B5 - Homeostasis & response

• Homeostasis


  The regulation/control of internal conditions of a cell/organism to maintain optimum conditions for function in response to internal and external changes
• Homeostasis is important because it maintains optimal conditions for enzyme action and all cell functions
• Conditions homeostasis controls

  • Body temperature
  • Blood glucose concentration
  • Water levels
• Components of a control system

  • Receptors (cells that detect stimuli)
  • Coordinator/CNS (brain, spinal cord, pancreas that receive and process info)
  • Effectors (muscles/glands that bring about a response)
• Information flow in a control system

  1. Stimulus

  2. Receptor

  3. Coordinator

  4. Effector

  5. Response
• Reflex action

  Automatic/rapid response that does not involve conscious part of brain
• Reflex actions

  • Allow the body to react quickly to protect itself/minimise damage from potentially harmful stimuli
  • Awareness of a response having happened occurs after the response has been carried out
• Types of neurones

  • Sensory neurones (carry impulses from sense organs to CNS)
  • Relay neurones (found inside CNS, connect sensory and motor neurones)
  • Motor neurones (carry impulses from CNS to effectors)
• Synapse


  Gap between neurones, When an impulse reaches the end of a neurone, a chemical (neurotransmitter) is released across the gap. The chemical then diffuses across the synapse. When the chemical reaches the next neurone this starts another impulse
• Reflex arc

  The nerve pathway that a reflex action takes is called a REFLEX ARC.

  
  

  1. Receptor detects stimuli

  2. Sensory neurone sends impulse from receptor to spinal cord

  3. Chemical crosses synapse between sensory and relay neurone

  4. Relay neurone sends impulses to motor neurone

  5. Motor neurone sends impulse from receptor to effector eg muscle contracting/gland secreting hormones
• Endocrine system


  Composed of glands that secrete hormones directly into bloodstream, which carry the hormone to a target organ to produce an effect. Effects are slower but act for longer compared to nervous system.
• Pituitary gland


  Master gland that secretes several hormones into the blood in response to body conditions, which then act on other glands to stimulate release of other hormones
• Blood glucose control

  1. If BGC is too high, pancreas releases insulin which causes glucose to move from blood into body cells, liver and muscle cells convert excess glucose into glycogen for storage

  
  

  2. If BGC is too low, pancreas produces glucagon that causes liver and muscle cells to convert glycogen into glucose and released into the blood
• Puberty

  Reproductive hormones cause secondary sex characteristics to develop
• At puberty, eggs begin to mature and one is released approximately every 28 days. (Ovulation)
• Male reproductive hormones

  Testosterone produced in testes, stimulates sperm production
• Female menstrual cycle

  1. FSH causes maturation of eggs

  2. LH stimulates release of egg/ovulation

  3. Oestrogen + progesterone maintain lining of uterus

  4. If egg not fertilised, egg and uterus lining released (menstruation)
• Stages of female menstrual cycle

  • Menstruation (bleeding for 4 days due to breakdown of uterus lining)
  • Uterus lining begins to build up (10 days)
  • Ovulation (day 14)
  • Maintaining uterus lining, if egg not fertilised lining breaks down (day 28)
• Hormonal control of female menstrual cycle

  1. Pituitary gland releases FSH, causing eggs to mature

  2. FSH stimulates ovary to release oestrogen, which inhibits further FSH release and thickens uterus lining

  3. Oestrogen stimulates pituitary to release LH, which peaks at ovulation

  4. Ovary releases progesterone, which inhibits FSH and LH to prevent further egg maturation/release, and thickens uterus lining

  5. If no fertilised egg, progesterone level falls, egg and uterus lining released (menstruation)
• Info from receptors passes along nerve cells/neurones


  1. As electrical impulses

  2. To the central nervous system (CNS)
• Central nervous system (CNS)


  Coordinates response of effectors
• Effectors

  • Muscles contracting
  • Glands secreting hormones
• Reflex arc

  1. Receptor detects stimulus

  2. Impulse generated and conducted through sensory neurone

  3. Impulse travels to spinal cord and reaches synapse

  4. Neurotransmitters released and absorbed by relay neurone, stimulating impulse

  5. Signal moves through another synapse into motor neurone

  6. Impulse moves through motor neurone to effector (muscle contracting or gland secreting hormones)
• difference between negative and positive feedback

  Negative feedback:

  occurs when there is a change in the body (i.e. blood glucose increases)

  the nervous system detects the change

  this stimulates an opposite hormonal response

  this reverses the effect back to homeostasis.

  
  

  Positive Feedback: (less common)

  a change starts

  the nervous system detects the change

  then stimulates more hormones to be released to accelerate the change.
• explain the roles of thyroxine and adrenaline in the body.


  Adrenaline is produced by the adrenal glands in times of fear or stress. It increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for ‘flight or fight’.

  
  

  Thyroxine from the thyroid gland stimulates the basal metabolic rate. It plays an important role in growth and development. Thyroxine levels are controlled by negative feedback.
• receptor cells

  receptor cells in:

  
  

  skin detect touch, pain, pressure and temperature

  nose detect chemicals in air

  tongue detect chemicals in food

  light sensitive cells in retina of eye detect changes in light/colour

  inner ear detect changes in sound
• type 1 and type 2 diabetes

  type 1:

  disorder in which pancreas fails to produce sufficient insulin. it is characterised by uncontrolled blood glucose levels. normally treaated w insulin injections

  type 2:

  in type 2, body cells no longer respond to insulin produced by pancreas. carb controlled diet and exercise regime are common treatments. obesity is risk factor.