Circulatory System

Unit 1: Circulatory system - The heart and blood vessels, The cardiac cycle, Heart rate.
Detailing important parts.

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The Heart

Mass transport systems:

  • All cells need energy (usually aerobic respiration).
  • Raw materials - Oxygen & Glucose
  • Single celled organisms - Diffuse directly, short distance.
  • Multicellular organisms - Transport system, long distance.
  • Mass transport systems:
    1. Carry raw materials from exchange organs to body (cells) and remove metabolic waste.
    2. In mammals - circulatory system.
    3. Cells get nutrients and oxygen from blood and blood removes metabolic waste.

The Heart:

Note: The left and right sides of the heart are reversed on diagrams.

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  • The Ventricles - have thicker walls than the atria, pushing blood further from the heart.
  • Left ventricle - thicker wall than right for pumping blood around the body.
  • Right ventricle - thinner, pumps blood to lungs.
  • Atrioventricular (AV) valves - stops blood flowing back into the atria from the ventricles.
  • Semi-lunar (SL) valves - Stops blood flowing back into the heart.
  • Chords - prevents atrioventricular valves being forced into atria during ventricular contraction.
  • Aorta
  • Pulmonary vein
  • Pulmonary artery
  • Vena cava
  • Apex
  • Cardiac muscle
  • His
  • Coronary Artery
  • AV node
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Valves and Blood Vessels


  • Prevent blood flowing the wrong way.
  • Atrioventricular valves link atria to ventricals.
  • Semi-luna valves link ventricals to aorta and pulmonary vein.
  • Stops blood flowing the wrong way.
  • Valves open only one way relative to pressure.
  • High pressure behind, valves forced open.
  • High pressure infront, valves forced closed.

Blood Vessels - 3 Types:

  • Ateries - carry blood to body. Thick walled, muscular, elastic tissue (cope with high pressure), endothelium (inner lining) allows expansion.
  • Veins - carry blood back to heart. Wide, very little muscle/elactic tissue. Contain valves, forced through with help from body muscles.
  • Capillaries - smallest blood vessles. Where metabolic exchange ocurrs, substances exchange. Large surface area, on cell thick, allows fast diffusion.
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Cardiac Cycle

Cardiac cycle - ongoing sequence of contraction (systole) and relaxation (diastole). Keeps blood contiuously circulating. Volume and pressure changes as the atria and venticles contract and relax.

  • Ventricular diastole, artrial systole - Ventricals are relaxed. The atria contract increasing pressure. This pushes blood into ventricals. Slight increase in ventricular pressure and chamber volume as ventricals recieve the ejected blood.
  • Ventricular systole, atrial diastole - Atria relax. Ventricals contract increasing pressure (higher in ventricals than atria) and AV valves shut. Pressure in ventricals higher than in aorta and pulmonary vein opening SL valves.
  • Ventricular diastole, artrial diastole - Ventricals and atria relax. SL vales close, blood returns to heart and atria fill again. Begins to increase pressure of atria, ventricals continue to relax, their pressure falling below pressure of atria therefore opening the AV valves, blood flows passivley into ventricals, arterial contraction not needed.
    Then atria contract and process begins again.
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Daphnia Experiment

Daphnia - Transparent invertebrates (see their internal organs) you can monitor their heart rate (number of heart beats per minutes) by observing through telescope.
1. Make a range of different concentration solutions including contol solution.
2. One Daphnia on cavity slide (in the dimple).
3. Place on microsope and focus on the heart.
4. Small drop of caffein solution on the daphnia.
5. Count number of heart beats in 10 seconds and multiply by 6.
6. Repeat 10 times (same solution, different daphnia).
7. Keep all other factors constant.
8. Repeat with all other concentrations.
9. Compare the results.

Graph: Average of 10 readings, plot graph. Should show positive correlation, as caffeine increases, heart rate increases.

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Ethical Issues:

  • Experiments on animals allows scientists to study things that are unethical in human experimentation.
  • Many believe it would be unethical in animals also (they give no consent), subjected to painful experimentation.
  • Some believe its more acceptable experimenting on invertebrates than vertebrates (eg. dogs).
  • Invertebrate considered simpler organisms, less sophisticated nervous system, and distantly related to humans.
  • Could cause distress and suffering in living organisms, ie; extream temperatures depriving them of food.
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