Tissue and Cell Injury Flashcards
What is homeostasis? How does it work?
Maintenance of a steady internal environment
Environmental changed must result in changed at organ and cellular level
How can homeostasis result in some sort of pathology?
If alterations made in response to changing environment are abnormal. Cell will not be able to cope and die
What are the types of adaptation that can occur?
Increased demand - hyperplasia, hypertrophy
Decreased demand - atrophy
Altered stimulus - metaplasia
What is hyperplasia? How does it occur?
Increase in cell number in response to an external stimulus (regresses on stimulus withdrawal) - excessive growth factor, hormonal stimulation of growth
Can be physiological or pathological
Results in increased organ volume
What are physiological examples of hyperplasia?
Growth of breast tissue
Pregnancy - hyperplasia of endometrial lining of uterus
When does compensatory hyperplasia occur and where?
Occurs after loss of tissue (not common)
Occurs in liver (regeneration via hyperplasia) after e.g: paracetamol induced injury
Also, in bone marrow (e.g: response to rbc decrease)
Mechanism of hyperplasia?
Production of increased growth factors - locally or from distant site (hormone may be a growth factor itself)
Increased growth factor receptors
Switch on genes encoding growth factors and cell cycle regulators to promote new cell growth (force cell to undergo multiple cell cycles)
How does pathological hyperplasia occur and give examples?
Hormonally induced:
Excess oestrogen leads to endometrial hyperplasia (abnormal menstrual bleeding - often post menopausal)
Androgens cause prostatic hyperplasia
Due to infection:
Areas in lymph nodes undergo hyperplasia
How is pathological hyperplasia reversed?
Will regress via withdrawal of stimulus
Describe prostatic hyperplasia
Enlargement of prostate (usually walnuts-sized)
Dangers of hyperplastic tissue? Give an example
Risk site for development of cancer; cancer grows in absence of stimulus
Endometrial (lining of womb) cancer - more common in obese individuals (background of hyperplasia) or in those with prolonged oestrogen exposure
What is hypertrophy?
Increase in cell SIZE (NOT cell number)
When does hypertrophy occur?
Often occurs in conjunction with hyperplasia
Often in isolation in non-dividing cells (cardiac myocytes, skeletal muscle)
Often in response to mechanical stress
When does sypertrophy become pathological in the heart? What does this result in?
Heart can no longer function and requires more blood than it is supplied with.
Muscle becomes less functional
May cause heart failure (inability of heart to pump normally)
What is atrophy?
A physiological or pathological reduction in cell SIZE
Example of physiological atrophy
Every month, breast and endometrial lining of uterus undergo proliferation followed by cell death and atrophy
Examples of pathological atrophy
Denervation of muscle or immobility results in disuse atrophy
Blocked blood supply (associated with atherosclerosis) is thought to account for decreased brain size with AGEING
Inadequate nutrition
Loss of hormonal stimulation (post menopausal uterus)
Due to excessive pressure (e.g: from tumour adjacent to normal tissue)
When does atrophy occur and how?
Blood flow is reduced
Nerve supply interrupted
Changes in hormone concentrations
Tissue experiences disuse or excessive pressure
Mechanism of atrophy?
Reduced cellular components
Protein degradation
“digested” in lysosomes and degraded
Importance of hormones associated with atrophy?
Glucocorticoids and thyroid hormone - promote degradation and atrophy
Insulin - opposes atrophy and promotes growth
This balance of growth and atrophy maintains homeostasis
What is metaplasia?
Reversible change from one mature cell type to another and is an adaptive response
Why does metaplasia occur?
Represents a change in signals delivered to stem cells - as a result, differentiate another way
What stimulates metaplasia?
Maybe a response to cytokines (affect activity of cells, e.g: due to local injury), growth factors and other chemicals
Commonly occurs as response to noxious stimulus
Give an examples of where metaplasia can occur
Squamous epithelium (cover skin) and are resistant to a range of noxious stimuli
Squamous metaplasia commonly found in response to injury - e.g: in lungs and salivary sucts
Metaplastic tissue danger? Giv examples
Risk site for cancer development
Although no squamous epithelia in lung, squamous cell carcinoma can occur (smoking results in columnar cell becoming squamous cells)
Adenocarcinoma (gland-forming tumour) can occur in oesophagus despite no glandular epithelium being present
