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Smooth muscle is grouped into two types: single-unit smooth muscle, also known as visceral smooth muscle, and multiunit smooth muscle. Most smooth muscle is of the single-unit type, and is found in the walls of most internal organs (viscera); and lines blood vessels (except large elastic arteries), the urinary tract , and the digestive tract .
In 1969, Don Fawcett labelled these cells as ‘peritubular myoid cells’. ‘Peritubular’ refers to their anatomical location: adjacent to the seminiferous tubule. ‘Myoid’ stems from the Greek ‘myo’ (/ˈmʌɪəʊ/), which means relating to muscle. (PTMs resemble smooth muscle cells under an electron microscope). [2]
Muscle fibers contain numerous tubular myofibrils. Myofibrils are composed of repeating sections of sarcomeres, which appear under the microscope as alternating dark and light bands. Sarcomeres are composed of long, fibrous proteins as filaments that slide past each other when a muscle contracts or relaxes.
The adrenergic receptors exert opposite physiologic effects in the vascular smooth muscle under activation: alpha-1 receptors. Under NE binding alpha-1 receptors cause vasoconstriction (contraction of the vascular smooth muscle cells decreasing the diameter of the vessels). These receptors are activated in response to shock or low blood ...
The muscularis mucosae, a thin layer of smooth muscle. The epithelium, the most exposed part of the mucosa, is a glandular epithelium with many goblet cells . Goblet cells secrete mucus , which lubricates the passage of food along and protects the intestinal wall from digestive enzymes.
Structure of muscle fibre (sarcomere) under electron microscope with schematic explanation. By the time Hugh Huxley earned his PhD from the University of Cambridge in 1952 on his research on the structure of muscle, Szent-Györgyi had turned his career into cancer research. [12]
Because the epithelium is often under external stress and is somewhat delicate, the lamina propria hosts many immune cells. [4] In the intestinal tract the immune system must have tolerance to the normal intestinal flora, yet respond to pathogenic microorganisms. Imbalance of this causes inflammation diseases such as inflammatory bowel disease ...
In the skin, smooth muscle cells such as those of the arrector pili cause hair to stand erect in response to cold temperature or fear. [19] Smooth muscle cells are spindle-shaped with wide middles, and tapering ends. They have a single nucleus and range from 30 to 200 micrometers in length. This is thousands of times shorter than skeletal ...