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Circulatory Anatomy
Sinus Venosus
Sinus venosus
The first chamber of the fish heart - a thin-walled venous reservoir that collects returning blood before delivering it to the atrium.
Region: Trunk Universal in fish Unique to: all
📖 Overview
The sinus venosus receives blood from the systemic veins (hepatic and cardinal) and delivers it to the atrium. In fish it is often considered the true 'first chamber' - a design retained from ancestral vertebrates and later lost or absorbed in mammals and birds.
🧬 Structure
Thin-walled, valve-guarded chamber posterior to the atrium.
⚙️ Function
Collects returning venous blood, prevents backflow via sinoatrial valves, and delivers blood to the atrium.
✨ Fun Fact
The sinus venosus is the developmental source of the mammalian sinoatrial node - the natural pacemaker of the human heart traces evolutionary origins to a fish chamber.
🔗 Related Circulatory Structures