B5 - Homeostasis

• Homeostasis


  Regulation of the conditions inside your body (and cells) to maintain a stable environment, in response to changed in both internal and external conditions.
• Factors the body needs to control

  - Water (Kidneys)

  - Temperature (Skin)

  - Glucose (pancreas)

  - Ion levels/ salt (Kidneys)
• Receptors


  Cells that detect stimuli (changes in the environment)
• Coordination centres


  Process the information received from the receptors, e.g. brain, spinal cord and pancreas
• Effectors


  Bring about responses to bring the conditions in the body back to optimum levels e.g. muscles or glands
• Nervous system function

  1. Receptor cells convert a stimulus into an electrical impulse

  2. This electrical impulse travels along cells called sensory neurons to the central nervous system (CNS)

  3. Here, the information is processed and the appropriate response is coordinated, resulting in an electrical impulse being sent along motor neurons to effectors

  4. The effectors carry out the response (this may be muscles contracting or glands secreting hormones)
• Reflex


  An instantaneous response to the stimuli without thinking (impulse does not pass through the conscious areas of your brain)
• How a reflex arc works


  1. A stimulus is detected by the receptors

  2 Impulses are sent along a sensory neuron

  3. In the CNS, the impulse passes to a relay neuron

  4 Impulses are sent along a motor neuron

  5. The impulse reaches an effector resulting in the appropriate response

  
• Synapses


  The gaps between two neurons.

  
  

  -When the impulse reaches the end of the first neuron, a chemical is released into the synapse and diffuses across it

  - When the chemical reaches the second e=neuron, it triggers the impulse to begin again the the next neuron
• The Brain


  Cerebral cortex: Controls consciousness, intelligence, memory, language

  
  

  Cerebellum: Controls balance, posture, muscular co-ordination

  
  

  Medulla: Controls unconscious actions such as heart beat and breathing

  
  

  - Brain is split into two halves called cerebral hemispheres

  
• Difficulties investigation brain function + treating damage


  - It is complex and delicate

  - It is easily damaged

  - It is not fully understood what part of the brain does what
• Neuroscientists can map out regions of the brain by


  - Studying patients with brain damage

  - Electrically stimulating different parts of the brain
• The eye


  Structures within the eye allow the eye to change shape in order to focus on near or distant objects (process of accommodation) and to dim the light.
• Eye structures:

  Retina


  Layer of light sensitive cells found at the back of the eye. The cells are stimulated when light hits the retina. Impulses are sent to the brain, which interprets the information to create an image.

  
  

  Contains;

  Cone cells & Rod cells

  
• Cone cells (Retina)


  Sensitive to the colour of light but don't work well in low light, allow us to see in colour.
• Rod cells (Retina)


  More sensitive to light, only allow us to see in black and white (can't see colours in the dark).
• Eye structures:

  Optic nerve


  A nerve that leaves the eye and leads to the brain. Carries the impulses from the retina to the brain to create an image.

  
• Eye structures:

  Sclera

  White outer layer which supports the structures inside the eye. Strong to prevent some damage to the eye.

  
• Eye structures:

  Cornea


  See-through layer at the front of the eye. It allows light through and the curved surface bends and focuses light onto the retina.

  
• Eye structures:

  Iris


  The coloured part of the eye. Muscles surrounding the pupil that contract or relax to alter the size of the pupil. In bright light, the circular muscles contract and radial muscles relax to make the pupil smaller (avoiding damage to the retina). In dim light, the circular muscles relax and the radial muscles contract to make the pupil larger (so more light can enter to make a better image).

  
• Process of accommodation

  Focus on a near object:

  - Ciliary muscles contract

  - Suspensory ligaments loosen

  - Lens is then thicker and more curved (refracts the light more)

  
  

  Focus on a distant object:

  - Ciliary muscles relax

  - Suspensory ligaments tighten

  - Lens then becomes thinner (light is refracted less)

  
• Eye defects

  Occur when light cannot focus on the retina.

  
  

  - Short sightedness (myopia) ; Lens is too curved, so distant objects appear blurry

  - Long sightedness (hyperopia); Lens is too flat, so it cannot refract light enough
• Treatment methods:

  Spectacle lenses

  Concave lenses spread out the light to treat myopia and convex lenses bring the rays together to treat hyperopia.
• Treatment methods:

  Contact lenses


  Allow you to do sports (unlike glasses), hard/soft contact lenses last for different periods of time.
• Treatment methods:

  Laser eye surgery

  Lasers can be used to either reduce thickness of cornea (so it refracts less) to treat myopia or change its curvature (reflects light more strongly) for hyperopia.
• Treatment methods:

  Replacement lens

  Treat hyperopia by replacing the lens with one made of clear plastic or adding plastic on top of the natural lens. Risks include damage to the retina.
• Thermoregulatory centre

  Monitors and controls body temperature, found in the brain. Has receptors that monitor the temperature of the blood. Has receptors in the skin that send impulses to the thermoregulatory centre.
• Vasoconstriction


  A response to being too cold. Involves a narrowing of blood vessels at the skin surface to reduce heat loss through the surface of the skin.
• Vasodilation

  A response to being too hot. Involves widening of blood vessels at the skin surface to increase heat loss though the surface of the skin
• Human endocrine system

  Sends hormones (chemical messengers) around the body.
• Hormone


  A chemical messenger, released by glands, that travel through the blood to act on target organs. Compared to the nervous system, the hormonal system is much slower but acts for longer.
• Glands:

  Pituitary gland


  The master gland, secretes hormones into the blood to either have an effect on the body or act on other glands to stimulate them to produce different hormones.
• Glands:

  Pancreas


  Secretes insulin, controls blood glucose levels.
• Glands:

  Thyroid

  Secretes thyroxine, controls metabolic rate, heart rate and temperature.
• Glands:

  Adrenal gland

  Secretes adrenaline, involved in the fight or flight response
• Glands:

  Ovary

  Secretes oestrogen, involved in the menstrual cycle
• Glands:

  Testes


  Secretes testosterone, controls puberty and sperm production.
• Insulin


  Hormone released by the pancreas to lower blood sugar levels
• Glucose

  Soluble
• Glycogen

  Stored form of glucose in humans, insoluble