(homeostasis)

• homeostasis is the maintenance of a constant internal environment (e.g. regulating body temperature, blood sugar, water content)
• thermoregulation is the maintenance of a constant internal body temperature (37 C). if temperature falls below the optimum, enzyme activity will slow down. if it is above the optimum, enzymes will denature, and cells will not function properly
• negative feedback:

  1. factor at normal level
  2. factor rises above/falls below normal level (stimulus)
  3. body detects change (receptor) and brings corrective mechanism (effector)
  4. factor at normal level
• positive feedback:

  1. factor at normal level
  2. factor rises above / falls below normal level (stimulus)
  3. body detects change and sends more stimulus (part of corrective mechanism)
  4. factor deviates more from normal level
  5. negative feedback is initiated after to bring back to normal level
• negative feedback is used to reverse a change in the body to bring it back to normal levels, positive feedback is used to quickly activate a process (will go back to negative feedback after process)
• cooling mechanisms:

  • vasodilation of skin capillaries (blood vessels near skin dilate, heat lost to environment through radiation)
  • sweating (evaporation cools skin)
  • flattening hairs (less insulating air)
• heating mechanisms:

  • vasoconstriction (constrict blood vessels, heat away from surface)
  • shivering (constrict muscles, releases glucose from respiration, energy as heat)
  • hair up (hair erector muscles contract to make hairs stand upright, trap warm insulating air)
• excretion is the removal of metabolic waste in the body
• the endocrine system consists of glands throughout the body that secrete specific hormones
• exocrine gland: glands that secrete products through duct to body

  (e.g. pancreas, sweat glands, salivary glands)

  endocrine gland: glands that secrete products into blood

  (e.g. pituitary gland, thyroid, adrenal)
• hormones are chemical messengers transported in blood to specific organs. target organs have receptors that recognize specific hormones, causing the organ to respond.
• hormone journey (endocrine):

  secreting cell -> blood vessel -> target cell
• pituitary gland: FSH (oestrogen production)

  LH (stimulates egg release)
• thyroid: thyroxin (regulate rate of metabolism, growth and development)
• adrenal gland (kidney): adrenaline (fight or flight mode, growth and development)
• pancreas: insulin (decrease blood glucose concentration)

  glucagon (increase level of glucose)
• testes: testosterone (sperm production)
• ovaries: oestrogen (menstrual cycle, egg production)

  FSH (rebuilds uterus lining)

  LH (causes ovulation)
• hypothalamus: ADH (regulates water level in blood)
• control of blood sugar:

  insulin decreases glucose level, glucagon increase glucose level.

  pancreas -> (insulin/glucagon) stimulates glycogen formation/breakdown -> liver lowers/raises blood sugar
• nervous system pathway:

  stimuli -> receptor -> relay -> CNS -> motor -> effector
• central nervous system (CNS) consists of brain and spinal cord

  peripheral nervous system carries information from sense organs -> CNS -> effectors
• nervous system is made of of cells called neurons. neurons are long cells that carry electrical impulses around the body (10-100 m/s)
• parts of a motor neuron:

  • cell body (soma)
  • dendrite
  • nucleus
  • myelin sheath
  • nodes of ranvier
  • axon
  • axon terminal button
• parts of a sensory neuron:

  • receptor cell
  • axon
  • axon terminal button
  • nodes of ranvier
  • cell body (soma)
  • nucleus
  • myelin sheath
  • dendrite
• parts of a relay neuron:

  • cell body (soma)
  • dendrite
  • nucleus
  • axon
  • axon terminal button
• myelin sheath is a fatty substance that acts as an insulator to prevent electrical impulses from travelling down the axon, instead impulses jump between nodes of ranvier (faster)
• types of neurones

  
• synapse is a connection between two neurones using neuro transmitters that diffuse across to transfer
• synapse process:

  1. impulse arrives at the end of presynaptic neuron
  2. vesicles move ad fuse wth membrane, releasing neurotransmitters into synaptic cleft
  3. neurotransmitters diffuse and attach to receptors
  4. triggers an impulse which travels along postsynaptic neuron
• synapse process:

  
• sensory neurons carry nerve impulses from sense organs to CNS
• relay neurons carry nerve impulses from one part of CNS to another
• motor neurons carry nerve impulses from CNS to other muscles/effector organs
• reflexes are automatic reactions that bypass the concious part of the brain so they prevent injury
• refllex pathway:

  1. stimulus (thing/object/action causes reflex)
  2. receptor (sensory neuron/cells)
  3. coordinator (motor neurone in CNS)
  4. effector (muslces/organs/glands)
  5. response (action/reaction)
• function of eye:

  • lens (refracts light to focus on fovea) (flat: faraway, rounded: nearby)
  • cornea (refracts light onto lens)
  • iris (ring of muscle changes size of pupil)
  • pupil (hole allows light in eye)
  • retina (covered in photoreceptors that are light sensitive, convery light energy into electrical impulses)
  • optic nerve (carry nerve impulses to brain)
• bright conditions: pupil constricts as radial muscles contract, circular muscles relax

  dark conditions: pupil dilates as radial muscles relax, circular muscles contract
• near object: ciliary muscles contract, suspensory ligaments slacken, fatter lens, more refracted light

  faraway object: ciliary muscles relax, suspensory ligaments contract, thinner lens, less refracted light
• short sighted: long eyeball, long sighted: short eyeball