Cellular Adaptations Flashcards
What is a cell population dependent on?
Rate of proliferation, differentiation and apoptosis
What genes regulate cell proliferation?
Proto-oncogenes
What are the three methods of cell signalling?
Autocrine - cells respond to signals that they have produced
Paracrine - cell produces signal that acts on adjacent cells
Endocrine - hormones synthesised by cells in an endocrine organ and travel in the blood to target cells.
What are growth factors?
They are polypeptides, coded for by proto-oncogenes, that act on specific cell surface receptors to mediate proliferation.
Name 4 types of growth factor and their roles
Epidermal: Mitogenic for epithelial cells, keratinocytes & fibroblasts.
Vascular Endothelial: Induces blood vessel development (vasculogenesis) & growth of new vessels (angiogenesis) in tumours, wound healing & chronic inflammation.
Platelet-derived: Released on platelet activation, causes migration & proliferation of fibroblasts, SMCs & tumour cells.
Granulocyte Colony-stimulating: Stimulates production of granulocytes (particularly neutrophils) in bone marrow & release into blood. Used in chemotherapy.
Give 2 ways the cell cycle is altered to increase growth of a tissue
Shortening the cell cycle
Converting quiescent cells to proliferating cells by making them enter the cell cycle.
How is the cell cycle controlled?
By key ‘checkpoints’ that check for damaged DNA and ensure that damaged cells don’t replicate.
Regulation by Cyclins and Cyclin-dependant kinases.
Where are the checkpoints in the cell cycle?
The Restriction (R) point is near the end of G1
Other checkpoints at the G1/S transition and the G2/M transition
What happens if the Restriction point in the cell cycle is activated?
The p53 protein suspends the cycle and triggers DNA repair mechanisms or apoptosis.
What is passage beyond the R point in the cell cycle governed by?
Phosphorylation of the Retinoblastoma protein (pRb)
How do cyclins and cyclin-dependent kinases (CDKs) regulate the cell cycle?
Cyclins bind to and activate the CDKs, causing them to phosphorylate proteins (such as the Retinoblastoma protein) that are critical for progression to the next stage of the cycle.
What regulates the activity of cyclin-CDK complexes?
CDK inhibitors, and levels of growth factors produced.
Growth factors either increase cyclin production or decrease CDK inhibitor production.
Describe labile cell populations and give examples
Rapid proliferation of cells as stem cells divide persistently to replenish losses.
Normal state is active cell division.
Eg. Epithelial, bone marrow and haemopoietic cells
Describe stable cell populations and give examples
Stem cells are present and are normally quiescent or proliferate slowly but can proliferate persistently when required. Speed of regeneration is variable.
Eg. Hepatocytes, osteoblasts, fibroblasts, SMCs, vascular endothelial cells
Describe permanent cell populations and give examples
Cells are unable to divide and regenerate. Stem cells may be present but are unable to mount an effective proliferative response to significant cell loss.
Eg. Neurones, cardiac myocytes
Define regeneration
The replacement of cell losses by identical cells to maintain the size of a tissue or organ
Why may cell regeneration be advantageous against viruses?
Viruses may spare regeneration cells as they have no receptor for the virus yet.
What determines how many times regeneration can occur?
The hayflick number of the species. In humans regeneration is limited due to telomere shortening.
Define reconstruction
The replacement of a lost body part by coordinated regeneration of several cell types.
Define hyperplasia
An increase in tissue/organ size due to increased cell numbers
What cell types can hyperplasia occur in?
Labile or stable cells
Give 2 physiological causes of hyperplasia
Proliferative endometrium
Increased bone marrow production of erythrocytes at altitude
Give 2 pathological causes of hyperplasia
Epidermal thickening in eczema
Thyroid goitre formation
Define hypertrophy
The increase in tissue/organ size due to increase in cell size
