What determines the size of cell population ?
- Rate of cell proliferation ( this could be pathological or physiological )
- Rate of cell differentiation
- Rate of cell death by apoptosis
What factors control cell proliferation ?
- Chemical mediators which either stimulate or inhibit cell proliferation
- Proto-oncogenes and tumours suppressor genes regulate normal cell proliferation
What are the two important check points in the cell cycle ?
G1 checkpoint ( before S phase ) : is the cell big enough , is the environment favourable , is the DNA damage ?
G2 checkpoint ( After G2) - is all DNA replication , is cell nog enough ,
What is the restriction point ?
Most critical checkpoint
Majority of cells that pass R point will complete cell cycle. There is no point of return.
Most commonly altered checkpoint in cancer cells.
Checkpoint activation delays cell cycle and triggers DNA repair mechanisms or apoptosis via P53.
If the restriction check point detects DNA damage , outline the process of what occurs
DNA damage leads to increased activation of p53. This induces apoptosis.
OR
The increase in activated p53 , increases p21. This prevents phosphorylation of cyclins which leads to cell cycle arrest and allows DNA repair.
What occurs if there is a mutation in p53 ?
More than 70% of people develop cancer.
How can cells adapt ?
- Hyperplasia
- Hypertrophy
- Atrophy
- Metaplasia - cells are replaced by cells of a different type
What is hyperplasia ?
Increase in tissue or organ size due to increased cell numbers
In which tissues do you tend to get hyperplasia ?
In labels or stable tissues. Labels tissues are tissues that are continuously dividing for example epithelium on the skin.
These tissues can become hyperplasmic due to increased functional demand or hormonal stimulation. It remains under physiological control and is reversible.
However , repeated cell divisions exposes the cell to the risk of mutations and neoplasia
What is a physiological example of hyperplasia .
.
Proliferation of endometrium which is under the influencers oestrogen.
At high altitudes when there is low Po2, bone marrow produces RBC in response to hypoxia
Give an example of pathological hyperplasia
Is psoriasis, your epidermis has undergone hyperplasia which leads to a thicker outlet layer of skin. This leads to scaley , silver skin
What is hypertrophy ?
Increase in tissue or organ size due to increased cell size
In what tissues does hypertrophy occur ?
Labile, stable but especially permanent tissues.
This can occur because an increased functional or hormonal stimulation.
Give an example of physiological hypertrophy
When people go gym , their skeletal muscles undergo hypertrophy
Also in pregnancy , the pregnant smooth muscle uterus undergoes both hypertrophy and hyperplasia.
What is an example of pathological hypertrophy
- Cardiac muscle cells undergo hypertrophy this could be due to increased pressure or workload l
- If you have pulmonary fibrosis , blood cannot enter the lungs easily from the pulmonary arteries. This would lead to right ventricular hypertrophy This could lead to heart failure.
Why is athlete cardiac hypertrophy not pathological ?
Because over time if they stop training , their heart will decrease in size. So it is reversible.
WHat is compensatory hypertrophy ?
For example , if you remove one kidney out of the body. The other kidney would compensate and undergo hypertrophy to take on the functional role of both kidneys.
What is atrophy ?
Shrinkage of a tissue or organ due to an acquired decrease in size or number of cells.
Shrinkage in the size of the cell to a size at which survival is still possible. Reduced structural components on the cells. This could eventually lead to cell death.
Is tissue atrophy only a result of cell atrophy ?
No , organ / tissue atrophy is due to a combination of cellular atrophy and apoptosis.
It is reversible , but only up to a point.
What is an example of physiological atrophy ?
Ovarian atrophy in post menopausal women .
What are examples of pathological atrophy
- Reduced functional demand / workload of muscles which could lead to muscle atrophy after disuse for example when you are in a cast. This is reversible with activity.
- Loss of innervation - eg wasted hand muscles after median nerve damage.
- Inadequate blood supply - thinning of skin on legs with peripheral vascular disease
- Inadequate nutrition - wasting of muscles with malnutrition.
- Loss of endocrine stimuli - which affects breast , reproductive organs l
- Aging : leads to senile atrophy of brain , heart
- Pressure : tissues around an enlarging benign tumour.
What is another example of a structure than undergoes atrophy ?
Extracellular matrix.
This also includes bones
What is metaplasia ?
Reversible change of one differentiated cell type to another.
In what tissues does metaplasia occurs ? ?
Labile or stable cell tissues
There is NO metaplasia across germ layers.
