Embryological Development of the CVS Quiz

See Development of the Right Atrium. Option A is correct. The early heart tube has an inflow end called the sinus venosus, which receives venous blood through a right and a left sinus horn. During development the venous return shifts to the right side. The left sinus horn recedes and becomes the coronary sinus, which drains the heart's own veins. The enlarged right sinus horn is taken up, or absorbed, into the growing right atrium, and it forms the smooth-walled posterior part of the atrium into which the superior and inferior venae cavae open, the sinus venarum. The rest of the right atrium, including the right atrial appendage, comes from the primitive atrium and keeps a rough, ridged internal surface made by the pectinate muscles (muscle ridges). The two textures are separated by a ridge, the crista terminalis, which marks the line where the two origins meet. A similar absorption happens on the left, where the pulmonary veins are taken up into the left atrium. Memory aid: The right horn is absorbed to make the smooth room the big veins open into.

• Right sinus horn: Absorbed into the right atrium to form the smooth-walled sinus venarum, where the venae cavae open.
• Left sinus horn: Recedes and becomes the coronary sinus.
• Rough part: Comes from the primitive atrium and has pectinate muscles, separated from the smooth part by the crista terminalis.