The Evidence Layer for Scientific AI

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How the circuit is organized

Closed means blood normally stays within arteries, capillaries, veins, and the heart rather than bathing organs directly in a body cavity. Double means there are two circuits in series: the right side of the heart sends oxygen-poor blood through the pulmonary circuit, while the left side sends oxygen-rich blood through the higher-resistance systemic circuit. This arrangement allows pressure to be rebuilt after the low-pressure pulmonary circuit before blood enters the systemic circuit. The supplied evidence directly supports the closed-loop physical interpretation, but does not provide a general comparative textbook survey of all vertebrate hearts. Pump-driven closed-loop model

Why “double” matters

• Pulmonary circuit: right ventricle → lungs → left atrium.
• Systemic circuit: left ventricle → body tissues → right atrium.
• Functional consequence: pulmonary and systemic pressures can be regulated separately; the supplied records do not provide normal human pressure values, so no numerical pressure comparison is asserted.

Important comparison

Not every double circulation is completely separated. In bullfrogs, measurements from multiple cardiac and vascular sites found substantial differences in blood-gas composition and evidence of arterialized and venous streams, yet the circulation is described as incompletely separated, reflecting intracardiac mixing. Thus, “double” alone does not guarantee complete separation of oxygen-rich and oxygen-poor blood. Incomplete separation in bullfrogs

Confidence: high for the definition and circuit logic; moderate for the fluid-physics qualification because the cited review relies partly on idealized mechanical models and limited in-vivo observations, including data from a single giraffe. Model limitations