biology homeostasis

• 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
• If changes are taking place outside of the body

  The body can still maintain its internal environment
• Automatic control systems


  • Receptors which detect a change
  • Coordination centres such as the brain or spinal cord which interpret the change and decide what needs to be done
  • Effectors which carry out the change, such as muscles or glands
• The nervous and endocrine systems are used to send signals between the different components of the automatic control systems
• 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


  The mechanism by which the automatic control systems work, decreasing or increasing the level of something to return it to normal
• Negative feedback mechanism


  1. Receptors detect a change

  2. Coordination centres interpret the change and send signals to effectors

  3. Effectors carry out a response to return the level to normal

  4. If the level goes too far in the opposite direction, the process repeats in the other direction
• Homeostasis is the overall process of maintaining a stable internal environment for the body
• 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


  Allows different parts of our body to communicate with each other
• Endocrine system


  Similar job to nervous system, but with lots of differences
• 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 of which directly tell the body what to do, and some which tell other glands to release their own hormones
  • Not actually part of the brain, but attached to it
• Thyroid gland


  • Produces the hormone thyroxine, which relates to the rate of our metabolism and plays an important role in growth and development
• Thyroid stimulating hormone (TSH)


  1. If the pituitary gland detects low levels of thyroxine, it releases TSH, which stimulates the thyroid to produce more thyroxine to bring the level back up to normal

  2. This is a negative feedback process
• Adrenal glands


  • Produce the hormone adrenaline, which is normally released during the fight-or-flight response, increasing heart rate and getting blood pumping faster
• Pancreas


  • Produces the hormone insulin, which helps regulate blood glucose concentrations
• Testes


  • Produce the hormone testosterone, which controls puberty, and produce sperm for reproduction
• Ovaries


  • Produce the hormone estrogen, which influences puberty and the menstrual cycle, and hold the female gametes (egg cells)
• Endocrine system vs. nervous system

  • Endocrine system uses hormones (small molecules secreted by glands and transported in the blood), while nervous system uses electrical impulses transferred along nerve cells
  • Hormones spread more slowly and have longer-lasting effects, while nerve impulses are sent very fast and have effects that don't last long
  • Hormones act more generally and interact with many different cells, while 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