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Image of caplets that supply lactase to the body

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This enzyme digests lactose, specifically the lactose in the cheese and butter, into glucose and galactose

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Red: Main path
Yellow: Ingredients
Blue: Enzymes
Green: Digestion Types
Purple: Concepts
White: Key

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Waste is excreted through here

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Overview

What is the anus?

Your anus is the end of your large intestine - the last three or four centimeters of it. This is where your large intestine opens to the outside to let your poop come out. At your anus, the tissue lining the inside of your large intestine begins to change from tender mucosa to normal skin. Ring-like muscles called sphincters surround your anus and keep it closed until they're activated to let your poop come out.

What is the difference between the anus vs. the rectum?

Your rectum is the section of your large intestine that comes just before your anus. It's about five or six inches long. This is the reservoir where poop collects before it's ready to come out. When your rectum is full, nerves trigger the urge to have a bowel movement, and your internal anal sphincter relaxes automatically. Your external sphincter is under your conscious control to activate when you're ready.

Function

What is the function of the anus?

Your anus facilitates your bowel movements. Nerves and muscles surrounding your anus coordinate to tell you when you need to poop, while allowing you to hold it in until you're able to reach a toilet. When you're ready, these nerves and muscles coordinate again to push poop out of your body. The mucous lining in your anus secretes mucus to lubricate the passage and help your poop pass smoothly through.

Anatomy

What is the anatomy of the anus?

A row of vertical folds in the inside lining divides your anus into upper and lower parts. The folds form columns (anal columns) that are separated by grooves (anal sinuses) that end in smaller folds (anal valves). Your anal sinuses contain mucus-secreting glands. The valves mark the end of the sinuses and the dividing line where the mucous lining begins changing into skin (the pectinate line or dentate line).

The upper and lower parts of your anus (above and below the pectinate line) have different vascular supply and nerve supply. This is why your anus is much more sensitive to pain and other sensations below the line (in the lower two-thirds). Your internal and external anal sphincters also have a different nerve supply, which is why the inner one is involuntary (out of your control) and the outer one is under voluntary control.

Conditions and Disorders

What are the common conditions and disorders that affect the anus?

Anal conditions and disorders include:

Hemorrhoids. Hemorrhoids are swollen blood vessels in your anus or rectum. They're called internal hemorrhoids above the pectinate line, and external hemorrhoids below it.

Anal fissure. An anal fissure is a tear in your anus lining. It can cause pain and bleeding.

Anal yeast infection. A infection (Candidiasis) can cause itching and pain in or around your anus (your perianal region).

Anal STIs. Sexually transmitted infections and diseases can affect your anus through anal sex, including anal penetration, oral and digital (finger) stimulation. Anal STIs include chlamydia, genital herpes, human papillomavirus (anal warts), syphilis, gonorrhea, hepatitis A, hepatitis B and HIV.

Anal abscess/anal fistula. When an anal gland becomes clogged and infected, an abscess, or pocket of pus, forms under your skin. More than half of drained anal abscesses leave behind an anal fistula, an abnormal, tunnel-like passageway leading from the gland to your outer skin.

Anal stenosis. Stenosis is when one of your body canals narrows, usually due to scar tissue on the inside. Injury, surgery or disease can cause scarring inside your anus that leads to stenosis.

Anorectal malformation. An anorectal malformation is a birth defect that causes your anus to develop abnormally. A missing or misplaced anus may need surgical repair (anoplasty).

Anismus. Anismus happens when the muscles and nerves involved in pooping can't coordinate correctly to make a bowel movement. It's also called dyssynergic defecation.

Anal incontinence. Fecal incontinence can occur when your anal sphincter muscles fail to control your bowel movements. It can cause poop to come out when you don't want it to.

Anal cancer. Anal cancer is a separate disease from rectal or colon cancer. Cancer that develops in your anal canal is usually squamous cell carcinoma.

What are the signs or symptoms of possible health issues in the anus?

You should see a healthcare provider if you notice symptoms such as:

Anal pain. Pain in your anus could be a sign of many different conditions.

Anal lesions. Warts, rashes, bumps, sores and tears can appear in and around your anus.

Anal itching. Itching in and around your anus could be related to an allergy or infection.

Anal bleeding. You might notice bleeding from your anus when you go to the bathroom or when you wash or scratch your anus. Bleeding may be painful or not, depending on the cause.

Anal discharge. Mucus or pus in your poop or in your underwear might be a sign of disease.

Difficulty with bowel movements. Difficulty getting poop out or holding poop in might involve your anal muscles. Missing or excessive bowel movement urges might involve your nerves.

What tests do healthcare providers use to check on the health of the anus?

Anal exams include:

Digital rectal exam. A digital (fingers) rectal exam is a physical exam using lubricated gloved fingers inside your anus and rectum.

Anoscopy. An anoscopy uses a small scope to look inside your anal canal. Sometimes, it uses a high-resolution magnifier with the scope.

Barium enema. This is a gastrointestinal X-ray exam that looks inside your colon, rectum and anus. It takes real-time video X-rays, called fluoroscopy. A barium enema helps your insides show up better in images. A technician will inject the barium into your anus.

Defecography. A defecography takes X-rays of your body mechanics as you poop. It's used to identify mechanical and functional pooping disorders.

Anorectal manometry. This test measures your anal muscle contractions and tests your level of anal sensation and nerve response, as well as muscle control.

Electromyogram. Electromyography (EMG) tests the electrical activity in your muscles. It can help diagnose issues with your anal sphincters.

Care

How can I keep my anus healthy?

You can help take care of your anus by:

Practicing safe sex. Screen your partners before sex, and when in doubt, use protection to prevent STIs. Use lubrication to prevent injuring your anal tissues.

Eating plenty of fiber. Whole foods, especially plants, are an important source of dietary fiber, which helps keep bowel movements smooth and regular.

Practicing gentle hygiene.Wash and wipe well, but don't use harsh soaps or wet wipes, which can disturb the sensitive skin and mucosa in your anus.

Taking symptoms seriously. Don't be too embarrassed to contact a healthcare provider about symptoms in your anus and get the care you need.

A note from Cleveland Clinic
Your anus is a gateway between your insides and the outside. This gives it an important role in your health. It opens to let food waste come out at the end of its journey through your digestive tract. It also closes to keep infections out. Your anus is small, but if it's injured or not working well, the symptoms and repercussions might be large. Don't hesitate to seek care for conditions affecting your anus.

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Your anus is the last two inches of your large intestine. Poop in your rectum triggers your anal sphincter muscles to release so it can come out.

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Nutrients pass through the villi and into the bloodstream, where it travels to different parts of the body

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Waste is stored here until it is excreted

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The rectum is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. The adult human rectum is about 12 centimetres (4.7 in) long, and begins at the rectosigmoid junction, the end of the sigmoid colon, at the level of the third sacral vertebra or the sacral promontory depending upon what definition is used. Its caliber is similar to that of the sigmoid colon at its commencement, but it is dilated near its termination, forming the rectal ampulla. It terminates at the level of the anorectal ring (the level of the puborectalis sling) or the dentate line, again depending upon which definition is used. In humans, the rectum is followed by the anal canal which is about 4 centimetres (1.6 in) long, before the gastrointestinal tract terminates at the anal verge. The word rectum comes from the Latin , meaning straight intestine.

The rectum is a part of the lower gastrointestinal tract. The rectum is a continuation of the sigmoid colon, and connects to the anus. The rectum follows the shape of the sacrum and ends in an expanded section called an ampulla where feces are stored before their release via the anal canal. An ampulla (from Latin bottle) is a cavity, or the dilated end of a duct, shaped like a Roman ampulla. The rectum joins with the sigmoid colon at the level of S3, and joins with the anal canal as it passes through the pelvic floor muscles.

Unlike other portions of the colon, the rectum does not have distinct taeniae coli. The taeniae blend with one another in the sigmoid colon five centimeters above the rectum, becoming a singular longitudinal muscle that surrounds the rectum on all sides for its entire length.

Blood supply and drainage

The blood supply of the rectum changes between the top and bottom portions. The top two thirds is supplied by the superior rectal artery. The lower third is supplied by the middle and inferior rectal arteries.

The superior rectal artery is a single artery that is a continuation of the inferior mesenteric artery, when it crosses the pelvic brim. It enters the mesorectum at the level of S3, and then splits into two branches, which run at the lateral back part of the rectum, and then the sides of the rectum. These then end in branches in the submucosa, which join with ( anastamose) with branches of the middle and inferior rectal arteries.

Microanatomy

The microanatomy of the wall of the rectum is similar to the rest of the gastrointestinal tract; namely, that it possesses a mucosa with a lining of a single layer of column-shaped cells with mucous-secreting goblet cells interspersed, resting on a lamina propria, with a layer of smooth muscle called muscularis mucosa. This sits on an underlying submucosa of connective tissue, surrounded by a muscularis propria of two bands of muscle, an inner circular band and an outer longitudinal one. There are a higher concentration of goblet cells in the rectal mucosa than other parts of the gastrointestinal tract.

The lining of the rectum changes sharply at the point where the rectum meets the anus. Here, the lining changes from the column-shaped cells of the rectum to multiple layers of flat cells.

The rectum acts as a temporary storage site for feces. The rectum receives faecal material from the descending colon, transmitted through regular muscle contractions called peristalsis. As the rectal walls expand due to the materials filling it from within, stretch receptors from the nervous system located in the rectal walls stimulate the desire to pass feces, a process called defecation.

An internal and external anal sphincter, and resting contraction of the puborectalis, prevent leakage of faeces ( faecal incontinence). As the rectum becomes more distended, the sphincters relax and a reflex expulsion of the contents of the rectum occurs. Expulsion occurs through contractions of the muscles of the rectum.

The urge to voluntarily defecate occurs after the rectal pressure increases to beyond 18 mmHg; and reflex expulsion at 55 mmHg. In voluntary defecation, in addition to contraction of the rectal muscles and relaxation of the external anal sphincter, abdominal muscle contraction, and relaxation of the puborectalis muscle occurs. This acts to make the angle between the rectum and anus straighter, and facilitate defecation.

Clinical significance

Examination

For the diagnosis of certain ailments, a rectal exam may be done. These include faecal impaction, prostatic cancer and benign prostatic hypertrophy in men, faecal incontinence, and internal haemorrhoids. Forms of medical imaging used to examine the rectum include CT scans and MRI scans. An ultrasound probe may be inserted into the rectum to view nearby structures such as the prostate.

Colonoscopy and sigmoidoscopy are forms of endoscopy that use a guided camera to directly view the rectum. The instruments may have the ability to take biopsies if needed, for diagnosis of diseases such as cancer. A proctoscope is another instrument that is used to visualise the rectum.

Body temperature can also be taken in the rectum. Rectal temperature can be taken by inserting a medical thermometer not more than 25 mm (1 inch) into the rectum via the anus. A mercury thermometer should be inserted for 3 to 5 minutes; a digital thermometer should remain inserted until it beeps. Normal rectal temperature generally ranges from 36 to 38 °C (96.8 to 100.4 °F) and is about 0.5 °C (1 °F) above oral (mouth) temperature and about 1 °C (2 °F) above axilla (armpit) temperature.[citation needed ] Availability of less invasive temperature-taking methods including tympanic (ear) and forehead thermometers has facilitated reduced use of this method.

Route of administration

Some medications are also administered via the rectum ( Latin: per rectum). By their definitions, suppositories are inserted, and enemas are injected into the rectum. Medications might be given via the rectum to relieve constipation, to treat conditions near the rectum, such as fissures or haemorrhoids, or to give medications that are systemically active when taking them by mouth is not possible. People do not tend to like medications administered by this route because of both cultural issues, discomfort, and issues that may affect the medication working, such as leakage.

Constipation

One cause of constipation is faecal impaction in the rectum, in which a dry, hard stool forms.[citation needed ] Constipation is most commonly because of dietary and lifestyle factors such as inadequate hydration, immobility, and lack of dietary fibre, although there are many potential causes. Such causes may include obstruction because of narrowing, local disease (such as Chron's disease, fissues or haemorrhoids), or diseases that affect the neurological control of the bowel, or slow bowel transit time, including spinal cord injury and multiple sclerosis; use of medications such as opioids, and conditions such as diabetes mellitus, as well as severe illness. High calcium levels and low thyroid activity may also cause constipation.

Testing might be carried out to investigate the cause. This may include blood tests such as biochemistry, calcium levels, thyroid function tests. A a digital rectal exam may be performed to see if there is stool in the rectum, and if there is an obstruction. When symptoms such as weight loss, bleeding through the rectum, or pain are present, addtional investigations such as a CT scan may be ordered. If constipation persists despite trying simple treatments, testing may also include anal manometry to measure pressures in the anus and rectum, electrophysiological studies, and magnetic resonance proctography.

In general however, constipation is treated by improving factors such as hydration, exercise, and dietary fibre. Laxatives may be used. Constipation that persists may require enemas or suppositories. Sometimes, use of the fingers or hand ( manual evacuation) is required.[citation needed ] Although peristalsis in the colon delivers material to the rectum, laxatives such as bisacodyl or senna that induce peristalsis in the large bowel do not appear to initiate peristalsis in the rectum. They induce a sensation of rectal fullness and contraction that frequently leads to defecation, but without the distinct waves of activity characteristic of peristalsis.

Inflammation

Other diseases

Other diseases of the rectum include:

Society and culture

Sexual stimulation

Due to the proximity of the anterior wall of the rectum to the vagina in females or to the prostate in males, and the shared nerves thereof, rectal stimulation or penetration can result in sexual arousal.

English rectum is derived from the full Latin expression intestinum rectum. The English name straight gut truly expresses the literal meaning of this expression, as Latin rectum means straight, and intestinum means gut. This Latin expression is a translation of Ancient Greek ἀπευθυσμένον ἔντερον, derived from ἀπευθύνειν, to make straight, and ἔντερον, gut, attested in the writings of Greek physician Galen. During his anatomic investigations on animal corpses, Galen observed the rectum to be straight instead of curved as in humans. The expressions ἀπευθυσμένον ἔντερον and intestinum rectum are therefore not appropriate descriptions of the rectum in humans. Apeuthysmenon can be considered as Latinization of ἀπευθυσμένον ἔντερον and euthyenteron has a similar meaning (εὐθύς = straight). Much of the knowledge of the anatomy of the rectum comes from detailed descriptions provided byn Andreus Vesalius in 1543.

References

Further reading

Ralston SH, Penman ID, Strachan MW, Hobson RP (2018). Davidson's principles and practice of medicine (23rd ed.). Elsevier. ISBN 978-0-7020-7028-0.

Standring S, ed. (2016). Gray's anatomy : the anatomical basis of clinical practice (41st ed.). Philadelphia. ISBN 9780702052309. OCLC 920806541.

Young B, O'Dowd G, Woodford P (2013). Wheater's functional histology: a text and colour atlas (6th ed.). Philadelphia: Elsevier. ISBN 9780702047473.

Barrett KE, Barman SM, Yuan JX, Brooks H (2019). Ganong's review of medical physiology (26th ed.). New York. ISBN 9781260122404. OCLC 1076268769.

Solomon EP, Schmidt RR, Adragna PJ (1990). Human anatomy & physiology (2nd ed.). Philadelphia: Sunders College Publishing. ISBN 0-03-011914-6.

External links

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The rectum is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. The adult human rectum is about 12 centimetres (4.7 in) long, and begins at the rectosigmoid junction, the end of the sigmoid colon, at the level of the third sacral vertebra or the sacral promontory depending upon what definition is used.

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Takes water and salt out of waste

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Similar to salivary amylase (left), except secreted by the pancreas

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Enzymes break down food again here until they can pass through the villi

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This enzyme is used to break down lipids (butter), into fatty acids. The fatty acids are absorbed and stored throughout the body

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The breakdown of complex molecules into smaller pieces through use of enzymes

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This enzyme digests protein, specifically the protein in the cheese, into amino acids

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The hydrochloric acid in it breaks down the food more and mushes remaining food after digestion together

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The connector of the throat and stomach

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The physical breaking down of food

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This enzyme digests the starch, specifically the starch in the bread, into glucose

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The food is chewed into small pieces

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Made up by fat (lipids)

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Made up of protein

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Made up of carbohydrates