Organs Rectum Wall
Circular Muscle of Rectum
The pelvic floor is a sheet of muscle through which the rectum passes and becomes the anal canal. The anal canal is surrounded by the anal sphincter complex, which is comprised of both an internal and external component. Many of the disorders above are due to improper functioning of the pelvic floor muscles. The levator ani muscle (also called the pelvic diaphragm) is the major component of the pelvic floor. The levator ani muscle is actually a pair of symmetrical muscular sheets comprised of 3 individual muscles – the iliococygeus, pubococcygeus, and puborectalis. The puborectalis is a U-shaped muscle that attaches to the pubic tubercle (“the pubic bone”) and wraps around the rectum – under normal circumstance, this muscle is contracted, maintaining a “bend” in the rectum and contributing to stool continence. The act of bearing down to pass a bowel movement typically causes this muscle to relax, allowing the rectum to straighten. In addition to the rectum, the urethra, which carries urine from the bladder to the outside of the body, also passes through the front portion of the pelvic floor, as does the vagina in females. Source
Peritoneum
The peritoneum is a layer of serous membrane that constitutes the inner lining of the abdominopelvic cavity. This article will highlight the main anatomical features of the peritoneum and its subdivisions, the omenta, the mesenteries, the peritoneal ligaments and the epiploic foramen. Source
Inferior Rectal Valve
Two to three large crescentlike folds known as rectal valves are located in the rectal ampulla. These valves are caused by an invagination, or infolding, of the circular muscle and submucosa. The columnar epithelium of the rectal mucosa, innervated by the autonomic nervous system, changes to the stratified squamous (scalelike) type, innervated by the peripheral nerves, in the lower rectum a few centimetres above the pectinate line, which is the junction between the squamous mucous membrane of the lower rectum and the skin lining the lower portion of the anal canal. Source
Internal Rectus Venous
It consists of two parts, an internal in the submucosa, and an external outside the muscular coat. The internal plexus presents a series of dilated pouches which are arranged in a circle around the tube, immediately above the anal orifice, and are connected by transverse branches. This internal plexus is also known in some medical communities as the Irving plexus.
Anal Sinus
These are furrows in the anal canal, that separate the anal columns from one another. The anal sinuses end below in small valve-like folds, termed anal valves.
Anal Column
These are a number of vertical folds, produced by an infolding of the mucous membrane and some of the muscular tissue in the upper half of the lumen of the anal canal. The lumen has folds of mucous membrane (anal columns) produced by arterial cavernous bodies (anal cushions) in the submucosa. These columns are connected to each other at their distal ends by transverse folds (anal valves). Behind the anal valves lie crypts (crypts of Morgagni) into which the excretory ducts of the anal glands open. All anal valves together form the dentate (or pectinate) line, a serrated line where the intestinal mucosa merges with the squamous epithelium of the anal canal. Source
Deep External Sphincter
This is a flat plane of muscular fibers, elliptical in shape and intimately adherent to the skin surrounding the margin of the anus. So the external sphincter is a layer of voluntary (striated) muscle encircling the outside wall of the anal canal and anal opening. Source
Internal Sphincter
The internal sphincter is part of the inner surface of the canal, it is composed of concentric layers of circular muscle tissue and is not under voluntary control. Source
Subcutaneous External Sphincter
The subcutaneous surrounds the lowermost portion of the canal.
Pectinate Line
This is a line which divides the upper two thirds and lower third of the anal canal. Developmentally, this line represents the hindgut-proctodeum junction.
External Rectus Venous
Surrounds the rectum and communicates in front with the vesical venous plexus in the male, and the vaginal venous plexus in the female.
Longitudinal Muscle of Rectum
Thsi also known as The longitudinal anal muscle. has been described as a vertical layer of muscular tissue interposed between the circular layers of the internal (IAS) and external (EAS) anal sphincters.
Pelvirectal Space
Of or relating to the pelvis and rectum.
Levator Ani Muscle
The levator ani is a broad, thin muscle, situated on either side of the pelvis. It is formed from three muscle components: the puborectalis, the pubococcygeus muscle (which includes the puborectalis) and the iliococcygeus muscle. It is attached to the inner surface of each side of the lesser pelvis, and these unite to form the greater part of the pelvic floor. The coccygeus muscle completes the pelvic floor which is also called the pelvic diaphragm. It supports the viscera in the pelvic cavity, and surrounds the various structures that pass through it. The levator ani is the main pelvic floor muscle and painfully contracts during vaginismus. It also contracts rhythmically during orgasm.
Ischiorectal Fossa
This is a fat-filled space of the perineum. The ischioanal fossa is a paired triangular-shaped space lateral to the anal canal with an apex directed anteromedially towards the pubic symphysis. Each ischioanal fossa is separated from the other by the anococcygeal body but they do still communicate superiorly to this and posterior to the anal canal. Source
Puborectalis Muscle
Puborectalis muscle is a band of muscle fibres that help to maintain faecal continence. This muscle contracts and relaxes to control the defecation process. It is a skeletal muscle and therefore, conscious thought, as well as posture, manipulates its function. It creates a loop like a sling around the rectum to pull it in a forward direction forming an acute angle between the anus and rectum. The anorectal angle is changed during defecation. When a person sits in an upright position to pass stool such as on the modern toilets – there is only a partial opening of the anal sphincter. This is due to the position of the puborectalis muscle during an upright sitting posture. However, in a squatting position, the muscle opens properly allowing a free passage of stool without any straining or discomfort. Source
Anal Crypt
The depression between rectal columns that encloses networks of veins that, when inflamed, are called hemorrhoids. Anal crypts are tiny recesses of epithelium at the upper end of the anal canal at the mucocutaneous junction. They are tiny mucus glands of lubrication arranged in a circle around the upper end of the anal canal. Located between normal structures called anal papillae, crypts are usually small, but visible enough to help give the pectinate line a serrated appearance on anoscopy. Crypts are normal structures causing no symptoms unless they become inflamed. They are small areas of skin situated between the anal papillae. Source
Anal Gland
The anal glands are located in the wall of the anal canal. They secrete into the anal canal via anal ducts which open into the anal crypts along the level of the dentate line. The glands themselves are located at varying depths in the anal canal wall, some in between the layers of the internal and external sphincter (the intersphincteric plane). The cryptoglandular theory states that obstruction of these ducts, presumably by accumulation of foreign material (e.g. fecal bacterial plugging) in the crypts, may lead to perianal abscess and fistula formation.
Anal Valve
The anal valves are small valve-like folds at the lower ends of the anal sinuses in the rectum. The anal valves join together the lower ends of the anal columns.
Anal Verge
The anal verge is the distal end of the anal canal, forming a transitional zone between the epithelium of the anal canal and the perianal skin. It should not be confused with the “pectinate line”.