B5

• Circulatory system


  An example of an organ system whose role is to transport oxygen and nutrients to the body's tissues
• Circulatory system


  • Relies on 3 main things: blood, blood vessels, heart
• Blood


  Carries oxygen and nutrients
• Heart


  Pumps the blood to keep it moving through the vessels
• The circulatory system can be thought of as a double circulatory system
• Path of blood through the heart

  1. Flows into right atrium and left atrium

  2. Atria contract to push blood into ventricles

  3. Ventricles contract to push blood out into pulmonary artery and aorta

  4. Atria refill with new blood

  5. Cycle repeats around 70 times per minute
• Pacemaker cells


  Produce electrical impulses to make the heart contract regularly
• Artificial pacemaker


  Small device implanted under the skin above the heart to regulate the heartbeat
• Artery


  Any vessel that carries blood away from the heart
• Vein


  Any vessel that carries blood to the heart
• Arteries don't always carry oxygenated blood, and veins don't always carry deoxygenated blood
• Coronary arteries


  Small arteries that branch off the aorta to supply the heart muscle with oxygenated blood
• The heart acts as the pump for the circulatory system
• Blood vessels


  1. Arteries carry blood away from the heart

  2. Capillaries exchange nutrients and oxygen with tissues

  3. Veins carry blood back to the heart
• Arteries


  • Carry blood directly from the heart
  • Blood inside is at high pressures
  • Have thick layers of muscle and elastic tissue to be strong and elastic
• Capillaries


  • Very small vessels that come into close contact with cells
  • Walls are only one cell thick and permeable
  • Total cross-sectional area is much higher than arteries, so blood flows more slowly
• Veins


  • Relatively large with biggest lumens
  • Walls are thin with small layers of elastic and muscle
  • Have valves to prevent backwards blood flow
• Calculating rate of blood flow

  Divide volume of blood by time taken
• 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


  • 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 their effects last longer
  • Nerve impulses are sent very fast and the effects don't last very long (often less than a second)
  • Hormones act more generally and interact with many different cells
  • Nerve impulses are sent to one specific area
• The endocrine system is often described as being less precise than the nervous system