CELL DEGENERATION
Cell degeneration is a process characterized by damage of the cells at cytoplasmic level, without affecting the nucleus. Degeneration may result in functional impairment or deterioration of a tissue or an organ. It is common in metabolically active organ like liver, heart and kidney. Degenerative changes are reversible in most of the cells.
Causes for Cell
Degeneration
Common causes for cell degeneration:
1. Atrophy, hypertrophy, hyperplasia
and/or dysplasia
of cell 2. Fluid accumulation in the
cell
3. Fat infiltration
into the cell
4. Calcification of
cellular organelles.
CELL AGING
Cell aging is the gradual structural
and functional changes in the cells that occur over the passage of time. It is
now suggested that cell aging is due to damage of cellular substances
like DNA, RNA, proteins and lipids, etc. when the cell becomes old. When more cellular
substances are damaged, the cellular function decreases. This causes deterioration
of tissues, organs or parts of the body. Finally, the health of the body starts
declining and this leads to death. So, the cell aging determines the health and
life span of the body.
STEM CELLS
Stem cells are the primary cells
capable of reforming themselves through mitotic division and differentiating into
specialized cells. These cells serve as repair system of the body and are
present in all multicellular organisms.
TYPES OF STEM CELLS
Stem cells are of two types:
1. Embryonic stem cells derived from
embryo
2. Adult stem cells derived from
adults.
1. Embryonic Stem
Cells
Embryonic stem cells are derived from
the inner cell mass of a blastocyst which is an early stage of embryo. It takes
about 4 to 5 days after fertilization to reach the blastocyst stage and it has
about 30 to 50 cells. Embryonic stem cells have two important qualities:
i. Self-renewal capacity
ii. Pluripotent nature, i.e. these
cells are capable of differentiating into all types of cells in ectodermal,
endodermal and mesodermal layers.
Because of these two qualities, the
embryonic stem cells can be used therapeutically for regeneration or
replacement of diseased or destroyed
tissues. In fact, embryonic pluripotent stem cells are now cultured and lot of
research is going on to explore the possibility of using these cells in curing
the disorders like diabetes mellitus by cell replacement technique. But,
ethical issues arise because the embryo has to be destroyed to collect the stem
cells.
Stem cells from
umbilical cord blood
Stem cells in umbilical cord blood are
collected from the placenta or umbilical cord. Use of these stem cells for
research and therapeutic purposes does not create any ethical issue because it
does not endanger the life of the fetus or newborn. Because of vitality and
easy availability, the umbilical cord blood stem cells are becoming a potent
resource for transplant therapies. Nowadays, these stem cells are used to treat
about 70 diseases and are used in many transplants worldwide.
2. Adult Stem
Cells
Embryonic stem cells do not disappear
after birth. But remain in the body as adult stem cells and play a role in
repair of damaged tissues. However, their number becomes less. Adult stem cells
are the undifferentiated multipotent progenitor cells found in growing children
and adults. These are also known as somatic stem cells and are found
everywhere in the body. These cells are capable of dividing and reforming the
dying cells and regenerating the damaged tissues. So, these stem cells can also
be used for research and therapeutic purposes. Adult stem cells are collected
from bone marrow.
Two types of stem cells are present in
bone marrow:
i. Hemopoietic stem cells, which give rise to
blood
cells
ii. Bone marrow stromal cells, which can
differentiate into cardiac and skeletal muscle cells.
ADVANTAGES OF STEM
CELLS
Adult stem cells from bone marrow are
used in bone marrow transplant to treat leukemia and other blood
disorders since 30 years. Recently, it
is known that these stem cells can develop into nerve cells, liver cells, skeletal
muscle cells and cardiac muscle cells. Recent discoveries also reveal that the
stem cells
are present in several tissues which
include blood, blood vessels, skeletal muscle, liver, skin and brain. It is
also found that these cells are capable of differentiating into multiple cell
types. So, the cell-based therapy using stem cells may be possible to treat
many diseases such as heart diseases, diabetes, Parkinson’s
disease,
Alzheimer’s dis e a se, spinal cord injury, stroke and rheumatoid
arthritis.
DEFINITION AND CLASSIFICATION
Cell junction is the connection
between the neighboring cells or the contact between the cell and extracellular
matrix. It is also called membrane junction.
Cell junctions are
classified into three types:
1. Occluding junctions
2. Communicating junctions
3. Anchoring junctions.
OCCLUDING JUNCTIONS
Cell junctions which
prevent intercellular exchange of substances are called occluding junctions,
i.e. these junctions prevent the movement of ions and molecules from one cell to
another cell. Tight junctions belong to this category.
TIGHT JUNCTION
Tight junction is the
intercellular occluding junction that prevents the passage of large molecules.
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