Human Reproduction

• Human reproductive system

  Organised as: Male and female paired structures that produce gametes, a series of tubes, and glandular structures that secrete hormones
• Life cycle of humans

  Consists of male and female reproductive systems
• Testes


  • Gonads that produce sex cells, two testes, develop inside body then descend into scrotum, kept at slightly lower than body temperature for sperm production, produce sperm by meiosis, also produce testosterone
• Epididymis

  Tubular structure on outside of testis where immature sperm mature and are stored

  
• Sperm duct and urethra

  Epididymis leads to sperm duct (vas deferens) which brings sperm to urethra, urethra carries sperm and urine out of body
• Associated glands

  • Seminal vesicles, prostate gland and Cowper's gland produce seminal fluid that nourishes and provides medium for sperm, semen is seminal fluid + sperm, ejaculation is release of semen from penis
• Penis


  • Urethra carries sperm (and urine) through penis, made of erectile tissue that becomes erect when aroused, inserted into female body during intercourse to deposit sperm around cervix
• Sperm structure

  Head contains haploid nucleus and acrosome, midpiece contains mitochondria for energy, tail allows for movement

  
• Male reproductive hormones

  • FSH causes sperm production, LH causes testosterone production, testosterone responsible for primary and secondary sexual characteristics
• Male secondary sexual characteristics

  • Growth of pubic, underarm, facial and body hair, enlargement of larynx causing voice to break and deepen, increased muscular and bone development, growth spurt at puberty, increased secretion of sebum
• Ovaries

  • Pair of organs in abdominal cavity above uterus, one ovary releases an egg every 28 days, produce eggs by meiosis, produce hormones oestrogen and progesterone
• Fallopian tubes


  • Muscular tubes approximately 12cm long, funnels at tip catch egg after release, lined with cilia to move egg towards uterus, site of fertilisation
• Uterus

  • Muscular structure approximately fist-sized, inner lining is endometrium which thickens each month, site of implantation and holds developing embryo, endometrium forms part of placenta, cervix is neck of womb
• Vagina

  • Muscular tube approximately 10cm long, penis inserted during intercourse, birth canal for baby, lined with cells producing acidic mucous to prevent pathogens
• Vulva

  • Outer lips of vagina, labia majora are outer lips, labia minora are inner lips, clitoris structure fully discovered in 2005
• Functions of female reproductive structures

  • Ovary: produce egg, produce oestrogen and progesterone
  • Fallopian tube: catch egg, transport egg, site of fertilisation
  • Uterus: site of implantation, hold developing embryo, form placenta
  • Vagina: allow entry of sperm, exit of baby
• Female hormones

  • Oestrogen, progesterone, FSH, LH
• Female secondary sexual characteristics

  • Maturing and enlargement of breasts, widening of pelvis, increased body fat, growth of pubic and underarm hair, growth spurt
• Ovaries

  • Produce oestrogen and progesterone, produce egg cells, female foetus has all potential eggs at birth, after puberty eggs produced by meiosis monthly with only one usually continuing to grow
• Ovulation

  Graafian follicle produces oestrogen, when mature it bursts to release egg, follicle then becomes corpus luteum which secretes progesterone
• Hormones involved in female reproduction

  • Oestrogen, progesterone, FSH, LH
• Differences between egg and sperm

  Egg is spherical, non-motile, larger, XX chromosomes, contributes cytoplasm and mitochondria

  Sperm is motile, smaller, XY chromosomes
• Menstrual cycle

  28 day sequence of events producing an egg and preparing the uterus, begins at puberty and ends at menopause, if egg not fertilised the endometrium is shed (menstruation)
• Fertile period


  Time when fertilisation is most likely, egg can survive 2 days, sperm can survive 7 days
• Hormones involved in menstrual cycle

  FSH, oestrogen, LH, progesterone - each causes production of next hormone and inhibits previous one
• Follicle Stimulating Hormone (FSH)


  • Produced by pituitary gland early in cycle, stimulates development of graafian follicles containing potential eggs
• Oestrogen

  • Produced by graafian follicle, causes endometrium development, inhibits FSH to prevent further egg development
• Luteinising Hormone (LH)


  • Produced by pituitary gland, causes ovulation and development of corpus luteum
• Progesterone


  • Produced by corpus luteum, maintains endometrium, inhibits FSH and LH to prevent further ovulation
• Fibroids

  Benign growths in uterus wall, can cause bleeding, prolonged periods, abdominal pain, miscarriage, infertility
• Cause of fibroids

  Uncertain, some uterine cells have abnormal response to oestrogen
• Treatment for fibroids

  Small ones monitored, large ones surgically removed, hysterectomy if many large ones present
• Stages of copulation

  Sexual arousal, penis erect, vagina lubricated, penis inserted and moved in vagina, orgasm and ejaculation, contractions of vagina and uterus
• Insemination


  Release of sperm into female, contractions move sperm to fallopian tube, egg releases chemicals to attract sperm
• Fertilisation


  Fusion of egg and sperm nuclei to form diploid zygote, occurs in fallopian tube, all zygote organelles come from egg
• Infertility


  Inability to produce offspring, can be due to problems with sperm, eggs, hormone production, or passage between ovary and uterus
• Male infertility - low sperm count


  Causes: drug/alcohol use, stress

  Corrective measures: lifestyle changes, IVF
• Female infertility - endocrine gland failure


  Causes: pituitary gland failure to produce FSH or LH

  Corrective measures: hormone replacement therapy, IVF
• In-vitro fertilisation (IVF)


  Fusion of gametes outside body, woman given hormones to produce multiple eggs, eggs removed and fertilised in lab, embryos placed in uterus
• Implantation


  Embedding of fertilised egg in uterine wall