Courses for Kids
Free study material
Offline Centres
Store Icon


share icon
share icon

What is a Sphincter Muscle?

To define sphincters, let us understand that these are special circular muscles able to open and close certain body parts. One of the vital sphincters muscle is the sphincter pylori, a thick middle layer of the stomach muscle opening to pylorus caving into the small intestine. Mostly, the sphincters muscle acts as a valve to regulate fluid such as bile, urine, or faecal substance. The mechanism of the sphincter may be involuntary depending on the autonomic nervous system or voluntary operated by the somatic nervous system. The sphincter ani externus control the anal opening by contracting.


The sphincter urethrae are the most paramount voluntary mechanism of urination. Sphincter papillae are located in the iris, making it contract in the presence of bright luminosity. 

(Image Will be Updated Soon)

The sphincter meaning is a ring-shaped muscle that relaxes or contracts to open or close a body passage or opening. To define sphincter, these muscles are smooth muscles that remain in a contraction state. These are specialized latch systems in the contractile filaments permitting sphincters to maintain contracting position with minimum effort. 

The internal anal sphincter is an exception that blocks the backward flow of intraluminal contents. The lower oesophagal sphincter thwarts gastric acid into the oesophagus. Dysfunction of the oesophagal sphincter causes continuous exposure of oesophagal mucosa to gastric acid, which can cause dysplastic heartburn that may become cancerous. The sphincters muscle function of external anal sphincters is to control defecation; it is a short tube of skeletal muscle surrounding the inferior portion of the anal canal.


Sphincters Muscle Stomach 

There are six different sphincter muscles in the abdomen. The upper oesophagal sphincter (UES) is located at the end of the pharynx, where it guards the opening of the oesophagus. UES prevents the induction of air in the oesophagus while breathing and prevents food from getting inside the respiratory system. Because of the location in the pharynx, it also controls vomiting and burping. 

The lower oesophagal sphincter (LES), also called cardiac sphincter, is located at the end of the oesophagus, where it joins the stomach. The principal function of LES is to permit food to pass from the oesophagus to the stomach and to enable air to pass from the stomach while burping. It also prevents the backward flow of gastric acid into the oesophagus.

Pyloric Sphincter

The pyloric sphincter is situated between the stomach and duodenum. This sphincter allows chyme (partially digested food) to transmit from the stomach to the duodenum for further digestion and absorption of nutrients through mucus into the blood. 

Sphincter of Oddi

The sphincter of Oddi (SO) is located at the influx of the bile duct and pancreatic duct at the duodenum. SO opens to allow bile from the gallbladder and enzymes from the pancreas to mix to break down food particles for assimilation. 

Ileocecal Sphincter

At the junction of the small and large intestine, the Ileocecal sphincter is situated. The functionality of this sphincter is not clear, except it allows chyme from the small intestine to the large intestine. 

Anal Sphincter

This sphincter is located at the end of the gastrointestinal tract at the last part of the rectum. This muscle has both inner and outer components to allow the passage of the stool. The automatic nervous system controls the inner sphincter while the outer is managed by the somatic nervous system. There are other sphincters in the body as well.

What is the Function of Sphincter Muscles?

The urethral sphincter controls the holding and pouring of urine. Similar to the anal sphincter, it has inner and outer muscles controlled by the involuntary and voluntary nervous system.


Iris Sphincter

This sphincter, also known as sphincter papilla, is located at the iris, the coloured part of the eye. It surrounds the pupil of the iris and contracts the pupil in bright light through the pupillary light reflex or during accommodation. The diameter of the pupil controls the amount of light that enters the iris reaching at the back of the eye at the retina. 

Sphincter muscles examples are iris sphincter, anal sphincter, ileocecal sphincter, pyloric sphincter; there are about fifty to sixty different types of sphincter muscles in the body. Some are microscopic, such as millions of precapillary sphincters in the circulatory system. Some are controlled by the involuntary nervous system; some respond to specific stimuli; others are controlled by the voluntary nervous system. Sphincter muscles can degenerate or be damaged, leading to several health issues. The dysfunction of the lower oesophagal sphincter (LES) permits gastro acid to enter the oesophagus resulting in acid reflux.

Want to read offline? download full PDF here
Download full PDF
Is this page helpful?

FAQs on Sphincters

1. What is a precapillary sphincter?

The hormone signals and physiological parameters discrete by nerves regulate blood flow through capillary beds. For instance, after a sumptuous meal, the blood flow to the stomach increases by vasodilation of the digestive vessels system and other vessels. On the other hand, during a workout, blood is diverted to skeletal muscle through vasodilation, while blood is reduced in the digestive system through vasoconstriction. The blood flow in capillary beds is controlled by the precapillary sphincter. If the sphincter is relaxed, blood will flow into associated branches of the capillary blow. If all the sphincters are closed, blood will flow directly to the venule from the arteriole via the thoroughfare channel. The precapillary sphincter precisely controls the flow of blood to capillary beds; at any given time, blood is flowing into 5 to 10% of the capillary beds.

2. What is the difference between valve and sphincter?

The main difference between valve and sphincter is that valve is a flutter-like object of hollow origin that allows one-way fluid flow, while sphincter is a ring-like muscle that is capable of contracting with minimum effort or closing a body passage or opening. Valves and sphincters carry out similar tasks in the human body but are designed to allow a one-way flow of fluids and avert backflow. A valve is similar to a door that opens only in one direction, while a sphincter is a circular muscle that can relax or contract. The pulmonary valve, aortic valve, mitral valve are some of the valves present in the body, while iris sphincter, anal sphincter, Ileocecal sphincter, pyloric sphincter are some of some examples of sphincter present in the body.

3. What is the somatic nervous system?

The somatic nervous system is an integral part of the peripheral nervous system associated with conscious activities like running. The somatic nervous system (SNS) transmits motor and sensory signals from and to the central nervous system, thus consisting of both motor and sensory neurons. The somatic nervous system receives and transmits signals from the senses and is also involved in reflex action bypassing the central nervous system for a quick response. The automatic system (ANS) and the somatic nervous system (SNS) are part of the peripheral nervous system and function in different ways. Both SNS and ANS work together to maintain an optimal internal environment called homeostasis, which is essential for survival.