Germ layers

Myopathies have been described in several sporadic cases with lactic acidosis, cytochrome oxidase (COX)-positive RRF in muscle, and isolated complex I deficiency, and have been attributed to various pathogenic mutations in ND genes. The sporadic nature of these myopathies suggests that the ND mutations are de novo, arising spontaneously in myogenic stem cells after germ-layer differentiation (somatic mutations) [14]. 

Stem cells are present in the earliest stage of embryonic development the blastocyst. Embryonic stem cells are pluripotent, meaning they are capable of generating any terminally differentiated cell in the human body that is derived from any one of the three embryonic germ layers ectoderm, mesoderm, or endoderm [8]. All the body s organs arise through a series of divisions and differentiations from the original embryonic stem cells that form the blastocyst [3]. 

Itskovitz-Eldor J, Schuldiner M, Karsenti D, Eden A, Yanuka O, Amit M, Soreq H, Benvenisty N. Differentiation of human embryonic stem cells into embryoid bodies compromising the three embryonic germ layers. Mo/MeJ 2000 6 88-95. 

The appearance of the embryonic germ layers, the ectoderm, endoderm, and mesoderm, is the next stage, with the gross segregation of cells into groups. Damage at this stage may be associated with specific effects. 

Entoderm The inner germ layer in developing animals which gives rise to the epithelium of the digestive tract, pharynx, and respiratory tract. 

Mesoderm The middle germ layer of animal embryos which in later development gives rise to the muscles, connective and supporting tissues, and blood and blood vessels. 

Triploblastic Having three primary germ layers. 

Ectoderm The outer germ layer of the animal embryo which in development gives rise to epidermis, epithelium of various organs, and to the nervous system. 

Segment I the early embryonic development (fertilized egg or zygote, prior to implantation and prior to formation of the three primary germ layers),... 

The blastocyst is a hollow, fluid-filled ball of approximately 1000 cells. The cells that form the outer layer are referred to as trophoblasts and will ultimately develop as extraembryonic tissues (e.g., placenta), while the cells of the inner cell mass are omnipotent (i.e., stem cells) and form the embryo. Depending on the species, the blastocyst arrives at the uterus within 5-10 days of fertilization, whereupon it hatches from the zona pellucida and implants into the uterine wall, which has been preconditioned by ovarian-derived steroid hormones (see Chapter 33). Shortly after implantation, the inner cell mass undergoes gastrulation to form a trilaminar embryo composed of three primary germ layers, the ectoderm, mesoderm, and endoderm. 

Ectoderm is the outermost layer of the three germ layers in the animal embryo. It develops mainly into the epidermis, the skin and the neuronal tissues. 

Endoderm is the innermost germ layer in the animal embryo which develops into the lining of the gut finm pharynx to rectum, including the liver, the pancreas and related organs. 

Mesoderm the middle of the three primary germ layers of an animal embryo. It is the source of bone, muscle, connective tissue and other structures. 

The nonstarch lipids in the aleurone, subaleurone, and germ layers were 86-91% neutral lipids, 2-5% glycohpids, and 7-9% phospholipids, although these are variable because of different milling degrees (11). The fatty acid composition of... 

Neural tissue is derived from wliich germ layer ... 

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