Study
Countercurrent heat exchange and vascular bundles in sloths
Scholander, Per Fredrik; Krog, Johan
Journal of Applied Physiology, 1957
Described the intertwined arterial and venous bundles in the limbs of sloths and measured the temperature gradients along them, quantifying the heat returned to the body.
- Studied in
- Mammalia
- Sample size
- anatomical and thermal measurements
Arteries and veins running alongside each other in opposite directions transfer heat from outgoing to incoming blood, so that a limb can be maintained far colder than the core with very little heat lost from the animal overall.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
Countercurrent arrangement of vessels is a general mechanism for retaining heat while permitting peripheral tissue to be cold.
How NatureHQ reads it
One of the founding measurements of countercurrent exchange in animals. NatureHQ uses it alongside the kangaroo rat’s nose to show the same geometric trick doing two different jobs — retaining heat in one case, retaining water in the other.
- Descriptive and anatomical rather than experimental manipulation.
- The efficiency figures depend strongly on flow rate, which varies with the animal’s state.
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Countercurrent exchange
Run two flows past each other in opposite directions and whatever is being exchanged transfers almost completely. The same arrangement retains heat in a bird’s legs and recovers water from a desert rat’s breath.
Countercurrent exchange
A countercurrent exchanger is not always on. An animal that needs to lose heat can send blood around it instead of through it, which turns the same limb from a heat conserver into a radiator.
Published by: Learned society journalsPublished in a learned society journal.
doi.org/10.1152/jappl.1957.10.3.405
Checked against Crossref on 2026-09-28, and they agree on the title, the authors and the year.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-09-03.