What are the basic principles of growth adapdations?
An organ is in homeostasis with the physiologic stress placed on it. An increase, decrease, or change in stress on an organ can result in growth adaptations.
What leads to an increase in organ size?
An increase in stress
Hypertrophy occurs via what?
an increase in the size
Hyperplasia occurs via what?
an increase in the number of cells
What does hypertrophy involve?
gene activation, protein synthesis, and production of organelles.
What does Hyperplasia involve?
the production of new cells from stem cells.
Permanent tissues are... Do they undergo hypertrophy or hyperplasia?
cardiac muscle, skeletal muscle, and nerve, cannot make new cells and undergo hypertrophy only.
Pathologic hyperplasia leads to what?
(e.g., endometrial hyperplasia) can progress to dysplasia and,eventually cancer.
What is an exception to pathologic hyperplasia leading to cancer?
benign prostatic hyperplasia (BPH), which does notincrease the risk for prostate cancer,
What leads to a decrease in organ size?
A decrease in stress (e.g., decreased hormonal stimulation, disuse, or decreased nutrients/blood supply) (atrophy).
Atrophy occurs via?
a decrease in the size and number of cells
How does a decrease in cell number occur?
Decrease in cell size occurs via what?
ubiquitin-proteosome degradation of the cytoskeleton and autophagy of cellular components.
What happens in ubiquitin-proteosome degradation?
intermediate filaments of the cytoskeleton are tagged with ubiquitin and destroyed by proteosomes.
What does autophagy of cellular components involve?
generation of autophagic vacuoles that fuse with lysosomes whose hydrolytic enzymes breakdown cellular components.
What happens in METAPLASIA?
change in stress on an organ leads to a change in cell type
Metaplasia most commonly involves?
change of one type of surface epithelium (squamous, columnar, or urothelial) to another
How do metaplastic cells handle the new stress?
they are better able to handle the new stress.
Esophagus is normally lined by what?
nonkeratinizing squamous epithelium (suited to handle friction of a food bolus)
Acid reflux from the stomach causes metaplasia to nonciliated mucin-producing columnar cells (better able to handle the stress of acid
Metaplasia occurs via what?
programming of stem cells, which then produce the new cell type.
Is Metaplasia reversible?
with removal of the driving stressor.
Can metaplasia progress to cancer?
Under persistent stress, can progress to dysplasia and eventually result in cancer.
What is an exception to metaplasia leading to cancer?
apocrine metaplasia of breast, which carries no increased risk for cancer.
Vitamin A deficiency can result in what?
Vitamin A is necessary for what?
differentiation of specialized epithelial surfaces such as the conjunctiva covering the eye.
In vitamin A deficiency, the thin squamous lining of the conjunctiva undergoes metaplasia into stratified keratinizing squamous epithelium.
Mesenchymal (connective) tissues can undergo metaplasia. A classic example is myositis ossificans in which muscle tissue changes to bone during healing after trauma
Disordered cellular growth
Dysplasia most often refers to?
proliferation of precancerous cells