LESSON 2

• Sexual Reproduction


  Involves fertilization of an egg (n, haploid) by a sperm (n, haploid) which produces a zygote (2n, diploid)

  
• Egg


  • Large cell compared to small and motile sperm

  
• Hermaphroditism


  Having both sex organs, so every individual is a possible mate
• Hydra can switch from asexual to sexual reproduction
• External Fertilization


  Used by aquatic animals such as fishes and amphibians, where both male and female release their gametes in the environment
• Internal Fertilization


  Used by terrestrial organisms, where the sperm should be near the egg inside the female reproductive tract for fertilization to take place

  
• Similarities in Female and Male Reproductive systems

  • Gonads for gamete production
  • Ducts for gamete delivery and stockpiling
  • Structures for copulation

  
• Ovary


  Female gonad where egg cells are produced
• Egg cells


  • Develop surrounded by follicle cells which nourish them
  • Estrogen are also produced by the follicles
• Females are born with finite number of follicle cells (approx. 1-2 million), only 500 of which are released during a female's reproductive years
• Ovulation


  Monthly release of one egg, starts at puberty and ends at menopause
• Egg cell movement


  1. From ovary towards oviduct/fallopian tube

  2. Swept from ovary by cilia at finger-like projections of oviduct

  
• Fertilization


  Can occur in the oviduct if sperm cells are present

  
• Zygote movement


  From oviduct towards uterus where pregnancy normally occurs
• Embryo and Fetus development


  Zygote divides and develops into an embryo until 9th week, then into a fetus
• Uterus


  • Endometrium lining is rich with blood vessels that pass nutrients to and wastes from the embryo to the mother
• Cervix


  Neck of the uterus found at its base
• Vagina


  Thin but composed of strong muscles, receives the sperm during copulation and functions as the canal where the fetus is delivered during birth
• Vulva


  All parts of the female external genitalia
• Labia minora


  Pair of thin skin folds which cover both the opening of the vagina and urethra
• Labia majora


  Pair of thick skin ridges that protect the genitalia
• Hymen


  Thin tissue that partially covers the vaginal opening but is easily torn by rigorous activities other than sexual intercourse
• Clitoris


  Highly sensitive small shaft with a head or glans and covered by a hood, the prepuce
• Testes


  Male gonads which produce the sperm
• Sperm movement


  1. From testes to epididymis where they further develop and are stored

  2. Then move to the vas deferens through muscular contractions

  3. Vas deferens circles the urinary bladder then joins with the duct of seminal vesicle to form the ejaculatory duct which empties into the urethra

  
• Penis


  Has structures similar to those in clitoris, such as glans (head), shaft (body), and prepuce (foreskin)
• Semen


  Made up of sperms secreted by three glands: seminal vesicle, prostate, and bulbourethral gland
• Ejaculation


  Release of the semen, occurs during male orgasm
• Gametogenesis


  Sperm and egg are produced through meiosis

  
• Spermatogenesis


  • Sperm production is prolific, continuous, starts during male puberty, and goes on until old age
  • For every one diploid parent cell, four haploid cells are produced

  
• Oogenesis


  • Egg cell production starts at birth, continues at puberty, and commonly waits for sperm to fertilize it
  • Only one haploid egg cell is produced from every one diploid parent cell

  
• Menopause


  End of oogenesis in females
• Ovarian cycle


  Cyclical production of an egg cell in the ovary, usually recurs every 28 days
• Menstrual cycle


  Events in the uterus that simultaneously happen with the ovarian cycle
• Female Reproductive Hormones


  • Gonadotropin-releasing hormone (GnRH) - Hypothalamus
  • Prolactin - Anterior Pituitary
  • Oxytocin - Posterior Pituitary
  • Androgens - Adrenal Gland
  • Human Chorionic Gonadotropin (hCG) - Embryo
• Fertilization


  The meeting of the sperm and egg where both gametes contribute haploid sets of chromosomes to form the diploid zygote

  
• Fertilization process


  Sperm has to penetrate the egg's covering and be recognized by receptors on its surface

  
• Embryonic Development


  1. Cleavage

  2. Blastula

  3. Gastrula (forms digestive tract, nervous system, and outer layer of skin)

  4. Mesoderm (forms other organs)

  
• Organogenesis


  1. Starts immediately after the germ layers are formed, each group of cells begins developing into embryonic organs

  2. Induction (cells influence behavior of other cells to develop into specific tissues)

  3. Cell migration (helps form differentiated tissues)

  4. Apoptosis (cells in between fingers are killed during hand development)
• Monozygotic twins


  One fertilized egg (ovum) splits and develops into two babies with exactly the same genetic information