Ch 46: Animal Reproduction (Abridged)

• Methods of reproduction

asexual & sexual

• Asexual

fission, budding, fragmentation, parthenogenesis

• Sexual

hermaphroditism, two sexes

• Fertilization

egg + sperm in sexual reproduction

• External fertilization

aquatic environment with egg+sperm released into water

• Internal fertilization

terrestrial

• Oviparous

egg hatch outside

• Ovoviviparous

eggs are retained, young hatch in the uterus

• Viviparous

embryo develops within the uterus nourished through a yolk sac placenta

• Male reproductive anatomy

• Testes: male gonads, produce sperm in highly coiled tubes (seminiferous tubules)

• Path of semen: Testis → epididymis → vas deferens → ejaculatory duct → urethra

• Semen: sperm + accessory glands secretions

  • Seminal vesicles: 60% of total volume

  • Prostate gland: secretes directly into urethra

  • Bulbourethral glands: secretion neutralizes acidic urine

• Penis: 3 cylinders of spongy erectile tissue

• Glans: surrounded by prepuce/foreskin

• Female reproductive anatomy

• Ovaries: female gonads, outer later of each ovary is packed with follicles, each consisting of an oocyte (partially developed egg)

• Oviduct/fallopian tube: upon ovulation, cilia on the epithelial lining of the oviduct begin beating, brings the egg down the duct to the uterus

• Uterus: thick muscular organ that expands during pregnancy

  • Endometrium: inner lining of the uterus, richly supplied with blood vessels

  • Cervix: neck of the uterus that opens to the vagina

• Vagina: muscular but elastic chamber that is the site for insertion of the penis and deposition of sperm during copulation, also birth canal

• Vulva: collective term for the external female genitalia

  • Labia majora, labia minora, clitoris

• Mammary glands: small sacs of epithelial tissues secrete milk within the glands, which drains into a series of ducts that open at the nipple

• Gametogenesis

gametes production

• Spermatogenesis

sperm production, continuous and prolific

• Oogenesis

mature egg development, prolonged process

• Hormones

• Sex hormones → gamete production, sexual behavior, sexual dimorphism characteristics

• Gonadotropin-releasing hormones (GnRH): hypothalamus → release FSH & LH from anterior pituitary

  • Follicle-stimulating hormones (FSH)

  • Luteinizing hormone (LH)

• Estrogen = estradiol & progesterone

• Hormonal control of testes

• FSH → Sertoli cells to nourish developing sperm

• LH → Leydig cells → testosterone & androgens

• Hormonal control of the ovaries

• Ovarian cycle: changes in the ovaries

• Follicular phase (days 1-13): LH & FSH stimulate follicle growth

• Ovulation (day 14): LH surge

• Luteal phase (days 15-28): corpus luteum secretes progesterone and estrogen

• Hormonal control of the uterus

• Uterine/menstrual cycle: changes in the uterus

• Menstrual flow phase (days 1-5): low progesterone causes menstrual flow

• Proliferative phase (days 5-14): estrogen increases with follicle growth

• Secretory phase (days 15-28): estrogen and progesterone stimulate thickening of the endometrium

• Menopause

cessation of ovulation and menstruation

• Pregnancy

three trimesters + labor

• First trimester

human chorionic gonadotropin (hCG) maintains progesterone and estrogens during early pregnancy

• Monozygotic twins

splitting of embryo during first month of development

• (genetically identical)

• Dizygotic twins

release and fertilization of two eggs

• (fraternal and genetically distinct)

• Second trimester

placenta takes over production of progesterone (hormone that maintains pregnancy)

• Third trimester

continual growth, fills space within embryonic membranes

• Labor

• Estradiol from ovaries activates oxytocin receptors in uterus

• Oxytocin → positive feedback loop

  • Oxytocin from fetus and mother’s posterior pituitary

  • Stimulates uterus to contract

  • Stimulates placenta to make prostaglandins → more uterus contractions

• Contraception

• prevention of pregnancy

  • Preventing gametes release, Gametes separation, Prevent embryo implantation

• Abortion

termination of pregnancy

• Infertility

inability to conceive a child or bring it to birth

• In vitro fertilization (IVF)

mixes egg & sperm in culture dish and returns the embryo to uterus at 8-cell stage

• Intracytoplasmic sperm injections (ICSI)

sperm directly injected into oocyte