Reproductive System Flashcards
(31 cards)
3-hormone chain beginning with the brain as the primary regulator
- hypothalamus secretes GnRH
- GnRH in hypothalamo-pituitary portal vessels
- Anterior Pituitary secretes LH and FSH
- LH and FSH
- Gonads secrete sex hormones
- reproductive tract and other organs respond
Meiosis
- meiosis is the process of producing gametes (egg and sperm) that have only one chromosome instead of a pair
- 4 haploid from 2 diploid
spermatogenesis
1) spermatogonia [mitosis differentiation)(46 chromosomes per cell, 2 chromatids per chromosome)
2) primary spermatocytes (1st meiotic division) (46 chromosomes/cell, 2 chromatids/chromsome)
3) secondary spermatocyte (secondary meiotic division) (23 chromosomes per cell, 2 chromatids/chromosome)
4) spermatids (differentiation) 23 chromosomes/cell, 1 chromatid/chromosome
5) spermatozoa (23 chromosomes/cell, 1 chromatid/chromosome)
spermatogenesis: testicular process in adult males that generates haploid gametes capable of fertilizing ova
- overall result: set of 23 pairs of homologous chromosomes is reduced to a set of 23 chromosomes/sperm; the corresponding 23 pairs are present in the ova
Leydid and Sertoli Cells
- in response to LH, Leydig cells produce steroids, including testosterone
- in response to FSH and testosterone, sertoli cells support spermatogenesis
Route spermatozoa take
1) seminiferous tubules
2) rete testis
3) epididymis (1st into efferent ductules, 2nd into vas deferens)
Semen
what happens after the sperm is released into the reproductive tract?
-spermatozoa propelled with flagellum
-at time of fertilization, acrosome at the head of an individual spermatozoan releases enzymes that allow it to gain access to the interior of the ova
-midpiece is packed with mitochondria (needs lots of ATP to keep sperm going)
-
Functions of Sertoli Cells
- provide sertoli cell barrier to chemicals in the plasma
- nourish developing sperm
- secrete luminal fluid, including androgen-binding protein
- respond to stimulation by testosterone and FSH to secrete paracrine agents that stimulate sperm proliferation and differentiation
- secrete protein inhibin, which inhibits FSH secretion from the pituitary
- secrete paracrine agents that influence the function of Leydig cells
- phagocytize defective sperm
Summary of hormonal control of male reproductive function
- hypothalamus secretes GnRH
- GnRH in hypothalamo-pituitary portal vessels
- Ant.Pitutiary secrete LH and FSH
- Sertoli cells secreted by FSH, in turns secretes inhibin which inhibits FSH
- Leydig cells secreted by LH, Leydig cells produce testosterone, testosterone is what helps produce sertoli cells
- testosterone produced from LH cells go to the reproductive tract and other organs, they respond accordingly
- sperm can stay viable for a few days (sometimes 48 hours), sperm with X chromosomes last longer than sperm with Y chromosome because x chromosome has more genetic information
oogenesis
- production of haploid gametes in females
- full sequence of meiosis is not completed until fertilization
- oogonia during fetal life stage, mitosis differentiation into primary oocyte
- childhood: 1st meiotic division
- adult reproductive life: secondary oocyte, 2nd meiotic division (completed after fertilization)
- identical twins: one oocyte was fertilized by one sperm very early on, split, identical
- during adult reproductive life: first polar body, second polar body
what happens when a spermatozoan is ejected into the female reproductive tract?
- must move through the cervix and uterus before it can fertilize and ovulated egg that has been moved from the ovaries to the uterine tube by the combined actions of fimbrial contractions, and oviduct’s ciliary escalator”
- if fertilized, completes mitosis 2
follicular cells vs sertoli cells
-follicular cells similar because they both try to help spermatogenesis, oogenesis, etc by providing nourishment
development of an ovarian follicle and oocyte
- mature follicle is 1.5 cm in diameter
- thecal cells develop from granulosa cells
- primordial follicle->primary follicle->preantral follicle->early antral follicle->mature follicle
- granulosa cells around oocyte
- thecal cells around entire follicle
Ovarian cycle
- ovarian cycle of changes in steroid production drives the rest of the changes that characterize the menstrual cycle in females
- follicular phase is marked by increasing levels of estrogens whereas the luteal phase is one marked by increasing levels of progesterone levels; transition between the two is ovulation
- Day 1: menstrual bleeding starts
- Day 7: one follicle becomes dominant
- Days 7-14: dominant follicle matures
- Day 14: ovulation occurs
- Day 14-25: corpus luteum functions
- Day 25-28: corpus luteum degenerates
What is ovulation provoked by?
- by a surge in LH-marks the transition to the luteal phase of the cycle, characterized by high levels of progesterone
- Eventually, a decrease in LH leads to luteolysis, and the withdrawal of steroid support for a thick, active uterus
- small increases in the secretion of gonadotropins (LH&FSH) lead to follicular maturation, including an increase in the synthesis and secretion of ovarian steroid hormones
- estrogen and progesterone help increase mother’s metabolism, which increases her body temperature, which helps nourish the potential fetus
Summary of major feedback effects of estrogen, progesterone, and inhibin
1) estrogen in low plasma concentrations: causes the anterior pituitary to secrete less FSH and LH in response to GnRH and also may inhibit the hypothalamic neurons that secrete GnRH
Result: Neg. feedback inhibition of FSH & LH secretion during the early and middle follicular phases
2) Inhibin: acts on the pituitary to inhibit the secretion of FSH
Result: Neg. feedback inhibition of FSH secretion throughout the cycle
3) Estrogen, when increasing dramatically: ant. pituitary cells secrete more LH and FSH in response to GnRH
Estrogen also stimulates the hypothalamic neurons to secrete GnRH
Result: pos. feedback stimulation of the LH surge triggers ovulation
4) high plasma concentration of progesterone, in the presence of estrogen, inhibit the hypothalamic neurons that secrete GnRH
Result: Neg. Feedback inhibition of FSH and LH secretion prevention of LH surges during the luteal phase and pregnancy
Summary of the hormonal control of ovarian function during the follicular phase
- hypothalamus secretes GnRH
- GnRH (in hypothalamo-pituitary portal vessels)
- ant. pituitary secrete FSH and LH
- FSH secrete granulosa cells-influence oocytes, inhibin
- thecal cells from LH secrete androgens
- granulosa cells convert androgens to estrogens
- reproductive tract and other organs respond to estrogen
Functions of granulosa cells
- nourish oocyte
- secrete chemical messengers that influence the oocyte and thecal cells
- secrete antral fluid
- the site of action for estrogen and FSH in the control of follicle development during early and middle follicular phases
- express aromatase, converts androgens (from theca cells) to estrogens
- secrete inhibin which inhibits FSH secretion via an action on the pituitary gland
- the site of action for LH induction of changes in the oocyte and follicle culminating in ovulation and formation of corpus luteum
Feedback relationship between the ovarian steroid hormones and the secretion from the hypothalamus/anterior pituitary
- relationship reverses in mid-cycle, eliciting the large, ovulatory surge in LH
1) large amounts of estrogen
2) causes secretion of GnRH from hypothalamus
3) increase of GnRH
4) increase of LH from ant. pituitary
5) LH surge
6) ovulation corpus luteum (high levels of progesterone and estrogen)
what happens after ovulation?
-the corpus luteum releases inhibin, progesterone, and estrogen which inhibit the release of gonadotropins
Estrogens and progestins
- estrogens=predominant steroid hormone prior to ovulation
- progestins predominate after ovulation
- follicular phase the menstrual and proliferative phases
- Luteal phase:secretory
- follicular: menstrual
- progesterone and estrogen help to make the endometrial wall thick
Summary of menstrual cycle
Days 1-5, estrogen and progesterone are low bc previous corpus luteum is regressing
Hence, the endometrial lining sloughs, secretion of LH and FSH
Day 7: single follicle usually becomes dominant
Days 7-12: plasma estrogen increases because of the secretion by the dominant follicle, therefore, endometrium is stimulated to proliferate
Days 7-12: LH and FSH decrease due to estrogen and inhibin feedback, therefore, degeneration of nondominant follicles
12-13: LH surge is induced by increasing plasma estrogen
-oocyte is induced to complete its first meiotic division and undergo cytoplasmic maturation
14: ovulation mediated by follicular enzymes and prostaglandin
15-25: corpus luteum forms and under influence of low but adequate levels of LH secretes estrogen progesterone, increasing plasma concentration of these hormones
25-28: corpus luteum degenerates if implantation doesn’t occur, then plasma estrogen and decrease. therefore, endometrium begins to slough off
Summary of Events from Ovulation and Fertilization to Implantation
Days After LH peak:
1. Ovulation. location: ovary
2. Fertilization. Fallopian tube.
2-4. Cell division to ~32 cells. Fallopian tube
5. blastocyst enters the uterine cavity. uterus.
6-7. implantation. uterus
9-10. Human chorionic gonadotropin (hCG) from implanted blastocyst rescues corpus luteum. trophoblast->maternal ovary
Why does only a single spermatozoan gain access to the ovum at time of fertilization?
-due to a biochemical clock; sperm penetration also triggers the completion of meiosis in the ovum so that fertilization can occur.
-fertilized egg called a zygote
1) many sperm bind to receptors on the zona pellucida and undergo the acrosome reaction
2) sperm move through zona pellucida
3) only one sperm binds to egg plasma membrane
THEN:
-either egg releases contents of secretory vesicles->enzymes enter zona pellucida->block to polyspermy occur
OR:
-sperm is drawn into egg->egg completes 2nd meiotic division->nuclei and sperm unite->zygote begins embryogenesis
OR:
-egg enzymes are activated->zygote begins embryogenesis
