Sphincters

What are sphincters?

Sphincters are circular-shaped muscles that open and close to control the flow of food, air, bile, pee and poop through your body. When a sphincter is relaxed, a substance can easily flow through it. But when it’s contracted or tightened, nothing can flow through it because it’s closed. Your sphincters play an important role in many bodily processes like digestion, urination (peeing) and defecation (pooping).

Most major sphincters are part of your digestive and urinary systems. But you also have sphincters in your eyes (iris sphincter) and blood vessels (precapillary sphincters).

What does a sphincter do?

The main job of a sphincter is to control the flow of a substance from one part of your body to another. They’re like tiny gates in your body that let substances in and out. Without sphincters, pee or poop would leak out of your body, and your stomach acids would constantly back up into your throat.

Sphincters can be voluntary or involuntary. A sphincter that operates without your control is involuntary or automatic. You don’t have to tell it to work because it’s stimulated by your autonomic nervous system. Other times, you can control a sphincter as part of your somatic nervous system. This means you have some control over the nerves that make it contract and relax (voluntary).

For example, the sphincter between your stomach and small intestine works without you needing to do anything. But you have control over one of the sphincters in your anus (butthole) because you can hold your poop in when you need to.

Where are sphincters in your body?

Sphincters are bands of muscle that surround openings in your body. You have lots of sphincters, although most people only know about the nine major sphincters. Those include:

• Upper esophageal sphincter (UES): This separates your esophagus from your throat. It controls the flow of food and liquid from your throat to your esophagus. It also keeps your airways clear.
• Lower esophageal sphincter (LES): This separates your esophagus and stomach. It prevents the contents of your stomach from coming back up your throat. It stays closed until you swallow, then opens so food can pass.
• Sphincter of Oddi: This controls the flow of bile from the liver and gallbladder and pancreatic juices from your pancreas into your small intestine.
• Pyloric sphincter: This controls the flow of food from your stomach to your small intestine.
• Ileocecal sphincter: This controls the flow of food from your small intestine to your large intestine (colon). It will seal off the small intestine until your food is digested and ready to go to the large intestine.
• Internal anal sphincter: This helps prevent poop or gas from leaking out of your rectum.
• External anal sphincter: This helps you control bowel movements by keeping your anus closed. You send a signal to it to open it (relax it) so you can poop. This means it’s voluntary, and ideally, you have control over when you poop.
• Internal urethral sphincter: This controls the flow of your pee at the bottom of your bladder into your urethra. It opens (or relaxes) to let pee flow out of the bladder.
• External urethral sphincter: This also controls the flow of your pee from your bladder to your urethra. But you can control this sphincter.

What does a sphincter look like?

The exact size and shape of a sphincter vary depending on where it is and what it does. The sphincters in your capillaries are microscopic, while the sphincters in your anus may be the size of a dime.

All sphincters are made of muscle tissue — either smooth muscle or striated muscle. They’re also circular — like a donut or ring.

What health conditions affect your sphincters?

Your sphincters play an important role in many bodily processes. When one is damaged or not working, it can lead to serious problems. Sometimes, sphincters weaken due to:

• Nerve damage
• Aging (muscles naturally weaken as you get older)
• Trauma (like an accidental tear) or stress (from sneezing or coughing)
• Complications from surgery or childbirth

When a sphincter weakens or loses its ability to contract and relax, you might notice:

• You’re leaking pee or have no control over your pee (urinary incontinence).
• You lose control of your bowels (fecal incontinence).
• You have acid reflex or bile reflux.
• You have difficulty swallowing (dysphagia).
• You have abdominal pain.

Possible options for strengthening or repairing a damaged sphincter are:

• Surgery (like to repair a torn sphincter or to place an artificial sphincter)
• Exercises like Kegels

Medications can also relieve the symptoms sphincter dysfunction causes. For example, you can take proton pump inhibitors (PPIs) for acid reflux or loperamide to slow down bowel movements.