Cell Adaptions Flashcards
What regulates normal cell proliferation?
- Proto-oncogenes
What does a cell population size depend on?
- Rate of cell proliferation
- Rate of cell differentiation
- Rate of cell death by apoptosis
What are the four possible outcomes for a cell?
- Survival - resist apoptosis
- Divide - enters cell cycle
- Differentiate
- Dies via apoptosis
How do multicellular organisms communicate?
- Chemical signals from:
- Microenvironment - stimulates/inhibits cell proliferation
- Signalling molecule binds to a receptor -> modulation of gene expression
What are the different type of signalling?
- Hormonal
- Local mediators
- Direct cell-cell or cell-stroma contact
What is meant by autocrine, paracrine and endocrine cell communication?
- Autocrine: cell secretes signalling molecules for itself
- Paracrine: cell secretes signalling molecules for a nearby cell
- Endocrine: cell secretes signalling molecules for a distant cell which travel in the circulation
What do growth factors affect in cells?
- Cell proliferation and inhibition
- Locomotion
- Contractility
- Differentiation
- Viability
- Activation
- Angiogenesis
What are the 4 main growth factors that affect cells?
- Epidermal GF
- Vascular endothelial GF
- Platelet derived GF
- Granulocyte colony-stimulating factor (Granulocyte production)
What is G0 in the cell cycle?
- Cells are able to leave G1 to go to G0 which is a resting state
- Leading to terminal differentiation or permanent exit from cell cycle
How does increased growth occur?
- Shortening of cell cycle
- Conversion of quiescent cells -> proliferating cells by making them enter the cell cycle
What happens in G1, S and G2 of the cell cycle?
- G1: presynthetic cell growth
- S: DNA synthesis
- G2: Premitotic, cells prepare to divide
What is the significance of the restriction point towards the end of G1?
- Most critical checkpoint
- Point of no return
- Commonly altered checkpoint in cancer
What happens when the checkpoint is activated?
- Delays cell cycle
- Triggers DNA repair mechanism
- Apoptosis via p53
What molecules are involved in the control of the cell cycle?
- ATP phosphorylates substrate
- Cyclin activates CDK and bins to the substrate
What are the possible ‘fates’ for stem cells?
- Self renewal
- Differentiation into mature cells
What is a labile cell?
- Stem cells divide persistently to replenish losses
What are stable cells?
- Normally quiescent or proliferate very slowly
- Can proliferate persistently if needed
What are permanent cells?
- Stem cells present: can’t mount an effective proliferation response to significant cell loss
What are the 5 main types of cell adaption?
- Regeneration: cells multiply to replace losses
- Hyperplasia: cells increase in number above normal
- Hypertrophy: cells increase in size
- Atrophy: cells decrease in size
- Metaplasia: cells are replaced by cells of a different type
What happens in hyperplasia?
- Increase in tissue/organ size due to an increase in cell numbers
- Can only occur in labile/stable cell populations
- Remains under physiological control and is reversible
- Can occur secondary to a pathological cause- proliferation is a normal response to another abnormal condition
- Repeated cell divisions expose cell to risk of mutation and neoplasm
What happens in hypertrophy?
- Occurs especially in permanent cells
- Can’t proliferate so cells must increase in size to increase organ size
- Caused by increase in functional demand or hormonal stimulation
- Cells contain more structural components as they’re greater in size
- Can happen alongside hyperplasia
What occurs in atrophy?
- Shrinkage of tissue/organ due to an acquired decrease in size +/- number of cells
Why may atrophy occur?
- Reduced functional demand/workload - disuse atrophy can be reversed by use
- Denervation atrophy
- Inadequate blood supply
- Inadequate nutrition
- Loss of endocrine stimuli
- Persistent injury - polymyositis (inflammation of muscle)
- Ageing
- Pressure - tissues around an enlarging benign tumour
- Osteoporosis - loss of bone matrix NOT calcium
What occurs in metaplasia?
- Reversible change of one differentiated cell types to another
- MAINLY epithelial tissues
- Altered stem cell differentiation
- Due to an adaptive process to protect under stressful environment
- Expression of new gene programme
- No metaplasia across germ layers
What is hypoplasia?
- Underdevelopment or incomplete development of tissue/organ at embryonic stage
- Inadequate number of cells
- Congenital
What is aplasia? (2 meanings)
- Complete failure of a specific tissue/organ to develop
- Embryonic development disorder
- Also used to describe an organ whose cells have ceased to proliferate
What is involution?
- Overlaps with atrophy
- Normal programmed shrinkage of an organ
What is atresia?
- No orifice
What is dysplasia?
- Abnormal maturation of tissues
- Precancerous tissues
