CELL DEGENERATION

 

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.