Question

a short note on development of heart in chick

Answer 1

1. Introduction to Development of Heart in Chick:

Two types of heart are present in the ver­tebrate groups – lymph hearts and the heart of the arteriovenous system. The latter one is a centralized, well-muscularized organ, pre­sent ventral to the oesophageal segment of the gut. Its function is to receive blood from the veins and to propel it forward via the arteries.

Fundamentally the embryonic heart is composed of the following structures:

i. A thin walled sinus venosus, that con­nects with a series of converging veins.

ii. The atrium lying anterior to the sinus.

iii. The ventricle lying anterior to the atrium.

iv. The bulbus cordis that contains a series of diverging arteries.

The bulbus cordis (to some extent) and the ventricle of the embryonic heart forms the main propulsive mechanism of the heart, while the atrium and sinus comprises the blood receiving areas.

While the above changes have been tak­ing place, the closure of the foregut at the level of the heart was also progressing. As a result the paired endocardial tubes were brought progressively close together. The two endocardial tubes finally fuse into a single tube lying in the midline [Fig. 5.74(c) and (d)].

At the time of fusion of the two primor­dia the tubes unite sequentially starting from the union of the truncus arteriosus, followed by the ventricle, atrium and finally the sinus venosus. Thus, in a chick embryo of 30 hours of incubation, fusion of the trunco-ventricular region is complete, while the atrium and sinus venosus are still double.

The entire fusion gets completed at about the 48 hour (Figs. 5.75). If the cardia primordia are pre­vented from fusing by either chemical or sur­gical means, then separate independently beating hearts are formed on each side of the body.

While the two endocardial tubes were fusing into one, the epimyocardial layers were bending towards the midline to form a single tube around the endocardium. Ventral to the endocardial tubes the epimyocardial layers of opposite sides come into contact with each other.

At the region of contact the limbs of the mesodermal folds next to the endo­cardium fuse with each other to form ventral mesocardium [Fig. 5.74(c) The ventral mesentery ruptures and disappears almost as rapidly as it is formed. Thus, the original right and left coelomic chambers become con­fluent to form a median unpaired pericardial cavity.