Homeostasis and response

• Homeostasis


  An organism's ability to regulate internal conditions even when external conditions change
• Homeostasis is important so that crucial chemical reactions involving enzymes can happen at an Optimum rate
• Our bodies work hard to regulate blood glucose concentration, temperature and water levels
• Nervous system


  Consists of the CNS (central nervous system - brain and spinal cord) and the PNS (peripheral nervous system - nerves that go through the rest of the body)
• Nervous system response


  1. Receptor detects change due to stimulus

  2. Electrical signal travels to spine through sensory and relay neurons

  3. Signal travels across synapse by neurotransmitter

  4. Signal goes to brain

  5. Brain makes conscious decision

  6. Signal goes back to effector via relay and motor neurons
• Reflex


  Signal bypasses the brain and goes straight through the spine to the effector
• Reflex arc is much faster than a conscious decision
• Glands


  Produce specific chemicals the body needs depending on the situation
• Investigating reaction time


  1. Hold ruler between finger and thumb and drop without warning

  2. Measure distance fallen before caught

  3. Repeat multiple times and take mean average
• Introducing independent variable (stimulant or depressant)


  Decreases or increases reaction time respectively
• Cerebral cortex


  Responsible for higher level functions like memory, speech and problem solving
• MRI scans


  Safely see activity in the brain
• Accommodation


  Eye's ability to change the shape of the lens to focus light from objects at different distances
• Accommodation for far objects

  Ciliary muscles relax, suspensory ligaments tighten, lens becomes thin, light refracted less
• Accommodation for near objects

  Ciliary muscles contract, suspensory ligaments slacken, lens becomes fatter/thicker, light refracted more
• Pupil


  Hole in the iris that can change size depending on light intensity
• Cornea


  Transparent outer layer where light enters the eye, has a slight lensing effect
• Retina


  Contains rod and cone cells that respond to light
• Rods


  Can only detect light intensity, no color
• Cones


  Three different types that detect green, blue or red wavelengths of light
• Myopia


  Shortsightedness, can't focus on far objects
• Hyperopia


  Longsightedness, can't focus on near objects
• Thermoregulation


  Body controlling its internal temperature
• Thermoregulation when too cold

  Blood vessels constrict, muscles shiver to produce more heat
• Endocrine system


  System of glands that produce or secrete hormones that travel to effectors via the blood
• Pituitary gland


  Main or master gland that produces hormones in response to stimuli and travels to other glands
• Pancreas


  Produces insulin to regulate blood glucose levels
• Thyroid


  Controls growth, heart muscle and digestive function
• Adrenal glands


  Produce adrenaline
• Ovaries/Testes


  Release eggs/produce sperm
• Type 1 diabetes


  Pancreas can't produce enough insulin, requires insulin injections
• Type 2 diabetes


  Cells no longer absorb glucose properly, requires careful diet and management
• Water and nitrogen balance

  Kidneys filter blood, absorb useful substances and regulate water levels
• Antidiuretic hormone (ADH)


  Produced in pituitary gland, travels to kidneys and causes them to reabsorb more water
• Negative feedback


  Body responds to return things to normal
• Dialysis


  Blood is sent through a machine that does the job of the kidneys
• Menstruation


  FSH causes egg maturation and estrogen production, LH causes egg release, progesterone maintains uterus lining
• Contraception options


  • Pills that inhibit FSH, progesterone injections, implants, condoms, diaphragms, IUDs, avoiding sex after ovulation
• Infertility


  Lack of FSH or LH production, can be treated with injections
• IVF


  Eggs harvested, fertilized in lab, embryos inserted into uterus