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 for conscious decision

  5. Signal goes back to effector (e.g. muscle) 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 (e.g. salivary glands producing saliva when eating)
• Investigating reaction time


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

  2. Measure distance fallen before caught

  3. Repeat multiple times, take mean average
• Independent variable (e.g. stimulant or depressant)


  Decreases or increases reaction time
• You can calculate reaction time from distance using S=1/2at^2 but you won't be expected to do that in this paper
• Cerebral cortex

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

  Responsible for motor skills, movement, balance and coordination
• Medulla oblongata


  Controls unconscious actions like heart rate and breathing
• MRI scans


  Safely show brain activity
• Treating brain issues can be very difficult or impossible without damaging important parts
• Accommodation

  The 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

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


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

  At the back of the eye, consists of 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
• Glasses, contact lenses or laser eye surgery can be used to mitigate myopia and hyperopia
• Thermoregulation


  Body controlling its internal temperature by the brain sensing blood temperature and sending signals to effectors
• Thermoregulation when too hot

  Sweat glands cause water evaporation, blood vessels dilate to increase heat loss
• Thermoregulation when too cold

  Blood vessels constrict to reduce heat loss, 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


  The 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/sperm
• Type 1 diabetes

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


  Cells don't absorb glucose properly, requires careful diet and management
• Water and nitrogen balance


  Kidneys filter blood, reabsorb useful substances, produce urine to maintain balance
• ADH (antidiuretic hormone)


  Produced in pituitary gland, travels to kidneys and causes more water reabsorption