B3

• Puberty


  The period during which adolescents start to develop secondary sexual characteristics
• Secondary sexual characteristics


  • Facial hair in men
  • Breasts in women
• Reproductive hormones


  Hormones that trigger puberty, including testosterone in men and oestrogen in women
• Testosterone is produced in the testes and stimulates sperm production
• Oestrogen is produced by the ovaries
• Menstrual cycle


  1. Menstruation

  2. Uterus lining building up

  3. Ovulation

  4. Maintaining uterus lining
• The average length of a menstrual cycle is around 28 days but varies between people
• Menstruation


  The period of bleeding that normally lasts about 4 days and is due to the breakdown of the uterus lining
• Uterus lining building up


  Lasts around 10 days up to day 14, preparing the uterus lining for a fertilized egg
• Ovulation


  The release of an egg from one of the ovaries, occurring on a single day
• Maintaining uterus lining


  Stretches from day 14 to day 28, maintaining the uterus lining if no fertilized egg has implanted
• If a fertilized egg implants, the menstrual cycle stops as the woman becomes pregnant
• Oestrogen

  Produced in the ovaries, stimulates the growth of the uterus lining
• Progesterone


  Produced in the ovaries, maintains the lining of the uterus
• Luteinizing hormone (LH)


  Produced in the pituitary gland, stimulates the release of the egg during ovulation
• Follicle stimulating hormone (FSH)


  Produced in the pituitary gland, stimulates the maturation of an egg in the ovaries
• FSH stimulates the ovaries to produce oestrogen


  As oestrogen levels increase, they start to inhibit FSH (negative feedback)
• High oestrogen levels

  Stimulate the release of LH, causing ovulation
• Progesterone


  Inhibits both LH and FSH
• Thermoregulation


  The control of our internal body temperature
• Why we need to regulate temperature


  • Allows our cells to function properly
  • 37 degrees Celsius is the perfect temperature for our enzymes to function
• Thermoregulatory sensor


  Part of the hypothalamus within our brain that acts as a thermostat for our body
• Receptors that detect changes in body temperature


  • Found mostly in the skin and blood vessels
  • Constantly send information about temperature to the thermoregulatory sensor
• Warming up mechanisms


  1. Vasoconstriction (constrict blood vessels near surface of skin)

  2. Contract erector muscles (making hairs stand on end)

  3. Shivering (muscles contract automatically)
• Vasoconstriction


  Less blood flows near the surface, less heat energy is lost to surroundings
• Erector muscles


  Trapping a small layer of insulating air, harder to lose heat from skin
• Shivering


  Muscle contraction requires energy from respiration, releases heat as waste
• Cooling down mechanisms


  1. Vasodilation (blood vessels expand)

  2. Sweating (release water and salts onto skin surface)
• Vasodilation


  More warm blood passes close to skin surface, allowing more heat transfer to surroundings
• Sweating


  Evaporation of sweat takes heat energy from body
• Homeostasis refers to the process of maintaining a stable internal environment
• Accommodation


  1. Reflex that changes the refractive power of the lens

  2. Allows seeing both near and distant objects
• Glasses


  • Help when the accommodation process doesn't work properly
• Cornea


  Refracts or bends light
• Lens


  Refracts or bends light
• Ciliary muscles


  Control the shape of the lens
• Suspensory ligaments


  Control the shape of the lens
• Focusing light on the fovea

  1. Light from object is refracted by cornea

  2. Light is further refracted by lens to converge on fovea
• Object is close


  Lens needs to be short and fat to refract light strongly
• Object is distant


  Lens needs to be stretched out to reduce refractive power