The diagram given below represents a section of the human heart. Answer the questions that follow: The diagram given below represents a section of the human heart. Answer the questions that follow:
Label the parts numbered 1 and 2 in the diagram. What type of blood flows through them?
Topic: Pulmonary artery and vein
Answer
1 — PULMONARY ARTERY, carrying DEOXYGENATED blood. 2 — PULMONARY VEIN(S), carrying OXYGENATED blood.
THESE TWO VESSELS ARE THE GREAT EXCEPTION to the usual rule, and that is exactly why the examiner asks what type of blood flows through them: PULMONARY ARTERY — carries DEOXYGENATED blood FROM the heart TO the lungs PULMONARY VEIN — carries OXYGENATED blood FROM the lungs TO the heart
Everywhere else an artery carries oxygenated blood and a vein deoxygenated. Here it is reversed, because these vessels run to and from the LUNGS rather than the body.
THE RULE THAT NEVER FAILS: an artery is defined by DIRECTION — it carries blood AWAY from the heart, a vein TOWARDS it. The oxygen content is merely usual, not definitional.
The umbilical vessels of a foetus are reversed in the same way.