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The Reproductive System Types of Reproduction: asexual and sexual Asexual:• CloneAdvantage: FAST, if env. is stableFission: parent separates into 2+ individuals of same sizeBudding: outgrowths from parent (eg. cnidarians, tunicates)Fragmentation: breaking of body into pieces, form into adults by regeneration (eg. sea stars, sponges, cnidarians)Parthenogenesis: female produces eggs that develop w/o fertilization (eg. male bees – haploid) Sexual:• Genetic diversityAdvantage: ability to change pop. when env. changes• Fusion of haploid gametesEgg (Ovum) + Sperm à Zygote Reproductive cycles and patternsOvulation: release of mature eggs– Young produced when survival is most likely– Hormonal changes influenced by day length, season temp, rainfall or lunar cyclesHermaphroditism: both M/F systems– Sessile/burrowing animals - barnacles, parasites (tapeworms), earthwormsSex reversal: sex change during its lifetime– Bluehead wrasse (reef fish) Fertilization = sperm + egg External fertilization:• Egg shed by female, fert. by male in water• Environmental cues / courtship behavior• Large # gametes à low survival• Eg. fish, amphibians Internal Fertilization:• Sperm deposited in female reprod. tract• Cooperative behavior• Dry environment• Fewer gametes, fewer zygotes à greater survival External Development: Tough eggshell, Eg. reptiles, birds, platypus Internal Development: High parental care, Eg. placentals, sharks, some reptiles Evolution of sexual reproduction:(least complex)• No gonads• Egg/sperm develop in undifferentiated cells• Released into coelom, shed into env.(most complex)• Distinct gonads (organs that produce gametes)• Delivery systems Human Reproductive System:
Female Anatomy:
• Ovaries – produce eggs, sex hormones
• Follicles – contain oocyte (egg); release 1/month; produce estrogens
• Ovulation – release of egg from follicle
– Remaining follicle à corpus luteum (↑hormones)
• egg à oviduct (fallopian tube) à uterus (baby) à cervix à vagina
• Mammary glands – secrete milk through nipples in breast
Male Anatomy:
• Testes (inside scrotum) – produce sperm, sex hormones
• Seminiferous tubules – make sperm
• seminiferous tubules à epididymis à vas deferens à urethra (penis)
• semen = alkaline fluid w/nutrients, enzymes
• 100-650 million sperm/ejaculation
Meiosis
Spermatogenesis
• Sperm production
• Stem cells à spermatids in seminiferous tubules
• Mature & add tail in epidymis
• 4 motile sperm
Oogenesis
• Ova production
• Before birth: oogonia à meiosis - STOP at Prophase I (primary oocytes)
• Puberty: each month, egg in follicle à Meiosis I (secondary oocytes) à fertilization à Meiosis II
• 1 ovum + 3 polar bodies
Menstrual cycle – humans & other primates
• Prepare and release egg for fertilization
• Prepare uterus to receive a fertilized egg
Estrous cycle – other mammals; no menstruation
Four Phases of Menstrual Cycle:
- Follicular Phase : low estrogen, FSH = egg develops in ovary
- Ovulation (Day 14): LH = egg released into Fallopian tube
- Luteal Phase :
• progesterone, estrogen = lining of uterus thickens to prepare for pregnancy
• Egg travels down Fallopian tube, waits for fertilization
- Menstruation (no fertilization) :
• ¯P/¯E = lining of uterus breaks down
• Blood and unfertilized egg discharged
Human embryonic development:
• Conception: in oviduct
• Implantation: in uterus
• Hormones:
– Human Chorionic Gonadotropin (hCG): maintain estrogens in early pregnancy; pregnancy test
• Human gestation (pregnancy) = 40 weeks
– Rodents (21 days); Dogs (60 days); Cows (270 days); Elephants (600 days)
• Egg lodged in oviduct = ectopic (tubal) pregnancy
Formation of zygote:
1. Ovulation from ovary
2. Fertilization occurs in the fallopian tube
3. cleavage starts in the fallopian tube
4. cleavage continues in transit
5. the blastocyst implants in the endometrium in the uterus
Circulation to the developing embryo via the placenta and umbilical cord
Labor proceeds via a positive feedback loop: stimulus increases response
Three stages of labor:
1. dialation of cervix
2. expultion: delivery of the infant
3. delivery of the placenta
How does “the Pill” work?
• “the Pill” is an oral contraceptive
• Contains estrogen and progesterone
• First available in 1960
• Main effect: Prevent ovulation
• Other effects:
– Thickens cervical mucus – slows down sperm
– Thins uterus lining – prevent implantation of fertilized egg
• Usage: active pill for 21 days, inactive pills for 7 days (“period”)
• Other medical uses:
– Medication for mild/moderate acne
– Decrease painful menstruation
– Treat polycystic ovary syndrome (PCOS)
– Correct irregular menstrual cycle
– Reduce risk of ovarian and endometrial cancers
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