human reproduction

• What is secondary sexual characteristics

  - the characteristics that develop at puberty

  - development by these characteristics is controlled by the production of oestrogen and testosterone
• What is the purpose of development of secondary sexual characteristics

  To prepare the body for reproduction
• testosterone


  - voice drop

  - pubic hair

  - acne

  - growth spurts

  - muscle development
• What route does the sperm take

  - comes from the testes

  - goes through sperm duct

  - passes prostate gland

  - goes through the urethra and out the penis

  - goes into vagina

  - goes through cervix

  - into uterus

  - along the oviduct then into the ovum
• Fertilisation in humans

  - male inserts penis into vagina

  - during ejaculation, semen (containing sperm) is forced out the penis

  - semen is deposited at the top of vagina, near cervix and then swims through the cervix into the uterus, then along the oviduct

  - if ovum is present fertilisation may occur

  - only one sperm can fertilise the ovum
• Oestrogen


  - period

  - development of breasts

  - pubic hair

  - wider hips

  - growth spurts
• Where does fertilisation take place

  Oviduct
• What happens during fertilisation

  - sperm reaches egg

  - releases a chemical that breaks down the outer layer of the egg

  - sperm then attaches itself to the egg cell membrane

  - the sperms nucleus enters and fuses with the egg cell nucleus
• What is the name of a fertilised egg cell

  Zygote
• How many chromosomes does a sperm cell and egg cell contain

  23
• How many chromosomes does a zygote contain

  46
• Haploid


  Contains half the number of chromosomes
• Diploid


  Contains all the number of chromosomes
• How is the sperm adapted for its function

  - contains acrosomes in the head meaning it can penetrate the ovum allowing fertilisation -> head also carries nucleus which carries chromosomes

  - has mitochondria which allows sperm to perform respiration to release energy

  - has a tale to help it swim towards the egg cell membrane
• Why are so many sperm cells deposited in the vagina during ejaculation

  Have a better chance of getting to the egg cells and fertilising it
• The placenta


  - allows constant exchange of substances between the mother and foetus

  - foetus joined to placenta by the umbilical cord which carries 2 arteries and a vein

  - arteries take blood from embryo into placenta

  - vein returns blood to embryo

  - in the wall of uterus is the intervillous space which is filled with the mothers blood

  - allows substances to pass across the thin membrane between mother and foetus
• Substances which pass from mothers blood to embryo blood

  - glucose

  - amino acids

  - oxygen

  - water
• Substances which pass from embryo blood to mother blood

  - carbon dioxide

  - urea
• How is the placenta adapted for the efficient exchange of substances

  - villi in placenta create a large surface which increases the rate of diffusion

  - wall of the placenta and blood vessels are thin walled making diffusion quicker

  - mother and foetal blood vessels are very close to allow constant exchange of substances e.g. oxygen, water (but blood doesn't mix)

  - plentiful blood supply to maintain steep concentration gradient
• Why does the mother blood not mix with the embryos blood

  - so foetus doesn't get damaged

  - so mothers blood pressure won't get too high
• Amniotic fluid


  - protects foetus from damage

  - acts as a shock absorber

  - regulates the temperature in the amniotic sac
• Pregnancy


  - fertilised ovum divided by mitosis

  - during its journey down an oviduct towards the uterus it develops into an embryo (a ball of cells)

  - in the uterus , the embryo embeds in the thicker lining -> called implantation

  - embryo develops into a foetus
• Role of FSH (follicle stimulating hormone) in menstrual cycle (paper 2)

  - produced in pituitary gland

  - triggers development of eggs in the ovary

  - causes egg to mature

  - stimulates ovaries to produce oestrogen
• Role of LH (Luteinising Hormone) in menstrual cycle (paper 2)

  - produced in pituitary gland

  - triggers ovulation ( the release of a mature egg)
• Role of oestrogen in menstrual cycle

  - produced in ovaries

  - inhibits FSH production

  - encourages production of LH

  - causes uterus lining to repair itself and build up again following menstruation
• role of progesterone in menstrual cycle

  - released from empty follicle in ovary

  - maintains uterus lining in anticipation of a fertilised egg

  - inhibits production of FSH and LH
• Diagram of male reproductive system

  - bladder

  - prostate gland

  - penis

  - urethra

  - sperm duct (vas deference)

  - testes

  - scrotum (below testes)

  
• Diagram of female reproductive system

  - oviduct

  - ovary

  - cervix

  - vagina

  - uterus