Development of Heart

Question 1

what forms the endocardium?

Answer 1

paired vitelline vessels ventral to embryonic pharynx fuse to form an endocardium tube = which develops into endocardium

Question 2

what forms the myoepicardium?

Answer 2

splanchnic mesoderm surrounds endocardium and becomes myoepicardium

Question 3

What forms the atria and what forms the ventricle?

Answer 3

• heart tube elongated and forms C-shaped loop which becomes ventricle
• second loop is presumptive atrium
• area where vitelline and cardinal veins enter the heart expands into sinus venous and external constrictions develop which delineate atrium, ventricle and truncus arteriosus
• this is accompanied by complex elongation and twisting

Question 4

What are the three stages of further heart development?

Answer 4

• > sinus venous is absorbed into presumptive right atrium as sinus venarum and coronary sinus. Pulmonary veins are segregated so that they open into presumptive left atrium
• > atrioventricular canal develops a constriction = endocardium cushions between atrium and ventricle. These contribute to fibrous skeleton of heart and support AV vavles
• > partitioning of truncus arteriosus by truncus septum forms aorta and pulmonary trunk

Question 5

What are the two septae to develop?

Answer 5

• two septae develop in atria and ventricles dividing heart into left and right sides
• septum I develops from dorsal wall of atrium in median plane + expands ventrally in horseshoe shape creating channel, foramen I, for passage of blood from right atrium directly to left atrium
  
  • foramen I gradullay closes, and foramen H develops dorsocaudal-cranially in septum, maintaining communication between right and left atria
• septum H develops to right septum I with one part developing parallel to septum I = christa dividens and other part extending along ventromedial surface of atrium = christa interveniens
  = foramen ovale is space between septae I and II