1) (Ch1, p.37) Stem Cells (most info from Wikipedia)
A) What are “stem” cells?
Stem cells have two defining properties—
• Renewal—they can undergo the process of cell division an indefinite number of times (i.e., they don’t age)
• Potency—although they are unspecialized, they can differentiate into specialized cell types. (Each “tissue” in the body consists of specialized cells that perform the functions of that type of tissue.)
B) Describe the different types of stem cells.
There are two different ways of categorizing stem cells— (ST.C. – stem cell)
• By source— ST.C come from two sources:
“Embryonic” ST.C are blastomeres that come from either the morula before differentiation occurs or from the inner layer of cells in the blastocyst.
“Adult” ST.C come from a developed organism (which can be an infant or child) since the body retains stem cells within its various tissues that can be called upon to specialize thereby produce replacement cells.
• By potency—stem cells occur in four different levels of ability to differentiate into other types of cells:
“Totipotent” ST.C can develop into any type of cell that occurs following fertilization. The egg cell (oocyte) becomes a zygote when a sperm cell enters, adds its genetic material, & fertilization occurs. Cell division begins about 30 hours later, producing blastomeres, & the 1st four cell divisions result in 16 identical blastomeres that are all totipotent ST.C.
“Pluripotent” ST.C can develop into any type of cell in a human body. Initially, the collection of blastomeres forms a solid ball. Through the period when the ball contains 12 to 32 cells it is called the “morula.” When 16 cells are present the next cell division produces cells of two different types. One type clusters together in the middle of the morula & the other type forms a layer on the outside. A cavity begins to form in the center of the morula & the ball of blastomeres starts to become a hollow sphere called the...