Once or twice through the heart
Single and double circulation.
Counting trips
Blood goes round the body in a loop. On each trip it can pass through the heart once or more than once.
How many times do you think blood passes through the heart in one full trip?
What this lesson covers
The idea
In fishes the two-chambered heart pumps blood to the gills, from where it passes directly to the body, so blood goes through the heart once per cycle; in other vertebrates it goes through twice, called double circulation.
Counting trips
Blood goes round the body in a loop. On each trip it can pass through the heart once or more than once.
How many times do you think blood passes through the heart in one full trip?
- It depends on the animal
- Always three times
- Never
Trace the loops
Press Next step.
Once or twice
Fishes have a two-chambered heart. It pumps blood to the gills, and from there the blood goes straight to the body. So blood passes through the heart once in each cycle. In other vertebrates the blood passes through the heart twice in each cycle: once on its way to the lungs and once on its way to the body. This is double circulation.
In fishes the two-chambered heart pumps blood to the gills, from where it passes directly to the body, so blood goes through the heart once per cycle; in other vertebrates it goes through twice, called double circulation.
Notes
In fishes blood goes through the heart once (heart to gills to body); in other vertebrates it goes through twice: double circulation.
Check yourself
In fishes, how many times does blood go through the heart in one cycle?
Answer: 1
The book says blood goes only once through the heart in the fish during one cycle.
Where does the heart of a fish pump the blood?
What is double circulation?
In which animals does blood go through the heart twice during each cycle?
- To the gills — correct. Yes!
- To the lungs. Fishes take up oxygen at their gills, not at lungs.
- Directly to the body, skipping the gills. The blood is pumped to the gills and is oxygenated there, then it passes to the rest of the body.
- The heart has two chambers. Fishes have a two-chambered heart, and in them blood goes through the heart once.
- Blood goes through the heart twice during each cycle — correct. Yes!
- Blood goes through the heart only once per cycle. That is the case in fishes.
- In fishes. In fishes the blood goes through the heart once.
- In no vertebrate. The book says that it goes through the heart twice in other vertebrates.
- In vertebrates other than fishes — correct. Yes!