Sexual Reproduction Life wants to create more life at any expense, short of losing its own life.

The egg: the female story Ovaries:Ovaries: –meiosis produce ova(eggs) Meiosis does not equally divide cytoplasm between daughter cellsMeiosis does not equally divide cytoplasm between daughter cells Most of it remains in one cell, called the ovum(the egg)primary oocyteMost of it remains in one cell, called the ovum(the egg)primary oocyte The small cells called polar bodies break down and disintegrateThe small cells called polar bodies break down and disintegrate

The female story Humans produce one egg per cycleHumans produce one egg per cycle The egg travels down oviducts “aka. Fallopian tubes,The egg travels down oviducts “aka. Fallopian tubes, Woman have two of these tubular structuresWoman have two of these tubular structures Connect ovaries to uterusConnect ovaries to uterus

The female story Uterus: a pear shaped organ, very muscularUterus: a pear shaped organ, very muscular –Where embryo will be developing –During labor, muscle contractions push the baby out through the vagina Vagina: muscular passagewayVagina: muscular passageway –Sperm must travel through –Menstrual fluid exits this way

The Menstrual Cycle The menstrual cycle :The menstrual cycle : –Lasts 28 days although this may vary –The first day of menstrual cycle is marked by beginning of menstrual flow –Several factors regulate the cycle Nervous system, several glands, organs, hormonesNervous system, several glands, organs, hormones Hypothalamus: gland in the brainHypothalamus: gland in the brain –adjust levels of hormones in circulatory system

Day 1: Start of Menstrual Cycle Day One:Day One: –Low levels of estrogen and progesterone HypothalamusHypothalamus –Senses low levels of estrogen and progesterone –Releases GnRH “ gonadotropin-releasing hormone”“ gonadotropin-releasing hormone” Travels to pituitary glandTravels to pituitary gland

Pituitary GlandPituitary Gland –Just below hypothalamus –Release FSH and LH 1. FSH: follicle stimulating hormone1. FSH: follicle stimulating hormone 2. LH: leutenizing hormone2. LH: leutenizing hormone -travel to ovary OvaryOvary

Around day 10? Ovaries:Ovaries: –High levels of FSH and LH –Stimulate egg maturing inside follicle A fluid filled sac in ovaryA fluid filled sac in ovary

Day 14: Halfway through cycle –Sudden increase of LH causes follicle to burst release egg “ovulation”release egg “ovulation” –Follicle that rupture is called corpus luteum Continues releasing estrogen and progesteroneContinues releasing estrogen and progesterone Stimulate buildup of uterine liningStimulate buildup of uterine lining

Halfway Through the Cycle Uterine lining is thickeningUterine lining is thickening High levels of estrogen and progesteroneHigh levels of estrogen and progesterone Hypothalamus sees high levelsHypothalamus sees high levels –Decreases GnRH –Pituitary gland stops producing LH and FSH

Follicle releases Egg Egg bursts out of ovaryEgg bursts out of ovary Travels down fallopian tubes(oviducts)Travels down fallopian tubes(oviducts) Travels into uterusTravels into uterus May be fertilized anywhere along pathMay be fertilized anywhere along path If not fertilized, signals end of menstrual cycleIf not fertilized, signals end of menstrual cycle

End of Menstrual Cycle –Egg is not fertilized –Corpus luteum degenerates Estrogen decreasesEstrogen decreases –Lining of uterus begins to break down –Menstruation begins as flood filled uterine tissues break down and flow out of the vagina(marking the beginning of the next cycle) –Back to Day One!!!

Fertilized Egg Called zygote, embryo, gameteCalled zygote, embryo, gamete Travel down fallopian tubes to uterusTravel down fallopian tubes to uterus Must implant itself onto uterus liningMust implant itself onto uterus lining Starts to form a placentaStarts to form a placenta

Placenta Forms from same cells baby doesForms from same cells baby does Allows mother to give oxygen and nutrients to babyAllows mother to give oxygen and nutrients to baby Takes waste and carbon dioxide away from babyTakes waste and carbon dioxide away from baby Filters out infectionFilters out infection Releases a hormone HCGReleases a hormone HCG –HCG: human chorionic goandotropin –Pregnancy tests test for HCG

Fertilization: When Egg met Sperm –HCG signals corpus leteum Release progesterone and estrogenRelease progesterone and estrogen Uterus lining does not break downUterus lining does not break down Prevents another menstrual cyclePrevents another menstrual cycle after three months, placenta stops releasing HCG and becomes source of estrogen and progesterone

Events after Birth –Oxytocin: released at time of birth –causes uterine muscles to contract, expel baby –stimulates milk release and shrinking of uterus –Estrogen and progesterone levels drop signal hypothalamus to release GnRH and start menstrual cyclesignal hypothalamus to release GnRH and start menstrual cycle

Menstruation in other animals –Mostly female primates –Most mammals don’t menstruate but do go into heat”estrus cycles” Dogs go into heat twice a yearDogs go into heat twice a year Tells the males that it is time to reproduceTells the males that it is time to reproduce