شرح هستولوجي العضلات من منهج جامعه الفيصل لطلبه الفرقه الاولي 
شرحت من الصفر تماما ووبالتفاصيل -- انتظرو المحاضرات الملخصه

Muscle Fiber Types

Fiber type composition reflects physiological function:

• Type I (slow-twitch, red): High myoglobin, rich capillary supply, abundant mitochondria for oxidative metabolism; fatigue-resistant (e.g., postural muscles).

• Type IIa (fast-fatigue resistant): Intermediate; anaerobic and aerobic metabolism.

• Type IIb/x (fast-fatigable, white): Low myoglobin, rich in glycogen; brief, high-power contractions (e.g., eye movements).

Fiber types can be differentiated by immunohistochemical staining for specific myosin heavy chain isoforms, and by classic histochemical staining methods

Connective Tissue Sheaths

• Endomysium: Surrounds individual fibers; reticular fibers, capillaries, and nerves reside here—visible in both cross- and longitudinal sections.

• Perimysium: Encloses fascicles (bundles of fibers); carries vessels and larger nerves.

• • Purkinje fibers: Modified cardiac muscle cells with pale cytoplasm (due to high glycogen), fewer myofibrils, and often binucleate, specializing in rapid impulse conduction within the ventricular heart wall.

  • Endocrine cardiomyocytes: Found in atria; secrete atrial natriuretic peptide (ANP), affecting blood pressure and volume
    
    

    Clinical Correlation

    Histological assessment of cardiac tissue is essential in diagnosing myocardial infarction (cell death, loss of striations, interstitial fibrosis), myocarditis (inflammation), and cardiomyopathies (structural and functional changes). Loss or alteration of normal features such as striations or intercalated discs provides insight into underlying disease

     

    Epimysium: Dense connective tissue ensheathing the entire muscle—critical for transmitting contractile force to the skeleton.

    Specialized Cardiac Muscle Cells