What Is the Anal Canal?

The anal canal refers to the part from the dentate line to the edge of the anus. The average length of an adult is 2.5 cm. The anal canal refers to the part from the anal canal to the anal canal rectal ring. The average length of an adult canal is 4 cm. The anal canal has 4 boundaries. 2) The sphincter sulcus, which is the white line, is between the edge of the anus and the line of the tooth, about 1 cm from the edge of the anus, facing the junction of the internal and external sphincter. For example, if you point your index finger into the anal canal, you can feel that there is a recessed groove between the internal anal sphincter and the lower part of the external anal sphincter skin, which is the sphincteric groove; About 2.5cm there is a ring of jagged lines called dental floss; (4) The surface between the dental floss and the white line is smooth and shiny, called anal comb.

The anal canal refers to the part from the dentate line to the edge of the anus. The average length of an adult is 2.5 cm. The anal canal refers to the part from the anal canal to the anal canal rectal ring. The average length of an adult canal is 4 cm. The anal canal has 4 boundaries. 2) The sphincter sulcus, which is the white line, is between the edge of the anus and the line of the tooth, about 1 cm from the edge of the anus, facing the junction of the internal and external sphincter. For example, if you point your index finger into the anal canal, you can feel that there is a recessed groove between the internal anal sphincter and the lower part of the external anal sphincter skin, which is the sphincteric groove; About 2.5cm there is a ring of jagged lines called dental floss; (4) The surface between the dental floss and the white line is smooth and shiny, called anal comb.

Chinese name

Anal canal

Department

The end of the digestive tract

Anal column

Longitudinal mucosal wall

Anal door

4cm below the tip of the coccyx

Anal canal morphology

1. Inside view, there are 6 to 10 longitudinal mucosal wrinkled walls in the anal canal, called anal column. The circular line at the upper end of the flat anal column, the anorectal line. The mucosal folds in the shape of a half-moon between the lower ends of adjacent anal columns are called anal valves. The small crypt formed by the anal valve and the lower end of the adjacent anal column is called the anal sinus. The anus and sinus openings are upwards, and there are often fecal debris in the sinuses, which can cause anal sinusitis after infection. In severe cases, anal fistula or sciatic rectal abscess can form. Through the lower end of the anal column and the edge of the anal valve into a zigzag ring line, called the dentate line or anal skin line. The epithelium, blood supply, lymphatic drainage, and nerve distribution covered by this line and below are completely different, and have clinical significance. Just below the dentate line, there is a smooth area with a ring-shaped bulge, called anal comb. Because the deep surface of its epithelium contains venous plexus, it is light blue on the living body. The lower edge of the anal comb is a slightly wavy line, called a white line, about 1.5 cm from the anus. The shallow groove that can be touched during clinical examination is the white line, also called the intermuscular groove, which is the junction of the internal and external anal sphincter. The anal canal mucosa and subcutaneous venous anastomosis plexus can be stagnated due to poor blood flow, causing varicose veins to become hemorrhoids. Those above the dentate line are internal hemorrhoids, those below the dentate line are external hemorrhoids, and those that cross the dentate line and below are mixed hemorrhoids.

2. The anus is an opening at the end of the anal canal, which is equivalent to 4cm below the tip of the coccyx, and it is usually a sagittal longitudinal fissure. Due to the tightening of the anal sphincter, the skin around the anus forms a radial wrinkle containing sweat and sebaceous glands.

3. The anal canal is the end of the digestive tract, and the length from the tooth line to the edge of the anus is about 3 ~ 4cm. Some people extend the upper boundary of the tube to the level of the anal canal rectum ring, called the surgical sacral canal. The front of the anal canal is connected to the perineal body. In men, the perineal body is adjacent to the urethral membrane, urethral bulb, and posterior edge of the urogenital septum. In women, the perineal body is connected to the vaginal vestibule and the lower 1/3 adjacent. The anus and tail ligament are connected to the tailbone by the anus and tail; the sciatic rectum fossa is surrounded on both sides by the anal canal, the external sphincter and the combined longitudinal muscle. The inner layer of the anal canal is the transitional epithelium on the head side and the squamous epithelium on the caudal side. The surface is smooth and white, without sweat glands and sebaceous glands. Excessive resection during surgery may cause anal canal skin defects, membrane eversion and mucus overflow. The anal canal is a muscular channel that connects the rectum to the inside. It is divided into five layers from the inside to the outside: the mucosal layer, the submucosa, the internal anal sphincter, the combined longitudinal muscle, and the external anal sphincter.

Anal canal anatomy status

Anatomy or embryology refers to the anal canal from the edge of the anus to the dentate line, about 3-4cm. In 1985, the World Anatomy Nomenclature Committee set the upper edge of the anorectal anal ring as the upper anal canal, accordingly the rectal column was renamed the anal column, the rectal sinus was renamed the anal sinus, and the anal canal was described by four lines and three bands.

Four lines of anal canal

(1) Anal skin line: the line between the anal canal and the skin, that is, the anus; (2) White line: The Hilton line, located 1 cm above the anal skin line, at the junction of the internal and external sphincter skin, also known as the sphincter groove, It is difficult to identify with the naked eye; (3) dentate line: 2 cm from the anal margin, which is the only circular line that describes the four lines of the anal canal; (4) anal straight line: also known as the Hermann line, on the dentate line 1.5cm.

Three anal canals

(1) Columnar belt: located between the anal canal rectum line and the dentate line, which is the area of the rectal column, an annular area of about 0.5-1.5cm; (2) the middle belt: the area between the dentate line and the white line , Also known as hemorrhoid band; (3) skin band: the area between the white line and the anal skin line, which is a deformed squamous epithelium.

Anal canal

Or rectal column, Morgagnis column, is a vertical mucosal fold on the inner wall of the rectum cavity, about 6-14, column length 1-2cm, width 0.3-0.6cm, is the result of anal sphincter contraction, this column disappears when the rectum expands. The lower edge of each rectal column is connected by a half-moon-shaped mucosal fold. These half-moon-shaped mucosal folds are called anal or rectal valves, and there are 6-12. They are the remains of the original anal membrane and have no valve function. The lower end of the two adjacent anal columns and the anal valve together form a small recess, called anal recess, 6-8, funnel-shaped, the sinus opening is facing the upper part of the intestinal cavity, the sinus floor extends outward and downward, and the depth of the sinus is about 0.3-0.5cm, there is an anal gland opening on the anal sinus floor or anal valve. Below the anal valve there are triangular epithelial protrusions, about 2-6, 0.1-0.3cm high, called anal papilla.