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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]
The development of plants involves similar processes to that of animals. However, plant cells are mostly immotile so morphogenesis is achieved by differential growth, without cell movements. Also, the inductive signals and the genes involved are different from those that control animal development.
In animals, the process involves a sperm fusing with an ovum, which eventually leads to the development of an embryo. Depending on the animal species, the process can occur within the body of the female in internal fertilization, or outside in the case of external fertilization. The fertilized egg cell is known as the zygote. [2] [5]
Live cells were stained with DiI (red) or DiO (green). The red cells were genetically altered and express higher levels of E-cadherin than the green cells. The mixed culture forms large multi-cellular aggregates. At a tissue level, ignoring the means of control, morphogenesis arises because of cellular proliferation and motility. [9]
Individual cells within a morphogenetic field in an embryo are flexible: thus, cells in a cardiac field can be redirected via cell-to-cell signaling to replace damaged or missing cells. [6] The Imaginal disc in larvae is an example of a discrete morphogenetic field region of cells in an insect embryo. [7]
Regeneration in biology is the process of renewal, restoration, and tissue growth that makes genomes, cells, organisms, and ecosystems resilient to natural fluctuations or events that cause disturbance or damage. [1] Every species is capable of regeneration, from bacteria to humans.
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.
Animal tissues are grouped into four basic types: connective, muscle, nervous, and epithelial. [4] Collections of tissues joined in units to serve a common function compose organs. While most animals can generally be considered to contain the four tissue types, the manifestation of these tissues can differ depending on the type of organism.