CELLULAR ADAPTATIONS
• For the sake of the survival of exposure to stress, the cells make adjustments with the changes in their environment (ie adapt) to the physiologic needs (physiological adaptation) and to non-lethal pathologic injury (pathologic adaptation).
• Broadly speaking, such physiologic and pathologic adaptations occur by the following processes:
° Atrophy
° Hypertrophy
° Hyperplasia
° Metaplasia
° Dysplasia
CELLULAR ADAPTATIONS
• For the sake of the survival of exposure to stress, the cells make adjustments with the changes in their environment (ie adapt) to the physiologic needs (physiological adaptation) and to non-lethal pathologic injury (pathologic adaptation).
• Broadly speaking, such physiologic and pathologic adaptations occur by the following processes:
° Atrophy
° Hypertrophy
° Hyperplasia
° Metaplasia
° Dysplasia
• In general, the adaptive responses are reversible on the withdrawal of stimulus. However, if the irritant stimulus persists for a long time, the cell may not be able to survive and may either die or progress further eg. cell death may occur in sustained atrophy, dysplasia may progress into carcinoma in situ.
Thus, the concept of evolution "Survival of the fittest" holds for the adaptation as "Survival of the adaptable".
• Various mechanisms which may be involved in adaptive cellular responses include:
° Altered cell surface receptor binding.
° Alterations in signal for protein synthesis.
° Synthesis of new proteins by the target cell such as Heat Shock Proteins (HSPs).
DEFINITION
Hypertrophy
• This is an increase in the size of parenchymal cells resulting in enlargement of the organ or tissue, without any change in the number of the cells
CAUSES
Hypertrophy may be physiologic or pathologic. In both cases, it's caused either by:
° Increased functional demand
° Hormonal stimulation
Hypertrophy without accompanying hyperplasia affects mainly muscles. In non-dividing cells too, hypertrophy occurs.
EXAMPLES
Physiologic Hypertrophy: Enlarged size of the uterus in pregnancy (both hypertrophy and hyperplasia occur here).
Pathologic Hypertrophy: Examples of certain diseases associated with hypertrophy are as under:
a.) Hypertrophy of cardiac muscle may occur in a number of cardiovascular diseases which include;
° Systemic hypertension
° Aortic valve disease (stenosis and insufficiency)
° Mitral insufficiency
b.) Hypertrophy of smooth muscles eg.
° Cardiac achalasia (in the oesophagus)
° Pyloric stenosis (in the stomach)
° Intestinal strictures
° Muscular arteries in hypertension
c.) Hypertrophy of skeletal muscle eg. hypertrophied muscles in athletes and manual laborers.
d.) Compensatory hypertrophy may occur in an organ when the contralateral organ is removed eg.
° Following nephrectomy on one side in a young patient.
° Following removal of one adrenal gland.
MORPHOLOGIC FEATURES
• The affected organ is enlarged and heavy. For example, a hypertrophied heart of a patient with systemic hypertension may weight 700-800g as compared to the average normal adult weight of 350g.
• There is enlargement of the muscle fibers as well as of nuclei.
• At ultrasound level, there's;
* Increased synthesis of DNA and RNA.
* Increased protein synthesis.
* Increased number of organelles like mitochondria, endoplasmic reticulum, and myofibrils
