16 week fetal heart and bronchial airways

3D Model

From a structural and functional perspective, the respiratory system is most logically considered as having conducting and gas exchange components, with the bifurcating airways and accompanying pulmonary arteries (PAs) conducting air and blood to peripheral capillary-lined airspaces for gas exchange. Heart development (also known as cardiogenesis) refers to the prenatal development of the heart. This begins with the formation of two endocardial tubes which merge to form the tubular heart, also called the primitive heart tube. The heart is the first functional organ in vertebrate embryos.

References: 1-netters atlas of human embryology (Updated Edition). 2-larsens human embryology (Sixth Edition). 3-the anatomy of human embryo electron microscope (1st Edition).