Development of sinus venosus
By the day 24 blood starts to circulate through the embryo. Sinus venosus received the venous blood from the right and left sinus horns. Blood enters each sinus horn by vitelline vein, umbilical vein and cardinal vein. The venous system developed so all systemic blood enters the right sinus horn by superior and inferior vena cava.
As a result of shifting blood to the right sinus the left sinus become small sinus. The coronary sinus and left oblique vein of the left atrium in adult heart is the remnant of the left sinus.
As a result of shifting blood to the right sinus the left sinus become small sinus. The coronary sinus and left oblique vein of the left atrium in adult heart is the remnant of the left sinus.
Sadler.T(2005) Langman`s medical embryology .copyright © Wolters Kluwer Health/ Lippincott Williams & Wilkins
The rapid growth of the right sinus horn and the vena cava displace the right primitive atrium wall to the right. Sinus venarum, the smooth right atrium wall formed by the right sinus horn. The opening of the coronary sinus and the superior and inferior vena cava orifices forming right and left venous valves. The two valves join superiorly as transient septum called the septum spurium. The left valve becomes part of septum secundum. The right venous valve forms the valve of inferior vena cava and the valve of the coronary sinus. Crista terminals originate from the right sinus horn separates the smooth part of the right atrium from the pectinate muscles. It fibers carry the impulses from the sinoatrial node to the atrioventricular node.
Sadler.T(2005) Langman`s medical embryology .copyright © Wolters Kluwer Health/ Lippincott Williams & Wilkins
Left atrium remodeling
The left pulmonary vein grow in the primitive left atrium at the beginning of the fourth week. The vein gives right and left branches, which bifurcate to give a total four veins. These veins grow toward the lungs and anastomose with the veins developing in the bronchial buds.
During the fifth week two pulmonary veins penetrate the posterior wall of the primitive left atrium. The smooth wall of the primitive left atrium grows more and the trabeculate wall forming the small left auricle. Other two pulmonary veins penetrate the left atrium wall. This process called Intussusception, A process in which new blood vessel created by the splitting of existing one into two.
During the fifth week two pulmonary veins penetrate the posterior wall of the primitive left atrium. The smooth wall of the primitive left atrium grows more and the trabeculate wall forming the small left auricle. Other two pulmonary veins penetrate the left atrium wall. This process called Intussusception, A process in which new blood vessel created by the splitting of existing one into two.