Muscle Tissue, Growth, and atrophy Flashcards
what stimuli can cause a change in tissue?
changes in physical demand
change in metabolic demand
change in endocrine demand
what is hypertrophy?
increase in cell size
what is hyperplasia?
increase in cell number
when does hypertrophy occur without hyperplasia?
in skeletal muscle with extra work
The adult skeletal muscle cannot produce new muscle cells (no hypertrophy
how can skeletal muscle cells under go hypertrophy?
sarcomere expansion (increase in number of myofibrils)
More sarcoplasmic reticulum
More nuclei
*often all things will occur at the same time
how do skeletal muscles develop?
Myoblasts are precursors of muscle cells that proliferate during development
These fuse to form muscle cells
genes can influence degree of proliferation
Myostatin slows myoblast proliferation
what is a myoblast?
precursor muscle cells that proliferate during development that fuse to form muscle cells
what is myostatin?
slows myoblast proliferation
what happens when myostatin expression is affected?
Mutated myostatin gene leads to more skeletal muscle fibres being produced during development
what is an example of cardiac hypertrophy?
Mice that swim have bigger hearts
Mice with aortic restriction also have bigger hearts
what is the pathology of myocardium hypertrophy?
Large, often polyploid nuclei
Thickened ventricular wall reduces outflow and impairs relaxation phase.
what can cause hypertrophy of smooth muscle?
obstruction of the bladder or intestine leads to hypertrophy of smooth muscle
when does hyperplasia with hypertrophy occur together?
cells in pregnant uterus are enlarged and have larger nuceli reflecting their increased protein synthesis. The number of cells also increases
what is involution?
when the uterus returns to normal size by physiological atrophy
what is cell atrophy?
reduced cell size
what is involution of tissue?
reduced cell number
what are some examples of cell atrophy?
- disuse atrophy occurs from a lack of physical exercise (reversible)
- Severe types of muscle atrophy is neurogenic atrophy. Occurs when there is injury or disease to a nerve. Tends to occur more suddenly than disuse
what reduction in anabolic hormones can cause muscle atrophy?
Testosterone
Growth hormone
IGF1
does aging cause muscle atrophy?
yes
what mechanisms underlye atrophy and involution?
Autophagy in cell atrophy
Apoptosis- programmed cell death
what is macroautophagy?
cellular component identified
creates autophagosome
Fuses with lysosome, where enzymes cause degradation
what mediates apoptosis?
mediated by caspases which exist in all cells as inactive procaspases. Activated by cleavage by other caspases.
what activates apoptosis?
initiated by extracellular or intracellular death signals
what is apoptosis?
Apoptosis is an important mechanism in developing and adult tissues for eliminating cells that are no longer needed
what are some examples of apoptosis?
Elimination of cells after hormonal growth stimulus (oestrogen sensitive tissues)
Elimination of cells in tissues with a high cell turnover (lining epithelia in the gut)
Removal of excess cells in embryogenesis (fingers, gut lumen)
what is the function of protease during apoptosis?
cell shrinkage
Loss of surface specialisations
Condensed chromatin
what is the degradation phase of apoptosis?
The cell splits up into smaller fragments called apoptotic bodies
The nucleus also fragments
Each fragment contains viable mitochondria and intact organelles
what is the phagocytic phase of apoptosis?
Apoptotic fragments are regognised and phagocytosed by adjacent cells where they are destroyed
Some fragments degenerate extracellularly
Some fragments are ingested by phagocytic cells
what is an example of physiological muscle hypertrophy?
skeletal muscle changes with exercise
what is an example of pathological muscle hypertrophy?
cardiac muscle hypertrophy
what is an example of hyperplasia and hypertrophy?
increased size of the myometrium during pregnancywhat do
what is an example of hyperplasia and hypertrophy?
increased size of the myometrium during pregnancy
what is an example of hyperplasia and hypertrophy?
increased size of the myometrium during pregnancy
what is an example of hyperplasia and hypertrophy?
increased size of the myometrium during pregnancywhat do
what is an example of hyperplasia and hypertrophy?
increased size of the myometrium during pregnancywhat do
what is an example of hyperplasia and hypertrophy?
increased size of the myometrium during pregnancy
