Stem Cells and Cell Differentiation

stem cells: - undifferentiated cells that have the ability to divide and develop into defferentiated (“specialized”) cells

undifferentiated cells with the ability to undergo cell division wilst maintaining their undifferentiated state

differentiation: the process by which cells become specialized

in some organisms a cells role is rigidly determined at a very specific point during development

e.g. round worm

every single cell division during development form zygote (=fertilized eggcell) to adult is a differentaion—>adult has exactly 959 cells with precisely determined functions

in mammals: more flexible pattern, but adult cells do generally reach a point where they are completely differentiated

in animals: differentiation is irreversible under, natural circumstances

mammals have two categories of stem cells: embryonic and adult stem cells

2 types of embryonic stem cells

totipotent stem cells can differentiate into every type of cell in a given organism

only zygote and cells resulting from the first few cell divisions are totipoten

pluripotent stem cells can differentiate into most, but not all cell types of a given organism

2 types of adult stem cells

multipotent stem cells can differentiate into more than one cell type, but are mcuh more limited than pluripotent stem cells

typically stem cells of a given organ or tissue produce only stem cell types unqiue to that organ or tissue

e.s. bone marrow stem cell —> can differentiate into different types of blood cells

unipotent stem cells can differentiate only into one specific type of cell

e.g. germ line cells—>produce gametes

e.g. epidermal stem cells—>produce skin cells