human reproduction

• Gonad


  Organ that produces sex cells in animals
• Follicle stimulating hormone


  Hormone that stimulates potential eggs to develop with a Graafian follicle, one of which survives
• Luteinising hormone


  Hormone that causes ovulation and the remains of the Graafian follicle to develop into the corpus luteum

  
• Androgens


  Male hormones
• Secondary sexual characteristics


  Features that distinguish males from females apart from the sex organs themselves
• Infertility


  Inability to produce offspring
• Ovulation

  Release of an egg from the ovary

  
• Menopause


  End of menstrual cycle
• Menstruation

  Shedding of the uterine lining
• Progesterone


  Hormone that maintains the structure of the endometrium
• Fibroids


  Benign tumours of the uterus
• Copulation


  Sexual intercourse
• Insemination


  Introduction of sperm into the female reproductive system

  
• Fertilisation


  Union of a sperm and an egg

  
• Implantation


  Attachment of the blastocyst to the uterine wall
• In-vitro fertilisation


  Fertilisation of an egg by a sperm outside the body

  
• Morula


  Early stage of embryonic development after fertilisation
• Blastocyte


  Hollow ball of cells formed during embryonic development
• Germ layers


  Layers of cells that form during embryonic development and give rise to different tissues and organs
• Lactation


  Production of milk
• Three structural levels of organisation

  • Pair of structures to produce sex cells
  • Series of transport tubes
  • Glands to secrete hormones
• Testes


  • Develop inside body
  • Descend into a pouch (scrotum) a few weeks before birth
  • 35°C ensures meiosis and sperm production

  
• Internal structure of testes

  1. Seminiferous tubule

  2. Sperm producing cells (2n)

  3. Sertoli cell – nourishes sperm

  4. Sperm

  5. Blood capillary

  6. Interstitial cells – produce testosterone
• Epididymis


  • Tubules from the testes combine to form the epididymis
  • Sperm mature here
  • Stored for up to 6 weeks
  • If sperm are not released they are broken down and taken back into the bloodstream - resorption
• Sperm duct


  • Epididymis leads to the sperm duct (vas deferens)
  • Vasectomy – operation to cut the sperm duct as a form of male sterilisation
  • Carries sperm to the urethra a tube located in the centre of the penis
  • Dual function

  
• Associated glands


  • Seminal vesicles
  • Prostate gland
  • Cowper's gland
• Seminal fluid


  Fluid added to the sperm to create semen, provides medium for sperm to swim in and provides nourishment as it contains fructose
• Ejaculation


  Release of semen from the penis
• Sperm


  • Produced by meiosis and are haploid – 23 chromosomes
  • First produced in the testes at the onset of sexual maturity called puberty and are formed continually throughout a man's life

  
• Penis


  • Adapted structure to introduce sperm into the female reproductive system
  • The swollen tip – glans
  • A fold of skin (foreskin) covers the glans
  • Circumcision is the removal of this skin
  • During arousal more blood flows into the penis than can flow out of it causing it to become erect

  
• Follicle stimulating hormone (FSH)


  Causes sperm producing cells to divide by meiosis and produce sperm
• Luteinising hormone (LH)


  Stimulates testes to produce testosterone
• Testosterone


  • Androgens are male hormones
  • Causes the primary male sex characteristic early in life i.e. growth of the penis and other reproductive parts
  • Production increases at puberty and leads to the development of the secondary male characteristics
• Secondary sexual characteristics


  • Growth of pubic, underarm, facial and body hair
  • Enlargement of the larynx – deeper voice
  • Increased muscular and bone development
  • Widening of the shoulders
  • Growth spurt
  • Increased secretion of sebum in the skin
• Male infertility


  Inability to produce offspring, main type is production of low numbers of sperm
• Causes of male infertility


  • Persistent smoking
  • Alcohol abuse
  • Use of marijuana or anabolic steroids
  • Low levels of male hormones
  • Mumps
  • Exposure to chemicals
• Corrective measures for male infertility

  • Changes in diet and lifestyle
  • Hormone treatment
  • Artificial fertilisation
• Functions of parts of male reproductive system


  • Testis - Produces sperm and testosterone
  • Epididymis - Matures and stores sperm
  • Sperm duct - Carries sperm from the epididymis to the urethra
  • Seminal vesicles, Cowper's gland and Prostate gland - Produces seminal fluid which feeds the sperm and allows them to swim. Sperm and seminal fluid are collectively called semen.
  • Urethra - Allows the passage of either urine or sperm.
  • Penis - Places sperm inside the body of a female
  • Scrotum - Keeps testes at a lower temperature (35°). This is the optimum temperature for Meiosis to occur.

  
• Ovaries


  • Produce eggs and female hormones
  • Eggs are produced by meiosis
  • Puberty occurs at about 11 or 12
  • Ovaries of a female foetus may contain up to 1 million eggs at birth
  • They have not yet divided and are diploid cells
  • By puberty the number of eggs has fallen to about 40,000
  • Each egg is surrounded by a cluster of cells forming a follicle in the ovary
  • After puberty about 20 eggs are produced each month, one egg will grow and the rest die
  • After meiosis a haploid egg is surrounded by a Graafian follicle – produces oestrogen
  • As the follicle matures it forms a swelling on the ovary and the follicle bursts to release the egg

  
• Inside the Ovary


  1. Potential egg

  2. Developing Graafian follicle – secretes oestrogen

  3. Graafian follicle now changes to the Corpus luteum which secretes progesterone

  4. Egg is released from ovary (ovulation)