Description
The frog heart is a three-chambered, dark red, muscular organ situated mid-ventrally in the anterior part of the body cavity, within a protective double-layered pericardium. It consists of two upper chambers (right and left atria/auricles) and a single lower chamber (ventricle).
Structure and Features
Atria (Auricles): The right atrium receives deoxygenated blood from the body via the sinus venosus, while the left atrium receives oxygenated blood from the lungs through the pulmonary veins. The atria are separated by an interatrial septum and open into the ventricle through auriculo-ventricular apertures with valves to prevent backflow.
Ventricle: A single, thick-walled, spongy chamber that mixes both oxygenated and deoxygenated blood, then pumps it out to the body and lungs. Its internal surface is highly trabeculated, which helps minimize complete mixing of the two blood types.
Sinus Venosus: A venous chamber at the back of the heart where venous blood collects before entering the right atrium; guarded by sinuauricular valves.
Truncus Arteriosus: An outflow tract that arises from the ventricle, guarded by semilunar valves and divided internally by a spiral valve into cavum aorticum and cavum pulmocutaneum, leading to three pairs of aortic arches (carotid, systemic, and pulmocutaneous).
Circulatory Function
The frog’s heart pumps both oxygenated and deoxygenated blood, ensuring partial separation in the atria and partial mixing in the ventricle before distribution.
Blood passes through the heart twice during a complete circuit (double circulation): first for oxygenation in the lungs and skin, then for distribution to the body, which is an evolutionary adaptation for amphibians.
Key Points for Models
Models usually depict color-coded chambers, the interatrial septum, valves, and main vessels for clear understanding.
The unique structure of the frog heart illustrates an evolutionary transition toward the more complex four-chambered mammalian heart.
The frog heart’s three-chambered structure is a classic example for teaching comparative anatomy, circulatory physiology, and adaptive evolution in vertebrates.