ANIMAL REPRODUCTION Ch – Bio 391

Animals Reproduce sexually –Gonads Produce gametes Ovaries  ovum Testes  sperm –Many simple animals (hydra, sponges) make both eggs & sperm but do NOT self-fertilize

Fertilization External Fertilization –Simple, aquatic animals –Gametes released into water –No guarantee of fertilization –No protection for zygote Internal Fertilization –Male ejaculates sperm into female –Fertilization inside female body –Gametes protected –Increased likelihood of fertilization Requires fewer gametes –Zygote protected inside female

Although internal fertilization uses less eggs, still lots of sperm required –Ensures fertilization –Sperm don’t live long –Must swim long distance & few make it –Enzymes within sperm head required to weaken egg’s membrane allowing one sperm to penetrate

Mating Rituals For fertilization to occur, sperm & egg must be released at about the same time –Mating rituals can… Signal the right time for fertilization Bring the gametes into close proximity Frogs: –Male sits on female, and grabs on –Triggers female to release eggs into water –Male follows with sperm release over eggs

Egg vs. Sperm Egg –Large –Immobile –Nutrient storehouse –Can survive longer Sperm –Mobile –Smaller –Nucleus, flagella, mitochondria –No stored food  cannot survive long

Mammalian Reproduction Have hair and produce milk Internal Fertilization Developmental location varies

3 Groups of Mammals MAMMALS MONOTREMES: egg-laying MARSUPIALS: Young are born at a very immature stage & complete development in a pouch of the mother’s body PLACENTAL: Placenta = organ through which nutrients, O2, CO2 & wastes are exchanged between the mother & the embryo. Forms during development of embryo.

Female Anatomy

Menstrual Cycle ~ 28 days Endometrium –Uterine lining –Thickens with blood vessels in prep for fertilized egg –If no egg, disintegrates and released “menstrual flow” Controlled by nervous system, glands, organs, hormones –Hypothalamus controls hormone levels, like a thermostat

Hormones and the Endocrine System GnRH, estrogen, progesterone, FSH, LH, oxytocin; testosterone

Menstrual Cycle Low estrogen & progesterone cause hypothalamus to secrete GnRH –Stimulates pituitary to release FSH  causes egg to mature in ovary LH  causes follicle to 14 days –FSH & LH stimulate maturing follicle to increase estrogen release

Menstrual Cycle Estrogen triggers uterine lining to thicken 14 days – LH triggers ovulation Ruptured follicle now = corpus luteum –Continues to release more estrogen & progesterone  continues to thicken uterine lining Hypothalamus slows down FSH & LH release

Menstrual Cycle If egg NOT fertilized… –Corpus luteum disintegrates –Decrease in estrogen & progesterone –Uterine lining breaks down –Menstrual flow

Oogenesis (meiosis I) begin at birth & proceed in discontinuous stages The second meiotic division occurs only after fertilization by sperm; gametogenesis in the female is dependent on fertilization for completion.

If egg IS fertilized… –Mitosis forms an embryo –Implantation –Placenta forms –Placenta releases HCG ( human chorionic gonadotropin) Signals corpus luteum to continue releasing high levels of estrogen & progesterone for uterine lining support –Corpus luteum lasts 3 months –Then placenta = source of estrogen & progesterone

Development & Birth Gestation –Development of embryo in uterus –“pregnancy” Birth –Oxytocin released  causes uterus to contract Also stimulates milk production & release Stimulates placenta to release prostaglandins that further trigger contractions –Baby born –Placenta released

A side note… Menstruation  female primates Estrus  most other mammals –“in heat” Number of times per year and the timing of the cycles vary by organism

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Male Reproductive System Ejaculation –What is it and why? –What happens to sperm that aren’t released? Male Hormones –Androgens Testosterone –GnRH from hypothalamus stimulates pituitary to release FSH and LH LH causes release of androgens FSH stimulates sperm production

Secondary Sex Characteristics Estrogen & Androgen Begin at puberty  the beginning of sexual maturation –Females – starts with first menstrual period Approx. ages in North America (what about in Africa?) –Males – approx. age 12 in North America Females –Breasts, fat deposits, bone structure Males –Voice changes, body hair

Infertility & Contraception Infertility –Males  weak sperm, low count, etc. –Females  blocked oviducts, irregular cycle, etc. –In-vitro fertilization, fertility drugs Contraception –Physical barriers  condoms, diaphragms, cervical cap –Chemical  prevent ovulation or implantation Hormone based “The pill”, injections, Norplant –Foams/Jellies/Sponges – in vagina before sex to immobilize or kill sperm –Surgery –Abstinence