Human reproduction

• Testis:

  • Produces sperm, testosterone
  • Responsible for development and maintenance of secondary sexual characteristics
• What happens during menstruation?

  Uterine lining + unfertilised egg break down → shed with some blood
• What happens after menstruation?

  1. Ovary produces oestrogen → cause uterine lining to repair and thicken
  2. High oestrogen concentration → ovulation
• What happens during ovulation?

  At around the 14th day: ovary releases 1 egg into fallopian tube
• What happens after ovulation?

  1. Ovary produces progesterone 
  2. Prevents ovulation and further development of eggs
  3. Causes uterine lining to thicken further, preparing for implantation and growth of embryo
  4. Oestrogen production decreases
  5. No fertilisation → progesterone production decreases
  6. Uterine lining breaks down, whole cycle repeats
• When no fertilisation occurs, the egg breaks down, blood progesterone decreases. On the 28th day, the uterine lining begins to break down, causing menstruation to begin. Whole cycle repeats
• When Fertilisation occurs:

  • Fertilised egg become zygote → turns into embryo
  • Ovary secretes progesterone and oestrogen → maintenance and thickening of uterine lining for implantation of the embryo
  • Embryo embeds itself in uterine lining until placenta is formed
  • Ovary continues to secrete progesterone and oestrogen until placenta is able to take over production of hormones
• Scrotum:

  • Contains testes
  • Outside main body cavity →  keep sperm-forming cells ~2 deg cooler to function normally
  • Special muscles in wall → contract and relax → move testicles closer to body for warmth and protection/ farther away to cool temp
• Sperm duct: Delivers sperm to urethra during ejaculation
• Prostate gland: Secretes fluid which nourishes sperm and provides protection from the natural acidity of vagina
• Male urethra:

  • Connects bladder to outside of the body
  • Semen and urine pass through
  • During sex, flow of urine blocked → only semen can be ejaculated
• Penis: deposits sperm in vagina
• What are the parts of sperm?

  Head

  • Contains large nucleus with small amt of cytoplasm
  • Carries haploid set of chromosomes

  Middle piece

  • Contains numerous mitochondria 
  • provide energy for sperm to swim towards egg

  Tail

  • Beating movement enables sperm to swim towards egg
• What is the route of sperm travel?

  Testis → sperm duct → urethra → vagina
• What are the functions of the female reproductive system?

  • Produce ova
  • Transport ova to fallopian tubes
  • Safe and favourable environment for foetal dvlpmt (uterus)
  • Produce female sex hormones to maintain cycle
• Ovary:

  • Produce ova
  • Corpus luteum produces oestrogen and progesterone →  development and maintenance of the secondary sexual characteristics in females.
  • When the eggs become mature, they are released from the ovaries
• Fallopian tube:

  • Site of fertilisation
  • Egg fertilised in the oviduct (about ⅓ away from the ovary)
  • Inner surface of the oviduct is lined with cilia → movement helps to move the egg along the oviduct.
• Uterus:

  • Site of pregnancy
  • elastic muscular walls lined with endometrium
  • smooth muscle tissue in the walls of the uterus contract to push the fetus out during birth.
• Cervix: Opening allows flow of menstrual blood into vagina, directs sperm into uterus
• Vagina: Where semen is deposited during sexual intercourse
• What are the differences between male and female gametes?

  Male gametes have a head, middle piece and tail while female gametes are spherical in shape.

  Male gametes contain either X or Y chromosomes while female gametes contain only X chromosome.

  Sperms are motile while eggs are not motile.

  A large number of sperm is released during ejaculation while only 1 egg is released during ovulation.
• How do hormone levels change during menstrual cycle?

  • Anterior pituitary gland releases FSH → stimulates growth of follicles in ovary
  • Developing follicles secrete oestrogen
  • Peak levels of oestrogen occurs about midpoint of cycle. High and sudden peak stimulates secretion of LH
  • Surge in LH stimulates ovulation
  • LH stimulates conversion of remaining follicle tissue to corpus luteum 
  • Corpus luteum secretes progesterone + some oestrogen
  • Falling levels of LH and FSH causes corpus luteum to degenerate.