Homeostasis and Control Systems

• What is homeostasis?

  The internal environment of an organism
• What does the external environment include?

  Fluctuations in temperature, diet, water
• What does the internal environment consist of?

  Small fluctuations in temperature, pH, glucose, blood pressure
• Who coined the term homeostasis and when?

  Walter B. Cannon in 1929
• What does the Greek word for homeostasis mean?

  Similar, maintenance of a constant internal environment
• What is a controlled variable?

  Examples include blood pressure and plasma
• What is a set point?

  The value at which a variable should be maintained
• What are the steps in the homeostatic control process?

  1. Change in variable
  2. Sensor (receptor cells)
  3. Integrating centre (CNS or endocrine gland)
  4. Effector (muscle or secretory cells)
• In the temperature regulation example, what acts as the receptor?

  Thermometer
• What is the control centre in the temperature regulation example?

  Thermostat
• What is the effector in the temperature regulation example?

  Air conditioner turns on
• What is the normal room temperature in the context of homeostasis?

  The set point for temperature regulation
• What are the afferent pathways in the sensory to integrating centre process?

  Pathways from sensory receptors to integrating centre
• What are the efferent pathways in the integrating centre to effector process?

  Pathways from integrating centre to effectors
• What is the regulation process of blood pressure?

  1. Baroreceptors detect changes
  2. Glossopharyngeal nerve sends signal to Medulla oblongata
  3. Autonomic nerves to heart and blood vessels
  4. Increases cardiac output and vasoconstriction
  5. Results in fall in blood pressure
• What do variables show in terms of diurnal changes?

  Set points vary throughout the day
• How do set points vary in animals?

  They can change at yearly cycles
• What is positive feedback in homeostasis?

  • Initial stimulus causes a response
  • Response reinforces itself
  • Examples: action potential, ovulation, blood clotting
• What are the characteristics of the nervous system control?

  • Rapid response
  • Short-term effects
• What are the characteristics of the endocrine system control?

  • Long-term response
  • Slower than nervous control
  • Regulates metabolism and blood volume
• What are the components of the peripheral nervous system?

  • Central NS
  • Somatic nerves
  • Autonomic nerves
• What are the types of autonomic nerves?

  • Parasympathetic nerves
  • Sympathetic nerves
• What do somatic nerves control?

  Skeletal muscle
• What is the role of the preganglionic neuron in the ANS?

  It is part of the CNS
• What is the role of the postganglionic neuron in the ANS?

  It is part of the peripheral ganglion
• What are the differences between sympathetic and parasympathetic fibers?

  • Sympathetic: short preganglionic, long postganglionic
  • Parasympathetic: long preganglionic, short postganglionic
• What neurotransmitter is used by the parasympathetic system?

  Acetylcholine
• What neurotransmitter is used by the sympathetic system?

  Noradrenaline
• What is the role of the adrenal medulla?

  • Secretes epinephrine into circulation
  • Similar effects to sympathetic nerve activity
• What are the general effects of the sympathetic and parasympathetic systems?

  • Sympathetic: stimulatory, fight or flight
  • Parasympathetic: inhibitory, rest and digest
• What is the role of thyroid hormones?

  Regulate metabolism
• What is the role of growth hormones?

  Promote growth
• What is the sequence of negative feedback involving CRH?

  CRH -> ACTH -> cortisol
• What is the positive feedback sequence involving suckling?

  Suckling -> oxytocin -> milk