Cellular adaptations Flashcards
Increased growth occurs by:
Shortening the cell cycle
Conversion of quiescent cells to proliferating cells by making them enter the cell cycle
G1 checkpoint
Enter S
Is cell big enough?
Is environment favourable?
Is DNA damaged?
G2 checkpoint
Enter M
Is all DNA replicated?
Is cell big enough?
What is the restriction (R) point?
- 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
How is the cell cycle controlled?
Cyclin dependent kinases (CDK) become active by binding to cyclins
Human Hayflick limit
61.3
How can cells adapt?
Hyperplasia - increase in number
Hypertrophy - increase in size
Atrophy - cells become smaller in size or number
Metaplasia - cells are replaced by cells of a different type
In which types of tissue does hyperplasia occur?
- Labile or stable
- Caused by increased functional demand or hormonal stimulation
- Reversible and under physiological control
Examples of physiological hyperplasia
- Proliferative endometrium under influence of oestrogen
- Bone marrow produces erythrocytes in response to hypoxia
Exampes of pathological hyperplasia
- Eczma
- Thyroid goitre in iodine deficiency
In which type of tissue
- Labile and stable
- Caused by increased functional demand or hormonal stimulation
- Cells contain more structural components
Compensatory hypertrophy
Increase in size of an organ or tissue when called upon to do additional work or to perform the work of destroyed tissue or of a paired organ.
Examples of physiological atrophy
- Ovarian atrophy in post menopausal women
- Uterus after child birth
Examples of pathological atrphy
- Atrophy of disuse
- Denervation atrophy
- Inadequate blood supply
- Inadequate nutrition
- Loss of endocrine stimuli
- Persistent injury (polymyositis)
- Senile atrophy
- Pressure (sometimes secondary to ischaemia in tumoirs)
What is metaplasia?
- Labile and stable tissues
- Due to altered stem cell differentiation
- May be adaptive, cells that can withstand stress better
- Metaplastic cells are fully differentiated and the process is reversible
- Sometimes a prelude to dysplasia and cancer
- No metaplasia across germ cells
- Expression of a new genetic programme
Examples of metaplasia
- Bronchial pseudostratified ciliated epithelium –> stratified squamous epithelium due to effect of cigarette smoke
- Stratified squamous epithelium –> gastric glandular epithelium with persistent acid reflux (Berrett’s oesophagus)
- If there is damage to bone marrow the spleen can take over blood cell production
Metaplasia predisposition to cancer
- Barrett’s epithelium and oesophageal adenocarcinoma
- Intestinal metaplasia of the stomach and gastric adenocarcinoma
What is aplasia?
- Complete failure of a specific tissue or organ to develop
- e.g. Thymic aplasia (infections and autoimmune problems), aplasia of a kidney
What is hypoplasia?
- Underdevelopment of incomplete development of tissue or organ at embryonic stage
- e.g. testicular in Klinefelter’s syndrome
What is involution?
- Normal programmed shrinkage of an organ
- e.g. uterus after childbirth, thymus in early life
What is reconstitution?
- Replacement of a lost part of the body
- e.g. reports of finger growing back in child under 4
What is atresia?
Congenital imperforation of an opening
What is dysplasia?
- Abnormal maturation of cells within a tissue
- Potentially reversible
- Often pre-cancerous condition
