cardiac muscle tissue (2023)

Cardiomicitos

Cardiomyocytes, also known as heart muscle cells, generally contain an elongatedKernlocated in the middle, which is a characteristic feature of skeletal muscles. When examining the ultrastructure, it becomes clear that theMyofibrillenThey separate as they approach the nucleus, orbit it and reassemble into their original pattern on the other side. You can visualize the arrangement by imagining two cones connected at their tips, representing the nucleus. In fact, cell organelles are also concentrated in this cytoplasmic region around the nucleus. These include mitochondria, Golgi apparatus, granules filled with lipofuscin and glycogen.lipofuscinaIt is a red-brown pigment, often referred to as wear pigment, that gradually accumulates in heart tissue with age. It is the remnant of the contents of lysosomal cells. The cytoplasm of cardiomyocytes, calledSarcoplasm, is eosinophilic and appears as a 3D network.

Due to the high energy requirements, heart muscle tissue contains larger and more elongatedmitochondrialocated between the myofibrils. They can run the entire length of the sarcomere and contain many internal cristae. Also additionalGlycogen granulesThey are also located between myofibrils to store energy. Threads of collagenous tissue fibers along with capillaries are also present between the muscle fibers to provide tissue support and blood supply.

Inserted discs

Cardiac muscle cells are connected byintercalated disksthat coincidez-Linien. Under the light microscope they appear as lines running perpendicularly through the muscle fibers. However, when examining the ultrastructure, the discs are far from linear, as they have finger-like interlockings to maximize the contact area. The intervertebral discs also contain two compartments oriented transversely and laterally (parallel) relative to the myofibrils, resembling a staircase.

To perform their binding functions, intercalated disks contain three types of cell junctions:

• adhesive connections (adherent tape)they are part of the transverse component and visualize the intercalated discs in hematoxylin and eosin (H&E) staining. They are responsible for connecting the ends of the myocytes into a fiber. In addition, they transmit the force of contractions from one cell to another because theactthe filaments of the terminal sarcomeres insert into these junctions.
• Desmosomas (sticky dots)They are part of both components and reinforce adhesive bonds. They prevent myocytes from separating during contractions by anchoring intermediate filaments.
• communication (crosses)they form part of the lateral component of the intercalated discs. They allow heart tissue to act as a syncytium by providing pathways for different ions to pass between adjacent cells, resulting in propagation of excitation and subsequent contraction.

myofibrils and sarcomeres

Sarcomerethey are the functional subunits of myofibrils and the contractile units of cardiac muscle tissue. They are arranged in a branched pattern, forming a 3D network in the cytoplasm. Sarcomeres are specific parts of myofibrils located between twoz-Linienand are responsible for the striated appearance of heart tissue. They are made up of thick and thin fibers.thick threadsThey are made up of polymerized myosin type II protein and are attached to a band called the M line, which lies in the middle of the sarcomere.thin threadsThey are formed from polymers of the protein alpha-actin and are linked to Z-lines which, together with the A-band, which corresponds to the length of the myosin filaments, are electron-rich and appear darker under the electron microscope. Bands I and H appear brighter, representing regions composed of only thin and thick filaments, respectively, but not both.

The cytoplasmic regions between the branches of the sarcomere are filled with mitochondria and are called the smooth endoplasmic reticulum (sER).sarcoplasmic crosshairs, which wraps around each myofibril. The membranous network of the sarcoplasmic reticulum is traversed by so-called structuresTubuli T, which are extensions of the sarcolemma (plasma membrane of muscle cells). They form the T-tubular system and itsLumenThey communicate directly with the extracellular space. Its course follows the Z-lines of the sarcomeres, resulting in a single T-tube for each sarcomere. The region formed by the pair of flat terminal cisternae of the sarcoplasmic reticulum and part of a T-tubule is called the T-tubuleTag.

Cardiac conduction cells

Contractions are triggered by specialized heart cells called cardiac cells and distributed throughout the heartCardiac conduction cells(they are not neurons). Together they form theconduction system of the heart. These cells form specific structures such as nodes, bundles, and conductive fibers. The initial spontaneous stimulus begins with theThe sinus nodeLocated on the wall of the right atrium at the level of the entrance to the superior vena cava. Impulses travel through the walls of the atria, causing a contraction. You will then be picked up by theatrioventricular (AV) Nodelocated above the tricuspidValvein the medial wall of the right atrium. These two ganglia are surrounded by collagenous tissue filled with capillaries and autonomic nerves. After the AV node, the impulse goes through thepackage from you, right and leftbar branches, and finally through thedes Purkinje-Systems. All three bundles stain quite pale due to their high content of glycogen granules and mitochondria. The Purkinje fibers also contain a central area that turns pale in color. Cardiac conduction cells are strictly connected only via desmosomes and gap junctions. They also don't have a T-tubule system.

As you can see, the heart is contractingspontaneous. However, despite their autonomy, the conductive cells are not isolated from thenervous system. IsArtbranch increases the pulse frequency of the nodes to the conducting system, while theparasympatheticthe branch decreases it. Since in normal situations each impulse is followed by a contraction, the rate of contraction increases or decreases.