Perineum

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Questions and Answers

What is the correct anatomical location of the rectum?

In front of the lower three pieces of the sacrum and coccyx (correct)

In the posterior part of the greater pelvis behind the coccyx

In front of the sigmoid colon and behind the urinary bladder

Behind the lower three pieces of the sacrum and in front of the uterus

Which plane does the rectum present flexures in the anteroposterior axis?

Sacral flexure (correct)

Middle lateral flexure

Right lateral flexure

Upper lateral flexure

What is the significance of the pectinate line in the anal canal?

It indicates where the anal canal connects to the sigmoid colon.

It separates the arterial supply of the anal canal from the rectum.

It delineates the transition between embryologically different parts of the anal canal. (correct)

It marks the boundary for lymphatic drainage to the urinary bladder.

What type of hemorrhoids are generally located above the pectinate line?

Internal hemorrhoids, usually painless Signup and view all the answers

Which structure has a distinct venous plexus in the anal canal?

The external anal sphincter Signup and view all the answers

What is the primary function of the anal sphincters?

Control the expulsion of feces Signup and view all the answers

What anatomical function does the rectum have in relation to the sigmoid colon?

It is a transitional part of the digestive tract. Signup and view all the answers

Why does extravasated urine not pass into the thighs or the ischioanal fossa?

Due to the presence of the pelvic diaphragm Signup and view all the answers

What is the primary function of the bulbospongiosus muscle?

Compresses the vestibule and evacuates the vestibular glands Signup and view all the answers

What is the significance of the perineal body in pelvic anatomy?

It acts as the central insertion for perineal and pelvic floor muscles. Signup and view all the answers

Which type of episiotomy is typically performed more often due to its ease of suturing and faster healing?

Left medio-lateral episiotomy Signup and view all the answers

In pelvic floor therapy, what is the primary purpose of Kegel exercises?

To contract the entire levator ani and strengthen pelvic muscles. Signup and view all the answers

What anatomical structure is filled with adipose tissue and surrounds the anus?

Ischioanal fossa Signup and view all the answers

What is the primary function of the levator ani muscle?

Support the pelvic organs Signup and view all the answers

Which structure connects the lower ends of adjacent anal columns?

Anal valves Signup and view all the answers

What type of epithelium lines the upper region of the anal canal (pecten)?

Non-keratinized stratified squamous epithelium Signup and view all the answers

Which muscle forms a sling around the rectum at the anorectal flexure?

Puborectalis Signup and view all the answers

What does the external anal sphincter consist of?

Skeletal muscle only Signup and view all the answers

Which nerve innervates the levator ani muscle?

Pudendal nerve Signup and view all the answers

What is the length of the upper region (pecten) of the anal canal?

15 mm Signup and view all the answers

Which structure is NOT part of the pelvic diaphragm?

Rectus abdominis Signup and view all the answers

What feature is characteristic of the lower region of the anal canal?

Consists of pigmented skin Signup and view all the answers

What is the main function of the internal anal sphincter?

Regulate involuntary closure of the anus Signup and view all the answers

What is defined as the protrusion of rectal mucosa through the anus due to excessive straining during defecation?

Incomplete prolapse Signup and view all the answers

What are the causative factors for complete prolapse of the rectum?

Laxity of the pelvic diaphragm and inadequate fixation of the rectum Signup and view all the answers

Which structure traverses the perineum in females?

Vagina Signup and view all the answers

What forms the anterior boundary of the perineum in males?

Scrotum Signup and view all the answers

Which of the following is NOT a component of the urogenital triangle?

Anal canal Signup and view all the answers

What is the posterior boundary of the perineum?

Coccyx Signup and view all the answers

Which structure is present in both males and females as a part of the urogenital triangle?

Urethra Signup and view all the answers

What defines the boundaries of the urogenital triangle?

Pubic symphysis, ischiopubic ramus, a line between ischial tuberosities Signup and view all the answers

What is the function of the paired ischiocavernosus muscle in males?

Aid in erection by compressing erectile tissue Signup and view all the answers

In which position is the perineum described as diamond-shaped?

Lithotomy position Signup and view all the answers

What is the role of the perineal membrane in the urogenital triangle?

Acts as a barrier between deep and superficial perineal pouches Signup and view all the answers

Which structure is continuous with Colles’ fascia?

Lower layer of the perineal membrane Signup and view all the answers

Which muscles are located superficial to the perineal membrane?

Ischiocavernosus and bulbospongiosus Signup and view all the answers

What forms the posterior border of the urogenital floor?

Superficial transverse perineal muscle Signup and view all the answers

What is the relationship of the deep perineal pouch to the perineal membrane?

It is above the perineal membrane Signup and view all the answers

In males, which muscle contributes to the process of erection?

Ischiocavernosus Signup and view all the answers

Which of the following describes the superficial perineal pouch?

It is a potential space between the perineal membrane and the superficial perineal fascia Signup and view all the answers

What role does the bulbospongiosus muscle play in males?

Plays a role in micturition and ejaculation Signup and view all the answers

Which of the following accurately describes the lesser vestibular glands?

They are paired glands located at the entrance of the vagina Signup and view all the answers

What is the primary composition of the perineal membrane?

Fibrous tissue with muscle fibers Signup and view all the answers

What anatomical structure is located posterior to the urinary bladder in males?

Rectum Signup and view all the answers

Which curvature is associated with the rectum in the lateral plane?

Upper lateral curvature Signup and view all the answers

How does the rectum's shape differ in humans compared to quadrupeds?

It is curved in humans. Signup and view all the answers

What anatomical structure is located anteriorly to the rectum?

Urinary bladder in males Signup and view all the answers

What is the meaning of the Latin term 'rectum'?

Straight Signup and view all the answers

What differentiates the location of the anal canal above and below the pectinate line?

Different lymphatic drainage Signup and view all the answers

Which structure is NOT located in the pelvis just in front of the lower sacrum?

Urinary bladder Signup and view all the answers

Which of the following describes one of the flexures of the rectum in the sagittal plane?

Sacral Signup and view all the answers

Which structure does the pudendal nerve NOT innervate?

Rectal mucosa Signup and view all the answers

What effect does a bilateral pudendal nerve block have?

Loss of sensation to the vulva and lower one-third of the vagina Signup and view all the answers

Which branch of the pudendal nerve is responsible for somatosensory innervation of the dorsal part of the scrotum?

Posterior scrotal nerves Signup and view all the answers

Which of the following is a contraindication for epidural anesthesia, making pudendal nerve block a better option?

Spinal anatomy abnormalities Signup and view all the answers

What is one significant outcome when a pudendal nerve block is successfully administered?

Relaxation of pelvic floor muscles Signup and view all the answers

What anatomical structure is found in the lower region of the rectum and is critical for fecal storage?

Rectal ampulla Signup and view all the answers

Which part of the anal canal is made up of stratified squamous epithelium?

Lower part Signup and view all the answers

The pectinate line in the anal canal is significant because it represents what?

Embryological attachment site of the anal membrane Signup and view all the answers

Which condition is related to the various folds in the rectum, particularly Houston's folds?

Fecal impaction Signup and view all the answers

What is the primary coverage of the peritoneum on the lower third of the rectum?

Not covered at all Signup and view all the answers

Which structure is specifically located in the female ventral field related to the rectum?

Uterus Signup and view all the answers

How many transverse folds of the rectum correspond to the rectal flexures?

Three Signup and view all the answers

The anal columns in the upper part of the anal canal are also known as what?

Columns of Morgagni Signup and view all the answers

What relation does the ampulla of the rectum have with the rectovesical pouch in males?

It lies below the pouch Signup and view all the answers

In both sexes, which structure is located dorsally to the rectum?

Coccyx Signup and view all the answers

What type of prolapse occurs when only the rectal mucosa protrudes through the anus?

Mucous prolapse Signup and view all the answers

Which factor is associated with causing complete prolapse (procidentia) of the rectum?

Laxity of the pelvic diaphragm Signup and view all the answers

What is found in the male urogenital triangle?

Paired crus of penis Signup and view all the answers

Which of the following correctly describes the posterior boundary of the perineum?

Buttocks Signup and view all the answers

Which structure is included in the female urogenital triangle?

Crus of clitoris Signup and view all the answers

Which structures traverse the male perineum?

Urethra and anal canal Signup and view all the answers

What is considered a superficial boundary of the perineum?

Scrotum in males Signup and view all the answers

What forms the anterior boundary of the urethra in the male urogenital triangle?

Pubic symphysis Signup and view all the answers

Which muscle contributes to the pelvic floor found in the urogenital triangle?

Bulbospongiosus Signup and view all the answers

What is the primary function of the ischiococcygeus muscle?

Pulls the coccyx ventrally Signup and view all the answers

What is the primary anatomical feature of the deep boundaries of the perineum?

Pelvic outlet boundaries Signup and view all the answers

Which part of the external anal sphincter plays a role in maintaining anorectal continence?

Deep part Signup and view all the answers

During defecation, what is the role of the muscular layer of the rectum?

Contracts to facilitate defecation Signup and view all the answers

Which artery is the chief supply to the rectum?

Superior rectal artery Signup and view all the answers

What forms the plexus that surrounds the anal canal above Hilton’s line?

Internal venous plexus Signup and view all the answers

Which veins are responsible for draining the superior rectal area?

Superior rectal vein Signup and view all the answers

What type of clinical pathology is commonly found above the pectinate line?

Adenocarcinoma Signup and view all the answers

What is the primary significance of anastomoses between the portal and systemic veins in the anal canal?

Site of portocaval anastomosis Signup and view all the answers

Which source supplies the middle rectal arteries?

Internal iliac artery Signup and view all the answers

What primarily causes problems related to portocaval anastomoses?

Portal vein thrombosis Signup and view all the answers

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 (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:
- 1. External anal sphincter
- 1. 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.