We chew our food to break it into smaller pieces, so that it is simpler for the body to digest. During digestion, the esophageal lumen is occupied with the food and liquids we swallow. However, when we are not swallowing, the elongated folds of the mucosa and submucosa work to close the lumen. There are two sphincters located within the esophagus. The sphincters maintain a circular shape, and act as a door shutting channels when appropriate (Circus, 2015). I will be focusing on the lower esophageal sphincter (LES) and its relation to gastroesophageal reflux disorder (GERD). The LES is composed of smooth muscle. The LES functions as a valve, relaxing when we swallow food or drinks so contents can easily pass into the stomach. It is
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The most obvious difference is the lack of striation components that uniformly align contractile units (Seller, 1988). Secondly, the regulation of calcium in smooth muscle is a result of phosphorylation of a myosin subunit by calcium calmodulin and myosin light chain kinase (MLCK). The cells are filled with dense bodies that serve as connection points between contractile units. Actin filaments project from one end of the dense bodies. Suspended in between the actin are the thick myosin filaments. When the smooth muscle is stimulated to contract, the myosin filaments will start inching toward the actin, resulting in the shortening of fibers. Essentially, once the mesh-like structure of the smooth muscle cell is activated, it will pull the cell membrane inward. The highest force output is generated when the actin and myosin overlap because there is room to shorten. If they are pulled a part a great distance and the interaction is lost between actin and myosin, a force can no longer be …show more content…
Most of the calcium that activates contraction comes from extracellular fluid traveling through slow calcium channels. When the cell is depolarized, it allows access to the voltage-gated calcium channel, thus calcium can pour into the cell. The crossbridge cycle is initiated by cytosolic calcium. Smooth muscle contraction begins when calcium binds to calmodulin. After binding, a transformation occurs that energizes the newly formed calcium-calmodulin product to bind and stimulate MLCK. Activated MLCK can now initiate the phosphorylation of myosin crossbridges, resulting in activity of crossbridges. The smooth muscle signal for calcium that initiates the crossbridge cycle is directed toward myosin filaments. Neural regulation of smooth muscle contraction is delivered by autonomic neurons. Autonomic refers to subconscious efforts of reactions. The sympathetic division, the parasympathetic division, or collective efforts from both pathways may control a smooth muscle cell. In skeletal muscle, all neural activity is explicitly excitatory. However, the autonomic systems can exert excitatory or inhibitory activation to smooth muscle cells (Stanfield, 5th ed). Contraction or relaxation of a smooth muscle cell relies on where the cell is located. In the gastrointestinal tract, contractions blend the chyme with intestinal secretions, which push the partially digested food from one area to
The most obvious difference is the lack of striation components that uniformly align contractile units (Seller, 1988). Secondly, the regulation of calcium in smooth muscle is a result of phosphorylation of a myosin subunit by calcium calmodulin and myosin light chain kinase (MLCK). The cells are filled with dense bodies that serve as connection points between contractile units. Actin filaments project from one end of the dense bodies. Suspended in between the actin are the thick myosin filaments. When the smooth muscle is stimulated to contract, the myosin filaments will start inching toward the actin, resulting in the shortening of fibers. Essentially, once the mesh-like structure of the smooth muscle cell is activated, it will pull the cell membrane inward. The highest force output is generated when the actin and myosin overlap because there is room to shorten. If they are pulled a part a great distance and the interaction is lost between actin and myosin, a force can no longer be …show more content…
Most of the calcium that activates contraction comes from extracellular fluid traveling through slow calcium channels. When the cell is depolarized, it allows access to the voltage-gated calcium channel, thus calcium can pour into the cell. The crossbridge cycle is initiated by cytosolic calcium. Smooth muscle contraction begins when calcium binds to calmodulin. After binding, a transformation occurs that energizes the newly formed calcium-calmodulin product to bind and stimulate MLCK. Activated MLCK can now initiate the phosphorylation of myosin crossbridges, resulting in activity of crossbridges. The smooth muscle signal for calcium that initiates the crossbridge cycle is directed toward myosin filaments. Neural regulation of smooth muscle contraction is delivered by autonomic neurons. Autonomic refers to subconscious efforts of reactions. The sympathetic division, the parasympathetic division, or collective efforts from both pathways may control a smooth muscle cell. In skeletal muscle, all neural activity is explicitly excitatory. However, the autonomic systems can exert excitatory or inhibitory activation to smooth muscle cells (Stanfield, 5th ed). Contraction or relaxation of a smooth muscle cell relies on where the cell is located. In the gastrointestinal tract, contractions blend the chyme with intestinal secretions, which push the partially digested food from one area to