11 - Cellular Adaptations Flashcards
What genes regulate normal cell proliferation?
Protooncogenes
How can you increase growth of a tissue?
- Shorten cell cycle
- Convert quiescent cells to proliferating cells
What are the three checkpoints in the cell cycle?
- Restriction point at end of G1 (most critical and those that pass will go through full cycle but if activated p53 comes into play)
- G1/S transition: DNA damage before replication
- G2/M transition: DNA damage after replication
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What is the relevance of the restriction checkpoint?
- Cells that pass this point normally complete the full cell cycle
- If checkpoint activation here p53 protein stops cell cycle and triggers DNA repair mechanisms or apoptosis if irreparable damage
What does the p53 protein do?
Tumour supression gene, regulates cell cycle
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What is the likely outcome of faulty cell cycle checkpoints?
Cancer
How is the cell cycle controlled?
- Proteins called cyclins work with enzymes CDKs
- CDK activated by binding and complexing with cyclins
- Activated CDKs phosphorylate proteins e.g RB protein, that are needed for progression of the cell cycle
- Activated CDK complexes regulated by CDK inhibitors and growth factors stimulate production of cyclins and shut off CDK inhibitors
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What is a retinoblastoma susceptibility (RB) protein?
- Tumour suppressor gene that is often defective in cancer, causing retinoblastoma
- Inactivated by phosphorylation by CDK4
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What is a cell adaptation and what are the different adaptations?
State between an unstressed cell and an overstressed injured cell, usually reversible
- Hyperplasia
- Hypertrophy
- Atrophy
- Metaplasia
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What is hyperplasia and where does it occur?
- Increase in tissue size due to increased cell numbers
- Occurs in labile or stable cell populations and is reversible
- Hormonal or compensatory
- Controlled and reversible but repeated division exposes cell to risk of mutations and neoplasia
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What is the difference between hormonal and compensatory hyperplasia?
Physiological hyperplasia
- Hormonal: increase in functional capacity
- Compensatory: increase in tissue mass e.g after injury
Why does pathological hyperplasia usually occur?
- Secondary to excessive hormonal stimulation or growth factor production
- Normal response to abnormal condition
What are some examples of physiological and pathological hyperplasia?
- Physiological: Proliferative endothelium and increased bone marrow production of RBC at altitude
- Pathological: goitre in iodine deficiency, epidermal thickening in chronic eczema and psoriasis
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What is hypertrophy and where does it occur?
- Mainly in permanent tissues as they have little replicatitive ability
- Response to increase in functional demand and/or hormone stimulation
- Cells synthesise more cytoplasm and may also undergo hyperplasia in response to endocrine stimulation
![](https://s3.amazonaws.com/brainscape-prod/system/cm/379/746/869/a_image_thumb.png?1551450383)
What are some examples of physiological and pathological hypertropy?
Physiological: skeletal muscle of bodybuilder, pregnant uterus under influence of oestrogen with hypertrophy and hyperplasia
Pathological: cardiac muscle hypertrophy due to valve disease/hypertension, smoot muscle hypertrophy of SI due to intestinal stenosis, bladder muscle hypertropy due to enlarged prostate
![](https://s3.amazonaws.com/brainscape-prod/system/cm/379/746/871/a_image_thumb.png?1551450628)
What happens when the stimulus for hypertrophy and hyperplasia is removed?
Cells and organs become normal size again