Sexual Sexual ReproductionReproduction

Life wants to create more life Life wants to create more life at any expense, short of at any expense, short of

losing its own life.losing its own life.

The egg: the female storyThe egg: the female story

• Ovaries: Ovaries: – meiosis produce ova(eggs)meiosis produce ova(eggs)

• Meiosis does not equally Meiosis does not equally divide cytoplasm between divide cytoplasm between daughter cells daughter cells

• Most of it remains in one Most of it remains in one cell, called the ovum(the cell, called the ovum(the egg)egg)primary oocyteprimary oocyte

• The small cells called The small cells called polar polar bodiesbodies break down and break down and disintegratedisintegrate

The female storyThe female story

• Humans produce one egg per Humans produce one egg per cyclecycle

• The egg travels down The egg travels down oviductsoviducts “aka. “aka. Fallopian Fallopian tubes, tubes,

• Woman have two of these Woman have two of these tubular structurestubular structures

• Connect ovaries to Connect ovaries to uterusuterus

The female storyThe female story

• Uterus: a pear shaped organ, very Uterus: a pear shaped organ, very muscularmuscular– Where embryo will be developingWhere embryo will be developing

– During labor, muscle contractions During labor, muscle contractions push the baby out through the vaginapush the baby out through the vagina

• VaginaVagina: muscular passageway: muscular passageway– Sperm must travel throughSperm must travel through

– Menstrual fluid exits this wayMenstrual fluid exits this way

The Menstrual CycleThe Menstrual Cycle

• The The menstrual cyclemenstrual cycle : :– Lasts 28 days although this may varyLasts 28 days although this may vary– The first day of menstrual cycle is The first day of menstrual cycle is

marked by beginning of menstrual marked by beginning of menstrual flowflow

– Several factors regulate the cycleSeveral factors regulate the cycle• Nervous system, several glands, organs, Nervous system, several glands, organs,

hormoneshormones• Hypothalamus: gland in the brainHypothalamus: gland in the brain

– adjust levels of hormones in circulatory systemadjust levels of hormones in circulatory system

Day 1: Start of Menstrual Day 1: Start of Menstrual CycleCycle

• Day One:Day One:– Low levels of estrogen and Low levels of estrogen and

progesteroneprogesterone

• HypothalamusHypothalamus– Senses low levels of estrogen and Senses low levels of estrogen and

progesteroneprogesterone– Releases GnRHReleases GnRH

• ““gonadotropin-releasing hormone”gonadotropin-releasing hormone”

• Travels to Travels to pituitary glandpituitary gland

• Pituitary GlandPituitary Gland– Just below hypothalamusJust below hypothalamus– Release FSH and LHRelease FSH and LH

• 1. FSH: follicle stimulating hormone1. FSH: follicle stimulating hormone• 2. LH: leutenizing hormone2. LH: leutenizing hormone

-travel to ovary-travel to ovary

• OvaryOvary

Around day 10?Around day 10?

• Ovaries:Ovaries:– High levels of FSH and LHHigh levels of FSH and LH– Stimulate egg maturing inside follicleStimulate egg maturing inside follicle

• A fluid filled sac in ovaryA fluid filled sac in ovary

Day 14: Halfway through Day 14: Halfway through cyclecycle– Sudden increase of LH Sudden increase of LH

causes follicle to burstcauses follicle to burst• release egg release egg

““ovulationovulation””– Follicle that rupture is Follicle that rupture is

called called corpus luteumcorpus luteum• Continues releasing Continues releasing

estrogen and estrogen and progesteroneprogesterone

• Stimulate buildup of Stimulate buildup of uterine lininguterine lining

Halfway Through the Halfway Through the CycleCycle

• Uterine lining is thickeningUterine lining is thickening• High levels of estrogen and High levels of estrogen and

progesteroneprogesterone• Hypothalamus sees high levelsHypothalamus sees high levels

– Decreases GnRHDecreases GnRH– Pituitary gland stops producing LH and Pituitary gland stops producing LH and

FSHFSH

Follicle releases EggFollicle releases Egg

• Egg bursts out of ovaryEgg bursts out of ovary• Travels down fallopian Travels down fallopian

tubes(oviducts)tubes(oviducts)• Travels into uterusTravels into uterus• May be fertilized anywhere along May be fertilized anywhere along

pathpath• If not fertilized, signals end of If not fertilized, signals end of

menstrual cyclemenstrual cycle

End of Menstrual CycleEnd of Menstrual Cycle

– Egg is not fertilizedEgg is not fertilized– Corpus luteumCorpus luteum degenerates degenerates

• Estrogen decreasesEstrogen decreases

– Lining of uterus begins to break downLining of uterus begins to break down– Menstruation begins as flood filled Menstruation begins as flood filled

uterine tissues break down and flow uterine tissues break down and flow out of the vagina(marking the out of the vagina(marking the beginning of the next cycle)beginning of the next cycle)

– Back to Day One!!!Back to Day One!!!

Fertilized EggFertilized Egg

• Called zygote, Called zygote, embryo, gameteembryo, gamete

• Travel down Travel down fallopian tubes to fallopian tubes to uterusuterus

• Must implant itself Must implant itself onto uterus liningonto uterus lining

• Starts to form a Starts to form a placentaplacenta

PlacentaPlacenta

• Forms from same cells baby doesForms from same cells baby does• Allows mother to give oxygen and Allows mother to give oxygen and

nutrients to babynutrients to baby• Takes waste and carbon dioxide away Takes waste and carbon dioxide away

from babyfrom baby• Filters out infectionFilters out infection• Releases a hormone HCGReleases a hormone HCG

– HCG: human chorionic goandotropinHCG: human chorionic goandotropin– Pregnancy tests test for HCGPregnancy tests test for HCG

Fertilization: When Egg Fertilization: When Egg met Spermmet Sperm

– HCG signals corpus HCG signals corpus leteumleteum

• Release progesterone Release progesterone and estrogenand estrogen

• Uterus lining does not Uterus lining does not break downbreak down

• Prevents another Prevents another menstrual cyclemenstrual cycle

after three months, placenta after three months, placenta stops releasing HCG stops releasing HCG and becomes source of and becomes source of estrogen and estrogen and progesteroneprogesterone

Events after BirthEvents after Birth

– OxytocinOxytocin: released at time of birth: released at time of birth– causes uterine muscles to contract, expel babycauses uterine muscles to contract, expel baby– stimulates milk release and shrinking of uterusstimulates milk release and shrinking of uterus

– Estrogen and progesterone levels dropEstrogen and progesterone levels drop• signal hypothalamus to release GnRH and start signal hypothalamus to release GnRH and start

menstrual cyclemenstrual cycle

Menstruation in other Menstruation in other animalsanimals

– Mostly female primatesMostly female primates– Most mammals don’t menstruate but Most mammals don’t menstruate but

do go into heat”do go into heat”estrus cycles”estrus cycles”

• Dogs go into heat twice a yearDogs go into heat twice a year

• Tells the males that it is time to Tells the males that it is time to reproducereproduce