what is adaptation?
the physiological ability to respond to prolonged exposure to stress agents
what is hyperplasia?
- increase in number of cells by mitosis
- leads to increase in size of organ
hyperplasia can only take place if cell population is …
capable of replication
physiological causes of hyperplasia
- muscle growth due to exercise
- hyperplasia of breat tissue at puberty, lactation & pregnancy - due to hormones like progesterone, oestrogen
- thyroid hyperplasia - due to increased mmetabolic demands during puberty & pregnancy
- growth of some organs after surgical resection e.g. liver transplant
pathological causes of hyperplasia - hormone stimulation
- acromegaly due to an increase in growth hormone
- gynaecomastia due to increased oestrogen
- polycythaemia due to increased erythropoietin
pathological causes of hyperplasia - chronic irritation
- thickened epidermis due to constant scratching
- bronchial mucous gland hyperplasia in smokers & asthmatics
- cirrhosis of liver in alcoholics
pathological causes of hyperplasia - chemical imbalance
- parathyroid gland hyperplasia from long term hypocalcaemia
- thyroid enlargement due to iodine deficiency
what is hypertrophy?
- increase in size of current cells
- leads to an increase in size of organ
- no new cells; just bigger cells
in hypertrophy tissues are … of dividing
incapable
what cells involved in hypertrophy?
- secretory cells
- contractile cells
causes of hypertrophy - physiological
any muscle that has an increased functional demand due to workload, not extent of time
causes of hypertrophy - pathological
- left ventricular hypertrophy due to increased preload & afterload
- smooth muscle hypertrophy in urinary bladder in response to urethal obstruction
- compensatory hypertrophy of healthy kidney after removal of other kidney
what is atrophy?
- decrease in size of abnormally formed tissue/organ
- causing diminished metabolism
atrophy - how is metabolism diminished?
- reduction in cell size
- reduction in cell numbers
mechanisms of atrophy
- decreased protein synthesis
- increased protein degradation
- loss of cells by apoptosis
causes of atrophy - physiological
general underuse of skeletal muscle
causes of atrophy - pathological
- tissue hypoxia due to atherosclerosis in carotid arteries
- trissue compression due to pressure from tumours
- cancer
- lack of nutrition with muscle as a source of energy
- skin thinning after prolonged use of steroids
what is metaplasia?
- one type of mature cell is replaced by a different type of mature cell
- because new cell is more resistant to a particular stress, better able to withstand adverse environment
- sometimes reversible if irritant is removed
causes of metaplasia
- intestinal metaplasia - caused by H.pylori ( increase in goblet & paneth cells )
- squamous metaplasia - induced by toxins ( tobacco )
what is dysplasia?
- presence of neoplastic epithelia confined within the basement membrane of the gland
most reliable method for dysplasia
microscopic examination
likely to be …. rate of cell multiplication and disordered maturation
increased
