Cellular adaptations Flashcards
what determines the size of a cell population?
size of cell population depends on rate of:
* cell proliferation
* cell death
chemical signals from microenvironment either stimulate or inhibit cell proliferation
when is hyperplasia seen?
increased cell proliferation or decreased cell death
what regulates normal cell proliferation?
proto-oncogenes and tumour supresssor genes
what causes an increase in tissue growth?
- shortening cell cycle
- conversion of quiescent cells to proliferating cells by making them entre the cell cycle
what factors controls the tightly regulated cell cycle?
proteins called cyclins + associated enzymes called cycline dependent kinases (CDK’s)
CDK’s are activated once they bind to cyclins - forming cyclin-CDK complex
activated CDK’s drive the cell cycle by phosphorylating proteins
(cyclin-CDK complex is regulated by CDK inhibitors)
what is the importance of the reinoblastoma susceptibility (RB) protein?
protein acts to prevent DNA replication
it is inactivated by phosphorylation with the cyclin D/CDK4 complex
what is meant by the term cell adaptation?
state between a normal unstressed cell and an overstressed injured cell
what are the 4 types of cell adaptation?
- hyperplasia
- hypertrophy
- atrophy - cell becomes smaller
- metaplasia - cell is replaced by a different type of cell
in which cell populations can hyperplasia occur?
hyperplasia occurs in response to increased demand or in response to external stimulation (only occurs in labile or stable tissue)
1. labile cells - continuously dividing cells (e.g. skin)
2. stable cells - low level of replication but can undergo rapid periods when stimulated (e.g. liver, smooth muscle)
what are the 2 types of physiological hyperplasia?
- hormonal - when result is an increase in functional capacity
- compensatory - when result is an increase in tissue mass after tissue damage
in which cells populations can hypertrophy occur?
- permanent cells (most common) - cant replicate
- labile cells
- stable cells
what is the differnce between physiological and pathological hypertrophy?
Physiological: exercise
* increased demand
* increased protein synthesis and muscle fibre formation
* increased force of contraction
* increased SV
Pathological: response to hypertension or valvular disease
* the muscle mass and size increases
* but capillaries dont increase so they cant meet metabolic needs which results in hypoxia and ischaemia
what is the difference between physiological and pathological atrophy?
Physiological: decrease in size of uterus after birth
Pathological: different examples
* atrophy of disues - caused by decreased workload
* atrophy of denervation - caused by loss of innervation
* cenile atrophy - caused by inadequated blood supply to brain - causes widening of gyri and deepening of sulci
* pressure atrophy
* immunological mechanisms
what is metaplasia?
- reversible change
- one differentiated cell is replaced by another cell type (due to stem cells in tissue reprogramming)
- often an adaptive response - new cells are better adapted to new environment
- doesnt occur in adult striated muscle cells or neurones
which tissue often shows metaplasia?
common in epithelial tissue:
* columnar epithelia (fragile) replaced by squamous (more resilient)
