Which are composed of peptides and promote the

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which are composed of peptides and promote the differentiation and mitosis of certain tissues - If two tissues both induce further cellular differentiation in each other, this is referred to as reciprocal development - It is important to note that one of the main methods of signaling occurs through the use of concentration gradients - For example unique combinations morphogen exposure throughout an organism is what will actually induce the differentiation of different cell types - Some common morphogens include include transforming growth factor beta ( TGF - β ) , sonic hedgehog (Shh), and epidermal growth factors (EGF) - Mechanism of Development: Cell Migration, Death, and Regeneration - Cell Migration: - Some cells may need to disconnect from their adjacent structures and migrate to their correct locations - Cell Death: - Apoptosis means programmed cell death and occurs at various times during the developmental process - During the process of apoptosis the cell undergoes changes in morphology and divides into many self-contained protrusions called apoptotic blebs - These apoptotic blebs can be broken apart into apoptotic bodies , which can then be digested by other cells and recycled for future use - Necrosis on the other hand is cellular death as a result of injury. Here internal substances can be leaked, causing irritation and even an immune response - Cell Regeneration: - Regeneration capacity , or the ability of an organism to regrow certain parts of the body, varies from species to species - Species that undergo complete regeneration can replace damaged or lost tissues with identical tissues - Species that undergo incomplete regeneration can cannot replace damaged or lost tissues with identical tissues
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- Humans exhibit incomplete regeneration in response to injury. However in humans the regenerative capacity (RC) varies by the tissue type - The liver has a high RC , the kidneys have a moderate RC , and the heart has a poor RC - Mechanism of Development: Senescence and Aging: - As organisms age, changes occur in both molecular and cellular structures. This results in the disruption of metabolism, and eventually, death of the organism - Sensence , biological aging, can occur at the cellular level and the organism level as these changes accumulate - As the cellular level, sensence results in the failure of cells to divide normally after 50 divisions in vitro , which is due to the shortening of telomeres , ends of chromosomes - Telomeres reduce the loss of genetic information from the ends of chromosomes and help prevent the DNA from unraveling - Telomeres are difficult to replicate, so they shorten during each round of DNA synthesis, eventually becoming too short, preventing the cell from dividing - There is an enzyme called telomerase , which actually replicates telomeres and is typically found in germ cells, fetal cells, and tumor cells - At the organism level, sensence represents changes in the bodies ability to respond to the changing environment - Aging is complex and often involves not only cellular sensence but as well as an accumulation of environmental and chemical insults overtime 3.3: Fetal Circulation: -
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