Cyclin-Cdk complexes provide internal control for cell cycle decisions. Cells in multicellular organisms must divide only when appropriate. They must respond to external signals, controls called growth factors.
Some cells respond to growth factors provided by other cells.
• Platelets release platelet-derived growth factor, which diffuses to the surface of
Cells to stimulate wound healing.
• Interleukins are released from one type of blood cell to stimulate division of
another type resulting in body immune system defenses.
• The cells of the kidney make erythropoietin, which stimulates bone marrow
Cells to divide and differentiate into red blood cells.
Cancer cells cycle inappropriately because they either make their own growth factors
Or no longer require them to start cycling.
Some cells respond to growth factors provided by other cells.
• Platelets release platelet-derived growth factor, which diffuses to the surface of
Cells to stimulate wound healing.
• Interleukins are released from one type of blood cell to stimulate division of
another type resulting in body immune system defenses.
• The cells of the kidney make erythropoietin, which stimulates bone marrow
Cells to divide and differentiate into red blood cells.
Cancer cells cycle inappropriately because they either make their own growth factors
Or no longer require them to start cycling.
