P2: Biology- Homeostasis and Response

• What is homeostasis?

  The regulation of internal conditions of a cell or organism in response to internal and external changes
• Why is homeostasis important?

  It keeps conditions constant for enzyme action and cell functions
• Homeostasis controls:

  -Blood glucose concentration

  -Body temperature

  -Water and ion levels
• Control systems may include:

  -Responses using nerves

  -Chemical responses using hormones
• All control systems include:

  -Cells called receptors

  -Co-ordination centres

  -Effectors
• What is the purpose of a receptor?

  Detecting stimuli
• What is a stimuli

  changes in the environment
• What is the purpose of the co-ordination centre?

  To receive and process information from receptors
• What is the purpose of effectors?

  To bring about responses that restore optimum levels
• Negative feedback

  A continuous cycle of events which responds when conditions change from the ideal or set point and return the conditions to the set point

  A) Conditions in body change from set point

  B) Receptor detects a change in stimulus

  C) Co-ordinating centre compares stimulus to a set point

  D) Effector produces a response to correct difference

  E) mechanisms are switched off

  
• What temperature should the human body be?

  37 degrees Celsius
• Why should the body be 37 degrees?

  It is the optimum temperature for enzymes to work
• What does the thermoregulatory centre in the brain do?

  -Monitors and controls body temperature

  -Has receptors which monitor the temperature of the blood

  -Receives information (impulses) from temperature receptors in the skin
• If the body temperature is too high then..

  -Blood vessels widen, directing more blood to the surface of the skin (vasodilation)

  -More sweat it produced from the sweat glands and evaporates

  -Both mechanisms cause a transfer of energy from the skin to the environment
• Why do blood vessels widen or narrow?

  As they cannot move
• If the body temperature is too low then...

  -Blood vessels narrow, directing blood away from the surface of the skin (vasoconstriction)

  -Sweating stops

  -Skeletal muscles contract and relax quickly (shiver) which transfers more heat to the blood
• What does the nervous system allow?

  Humans to react to their surroundings and coordinate their behaviour
• Where does information from receptors pass to

  the Central Nervous System (CNS)
• What does the CNS do?

  Coordinated the response of effectors
• What are reflex actions?

  Automatic and rapid so they can protect the body, do not involve the conscious part of the brain
• Process of a reflex:

  1.The pain stimulus is detected by receptors

  2.Impulses from the receptor pass along a sensory neurone to the CNS

  3.An impulse passes through the relay neurone

  4.A motor neurone carries an impulse to the effector

  5.The effector responds
• Stimulus-Response

  1. Stimulus

  2. Receptor

  3. Sensory Neurone

  4 .CNS

  4.Relay Neurone

  5.Motor Neurone

  6.Effector

  7.Response
• Are neurones connected together?

  Not directly
• How do neurones communicate with each other?

  Synapses
• What is a synapse?

  Gaps between neurones
• What happens when an electrical impulse reaches a synapse?


  A chemical is released which diffuses across the gap between the two neurones, causing an electrical impulse to be generated in the second neurone
• What does the brain control?

  Complex behaviours
• What is the brain made out of?

  Billions of interconnected neurones and has different regions
• 3 Key regions of the brain

  -Cerebral Cortex

  -Cerebellum

  -Medulla
• What does the cerebral cortex do?

  Responsible for consciousness, intelligence, memory and language
• What does the cerebellum do?

  Co-ordinates movement and balance
• What does the medulla do?

  Controls automatic actions such as heartbeat and breathing
• What does the Prefrontal Cortex do?

  Controls higher mental functions eg, memory and choice
• Brain labels:

  Label:

  A) Cerebral cortex

  B) cerebellum

  C) Spinal cord

  D) Medulla

  E) Pituitary gland

  F) Hypothalamus

  
• What is the Endocrine System made up of?

  Glands which secrete hormones directly into the blood stream
• What are hormones?

  Chemical messengers which are carried in the blood to a target organ where they produce an effect
• What are the effects of hormones like?

  Slower and act for longer than the effects of the nervous system
• Where is the Pituitary Gland?

  In the brain
• What is the Pituitary Gland also known as?

  The master gland
• How many hormones does the Pituitary Gland secrete?

  Several