Truncus Arteriosus and Bulbus Cordis

TRUNCUS ARTERIOSUS AND BULBUS CORDIS Potentially confusing terms have been used to describe these structures; some consider these two outflow chambers to be a single structure, sometimes referred to as the bulbus cordis, sometimes as the truncus arteriosus. Another term used for the interface between the two is the “conus cordis.” Word combinations are also used, such as “truncoconal” to describe septal swellings Some textbooks divide it the into In all my lectures , I would use the terms bulbus cordis truncus arteriosus Distal 1/3 Truncus arteriosus Middle 1/3 conus Proximal 1/3 Two opposing ridges are developed in the walls of the truncus arteriosus Truncal ridges And in the walls of bulbus cordis (bulbar ridges) ridges are derived mainly from the neural crest A-in the lower part of the truncus the ridges are right and left as traced upwards B- in the middle of the truncus the right ridge becomes anterior while the left ridge becomes posterior C- in the upper part of the truncus the anterior ridge becomes left while the posterior ridge becomes right R A P L A L A P B R A L P R C 2- When the two ridges fuse together a spiral septum is formed which is called the Spiral aortico-pulmonary septum The bulbar and truncal ridges undergo 180-degree spiraling results in the formation of a spiral aorticopulmonary septum when the ridges fuse This septum the truncus arteriosus into two arterial channels 5 The Ascending AORTA and the PULMONARY TRUNK The distal bulbar septum 1- Four endocardinal cushions ( one anterior, one posterior, and two lateral right and left) are developed in the distal part of the bulbus cordis. 2- A ridge is developed in the middle of each of the two lateral cushions. It should be noted that the development of these ridges will divide each of the lateral cushions into two 3-These ridges will fuse to form a complete septum called the distal bulbar septum. Posterior 4- The distal bulbar septum will divide the cranial end of bulbus cordis into into two orifices: The pulmonary orifice anteriorly and The aortic orifice posteriorly Anterior 5- The distal bulbar septum will also divide the pulmonary and aortic orifices three cushions. These cushions form the cusps 6- The cusps of the pulmonary valve are one anterior and two posterior but as a result of rotation of the vessels the two cusps become anterior and one posterior 7- The cusps of the aortic valve are two anterior and one posterior but as a result of rotation of the vessels one cusp becomes anterior and two posterior. posterior NO rotation 45 degrees rotation to the left two anterior and one posterior anterior 10 Because of the spiraling of the aorticopulmonary septum, the pulmonary trunk twists around the ascending aorta one cusp becomes anterior and two posterior. The cusps of the pulmonary and aortic valves are named according to their position in the fetus before the heart has rotated to the left. This, unfortunately, causes a great deal of unnecessary confusion It is difficult to name the cusps and corresponding sinuses of the pulmonary valve and trunk precisely according to the coordinates of the body, because the valvular orifice is obliquely positioned. The official nomenclature (Terminologia Anatomica 1998) refers to an anterior, a posterior and a septal cusp, based on their position in the fetus. The position changes with development and in the adult there is one anterior semilunar cusp, and right and left semilunar cusps The proximal bulbar septum develops as two ridges which fuse together they share in closing the interventricular foramen And they divide the mid portion of the bulbus cordis into the infundibulum and the vestibule The bulbus cordis is incorporated into the walls of the definitive ventricles in several ways In the right ventricle, the bulbus cordis is represented by the conus arteriosus (infundibulum), which gives origin to the pulmonary trunk In the left ventricle, the bulbus cordis forms the walls of the aortic vestibule, the part of the ventricular cavity just inferior to the aortic valve. The Left horn At 10 weeks the left common cardinal vein is obliterated The left sinus horn rapidly loses its importance all that remains of the left sinus horn is The oblique vein of the left atrium and the coronary sinus Thus, what has been left from the sinus venosus is the right horn the sinus venosus (the right horn) and the primordial atrium of the cardiac tube communicate with each other through the sinuatrial orifice Remember • The atrium is made of one chamber that has began to divided • Initially, the sinus venosus opens into the center of the posterior wall of the primordial atrium  By the end of the fourth week, the right sinual horn becomes larger than the left sinual horn  As this occurs the sinuatrial orifice moves to the right and opens in the part of the primordial atrium that will become the adult right atrium  As the right sinuatrial horn enlarges, it receives all the blood from the head and neck through the SVC, and from the placenta and caudal regions of the body through the IVC At first communication between the sinus and the atrium is wide. Soon, however, the entrance of the sinus shifts to the right This shift is caused primarily by left-to-right shunts of blood, which occur in the venous system during the fourth and fifth weeks of development The right horn of the sinus Venosus is incorporated into the right atrium to form the smooth-walled part of the right atrium Its entrance, the sinuatrial orifice, is flanked on each side by a valvular fold the right and left venous valves Dorso cranially the valves fuse, forming a ridge known as the septum spurium The right sinuatrial valve The cranial part of the right sinuatrial valve of the right venous valve becomes The crista terminalis The inferior portion develops into two parts: (a) The valve of the inferior vena cava (b) (b) The valve of the coronary sinus The left venous valve The left venous valve and the septum spurium fuse with the developing atrial septum  The right horn of the sinus venosus is incorporated into the wall of the right atrium becomes the smooth part of the internal wall of the right atrium— THE SINUS VENARUM Primordial Pulmonary Vein and Formation of Left Atrium  Most of the wall of the left atrium is smooth because it is formed by the incorporation of the primordial pulmonary vein  This vein develops as an outgrowth of the dorsal atrial wall, just to the left of the septum primum.  As the atrium expands, the primordial pulmonary vein and its main branches are gradually incorporated into the wall of the left atrium  As a result, four pulmonary veins are formed  The small left auricle is derived from the primordial atrium; its internal surface has a rough, trabeculated appearance