Muscle Tissue Repair and Regeneration

Skeletal muscle cells divide during growth, especially in the first year of life.
During infancy, cells are forming their normal shape and structure.
After approximately the first year, they primarily grow in length rather than increasing in cell number.
Skeletal muscle cells have limited repair capabilities due to a finite number of satellite cells.
Satellite cells, which haven't differentiated into muscle cells, reside on the cell surface and can replace damaged areas.
Frequently, damage results in fibrosis, leading to scar tissue formation.

Cardiac muscle cells do not repair, regenerate, or divide.
Myocardial infarction (heart attack) occurs due to a lack of oxygen to cardiac muscle cells, causing cell death.
To heal and prevent necrosis, collagen fibers are deposited, forming a scar.
Scar tissue (collagen deposits) impairs heart function because:
- It lacks contractile cells.
- It lacks cells with gap junctions for communication.
Scar tissue in the heart muscle wall prevents normal heart function.
This places extra load on remaining cells, increasing the risk of subsequent heart attacks.

Smooth muscle cells are highly flexible and capable of regeneration.
They can grow in both size (hypertrophy) and number (hyperplasia).
- Hypertrophy: Increase in cell size.
- Hyperplasia: Increase in cell number through cell division.
An example of hypertrophy and hyperplasia is the muscle layer of the uterus.
During the menstrual cycle, the uterine wall thickens with increased blood vessels.
At the end of the cycle, this layer sheds, resulting in menstruation.
This process is largely due to hypertrophy and hyperplasia of uterine cells and tissues.
Reference to Professor Mario Ricci, who will discuss the reproductive cycle in detail later in the semester.