Introduction:
According to the surroundings, cells can change their structure and function. This helps them maintain their function and survive. The cells adapt to their surroundings. These changes occur in response to stimuli. Removal of stimulus can reverse these changes. The state of the cell is different, but the function remains the same. These changes can be responses to changes in blood or nutrient supply, prolonged irritation, or an increase in need.
What Is Cellular Adaptation?
Cells can transform to adapt to their surroundings. This helps them function better.
What Are the Types of Cellular Adaptation?
1. Proliferation:
Proliferation is an increased number of cells due to rapid division. Our body has three types of cells. These cells have different rates of turnover. Following are the types of cells in our body.
- Labile Tissue: They can divide and renew at an increased rate. Their life is of short duration. They are derived from stem cells. The lining of the gastrointestinal tract, skin, and respiratory tract have labile cells. They can regenerate as and when needed. A skin injury can heal itself due to the high turnover rate of skin cells.
- Stable Tissue: These cells have a low rate of turnover. They divide and die at a slower rate. However, the rate increases if the tissue suffers any damage. This facilitates complete recovery of the organ. Liver and kidney cells have stable cells. The liver and kidney cells can regenerate post-surgery.
- Permanent Tissue: These cells have little or absolutely no turnover. Heart and brain cells cannot replicate.
2. Regeneration:
Regeneration is the natural process of replacement.
- Complete Regeneration: As the name suggests, complete repair of damaged tissue takes place. The repair is adequate in function as well as structure. This takes place only in labile and stable cells. When skin healing occurs without scarring, it is called complete regeneration.
- Incomplete Regeneration: The repair of tissue is incomplete and inadequate in function. The quality of tissue is compromised. This takes place in permanent and stable tissue. When skin healing occurs with scarring, it is called incomplete regeneration.
3. Anaplasia:
Anaplasia is when cells lose the ability to differentiate into mature cells. This is seen in cancerous cell division.
4. Hypertrophy:
Hypertrophy is an increase in cellular size and function; however, the number of cells remains the same. This leads to an increase in the size of the organ also.
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Physiologic Hypertrophy: This mainly occurs due to hormonal stimulus or the presence of growth factors. One can correlate hypertrophy with the growth of muscle tissue after a vigorous workout. Another classic example is an expansion of uterine tissue during pregnancy.
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Pathologic Hypertrophy: This occurs when the increase in cellular activity is uncontrolled. Hypertrophy has a limited rate of increase in cell size. It is not an unlimited phenomenon. If the stimuli are continuous, it might lead to cell death. This can be explained when blood pressure is high; there is undue pressure on the heart muscle. Muscles have to work extra to pump blood. This leads to the thickening of the left ventricle (lower chamber of the heart). This condition is also termed left ventricular hypertrophy.
5. Hyperplasia:
Hyperplasia means an increase in the number of cells. This occurs due to stimuli. This is characteristic of only cells that can divide. This also leads to an increase in the size of organs.
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Physiologic Hyperplasia: When it takes place due to natural hormones, as seen concerning the growth of mammary glands during puberty.
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Compensatory Hyperplasia: It is the process when cell division or an increase in the number of cells takes place to repair any damaged part of the organ. This is seen in cases of liver or kidney resection after surgeries when the resected part grows back.
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Pathologic Hyperplasia: It occurs when there is an excessive or abnormal hormonal response. This response causes an increase in growth factors. This leads to increased cellular proliferation. If this does not stop, there is an increased risk of cancer. This is seen in cases when increased estrogen production causes the overgrowth of endometrial tissue. This increases the risk of cysts and tumors.
6. Atrophy:
Atrophy is the reduction in the size and number of cells. This also reduces the metabolic activity of the cell. When there is increased protein breakdown and decreased production, atrophy is seen. Autophagy is a part of atrophy in which the cell eats its own contents. It is a self-destructive process. It reduces the blood supply. This type of cell response is irreversible. If this process continues, it can cause organ shrinkage.
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Physiological Atrophy: It is seen when the cell size decreases naturally after the removal of the stimulus. This is seen when uterine tissue goes back to average size after childbirth.
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Pathologic Atrophy: This occurs when cells reduce in size due to a decrease or absence in activity or function, like the loss of muscle mass seen on discontinuation of a physical workout. When estrogen levels decrease during menopause, vaginal atrophy occurs.
7. Metaplasia:
Metaplasia is a change in cell type due to long-term irritation or stress. This causes a decrease in functional activity. This changes the cells and makes them resistant to adverse environments. Stimuli can sometimes lead to malignant changes or cause regressive changes.
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Physiological Metaplasia: It is seen in cervical ectopy.
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Pathologic Metaplasia: It is seen in Barrett's esophagus when constant acid reflux can lead to adenocarcinoma. Another classic example is seen with vitamin A deficiency; metaplasia of corneal squamous cells takes place called the Bitot’s spot. Long-term smoking can change the epithelium of the respiratory tract from ciliated columnar to stratified squamous epithelium.
8. Dysplasia:
Cells are of different sizes and shapes due to irregular growth patterns. This is a false adaptation of the cells. Mild to moderate changes do not alter the underlying epithelium. Severe dysplasia can be precancerous in nature. Stimuli change the differentiation mechanics of the cells. They resemble the cells of the surrounding structure.
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Congenital Dysplasia: When cell growth is altered during development.
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Acquired Dysplasia: It is acquired when cell growth is altered as a response to metaplasia or hyperplasia.
Conclusion
Cells undergo changes to adapt to their surroundings. These cellular adaptations are reversible. The cell returns to its normal state when the stimuli are taken away. However, the prolonged presence of stimuli can impact the function of cells and lead to cell injury.