Heart Physiology - Amphibians

Introduction

Amphibians are a group of organisms with a unique circulatory system, adapted to their semi-aquatic lifestyles.
Their circulatory system differs from mammals and birds.

Amphibian Heart Diagram

Amphibians have a three-chambered heart composed of:
- Two atria.
- One ventricle.
The presence of only one ventricle results in partial mixing of oxygenated and deoxygenated blood, leading to an incomplete double circulatory system.

Despite having an incomplete double circulatory system, amphibians minimise blood mixing by coordinating the timing of atrial contractions.
The contractions of the atria are carefully timed to reduce the mixing of oxygenated and deoxygenated blood.

Amphibians have unique adaptations for respiration:
- Their lungs are balloon-like structures with limited gas exchange capabilities.
- Oxygen uptake is supplemented by diffusion through their moist skin.
- Some amphibians may also exchange gases through their mouths.

To facilitate lung ventilation, amphibians employ a process known as buccal pumping:
- Throat muscles force air into the lungs.
- This rhythmic pumping action aids in gas exchange.
- Buccal pumping is particularly important when amphibians are on land and unable to rely solely on skin respiration.

Diagram 1

Amphibians' unique circulatory and respiratory adaptations are well-suited for their semi-aquatic existence.
They can efficiently exchange gases both in water and on land, allowing them to thrive in diverse environments.

Diagram 2

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Summary

Amphibians possess a three-chambered heart, consisting of two atria and one ventricle, resulting in an incomplete double circulatory system.
They minimise the mixing of oxygenated and deoxygenated blood by coordinating atrial contractions.
Amphibians rely on both lung respiration and skin respiration for gas exchange, with some species using buccal pumping to aid ventilation.
These adaptations enable amphibians to thrive in aquatic and terrestrial habitats.