The Anatomy of Anal Sex

The Anatomy of Anal Sex

The Anatomy: Starting from the Outside

The anus is the opening behind the perineum and is the last section of the digestive tract before elimination occurs. In just 2-4 cm of length, the anus houses a complex interplay between subconsciously and consciously controlled muscles, nerves, and mucosal tissue that allow this system to hold back stool, differentiate solid, liquid, and gas, and protect the digestive tract from pathogens (1). You can say the phrase “smart ass” really comes from the anatomy in this region being quite smart.

The Anus

The anus contains two significant muscles: the internal anal sphincter (IAS) and the external anal sphincter (EAS). A sphincter is a circular muscle which could open and close to allow passage through. You could think of these two sphincters as circling around the anus (2). There are additional muscles in this region, the pelvic floor muscles, which help to support the rectum, anus, and the rest of the pelvic floor.

Internal Anal Sphincter (IAS): The IAS sits just inside the EAS and there is no voluntary control over this muscle. It will relax when stool arrives in the rectum above through the rectoanal inhibitory reflex (2). You cannot sit here reading this article and get this muscle to relax through your own will power. The IAS will only relax through the control of a part of our involuntary nervous system, the parasympathetic nervous system (PNS) (3). The PNS is most
commonly heard of as the “rest and digest” nervous system and is more predominant when the body is relaxed. It is helpful to feel relaxed during anal play to help facilitate this muscle to also relax.

External Anal Sphincter (EAS): The EAS sits just outside the IAS and there is voluntary control over this muscle. That means you could sit here right now and intentionally squeeze your EAS. It will feel like you are holding back gas.

The IAS relaxes when stool arrives and the EAS will react by contracting to prevent gas or stool from leaving the anus until you are in a place where you can empty your bowel. The body controls the EAS and when ready it relaxes and opens by your own will power.

The tissue at the beginning of the anus is supplied by a nerve called the pudendal nerve, which also controls the EAS (1). Remember this is part of our conscious nervous system which makes this region of the anus more sensitive to touch. This also makes this area more susceptible to the sensation of pain (1). Learning to relax the EAS is important for comfortable anal play.

The Rectum

The rectum is above the anus that extends 12-15 cm (4.72 inches - 5.90 inches) and connects to the large intestines (4). It has a significant curvature towards the back called the anorectal angle which, with teamwork from your musculature, helps hold in stool. To compare with the ranges of sizes of objects typically inserted into the anus including penises, toys, and fingers, there is room. Stool reaches here by way of the large intestines. It stretches and widens as
stool arrives until final passage through the anus (4). There is not always stool in the rectum as it is not meant to function as a storage tank. You pass a bowel movement, empty the rectum, and more stool typically does not arrive until just
before you are ready to pass stool again.

A diagram of the rectum and rectal systems made by a pelvic floor PT

Introduction to Anal Play and Penetration

Learn to relax your anus
Remember you could only control the external anal sphincter (EAS). With time and a feeling of relaxation the internal anal sphincter will follow. It could be helpful to start with touch around the anus either solo or with a partner. Experiment with different types of pressure. A firm and broad touch to start could often help if this is feeling too sensitive. Practice relaxing the sphincter here. If you’re comfortable and this feels pleasurable, try inserting a finger and continue as far as is pleasurable.

Use lubricant
The anus and rectum do not sufficiently lubricate for penetrations for toys, a penis, or toys. Insufficient lubrication could increase irritation to the rectum and increase risk for sexually transmitting infections (6). There are specific lubricants for anal penetration but it is okay to use any good quality water, silicone, or oil-based lubricant that you like (Read my article The Myth of Wet and Ready if you need more guidance on the benefits of each).

Try a Toy
Toys are a great option to get more comfortable with anal play. Buy something that excites you or excites both you and your partner. Toys gives you the option to start small and progressively increase width and size as pleasure allows. You could stay in control and use it on your own or use it for partner play. Your toy must be appropriate for anal penetration. A flared base, or flange, is essential for anything being inserted into the anus.

Go Slow
Take your time as you start exploring anal play. It is always okay to stop where you are, take a few deep breaths, and try to relax your anus if you are experiencing any pain. It is also okay to just stop. Exploring should be wanted and fun. Take your pleasure at your own pace.

Happy exploring!


All content copyright Ariel Zablocki

1. Ahmed A, Arbor TC, Qureshi WA. Anatomy, Abdomen and Pelvis: Anal Canal. [Updated 2023 May 22]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from:
2. Tobias A, Sadiq NM. Physiology, Gastrointestinal Nervous Control. In: StatPearls.
StatPearls Publishing, Treasure Island (FL); 2022. PMID: 31424852.
3. Tindle J, Tadi P. Neuroanatomy, Parasympathetic Nervous System. [Updated 2022 Oct 31].
In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available
4. Wang YHW, Wiseman J. Anatomy, Abdomen and Pelvis, Rectum. In: StatPearls. StatPearls Publishing, Treasure Island (FL); 2022. PMID: 30725930.
5. Levan, M. Anatomy and Physiology of Anorectum: the Hypothesis of Fecal Retention, and Defecation. In: Pelvipeineology; 2021. DOI: 10.34057/PPj.2021.40.01.008
6. Fox J, Fidler S. Sexual transmission of HIV-1. Antiviral Res. 2010;85:276–285. doi: 10.1016/ j.antiviral.2009.10.012

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