Page 3 - LN

 One circulation involves entry of blood from all body parts to heart. This blood is
deoxygenated which goes to lungs for oxygenation. The second circulation involves
entry of oxygenated blood from lungs to heart and then to all body parts.
 Oxygen rich blood from the lungs comes to the thin walled left atrium.
 The left atrium relaxes when it is collecting the blood.it then contracts while the next
chamber, the left ventricle expands so the blood is transferred to it.
 When the muscular left ventricle contracts in its turn, the blood is pumped out to the
body.
 Deoxygenated blood comes from the body to the upper chamber on the right, the
right atrium, as it expands, as the right atrium contracts the corresponding lower
chamber, the right ventricle, dilates.
 This transfers the blood to the right ventricle which in turn pumps it to the lungs for
oxygenation.
Note: Since ventricles have to pump blood into various organs, they have thicker,
muscular walls than the atria.