Intercalated disc

Template:Short description Template:Infobox microanatomy Intercalated discs or lines of Eberth are microscopic identifying features of cardiac muscle. Cardiac muscle consists of individual heart muscle cells (cardiomyocytes) connected by intercalated discs to work as a single functional syncytium. By contrast, skeletal muscle consists of multinucleated muscle fibers and exhibits no intercalated discs. Intercalated discs support synchronized contraction of cardiac tissue in a wave-like pattern so that the heart can work like a pump.<ref name="Openstax Anatomy & Physiology attribution">Template:CC-notice Template:Cite book</ref> They occur at the Z line of the sarcomere and can be visualized easily when observing a longitudinal section of the tissue.

Structure

Intercalated discs are complex structures that connect adjacent cardiac muscle cells. The three types of cell junction recognised as making up an intercalated disc are desmosomes, fascia adherens junctions, and gap junctions.<ref name="Zhao">Template:Cite journal</ref>

• Fascia adherens are anchoring sites for actin, and connect to the closest sarcomere.<ref name=":0">Template:Citation</ref>
• Desmosomes prevent separation during contraction by binding intermediate filaments, anchoring the cell membrane to the intermediate filament network, joining the cells together. <ref name="Zhao"/><ref name=":0" />
• Gap junctions connect the cytoplasms of neighboring cells electrically allowing cardiac action potentials to spread between cardiac cells by permitting the passage of ions between cells, producing depolarization of the heart muscle.<ref name=":0" /><ref name="Zhao"/>

All of these junctions work together as a single unit called the area composita.<ref name="Zhao"/>

Clinical significance

Mutations in the intercalated disc gene are responsible for various cardiomyopathies that can lead to heart failure.<ref name="Zhao"/>

File:Histopathology of ruptured intercalated discs.jpg

Ruptured intercalated discs, in this case regarded as a visual artifact.

Ruptured intercalated discs, when seen on histopathology, have two main causes:

• Microtome sectioning, thereby being a visual artifact.<ref>Page 38 in: Template:Cite book</ref>
• Forceful myocardial contraction, in turn mainly caused by ventricular fibrillation<ref name=Fineschi2016>Page 55 in: Template:Cite book</ref> or electrical injury.<ref name="FineschiKarch2005">Template:Cite journal</ref>

Additional signs indicating forceful myocardial contraction are:<ref name=Fineschi2016/><ref name="FineschiKarch2005"/>

• Alternating bundles of hypercontracted myocytes with hyperdistended ones.
• Square-shaped myocardiocyte nuclei.
• Hyperdistended myocardiocytes with detached sarcomeres, and in proximity of hypercontracted myocardiocytes.

• Cardiac myofiberbreak-up -- very high mag.jpg

  Square-shaped nuclei, indicating forceful myocardial contraction.

External links

• Template:BUHistology — "Ultrastructure of the Cell: cardiac muscle, intercalated disk "