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Sphincter muscles are circular muscles that open and close passages in the body to regulate the flow of substances, such as bile, urine, and faeces. There are over 50 types of sphincter muscles in the human body, some of which function involuntarily, some respond to stimuli, and others are controlled voluntarily. One of the most important human sphincter muscles is the sphincter pylori, which holds food in the stomach until it is thoroughly mixed with gastric juices.
| Characteristics | Values |
|---|---|
| Shape | Circular |
| Location | Natural body passage or orifice |
| Function | Regulate the flow of substances through the body |
| Types | Over 50 distinct types in the human body |
| Size | Some are as large as a walnut, others are microscopic |
| Control | Some function involuntarily, some respond to stimuli, and others are controlled voluntarily |
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What You'll Learn
Sphincter muscles regulate urine flow through the urethra
Sphincter muscles are circular muscles that open and close passages in the body to regulate the flow of substances, such as bile, urine and faeces. There are over 50 distinct types of sphincters in the human body, some of which function involuntarily, some respond to stimuli and others are controlled voluntarily.
The urethral sphincter has inner and outer muscles that regulate urine flow through the urethra. The inner muscle has involuntary control, and the outer muscle has voluntary control. The urethra is the narrow tube through which urine exits the body. When the sphincter muscle is contracted, its length is shortened and the lumen is constricted (closed). Relaxation of the muscle causes it to lengthen, opening the lumen and allowing the passage of urine.
The urethral sphincter is the most important voluntary control of urination. Dysfunction of the urethral sphincter can lead to urinary incontinence (the loss of bladder control).
Other sphincters are involved in the excretion of waste. For example, the sphincter ani externus keeps the anal opening closed by its normal contraction.
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Sphincter muscles are involved in excretion of waste
Sphincter muscles are involved in the excretion of waste. They are ring-like muscles that surround and are able to contract or close a bodily passage or opening.
The most important human sphincter muscle is the sphincter pylori, which is a thickening of the middle layer of stomach muscle around the pylorus (the opening into the small intestine). This holds food in the stomach until it is thoroughly mixed with gastric juices.
The sphincter ani externus keeps the anal opening closed by its normal contraction. The urethral sphincter has inner and outer muscles that regulate urine flow through the urethra. The inner muscle has involuntary control, and the outer muscle has voluntary control. Dysfunction of the urethral sphincter can lead to urinary incontinence (the loss of bladder control).
There are over 50 distinct types of sphincters in the human body, some of which function involuntarily, some respond to stimuli, and others are controlled voluntarily. Some are as large as a walnut, while others are microscopic.
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There are over 60 types of sphincter muscles in the human body
One of the most important human sphincter muscles is the sphincter pylori, a thickening of the middle layer of stomach muscle around the pylorus (opening into the small intestine) that holds food in the stomach until it is thoroughly mixed with gastric juices. The urethral sphincter has inner and outer muscles that regulate urine flow through the urethra. The inner muscle has involuntary control, and the outer muscle has voluntary control. Dysfunction of the urethral sphincter can lead to urinary incontinence.
Precapillary sphincters are the most numerous type of sphincter in the human body. These involuntary sphincters regulate the flow of blood into the tiniest blood vessels in the body, called capillaries. There are millions of these microscopic sphincters located throughout the body, including those that service capillaries of the brain.
Some sphincters are as large as a walnut, while others are microscopic. Sphincters relax at death, often releasing fluids and faeces.
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Sphincter muscles are found in many animals
One of the most important human sphincter muscles is the sphincter pylori, a thickening of the middle layer of stomach muscle around the pylorus (the opening into the small intestine). This holds food in the stomach until it is thoroughly mixed with gastric juices. Other sphincters are involved in excretion of waste: the sphincter ani externus keeps the anal opening closed by its normal contraction, and the sphincter urethrae is the most important voluntary control of urination.
The urethral sphincter has inner and outer muscles that regulate urine flow through the urethra. The inner muscle has involuntary control, and the outer muscle has voluntary control. Dysfunction of the urethral sphincter can lead to urinary incontinence.
There are also sphincters in the eyes that regulate the flow of light. The sphincter pupillae is a ring of fibres in the iris that contracts the pupil in the presence of bright light.
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Sphincter muscles can be controlled involuntarily, or voluntarily
The urethral sphincter, for example, has inner and outer muscles. The inner muscle has involuntary control, while the outer muscle has voluntary control. The outer muscle is the most important voluntary control of urination. Similarly, the anal sphincter, sphincter ani externus, keeps the anal opening closed by its normal contraction.
The sphincter pylori is another example of a sphincter muscle. It is a thickening of the middle layer of stomach muscle around the pylorus (opening into the small intestine). It holds food in the stomach until it is thoroughly mixed with gastric juices.
Precapillary sphincters are the most numerous type of sphincter in the human body. These involuntary sphincters regulate the flow of blood into the tiniest blood vessels in the body, called capillaries.
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Frequently asked questions
Sphincter muscles are circular muscles that surround and are able to contract or close a bodily passage or opening.
Sphincter muscles maintain constriction of a natural body passage or orifice and relax as required by normal physiological functioning. When contracted, the muscle shortens and the opening is closed. When the muscle relaxes, it lengthens, opening the passage and allowing the flow of liquids, solids or gases.
Sphincter muscles open and close passages in the body to regulate the flow of substances, such as bile, urine and faeces.
Sphincter muscles are found in many animals. There are over 50-60 types in the human body, some of which are microscopically small. They are found in the gastrointestinal (GI) tract, urinary tract and blood vessels.
