Anus Definition and 5 Steps of Excretion with Diagram

Did you REALLY know? Anus – a 2 canal part that could be the highest-risk factor for AID? And you’d die without this ‘MOST UNDERAPPRECIATED’ part of the body. Read on to discover the quirks and mysteries surrounding the function of anus, its parts, and diseases with a dose of wow.

Anus Definition

The Merriam Webster Dictionary gives different anus definition for the medical students and the English language learners. For medical students, it defines anus as:

Fig. 1: The human anus & nearby body parts.

"The posterior opening of the digestive tract".

For English language learners, on the other hand, it defines the anal opening as:

"The opening on the body present between the person’s buttocks through which the digestive waste passes from the body."

Wikipedia the Free Encyclopedia gives the definition of the anus in these words:

"The anus is an opening at the opposite end of an animal’s digestive tract from the mouth."

On the Dictionary.com, you will find a bit detailed definition:

"The human anus is an opening at the lower end of the alimentary canal for the excretion of the solid waste of the body."

Here is a bit more comprehensive anus definition:

"Playing an important regulatory role in the excretion of digestive wastes, the anal opening is surrounded by a voluntary and an involuntary sphincter, and constitutes the terminal part of the digestive system".

Two round muscular structures line the anus. These muscular structures assist in the opening and closing of the anal aperture.

Anus Definition in Biology

The anus definition biology is specifically for the medical students. “The Online Medical Dictionary” provides the biological definition in these words:

"The lower opening of the digestive tract that is associated with the anal sphincter and lies in the cleft between the buttocks to help in the extrusion of the fecal matter."

So, here you also get a bit understanding of the structure and function of this organ of digestive system. The opening and closing of the hole is under the voluntary control of an individual, particularly, the external sphincter. It is not completely functional in the human babies. However, as the child advances towards maturity, it comes under their deliberate command.

On the attainment of puberty in an individual, pubis hair starts to grow around the anal opening.

Just imagine, "How would your social life be if you were unable to hold and prolong feces before you reach toilet for defecation?"

When you prolong defecation for a longer duration, the excretory matter goes backwards into colon. Here there is further absorption of fluids, salts and any other useful substances. You will learn about the details of the things related to anus definition in the succeeding parts of the article.

Anus Diagram and 5 Steps for Excretion

Looking at the anus diagram, you can easily understand various steps for excretion. Different nearby parts of anus experience physical changes as waste matter reaches there. Here is a brief discussion of the 5-step procedure for excretion.

Fig. 4: Anus Diagram showing different parts of anal canal.

First Step

After digestion in the stomach and the small intestine, the small food particles are taken into the blood stream for use in the body. On the other hand, the undigested material descends to the large intestine for further absorption of left over water and salts. After that, the taste materials reach the rectal region. It is the first step in the process of defecation.

Second Step

In the second step, the waste, semi-solid substances fill the rectum and anal canal. Therefore, the surrounding walls stretch to accommodate it.

Third Step

The nerve endings present at the rectal region deliver the stimulus to the brain. The brain processes this stimulus to generate an appropriate response.

Fourth Step

In the fourth step of the process of defecation, the responding signal reaches the target place. It induces the desire for defecation in the individual. Afterwards, the individual takes appropriate action accordingly.

Fifth Step

The fifth and final step involves the relaxation of the internal and external anal sphincters. The internal sphincter opens through an involuntary action while the external one is under the voluntary control of the individual.

Anus Serving 3 Body Systems

The anus simultaneously serves 3 major body systems, i.e. the digestive, excretory, and reproductive systems.

Digestive System and the Anus

It forms the last piece of the gastrointestinal system. The anus function in the digestive system is to provide an outlet for disposing of the undigested matter out of the body.

Excretory System and the Anus

It performs several jobs in its capacity as an excretory organ. For example, in addition to being an aperture for defecation, the anus regulates bowel movements. Also, it gives the individual conscious control over the process.

Reproductive System and the Anus

Interestingly, the anal hair conducts scents that our ancient selves used for reproductive purposes.

Difference Between Rectum and Anus:

Anus Parts:

Being the last part of the digestive system, there are different parts of the anus as well. All these parts have several roles in performing the excretory function of the fossil materials out of the body.
Read About Anus Parts and Their Functions in Detail

Anus Diseases

Various conditions of the anal canal and anus orifice are common nowadays. The anus diseases also affect the anal glands, muscles and sphincters.
Read About The Anus Diseases and Their Causes in Detail

Simultaneously serving 3 body systems, the anus structure is a complex of internal and external sphincters. It literally means a ring or a circle.

Which one of the anal sphincters helps you consciously hold stools back? Read on to get the answer.

Its thin epithelium and many blood vessels are prone to mild abrasive damages.

Recall if you ever experienced tearing sharp pain during defecation. It could be due to acute or chronic anal fissures.

People may live with and die due to anal diseases like carcinomas without knowing about it!

Did you know? “Soap and shampoo can damage the delicate skin of the anus”, claims Rafael Lugo, a colorectal surgeon from Houston.

Water and wiping are enough for the hygiene of the anus.

Sticks, stones, snow, grass, and leaves are some of the things people used over centuries to wipe their buttocks.

You can read about these anal functions in detail with anus pictures in the succeeding sections. Also, get interesting answers to the FAQs about the anus like:

• Why do human babies not have bowel control?
• What is achieved first: anus control or bladder control?
• How to train children for the voluntary passing of stool?
• Who first develop control over their bladder and anus, a girl or a boy?
• What is the function of anus hair?
• What are anus worms?
• How can anus inflammation be treated?
• Which diseases cause anal cramps?
• How dangerous are the anus tumors?