Flashcards in Pathology - Cellular Adaptations Deck (31)
How is cell proliferation controlled?
- chemical signals from the microenvironment can simulate/inhibit cell proliferation
- signalling molecules bind to a receptor, causing modulation of gene expression
- receptors usually in cell membrane, but can be in cytoplasm/nucleus
How can a cell population be increased?
- shorten the cell cycle
- convert quiescent cells to proliferating cells by making them enter the cell cycle
How does the body determine whether a cell is able to replicate?
It has checkpoints in mitosis, where it checks that the DNA has replicated successfully and the cell is big enough
What is the restriction point?
Most critical checkpoint - the majority of cells which pass this will complete the cell cycle. Checkpoint activation delays cell cycle and triggers DNA repair mechanisms/apoptosis via p53
What are cyclins?
Cyclins and cyclin dependent kinases (CDKs) are active during different phases of the cell cycle. Cyclin activates CDK, which phosphorylates the target protein (which is bound to cyclin)
What is hyperplasia?
Increase in tissue or organ size due to increased cell numbers
What is hypertrophy?
Increase in tissue or organ size due to increased cell size
What is atrophy?
Shrinkage of a tissue or organ due to an acquired decrease in size and/or number of cells.
What is metaplasia?
Reversible change of one differentiated cell type to another
What types of tissue does hyperplasia occur in?
What causes hyperplasia?
- increased functional demand/hormonal stimulation
- can occur secondary to a pathological cause but proliferation is normal response
Is hyperplasia reversible?
In which types of tissue does hypertrophy occur?
Labile, stable but especially permanent
Does hypertrophy usually occur alone in tissue?
No, it usually occurs along with hyperplasia
Why don't athletes get cardiac muscle hypertrophy despite their muscle being under more strain?
They have a rest between exercises, so the strain on their heart goes back to normal. Obese people cannot 'rest' their heart, so they always have stress on it
What is compensatory hypertrophy?
If one of a pair of organs is damaged/removed, the other will enlarge, eg kidneys
What happens to a cell in atrophy?
The cell shrinks to a size at which survival is still possible. There are reduced structural components, which may eventually result in cell death.
What is the relationship between cell atrophy and tissue atrophy?
Organ/tissue atrophy is typically due to combination of cellular atrophy and apoptosis, which is reversible up to a point
What are 'residual bodies'?
These break off from cells undergoing atrophy, and contain unnecessary organelles
Give an example of atrophy due to reduced functional demand/workload
Muscle atrophy after disuse - this is reversible with activity
Why may the hand muscles become wasted in just one part of the hand?
Median nerve damage leads to atrophy
Give an example of atrophy due to inadequate blood supply
Thinning of skin on legs with peripheral vascular disease
What is atrophy of the extracellular matrix called in older people?
Which cell types have metaplasia?
Labile or stable tissues
Is there a link between metaplasia and cancer?
Epithelial metaplasia can be a prelude to to dysplasia and cancer
What is aplasia?
Complete failure of a specific tissue/organ to develop - this is an embryonic developmental disorder eg. Aplasia of a kidney
What is hypoplasia?
Underdevelopment or incomplete development of a tissue or organ at embryonic stage due to an inadequate number of cells
What is involution?
Normal programmed shrinkage of an organ which overlaps with atrophy. Eg. Occurs in uterus after childbirth
What is reconstitution?
Replacement of a lost part of the body. Angiogenesis is the only mechanism for this in humans