Reproduction

• Reproduction


  One of the seven vital functions of life, the process by which an organism increases the number of individuals in its species
• Reproduction


  Process by which an organism increases the number of individuals in its species
• Categories of reproduction


  • Sexual reproduction
  • Asexual reproduction
• Sexual reproduction


  • Requires more than one individual
  • Involves the fusion of two gametes (sex cells) to produce a zygote (the product of fusion of gametes), which later grows and develops into a new organism
• Asexual reproduction


  • Usually involves an organism reproducing on its own, without the help of other individuals
  • The nucleus divides by mitosis to produce 2 daughter cells, which would have the same genetic material as the parent
  • Different forms include binary fission (the nucleus divides in 2, the cytoplasm divides into 2 equal parts and the cell splits in 2)
• Sexual Reproduction


  Two individuals (can be either male or female, or hermaphrodite, meaning they have both male and female reproductive organs) must be present for sexual reproduction to occur
• External fertilisation

  Gametes (the sperm and eggs) are released to the outside, where the sperm fertilises the eggs
• Internal fertilisation


  The male and female come together and copulate, the sperm fertilises the egg/s inside the female
• Reproduction in Mammals


  • Mammals have sexes that are separate in male and female individuals (dioecious)
  • The embryo can develop in various ways: in egg-laying mammals, marsupials, or placental mammals
  • All young mammals feed on milk produced by the mammary glands
• Egg-laying mammals


  The embryo develops in a soft shelled egg
• Marsupials


  The immature offspring are produced and continue to develop in a marsupium (the pouch)
• Placental mammals


  The embryo develops inside the mother, specifically in the uterus, and it is protected and nourished by embryonic membrane and a placenta. Such placental embryos are called viviparous (meaning they can hear, see, smell and feel)
• Puberty


  Production of gametes is brought about by puberty in both males and females
• Puberty in males


  1. Starts at about 11 - 13 years of age

  2. Hormonal changes stimulate an increase in growth rate, alterations in behaviour, enlargement of genitals, and the appearance of secondary sexual characteristics

  3. Boys usually start their final growth spurt later than girls, they have a longer period of steady growth, and usually attain a greater adult height
• Puberty in females


  1. Starts usually at the age of around 10-11 years of age

  2. Their growth spurt starts earlier than that of boys, and girls usually would have attained their adult height by the age of 16

  3. Menstruation does not begin until towards the end of the growth period, when the girl has reached an optimum body weight

  4. Ovulation occurs when a regular menstrual cycle is obtained
• Follicle stimulating hormone


  Hormone released by pituitary gland that prompts testes to increase testosterone secretion
• Luteinizing hormone

  Hormone released by pituitary gland that prompts testes to increase testosterone secretion
• Testosterone production in testes

  1. Pituitary gland releases FSH and LH

  2. Testes increase testosterone secretion

  3. Activates sperm producing cells to start producing sperm
• Testosterone


  • Levels rise rapidly at puberty
  • Stimulates production of sperm
  • Causes development of male secondary sexual characteristics
• Spermatozoon

  Male gamete, also called sperm
• Testes

  • Glands where sperm are produced
  • Located outside body in scrotum
  • Temperature must be slightly lower than body temperature for sperm production
• Spermatogenesis

  Process by which spermatozoa are produced
• Seminiferous tubules

  • Sperm producing tubules in testes
  • Cells in walls continuously divide and differentiate into spermatozoa by meiosis
• Epididymis

  • Highly coiled tube where sperm are temporarily stored after production
  • Connects to seminiferous tubules and leads to sperm duct
• Sperm duct


  • Muscular tube that carries sperm from epididymis to urethra
• Seminal vesicles and prostate gland

  • Glands that secrete semen and other substances to activate sperm
• Ejaculation

  1. Contraction of epididymis and sperm ducts forces sperm out into urethra

  2. Semen added by glands

  3. Ejected out of penis
• Ovary

  Female sex gland that produces ova
• Ovaries

  • Oval shaped, around 3-4cm long
  • Located in lower abdomen on each side of uterus
• Ovum

  Female gamete
• Each ovary in a newborn female contains 500,000 to 1 million ova, of which only around 400 will be released during reproductive life
• Ovulation

  1. One ovum produced and released from ovary every 28 days or so

  2. Passes into Fallopian tube
• Fallopian tube

  • Narrow tube that opens into uterus
  • Expanded funnel-shaped opening receives ovum from ovary
• Uterus

  • Cavity where embryo develops
  • About 80mm in length when no embryo
  • Has muscular cervix at lower end that produces mucus to facilitate sperm movement
• Vagina

  • Muscular tube leading from uterus to outside
  • Separate opening from urethra
• Hormones in girls


  Estrogen and progesterone are essential to sexual development and fertility
• Estrogen production


  1. Egg develops inside follicle

  2. Mature egg is released

  3. Empty follicle forms corpus luteum

  4. Corpus luteum secretes progesterone
• Egg development


  1. Egg starts developing in ovary

  2. Egg develops within follicle

  3. Follicle matures into Graafian follicle

  4. Graafian follicle projects from ovary

  5. Follicle bursts and releases ovum
• Corpus luteum


  Important for secretion of progesterone
• Ovum


  • Enclosed in zona pellucida
  • Surrounded by follicle cells