Human reproduction

• Testes


  Male gonads that produce sex cells (sperm)
• Testes


  • Develop inside body
  • Descend to scrotum a few weeks before birth
  • Kept at slightly lower temperature (35°C) which is ideal for sperm production
• Sperm production


  1. Seminiferous tubules inside testes

  2. Leydig cells between tubules produce testosterone hormone
• Epididymis


  Stores and matures sperm
• Vas deferens


  Carries sperm from epididymis to urethra
• Seminal vesicles, prostate gland, Cowper's gland


  Produce seminal fluid which nourishes and provides motility to sperm
• Semen


  Collective term for seminal fluid and sperm
• Sperm structure


  • Acrosome (contains digestive enzymes)
  • Nucleus (contains chromosomes)
  • Tail (allows sperm to swim)
• Role of meiosis in sperm production


  1. Sperm and egg producing cells undergo meiosis to produce haploid gametes

  2. Fertilisation combines the haploid gametes to form a diploid zygote
• Testosterone


  Male hormone responsible for development of primary and secondary sexual characteristics
• Male secondary sexual characteristics


  • Pubic and facial hair growth
  • Enlargement of larynx ("breaking of voice")
  • Increased muscle and bone development
  • Increased sebum secretion in skin
• Ovary


  Produces eggs and female hormones (estrogen and progesterone)
• Ovary


  • All eggs present at birth
  • After puberty, one egg matures and is released each month, the rest die
• Fallopian tube


  Muscular tube that catches the egg released from the ovary and transports it to the uterus
• Uterus


  • Muscular structure where the embryo implants and develops
  • Lining (endometrium) thickens each month in preparation for implantation
• Vagina


  Elastic muscular canal that allows entry of sperm and exit of the baby during childbirth
• Estrogen and progesterone


  Female hormones that control the menstrual cycle and development of secondary sexual characteristics
• Menstrual cycle


  1. Days 1-5: Shedding of uterine lining (menstruation)

  2. Days 6-14: Uterine lining builds up, ovulation occurs

  3. Days 14-28: Corpus luteum produces progesterone to maintain uterine lining, if no fertilisation occurs lining is shed
• Fertilisation


  Fusion of sperm and egg nuclei to form a diploid zygote
• Implantation


  Embedding of the fertilised egg (zygote) into the uterine lining, 6-9 days after fertilisation
• Placenta formation


  1. Chorionic villi of the embryo develop blood vessels that connect to the mother's blood supply

  2. Allows exchange of nutrients, waste, gases and hormones between mother and embryo
• Zygote


  Contains 46 chromosomes (23 from egg + 23 from sperm)
• Embryo development


  1. Zygote divides rapidly by mitosis to form a morula, then a blastocyst

  2. Inner cell mass of blastocyst forms the embryo, outer layer forms the placenta
• blood vessels of mother in endometrium


  Form the placenta
• Placenta


  • Makes the hormone progesterone
  • Temporary endocrine gland
• umbilical cord


  Connects placenta to embryo, contains blood vessels which circulate blood between embryo and placenta
• Zygote formation


  1. Contains 46 chromosomes (23 from egg + 23 from sperm)

  2. Divides rapidly by mitosis to produce 2 cells, 4 cells, etc.

  3. Develops into a morula

  4. Around 5 days after fertilisation, morula cells form a blastocyst
• Blastocyst


  • Outer layer forms trophoblast, which will later develop into the placenta
  • Inner cell mass will form the embryo
• Stem cells


  Cells from the inner cell mass that have the potential to differentiate into many different cell types
• Blastocyst development

  1. About 10 days after fertilisation, inner cell mass forms the embryonic disc

  2. Embryonic disc consists of 3 layers: ectoderm, mesoderm, endoderm

  3. Mesoderm splits to form the coelom, allowing space for more complex organ development
• Embryo development


  1. 4-5 weeks: heart forms and starts to beat, brain develops, limbs start to form

  2. 6th week: eyes visible, mouth, nose, ears forming, skeleton starts to develop

  3. 8th week: major body organs form, sex glands develop
• Fetus


  Term used to refer to the developing human from 8 weeks after fertilisation until birth
• Pregnancy and birth


  1. Corpus luteum produces hormones for first 3 months, then placenta takes over

  2. Immediately before birth, placenta stops producing progesterone, uterine contractions begin

  3. Stage 1 of labour: contractions push fetus towards cervix, amniotic fluid released

  4. Stage 2: fetus passes through cervix and is born

  5. Stage 3: placenta is expelled
• Breastfeeding


  • Milk production triggered by release of prolactin from pituitary gland
  • Breastmilk provides better nutrition and antibodies for baby compared to formula
• Male infertility


  Low sperm count, poor sperm motility, abnormalities in sperm production or transport
• Female infertility


  Blockage of fallopian tubes, endocrine gland dysfunction
• In vitro fertilisation (IVF)

  1. Stimulate ovaries to produce multiple eggs

  2. Retrieve eggs and fertilise with sperm in lab

  3. Transfer fertilised embryo back into uterus for implantation
• Fibroids


  • Growths in the uterus caused by overproduction of cells
  • Can cause prolonged menstrual bleeding, pain, infertility
• Endometriosis


  • Growth of endometrial cells outside the uterus
  • Causes internal bleeding, inflammation, scarring, infertility