Stem cells

• What is a stem cell?

  An undifferentiated cell that can specialize into any cell within an organism
• Totipotency - the ability to form all cell types in the body. Including extra eukaryotic cells (placenta, umbilical cord)

  Pluripotency - Capable of differentiating into all cells excluding extra eukaryotic cells

  Multipotent - Capable of differentiating into a few cell types
• Erythrocytes are red blood cells, the main function of which is the transport of oxygen around the body and the transport of carbon dioxide.
• Erythrocytes lack a nucleus, meaning they cannot divide, and new erythrocytes are constantly being formed from bone marrow stem cells in order to maintain the red blood cell count in the blood.
• During erythropoiesis, changes occur that adapt the structure of the original stem cell to enable it to function as an erythrocyte.
• The changing of the cell into a biconcave shape has a larger surface area, allowing for more oxygen to be absorbed through the cell surface.
• The building up of haemoglobin in the cytoplasm is the pigment that binds with oxygen and only releases it when oxygen concentrations decrease below a certain level.
• The ejection of the nucleus and other organelles including mitochondria, endoplasmic reticulum and Golgi apparatus creates more room in the cytoplasm for haemoglobin, increasing the oxygen-carrying capacity.
• An elastic membrane allows erythrocytes to change shape and therefore squeeze through narrow capillaries.
• The same stem cells that form erythrocytes also form neutrophils, a type of white blood cell.
• As the stem cells differentiate into neutrophils, indentations form in the nucleus, giving it a lobed structure, and granules accumulate, these are lysosomes that contain hydrolytic enzymes.
• Neutrophils are the first white blood cells to arrive at an infection site on or in the body.
• Neutrophils exit the blood through the tiny gaps in capillary walls and collect around foreign bodies, such as pathogens.
• Neutrophils destroy these by engulfing them (phagocytosis) and digesting them using their hydrolytic enzymes.
• Neutrophils contain many lysosomes that contain digestive enzymes that destroy invading cells.
• Table

  A) Totipotent

  
• Ethical consideration: