![]() As a result of these interactions, some genes can be expressed in a given cell, but others cannot. For example, receptors on the cell will bind to specific molecular elements in the ECM, and this binding activates intracellular signal transduction pathways that turn certain genes on or off. Regulation of Cell DifferentiationĬell differentiation is incompletely understood, but it involves the activation or inactivation of certain genes in response to the cell's interactions with its neighboring cells and with its extracellular matrix (ECM). These processes - cell division and differentiation - are tightly regulated by many signals and signal pathways. In addition, most cells in an adult will be differentiated to serve a particular purpose. In a fully grown adult, of course, the rate of cell proliferation is much less, and under normal circumstances, cell division in an adult takes place only when signals indicate the need to grow or to replace cells that have been lost, damaged, or worn out. A fertilized egg divides into two cells, which give rise to four, and those give rise to eight, and then to 16, and 32, and 64, and so on. The need for new cells continues throughout our lives, but it is greatest in early life. Virchow was correct when he concluded that cells arise from others cells, i.e., new cells are born through the division of one cell into two through the process of mitosis. Regulation of Differentiation, Cell Division, and Apoptosis Watch the video below to see a short (2 min 18 sec) explanation of hematopoetic stem cells and somatic stem cells in the intestine. Whenever stem cells are called upon to generate a particular type of cell, they undergo an asymmetric cell division in which one of the daughter cells has a finite capacity for cell division and begins to differentiate, whereas the other daughter cell remains a stem cell with unlimited proliferative ability. Bone marrow stromal stem cells (also called mesenchymal stem cells, or skeletal stem cells) can generate bone, cartilage, and fat cells. In the adult, however, the replacement of shed or worn out cells takes place by division of somatic stem cells (also called adult stem cells), which are not fully differentiated, but can give rise to only a limited array of cells.įor example, hematopoetic stem cells in the bone marrow can divide and give rise to progenitor cells that can differentiate into cellular element of blood and the immune system, including red blood cells, lymphocytes, neutrophils, eosinophils, basophils, monocytes, and platelets. In contrast, the cells in the early morula stage of an embryo (shown below to the left) consists of cells that are totipotent - they have the capacity to divide and give rise to any of the specialized cells in the body. Muscle cells are elongated and contain and abundance of contractile proteins, whereas pancreatic cells are specialized for secretion of digestive enzymes or, in the case of pancreatic beta cells, for the synthesis of insulin. In a fully grown adult, of course, the rate of cell proliferation is much less, and under normal circumstances, cell division in an adult takes place only when signals indicate the need to replace cells that have been lost, damaged, or worn out.Īnother big difference between cells in a growing embryo and cells in an adult is that most of an adult's cells are differentiated - they have become specialized in structure and function. ![]() Normal Cell Division: Growth & Replacement
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