Cellular Adaptations Flashcards
Define it ..
Adaptations are reversible changes in the number, size, phenotype, metabolic activity or functions of cells in response to changes in their environment.
Two types of adaptations:
Physiologic adaptations: represent response of cells to normal stimulation by hormones or endogenous chemical mediators.
Pathologic adaptations: responses to stress that allow cells to modulate their structure and function and thus escape injury.
E.g of physiologic adaptation
The hormone-induced enlargement of the breast abd uterus during pregnancy
Shrinkage in the size of the cell by the loss of cell substance
Atrophy
Atrophic cells may have diminished function but:
They are not dead, but if the stimulus continues, die often by apoptosis
Atrophy represents a reduction in the structural components of the cell:
The cell contains fewer mitochonria, myofilaments, a lesser amount of endoplasmic reticulum
In atrophy: increase in number of:
Autophagic vaculoes, residual bodies and lipofuscin granules.
Mechanism of atrophy:
– sythesis of protein》 because of reduced metabolic activity
++ degradation of protein
In atrophy: the degradation of cellular proteins occurs mainly by :
The ubiquitin-proteasome pathway.
Mechanism of ubiquitib-proteasome pathway:
Nutient deficiency and disuse may activate ubiquitin ligases
Attach copies of small peptide ubiquitin to proteins》proteasome
The ubiquitin pathway is responsible for :
For the accelerated proteolysis seen in a variety of catabolic conditions, including cancer cachexia
Why atrophic cell shows autophagy:
It is the process in which the starved cell eats its components in an attempt to find nutrients and survive
How do the residual bodies appear?
Some of the cell debris within the autophage vacuole may resist digestion and persist as membrane bound residual bodies that may remain as a sarcophagus in the cytoplasm
Common causes of atrophy:
Reduced workload Inadequate nutrition Ageing Loss of innervation Reduced blood supply Loss of endocrine stimulation
E.g of physiologic atrophy:
Atrophy of ductus arteriosus in infants
Atrophy of thymus in adults
Atrophy of gonads in old age
E.g of generalized atrophy:
Atrophy due to starvation
Senile atrophy due to aging
E.g of ischaemic atrophy:
Small atrophic kidney in atherosclerosis
Atrophy of brain in cerebral atherosclerosis
Prolonged diminshed functional activity is associated with :
Disuse atrophy of tge organ
E.g of disuse atrophy:
Wasting of muscles of limb immobilised in cast
Atrophy of the pancreas in obstruction of panceatic duct.
In neuropathic atrophy interruption in nerve supply leads to:
Wasting of muscles e.g:
Poliomyelitis,, motor neuron disease and nerve section.
Endocrine atrophy:
Loss of endocrine regulatory mechanism results in reduced metabolic activity of tissue and hance atrophy
E.g of endocirne atrophy :
Hypopituitarism may lead to atrophy of thyroid, adrenal and gonads.
Hypothyroidism may cause atrophy of the skin and its adnexal structures
Pressure atrophy:
Prolonged pressure from benign tumours or cyst or aneurysm may cause compression and atrophy of the tissues
E.g of pressure atrophy:
Erosion of spine by tumour in nerve root.
Erosion of skull by meningioma arising from piaarachnoid.
Erosion of sternum by aneurysm of arch of aorta.
Other causes of a small organ ther than atrophy :
Hypoplasia :incomplete growth of an organ.
Agenesis : complete failure of development of an organ in embryogenesis
Aplasia : failure of development of organ.
Hypertrophy:
It is an increase in the size of the cell resulting in increase in the size of organ.
Hyperplasia is characterized by :
An increase in cell number because of proliferation of differentiated cells and replacement by tissue stem cells
T or F
In pure hypertrophy there are no new cells, just bigger cells containing increased amounts of structural protein and organelles.
T