Regulation of tissue growth and Principles Flashcards
How is normal tissue architecture maintained?
Maintenance of genomic integrity
When do quantitative changes to cells occur?
- occur during development or in post natal life –
2. be physiological and part of normal processes or a consequence of pathological events
What is atrophy?
an acquired diminution of growth due to a decrease in the size or number of constituent parts (cells) of a tissue
eg decrease in size of ovaries post menopause
What is hypertrophy?
the converse of atrophy - an increase in the size of an organ or tissue due to an increase in the size of individual cells. Hypertrophy is the cellular response to excessive or prolonged demand for increased function. It is seen most dramatically in muscular organs.
eg pregnant uterus- expand to accommodate foetus
What happens when the demand for increased work ceases?
the organ returns to normal size unless there have been irreversible changes in the architecture as a consequence of the prolonged demand
What is hyperplasia?
an increase in the size of an organ due to an increase in the number of the component cells - increased proliferation. eg lactating breast, prostatic enlargement in older men
What are the differences between hyperplasia and neoplasia?
The enhanced proliferation of hyperplasia persists only as long as the “cause” and the architecture of the organ is retained despite the increase in size
Describe the cell cycle
DNA replication or synthesis (S phase) and mitotic cell division (M phase) - the Cell Cycle(G1 = Gap 1; G2 = Gap2; G0 = resting/quiescent phase).
What are the extrinsic factors affecting the cell cycle?
Physical interactions with the environment
Competence factors
Commitment factors
What are physical interactions with the environment?
mammalian cells must adhere to a substratum, such as the extra-cellular matrix or other cells (cell: cell adhesion), before entering the cycle
What are competence factors?
growth factor or ligand for a cell surface receptor to be competent to enter the cycle- the effects of these receptor ligand interactions is to effect transcription of critical genes (enter cycle)
What are commitment factors?
polypeptide growth factors and hormones, which drive expression of genes required for progression through G1
What are the intrinsic factors affecting the cell cycle?
cyclin dependent kinases (cdks) which phosphorylate selected proteins
cyclins so named because their concentrations rise and fall in a regular pattern through the cell cycle
These complexes are regulated by another family of proteins: Cyclin dependent kinase inhibitors (CKIs) effectively the brakes on the cyclin/CDK functions
What are the checkpoints of the cell cycle?
G1/S Checkpoint
G2/M Checkpoint
Spindle assembly checkpoint
Why is the G1 phase crucial?
Period of intense metabolic activity when many cellular components are duplicated
Duration varies in response to external factors such as growth factors and hormones
it contains a critical checkpoint when the cell is committed to replicate its DNA and is no longer influenced by external factors
What are the options for the G1 phase of the cycle to commit to?
- To “recycle” and embark upon another round of DNA replication, chromosome condensation and cell division.
- To “decycle” and enter a resting phase Go, a phase from which the cell can re-enter the cycle if conditions so demand/ quiescence
- To “decycle” permanently and commit itself to functions incompatible with replication – terminal differentiation.