Summary A textbook of human embryology could begin at any of several points in the human life cycle. This textbook starts with a discussion of the origin of specialized cells called primordial germ cells (PGCs) . PGCs can be first…
Chapter 1 Clinical Vignette 3. Although most tissues of the body are affected to some extent, the heart is not a primary target tissue of ovarian steroid hormones. Review Questions 1. D 2. E 3. B 4. A mediastinal teratoma,…
After the eighth week of pregnancy, the period of organogenesis (embryonic period) is largely completed, and the fetal period begins. By the end of the embryonic period, almost all the organs are present in a grossly recognizable form. The external…
This chapter follows the development of the heart from a simple tubular structure to the four-chambered organ that can assume the full burden of maintaining independent circulation at birth. Similarly, the pattern of blood vessels is traced from their first…
The urogenital system arises from the intermediate mesoderm of the early embryo (see Figure 6.11 ). Several major themes underlie the development of urinary and genital structures from this common precursor. The first is the interconnectedness of urinary and genital development,…
The initial formation of the digestive system by the lateral folding of the endodermal germ layer into a tube is described in Chapter 6 . From its beginnings as a simple tubular gut, development of the digestive system proceeds on…
Among the earliest vertebrates, the cranial region consisted of two principal components: (1) a chondrocranium, associated with the brain and the major sense organs (nose, eye, ear); and (2) a viscerocranium , a series of branchial (pharyngeal) arches associated with…
The major sense organs arise in large measure from the thickened ectodermal placodes that appear lateral to the neural plate in the early embryo (see Figure 6.10 ). The following descriptions begin with the most cranial placodes and continue to the…
The neural crest, the existence of which has been recognized for more than a century, forms an exceptionally wide range of cell types and structures, including several types of nerves and glia, connective tissue, bones, and pigment cells. Its importance…
Many fundamental developmental processes are involved in the formation of the nervous system. Some of these dominate certain stages of embryogenesis; others occur only at limited times and in restricted locations. The major processes are as follows: 1. induction ,…