Cardiac muscle histology

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There are three types of muscles: cardiac, skeletal, and smooth muscle.

Each type has distinct functions as well as structural characteristics that can be identified histologically.

Cardiac muscle makes up the majority of tissue found in the wall of the heart.

Each mature cardiac muscle cell or cardiomyocyte is relatively short, with a length approximately 85-120 µm long and a diameter approximately 15-30 µm.

Histologically, cardiac muscles have quite a few unique characteristics that make it easier to differentiate them from skeletal muscles.

Unlike skeletal musclecardiac muscle fibers are branched cells with only 1-2 centrally located nuclei.

Also unique to cardiac muscles are the intercalated discs, which are the specialized junctions between neighboring cells that allow the cells to have synchronized contractions and pump blood out of the heart efficiently.

Let’s first take a look at a longitudinal section of cardiac muscle cells that was stained with Hematoxylin and Eosin (or H&E for short).

If we compare cardiac muscle cells to skeletal muscle cells, we can see there are some key differences between the two muscle types.


The cardiac muscle is a specialized type of involuntary muscle tissue that makes up the bulk of the heart. Cardiac muscle cells, or cardiomyocytes, are elongated and spindle-shaped, with one to two centrally located nuclei. These cell fibers are arranged in a branching network and intercalated discs, which are junctions that allow these muscle cells to contract in synchronization. The cardiac muscle is capable of self-excitation, meaning it can generate electrical impulses that coordinately contract all of the heart muscles to pump blood. The cardiac muscle has many unique properties that allow it to function effectively. For example, cardiomyocytes have a high mitochondria density, providing them adequate energy to contract repeatedly. In addition, cardiac muscle cells have a large number of myofibrils, which are specialized protein filaments that allow for efficient contraction. Finally, the intercalation between cardiac muscle cells allows for rapid and coordinated contractions of the heart.


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