Cellular Adaptions Flashcards
What is the only stage of the cell cycle that can be seen by light microscopy?
Mitosis
Where is the most important checkpoint in the cell cycle and what is it called?
The Restriction Point
Found towards the end of G1
In terms of the cell cycle, by which 2 ways can increased growth of a tissue occur?
1. Shortening the cell cycle
2. Conversion of quiescent cells to proliferating cells by re-entering the cell cycle
What protein comes into play if the restriction point is activated?
p53 ‘guardian of the genome’
Give some of the actions of p53
- senescence
- cell-cycle arrest
- migration
- apoptosis
- DNA repair
- Metabolism
Explain how cyclins and CDK’s control progression through the cell cycle
- cyclins bind to CDKs which causes them to activate
- actived CDKs phosphorylate proteins to drive the cell cycle
- CDKI (inhibitors) tightly regulate CDKs
What is the normal function of Retinoblastoma protein?
Rb holds on the proteins, therefore stops cell cycle progression i.e. it is a TUMOUR SUPPRESSOR GENE
How many mutations of Rb are required to inactive it’s function?
2 mutations (1 in each Rb allele)
How is Retinoblastoma protein inactivated?
By cyclin D binding to CDK4
Define Hyperplasia
Increase in tissue or organ size due to increased cell numbers
What types of cell population can hyperplasia occur in?
Labile or Stable cells
Give 2 reasons why physiological hyperplasia occurs
1. Hormonal- to increase the functional capacity
2. Compensatory- increasing tissue mass after tissue damage
Why does pathological hyperplasia occur?
Secondary to excessive hormonal stimulation or growth factor production
Give 2 examples of physiological hyperplasia
- Increased bone marrow production of erythrocytes in response to hypoxia
- Proliferation of the endometrium under the influence of oestrogen
Give 2 examples of pathological hyperplasia
- epidermal thickening in chronic eczema or psoriasis -
- thyroid gland enlargement in response to iodine deficiency
Define hypertrophy
Increase in tissue or organ size due to an increased cell size
In what cell populations does hypertrophy occur?
All cell types but especially permanent cell types - in labile and stable tissues hypertrophy usually occurs alongside hyperplasia
Why does hypertrophy occur?
Increased functional demand or increased hormonal stimulation
Give 2 examples of physiological hypertrophy
- skeletal muscle of a body builder
- smooth muscle hypertrophy in the pregnant uterus
Give 3 examples of pathological hypertrophy
- left ventricular hypertrophy due to hypertension or calcified aortic valve
- smooth muscle hypertrophy in the bladder due to obstruction by an enlarged prostate gland
- smooth muscle hypertrophy in the intestine above an intestinal stenosis
Give an example of compensatory hypertrophy
removal of one kidney causing the other to enlarge (combination of hypertrophy and hyperplasia)
Define atrophy
Shrinkage of a tissue or organ due to an acquired decrease in size and/ or number of cells
What is the difference between cellular atrophy and organ/tissue atrophy?
Cellular atrophy = decreased cell size to a size where survival is still possible
Organ/ tissue atrophy = decreased cell size AND apoptosis
In organ atrophy, which cells are the first to undergo apoptosis?
Parenchymal cells apoptosis first, followed by stromal cells
Atrophic organs will therefore contain large amounts of connective tissue
What is the best way to treat atrophy?
remove the cause
Is atrophy reversible?
Yes, up to a point by will be less reversible after many years of parenchymal cells being replaced by connective tissue
Give 2 examples of physiological atrophy
- ovarian atrophy in post menopausal women
- decrease in the size of the uterus after birth
Give 8 examples of pathological atrophy
- atrophy of disuse e.g muscles after inactivity
- loss of nerve innervation
- inadequate blood supply (legs thin in peripheral vascular disease)
- inadequate nutrition
- loss of endocrine stimulus
- persistent injury e.g polymyositis (muscle inflammation)
- ageing e.g, senile atrophy of the brain or heart
- pressure e.g tissues around an enlarging tumour
Define metaplasia
Reversible change of one differentiated cell type to another
In what cell types can metaplasia occur?
Only in varieties of epithelia or connective tissue
Can metaplasia occur across germ lines?
No
What is the purpose of cells undergoing metaplasia?
To change to a cell type that is more suited to that altered environment
Describe how cells in the bronchioles undergo metaplasia in response to cigarette smoke
- Normal bronchial cells are pseudo stratified, ciliated, columnar cells
- cigarette smoke causes metaplasia to simple, squamous epithelium
What is Barret’s oesophagus?
When cells in the lower oesophagus change from stratified squamous epithelium to gastric/ intestinal type epithelium in response to acid reflux
What is traumatic myositis ossificans?
When skeletal muscle fibroblasts change to osteoblasts causing metaplastic bone to develop in muscle -usually occurs after trauma when patient returns from injury before fully healed
Define aplasia
The complete failure of a specific tissue or organ to develop
Give an example of aplasia
- Thymic aplasia - results in infections and auto-immune problems
- Aplasia of the kidney
Define hypoplasia
The congenital underdevelopment or incomplete development of a tissue/organ
Give an example of hypoplasia
- hypoplasia of heart chambers
- renal hypoplasia
- breast hypoplasia
- testicular hypoplasia (seen in Klinefelter’s syndrome)
Define atresia
congenital abnormality where no orifice forms e.g. anus or vagina
Define reconstitution
Replacement of a lost part of the body e.g regrowth of antlers
Define involution
Normal, programmed shrinkage of an organ
Give examples of involution
- Uterus shrinkage after childbirth
- thymus in early life
Define dysplasia
The abnormal maturation of cells within a tissue
What happens to smooth muscle of a blocked duct?
Undergoes hypertrophy to try and eliminate blockage
How do high doses of prednisone (glucocorticoids) affect adrenal glands?
Prednisone is used to treat asthma
In high doses is causes adrenal gland atrophy
What is a side effect of tamoxifen? (Breast cancer adjuvant treatment)
Endometrial gland hyperplasia
Name some of the causes of left ventricular hyperplasia
- systemic hypertrophy
- ischaemic heart disease
- aortic stenosis/ regurgitation
- mitral regurgitation
Which cellular adaptations DO NOT predispose to neoplasia?
- atrophy
- hypertrophy
