Dominic Stone
Sphincters are ring-like muscles that maintain constriction of a body passage or orifice and relax as required by normal physiological functioning. There are over 60 types of sphincter in the human body, some of which are microscopically small. Sphincters can be found in many animals. In this article, we will explore how sphincter muscles constrict.
| 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 in the human body, some microscopically small, in particular the millions of precapillary sphincters |
| Function | Sphincters control the release of urine and faeces |
| Location | There are two sphincters at the anus, one internal and one external |
| Relaxation | Relaxation of the muscle causes it to lengthen, opening the lumen and allowing the passage of liquids, solids, or gases |
| Contraction | As long as the sphincter muscle is contracted, its length is shortened and the lumen is constricted (closed) |
| Example | The lower oesophageal sphincter (or cardiac sphincter) is closed most of the time, keeping acids and other stomach contents from pushing up and into the oesophagus, but opens to let swallowed food pass into the stomach |
| Repair | Current options for repair of the internal anal sphincter include grafts of skeletal muscle, injectable silicone material or implantation of mechanical devices |
| Failure | If precapillary sphincters don't work as they should, blood can flow freely into the capillaries and create excessive pressure, leading to edema (fluid buildup) in places like the legs, lungs, or brain |
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What You'll Learn
- The lower oesophageal sphincter (or cardiac sphincter) keeps acids and other stomach contents from pushing into the oesophagus
- The internal anal sphincter contracts to close the anal canal and inhibit the passage of faeces
- The external anal sphincter is a skeletal muscle that acts voluntarily to maintain continence
- The iris sphincter, also known as the pupillary sphincter, is an involuntary sphincter that regulates the constriction of the pupil in the eye
- Precapillary sphincters control the flow of blood into the capillaries
The lower oesophageal sphincter (or cardiac sphincter) keeps acids and other stomach contents from pushing into the oesophagus
The lower oesophageal sphincter (LES), also known as the cardiac sphincter, is a circular muscle that resides at the top of the stomach. It is closed most of the time, keeping acids and other stomach contents from pushing up and into the oesophagus.
The LES opens when you swallow to let food pass into the stomach. It also opens a little to let gas bubbles out when you burp or have hiccups. The LES stays open for about five seconds after you swallow, before closing again.
If the LES doesn't close tightly enough, stomach acid and food particles can rise back up into the oesophagus. This is called acid reflux, and it can cause heartburn. Acid reflux happens when the LES weakens or relaxes enough to let acid pass. Some temporary things can relax the LES, such as lying down after a large meal.
A weak LES is a common cause of gastroesophageal reflux disease (GERD), in which the oesophagus is irritated by stomach acid or bile.
Sphincters are ring-like muscles that maintain constriction of a body passage. They are found in many animals, and there are over 60 types in the human body. Sphincters relax at death, often releasing fluids and faeces.
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The internal anal sphincter contracts to close the anal canal and inhibit the passage of faeces
The internal anal sphincter is a ring-like muscle that contracts to close the anal canal and prevent faeces from passing through. It is one of two sphincters at the anus, the other being the external anal sphincter. The internal sphincter remains in a constant state of contraction, only relaxing in response to inhibitory neural input. This relaxation allows faeces to pass through the anal canal.
The external anal sphincter is a skeletal muscle that acts voluntarily, responding to commands to contract and maintain continence when faeces are propelled into the rectum.
Sphincters are found throughout the human body, with over 60 types, some of which are microscopically small. They are circular muscles that maintain constriction of a natural body passage or orifice and relax as required by normal physiological functioning. For example, the lower oesophageal sphincter (or cardiac sphincter) at the top of the stomach is closed most of the time, preventing stomach acids and contents from entering the oesophagus. However, it opens to allow swallowed food to pass into the stomach.
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The external anal sphincter is a skeletal muscle that acts voluntarily to maintain continence
The internal anal sphincter, on the other hand, is a smooth muscle that remains in continuous contraction, only relaxing in response to inhibitory neural input. This relaxation is part of the rectoanal inhibitory reflex (RAIR), which involves the reflexive relaxation of the internal anal sphincter in response to rectal distension.
Sphincters are ring-like muscles that maintain constriction of a body passage. There are over 60 types in the human body, some of which are microscopically small, such as the millions of precapillary sphincters. Sphincters are found in many animals and are associated with the lumen (opening) they surround. When contracted, the sphincter muscle shortens and the lumen is constricted (closed). Relaxation of the muscle causes it to lengthen, opening the lumen and allowing the passage of liquids, solids, or gases.
For example, the lower oesophageal sphincter (or cardiac sphincter) at the top of the stomach is closed most of the time, preventing stomach acids and contents from entering the oesophagus. However, it opens to allow swallowed food to pass into the stomach. Another example is the iris sphincter, also known as the pupillary sphincter, which is an involuntary sphincter that regulates the constriction of the pupil in the eye.
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The iris sphincter, also known as the pupillary sphincter, is an involuntary sphincter that regulates the constriction of the pupil in the eye
The iris sphincter, also known as the pupillary sphincter or sphincter pupillae, is an involuntary sphincter muscle located in the coloured part of the eye called the iris. It encircles the pupil of the iris and functions to constrict the pupil in bright light via the pupillary light reflex or during accommodation. By controlling the pupil's diameter, the iris controls the amount of light that reaches the back of the eye at the retina.
The iris sphincter is an example of a sphincter muscle, which is a circular muscle that normally 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 ring-like muscles that maintain constriction of a body passage. For example, the lower oesophageal sphincter (or cardiac sphincter), which resides at the top of the stomach, is closed most of the time, keeping acids and other stomach contents from pushing up and into the oesophagus, but opens to let swallowed food pass into the stomach. Sphincters relax at death, often releasing fluids and faeces.
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Precapillary sphincters control the flow of blood into the capillaries
Precapillary sphincters are one of the over 60 types of sphincters in the human body. They are microscopically small, with millions found in the body. Precapillary sphincters control the flow of blood into the capillaries.
Sphincters are ring-like muscles that maintain constriction of a body passage. They are found in many animals. Sphincters relax at death, often releasing fluids and faeces. Each sphincter is associated with the lumen (opening) it surrounds. When contracted, the sphincter muscle shortens and the lumen is constricted (closed). Relaxation of the muscle causes it to lengthen, opening the lumen and allowing the passage of liquids, solids, or gases.
The lower oesophageal sphincter (or cardiac sphincter), for example, resides at the top of the stomach and is closed most of the time, keeping acids and other stomach contents from pushing up and into the oesophagus. It opens to let swallowed food pass into the stomach. The internal anal sphincter contracts to close the anal canal and inhibit the passage of faeces and relaxes to propel faeces. It remains in continuous contraction and relaxes only in response to inhibitory neural input.
If precapillary sphincters don't work as they should, blood can flow freely into the capillaries and create excessive pressure. This can cause fluids to leak out of the capillary walls, leading to edema (fluid buildup) in places like the legs (peripheral edema), lungs (pulmonary edema), or brain (cerebral edema).
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Frequently asked questions
Sphincters are ring-like muscles that constrict a body passage. As long as the sphincter muscle is contracted, its length is shortened and the lumen is constricted (closed).
Sphincters maintain constriction of a natural body passage or orifice and relax as required by normal physiological functioning. For example, the lower oesophageal sphincter (or cardiac sphincter) is closed most of the time, keeping acids and other stomach contents from pushing up and into the oesophagus, but opens to let swallowed food pass into the stomach.
Relaxation of the muscle causes it to lengthen, opening the lumen and allowing the passage of liquids, solids, or gases.
The internal anal sphincter contracts to close the anal canal and inhibit the passage of faeces. It relaxes to propel faeces.
If a sphincter doesn't work as it should, fluids can leak out. For example, if precapillary sphincters don't work properly, blood can flow freely into the capillaries and create excessive pressure. This can lead to edema (fluid buildup) in places like the legs, lungs, or brain.
