Biology 2

• Neurons


  Messages sent around the body in the form of electrical impulses
• Hormones


  Messages sent around the body in the form of chemical messengers that travel in the blood
• Neurons are much more quicker


  They travel through electrical impulses
• Hormones travel


  At the speed of blood
• Neurons have


  Short lived effects
• Hormones


  Last longer
• Neurons act


  On a local area of the body
• Hormones act


  In a more General way throughout your whole body
• Hormone


  A chemical messenger that travels in the blood and binds to a Target cell
• Endocrine glands


  Special glands in the body that release hormones
• Examples of endocrine glands

  • Pituitary gland
  • Thyroid gland
  • Adrenal gland
  • Testes
  • Ovaries
  • Pancreas
• How thyroxin levels are controlled

  1. Pituitary gland releases TSH which goes to thyroid gland causing it to release thyroxin

  2. Thyroxin goes back to pituitary gland and stops it from making more TSH
• Adrenaline


  Hormone produced by the adrenal gland that increases heart rate and respiration
• Testosterone


  Hormone produced by the testes that is important for male development
• Estrogen


  Hormone produced by the ovaries that is important for female characteristics
• Insulin


  Hormone produced by the pancreas that helps lower blood glucose levels
• Glucagon


  Hormone produced by the pancreas that helps raise blood glucose levels
• How blood glucose levels are controlled

  1. Pancreas releases insulin which travels to liver and tells it to store glucose as glycogen

  2. Pancreas releases glucagon which travels to liver and tells it to release glucose from glycogen
• Type 1 diabetes


  Caused by a faulty pancreas that doesn't produce insulin
• Type 2 diabetes


  Caused by an unresponsive liver to insulin, often due to obesity
• Treating type 1 diabetes

  Give insulin injections
• Treating type 2 diabetes

  1. Recommend exercise to burn glucose

  2. Give insulin injections to force liver to absorb glucose
• Menstrual cycle


  28 day cycle where one egg is released through ovulation
• Hormones involved in menstrual cycle

  • FSH
  • Estrogen
  • LH
  • Progesterone
• How menstrual cycle works

  1. FSH causes follicle to mature and ovaries to produce estrogen

  2. Estrogen tells pituitary to stop FSH and produce LH

  3. LH causes ovary to release egg

  4. Progesterone helps maintain uterus lining
• Types of contraception


  • Hormonal
  • Barrier
  • Sterilization
• Homeostasis


  Maintaining a stable internal environment
• Negative feedback


  Mechanism that counteracts a change to return it back to normal
• How body temperature is regulated

  1. Sweat glands produce sweat to cool body

  2. Erector muscles relax to allow hair to lie flat and not trap heat

  3. Blood vessels dilate to allow more heat loss

  4. Erector muscles contract, blood vessels constrict, and shivering occurs to retain heat
• What happens when you're hot

  1. Sweat

  2. Erector muscles relax and hair falls down

  3. Vasodilation - blood vessels near skin surface become wider, allowing heat to escape
• What happens when you're cold

  1. No sweat

  2. Erector muscles contract, hair stands up to trap warm air

  3. Vasoconstriction - blood vessels in skin constrict, less heat escapes

  4. Shivering - causes muscles to respire exothermically, releasing heat
• Homeostasis


  Regulation of the internal environment to maintain a stable, constant condition
• Reflex arc


  1. Stimulus

  2. Receptor

  3. Sensory neuron

  4. Relay neuron

  5. Motor neuron

  6. Effector (muscle or gland)

  7. Response
• Synapse


  Connection between neurons where neurotransmitters are released and diffuse across the gap to bind to receptors on the next neuron, generating a new impulse
• Natural selection


  1. Variation in population due to mutations

  2. Selective pressure (e.g. lack of food, new predator)

  3. Individuals with advantageous alleles survive, reproduce and pass on genes

  4. Individuals with disadvantageous alleles die

  5. Advantageous alleles become more common over generations
• Evolution


  Gradual change of a species over time
• Reasons why Charles Darwin's theory of evolution was not accepted initially: it went against religious beliefs, there was insufficient evidence, and the mechanism of inheritance was not known
• Lamarck's idea of acquired characteristics is incorrect - traits acquired during an organism's lifetime are not passed on to offspring
• Meiosis


  1. Chromosomes line up in pairs

  2. Spindle fibers pull apart chromosome pairs

  3. Nucleus forms around each set of chromosomes, cell divides

  4. Chromosomes line up singly, spindle fibers pull apart chromatids, nucleus forms, cell divides
• Allele


  Different versions of the same gene