part of part of develops from develops from immediate transformation of sinus venosus http://upload.wikimedia.org/wikipedia/commons/c/c7/Gray465.png UMLS:C0225857 TAO:0000154 venosus venarum sinus Part of the circulatory system which receives blood from the systemic veins and contracts to pump the blood into the atrium of the heart.[AAO] Wikipedia:Sinus_venosus NCIT:C34299 sinus venarum EHDAA2:0001839 UBERON:0002063 venarum Heart region collecting blood from the paired common cardinal veins and delivering to the atrium. One of four components of the heart. The sinus venosus also acts as a pacemaker and is the first to contract. Kimmel et al, 1995.[TAO] inflow tract In zebrafish, the sinus venosus also acts as a pacemaker and is the first to contract EHDAA:480 In humans, it exists distinctly only in the embryonic heart, where it is found between the two venae cavae. In the adult, it is incorporated into the wall of the right atrium to form a smooth part called the sinus venarum, also known as the venarum sinus, which is separated from the rest of the atrium by a ridge of fibres called the crista terminalis. The sinus venosus also forms the SA node and the coronary sinus. In the embryo, the thin walls of the sinus venosus are connected below with the right ventricle, and medially with the left atrium, but are free in the rest of their extent. It receives blood from the vitelline vein, umbilical vein and common cardinal vein. It originally starts as a paired structure but shifts towards associating only with the right atrium as the embryonic heart develops. The left portion shrinks in size and eventually forms the coronary sinus and oblique vein of the left atrium, whereas the right part becomes incorporated into the right atrium to form the sinus venarmu VHOG:0000177 FMA:70303 NCIT:C34300 ZFA:0000154 sinus venosus cordis AAO:0010505 In fish, receives venous blood from the systemic circulation through paired hepatic veins, anterior jugular veins and Cuvierian ducts[PMID:20735616] EMAPA:16237 The sinus venosus is a large cardiac chamber at the inflow tract that receives venous blood from systemic circulation. precedes the atrium on the venous side of the chordate heart. UMLS:C0231084 In the primitive vertebrate heart the four chambers are: 1. Sinus venosus (...) 2. Atrium (...) 3. Ventricle (...) 4. Conus arteriosus (...).[well established][VHOG] conducting system of heart mesoderm-derived structure heart tube cardiac chamber venous sinus presumptive sinus venosus