Pelvic Floor Anatomy and Applied Physiology
Section snippets
Internal Anal Sphincter
Circular muscle layer of the rectum expands caudally into the anal canal and becomes the IAS. The circular muscles in the sphincteric region are thicker than those of the rectal circular smooth muscle with discrete septa in between the muscle bundles. Similarly, the longitudinal muscles of the rectum extend into the anal canal and end up as thin septa that penetrate into the puborectalis and EAS muscles. Longitudinal muscle of the anal canal is also referred to as the “conjoined tendon”
Puborectalis and deep pelvic floor muscles
In 1555, Vesalius14 wrote an account of the pelvic floor muscles, which he named “musculus sedem attollens.” This was later replaced by the more definitive name of “levator ani” by Von Behr and coworkers.15 The pelvic diaphragm, first so named in 1861 by Meyer,16 included primitive flexors and abductors of the caudal part of the vertebral column. These muscles included coccygeus (also referred to as “ischiococcygeus”), ileococcygeus, and pubococcygeus and these three muscles were believed to
Pelvic floor imaging
Advances in MRI, CT scanning, and three-dimensional US imaging have provided novel insights into the anatomy and function of the pelvic floor muscles. Ultrafast CT scanning can image dynamic changes in the pelvic floor muscle during contraction and defecation.25 These studies reveal that the levator hiatus becomes smaller during pelvic floor contraction and larger during the act of defecation (Fig. 5). The changes in the pelvic floor hiatus size are predominantly related to the puborectalis
Sensory function of the rectum and anal canal
Similar to other viscera, colonic distention results in nondescript discomfort and at higher degrees of distention one feels pain that is poorly localized. Rectal distention, however, is perceived as rectal fullness that is more localized and somewhat defined (ie, as a desire to defecate). In addition to mucosal nerve endings, there are also low threshold, slowly adapting mechanoreceptors in the muscularis propria of the rectum. These intraganglionic laminar endings detect mechanical
Applied physiology
Ideally speaking, one should describe the function of each component of the pelvic floor muscle individually; however, no such information is available. Broadly, the pelvic floor muscles can be considered to have two important functions. They provide support or “floor” to the pelvic viscera; and they provide constrictor functions to the urethra, vagina, and anal canal. Described next is the role of the pelvic floor muscles on the rectum and anal canal, touching on their role in the closure
Anal canal pressure
Anal canal pressure is a major determinant of the strength of anal continence mechanism and its brief discussion is extremely relevant. Anal canal pressure can be measured with perfusion manometry (using either side hole or sleeve sensor); solid-state transducers; or more recently with a large number of closely spaced array of pressure sensors (high-resolution manometry).29 Furthermore, the pressures can be displayed in the form of colored topographic (contour) plots, which are convenient to
Vaginal high-pressure zone
How does puborectalis, a U-shaped muscle, increase the anal canal pressure? The two anterior limbs of puborectalis muscle are attached to the two pubic rami and posteriorly they join each other behind the anal canal. Contraction of the puborectalis muscle lifts up the anal canal in the ventral or anterior direction and in so doing causes compression of the anal canal, vagina, and urethra against the back of pubic symphysis (Fig. 11). It then follows that there would be a high-pressure zone in
Summary
Pelvic floor muscles have two important functions: they provide physical support to the pelvic viscera; and they provide constrictor mechanism to the anal canal, vagina, and urethra. Newer imaging and physiologic studies strongly suggest that these two functions of the pelvic floor are quite distinct and are likely related to different components of the pelvic floor muscles. The pubococcygeus, ileococcygeus, and ischiococcygeus most likely provide the physical support or act as a floor for the
References (57)
- et al.
Cross-sectional imaging anatomy of the anal sphincters
Obstet Gynecol
(1997) - et al.
Longitudinal and radial variations of pressure in the human anal sphincter
Gastroenterology
(1984) - et al.
Electrophysiological study of motor nerve supply of pelvic floor
Lancet
(1981) - et al.
Levator ani thickness variations in symptomatic and asymptomatic women using magnetic resonance-based 3-dimensional color mapping
Am J Obstet Gynecol
(2004) - et al.
Magnetic resonance imaging of anatomic and dynamic defects of the pelvic floor in defecatory disorders
Am J Gastroenterol
(2003) - et al.
Recent advances in assessing anorectal structure and functions
Gastroenterology
(2007) - et al.
Three-dimensional magnetic resonance imaging assessment of levator ani morphologic features in different grades of prolapse
Am J Obstet Gynecol
(2003) - et al.
Phenotypic variation in functional disorders of defecation
Gastroenterology
(2005) - et al.
Use of anorectal manometry during rectal infusion of saline to investigate sphincter function in incontinent patients
Gastroenterology
(1983) - et al.
Impaired internal anal sphincter in a subgroup of patients with idiopathic fecal incontinence
Gastroenterology
(1989)
Significance of pelvic floor muscles in anal incontinence
Gastroenterology
The appearance of levator ani muscle abnormalities in magnetic resonance images after vaginal delivery
Obstet Gynecol
Biofeedback is superior to laxatives for normal transit constipation due to pelvic floor dyssynergia
Gastroenterology
Clinical neurophysiology and electrodiagnostic testing of the pelvic floor
Gastroenterol Clin North Am
Biofeedback benefits only patients with outlet dysfunction, not patients with isolated slow transit constipation
Gastroenterology
Anal sphincter complex: reinterpreted morphology and its clinical relevance
Dis Colon Rectum
Epithelial and muscular regionalization of the human developing anorectum
Anat Rec (Hoboken)
Autonomic and somatic systems to the anorectum and pelvic floor
The internal anal sphincter: regulation of smooth muscle tone and relaxation
Neurogastroenterol Motil
The enteric nervous system
N Engl J Med
Issues in anatomy: the external anal sphincter revisited
Aust N Z J Surg
Anatomy of the external anal sphincter in man
Acta Anat (Basel)
A new concept of the anatomy of the anal sphincter mechanism and the physiology of defecation. The external anal sphincter: a triple-loop system
Invest Urol
Pelvic floor: anatomy and function
Neurogastroenterol Motil
Pelvic floor imaging
Radiology
Handbook of human anatomy
Cited by (0)
Supported by National Institutes of Health grant RO1-DK60733.