Podcast
Questions and Answers
What is the correct anatomical location of the rectum?
What is the correct anatomical location of the rectum?
Which plane does the rectum present flexures in the anteroposterior axis?
Which plane does the rectum present flexures in the anteroposterior axis?
What is the significance of the pectinate line in the anal canal?
What is the significance of the pectinate line in the anal canal?
What type of hemorrhoids are generally located above the pectinate line?
What type of hemorrhoids are generally located above the pectinate line?
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Which structure has a distinct venous plexus in the anal canal?
Which structure has a distinct venous plexus in the anal canal?
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What is the primary function of the anal sphincters?
What is the primary function of the anal sphincters?
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What anatomical function does the rectum have in relation to the sigmoid colon?
What anatomical function does the rectum have in relation to the sigmoid colon?
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Why does extravasated urine not pass into the thighs or the ischioanal fossa?
Why does extravasated urine not pass into the thighs or the ischioanal fossa?
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What is the primary function of the bulbospongiosus muscle?
What is the primary function of the bulbospongiosus muscle?
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What is the significance of the perineal body in pelvic anatomy?
What is the significance of the perineal body in pelvic anatomy?
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Which type of episiotomy is typically performed more often due to its ease of suturing and faster healing?
Which type of episiotomy is typically performed more often due to its ease of suturing and faster healing?
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In pelvic floor therapy, what is the primary purpose of Kegel exercises?
In pelvic floor therapy, what is the primary purpose of Kegel exercises?
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What anatomical structure is filled with adipose tissue and surrounds the anus?
What anatomical structure is filled with adipose tissue and surrounds the anus?
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What is the primary function of the levator ani muscle?
What is the primary function of the levator ani muscle?
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Which structure connects the lower ends of adjacent anal columns?
Which structure connects the lower ends of adjacent anal columns?
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What type of epithelium lines the upper region of the anal canal (pecten)?
What type of epithelium lines the upper region of the anal canal (pecten)?
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Which muscle forms a sling around the rectum at the anorectal flexure?
Which muscle forms a sling around the rectum at the anorectal flexure?
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What does the external anal sphincter consist of?
What does the external anal sphincter consist of?
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Which nerve innervates the levator ani muscle?
Which nerve innervates the levator ani muscle?
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What is the length of the upper region (pecten) of the anal canal?
What is the length of the upper region (pecten) of the anal canal?
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Which structure is NOT part of the pelvic diaphragm?
Which structure is NOT part of the pelvic diaphragm?
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What feature is characteristic of the lower region of the anal canal?
What feature is characteristic of the lower region of the anal canal?
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What is the main function of the internal anal sphincter?
What is the main function of the internal anal sphincter?
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What is defined as the protrusion of rectal mucosa through the anus due to excessive straining during defecation?
What is defined as the protrusion of rectal mucosa through the anus due to excessive straining during defecation?
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What are the causative factors for complete prolapse of the rectum?
What are the causative factors for complete prolapse of the rectum?
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Which structure traverses the perineum in females?
Which structure traverses the perineum in females?
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What forms the anterior boundary of the perineum in males?
What forms the anterior boundary of the perineum in males?
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Which of the following is NOT a component of the urogenital triangle?
Which of the following is NOT a component of the urogenital triangle?
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What is the posterior boundary of the perineum?
What is the posterior boundary of the perineum?
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Which structure is present in both males and females as a part of the urogenital triangle?
Which structure is present in both males and females as a part of the urogenital triangle?
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What defines the boundaries of the urogenital triangle?
What defines the boundaries of the urogenital triangle?
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What is the function of the paired ischiocavernosus muscle in males?
What is the function of the paired ischiocavernosus muscle in males?
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In which position is the perineum described as diamond-shaped?
In which position is the perineum described as diamond-shaped?
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What is the role of the perineal membrane in the urogenital triangle?
What is the role of the perineal membrane in the urogenital triangle?
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Which structure is continuous with Colles’ fascia?
Which structure is continuous with Colles’ fascia?
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Which muscles are located superficial to the perineal membrane?
Which muscles are located superficial to the perineal membrane?
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What forms the posterior border of the urogenital floor?
What forms the posterior border of the urogenital floor?
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What is the relationship of the deep perineal pouch to the perineal membrane?
What is the relationship of the deep perineal pouch to the perineal membrane?
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In males, which muscle contributes to the process of erection?
In males, which muscle contributes to the process of erection?
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Which of the following describes the superficial perineal pouch?
Which of the following describes the superficial perineal pouch?
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What role does the bulbospongiosus muscle play in males?
What role does the bulbospongiosus muscle play in males?
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Which of the following accurately describes the lesser vestibular glands?
Which of the following accurately describes the lesser vestibular glands?
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What is the primary composition of the perineal membrane?
What is the primary composition of the perineal membrane?
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What anatomical structure is located posterior to the urinary bladder in males?
What anatomical structure is located posterior to the urinary bladder in males?
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Which curvature is associated with the rectum in the lateral plane?
Which curvature is associated with the rectum in the lateral plane?
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How does the rectum's shape differ in humans compared to quadrupeds?
How does the rectum's shape differ in humans compared to quadrupeds?
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What anatomical structure is located anteriorly to the rectum?
What anatomical structure is located anteriorly to the rectum?
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What is the meaning of the Latin term 'rectum'?
What is the meaning of the Latin term 'rectum'?
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What differentiates the location of the anal canal above and below the pectinate line?
What differentiates the location of the anal canal above and below the pectinate line?
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Which structure is NOT located in the pelvis just in front of the lower sacrum?
Which structure is NOT located in the pelvis just in front of the lower sacrum?
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Which of the following describes one of the flexures of the rectum in the sagittal plane?
Which of the following describes one of the flexures of the rectum in the sagittal plane?
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Which structure does the pudendal nerve NOT innervate?
Which structure does the pudendal nerve NOT innervate?
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What effect does a bilateral pudendal nerve block have?
What effect does a bilateral pudendal nerve block have?
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Which branch of the pudendal nerve is responsible for somatosensory innervation of the dorsal part of the scrotum?
Which branch of the pudendal nerve is responsible for somatosensory innervation of the dorsal part of the scrotum?
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Which of the following is a contraindication for epidural anesthesia, making pudendal nerve block a better option?
Which of the following is a contraindication for epidural anesthesia, making pudendal nerve block a better option?
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What is one significant outcome when a pudendal nerve block is successfully administered?
What is one significant outcome when a pudendal nerve block is successfully administered?
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What anatomical structure is found in the lower region of the rectum and is critical for fecal storage?
What anatomical structure is found in the lower region of the rectum and is critical for fecal storage?
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Which part of the anal canal is made up of stratified squamous epithelium?
Which part of the anal canal is made up of stratified squamous epithelium?
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The pectinate line in the anal canal is significant because it represents what?
The pectinate line in the anal canal is significant because it represents what?
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Which condition is related to the various folds in the rectum, particularly Houston's folds?
Which condition is related to the various folds in the rectum, particularly Houston's folds?
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What is the primary coverage of the peritoneum on the lower third of the rectum?
What is the primary coverage of the peritoneum on the lower third of the rectum?
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Which structure is specifically located in the female ventral field related to the rectum?
Which structure is specifically located in the female ventral field related to the rectum?
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How many transverse folds of the rectum correspond to the rectal flexures?
How many transverse folds of the rectum correspond to the rectal flexures?
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The anal columns in the upper part of the anal canal are also known as what?
The anal columns in the upper part of the anal canal are also known as what?
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What relation does the ampulla of the rectum have with the rectovesical pouch in males?
What relation does the ampulla of the rectum have with the rectovesical pouch in males?
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In both sexes, which structure is located dorsally to the rectum?
In both sexes, which structure is located dorsally to the rectum?
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What type of prolapse occurs when only the rectal mucosa protrudes through the anus?
What type of prolapse occurs when only the rectal mucosa protrudes through the anus?
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Which factor is associated with causing complete prolapse (procidentia) of the rectum?
Which factor is associated with causing complete prolapse (procidentia) of the rectum?
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What is found in the male urogenital triangle?
What is found in the male urogenital triangle?
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Which of the following correctly describes the posterior boundary of the perineum?
Which of the following correctly describes the posterior boundary of the perineum?
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Which structure is included in the female urogenital triangle?
Which structure is included in the female urogenital triangle?
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Which structures traverse the male perineum?
Which structures traverse the male perineum?
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What is considered a superficial boundary of the perineum?
What is considered a superficial boundary of the perineum?
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What forms the anterior boundary of the urethra in the male urogenital triangle?
What forms the anterior boundary of the urethra in the male urogenital triangle?
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Which muscle contributes to the pelvic floor found in the urogenital triangle?
Which muscle contributes to the pelvic floor found in the urogenital triangle?
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What is the primary function of the ischiococcygeus muscle?
What is the primary function of the ischiococcygeus muscle?
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What is the primary anatomical feature of the deep boundaries of the perineum?
What is the primary anatomical feature of the deep boundaries of the perineum?
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Which part of the external anal sphincter plays a role in maintaining anorectal continence?
Which part of the external anal sphincter plays a role in maintaining anorectal continence?
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During defecation, what is the role of the muscular layer of the rectum?
During defecation, what is the role of the muscular layer of the rectum?
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Which artery is the chief supply to the rectum?
Which artery is the chief supply to the rectum?
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What forms the plexus that surrounds the anal canal above Hilton’s line?
What forms the plexus that surrounds the anal canal above Hilton’s line?
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Which veins are responsible for draining the superior rectal area?
Which veins are responsible for draining the superior rectal area?
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What type of clinical pathology is commonly found above the pectinate line?
What type of clinical pathology is commonly found above the pectinate line?
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What is the primary significance of anastomoses between the portal and systemic veins in the anal canal?
What is the primary significance of anastomoses between the portal and systemic veins in the anal canal?
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Which source supplies the middle rectal arteries?
Which source supplies the middle rectal arteries?
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What primarily causes problems related to portocaval anastomoses?
What primarily causes problems related to portocaval anastomoses?
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Study Notes
The Rectum
- The rectum is the lower part of the large intestine.
- It is continuous with the sigmoid colon (proximally) and anal canal (distally).
- Location: posterior part of the lesser pelvis in front of the lower three pieces of the sacrum and the coccyx; behind the urinary bladder in the male and uterus in the female.
- The rectum has flexures in both anteroposterior (sagittal) and lateral planes.
- The rectum is not straight in humans, it is straight in quadrupeds.
Anal Canal
- Anal valves (valves of Morgagni): crescentic folds of the mucousa which connect the lower ends of adjacent anal columns.
- Anal sinuses: vertical recesses between the anal columns and above the anal valves.
Features in the Lower Part of Anal Canal
- The lower part of the anal canal is divided into two regions.
- Upper region (pecten): 15 mm long and extends from the pectinate line to Hilton’s/white line; lined by non-keratinised stratified squamous epithelium.
- Lower region of lower anal canal: 8 mm long, lined by pigmented skin (keratinised stratified squamous epithelium) containing sweat and sebaceous gland.
- Anus: hole covered by the skin with skin adnexa.
Muscles of the Rectum
- Internal anal sphincter: smooth muscle located in the anal canal.
- External anal sphincter: skeletal muscle, attached externally to the internal anal sphincter and from below to the levator ani.
- Puborectalis: skeletal muscle, the most medial part of the levator ani, forms a sling around the rectum at the level of the anorectal flexure.
Muscles of the Pelvic Floor/Pelvic Diaphragm
- The muscles of the pelvic floor are organized into the shape of a funnel.
- They attach to the walls of the lesser pelvis and contain passages for the rectum, vagina and urethra.
- Muscles of the pelvic diaphragm contribute to the creation of intra-abdominal pressure and are part of the deep stabilizing system.
-
Levator ani (m.levator ani):
- Iliococcygeus (m.iliococcygeus) - tendinous arch of the levator ani
- Pubococcygeus (m.pubococcygeus) - muscular bands between the coccyx and pubis
- Puborectal (m.puborectalis) - muscular bands below the pubococcygeus.
- Ischiococcygeus / coccygeus (m.ischococcygeus / coccygeus)
- External anal sphincter (m.sphincter ani externus)
-
Levator ani (m.levator ani):
Levator Ani (Musculus Levator Ani)
- Functions:
- compresses the organs of the pelvic outlet
- elevates the pelvic floor and anus
- contributes to the support of the uterus
- contributes to anorectal and urine continence (accessory sphincter of the anus)
- contributes to intra-abdominal pressure
- belongs to the deep stabilising system (together with the deep back muscles, diaphragm and muscles of the abdomen maintains the stability of the vertebral column)
- Innervation: pudendal nerve.
Clinical Correlation - Prolapse of Rectum
- Prolapse of rectum: protrusion of the rectum through the anus.
- Incomplete prolapse (mucous prolapse): protrusion of rectal mucosa through the anus and occurs due to excessive straining during defecation. Pathogenesis: imperfect support of the rectal mucosa by the submucosa.
- Complete prolapse (procidentia): whole thickness of the rectal wall protrudes through the anus. Causative factors: laxity of the pelvic diaphragm, excessively deep rectovesical or rectouterine pouch and inadequate fixation of the rectum in its presacral bed.
Perineum
- The perineum is the lowest region of the trunk below the pelvic diaphragm, between the upper parts of the thighs and the lower parts of the buttocks.
- The perineum contains external genitals and perineal muscles and is composed of the urogenital triangle and anal triangle.
- The perineum is traversed by:
- urethra and anal canal in male,
- urethra, vagina, and anal canal in female.
- Surface features of the perineum:
- in male: penis, scrotum, and anal orifice,
- in female: vulva (female external genitalia) and anal orifice.
Boundaries - Perineum
-
Superficial Boundaries:
- Anteriorly: scrotum in male and mons pubis in female.
- Posteriorly: buttocks.
- On each side: upper medial aspect of the thigh.
-
Deep Boundaries:
- Anteriorly: Inferior margin of the pubic symphysis (actually arcuate pubic ligament)
- Posteriorly: Tip of the coccyx
-
On each side:
- Anterolaterally: conjoint ischiopubic ramus
- Laterally: ischial tuberosity
- Posterolaterally: sacrotuberous ligament.
Urogenital Triangle (Trigonum Urogenitale)
- The urogenital triangle is located ventrally.
-
Borders:
- Ventrally: pubic symphysis
- Dorsally: a line connecting the left and right ischial tuberosities
- Laterally: ischiopubic ramus
- Floor (cranially): perineal membrane
- The urogenital triangle contains the pelvic floor and perineal muscles.
Content of Urogenital Triangle
-
Male:
- Paired crus of penis and paired ischiocavernosus
- Unpaired bulb of penis and unpaired bulbospongiosus
- Paired bulbo-urethral glands of Cowper
-
Female:
- Paired crus of clitoris and paired ischiocavernosus
- Paired bulb of vestibule and paired bulbospongiosus
- Paired greater vestibular glands of Bartholin and lesser vestibular glands
Perineal Membrane
- The perineal membrane is a strong triangular membrane (fascial sheath) that stretches across the urogenital triangle between the ischiopubic rami at the sides.
- The perineal membrane has pouches on its superior and inferior surfaces.
- The perineal membrane forms the inferior boundary of the deep perineal pouch and the superior boundary of the superficial perineal pouch.
- In front, it is thickened to form the transverse perineal ligament and is continuous with the superior fascia of the urogenital diaphragm.
- Behind, it is fixed to the perineal body in the midline and splits into two layers.
- The upper layer is continuous with the superior fascia of the urogenital diaphragm,
- The inferior layer is continuous as Colles’ fascia.
Perineal Pouches
- Deep perineal pouch: a potential space between the deep fascia of the pelvic floor (superiorly) and the perineal membrane (inferiorly).
- Superficial perineal pouch: a potential space between the perineal membrane (superiorly) and the superficial perineal fascia (inferiorly).
Urogenital Floor in Male
- Perineal membrane (membrana perinei): a fibrous sheet covering the inferior aspect of the deep transverse perineal muscle
- Deep transverse perineal muscle (m.transversus perinei profundus): deep muscular part of the urogenital floor
-
Superficial transverse perineal muscle (m.transversus perinei superficialis): forms the posterior border of the urogenital floor
- Muscles located superficial to the perineal membrane 4. Ischiocavernosus (m.ischiocavernosus): compresses the crus of the penis, contributing to erection 5. Bulbospongiosus (m.bulbospongiosus): evacuates the urethra during micturition and ejaculation
- Muscles located deep to the perineal membrane 6. External urethral sphincter (m.sphincter urethrae externus)
Urogenital Floor in Female
- Perineal membrane: a fibrous sheet containing disperse muscle fibers
-
Superficial transverse perineal muscle (m.transversus perinei superficialis): adjacent to the posterior edge of urogenital floor, weak or often absent
- Muscles located superficial to the perineal membrane 3. Ischiocavernosus: compresses the crus of the clitoris 4. Bulbospongiosus: compresses the vestibule, evacuating the vestibular glands
- Muscles located deep to the perineal membrane 5. External urethral sphincter 6. Compressor urethrae (m.compressor urethrae): compresses and extends the urethra 7. Sphincter urethrovaginalis (m.sphincter urethrovaginalis): compresses and extends the urethra
Perineal Body - Corpus Perineale
- The perineal body is a pyramidal fibromuscular structure located in the midline of the perineum between the urogenital and anal triangles.
- It is the central insertion of the perineal and pelvic floor muscles.
Clinical Correlation - Episiotomy
-
Episiotomy: a surgical incision of the perineum during labour to prevent uncontrolled injury of the vagina, perineum and the baby.
- Midline episiotomy crosses the perineal body.
- Medio-lateral episiotomy (30° from the midline) cuts through the bulbospongiosus and the superficial transverse perineal muscle.
- Left medio-lateral episiotomy is easily sutured, heals faster and therefore is performed more often.
Pelvic Floor Physical Therapy
- Kegel exercises: involve the contraction of the entire levator ani. Kegel exercises strengthen the pubococcygeus muscles, which can treat stress incontinence, urge incontinence, and pelvic organ prolapse and assists in ejaculation.
- Weighted vaginal cones: increase efficacy of Kegel exercises.
- Biofeedback: increase efficacy of Kegel exercises.
Anal Triangle - Trigonum Anale
- The anal triangle is situated dorsally.
-
Borders:
- Ventrally: line connecting the left and right ischial tuberosities
- Dorsally: coccyx
- Laterally: sacrotuberous ligament and gluteus maximus.
- There are no perineal muscles in this area, the pelvic outlet is closed by the pelvic floor muscles.
Ischioanal Fossa - Fossa Ischioanalis
- The ischioanal fossa is a paired space filled by adipose tissue surrounding the anus.
- Two fossae communicate with each other dorsally behind the anus.
- Function: form a space that allows the pelvic floor to span out during defecation and parturition.
Boundaries of Ischioanal Fossa
-
Medio-cranially:
-
- External anal sphincter
-
- Inferior fascia of the pelvic diaphragm
-
-
Rectum
- The rectum is the pelvic part of the digestive tract, continuous with the sigmoid colon and the anal canal.
- It is located in the posterior part of the lesser pelvis, in front of the lower three pieces of the sacrum and the coccyx.
- In males, it is behind the urinary bladder, and in females, behind the uterus.
- The rectum has flexures/curvatures in both the anteroposterior and lateral planes.
- The interior of the rectum features transverse folds, also known as Houston's folds, located on the left and right sides.
- The upper 1/3 of the rectum is covered with peritoneum on the front and sides.
- The middle 1/3 is covered only on the front, and the lower 1/3 (ampulla) is not at all covered.
Anal Canal
- The anal canal begins at the anorectal junction, passes downward and backward, and opens at the anal orifice.
- The anal orifice is located in the natal cleft, about 4 cm below and in front of the coccyx's tip.
- The anal canal is divided into two parts by the pectinate/dentate line.
- The upper part extends from the anorectal junction to the pectinate line, while the lower extends from the pectinate line to the anal verge.
Muscles of the Perineum
- The ischiococcygeus/coccygeus is a thin muscle that merges with the sacrospinous ligament. It pulls the coccyx ventrally to its original position during defecation or delivery.
- The external anal sphincter, composed of three parts, compresses the anal canal to maintain anorectal continence. It is innervated by the pudendal nerve.
Defecation
- The process of defecation begins with the accumulation of stool in the rectal ampulla.
- This expansion causes reflex relaxation of the internal anal sphincter.
- Voluntary relaxation of the external anal sphincter and puborectalis, alongside contractions of the rectum's muscular layer, leads to defecation.
Arterial Supply of the Rectum
- The superior rectal artery, a continuation of the inferior mesenteric artery, is the main artery of the rectum.
- The middle rectal arteries (two in number) originate from the internal iliac artery.
- The inferior rectal arteries (two in number) originate from the internal pudendal artery.
- The median sacral artery, a branch of the abdominal aorta, also contributes to the arterial supply.
Venous Supply of the Rectum
- Blood is drained from the rectum by the superior, middle, and inferior rectal veins.
- These veins arise from internal and external venous plexuses.
- The internal venous plexus is located in the submucosa and surrounds the anal canal above Hilton's line.
- The external venous plexus is between the perianal skin and the external anal sphincter, surrounding the anus.
Anastomoses of the Rectum
- The superior rectal vein connects to the inferior mesenteric vein, which in turn connects to the portal vein.
- The middle and inferior rectal veins connect to the internal iliac vein, eventually joining the inferior vena cava.
- Anastomoses between the portal and systemic veins exist in the anal canal, making it a site of portocaval anastomosis.
Clinical Correlation
- Common pathologies above the pectinate line include internal hemorrhoids and adenocarcinoma.
- Prolapse of the rectum involves protrusion of the rectum through the anus.
- Incomplete prolapse (mucous prolapse) is characterized by protrusion of the rectal mucosa due to excessive straining.
- Complete prolapse (procidentia) involves protrusion of the entire rectal wall.
Perineum
- The perineum is the lowest region of the trunk, located below the pelvic diaphragm and between the upper thighs and lower buttocks.
- It contains external genitalia, perineal muscles, and is divided into the urogenital triangle and anal triangle.
- Surface features include the penis and scrotum in males, and the vulva and anal orifice in females.
Boundaries of the Perineum
- The superficial boundaries of the diamond-shaped perineum (in lithotomy position) include the scrotum/mons pubis anteriorly, buttocks posteriorly, and the upper medial aspect of the thighs on either side.
- Deep boundaries correspond to the pelvic outlet, including the inferior margin of the pubic symphysis/arcuate pubic ligament anteriorly, the tip of the coccyx posteriorly, and the ischiopubic ramus, ischial tuberosity, and sacrotuberous ligament on each side.
Urogenital Triangle
- Located ventrally in the perineum, bounded by the pubic symphysis, the line connecting the ischial tuberosities, the ischiopubic ramus, and the perineal membrane.
- Contains the pelvic floor and perineal muscles.
Content of the Urogenital Triangle
- Males: paired crus of penis and ischiocavernosus, unpaired bulb of penis and bulbospongiosus, paired bulbo-urethral glands
- Females: paired crus of clitoris and ischiocavernosus, paired bulb of vestibule and bulbospongiosus
Pudendal Nerve
- Innervates various structures in the perineum through its branches, including the levator ani, ischiococcygeus, external anal sphincter, transversus perinei superficialis, transversus perinei profundus, bulbospongiosus, ischiocavernosus, and provides somatosensory innervation for the skin around the intergluteal crest, scrotum, labia, penis, and urethral mucosa.
Pudendal Nerve Block
- Used to relieve pain associated with childbirth, certain types of chronic pelvic pain, and in some rectal or urological procedures.
- Involves infiltrating the pudendal nerve with a local anesthetic as it crosses the ischial spine.
- A bilateral block leads to loss of anal reflex, relaxation of pelvic floor muscles, and loss of sensation to the vulva and lower vagina.
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Description
This quiz explores the anatomy and functions of the rectum and anal canal. It covers their structures, locations, and features, as well as the distinctions between various regions of the anal canal. Test your knowledge on these vital components of the digestive system.