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In biological terms, human development entails growth from a one-celled zygote to an adult human being. Fertilization occurs when the sperm cell successfully enters and fuses with an egg cell . [2] The genetic material of the sperm and egg then combine to form a single cell called a zygote and the germinal stage of prenatal development commences.
Cell growth refers to an increase in the total mass of a cell, including both cytoplasmic, nuclear and organelle volume. [1] Cell growth occurs when the overall rate of cellular biosynthesis (production of biomolecules or anabolism) is greater than the overall rate of cellular degradation (the destruction of biomolecules via the proteasome, lysosome or autophagy, or catabolism).
This cell potency means that some cells can be removed from the preimplantation embryo and the remaining cells will compensate for their absence. This has allowed the development of a technique known as preimplantation genetic diagnosis , whereby a small number of cells from the preimplantation embryo created by IVF , can be removed by biopsy ...
Tissue growth is the process by which a tissue increases its size. In animals, tissue growth occurs during embryonic development, post-natal growth, and tissue regeneration. The fundamental cellular basis for tissue growth is the process of cell proliferation, which involves both cell growth and cell division occurring in parallel. [1] [2] [3] [4]
Morphogenesis of Drosophila fruit flies is intensively studied in the laboratory. A morphogen is a substance whose non-uniform distribution governs the pattern of tissue development in the process of morphogenesis or pattern formation, one of the core processes of developmental biology, establishing positions of the various specialized cell types within a tissue.
Growth is not uniform in rate and timing across all parts of the body. At birth, head size is already relatively near that of an adult, but the lower parts of the body are much smaller than adult size. Thus during development, the head grows relatively little, while the torso and limbs undergo a great deal of growth. [83]
Cell proliferation requires both cell growth and cell division to occur at the same time, such that the average size of cells remains constant in the population. Cell division can occur without cell growth, producing many progressively smaller cells (as in cleavage of the zygote), while cell growth can occur without cell division to produce a ...
Neuronal precursor cells proliferate in the ventricular zone of the developing neocortex, where the principal neural stem cell is the radial glial cell. The first postmitotic cells must leave the stem cell niche and migrate outward to form the preplate, which is destined to become Cajal–Retzius cells and subplate neurons. These cells do so by ...