Logan Steele
A sphincter is a circular muscle that surrounds a bodily passage or opening. It maintains constriction of a natural body passage or orifice and relaxes as required by normal physiological functioning. Sphincters are found in many animals, and there are over 60 types in the human body. They are involved in various bodily functions, including digestion, excretion, and blood flow regulation. For example, the internal and external anal sphincters control the exit of faeces, while the urethral sphincter regulates the passing of urine. The lower oesophageal sphincter prevents stomach acid from moving up into the oesophagus, and the pyloric sphincter is located at the lower end of the stomach. Sphincters can be composed of smooth or striated muscles, with some functioning involuntarily and others voluntarily.
| Characteristics | Values |
|---|---|
| Definition | A sphincter is a circular muscle that maintains constriction of a natural body passage or orifice and relaxes as required by normal physiological functioning. |
| Types | There are over 60 types of sphincters in the human body, some of which are microscopically small. |
| Location | Sphincters are found in the gastrointestinal (GI) tract, urinary tract, blood vessels, and eyes. |
| Examples | Some examples of sphincters include the lower oesophageal sphincter, pyloric sphincter, ileocecal sphincter, sphincter of Oddi, and the internal and external anal sphincters. |
| Function | Sphincters help regulate the flow of liquids, solids, or gases in the body. For example, the anal sphincter regulates defecation, while the urethral sphincter controls the passing of urine. |
| Muscle Type | Sphincters can consist of smooth muscles that function involuntarily or striated muscles that function voluntarily. |
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What You'll Learn
Types of sphincter muscles
A sphincter is a circular muscle that maintains constriction of a natural body passage or orifice and relaxes as required by normal physiological functioning. There are over 50 types of sphincters in the human body, some of which are detailed below:
Upper Esophageal Sphincter (UES)
Also known as the inferior pharyngeal sphincter, it is an involuntary sphincter found at the end of the pharynx (throat). The UES protects the entrance to the oesophagus, which carries food from the throat to the stomach. It also prevents air from entering the oesophagus during breathing and plays a role in burping and vomiting.
Lower Esophageal Sphincter (LES)
Also known as the cardiac sphincter, it is located at the upper portion (cardia) of the stomach. This sphincter prevents the acidic contents of the stomach from moving upward into the oesophagus.
Sphincter of Oddi
Also known as Glisson's sphincter, it controls secretions from the liver, pancreas and gall bladder into the duodenum.
Sphincter Urethrae
Also known as the urethral sphincter, it controls the exit of urine from the body. It has inner and outer muscles that regulate urine flow through the urethra. The inner muscle has involuntary control, while the outer muscle is under voluntary control.
Anal Sphincter
Located at the opening of the rectum at the end of the digestive tract, the anal sphincter has both inner and outer muscles. The inner sphincter is involuntary and prevents stool from leaking out, while the outer sphincter is voluntary and allows the passing or holding of stool on demand.
Sphincter Pupillae
Also known as the pupillary sphincter or iris sphincter, it is an involuntary sphincter that regulates the constriction of the pupil in the eye. The iris dilator muscles are responsible for dilation, while the sphincter pupillae muscles cause constriction.
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Functions of a sphincter
A sphincter is a circular muscle that maintains constriction of a natural body passage or orifice and relaxes as required by normal physiological functioning. There are over 60 types of sphincters in the human body, some of which function involuntarily, some respond to stimuli, and others are controlled voluntarily. Here are some of the functions of sphincters:
Upper Oesophageal Sphincter (UES)
Also known as the inferior pharyngeal sphincter, the UES is an involuntary sphincter found at the end of the pharynx (throat). It protects the entrance to the oesophagus, which carries food from the throat to the stomach. The UES also prevents air from entering the oesophagus during breathing and plays a role in burping and vomiting.
Lower Oesophageal Sphincter (LES)
The LES, or cardiac sphincter, is an involuntary sphincter located at the bottom of the oesophagus, where it connects with the stomach. It allows food to pass from the oesophagus into the stomach and prevents stomach acid from flowing back into the oesophagus. A weakened or dysfunctional LES can lead to gastroesophageal reflux disease (GERD).
Pyloric Sphincter
The pyloric sphincter is located between the stomach and the duodenum, the first part of the small intestine. It opens to allow partially digested food to pass from the stomach into the duodenum, where it mixes with bile and other digestive enzymes. The pyloric sphincter also ensures that stomach contents are thoroughly mixed with gastric juices before entering the small intestine.
Sphincter of Oddi
The sphincter of Oddi, or Glisson's sphincter, is an involuntary sphincter that controls the release of digestive fluids from the liver, pancreas, and gall bladder into the duodenum. These fluids are essential for fat digestion and neutralising stomach acid.
Ileocecal Sphincter
The ileocecal sphincter, also known as the ileocecal valve, is an involuntary sphincter located at the junction of the small intestine and large intestine. It regulates the movement of partially digested food from the small intestine to the large intestine and limits the reflux of colonic contents back into the small intestine.
Anal Sphincter
The anal sphincter is located at the opening of the rectum and regulates defecation. It has both inner and outer muscles: the inner sphincter is involuntary and prevents stool leakage, while the outer sphincter is voluntary and allows control over passing or holding stool.
Urethral Sphincter
The urethral sphincter, or sphincter urethrae, controls the passing of urine from the body. Like the anal sphincter, it has inner and outer muscles that regulate urine flow. The inner muscle is involuntary, while the outer muscle is voluntary.
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Sphincters in the GI tract
A sphincter is a circular muscle that maintains constriction of a natural body passage or orifice and relaxes as required by normal physiological functioning. There are over 50 types of sphincters in the human body, with six distinct sphincters situated within the gastrointestinal (GI) tract, also known as the digestive system.
The upper oesophageal sphincter (UES), also known as the inferior pharyngeal sphincter, is an involuntary sphincter found at the end of the pharynx (throat). The UES protects the entrance to the oesophagus, which carries food from the throat to the stomach. The swallowing reflex triggers the opening of this sphincter, and it also plays a role in burping and vomiting. A malfunctioning UES can cause problems with swallowing, known as dysphagia, and gastroesophageal reflux disease (GERD).
The lower oesophageal sphincter (LES), or cardiac sphincter, is an involuntary sphincter located at the bottom of the oesophagus, where it connects with the stomach. The LES lets food pass from the oesophagus into the stomach and prevents stomach acid and digestive enzymes from flowing back into the oesophagus. When the LES is weakened or dysfunctional, it can lead to GERD.
The pyloric sphincter, also known as the sphincter pylori, is located at the bottom of the stomach and governs the passage of food out of the stomach into the small intestine. It ensures that the stomach contents are properly mixed with gastric juices and only released in small amounts to avoid overwhelming the digestive process.
The ileocecal sphincter is located at the junction of the small intestine (ileum) and the large intestine, limiting the reflux of colonic contents back into the ileum.
The anal sphincter is located at the opening of the rectum at the end of the digestive tract. It has both inner and outer muscles: the inner sphincter is involuntary and prevents stool from leaking out, while the outer sphincter is predominantly voluntary and allows the passing or holding of stool on demand. A malfunction of the anal sphincter can cause faecal incontinence.
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Sphincter disorders
A sphincter is a circular muscle that maintains constriction of a natural body passage or orifice and relaxes as required by normal physiological functioning. Sphincters are found in many animals, and there are over 60 types in the human body. Sphincter disorders can cause severe pain and discomfort. Here are some examples of sphincter disorders:
Sphincter of Oddi Dysfunction (SOD)
The sphincter of Oddi is a muscle that controls the flow of bile and pancreatic juice into the small intestine. Sphincter of Oddi dysfunction occurs when the sphincter fails to open, causing a backup of digestive juices and severe abdominal pain. This condition is often associated with gallbladder surgery, gallstones, pancreatitis, and other conditions. It can be treated with medications or a procedure called a sphincterotomy.
Anal Sphincter Dysfunction
The anal sphincter, located at the opening of the rectum, regulates defecation. A malfunction of this sphincter can lead to faecal incontinence, or the loss of bowel control. This can be caused by damage to the muscles or nerves in the pelvic floor, or by conditions such as multiple sclerosis or spinal cord injuries. Treatment options may include biofeedback, electrical stimulation, or surgery.
Upper Esophageal Sphincter (UES) Dysfunction
The UES is an involuntary sphincter found at the end of the pharynx that protects the entrance to the esophagus. Malfunction of the UES can cause dysphagia, or difficulty swallowing. It can also be affected by gastroesophageal reflux disease (GERD), leading to persistent acid reflux. Treatment options may include dietary changes, medication, or surgery.
Iris Sphincter Dysfunction
The iris sphincter, or pupillary sphincter, regulates the constriction of the pupil in response to changes in light. When this sphincter malfunctions, it can cause blurred vision and light sensitivity due to abnormal pupil size. Treatment options may include medication or, in some cases, surgery.
Other Sphincter Disorders
Other sphincters in the body, such as those in the gastrointestinal tract, urinary tract, and blood vessels, can also be affected by disorders. These disorders can cause a range of symptoms and may require various treatments depending on the specific sphincter and the nature of the dysfunction.
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Sphincter treatment
A sphincter is a circular muscle that maintains constriction of a natural body passage or orifice and relaxes as required by normal physiological functioning. Sphincters are found in many animals, and there are over 60 types in the human body. They are involved in various bodily functions, including digestion, excretion of waste, and blood flow control.
The treatment for sphincter-related issues depends on the specific sphincter involved and the nature of the problem. Here are some common treatments for sphincter-related disorders:
Esophageal Disorders:
Esophageal disorders, such as gastroesophageal reflux disease (GERD), Barrett's esophagus, and achalasia, can affect the functioning of the lower esophageal sphincter (LES). Treatments for these conditions include:
- Antacids, proton pump inhibitors, and histamine receptor (H2) blockers to reduce stomach acid.
- Endoscopic dilation to open a narrowed esophagus or relax the LES.
- Botulinum toxin (Botox) injections to temporarily stop esophageal spasms or relax the LES.
- Laparoscopic antireflux surgery (Nissen fundoplication) to reinforce the LES and treat GERD or a hiatal hernia.
- Heller myotomy and peroral endoscopic myotomy (POEM) to treat achalasia and esophageal spasms.
- Resistance training: A novel exercise approach involves resistance training for the LES, which has been reported to eliminate gastroesophageal reflux.
Anal Sphincter Dysfunction:
Malfunction of the anal sphincter can lead to fecal incontinence. Treatment options may include:
- Pelvic floor muscle exercises: Strengthening the muscles around the sphincter can help improve voluntary control and reduce incontinence.
- Biofeedback therapy: This involves using sensors to provide information about the sphincter's functioning, helping individuals learn to control the muscles and improve bowel control.
- Surgery: In severe cases, surgical interventions may be considered to improve sphincter function and reduce incontinence.
Urethral Sphincter Dysfunction:
Disorders of the urethral sphincter, which controls the passing of urine, can lead to urinary incontinence. Treatments may include:
- Pelvic floor muscle exercises: Strengthening the muscles around the urethral sphincter can help improve voluntary control and reduce urinary leakage.
- Electrical stimulation: This technique uses mild electrical currents to stimulate the sphincter muscles and improve their function.
- Surgery: In cases of severe urinary incontinence, surgery may be an option to improve sphincter function and reduce urine leakage.
Eye-Related Sphincter Disorders:
Issues with the iris sphincter (pupillary sphincter) in the eye can lead to blurred vision and light sensitivity. Treatments may involve:
- Medication: Certain medications can help regulate the functioning of the iris sphincter and dilator muscles, improving constriction and dilation of the pupils.
- Eye drops: Specific eye drops may be prescribed to help manage light sensitivity and improve pupil response.
- Surgery: In severe cases, surgery may be considered to correct the sphincter muscles' functioning and improve vision and light sensitivity.
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Frequently asked questions
A sphincter is a circular muscle that maintains constriction of a natural body passage or orifice and relaxes as required by normal physiological functioning.
Sphincters are found in many animals, including humans. In the human body, there are over 60 types of sphincters, some of which are microscopically small, such as the precapillary sphincters. Sphincters are found in the gastrointestinal (GI) tract, urinary tract, blood vessels, and eyes.
Some examples of sphincters in the human body include the upper oesophageal sphincter (UES), lower oesophageal sphincter, pyloric sphincter, internal and external anal sphincters, and the sphincter urethrae.
Sphincters are muscles that can contract or close a bodily passage or opening. When a sphincter muscle is contracted, its length is shortened, and the opening is constricted or closed. Relaxation of the muscle causes it to lengthen, opening the passage and allowing the movement of liquids, solids, or gases.
