A+P: Reproduction II Flashcards
Define spermatogenesis.
process of forming male gametes via meiosis
Where does spermatogenesis occur?
seminiferous tubules
When does spermatogenesis occur?
at puberty, around 14 years old
Males make about how much sperm daily?
~90 million sperm daily
Seminiferous tubules consists of a thick ___ surrounding a central fluid-filled lumen containing four important types of cells: Name the cells.
- stratified epithelium
1. Sustentocytes (Sertoli cells)
2. Spermatogenic cells
3. Myoid cells
4. Interstitial endocrine cells (Leydig cells)
Function of sustentocytes (Sertoli cells)
- Blood-testes barrier
- supporting cells; help w/ sperm production
- also provide nutrients & signals to dividing cells
- move sperm cells & spermatids along lumen & secrete testicular fluid
Function of Spermatogenic cells
- surrounded by sustentocytes & dividing to give rise to sperm cells
Function of myoid cells
- SM-like cells surrounding seminiferous tubule - contract to squeeze sperm & testicular fluid through tubules/epididymis
Function of insterstitual endocrine cells (Leydig cells)
- Produce androgens & some estrogen
- creates testosterone to help drive this process
3 steps of spermatogenesis
- Mitosis of spermatogonia (stem cell) forms two spermatocytes
- Meiosis: spermatocytes form 2ndary spermatocytes, which form spermatids
- Spermiogenesis: spermatids become sperm
When does mitosis of spermatogonia begin?
at puberty
After puberty in males, each division via mitosis produces:
- Type A daughter cells
- Type B daughter cells
Describe Type A daughter cells?
remain at basal lamina to maintain pool of dividing germ cells
Describe Type B daughter cells?
move toward lumen & develop into primary spermatocytes
Describe the process of Meiosis: spermatocytes to spermatids–> Meiosis I
Primary spermatocyte (2n) undergoes meiosis I, forming two secondary spermatocytes (n)
Describe the process of Meiosis: spermatocytes to spermatids–> Meiosis II
2ndary spermatocyte (n) rapidly undergoes meiosis II to become two spermatids (n)
–>Spermatids: small, round cells w/ large nuclei found close to lumen of tubule
–> Nearly all genes are turned off and DNA compacted into dense pellets
Describe process of Spermiogenesis: spermatids to sperm
- Spermatids contain correct haploid chromosome # needed for fertilization (n)
–> Are still nonmotile - Spermiogenesis
–> Streamlining process where spermatid elongates, loses excess cytoplasm & forms a tail.
What are the major regions of sperm?
head, midpiece & tail
Describe the sperm head.
genetic region
- includes nucleus & helmetlike acrosome containing hydrolytic enzymes that enable sperm to penetrate egg
Describe the sperm midpiece.
metabolic region containing mitochondria that produce ATP to move tail
Describe the sperm tail.
locomotor region that includes flagellum
How longs does spermatogenesis take?
64-72 days (in good conditions)
Where does the final maturation of sperm occur?
epididymis
Define infertility
lack of pregnancy after trying a year of unprotected intercourse
Infertility affects how many couples in America?
1 in 7
What are the usual causes of infertility?
problems w/ sperm quality or quantity
Possible causes for infertility
- environmental toxins
- phthalates (in plastics)
- pesticides
- herbicides
What are some other poss causes of infertility?
- Estrogen-like compounds block action of male sex hormones
- Abx (tetracycline may suppress sperm formation)
- Radiation, lead, marijuana, and excessive alcohol
- Defects in Ca+ channels, hormonal imbalances & oxidative stress
- Thermal related events (hot tubs) may inhibit sperm maturation
What is a Mittelschmerz?
twinge of pain sometimes felt at ovulation by some women
–> scar tissue stretching from previous ovulations??
Production of gametes and sex hormones is regulated by sequence of hormonal events involving the ___, ___, & ___. aka?
- hypothalamus, anterior pituitary gland, and testes
- hypothalamic-pituitary-gonadal (HPG) axis
What happens to the remaining granulosa cells and thecal cells during the luteal phase?
they enlarge to form corpus luteum that secretes progesterone & estrogen
What interacting hormones are involved w/ male reproductive physiology?
- GnRH
- FSH
- LH
- testosterone
- inhibin
Sequence of regulatory events: Male Reproductive Physiology (7)
- Hypothalamus releases (GnRH)
- GnRH binds to ant pituitary gonadotropic cells, causing them to secrete: FSH & LH
- FSH stimulates spermatogenesis indirectly by stimulating sustentocytes to release androgen-binding PRO (ABP)
–> ABP keeps [] of testosterone high near spermatogenic cells, promoting spermatogenesis - LH binds to interstitial endocrine cells, prodding them to secrete testosterone
–> Rising testosterone levels trigger spermatogenesis - Testosterone entering blood stimulates sex organ maturation, development/maintenance of 2ndary sex characteristics & libido
- Rising testosterone levels feed back on hypothalamus to inhibit GnRH & on pituitary to inhibit gonadotropin release
- Inhibin: released by sustentocytes when sperm count high; inhibits GnRH & FSH release
NOTE
- Before birth, male infant has testosterone levels 2/3s of adult
- After brief rise in early infancy, blood levels recede & remain low through childhood
- As puberty nears, higher levels of testosterone are required to suppress hypothalamic release of GnRH & adult pattern is established
NOTE
Amount of testosterone & sperm produced by testes reflects balance among interacting hormones of HPG axis.
What long does it take for testosterone & sperm production to stabilize?
3 years and then stable throughout life
Without GnRH & gonadotropins what happens?
- testes atrophy
- sperm & testosterone production ceases
What is testosterone synthesized from?
cholesterol
Testosterone is converted to what in the prostate?
dihydrotestosterone
Testosterone is converted to what in some brain neurons?
estradiol
What are the 2 functions of testosterone?
- Prompts spermatogenesis & targets all accessory organs
- Has multiple anabolic effects throughout body
Testosterone def. can lead to:
- atrophy of accessory organs
- semen volume declines
- erection/ejaculation impairment
What is the tx for testosterone def.?
testosterone replacement
What are male secondary sex characteristics?
features induced in nonreprod. organs by male sex hormones (mainly testosterone)
List some male sex characteristics.
- pubic, axillary & facial hair
- hair on chest
- larynx enlargements–> deep voice
- skin thickens & becomes oily
- Bones grow, incr in density
- Skeletal muscles incr size & mass
- Boosts BMR
- Basis of sex drive (libido)
When does oogenesis begin?
in fetal period
Describes the steps of oogenesis.
Oogonia (diploid stem cells) divide by mitosis to produce:
Primary oocytes that undergo meiosis I to produce:
Secondary oocytes that undergo meiosis II to produce:
Ova
What are the 3 key differences b/t oogenesis & spermatogenesis?
- Production of primary oocytes occurs only fetus
- In primary oocytes, meiosis is arrested in late prophase I & resumes only years later (if at all)
- In secondary oocytes, meiosis is arrested in metaphase II & is only completed if fertilization occurs
What are the fates of follicles?
atresia or ovulation
Describe atresia.
apoptosis (programmed cell death) of oocyte & surrounding cells
99.9% of all follicles are never recruited
Describe ovulation (more specific)
- Each month after puberty, a select few primary oocytes are activated
- Caused by high hormonal levels, especially FSH
- 1 from this group is “selected” each month to become dominant follicle
of gametes per lifetime for males
> 1 trillion
of gametes per lifetime for females
<500
What cells sustains spermatocytes?
sustentocytes
What cells sustains oocytes?
granulosa cells
Number of functional gametes differ: Oogenesis vs Spermatogenesis
- Oogenesis produces 1 viable haploid ovum w/ 2-3 haploid polar bodies
- Spermatogenesis produces 4 viable sperm
Occurrence during lifetime: Oogenesis vs Spermatogenesis
- Oogenesis begins in fetal life, ends in menopause
- Spermatogenesis begins in puberty to old age (80s)
Why is the error rate higher in females?
b/c they are sitting in that “frozen” state for so long
Describe the ovarian cycle.
montly (28-day) series of events assoc. w/ maturation of egg
Describe the two phases of the ovarian cycle?
follicular & luteal
NOTE
2 consecutive phases w/ ovulation occurring midcycle (~ day 14-15) b/t phases
What is the follicular phase?
period of vesicular follicle growth
- days 1-14
Describe what’s happening during the follicular phase?
- the follicle is undergoing development caves in which the ova are kept
- 5-10 will grow in one ovary. They will alternate which ovary has the growing ova
What is the luteal phase?
period of corpus luteum activity
- days 14 - 28
this is what’s happening inside the ovary
What phases vary and which stay the same? Describe.
- follicular phase varies
- luteal phase is always 14 days from ovulation to end of cycle
What happens during the follicular phase?
several follicles become sensitive to FSH & are stimulated to grow
What happens around the middle of the follicular phase?
FSH levels drop
What happens to non-dominant follicles?
atresia (breakdown)
Describe ovulation.
ballooning ovary wall ruptures, expelling into peritoneal cavity
When does fraternal twins occur? Explain.
ovulation releases >1 2ndary oocyte
–> if fertilized = fraternal twins
When does identical twins occur? Explain.
- after fertilization
–> fertilization of 1 oocyte, then separation of daughter cells
Can oocytes be released at times unrelated to hormone levels?
YES
What happens during the luteal phase of ovarian cycle?
After ovulation, ruptured follicle collapses & antrum part of the follicle fills w/ clotted blood
- Referred to as corpus hemorrhagicum; will eventually be absorbed
What happens if NO pregnancy does occur during the luteal phase?
corpus luteum degenerates into corpus albicans (scar) in 10 days
What is the luteolytic or ischemic phase?
last 2–3 days of luteal phase, when endometrium begins to erode
What happens if pregnancy does occur during the luteal phase?
corpus luteum produces hormones that sustain pregnancy until placenta takes over at about 3mos
Function of estrogen & progesterone during the luteal phase?
working on the uterus
- getting it ready for a fertilized egg
What makes beta-hCG?
the fertilized ovum
What is Beta-hCG?
marker to the corpus luteum to maintain the lining of the uterus
Which phase do miscarriages usually occur?
Luteal phase of ovarian cycle
How long does hormonal regulations occur for establishing ?hormonal regulation continue?
until an adult cycle pattern in achieved and menarche occurs
What is the average age of menarche?
11-12 yo
List 6 key steps of hormonal interaction during ovarian cycle
- GnRH stimulates FSH & LH secretion
- FSH & LH stimulate follicles to grow, mature & secrete sex hormones
- Neg feedback inhibits gonadotropin release
- Pos feedback stimulates gonadotropin release
- LH surge triggers ovulation & formation of the corpus luteum
- Neg feedback inhibits LH & FSH release
Describe how GnRH stimulates FSH & LH secretion.
the pulsatile release tells the ant pituitary which hormone will be released
Describe how FSH & LH stimulate follicles to grow, mature & secrete sex hormones
- FSH stimulates the release of estrogen
- LH stimulate the production of androgens, which are converted to estrogens
Describe how neg feedback inhibits gonadotropin release.
Incr levels of plasma estrogen levels exert neg feedback inhibition on FSH & LH release
- only 1 dominant follicle can withstand the dip in FSH; other developing follicles deteriorate
What is inhibin?
a hormone released by the granulosa cells of the ovaries that also inhibits FSH release
Describe how pos feedback stimulates gonadotropin release in women
- Estrogen levels cont. to rise as a result of continued release by dominant follicle
- When levels reach a critical high value, a brief pos feedback occurs on brain & anterior pituitary
- Triggers LH surge
Describe how LH surge triggers ovulation & formation of the corpus luteum.
- High estrogen levels trigger release of stored LH, by anterior pituitary at midcycle
- Surge triggers ovulation
What happens shortly after ovulation?
- Estrogen levels decline
- LH transforms ruptured follicle into corpus luteum
- LH stimulates corpus luteum to secrete progesterone & some estrogen almost immediately
–> Progesterone helps maintain stratum functionalis of the endometrium
–> Maintains pregnancy, if it occurs
Describe how neg feedback inhibits LH & FSH release
- Neg feedback from rising plasma progesterone & estrogen levels inhibits LH & FSH release
–> Inhibin, from corpus luteum & granulosa cells, enhances inhibitory effect
–> Declining LH ends luteal activity & inhibits follicle development (& therefore starts degradation)
Describe the uterine menstrual cycle.
cyclic series of changes in endometrium that occur in response to fluctuating ovarian hormone levels
What are the 3 phases of the menstrual cycle?
- Days 1–5: menstrual phase
- Days 6–14: proliferative (preovulatory) phase
- Days 15–28: secretory (postovulatory) phase
What occurs during the menstrual phase?
- Ovarian hormones are at lowest levels
- Gonadotropin levels are beginning to rise
- Stratum functionalis detaches from uterine wall & is shed
Menstrual flow of blood & tissue lasts 3–5 days - By day 5, growing ovarian follicles start to produce more estrogen
What occurs during the proliferative (preovulatory) phase?
- ^^ estrogen levels prompt generation of new stratum functionalis layer
–> As layer thickens, glands enlarge, & spiral arteries incr in # - Estrogen increases synthesis of progesterone receptors in endometrium
- Thins out normally thick, sticky cervical mucus to facilitate sperm passage
- Ovulation occurs at end of proliferative phase on day 14
starts rebuilding of the uterine lining
What occurs during the secretory (postovulatory) phase?
- Phase that is most consistent in duration
- Endometrium prepares for embryo to implant
- Rising progesterone levels from corpus luteum prompt:
–> Functional layer to become a secretory mucosa
–> Endometrial glands enlarge & secrete nutrients into uterine cavity
–> Thickened mucus to form cervical mucus plug - blocks entry of more sperm, pathogens, or debris
Describe what happens if fertilization doesn’t occur during the secretory phase?
- Corpus luteum degenerates toward end of secretory phase; progesterone levels fall
- Causes spiral arteries to kink & spasm
- Endometrial cells die & glands regress
- Spiral arteries constrict again, then relax & open wide, causing a rush of blood into weakened capillary beds
- BVs fragment & functional layer sloughs off & uterine cycle starts all over again - 1st day of menstruation
At what age does the descend of gonads start?
2 months before birth
What stimulates migration of testes toward scrotum?
testosterone
Do the ovaries descend?
YES
Describe boundaries where ovaries stop their descent.
ovaries stop descending by broad ligament at pelvic brim
What is cryptorchidism?
failure of testes to make their normal descent
Cryptorchidism can increase risk of…
sterility & increased risk of testicular cancer
What is the usual treatment for unresolved cryptorchidism?
surgery
How long does sperm last?
5 days
How long is the window for a woman to become pregnant after intercourse?
5-day window
How long should you wait for cryptorchidism?
If it hasn’t descended in about 1 year they have to go find it.
What is the gubernaculum?
fibrous cord that guides the testicles into it’s right position
When does menopause occur?
when menses have ceased for an entire year
Describe perimenopause
starts in late 30s/early 40s
- periods can become more irregular
Is there a menopause equivalent in men?
NO
Describe sperm production in males as they age.
Males cont to produce sperm into 80s, #s & motility decreases
Declining estrogen levels cause:
- Irregular menses / menorrhagia
- Atrophy of reprod. organs/breasts
- Irritability & depression in some
- Hot flashes as skin BVs undergo intense vasodilation
- Gradual thinning of skin & bone loss
- Incr total blood cholesterol levels & falling HDL
Treatment for menopause
estrogen-progesterone preps
NOTE
Less estrogen feeds back on the hypothalamus–> produces FSH goes up
- a rise in FSH to a certain levels is a dx marker for menopause)
Describe premature menopause & when it occurs.
- ovaries stop responding to estrogen
- as early as 25yo
