Cellular Adaptations Flashcards
How is cell proliferation controlled
Chemical signals which either stimulate or inhibit cell proliferation
When a signalling molecule binds to a receptor, it results in the modulation of gene expression
Receptors usually in cell membrane but can be in the cytoplasm or nucleus
What can chemical signals make the cells do
Survive - resist apoptosis
Divide - enter cell cycle
Differentiate - take on specialised form and function
Die - undergo apoptosis
How can a cell population increase its number
Shortening the cell cycle or conversion of quiescent (dormant) cells to proliferating cells by making them enter the cell cycle
What do cell checkpoints do
Check damage to DNA, all of DNA has replicated
Cell will try to fix it or go into apoptosis
Damaged cells cannot replicate
What is the restriction point
Near the end of G1
Majority of cells that pass R point will likely complete cell cycle
Most commonly altered checkpoint in cancer cells
Checkpoint activation delays cell cycle and triggers DNA repair mechanisms or apoptosis via p53
Proto-oncogenes regulate normal cell proliferation
Other than the restriction point, what other cell checkpoints are there
G1/S transition -checks for DNA damage before
DNA replication
G2/M transition - checks for DNA damage after
DNA replication
How is the cell cycle controlled
Controlled by cyclins binding to cyclin dependent kinases (CDK)
Once CDK is activated, it drives the cell cycle by phosphorylating proteins such as retinoblastoma susceptibility (RB) protein
Cyclin - CDK complex tightly regulated by CDK inhibitors
Growth factors work by stimulating production of cyclin D or inhibiting CDK inhibitors
Once pRb retinoblastoma is inactivated, cell cycle progression occurs
Retinoblastoma normally inhibits restriction point
Tumour suppressor gene
How many times can a cell divide
Hayflick limit - depends on telomere shortening
61.3 divisions in humans
How can cells adapt
Multiply to replace loses (regeneration)
Increase in number above normal (hyperplasia)
Increase in size (hypertrophy)
Become smaller (atrophy)
Be replaced by a different type of cell (metaplasia)
What is regeneration and give an example
Replacement of cell losses by identical cells in order to maintain the size of a tissue or organ
Eg. Replacement or red and white cells in the bone marrow
What types of tissue can regeneration occur in
Only occurs in labile and stable cells and where collagen framework is not damaged
What is hyperplasia
Increase in tissue or organ size due to increased cell numbers
In which types of tissue can hyperplasia occur in
Labile or stabile - only cells able to divide
Caused by increased functional demand or hormonal stimulation
Remains under physiological control and is reversible (unlike neoplasia)
Can occur secondary to a pathological cause but the proliferation itself is a normal response (unlike neoplasia where proliferation is abnormal)
Repeated cell divisions exposes the cell of the risk of mutations and neoplasia
What are examples of physiological hyperplasia
Proliferative endometrium under influence of oestrogen
Bone marrow produces erythrocytes in response to hypoxia
What are examples of pathological hyperplasia
Epidermal thickening in chronic eczema or psoriasis
Thyroid goitre in iodine deficiency
What is hypertrophy
Increase in tissue or organ size due to increased cell size
In which types of tissue can hypertrophy occur in
Labile, stable but especially permanent tissues
In labile and stable tissues, hypertrophy usually occurs along with hyperplasia
Like hyperplasia, caused by increased functional demand or hormonal stimulation
Cells contain more structural components - workload is shared by a greater mass of cellular components
What are examples of physiological hypertrophy
Skeletal muscle hypertrophy of a bodybuilder and the smooth muscle hypertrophy of a pregnant uterus (which also involves hyperplasia)
What are examples of pathological hypertrophy
Heart hypertrophy (ventricular hypertrophy) - problem with systemic or valvular heart disease is that it does not rest Bladder hypertrophy - with a prostate enlargement, bladder always pushes against it causing hypertrophy
What is compensatory hypertrophy
Damage to one of 2 organs causes other organ to work harder
eg. removal of kidney
Why do athletes not get heart hypertrophy
Rest after exercise - are not constantly overstrained
What is atrophy
Shrinkage of a tissue or organ due to an acquired decrease in size and/or number of cells
What is happening in the cell during atrophy
Shrinkage in size to the smallest at which it can survive
Reduced structural components of the cell
May eventually result in cell death
How does organ/tissue atrophy occur
Organ atrophy typically due to combination of cellular atrophy and apoptosis
Reversible up until a certain point
