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Learning Objectives

Learning Objectives

By the end of this chapter the student will be able to:

  • Discuss the development of the heart tube.

  • Describe heart tube looping, chamber formation, and the series of septation that occur for the development of atria, ventricles, and great vessels.

  • Recognize the relationship of heart tubes to the pericardial cavity.

  • Indicate the development of valves and conducting system of the heart.

  • Distinguish the development of the aortic arches and list its derivatives.

  • Indicate the major changes that happened in development of the sinus venosus.

  • List and provide a brief anatomical description of the congenital anomalies of the heart and major blood vessels.

  • Diagram the fetal circulation and recall the changes that occur after birth.


Unlike most other organ systems, the function of the cardiovascular system is critical for embryonic survival. Thus, development of the heart and vascular system begins very early, originating from both the embryonic and extra embryonic mesoderm of the embryo. The heart is the first organ to form during embryogenesis.

Before the age of 3 weeks, the nutrient materials reach the fetus by simple diffusion. After that age, the embryo is no longer able to satisfy its nutritional requirements by diffusion alone, thus the blood vessels begin to develop and nourish the embryo. Blood cells and blood vessels arise from the mesoderm. Blood vessels form in two ways: vasculogenesis, whereby vessels arise from blood islands, and angiogenesis, which entails sprouting from existing vessels (Fig. 1.1).

Figure 1.1

Schematic illustration showing angioblasts in the embryo, which assemble in a primitive network (vasculogenesis) that expands and remodels (angiogenesis). Smooth muscle cells cover the endothelial cells during vascular myogenesis and stabilize vessels during arteriogenesis.

Development of the Heart Tube

The first sign of the development of the heart is the formation of cardiogenic cords. These are canalized to form 2 endocardial tubes (day 19). These tubes develop from condensation of splanchnopleuric mesoderm in the cardiogenic region of the trilaminar germ disc. The cardiogenic region is cranial to the neural plate (Fig. 1.2A).

Figure 1.2

Schematic depiction of a transverse section through an early embryo. A. Depicts the bilateral region where early heart tubes form. B. Shows the bilateral heart tubes subsequently migrating to the midline and fusing to form the linear heart tube. (Reproduced, with permission, from Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J, eds. Harrison’s Principles of Internal Medicine. 18th ed. New York: McGraw-Hill; 2011.)

On day 20, lateral and cephalic folding of the trilaminar germ disc over the course of several days brings the endocardial tubes together and tucks them ventrally in the ...

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