Cell Adaptations Flashcards
What does the size of a cell population depend on? (3)
- Rate of proliferation
- Rate of differentiation
- Rate of apoptosis
What molecules can stimulate or inhibit cell proliferation?
Growth factors
How to growth factors affect cell proliferation?
Bind to specific receptors on the cell surface membrane and stimulate transcription of genes that regulate entry into the cell cycle and the cell’s passage through it
Where is the R point in the cell cycle? Why is it significant?
- R point is at the end of G1 before S phase
- Point of no return - devotes the cell into the cell cycle
- Checkpoint activation delays cell cycle and triggers DNA repair or apoptosis via p53
- Most commonly altered checkpoint in cancer cells
What gene inhibits entry into the cell cycle?
Retinoblastoma gene (RB)
When do cellular adaptations occur?
In response to changes in homeostasis in order to prevent cell injury and cell death
Name the 5 main types of cell adaptations
- Regeneration
- Hyperplasia
- Hypertrophy
- Atrophy
- Metaplasia
What is regeneration? What tissues can this occur in?
- Replacement of lost/damaged cells with new functional differentiated cells
- Can occur in labile and stable tissues (not permanent tissues)
What are the outcomes of regeneration? (2)
- RESOLUTION if the harmful agent is removed
- TISSUE DAMAGE AND SCAR FORMATION if the harmful agent persists
When can newly regenerated cells which are not fully matured be advantageous?
- Influenza viral infection
- Influenza virus infects and multiplies in many cells, causing cell death
- Replaced by immature cells which do not have the receptor for influenza so are not harmed
What is reconstitution? Is this common in mammals?
- Replacement of a lost body part
- Not common in mammals, but can occur in other organisms e.g. Lizard tail can reconstitute itself after being severed
What is the difference between hyperplasia and hypertrophy?
- Hyperplasia is increase in tissue size due to increase in the NUMBER of cells, whereas hypertrophy is increase in tissue size due to increase in CELL SIZE
- Hyperplasia cannot occur in permanent cell populations as there are no stem cells present, so cells must undergo hypertrophy to increase organ size
Give 2 physiological examples of hyperplasia
- Proliferation of the endometrium under the influence of oestrogen
- Erythropoiesis in bone marrow in response to hypoxia at high altitudes
Give 2 pathological examples of hyperplasia
- Proliferation of epidermal basal layer in skin conditions such as eczema and psoriasis
- Hyperplasia of thyroid in iodine deficiency (goitre)
Why do permanent cells undergo hypertrophy instead of hyperplasia to increase organ size?
- Permanent cell types cannot regenerate or proliferate in post natal life as there are no stem cells present in the tissue
- Must undergo increase in cell size in order to increase organ size
- Hypertrophy results in more structural components so workload is shared
Give 2 examples of when hypertrophy of tissue is physiological
- Skeletal muscle in response to weight lifting/exercise
- Pregnant uterus undergoes both hypertrophy and hyperplasia of smooth muscle cells
When can hypertrophy be pathological? (2)
- Ventricular hypertrophy in the heart in response to increased workload (e.g. due to hypertension, aortic stenosis etc.)
- Bladder when prostate is enlarged, as it compresses the urethra
Why is hypertrophy of the heart not a problem in athletes?
Athletes are able to rest following intense exercise, whereas pathological hypertrophy of the heart is due to consistent high workload of the heart due to an underlying condition e.g. Hypertension, aortic stenosis etc. so does not rest
When can hypertrophy be compensatory?
- Kidneys
- If one kidney is removed, the other undergoes hypertrophy to compensate for the workload of both
What is atrophy?
Shrinkage of a tissue/organ due to an acquired decrease in cell size and/or cell number
When can atrophy be physiological?
Atrophy of the ovaries post menopause due to lack of oestrogen production
Give 5 examples of pathological atrophy of tissues
- Disuse atrophy (e.g. of muscles if immobile)
- Denervation atrophy (e.g. thenar wastage following median nerve damage)
- Atrophy of the bone matrix in osteoporosis
- Atrophy of the exocrine pancreas due to blocked duct (replaced by connective tissue)
- Senile atrophy (of various organs due to ageing)
What is metaplasia?
- Reversible change of one differentiated cell type to another in response to changes in homeostasis/internal environment
- Mainly occurs in epithelia - replacement cells are better adapted to withstand the harsh environment
What can metaplasia progress to?
- Dysplasia (reversible abnormal cell growth and differentiation)
- Dysplasia may progress to neoplasia, which is irreversible
Why can metaplasia not occur in germ layers?
Involves expression of a new genetic programme
Which cell types can undergo metaplasia?
Labile and stable cell types (only those that can proliferate)
Give 2 examples of metaplasia
- Barrett’s oesophagus - stratified squamous epithelia of the oesophagus is replaced by gastric glandular epithelia in response to persistent acid reflux
- Smoking - bronchial pseudostratified ciliated epithelia replaced by stratified squamous in response to damage by cigarette smoke
What is hypoplasia? How does this differ from aplasia?
- Hypoplasia is the underdevelopment of an organ at the embryonic stage e.g. chambers of the heart
- Aplasia is the complete failure of an organ to develop at the embryonic stage e.g. aplasia of one kidney
What is involution and when does this occur?
- Normal programmed shrinkage of an organ
- Occurs in the uterus after childbirth
What is atresia?
Absence or abnormal narrowing of a passageway or opening in the body e.g. anus, tricuspid valve atresia
What is dysplasia and why is it significant?
- Dysplasia is abnormal cell growth and differentiation
- It is reversible and can arise from metaplasia
- However it can prelude to neoplasia, where is becomes irreversible
