EXP๐
Correct Answer - B
Ans. is 'B' i.e., Increase in cell size
Hypertrophy
* Hypertrophy refers to an increase in the size of cells without
increase in the number, resulting in an increase in the size of tissue.
* Hypertrophy involves cell enlargement without cell division.
* So, hypertrophied organ has just larger cells, but no new cells (by
contrast, in hyperplasia there is increase in number of new cells
without increase in size).
* Nuclei in hypertrophied cells have a higher DNA content than in
normal cells because the cells arrest in the cell cycle without
undergoing mitosis.
* Myocardium (heart muscle) and skeletal muscle undergo
hypertrophy.
* The most common stimulus for hypertrophy is increased workload.
Mechanism of hypertrophy
* The increase in cell size is due to synthesis of more structural
proteins.
* The genes that are induced during hypertrophy include those
encoding transcription factors (C-fos, C-jun), growth factors (TGF-(3,
TGF- 1, FGF); and vasoactive agents (a-agonists, endothelin-1,
angiotensin II).
* There may also be a switch of contractile proteins from adult tofetal or neonatal forms, e.g., during myocardial hypertrophy, the a-
myosin heavy chain is replaced by 13-form of the myosin heavy
chain, which leads to decrease myosine ATPase activity and a
slower, more energetically economical contraction.
* In addition, some genes that are expressed only in embryonic life
are re-expressed in hypertrophied myocardium, e.g., in the
embryonic heart, the gene for Atrial natriuratic peptide (ANP) is
expressed in both atrium and ventricle. After birth, ventricular
regulation of the gene is down regulated. Myocardial hypertrophy is
associated with reinduction of ANF gene expression. ANP induces
salt excretion by kidney L blood volume & pressure, decrease work
load.
Why do these changes occur ?
* As already explained, the most common stimulus for myocardial
hypertrophy is increased workload.
* All the above morphological changes that occur in hypertrophy
either increase muscle activity (to handle the increased workload) or
decrease the workload to heart.
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