Homeostasis

• What is homeostasis?


  Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to an internal and external changes
• features of an automatic control system

  involve the nervous system or hormones
• Receptor cells 


  Detect changes in the environment from a stimulus
• Coordination centre 


  Receptor cells pass information to a coordination centre For example, the brain the spinal cord or the pancreas. it receives and processes the information from the recepto cells
• Effector 


  Coordination centre passes instructions to the effector. A muscle or gland. job is to carry out the response
• Nervous system


  Central nervous system which is the brain and the spinal cord and then we have other nerves running to and from the central nervous system
• Reflex arc


  First the stimulus is detected by A receptor then electrical impulses pass from the receptor along a sensory neuron to their central nervous system. reaches a signups and then goes onto the relay neuron. Then motor neurone. theneffector.
• Cerebral cortex 


  Language memory and consciousness
• Cerebellum 


  Balance and coordinates our movements
• Medulla


  Heart rate and breathing rate
• Why is it difficult to treat the brain?

  The brain is protected by the skull, so it’s very tricky to access and the structures of the brain are extremely complex The brain is extremely delicate and easy to damage.
• How do you scientists investigate the brain?

  Scientist look at patients who have suffered brain damage Also they can electrically stimulate different parts of the brain And MRI scanning
• Cornea 


  Transparent. Focuses light rays
• lens


  Focus the light rays onto the back of the eye and can change shape
• Retina 


  Contains receptor cells for light whick allow us to detect light intensity and light colour
• Optic nerve


  send electrical impulses to the brain
• Sclera


  Tough outer structure protects the eye
• Ciliary muscles and suspensory ligaments

  work with the lens to allow us to focus on distant or near objects
• Pupil and iris 


  Iris is the coloured part and the pupil is the space in the centre of the iris which light passes through. iris controls the size of the pupil
• Accommodation 


  The ability to change the shape of the lens to focus on near or distant objects
• Ciliary muscle 


  Change the thickness of the lens
• When the celery muscle contracts the suspensory ligaments loosen the lens is now thicker and refracts light rays more strongly
• When the celery muscle relaxes does suspensory ligaments are pull tight the lens is now pulled thin and only slightly refracts light rays
• Focusing on distant objects


  Light from distant objects needs to be focused only a relatively small amount so celery muscles relax and suspensory ligaments are all tight
• Focusing on near objects


  Light from near objects needs to be focused a large amount distillery muscle contracts and the suspensory ligaments loosen
• Long sight (hyperopia)


  can’t focus on nearby objects. eyeball is too short so light is focused behind the retina. Convex lens
• Short sight (myopia)


  Can’t focus on distant objects Eyeball is too long so light is focused at a point in front of the retina. Concave lens.
• Thermoregulatory centre 


  Body temperature is monitored and controlled by the brain. Contains recrotors which are sensitive to the temperature of blood. skin also contains temp receptors
• Body temperature gets too high


  Sweat glands release sweat, which evaporate. this takes energy from the body. also by flushing. blood vessels vasodilate. Heat can now transfer out of the blood
• Body temp too low

  Vasoconstriction. Less heat is lost. shiver. muscles contract. this increases rate of respiration which releases heat. We stop sweating.
• The endocrine system 


  Consists of glands which secrete hormones directly into the blood stream.
• Key glands 


  Pancreas- controlling concentration of glucose.

  ovaries and testes

  thyroid gland- growth, metabolic rate

  adrenal glands
• Pituitary gland 


  In the brain.pituitary hormones act on other glands and they cause other hormones to be release.
• Concentration of blood glucose is high

  Sensed by the pancreas. pancreas produces insulin. Incident triggers body cells to take up glucose from the blood it’s also triggers liver and muscle cells to store excess glucose

  as glycogen
• Type 1 diabetes

  Pancreas does not produce enough insulin
• Type 2 diabetes 


  The body cells stop responding to insulin produced by the pancreas
• Blood glucose concentration falls

  Pancreas releases the hormone glucagon into the bloodstream This triggers liver cells to convert glycogen stores back to glucose this glucose is released into the blood
• Loose water 


  Lungs when we exhale

  sweat

  via the kidneys in urine
• Kidneys 


  Blood enters. it removes urea as well as excess irons and water. These leave the kidney as you were in and stored in the bladder.
• Kidneys


  Blood passes through the capillaries. Small molecules are filtered out of the blood. These passing into a tube where all of the glucose some of the irons and some of the water is re-absorbed back into the blood. Selective reabsorption.