Cellular Adaptation Of Growth & Differentiation Flashcards
What is cellular adaptation?
Reversible changes in the number, size, phenotype, metabolic activity, or functions of cells in response to changes in their environment.
What is atrophy?
Atrophy is shrinkage in the cell size. The number of cells also decreases.
What are the effects of atrophy?
- Atrophic cells have diminished function
- reduced metabolic needs of the cell for survival
Causes of atrophy
- Decrease workload
- Loss of innervation
- Diminished blood supply
- Inadequate nutrition
- Loss of endocrine stimulation
- Pressure
Mechanism of atrophy
- Decrease protein synthesis due to reduced metabolic activity
- Increased protein degradation of cellular proteins (proteolysis) by ubiquitin-proteasome complex
- Autophagy (self-eating) as an attempt to reduce nutrient demand to match the supply
- Loss of cells through apoptosis
What is hypertrophy?
Increase in the size of cells, results in the increase of the size of the organ
What are the causes of hypertrophy?
- Increased functional demands
2. Stimulation by hormones and growth factors
Mechanism of hypertrophy
Increased production of cellular proteins
What is hyperplasia?
- Increase in number of cells
- increased proliferation of cells
What usually occurs concurrently with hypertrophy?
Hyperplasia
Where does hyperplasia occur?
In tissues/cells that have the capability to divide
What are the causes of hyperplasia?
- Increased hormonal stimulation (can be physiologic and pathologic)
- Compensatory hyperplasia
- e.g. liver can be donated cos able to regenerate and go back to its normal size - Chronic irritation
- e.g. constant scratching of itchy skin produces hyperplasia - Chemical imbalance
- Stimulating antibodies
- e.g. enlargement of thyroid gland (hyperthyroidism is Graves’ disease) - Viral infection
- e.g. papillomavirus causes epithelial hyperplasia (warts)
How hyperplasia occurs (mechanism)?
- as a result of growth factor-driven proliferation of differentiated cells and, in some cases, progenitor (stem) cells
What is metaplasia?
One differentiatied cell type is replaced by another cell type (e.g. from columnar to squamous).
Happens when there is a stress and the cell will be replaced by another cell type that is better to able to adapt to the different environment or injurious stimulus
What are the 5 types of metaplasia?
- Metaplasia from columnar to squamous (in smokers)
- Metaplasia from squamous to columnar (stomach acid reflux)
- Metaplasia from one columnar cell type to other columnar cell type (Helicobacter pylori infection)
- Metaplasia from urothelium to squamous (presence of Schistosoma hematobium infection in bladder)
- Connective tissue metaplasia (myositis ossificans)
