Define embryonic stem cells. Explain the pros and cons of Embryonic Stem Cells

Embryonic stem cells are pluripotent stem cells derived from the inner cell mass of a blastocyst, an early-stage pre-implantation embryo. Human embryos reach the blastocyst stage 4–5 days post fertilization, at which time they consist of 50–150 cells.

Explanation:

 Adult Stem Cells  

Embryonic Stem Cells      

Induced Pluripotent Stem Cells      

Pros

Trans differentiate and and reprogramming of these cells is possible but is not well studied

Thought to be less likely to be rejected if used in transplants

Success has already been demonstrated in various clinical applications  

Can maintain and grow for 1 year or more in culture

Established protocols for maintenance in culture

ESCs are pluripotent cells that can generate most cell types

By studying ESCs, more can be learned about the process of development

Abundant somatic cells of donor can be used

Issues of histocompatibility with donor/recipient transplants can be avoided

Very useful for drug development and developmental studies

Information learned from the “reprogramming” process may be transferable for in vivo therapies to reprogram damaged or diseased cells/tissues  

Cons

Limitations on ASC ability to differentiate are still uncertain; currently thought to be multi or unipotent.

Cannot be grown for long periods of time in culture

Usually a very small number in each tissue making them difficult to find and purify

Currently there is no technology available to generate large quantities of stem cells in culture

Process to generate ESC lines is inefficient

Unsure whether they would be rejected if used in transplants.

Therapies using ESC avenues are largely new and much more research and testing is needed

If used directly from the ESC undifferentiated culture prep for tissue transplants, they can cause tumors (teratomas) or cancer development    

Methods for ensured reproducibility and maintenance, as differentiated tissues are not certain.

Viruses are currently used to introduce embryonic genes and has been shown to cause cancers in mouse studies    

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answer : haversian

[explanation: -(compact bone is organized as parallel columns, known as haversian systems, which run lengthwise down the axis of long bones. these columns are composed of lamellae, concentric rings of bone, surrounding a central channel, or haversian canal, that contains the nerves, blood vessels, and lymphatic system of the bone)]