What determines the size of a cell population?
- Depends on rate of cell proliferation, cell differentiation and cell death by apoptosis
- Increased numbers 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 regulate normal cell proliferation
How is cell proliferation controlled?
- Largely by chemical signals from the microenvironment 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 (e.g., steroid receptors)
What can chemical signals make a cell do?
- Survive (resist apoptosis)
- Divide (enter cell cycle)
- Differentiate (take on specialised from and function)
- Die (undergo apoptosis)
How can a cell population increase it’s numbers?
Increased growth occurs by:
- Shortening the cell cycle
- Conversion of inactive cells to proliferating cells by making them enter the cell cycle.
Can you see the cell cycle by microscopy?
Interphase cannot be seen but mitosis and cytokinesis can be.
Can cells with damaged DNA replicate?
- Mutation produces other cells with these changes (cancer) = not in normal state
- Checkpoints within cell cycle (before M and S phase)
- If there is damaged DNA cells try to fix it, if they can’t then the cell enters apoptosis
What is the restriction (R) point?
- Most critical checkpoint
- Majority of cells that pass R point will complete cell cycle
- Most commonly altered checkpoint in cancer cells
- Checkpoint activation delays cell cycle and triggers DNA repair mechanisms or apoptosis via p53 (guardian of the genome)
How is the cell cycle controlled?
- Cyclins and cyclin dependant kinases (CDK’s)
- CDK’s become active by binding with cyclins
- CDK phosphorylates target proteins.
How many times can cells divide?
61.3 (due to telomere length etc)
How can cells adapt?
Hyperplasia
Hypertrophy
Atrophy
Metaplasia
What is hyperplasia?
Increase in tissue or organ size due to increased cell numbers
What is hypertrophy?
Increase in tissue or organ size due to increased cell size
What is atrophy?
Shrinkage of a tissue or organ due to an acquired decrease in size and/or number of cells.
What is metaplasia?
Reversible change of one differentiated cell type to another
In which types of tissues does hyperplasia occur?
- Labile or stable tissues
- Caused by increased functional demand or hormonal
stimulation - Remains under physiological control and is reversible
- Can occur secondary to a pathological cause but the proliferation itself is a normal response
- Repeated cell divisions exposes the cell to the risk of mutations and neoplasia
Give an example of physiological hyperplasia
- Proliferative endometrium under the influence of oestrogen
- Bone marrow produces erythrocytes in response to hypoxia
Give a pathological example of hyperplasia
- Eczema
- Thyroid goitre in iodine deficiency
In which types of tissue does hypertrophy occur?
- Labile, stable but especially permanent tissues
- 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
- In labile and stable tissues hypertrophy usually occurs along with hyperplasia
Give an example of physiological hypertrophy
- Skeletal muscle
- Pregnant uterus (hypertrophy and hyperplasia)
Give an example of pathological hypertrophy
- Hypertrophy of cardiac muscle to combat hypertension
- Proximal to a bowel stricture = hypertrophy of smooth muscle to push things through stricture
- Smooth muscle of bladder due to enlarged prostate gland (push harder to pass urine)
What is compensatory hypertrophy?
Damage to one of two paired organs (e.g. kidney) or part of an organ. Small kidney at birth/ if one is removed the other undergoes hypertrophy and hyperplasia.
What is happening in the cell in atrophy?
- Shrinkage in the size of the cell to a size at which survival is still possible
- Reduced structural components 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
Give an example of physiological atrophy
- Decrease in size of uterus after child birth
- Ovarian atrophy in post menopausal women
-
Introduction34
-
Cell Injury115
-
Why And How Neoplasms Occur39
-
The Incidence, Prognosis And Treatment Of Malignant Neoplasms27
-
Acute Inflammation52
-
Learning From The Dead9
-
Chronic Inflammation25
-
Healing: Regeneration and Repair52
-
Haemostasis40
-
Thrombosis and Embolism57
-
Atherosclerosis49
-
Cellular Adaptations38
-
Neoplasia61
