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12. The extracellular calcium (Ca++) is important for the contraction of the following structures. ex cept: A) Iris of the eye B) Cardiac muscle C) Skeletal muscle D) Gl tract wall E) Urinary bladder
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(193 Oylar)
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Elit · 8 yıl öğretmeni
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The correct answer is C) Skeletal muscle.Extracellular calcium (Ca++) plays a crucial role in the contraction of various structures in the body. Let's examine each option:A) Iris of the eye: The iris of the eye contains smooth muscle fibers that control the size of the pupil. Calcium ions are involved in the contraction of these smooth muscle fibers, making extracellular calcium important for the function of the iris.B) Cardiac muscle: The heart muscle, or cardiac muscle, relies on calcium ions for contraction. Calcium ions trigger the release of calcium from the sarcoplasmic reticulum, leading to muscle contraction. Therefore, extracellular calcium is essential for the contraction of cardiac muscle.C) Skeletal muscle: Skeletal muscle contraction is primarily driven by the release of calcium from the sarcoplasmic reticulum within the muscle cells. This process is regulated by calcium ions, but skeletal muscle does not rely on extracellular calcium for contraction. Therefore, extracellular calcium is not important for the contraction of skeletal muscle.D) Gastrointestinal (GI) tract wall: The muscles in the walls of the gastrointestinal tract are responsible for peristalsis and other movements. Calcium ions play a role in the contraction of these muscles, making extracellular calcium important for the function of the GI tract wall.E) Urinary bladder: The bladder muscle, or detrusor muscle, relies on calcium ions for contraction. Calcium ions trigger the release of calcium from the sarcoplasmic reticulum, leading to muscle contraction. Therefore, extracellular calcium is important for the contraction of the urinary bladder.In summary, extracellular calcium is important for the contraction of the iris of the eye, cardiac muscle, gastrointestinal tract wall, and urinary bladder. However, skeletal muscle does not rely on extracellular calcium for contraction, making option C the correct answer.