Smooth Muscle Histology Notes PDF

Histology Lecture Notes Dr. Shaimaa Kashef III- Smooth Muscle - Smooth muscles are non-striated and involuntary in action. Sites: i- Walls of hollow viscera as the digestive tract and associated ducts. ii- Walls of blood and large l...

Histology Lecture Notes Dr. Shaimaa Kashef III- Smooth Muscle - Smooth muscles are non-striated and involuntary in action. Sites: i- Walls of hollow viscera as the digestive tract and associated ducts. ii- Walls of blood and large lymphatic vessels. iii- Respiratory passages. iv- Urinary and genital ducts. Structure: L/M Shape: Smooth muscle cells are non striated fusiform and elongated cells. Nucleus: Each cell has a central single oval nucleus located in the broadest part of the cell. The narrow part of one cell lies adjacent to the broad part of the neighboring cell (Fig. 17). Cytoplasm: The cytoplasm is homogenous and acidophilic. A basal lamina surrounds it. Figure (17): Structure of smooth muscle 1 Histology Lecture Notes Dr. Shaimaa Kashef E/M (Figs 18& 19): Smooth muscle cells are interconnected by gap junctions (nexus). The sarcoplasm near the poles of the nucleus contains numerous mitochondria, Golgi complex, RER, SER, free ribosomes, and glycogen granules. The sarcoplasm contains three types of filaments; actin, myosin, and intermediate filaments. Actin and myosin run parallel to the longitudinal axis of the cell. They are not arranged regularly to form sarcomeres, but they overlap each other more than those of striated muscles, so there are no cross- striations in smooth muscles. (Fig. 18) Figure (18): Dense bodies and filaments of smooth muscle ▪ There are two types of dense bodies (are character of smooth muscle): 1. Membrane-associated dense bodies present under the sarcolemma ii- Cytoplasmic dense bodies. These bodies represent the Z–lines present in the striated muscles, but in irregular way. 2 Histology Lecture Notes Dr. Shaimaa Kashef Figure (19): Ultrastructure of smooth muscle Test yourself Ultrashort questions: 1. Complete the missing data: Item Skeletal muscle Cardiac muscle Smooth muscle Striation of the muscle Site of the nuclei Number of the nuclei Type of filaments in sarcoplasm MCQ Which type of junctions present in the smooth muscle cells? A- Gap junctions (nexus). B- Intercalated discs. C- Tight junctions. D- Desmosomes. 3