Page 69 - Concise Pathology for Exam Preparation ( PDFDrive )

54 SECTION I General Pathology

Totipotent stem cell Pluripotent stem cells Multipotent stem cells

Endoderm derived cells

Mesoderm derived cells
Ectoderm derived cells

Lineage commihed
stem cells
FIGURE 3.1. Embryonic stem cells.

generally referred to as tissue stem cells, eg, liver stem cells which differentiate into he-
patocytes and biliary cells. Tissue stem cells are located within a protected microenviron-
ment called ‘stem cell niches’. Neural tissue stem cells are located in the subventricular
area and dentate gyrus; whereas, skin stem cells are found in the hair follicle bulge and
corneal stem cells are present in the limbus.
The most elaborately studied stem cells are haematopoietic stem cells as well as stro-
mal cells located in the bone marrow. The former are capable of differentiating into
various blood cell lineages, while the latter, also called mesenchymal stem cells, are
multipotent and can differentiate into a variety of stromal cells (chondrocytes, osteo-
cytes, adipocytes and myocytes). Haematopoietic stem cells can be clinically used to
replace depleted marrow cells (following chemotherapy for leukaemia) or provide nor-
mal cells to overcome red cell defects (sickle cell disease). Marrow stromal cells (mesen-
chymal stem cells) can be used clinically to provide stromal cellular scaffolding for tissue
regeneration.

Q. Enumerate the sequence of events involved in reparative response
following an injury.

Ans. Pathways of reparative response following an injury (Flowchart 3.1):

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