Anus

The anus is the last part of the body’s gastrointestinal tract (GIT). At this last part, temporary storage of faecal matter occurs and discharges them out of the body. The anus is about 4 cm long. The excreta from the fully-digested food is sent to the anus after the digestion process completes. The rectum can temporarily store the faecal matter. Some circular muscles help in controlling the opening of the anus. Internal rectal pressure is developed in the rectum to discharge the faecal matter.  

The GIT system consists of four layers:

1) Outer layer – Serosa

2) Muscularis

3) Sub-mucosa
4) Inner-mucosa

Muscular sphincter of anus

The anus is surrounded by two muscular sphincters, which cover the lumen.

Internal anal sphincter: 

The internal anal sphincter is made up of smooth muscle fibre. It is involuntary in nature as well as myogenic due to the presence of smooth muscle. Therefore, calcium is necessary for the working of the internal anal sphincter. It’s about 2-4 cm in length. The parasympathetic nervous system (PANS) inhibits the contraction of the internal anal sphincter. 

External Anal Sphincter:

The external anal sphincter is made up of skeletal muscle fibre. It is involuntary, and it is about 8-10cm. The autonomic nervous system (ANS) controls the external anal sphincter.

Blood supply

Blood is supplied to the anus by the superior rectal artery, which is a branch of mesenteric artery, and by the superior rectal vein, a part of the hepatic portal system.

Histology of anus:

Colorectal zones: It consists of simple columnar epithelium. There are small arteries present and have some folds of the mucous membrane.

Transitional zones also consist of simple columnar epithelium and stratified squamous epithelium. The transitional zones’ characteristic feature is the tubular epithelial ducts.

Endoderm: It consists of stratified squamous non-keratinized epithelium. This zone contains neurons, which help identify whether the faecal matter state is solid, liquid or gas. The endoderm is associated with only the internal anal sphincter.

Cutaneous zone: This zone consists of stratified squamous keratinised epithelium. In this zone, the skin is associated. This zone also contains glands like sweat and sebaceous. Hair follicles are also present in this zone.

Diseases

Various diseases can affect the anus. Some of them are:

Anal cancer

Anal stenosis

Anal Crohn’s disease

Haemorrhoids, ie, swollen veins of the lower rectum or piles

Faecal incontinence

Anal cancer

Anal cancer is a serious disease that affects the anus. It’s also called anal carcinoma.

What causes anus cancer?

It is majorly caused due to human papillomavirus (HPV) infection. Due to the HPV, the immune system weakens and causes conditions like HIV infection or organ transplant. Anus cancer is also caused by other factors like smoking, anal sexual intercourse, too many sexual partners, etc.

Signs or symptoms of anal cancer

There are a set of symptoms of anal cancer:

• Pain around the anus.
• Bleeding or discharge from the anus.
• Itching around the anus area.
• Irregular bowel habitat.
• High pressure during defecation.

Test to diagnose anal and rectum Cancer:

• Digital rectal examination. (DRE) –

In this test, a nurse or Doctor uses lubricated gloves on the hands and puts them in the lower part of the rectum to examine the anus or rectum.

• Anoscopy

In this technique, a small tube is inserted into the anal region to examine cancer.

• Proctoscopy

It is a procedure in which a thin tube-like instrument is inserted with having light, lens, camera to examine the anal and rectum region.

• Biopsy

From the abnormal region, small cell/tissue is extracted and examined by the pathologists under a microscope to detect and check the signs or symptoms of cancers.

• Ecto and endo anal ultrasound technique:

In this technique, a high energy sound wave is produced in the anus or the rectum region, forming a picture through sonography.

Treatment of anal cancer

Anal cancer is a life-threatening disease. Yet, a few forms of treatment are often used to treat anal cancer. Some of them are:

• Surgery

Surgery is often done to remove the tumour formed during cancer from the anus along with some healthy tissue.

In some instances, even the anus, the rectum and a tiny part of the colon from the large intestine are surgically removed. Disposal bags are used in this case to collect the excreta.

• Radiation therapy

In many cases, where surgery isn’t feasible, the doctors use radiation to kill the tumour or cancerous cells from the anus. X-ray is used at times to kill the cells.

• Chemotherapy

Like other cancer treatment cases, chemotherapy has also been used to inhibit or kill anus cancer cells. The drugs may be intravenous or orally taken.

Conclusions

The anus is the terminal part of the gastrointestinal tract through which the body discharges the excreta of the digested food. The anus is about 4 cm long with different layers like Serosa, Muscularis, Submucosa, Mucosa. The anus consists of four types of cells – colorectal zones, transitional zones, endodermic and cutaneous zones. Each has different types of epithelial tissue like columnar, stratified, squamous and keratinised. The superior rectal artery and veins do blood supply to the anus.

Some of the diseases affecting the anus are – anal cancer, anal stenosis, anal Crohn’s Disease, haemorrhoids (swollen veins of the lower rectum or piles) and faecal incontinence. Anal cancer is a major disorder of the anus. Some of the symptoms related to anal cancer are bleeding or discharge of fluid, painful defecation, irregular bowel movement, etc. Anal cancer is detected by digital rectal examination, anoscopy, proctoscopy, biopsy, ecto and endo anal ultrasound technique, etc. Treatment is also done by radiotherapy, chemotherapy and surgical methods.