WEEK 2: Cellular adaptations of growth and Differentiation Flashcards
There 4 main principle adaptive responses. Name them.
Hypertrophy
Hyperplasia
Atrophy
Metaplasia
An organ is in homeostasis with the physiologic stress placed on it
An increase, decrease, or change in stress on an organ can result in growth adaptation.
1.What is cellular adaptation?
- Describe the 2 types of cellular adaptations
Cellular adaptations refer to the changes made by cells in response to various stimuli or changes in their local environment.
This can involve changing the number of cells or their morphological appearance.
- It can be physiological, where it occurs in normal tissues or organs.
*Pathological, i.e., occurring in disease states.
What are stem cells?
Stem cells are immature cells that can go on to differentiate into variousspecialised, mature cell typeswithin a certain lineage.
They are key to determining a tissue’s ability to replenish lost cells, as they are able toself-renew indefinitely.
There are 3 types of tissues based on the ability to self-repair.
Describe them and give examples.
1.LABILE TISSUES
*Stem cells divide repeatedly to replenish losses
EXAMPLES
*Surface epithelium e.g., gut mucosa
*Bone merrow (hematopoietic cells)
- STABLE TISSUES
*Stem cells proliferate slowly or lie dormant but can rapidly proliferate when required.
EXAMPLES
*Hepatocytes
*Osteoblasts
3.PERMANENT CELLS
*Stem cells are present but cannot proliferate to replenish lost cells. A scar tissue is usually formed.
EXAMPLES
*Neurons
*Cardiac m.
*Skeletal m.
When a tissue is exposed to a harmful agent, it undergoes some tissue damage. If the harmful agent is removed, damage is limited and regeneration can occur, resulting in full resolution of the damage.
However, if the agent persists, extensive tissue damage occurs, often resulting in permanent damage and the formation of scar tissue instead of the regeneration of functional tissue.
What is regeneration?
Regeneration is the replacement of cell losses by identical cells to maintain tissue or organ size.
An increase in stress leads to an increase in organ size.
Occurs via hypertrophy and/or hyperplasia of cells.
Define hypertrophy and hyperplasia.
Occurs via an increase in the size (hypertrophy) and/or the number (hyperplasia) of cells.
Hypertrophy involves gene activation, protein synthesis, and production of organelles.
Hyperplasia involves the production of new cells from stem cells.
Which tissues cannot make new cells and undergo hypertrophy only?
Permanent tissues’, however, cannot make new cells and undergo hypertrophy only.
For example, cardiac myocytes undergo hypertrophy, not hyperplasia, in response to systemic hypertension.
Outline triggers of the cells to undergo hypertrophy.
*Increased functional demand.
*Growth factor stimulation
*Hormonal stimulation
Give examples of hypertrophy.
*Right ventricular hypertrophy in response to pulmonary hypertension
*Compensatory hypertrophy in paired organs such as the kidneys, where one organ is removed or dysfunctional and the other hypertrophies to increase its functional ability
*Expansion of the pregnant uterus (combination of hypertrophy and hyperplasia)
Hyperplasia can be physiologic or pathologic.
In both cases the cellular proliferation is triggered by growth factors.
There are 2 types of physiologic hyperplasia. Describe them with examples.
- HORMONAL HYPERPLASIA:
Examples:
*Enlargement of the breasts during puberty and pregnancy
*Enlargement of the uterus during pregnancy
*Endometrial proliferation under the influence of estrogen during the menstrual cycle
2.COMPENSATORY HYPERPLASIA
*Residual tissues grow after removal or loss of part of an organ.
EXAMPLES
*Growth of liver after resected.
State 2 examples of pathologic hyperplasia.
*Thyroid goitre in response to iodine deficiency
*Epidermal thickening in eczema
Define atrophy.
Outline causes of atrophy.
Decrease in cell number occurs via what?
- Decrease in organ size (atrophy).
Occurs via a decrease in the size and number of cells. - A decrease in stress
*Decreased hormonal stimulation
*Loss of innervation
*Diminished blood supply
*Inadequate nutrition
*Aging
Decrease in cell number occurs via apoptosis.
Describe the 2 main mechanisms of atrophy.
- Decreased protein synthesis
2.Increased protein degradation in cells.
Decrease in cell size occurs via:
1.Ubiquitin-proteosome degradation of the cytoskeleton
- Autophagy of cellular components.
Describe these 2 processes.
- What is autophagy?
1.Nutrient deficiency and disuse may activate ubiquitin ligases, which attach multiple copies of the small peptide ubiquitin to cellular proteins and target them for degradation in proteasomes.
2.Autophagy of cellular components involves generation of autophagic vacuoles.
These vacuoles fuse with lysosomes whose hydrolytic enzymes breakdown cellular components.
- Consumption of the body’s own tissue as a metabolic process occurring in starvation and certain diseases.
’’ Self- eating’’
What is metaplasia?
What does it commonly involve?
A change in stress on an organ leads to a change in cell type (metaplasia).
Metaplasia is reversible, in theory, with removal of the driving stressor. For example, treatment of gastroesophageal reflux may reverse Barrett esophagus.
Most commonly involves change of one type of surface epithelium to another.
Metaplastic cells are better able to handle the new stress.
Give examples of metaplasia.
- Bronchial pseudostratified ciliated epithelium becoming stratified squamous epithelium in response to cigarette smoke.
2.Stratified squamous epithelium in the esophagus becoming gastric epithelium when exposed to persistent acid reflux (Barrett’s esophagus)
