Human biology

• Gamete


  Male gamete is called a sperm, female gamete is called an ovum
• Fertilisation


  Nucleus of a sperm fuses with nucleus of an ovum, forming a zygote

  
• Embryo development


  1. Zygote divides by mitosis to produce an embryo

  2. Embryo implants into uterine lining (endometrium)

  3. Embryo develops into a fetus
• Sperm production


  • Produced in testes
  • Leave testes in sperm duct
  • Fluids from seminal vesicles and prostate gland added to form semen
  • Semen exits through urethra

  
• Seminiferous tubules


  • Where sperm cells are produced
  • Surrounded by interstitial cells

  
• Sperm cell production


  1. Germline stem cells divide by meiosis and differentiate into sperm cells

  2. Interstitial cells produce testosterone to stimulate sperm production
• Ovum production


  • Produced in ovaries
  • Ovum released from ovary enters oviduct and travels to uterus

  
• Uterus


  • Muscular wall
  • Endometrium lining where embryo implants

  
• Ovarian follicles


  • Protect ovum and secrete hormones
  • One follicle develops to maturity and ruptures, releasing ovum (ovulation)

  
• Corpus luteum formation


  1. Ruptured follicle turns into corpus luteum

  2. Corpus luteum secretes hormones
• Zygote development


  1. Zygote undergoes mitosis as it travels to uterus

  2. Becomes an early embryo by time it reaches uterus
• Hormone


  Chemical messenger secreted by endocrine glands and travels in bloodstream
• Onset of puberty


  • Hypothalamus secretes releaser hormone
  • Pituitary gland secretes FSH and ICSH in males, FSH and LH in females
• Hormonal control of sperm production

  1. FSH stimulates seminiferous tubules to produce sperm

  2. ICSH stimulates interstitial cells to produce testosterone

  3. Testosterone stimulates sperm production and activates accessory glands

  
• Negative feedback


  High testosterone inhibits pituitary gland to decrease ICSH and reduce testosterone production
• Hormonal control of menstrual cycle

  1. Follicular phase: FSH stimulates follicle development and oestrogen production

  2. Ovulation: LH surge triggers follicle rupture and ovum release

  3. Luteal phase: LH stimulates corpus luteum to produce progesterone

  
• No fertilisation


  Progesterone decreases, causing menstruation
• Fertilisation occurs


  Corpus luteum maintained, no menstruation
• Cyclical fertility in females


  • Only fertile for a few days per cycle
• Continuous fertility in males

  • Sperm produced continuously in testes
• Fertile period indicators


  • Increased body temperature
  • Thin, watery cervical mucus
• Ovulation stimulation


  1. Drugs prevent negative feedback of oestrogen on FSH

  2. Drugs mimic FSH and LH, causing super-ovulation
• Artificial insemination


  1. Male's semen collected and frozen

  2. Semen inserted into female's uterus

  
• IVF


  1. Hormone treatment to stimulate multiple follicles

  2. Ova surgically removed and fertilised in lab

  3. Embryos incubated and transferred to uterus

  
• PGD


  Genetic testing of embryos before transfer to detect disorders
• ICSI


  Sperm head injected directly into ovum cytoplasm

  
• Barrier contraception


  • Condoms, diaphragms, cervical caps prevent sperm reaching ovum
• IUD


  • Implanted in uterus, thickens cervical mucus to prevent sperm reaching ovum

  
• Sterilisation


  • Vasectomy in males, tubal ligation in females to block sperm/ova transport

  
• Oral contraceptive pill


  Synthetic oestrogen and progesterone mimic negative feedback, preventing ovulation
• Progesterone-only pill


  Thickens cervical mucus to prevent sperm reaching ovum
• Morning-after pill


  Prevents implantation of fertilised ovum
• Contraception


  Preventing pregnancy
• Surgical contraception


  Cutting and tying the oviducts so ova cannot reach the uterus
• Oral contraceptive pill


  Chemical method of contraception containing synthetic oestrogen and progesterone
• How oral contraceptive pill works

  Synthetic hormones mimic natural negative feedback on pituitary gland, stopping FSH and LH secretion, preventing follicle development and ovulation
• Progesterone-only pill


  Alternative to oral contraceptive pill, also known as 'mini pill'
• How progesterone-only pill works

  Thickens cervical mucus to prevent sperm reaching ova
• Morning-after pill


  Also known as emergency contraception, can be taken after unprotected sex to prevent pregnancy
• How morning-after pill works

  Prevents implantation of embryo