Ans. is 'c' i.e., Increase in cell size Hyperophy o Hyperophy refers to an increase in the size of cells without increase in the number, resulting in an increase in the size of tissue. o Hyperophy involves cell enlargement without cell division. o So, hyperophied 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). o Nuclei in hyperophied cells have a higher DNA content than in normal cells because the cells arrest in the cell cycle without undergoing mitosis. o Myocardium (hea muscle) and skeletal muscle undergo hyperophy. o The most common stimulus for hyperophy is increased workload. Mechanism of hyperophy o The increase in cell size is due to synthesis of more structural proteins. o The genes that are induced during hyperophy 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). o There may also be a switch of contractile proteins from adult to fetal or neonatal forms, e.g., during myocardial hyperophy, 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. o In addition, some genes that are expressed only in embryonic life are re-expressed in hyperophied myocardium, e.g., in the embryonic hea, the gene for Atrial natriuratic peptide (ANP) is expressed in both atrium and ventricle. After bih, ventricular regulation of the gene is down regulated. Myocardial hyperophy 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 ? o As already explained, the most common stimulus for myocardial hyperophy is increased workload. o All the above morphological changes that occur in hyperophy either increase muscle activity (to handle the increased workload) or decrease the workload to hea.