Structure of sperm
- head = acrosome (contains enzymes for penetration of ovum)
- nucleus contains genetic material
- centriole
- tail provides motility; packed with microtubules and energised by mitochondria
Sertoli cells role in blood-testes barrier
- tight junctions protect sperm from antibody attack
- provides a regulated fluid composition which allows for later stages development of sperm
Sertoli cells role in phagocytosis
remove surplus cytoplasm from packaging and destory defective cells
Seminiferous tubule fluid secreted from Sertoli cells
used to carry cells to epididymis along pressure gradient
Androgen binding protein secreted from Sertoli cells
- binds to testosterone so that concentration remains high in lumen - essential for sperm production
Inhibin
- secreted from Sertoli cells
- hormone that regulates FSH secretion via negative feedback and controls spermatogenesis
Hormones that control the testes
- 2 gonadotropic hormones secreted by anterior pituitary
- Lutenizing hormone (LH); acts on Leydig cells to promote testosterone secretion
- Follicle-stimulating hormone (FSH); acts on Sertoli cells to enhance spermatogenesis - essential for spermatid remodeling
- GnRH stimulates release of LH and FSH
Control of testicular function
- GnRH secreted from anterior pituitary to stimulate gonadotrope secretion of LH and FSH
- LH acts on Leydig cells to stimulate secretion of testosterone
- testosterone produces masculinising effects, selectively inhibits LH secretion, and acts on hypothalamus to secrete GnRH
- FSH acts on Sertoli cells to stimulate spermatogenesis and secretion of inhibin
- inhibin selectively inhibits FSH secretion from gonadotrope
Importance of female reproduction system
- production of ova
- reception of sperm
- transport of sperm and ova to site of fertilisation
- gestation
- parturition
- nourishment of the infant by lactation
Oogenesis
- identical mitotic and meiotic divisions to male
- takes many years to complete
- begins in utero
- suspended for many years
- begins again at puberty
- completed at fertilisation
- oogenesis ceases at menopause
Stages of oogenesis
- mitotic proliferation occurs prior to birth
- primary oocytes are formed at birth and are suspended at the end of the first meiotic division, which is completed prior to ovulation
- ovulation commences the secondary oocyte, which has not completed the second meiotic division
- mature ovum contains haploid chromosomes and half the genetic content
- second meiotic division completed only at fertilisation
What is adrenarche
- 6-8 years of age
- adrenal gland secretes androgens
- growth spurt
- pubic hair growth starts as consequence of androgen secretion
What is thelarce
the start of breast development
What is menarche
- onset of menstrual cycle at 10-16 years old
- increase FSH and LH from pituitary
- ovaries produce steroids
- establishment of oestrogen inducing ovulation by positive feedback
- onset related to critical level of body fat which triggers GnRH release
In females, secondary sexual characteristics are induced by
- ovarian oestrogens
- causes pubic hair, growth and maturation of repro tract and external genitalia, fat deposition - breasts, butt, thighs, closure of epiphyseal plates
Somatic growth in females
- begins two years earlier in girls
- induced by gonadal sex steroids, growth hormone, and insulin-like growth factor
Menopause
- 5th decade of life as ovaries atrophy
- decrease in fertility, shortening of menstrual cycle
- FSH levels rise, causing ovarian oestrogen, progesterone and inhibin to fall
- cessation of ovulation and menstruation
- hot flushes
- vaginal and uterine atrophy, decreased breast size
- longer-term susceptibility to osteoporosis and cardiovascular disease
The 1st half of the ovarian cycle
- follicular phase
- maturation of egg, ready for ovulation at midcycle - ovulation signals end of follicular phase
The 2nd half of the ovarian cycle
- luteal phase
- development of corpus luteum
- induces preparation of reproductive tract for pregnancy
The primary follicle of the follicular phase
- primary oocyte is surrounded by single layer of granulosa cells before birth (primary follicle)
- each is capable of producing single ovum
- until puberty, all primary follicles degenerate to scar tissue
- after puberty, secondary follicles develop cyclically
The secondary follicle of the follicular phase
- oocyte grows and follicle expands and becomes differentiated under hormonal influence
- after puberty, about 400 will be ovulated, the rest will undergo atresia
- follicular phase ends with ovulation
The luteal phase
- follicluar cells left behind after ovulation undergo lutenisation and transform the corpus luteum
- CL secretes progesterone and oestrogen
- oestrogen secreted is essential for preparation of uterine lining for implantation
Corpus luteum
- after ovulation, CL grows for 8-9 days
- if no fertilisation has occurred, it will survive for no longer than 14 days after ovulation
- corpus albicans is formed (white body, fibrous tissue)
- degeneration of corpus luteum signals start a new follicular phase
- if fertilisation, CL persists and produces increasing quantities of progesterone and oestrogen until after pregnancy
Hormonal control of uterine and ovarian cycles
- oestrogen inhibits LH and FSH release
- oestrogen stimulates LH and FSH release at approx day 14 of cycle
What marks the beginning of both uterine and ovarian cycles
mensturation
The anterior pituitary secretes
FSH and LH a few days before menstruation
Follicle maturation
increases production of oestrogen
The one remaining follicle
secretes increasing amounts of oestrogen and stimulates uterus to grow
The first 12 days of the ovarian cycle
oestrogen exerts negative feedback on gonadotropin release
Days 12-14 of ovarian cycle
oestrogen exerts positive feedback on the pituitary
What triggers ovulation
- LH surge
- stimulates follicle cells to develop into the corpus luteum and secretes progesterone and oestrogen
Role of oestrogen and progesterone
- maintenance of uterine lineing
- send negative feedback to anterior pituitary to inhibit gonadotropin release
What happens to corpus luteum if fertilisation does not occur
degenerates on day 26
What happens to uterine lining in absence of progesterone
sloughs off and menstruation occurs
Negative feedback on anterior pituitary
decrease in oestrogen and progesterone relieves the negative feedback on anterior pituitary, causing an increase in GnRH, FSH, and LH
Feedback control of FSH and LH secretion during follicular phase
- Hypothalamus sends signal to stimulate GnRH in anterior pituitary
- GnRH acts on gonadotrope to secrete LH and FSH
- LH and FSH act on developing follicle to increase and moderate levels of oestrogen
- Rising levels of oestrogen act on hypothalamus and gonadotrope to selectively inhibit FSH secretion
- inhibin is secreted from the developing follicle and acts on gonadotrope to selectively inhibit FSH
