Bacterial Taxonomy 1 – Classification Based on Morphology and the Gram Stain

This topic is another introductory topic in Microbiology. The aim is to understand the gram stain, and then by extension, what bacteria are gram positive, and what bacteria are gram negative. Emphasis will also be given to taxonomy based on morphology – namely, cocci, baccili, spirilla or pleomorphic. Continue reading Bacterial Taxonomy 1 – Classification Based on Morphology and the Gram Stain

Cellular Adaptation To Stress

Cellular Adaption To Stress


Cellular adaptation refer to (usually) reversible changes in size, number, phenotype or appearance, metabolic activity or functions of cells in response to adverse environmental conditions or internal bodily stresses.

Basically, just as we react to something in our environment, cells don’t just sit there and take their punishment – they change to try to conquer the problem.

There are 4 important ways in which they do this:

  1. Hypertrophy
  2. Hyperplasia
  3. Atrophy
  4. Metaplasia

Hypertrophy and Hyperplasia

Hypertrophy is a cellular response that involves the increased size of cells, that results in an increase in size of the affected organ.

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Note that there is no increase in the number of cells, rather JUST the size. This type of cellular adaptation to stress occurs in a number of different cells, and is usually coupled with another type of cellular adaptation, hyperplasia.

Hyperplasia is a cellular response that involves the increase in number of cells in response to a stimulus.

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Both hyperplasia and hypertrophy occur as compensatory mechanisms to an increased workload on the organ or cell.

To remember which is which, think of the prefix and suffix that make up the word. The suffix “plasia” means “development” and thus hyperplasia means “increased development,” corresponding to an increase in the number of cells. Similarly, “-trophy” means “sustenance, nutrition” and thus, hypertrophy refers, in fact to the very mechanism of hypertrophy, an increase in factors that sustain and allow growth of the cells, which will be explained later.

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If cells are divided into cells that are capable of dividing, and cells that are incapable of dividing, we can also divide the way they react to increased stress.

  1. Cells capable of dividing respond to an increased workload using both hyperplasia and hypertrophy.
  2. Cells incapable of dividing can only respond to an increased workload by hypertrophy. An example of this is in myocytes, or cardiac muscle cells in myocardial fibres. Thus, the heart mainly responds to an increased workload by hypertrophy. Other examples are adult skeletal muscles and neurons.

Physiologic vs Pathologic Hypertrophy and Hyperplasia:

Hypertrophy and hyperplasia, while it can be physiological to aid the body, may also be disease related, or pathological, and is a very important indicator of disease.

Physiologic Hypertrophy: is caused by an increased workload, increased functional demand or stimulation by hormones and growth factors. Of these, the most common stimulus for hypertrophy is increased workload. An example of workload induced hypertrophy would be the muscle enlargement in bodybuilders as muscles are forced to tolerate new loads. An example of hormone-induced hypertrophy is within the endometrium and myometrium of the uterus, as estrogen upregulation during the follicular stage of the menstrual cycle stimulates an increase in muscle proteins in the stroma of the endometrium and the large smooth muscle layer of the myometrium, and thus, muscle size.

Continue reading “Cellular Adaptation To Stress”