4- Stem cells

What is a stem cell?

An undifferentiated cell which is capable of becoming many different cell types in the organism

What are the 3 types of stem cell?

• Totipotent- first 8 cells after 3 divisions, can differentiate into any cell of the body and placenta

• Pluripotent- ‘embryonic’ stem cells- inner cells of the blastocyst, can make most but not all types of cell of the adult

• Multipotent- can form more they one cell type, these are present in the adult e.g. bone marrow, also obtained from the umbilical cord

Formation of blood cells from bone marrow

Xylem and phloem

• Xylem and phloem develops from meristem

• In plants, the only cells which undergo mitosis are meristem cells (cambium)

• Xylem:

  • Lignin is deposited in cell walls which reinforces, waterproofs and kills cells

  • The ends of the cell break dew on so that xylem forms continuous columns with wide lumens to carry water and dissolved nutrients

• Phloem, sieve tubes and companion cells:

  • Sieve tubes lose most of the organelles and sieve plates develop between them

  • Companion cells retain their organelles and continue metabolic functions to provide ATP for active loading

Sources of stem cells: embryonic stem cells

Sources of stem cells: umbilical cord stem cells

• Taken after birth and stored by freezing

• 15 cm sample taken

• Wharton’s jelly contains MSCs

• Artery used in extraction of cord blood stem cells

• Vein used in extraction of cord blood stem cells

Sources of stem cells: adult stem cells

• Found in blood, brain, muscle, bone, adipose, tissue and skin

Sources of stem cells: Induced pluripotent stem cells

Creation:

• Isolate cells from patient (skin/ fibroblasts), grow in a dish

• Treat cells with reprogramming factors

• Wait a few weeks

• Pluripotent stem cells

• Change culture conditions to stimulate cells to differentiate into a variety of cell types: blood cells, gut cells, cardiac muscle cells

Ethical issues

• Adult stem cells have been used for many years in bone marrow transplants

• Embryos from IVF are discarded

• Embryos created in as lab for stem cells

• Religious objections (life begins at conception)

• Embryo can’t give consent for research

Uses of stem cells

• Bone marrow transplants

• Drug research

• Developmental biology

• Repair or replacement of damaged tissues

Bone marrow transplants

• Can be used to treat sickle cell anemia and leukaemia, sever combined immunodeficiency (SCID)

• Can be used to restore the blood system after treatment for some types of cancer

Drug research

• can use stem cells to develop tissues

• New drugs can be tested directly on tissue instead of animals

Developmental biology

• Develop better understanding of how multicellular organisms develop and grow

• Can study cell differentiation

• Can study effect of disease on cell types

• Can research if the capacity of embryos to grow and have tissues repair can be extended into later life

Repair or replacement of damaged tissues

• Treating diabetic mice with programmed iPS cells to become pancreatic beta cells which produce insulin

• Bone marrow stem cells can be made to develop into I’ve cells

• Stem cells could be used to treat Alzheimer’s and Parkinson’s

• Regenerative medicine

• Arthritis, stroke, burns, vision and hearing loss