even after the embryo has grown into an adult many of the body's cells continually die of and need to be replaced for example billion to red blood cells need to be replaced each day this is the work of stem cells known as matter poetic stem cells which are located in the bone marrow residind in a complex cellular environment the home at a poetic stem cell is able to generate precursors to every type a blood cell and indeed the stem cells have been used by positions for decades to replenish patient's blood supplies following rafiation treatment for cancer the stepwise differentiation have a stem cells progeny depends on combinations genetic and environmental factors that gradually stir the cells into following a specific lineage this process involves different sets of stimulating factors operating in the cell environment at its surface membrane and within its nucleus each step down the path draws it closer to becoming a functional red blood cell entering the bloodstream the lining of the small intestine turns over even faster than the blood at the microscopic level this epithelial surface consists a billion to projections called bill I with stem cell containing areas known as scripts near their bases the intestina crypt contain slowly dividing stem cells that maintain their own numbers while also producing rapidly dividing progenitors these transit amplifying cells churn out all the differentiated cell types needed to migrate upwards and replace older cells as their shared from the tips at the bill I.
this constant self-renewal by stem cell is a feature of many of the body's systems including skin here and bone