Homeostasis & Response

• Homeostasis

  The regulation of conditions inside the body to maintain a stable internal environment in response to changes in both internal and external conditions
• Cells in the body need certain conditions to function properly, such as not being too hot or too cold, not being too acidic or too alkaline, and having a good supply of glucose and water
• The body regulates everything and makes sure that everything is kept around the right levels
• Temperature and glucose levels do fluctuate, but only within small bounds
• Automatic control systems

  • Receptors which detect a change
  • Coordination centres which interpret the change and decide what to do
  • Effectors which carry out the change
• Nervous system

  Sends fast and precise electrical impulses through nerves, allowing for quick responses
• Endocrine system

  Relies on hormones released into the bloodstream, which are slower, longer-lasting, and more generalized than the nervous system
• Negative feedback mechanism

  1. If the level of something gets too high, negative feedback decreases it to return it to normal

  2. If the level gets too low, negative feedback increases it to return it to normal
• Homeostasis is the overall process of maintaining a stable internal environment through a loop of negative feedback
• Nerve cell

  Also called a neuron
• Nerve cell

  • Long
  • Thin
  • Lots of branch connections to either end
  • Adapted to carry electrical impulses from one point to another
• Synapse

  Connection between nerve cells where electrical impulses are converted to chemical signals to pass between cells
• Nerve cell communication

  1. Electrical impulse hits end of nerve

  2. Causes release of chemicals

  3. Chemicals diffuse across gap to next nerve cell

  4. Triggers another electrical impulse

  5. Electrical impulse continues along new neuron
• Central nervous system

  • Made up of brain and spinal cord
  • Where 'thinking' takes place
  • Takes in sensory information, decides what to do, sends out orders to the body
• Sensory neurons

  Carry information from receptors all over the body to the central nervous system
• Motor neurons

  Carry impulses from the central nervous system to effectors (muscles or glands)
• Reflex arc

  Nerve pathway that underlies unconscious reflexes
• Reflex arc

  1. Stimulus detected by receptor cells

  2. Sensory neuron carries impulse to spinal cord

  3. Relay neuron transfers impulse to motor neuron

  4. Motor neuron carries impulse to effector (muscle) to cause movement
• Endocrine system

  • Consists of a series of glands found throughout the body
  • Glands secrete hormones, which are small chemical molecules passed into the blood and spread throughout the body
• Hormones

  Act as signals to trigger certain changes inside cells
• Pituitary gland

  • Produces multiple different hormones
  • Some hormones directly tell the body what to do
  • Some hormones tell other glands to release their own hormones
  • Not actually part of the brain, but attached to it
• Thyroid gland

  • Produces the hormone thyroxine
  • Relates to the rate of our metabolism
  • Plays an important role in growth and development
• Thyroid stimulating hormone (TSH)

  1. Pituitary gland detects low levels of thyroxine

  2. Pituitary gland releases TSH

  3. TSH stimulates the thyroid to produce more thyroxine

  4. Brings the level of thyroxine back up to normal
• Negative feedback

  If thyroxine levels are too low, they are stimulated to rise again, and if they went too high, they are brought back down
• Adrenal glands

  • Produce the hormone adrenaline
  • Normally released during the fight-or-flight response
  • Increases heart rate and gets blood pumping faster
• Pancreas

  • Produces the hormone insulin
  • Helps regulate blood glucose concentrations
• Testes

  • Produce the hormone testosterone
  • Control puberty
  • Produce male gametes (sperm) for reproduction
• Ovaries

  • Produce the hormone estrogen
  • Influence puberty and the menstrual cycle
  • Hold female gametes (egg cells)
• Endocrine system vs. Nervous system

  • Endocrine system uses hormones (small molecules secreted by glands and transported in the blood)
  • Nervous system uses electrical impulses transferred along nerve cells
  • Hormones spread more slowly and have longer-lasting effects
  • Nerve impulses are sent very fast and have short-lasting effects
  • Hormones act more generally and interact with many different cells
  • Nerve impulses are sent to one specific area
• Blood glucose concentration

  The amount of sugar in our bloodstream
• We need a decent amount of sugar in our blood so that our cells have a constant supply of glucose for respiration
• If the blood glucose concentration gets too high it can start to damage our tissues
• What happens when we eat a big meal with lots of carbohydrates

  1. Carbohydrates broken down in intestines into glucose

  2. Glucose absorbed into bloodstream

  3. Blood glucose concentration increases
• Pancreas

  • Organ that sits just behind the stomach
  • Releases insulin and glucagon hormones
• How insulin regulates high blood glucose

  1. Pancreas detects high glucose

  2. Releases insulin into bloodstream

  3. Insulin binds to cells (liver, muscle)

  4. Cells take up glucose from blood

  5. Blood glucose concentration decreases
• Glycogen

  Long-term storage form of glucose
• How glucagon regulates low blood glucose

  1. Pancreas detects low glucose

  2. Releases glucagon into bloodstream

  3. Glucagon binds to liver cells

  4. Liver breaks down glycogen into glucose

  5. Glucose released into blood

  6. Blood glucose concentration increases
• Insulin and glucagon

  Create a negative feedback loop to keep blood glucose at the right level
• Our bodies constantly release insulin and glucagon to ensure blood glucose is kept at the right level
• Insulin

  A hormone that the pancreas releases when the concentration of glucose in the bloodstream gets too high, which binds to cells and tells them to absorb some of the excess glucose and turn it into glycogen