Lecture 31 Reproductive Flashcards
Organs
gonads = testes + ovaries
ducts
accessory glands
external genitalia
Meiosis
46 chromosomes (2n, diploid) → 23 chromosomes (n, haploid)
46 Chromosomes
when does DNA replicate
22 homologous pairs of autosomes + 1 pair of sex chromosomes (XX = female, XY = male)
DNA replicates prior to meiosis; each chromosome is duplicated, consists of 2 sister chromatids
Meiosis I
homologous pairs separate, 2n (duplicated) → n(duplicated)
Meiosis II
sister chromatids separate, n (duplicated) → n (single chromosomes)
male
1 primary spermatocyte (2n) → → 4 sperm cells (n)
female
1 primary oocyte (2n) → 1 egg cell (n) … → 1 fertilized egg + polar bodies
Spermatogenesis
occurs in seminiferous tubules of testes
spermatogonia → primary spermatocyte → secondary spermatocytes → spermatids → sperm
Sertoli cells
support developing spermatocytes + endocrine function
blood testis barrier
tight junctions between Sertoli cells form barrier to immune system
hormonal control
general pattern
hypothalamus: GnRH → anterior pituitary: FSH & LH → gonads: steroid sex hormones + others
FSH
stimulates gamete production in male and female
LH
stimulates secretion of sex hormones by gonads and stimulates ovulation in females
Steroid sex hormones
♂: testosterone, DHT; ♀: estrogen [estradiol], progesterone
- stimulate gamete production, overall reproductive function, development
of reproductive organs and secondary sexual characteristics
Negative feedback
Negative feedback control regulates hormone levels in males and partly in females
Positive feedback
Positive feedback control triggers ovulation in females
Hormonal Control of Spermatogenesis
Sertoli cells
Leydig (interstitial) cells
Negative feedback control
Sertoli cells
respond to FSH, support developing spermatocytes
- androgen binding protein (ABP) binds and concentrates testosterone
Leydig (interstitial) cells
produce testosterone in response to LH
- testosterone binds to ABP in Sertoli cells → promotes spermatogenesis
Negative feedback control
(Spermatogenesis)
inhibin - secreted by Sertoli cells, inhibits FSH secretion
testosterone inhibits GnRH and LH secretion
Oogenesis
occurs in ovarian follicles in ovaries follicular cells (granulosa cells and theca cells) surround a developing egg cell (oocyte)
Follicle
primary follicle → secondary follicle → mature follicle → (Ovulation) corpus luteum
Egg
oogonia → primary oocyte → (meiosis 1) secondary oocyte (egg) → (requires fertilization, meiosis 11)
Ovarian Cycle
follicular phase (day 0-14) ovulation (day 14) luteal phase (day 14-28)
follicular phase
growth and maturation of follicle, oocyte goes through meiosis I
ovulation
egg bursts through wall of ovary, swept into uterine tube
luteal phase
corpus luteum forms from remaining follicle cells;
- corpus luteum continues to secrete estrogen and progesterone;
degenerates at the end of the cycle unless fertilization occurs
Uterine Cycle
menses (0) proliferative phase (14) secretory phase (28)
menses
- uterine lining (endometrium) is sloughed off and discharged
proliferative phase
endometrium regrows, becomes thicker and vascularized
secretory phase
endometrium continues to thicken and becomes secretory
Hormonal Control of the Female Reproductive System
Early follicular phase
Late follicular phase
Luteal phase
Early follicular phase
- FSH and LH secretion begins to increase
- follicular cells stimulated to produce steroid sex hormones:
theca cells: produce androgens → granulosa cells: convert androgens to estrogens - estrogen levels rise → stimulates proliferative phase
- at low to moderate levels, estrogen inhibits FSH and LH secretion (negative feedback)
Late follicular phase
- estrogen secretion peaks
- at high levels, estrogen exerts positive feedback → stimulates FSH and LH secretion
- LH surge triggers ovulation
- high estrogen level prepares reproductive tract for ovulation and sperm entry
Luteal phase
- after ovulation, corpus luteum secretes estrogen and progesterone
- progesterone levels rise → stimulates secretory phase, prepares uterus for pregnancy
- estrogen, progesterone and inhibin exert negative feedback, inhibit FSH and LH secretion
if fertilization occurs
zygote undergoes cell divisions to form a blastocyst (~100 cells)
- blastocyst implants in the uterus about 7 days after fertilization
- implanted embryo secretes human chorionic gonadotropin (hCG)
hCG “rescues” the corpus luteum → continues secretion of estrogen and progesterone,
keeps endometrium intact for the developing embryo
- placenta takes over production of progesterone and estrogen by the 7
th week
if fertilization does not occur
corpus luteum degenerates (→ corpus albicans)
→ estrogen and progesterone levels decrease → menstruation
