Reproduction in Humans

• Hormone


  Chemical messenger secreted by an endocrine gland, secreted into the blood to alter the activity of the target organ
• Adrenaline


  • Increases heart rate
  • Increases breathing rate and depth
  • Increases alertness
  • Causes vasodilation in muscles and vasoconstriction to digestive system
  • Stimulates the breakdown of glycogen in liver into glucose
  • Causes eye pupil to dilate
• Situations in which adrenaline is released

  • Fight
  • Exam due to stress
  • Running from a predator
  • Predator chasing a prey
  • Exercise
• Testes


  Produce sperm cells and testosterone
• Epididymis


  Storage of sperm cells till time of ejaculation
• Scrotum


  Protect the testes from physical damage, keep the testes at cooler temperature than body temperature
• Sperm duct/vas deferens


  Transport the sperm cells from epididymis to the urethra by peristalsis
• Seminal vesicle and prostate gland


  Produce the seminal fluid (provide nutrients for the sperm, medium for the sperm to swim, alkaline pH to neutralize the acidity of the vagina)
• Urethra


  Carry the semen from the sperm duct to tip of the penis, and carry urine out of the body
• Urine and semen never mix as there are rings of muscles that close during sexual intercourse to ensure that there is no chance for semen and urine to get mixed, so they never get out of urethra at the same time
• Ovary


  Produce egg cell (ovum), site of ovulation, produce oestrogen and progesterone
• Oviduct


  Site of fertilisation, lined with cilia to beat and move the zygote or embryo down the oviduct into the uterus
• Uterus


  Site of implantation of the embryo, site of growth and development of the embryo into fetus, uterus muscle contracts at birth time to help push the baby out through vagina
• Cervix


  Muscular rings close during pregnancy to help the fetus stay in place, dilates at birth time and opens to pass the baby out
• Vagina


  Site of copulation and sperm deposition, as well as birth canal

  
• Puberty


  Testosterone released from testes in males, oestrogen released from the ovary in females, responsible for the development of secondary sexual characteristics
• Secondary sexual characteristics in boys

  • Voice deepens
  • Shoulder widens
  • Testes stimulated to start producing sperm cells
  • Facial hair develops
• Secondary sexual characteristics in girls

  • Hips widen
  • Menstruations start
  • Breast develops
  • Ovaries release egg cells
• Common changes in both girls and boys during puberty

  • Hair grown in arm pits
  • Hair grown in pubic regions
  • Growth spurt (sudden fast rate of growth)
  • Body smells increase
• Menstrual cycle


  A cycle that lasts for 28 days involving changes in uterus lining and ovary under the control of 4 hormones: oestrogen, progesterone, FSH, and LH
• FSH


  Produced during early days of menstrual cycle, produced from pituitary gland, targets the ovary, stimulates the development of follicle around an egg to allow maturation of egg, stimulates the release of oestrogen
• Oestrogen


  Repairs the uterus lining, increases thickness of uterus lining to be ready for implantation of embryo, stimulates the release of LH, inhibits/slows down the release of FSH to prevent maturation of another egg
• LH


  Stimulates the ovulation, by stimulating the release of egg from ovary into the oviduct to be ready for fertilisation, changes the remaining follicle into corpus luteum to release progesterone, produced/secreted from pituitary gland
• Progesterone


  Maintains the thickness of uterus lining to be ready for implantation, inhibits the release of FSH (prevent maturation of another egg), inhibits the release of LH (prevent release of another egg), released from corpus luteum in first 3 months of pregnancy, released from placenta in last 6 months of pregnancy
• Fertilisation


  1. Takes place in the first third of oviduct

  2. Sperm releases enzymes that digest and dissolve the jelly coat around the egg

  3. Male and female nuclei (haploid) fuse and form a zygote (diploid)

  4. Zygote divides by mitosis forming a ball of cells called embryo

  5. Embryo moves down the oviduct into the uterus by action of cilia

  6. Embryo implants into the uterus lining