The diagrams on this page show the general pattern of blood flow in the two and a half day chick embryo. Note that the view of the aortic arches in the following diagrams is a "cut-away" view. The mesenchymal tissues of the surrounding pharyngeal arches have been left out in order to show the aortic arches and the endodermal lining of the wall of the pharynx (foregut). Recall that aortic arches pass through the pharyngeal arches which are bars of tissue making up the walls of the pharynx. Also note that in these pictures, some details have been omitted for clarity: the gut is incomplete posteriorly and the dorsal aortae are cut off before they enter the head. In the chick embryo there are arteries delivering blood throughout the body (including the head!) and veins returning it to the heart. The circulation circuit shown does not include any of these smaller arteries and veins.
The heart is shown as a loop here, as this is how it looks at this stage of development (this diagram is somewhere between 48 and 72 hours of incubation). The heart develops from a straight tube which then loops in the middle. The upper bend in the loop forms the atria and the lower bend, the ventricles. This can be confusing, as right now, there is only one atrium and one ventricle. Eventually, however, septae will grow to divide the atrium into two atria and the ventricle into two ventricles. Soon after, valves will form, which will physically divide the atrial and ventricular pair. This leads to the basic four chambered heart with which we are familiar.
|To the right we see the entire chick embryo (dashed outline) and the blood vessels, heart and foregut within. The red arrows indicate the general direction of blood flow which makes up the circulation. Note that there is no blood flow shown to the head and to the rest of the body. Arteries and veins for this flow do exist however, they were omitted for clarity. Also, the dashed red arrows show the flow of blood between the vitelline arteries and veins, but indicate that most of the extraembryonic circulation has been omitted from this diagram.|
|Here, the image to the right shows some of the details of the heart and aortic arches. Note how the heart is actually a straight tube with a loop in it at this stage. The atria and ventricles will develop (as described above) from the areas shown.|
|In this final image, we see a close-up of the chick embryo's aortic arches. Note how the arches are paired and numbered cranially to caudally. The pharyngeal clefts are out-pocketings of the foregut which are in communication with the exterior (the gut epithelium and external ectoderm have fused, allowing the foregut to open to the exterior). The clefts are numbered in the same way as the aortic arches (note that the pharyngeal cleft is caudal to the aortic arch of the same number). In the living embryo, there is tissue suspending and surrounding each aortic arch. These bands of tissue which the aortic arches run through are called the pharyngeal arches.|
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Department of Integrative Biology, University of Guelph, Guelph, Ontario,
Canada N1G 2W1.
Page revised: May 2012