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Cardiac sphincter muscle is a circular band of
A. Striated muscles
B. Smooth muscles
C. Cardiac muscles
D. All of the above

Last updated date: 24th Jun 2024
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Hint: Cardiac sphincter muscle is an involuntary muscle as it ensures that the acidic content from the stomach is not moving in the upward direction. In addition, skeletal muscle and smooth muscle are also called voluntary muscle and involuntary muscle respectively.

Step by step answer:
Sarcomere is the smallest and functional unit of striated muscle tissue. Series of sarcomere appears as a band of muscle tissue that is responsible for the striations to appear. This can be visualized using a microscope. Cardiac muscle and skeletal muscle are two types of striated muscle. Skeletal muscles are attached to the skeleton of the body for skeletal movements like maintaining body posture and locomotion. These muscles are voluntary in nature and are controlled by the central nervous system (CNS). Cardiac muscle is involuntary in nature and is found only in the heart. The sarcomeres in cardiac muscles are not regularly arranged and hence striations cannot be seen.
Smooth muscles or non-striated muscles are involuntary in nature and are found in the linings of the stomach, esophagus, urinary bladder, sphincters, and all other internal organs. It mainly controls the function of contraction and relaxation. Sphincters are flap-like structures that ensure the unidirectional flow of fluid in the body. The cardiac sphincter is located above the stomach and at the lower end of the esophagus. It is responsible for the one-way passage of undigested food. The action performed by the sphincter is not in human control that is involuntary in nature and is controlled by the autonomic nervous system (ANS).
Hence option B is correct.

Note: The sphincters play an important role in the course of digestion, like the cardiac sphincter which does not allow stomach acid to enter reverse back in the oesophagus and the sphincter present at the upper end of the oesophagus ensures the unidirectional flow of food from the mouth to the stomach via the oesophagus. Other examples of sphincters are the pupillary sphincter present in the eye, pyloric sphincter located at the lower end of the stomach. The sphincter is mainly involuntary in nature except for the sphincter present in the anus. Anus consists of 2 sphincters, the internal one is involuntary in function while the external sphincter is voluntary inaction which controls the defecation.