Lesson 1 of 9 / Transport in humans
Blood vessels and circulation routes
Which vessel takes blood to each organ, and which brings it back?
I can trace the main vessels linking the heart, lungs, liver and kidneys.
I can trace vessels linking heart, lungs, liver and kidneys.Syllabus
Syllabus K325, Topic 5(a). Trace vessels linking heart, lungs, liver and kidneys.
About 5 min
Make a guess. You are not marked.
Arteries are often drawn in red for oxygen-rich blood. Is there an artery that carries oxygen-poor blood?
Show the answer
Yes, the pulmonary artery to the lungs.
An artery is any vessel carrying blood away from the heart. The pulmonary artery carries oxygen-poor blood to the lungs.
The key idea
Arteries carry blood away from the heart; veins return it. The vessel name identifies the organ or route.
A circulation map shows connections, not the positions or sizes of organs. Follow each arrow before deciding what the blood contains.
- Pulmonary artery: right ventricle to lungs
- Pulmonary veins: lungs to left atrium
Explanation
Humans have a double circulation. In one complete journey through the lungs and the rest of the body, blood passes through the heart twice. The right side pumps to the lungs; the left side pumps to the body.
Blood leaves the right ventricle through the pulmonary artery. It gains oxygen in lung capillaries and returns through the pulmonary veins to the left atrium. The left ventricle pumps it into the aorta. Branches supply body organs, and veins eventually join the venae cavae returning to the right atrium.
The liver has two incoming supplies. The hepatic artery brings oxygen-rich blood from the aorta. The hepatic portal vein brings blood rich in absorbed nutrients from the small intestine. Blood leaves the liver through the hepatic vein and enters the vena cava.
A renal artery supplies each kidney from the aorta. The renal vein returns blood from the kidney to the vena cava. A ureter carries urine, so it is not part of this blood route.
Oxygenated and deoxygenated describe relative oxygen content. Deoxygenated blood still contains some oxygen. An artery is not automatically oxygenated: the pulmonary artery carries relatively oxygen-poor blood.
Step by step
- 1
Choose a starting point
For example, begin at the left ventricle rather than listing disconnected vessel names.
- 2
Follow the direction
Use an artery on the outward journey and a vein on the return journey.
- 3
Check the special liver route
Blood from the small intestine reaches the liver through the hepatic portal vein before returning to the heart.
Worked example
From intestine to heart
Trace blood carrying recently absorbed glucose from the small intestine to the right atrium.
One way to explain it
Small-intestinal capillaries -> hepatic portal vein -> liver capillaries -> hepatic vein -> vena cava -> right atrium.
Why this answer works
- The liver receives absorbed nutrients before they reach the general circulation.
- Portal identifies the connection between two capillary beds.
- The hepatic vein, not the portal vein, leaves the liver for the vena cava.
Watch out for this
A student says: "The hepatic portal vein carries blood out of the liver." What is wrong with this?
Show the answer
It brings blood from the small intestine into the liver. The hepatic vein carries blood out.
Check your understanding
Which route correctly takes blood from the aorta through a kidney and back towards the heart?
Show the answer
Aorta -> renal artery -> kidney -> renal vein -> vena cava
Arterial blood reaches the kidney, and venous blood returns towards the heart.
Quick recall
Which vessel takes blood to each organ, and which brings it back?