Cellular Adaptations Flashcards
(37 cards)
What determines the size of a cell population?
- Depends on the rate of cell proliferation, cell differentiation and cell death by apoptosis.
- Increased numbers of cells are seen with increased proliferation or decreased cell death.
- Cell proliferation occurs in physiological and pathological conditions.
- Excessive physiological stimulation can become pathological e.g. prostatic hypertrophy.
- Proto-oncogenes regulation normmal cell proliferation.
How is cell proliferation controlled?
- Largely by chemical signals from the microenvironment which wither stimulates or inhibit cell proliferation
- When a signalling molecule binds to a receptor it results in the modulation of gene expression
- Receptor usually in cell membrane but can be in the cytoplasm or nucleus (e.g. storoid receptors)
What can the chemical signal make the cell do?
- Survive - resist apoptosis
- Divide - enter the cell cycle
- Differentiate - take on specialised form and finction
- Die - undergo apoptosis
How can a cell population increase it’s number?
Increased growth occurs by:
- Shortening the cell cyle
- Conversion of quiescent cells to proliferating cells by making them enter the cell cycle.
Can you see the cell cycle by light microscopy?
You can only see mitosis
Can cells with damaged DNA replicate?
No!
There are three checkpoints to confirm its not mutated.
Restiction (in G1) , between G1 and S and between G2 and M
What is the restiction (R) point?
- Most critical checkpoint
- Majority of cell that complete cell cycle - point of no retun
- Most commonly altered checkpoint in cancer cells.
- Checkpoint activation delays cell cycle and triggers DNA repair mechanisms or apoptosis via P53
How is the cell cycle controlled?
- Cyclins and cyclin dependant kinases (CDKs)
- CDKs become active by binding with cyclins
How many times can cells divide (not stem cells)?
Leonard Hayflick discovered Hayflick numbers / limits in 1961. This number vaires according to species (to do with size). It is the amount of times cell can divide.
Humans = 61.3
How can cels adapt?
- Hyperplasia – cells increase in number above normal
- Hypertrophy – cells increase in size
- Atrophy – cells become smaller
- Metaplasia – cells are replaced by cells of a different
type
Are cellular adaptations reversible?
Yes
What is hyperplasia?
Increase in tissue or organ size due to increase cell numbers.
In which types of tissues does hyperplasia occur?
- Labile or stable conditions
- Caused by increased functional demand or hormonal stimulation.
- Remains under physiological control and is reversible (cf neoplasia)
- Can occur secondary to a pathological cuase but the proliferation itself is a normal response. (cf neoplasia when the proliferation itself it not normal)
- Repreated cell divisions exposes the cell to the risk of mutations and neoplasia.
What physological examples are there of hyperplasia?
- Proliferative endometrium under the infuence of oestrogen
- Bone marrow produces erythrocytes in response to hypoxia
What pathological examples are there of hyperplasia?
- Eczema
- Thyroid goitre in iodine deficiency
What is hypertrophy?
Increase in tissue or organ size due to increased cell size.
In what types of tissue does hypertrophy occur?
- Labile, stable but especially permanent tissues.
- Like hyperplasia, caused by increased functional demaind or hormonal stimulation.
- Cells contain more structural components - workload is shared by a greater mass of cellular compoments
- In labile and stable tissues hypertrophy usually occurs along with hyperplasia.
What physiological examples are there of physiological hypertrophy?
- Skeletal muscle
- Pregnant uterus (hypertrophy and hyperplasia)
What pathological examples are there of hypertrophy?
- Bowel - muscles undergo hypertrophy to push contents out.
- Bladder
- Ventricular hypertrophy of the heart
Why don’t atheletes get cardiac muscle hypertrophy?
Pathological cardiac hypertrophy - increase in amount of capillaries but not enough for size. Anopthia so get areas of fibrosis secondary to ischaemia. This can affect AP passage so arrythmias.
But, atheltes have hypertrophic heart and is fit because he can rest after it has been beating lots. But, if problems with bowels ect.. then no time off.
What is compensatory hypertrophy?
If one of a pair gets smaller / stops working the the other will undergo hypertrophy to compensate. e.g. the kidneys
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 in atrophy?
- Shrinkage in the size of the cell to a size at which survivial is still possible.
- Reduced structural componants of the cell
- May eventually result in cell death.
Is tissue atrophy only a result of cell atrophy?
- Organ / tissue atrophy typically due to combination of cellular atrophy and apoptosis
- Is reversible but only up to a point.
