Development of the Respiratory Tree The development of the respiratory system can be conceptualized as the growth of six intertwined trees: the bronchial tree of conducting airways and terminal gas-exchanging sacs; the systemic arterial and venous trees that perfuse and…
Overarching concepts The limbs develop from permissive and instructive interactions between epithelium and mesenchyme at specified times and places along the lateral body wall. The outgrowths are initiated at defined positions along the embryonic axis where these cell lines continue…
Vertebrae and their alternating intervertebral discs are one of the main manifestations of body segmentation or metamerism. A chain of segments arranged in sequence allows the overall structure to bend when it is moved by the associated muscles. The original…
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…