Circulatory System

• Understand how organisms are able to respond to changes in their environment
• Homeostasis


  The maintenance of a constant internal environment
• Body water content and body temperature


  Examples of homeostasis
• Co-ordinated response


  Requires a stimulus, a receptor and an effector
• Systems that control responses

  • Nervous system
  • Hormonal system
• Central nervous system


  Consists of the brain and spinal cord, linked to sense organs by nerves
• Stimulation of receptors in sense organs

  Sends electrical impulses along nerves into and out of the central nervous system, resulting in rapid responses
• Neurotransmitters


  Role at synapses
• Reflex arc


  1. Stimulus

  2. Receptor

  3. Coordinator

  4. Effector

  5. Response
• Eye


  Structure and function as a receptor
• Eye focusing


  On near and distant objects, and responding to changes in light intensity
• Skin


  Role in temperature regulation, with reference to sweating, vasoconstriction and vasodilation
• Hormones


  • Adrenaline
  • Insulin
  • Testosterone
  • Progesterone
  • Oestrogen
• Hormones


  • ADH
  • FSH
  • LH
• Any change in an environment is known as a stimulus (plural: stimuli)
• Organisms have receptors that allow them to detect stimuli
• Cells must be kept in the right conditions for all the metabolic reactions and enzymes to work properly
• Homeostasis


  Maintaining a constant internal environment
• Things that need to be maintained in homeostasis

  • Water
  • pH
  • Temperature
  • Salts
  • Glucose
  • Carbon dioxide
• Receptor cells


  Detect stimuli
• Effector cells


  Bring about the required response, usually muscle cells or a gland
• Systems that connect receptors to effectors

  • Nervous system
  • Endocrine system
• Nervous system


  • Communication is via impulses that travel down neurones
  • The response happens instantly
  • The response is short-lived
  • The impulse acts on one or a few cells only
• Endocrine system


  • Communication is via hormones that travel in the blood
  • The response can take a long time to happen
  • The response can last for a long time
  • Hormones can have a widespread affect on many cells and organs
• Central Nervous System (CNS)

  Consists of the brain and spinal cord
• Peripheral Nervous System


  All the nerves that take information from our sense organs into the CNS and from the CNS out to effectors (muscles or glands)
• Neurones


  Cells that carry electrical impulses around the body at high speeds of between 10 and 100 m/s
• Main types of neurones

  • Sensory
  • Relay
  • Motor
• Synapse


  Connection between two neurones, where the impulse is transferred using chemicals called neurotransmitters
• Reflex


  Automatic and rapid response that bypasses the conscious part of the brain
• Reflex arc


  1. Sensory neurone

  2. Relay neurone

  3. Motor neurone

  4. Spinal cord
• Components of a reflex arc

  • Stimulus
  • Receptor
  • Coordinator
  • Effector
  • Response
• Examples of reflexes


  • Iris constricting in bright light
  • Touching something very hot
• Receptor cells


  Special cells adapted to detect stimuli, found in sense organs
• Types of stimuli detected by sense organs

  • Light
  • Chemical
  • Chemical
  • Pressure/heat
  • Movement of sound waves
• Eye


  Structure and function as a sense organ
• Parts of the eye

  • Sclera
  • Cornea
  • Optic Nerve
  • Vitreous Humour
  • Aqueous Humour
  • Retina
  • Choroid
  • Blind Spot
  • Suspensory Ligament
  • Ciliary Muscle
  • Iris
  • Pupil
  • Fovea
• Functions of eye structures

  • Cornea: Refracts light and protects the eye
  • Iris: Controls how much light enters the pupil
  • Lens: Focuses light onto the retina
  • Optic Nerve: Bundle of sensory neurones that carry the impulses to the brain
  • Retina: Layer of tissue at the back of the eye that contains light receptor cells (rods and cones)
  • Fovea: Area of the retina with highest concentration of cone cells that provides sharp vision
  • Aqueous Humour: Maintains the pressure in the eye and nourishes the cornea
  • Vitreous Humour: Maintains the shape of the eye and attaches to the retina
  • Ciliary muscles: Help change the shape of the lens in accommodation
  • Sclera: Tough outer layer that the muscles that move the eyeball attach to
  • Pupil: Hole in the center of the eye that lets light in
• Rods


  Rod cells respond to differences in light intensity, not wavelength, and are more sensitive at low light intensity
• Cones


  Cone cells respond to light of a certain wavelength, i.e. colour, and only work well in bright light