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…
In this chapter, the types and functions of skin in different parts of the body are described first, followed by the microstructure of the epidermis and dermis, and the appendages of skin, including the pilosebaceous units, sweat glands and nails.…
The cardiovascular system carries blood from the heart to all parts of the body through a series of tubes, all but the smallest of which are muscular. The muscle in these tubes is of two types: smooth muscle is characteristic…
The musculoskeletal system comprises the specialized connective tissues of the articulated bony skeleton (including bone, cartilage and tendon) and the skeletal muscles that act across the articulations. Connective tissues are characterized by a sparse population of cells within an abundant…
Blood is an opaque fluid with a viscosity greater than that of water (mean relative viscosity 4.75 at 18 °C), and a specific gravity of 1.06 at 15 °C. It is bright red when oxygenated, as in the systemic arteries,…
The nervous system has two major divisions, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain, spinal cord, optic nerve and retina, and contains the majority of neuronal cell bodies. The PNS…