B5

• Homeostasis is the maintenance of a constant internal environment of a cell or organism to maintain optimum conditions for function of enzyme activity and cell function
• Ways the body keeps itself warm:

  Shivers

  Blood vessels constrict so blood is further from the surface (Vasoconstriction)

  Burn excess fat

  Goosebumps

  Hairs stand up
• Ways the body tries to cool down:

  Sweats

  Blood vessels expand so that blood is closer to the surface (Vasodilation)

  Hairs lie flat close to the skin
• Homeostasis is controlled by the hypothalamus in the brain
• Homeostasis included the control of:

  Blood glucose concentration

  Body temperature

  Water and ion levels
• All control systems include:

  Cells called receptors - which detect stimuli

  Coordination centres (such as brain and spinal cord) - which receive and process information from the receptors

  Effectors (muscles or glands) - respond and restore optimum levels
• Control systems are controlled by a negative feedback
• Negative Feedback:

  A receptor detects a change in stimuluss

  Coordinating centres compare the stimuli to a set point

  An effector then produce a response to correct the difference from the set point
• Human body temperature should be 37 degrees
• If the body temperature is to high it causes enzymes to denature
• The thermoregulatory centre in the brain:

  Monitors and controls body temperature

  Has receptors monitor the temperature of the blood

  Receives information (impulses) from temperature receptors in the skin
• If the body temperature is to high:

  The blood vessels widen - Vasodilation

  More sweat is produced

  Transfer energy from the skin to the environment
• If the body temperature is to low:

  Blood vessels narrow - Vasoconstriction

  Hairs stand up on end

  Shivers
• The nervous system enables humans to react to their surroundings and coordinate behaviour
• CNS = central nervous system
• The CNS coordinates the response of the effectors - muscles contracting or hormones being produced
• Reflex actions are automatic. They involve the unconscious part of the brain:

  The pain stimulus is detected by the receptors

  Impulses from the receptor are passed along a sensory neuron to the CNS

  An impulse is then passes to the relay neurone

  The motor neutron them carries the impulse to the effector

  The effector responds
• Neurone are not directly connected to each other and communicate through synapses
• When an electrical impulse reaches the synapse a chemical is released that diffuses across the gap between the two neurones. This cuases an electrical impluse to be generated in the second neurone
• The brain is made of billion of interconnected neurons and has three main regions

  Cerebral cortex - responsible for consciousness, intelligence, memory and language

  Cerebellum - coordinates movement and balance

  Medulla - control unconscious action e.g. breathing and rate
• Neuroscientist have been able to map the brain regions through:

  Studying patients with brain damage

  Using MRI scans

  Electrically stimulating parts of the brain

  The complexity and delicacy of the brain makes investigating and treating brain disorders very difficult
• The eye is a sense organ and contains:

  Retina - contains receptor cells which are sensitive to brightness and colour of light

  Optic nerve - carries impulses from the retina to the brain

  Sclera - form a a tough outer layer with a transparent region at the front called the cornea

  Iris - Controls the size of the pupil and the amount of light which reaches the retina

  Ciliary muscles an suspensory muscles - can change the shape of the lens to focus light onto the retina
• Complete the diagram

  A) Sclera

  B) Iris

  C) Cornea

  D) Pupil

  E) Lens

  F) Ciliary

  G) Optic nerve

  H) Retina

  
• Accommodation is the process of changing the shape of a lens to focus on a near or distant object
• For the eye to focus on a near object:

  The ciliary muscles contract

  Suspensory ligaments loosen

  Lens becomes thicker and refracts light rays stronger
• For the eye to focus on a distant object:

  The ciliary muscles relax

  Suspensory ligaments tighten

  Lens becomes thinner and refracts light rays weaker
• Myopia = short sighted

  Hyperopia = long sighted
• Eye defects are treated with:

  Spectacle lens

  Contact lens

  Laser eye surgery to change the shape of the lens

  Replacement eye lenses
• The endocrine system is make up of glands that secrete hormones into the bloodstream
• Hormones are chemical messengers which are carried in the blood to a target organ
• the pituitary gland in the brain is the master gland
• adrenaline

  is produced by the adrenal glands in times of fear increases heart rate boosting the delivery of oxygen and glucose to the membrane and muscles. Prepares the body for fight or flight
• thyroxine

  is produced by the thyroid gland it increases the metabolic rate and controls growth and development in young animals this is also controlled by negative feedback
• blood glucose concentration is monitored and controlled by the pancreas
• if the blood glucose concentration is too high:

  the pancreas releases more of the hormone insulin

  insulin causes glucose to move from the blood into the cells

  in liver and muscle cells excess glucose is converted to glycogen for storage
• if the blood glucose is too low:

  the pancreas releases Glucagon

  Glucagon stimulates glycogen to be converted into glucose and release into the blood

  this is negative feedback
• type one diabetes is disorder that:

  is caused by the pancreas failing to provide insulin

  results in uncontrollably high glucose levels

  created with insulin injections
• type 2 diabetes is a disorder that:

  is caused by the body cell no longer responding to insulin

  has obesity as a high risk factor

  is treated with a carbohydrate controlled diet and regular exercise
• water leaves the body from the lungs during breathing, from the skin in sweat and in the urine (along with ions and urea)
• The water balance concentration of the blood changes then body cells will lose or gain too much water by osmosis