Lecture 13 Flashcards
Adaptive responses resulting in increased tissue mass
When is hypertrophy without hypoplaisa seen? Why?
- seen in skeletal muscle with extra work
- adult skeletal muscle cannot produce new cells
What changes to the cell cause hypertrophy
What is an example of when we see hyertrophy without hyperplasia
Adult skeletal muscles show hypertrophy without hyperplasia as muscle cells cannot divide
Adult skeletal muscle cannot produce new muscle cells
Can muscle fibres in adults increase
Yes
Skeletal muscle development
- skeletal muscle fibres are produced by myoblasts
- myoblasts are procursors of muscle cells
- myoblasts proliferate during development
- these fuse to form muscle cells
- genes can influence degree of proliferation of myoblasts
- the gene called myostatin slows myoblast proliferation , and when gone can speed up proliferation
Mutated myostatin gene leads to…
… more skeletal muscle fibres being produced during development
Knocking out myostatin causes
Hypertrpy and hyperplasia due to gene mutation
Cardiac hypertrophy
Heart muscles increase in size in response to demand
- mice with aortic restriction also have bigger hearts
Normal myocardium vs hypertrophic myocardium
Example of hypertrophy of smooth muscle
- obstructions of bladder lead to hypertrophy of smooth muscle, e.g. with prostate cancer
- obstructions of intestines can have similar effects
When does hyperplasia and hypertrophy occur together
- in response to increased functional requirements
E.g pregnant myometrium - cells in pregnant uterus are enlarges and have larger nuclei reflecting their increased protein synthesis, number of cells is also increased
Following pregnancy the uterus returns to normal size by physiological atrophy termed involution
An increase in functional muscle mass can occur via 2 mechanisms:
- Increased cell number - hyperplasia (only certain circumstances)
- increased cell size - hypertrophy
In certain circumstances is can be a combination of bot, e.g myometrium in pregnancy
A key feature of these types of increased cell mass is that on removal of the causative environmental stimulus, the altered pattern of cell growth ceases and the tissue reverts to its former state
Responses resulting in decreased tissue mass
Two main types of muscle atrophy and their differences
- Disuse atrophy occurs from a lack of physical exercise (reversible) - Ben-riden, austonought
- Severe type of muscle atrophy is neurogenic atrophy. It occurs when there is injury or disease to a nerve. Tends to occur more suddenly than disuse atrophy
What happens if nervous stimulation of muscle ceases?
Then the muscle fibres decrease in size = atrophy
How to reduce muscle atrophy in aging mice
Macroautophagy
Can break down whole organelles
- ideifitdation
- enclosed by membrane
- ecnloses in a second membrane creating autophagosome
- autophagosome fuses with lysosome where enzymes cause degradation
Uterine involution in mice
Autophagy is important
Key features of apoptosis - programmed cell death
- apoptosis is an important mechanism in developeing and adult tissues for eliminating cells that are no longer needed
- activation is initiated by extracellular or intracellular death signals
- mediated by caspases which exist in all cells as inactive procaspases, activated by cleavage by other caspases.
Features of induction / signalling phase
- normal cells are in close contact and united by junctions
- cells receives either an internal or external signal that initiated apoptosis
- cell looks normal at this stage
Features of apoptosis effector / executioner phase
Protease enzymes cause severe structural changes
- cell shrinkage
- loss of surface specialisations
- condensed chromatin
Features of apoptosis degradation phase
- the cell splits up into smaller fragments called apoptotic bodies
- the nucleus also fragments
- each fragment contains viable mitochondria and intact organelles
Features of apoptosis phagocytic phase
- apoptotic fragments are recognised and phagocytoses by adjacent cells where they are destroyed
- some fragments degenerate extracellularly
- some fragments are ingested by phagocytic cells
