organogenesis

Organogenesis is the phase of embryonic development that starts at the end of gastrulation and continues until birth. During organogenesis, the three germ layers formed from gastrulation (the ectoderm, endoderm, and mesoderm) form the tissues and internal organs of the organism. thumb|590x590px|The endoderm of [[vertebrates produces tissue within the lungs, thyroid, and pancreas. The mesoderm aids in the production of cardiac muscle, skeletal muscle, smooth muscle, tissues within the kidneys, and red blood cells. The ectoderm produces tissues within the epidermis and aids in the formation of neurons within the brain, and melanocytes.]]

The cells of each of the three germ layers undergo differentiation, a process where less-specialized cells become more-specialized through the expression of a specific set of genes. Cell differentiation is driven by cell signaling cascades. Differentiation is influenced by extracellular signals such as growth factors that are exchanged to adjacent cells which is called juxtacrine signaling or to neighboring cells over short distances which is called paracrine signaling. Intracellular signals – a cell signaling itself (autocrine signaling) – also play a role in organ formation. These signaling pathways allow for cell rearrangement and ensure that organs form at specific sites within the organism. The organogenesis process can be studied using embryos and organoids.