Development of the Heart
The heart is the first functional organism in a vertebrate embryo and there are 5 different stages to heart development.
The first stage of heart development involves the forming of the primitive heart tube. The primitive heart tube consisits of a single tube which is formed when cardiac precurser cells fuse together. Even at this early stage of development the heart consists of different regions and layers, these regions are:
- cranial
- caudal
- bulbs ordis (which develops to form the aorta and ventricles)
The developing layers of the heart are:
- cardiac jelly
- cardiac mantle layers (which will form the myometrium and epicardium of the heart)
The heart first begins to beat during this stage of heart development, about 22-23 days after conception. This can be detected via vaginal ultra sound.
The second stage of heart development then occurs within 24 hours of the end of the first stage, this stage is known as heart looping. The tube shaped heart concorts into an "S" shape and bends to the right, this is known as d-looping. This process creates a new shape, which provides a primitive region for the ventricles to begin forming. This stage of development is initiated by activated heart-specific proteins.
The third stage of heart development is known as the two-chambered stage, consisting of one atrium and one ventricle. During this stage the cardiac jelly serves to act as a valve inbetween the atrium and the ventricle. The developing heart at this two-chambered stage is said to resemble the heart of a frog.
The fourth stage of heart development begins by the atria dividing. The heart at this point of development is therefore known as the three-chambered heart, consisting of two newly divided atria which sit ontop of the remaining ventricle, the third chamber. This three-chambered heart is said to resemble the heart of a snake or turtle.
The fifth and final stage of heart development occurs 10 weeks after conception. In this stage of development the single ventricle divides to form 2 new ventricles. This leaves the heart complete with all 4 chambers; 2 atria and 2 ventricles, and two large blood vessels to carry blood to and from the heart.