Head and neck development is distinct from that of the trunk, utilizing region-specific genes, signalling mechanisms and morphogenetic processes. The boundary between the head and trunk is not always clear. The neck is contiguous rostrally with the head but it…
Inner ear The production of a precisely positioned and functionally well-tuned inner ear depends on genetic patterning and a cascade of transcription signals expressed by numerous tissues, including the developing inner ear and its surrounding periotic mesenchyme, the adjacent hindbrain,…
The development of the eye involves a series of inductive interactions between neighbouring tissues in the embryonic head. These are the neurectoderm of the forebrain (which forms the sensory retina and accessory pigmented structures), the surface ectoderm (which forms the…
The entire nervous system and the special sense organs originate from three sources, each derived from specific cell populations of the early epiblast termed neural ectoderm. The first source to be clearly delineated is the neural plate, which gives rise…
The early embryonic circulation is symmetric ( Fig. 13.1 ). It is modified throughout development to produce a functioning heart and fetal circulation that is connected to the placenta, and changes rapidly at birth to accommodate disconnection from the placenta…
Specification of the Body Axes and The Body Plan Embryos can be thought of as being constructed with three orthogonal spatial axes (cephalocaudal, dorsoventral and laterolateral), plus a temporal axis. In mammalian embryos, axes cannot be specified at very early…
Genes in Development Study of secondary oocytes before and after fertilization, and of the selection of embryos for implantation after in vitro fertilization, has identified the range of maternal genes ready for expression to ensure cleavage, morula and blastocyst formation. Embryonic…
Conceptus with a Bilaminar Embryonic Disc At stage 6 the conceptus is composed of the walls of three cavities. The large chorionic cavity is surrounded by a meshwork of trophoblast and developing villi, and lined with extraembryonic mesoblast. The chorion,…
Implantation Implantation involves the initial attachment of the trophoblastic wall of the blastocyst to the endometrial luminal epithelium, stimulating the decidual response. The blastocyst is present within the uterine cavity for some 72 hours prior to implantation, and during this…
Understanding the spatial and temporal developmental processes that take place within an embryo as it develops from a single cell into a recognizable human is the challenge of embryology. The control of these processes resides within the genome; fundamental questions…