Anatomy: Perineum
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Questions and Answers

What type of epithelium lines the anal canal?

  • Columnar epithelium (correct)
  • Stratified squamous epithelium
  • Transitional epithelium
  • Cuboidal epithelium

    • What is the name of the vertical folds in the anal canal?

  • Anal papillae
  • Anal valves
  • Anal cervices
  • Anal columns (correct)

    • What nerve supplies the anal canal?

  • Somatic inferior rectal nerve (correct)
  • Pudendal nerve
  • Autonomic hypogastric nerve
  • Inferior rectal nerve

    • What is the arterial supply to the anal canal?

    <p>Inferior rectal artery</p> Signup and view all the answers

    What is the venous drainage of the anal canal?

    <p>Inferior rectal vein</p> Signup and view all the answers

    What type of sensation can the anal mucosa detect?

    <p>Stretch only</p> Signup and view all the answers

    What is the approximate length of the anal canal?

    <p>1.5 inches (4 cm)</p> Signup and view all the answers

    Which muscle helps to keep the lateral walls of the anal canal in apposition?

    <p>Levator ani</p> Signup and view all the answers

    What is the name of the ligament that overlies the border of the gluteus maximus muscle?

    <p>Sacrotuberous ligament</p> Signup and view all the answers

    In which direction does the anal canal pass from the rectal ampulla to the anus?

    <p>Downward and backward</p> Signup and view all the answers

    What is the name of the triangle that contains the anus and the anal canal?

    <p>Anal triangle</p> Signup and view all the answers

    What is the name of the muscle that forms the boundary of the anal triangle?

    <p>Gluteus maximus</p> Signup and view all the answers

    What is the name of the structure that lies in the midline of the anal canal?

    <p>Icbloanal fossa</p> Signup and view all the answers

    What is the name of the nerve that supplies the anal canal?

    <p>Inferior rectal nerve</p> Signup and view all the answers

    What is the function of the longitudinal fibers of the anal walls and the puborectalis muscle?

    <p>To return the mucosa to the anal canal</p> Signup and view all the answers

    Which artery supplies the lower half of the anal canal?

    <p>Inferior rectal artery</p> Signup and view all the answers

    What is the function of the anal sphincters?

    <p>To close the lumen of the anal canal</p> Signup and view all the answers

    Through which foramen does the internal pudendal artery pass?

    <p>Lesser sciatic foramen</p> Signup and view all the answers

    What is the main tributary of the inferior mesenteric vein?

    <p>Superior rectal vein</p> Signup and view all the answers

    What is the mass of fibrous tissue lying between the anal canal and the coccyx?

    <p>Anococcygeal body</p> Signup and view all the answers

    What is the ischioanal fossa also known as?

    <p>Ischiore</p> Signup and view all the answers

    Which nerve travels with the internal pudendal artery?

    <p>Pudendal nerve</p> Signup and view all the answers

    What is the origin of the mucous membrane of the upper half of the anal canal?

    <p>Hindgut entoderm</p> Signup and view all the answers

    What is the main direction of lymphatic drainage of the anal canal?

    <p>Upward along the superior rectal artery</p> Signup and view all the answers

    What is the structure that lies posteriorly to the anal canal?

    <p>Anococcygeal body</p> Signup and view all the answers

    What is the artery that supplies the anal canal?

    <p>Superior rectal artery</p> Signup and view all the answers

    What is the structure that lies anteriorly to the anal canal in the male?

    <p>Membranous part of the urethra</p> Signup and view all the answers

    What is the origin of the mucous membrane of the lower half of the anal canal?

    <p>Ectoderm of the proctodeum</p> Signup and view all the answers

    What is the primary function of the puborectalis muscle?

    <p>To form a sling around the junction of the rectum and anal canal</p> Signup and view all the answers

    Which nerve supplies the deep part of the external anal sphincter?

    <p>Perineal branch of the fourth sacral nerve</p> Signup and view all the answers

    What is the attachment point for the deep part of the external anal sphincter?

    <p>No bony attachment</p> Signup and view all the answers

    What is the primary function of the external anal sphincter?

    <p>To maintain continence</p> Signup and view all the answers

    Which muscle is responsible for encircling the anal canal?

    <p>Puborectalis muscle</p> Signup and view all the answers

    What is the origin of the deep part of the external anal sphincter?

    <p>Pubic bone</p> Signup and view all the answers

    Which structure is formed by the combination of the external anal sphincter and puborectalis muscle?

    <p>Voluntary anal sphincter</p> Signup and view all the answers

    What is the nerve supply of the puborectalis muscle?

    <p>Perineal branch of the fourth sacral nerve</p> Signup and view all the answers

    What is the purpose of the rhythmic contractions of the bulbospongiosus muscles during ejaculation?

    <p>To compress the urethra and facilitate ejaculation</p> Signup and view all the answers

    What is the function of the internal urethral sphincter during ejaculation?

    <p>To prevent reflux of spermatozoa into the bladder</p> Signup and view all the answers

    What is the origin of the dorsal artery of the penis?

    <p>The internal pudendal artery</p> Signup and view all the answers

    What is the name of the space that the internal pudendal artery enters after piercing the perineal membrane?

    <p>Deep perineal space</p> Signup and view all the answers

    What is the term for the fluid that constitutes the spermatozoa and the secretions of the several accessory glands?

    <p>Semen</p> Signup and view all the answers

    What is the length of the prostatic urethra?

    <p>1.25 in.</p> Signup and view all the answers

    What is the direction of the anal canal from the rectal ampulla to the anus?

    <p>Not mentioned</p> Signup and view all the answers

    What is the possible consequence of repeated inflammation of the prepuce?

    <p>All of the above</p> Signup and view all the answers

    What is the site of the passage of the internal pudendal artery?

    <p>Through the perineal membrane</p> Signup and view all the answers

    At what angle is the penis held during circumcision?

    <p>Right angle to the anterior abdominal wall</p> Signup and view all the answers

    What is felt when the catheter reaches the intermediate part of the urethra?

    <p>Resistance due to the tone of the external urethral sphincter</p> Signup and view all the answers

    What is the narrowest part of the entire urethra?

    <p>External orifice at the glans penis</p> Signup and view all the answers

    What is the location of the parasympathetic outflow in the pelvic splanchnic nerves?

    <p>Second, third, and fourth sacral segments</p> Signup and view all the answers

    Why is prophylactic circumcision commonly practiced?

    <p>Both a and b</p> Signup and view all the answers

    What happens to the urethra within the glans?

    <p>It dilates to form the fossa navicularis</p> Signup and view all the answers

    What is the function of the upper part of the external urethral sphincter?

    <p>To extend up along the prostatic urethra as far as the neck of the bladder</p> Signup and view all the answers

    What is the purpose of gentle traction during circumcision?

    <p>To hold the penis erect</p> Signup and view all the answers

    What is the name of the muscle that forms a true sphincter-like unit encircling the intermediate part of the urethra?

    <p>Sphincter Urethrae Muscle</p> Signup and view all the answers

    What is the effect of parasympathetic stimulation on the helicine arteries?

    <p>Vasodilatation</p> Signup and view all the answers

    What is the next step after the penis is lowered towards the thighs during circumcision?

    <p>The catheter is gently pushed through the sphincter</p> Signup and view all the answers

    What is the path of the postganglionic fibers after synapsing on the postganglionic neurons?

    <p>They run through the prostadc nerve plexm and join the cavernous nerves</p> Signup and view all the answers

    What is the effect of parasympathetic stimulation on the erectile tissue?

    <p>It causes the erectile tissue to expand</p> Signup and view all the answers

    What is the name of the part of the external urethral sphincter that is between the perinea membrane and the prostate?

    <p>Inferior portion of the external sphincter</p> Signup and view all the answers

    What is the function of the sphincter urethrae muscle?

    <p>To compress the intermediate part of the urethra</p> Signup and view all the answers

    What is the function of the sensory endings in the epithelium of the glans?

    <p>To detect various types of sensations</p> Signup and view all the answers

    Which artery supplies the clitoris and most of the surrounding area?

    <p>Internal pudendal artery</p> Signup and view all the answers

    What is the name of the space posterior to the glans clitoris and between the labia minora?

    <p>Vestibule space</p> Signup and view all the answers

    What is the function of the branches of the pudendal nerve?

    <p>To carry sensory fibers from the clitoris</p> Signup and view all the answers

    What is the path of lymph drainage from the skin of the vulva?

    <p>Medial group of superficial inguinal nodes</p> Signup and view all the answers

    What is the function of the labia majora, labia minora, and mons pubis?

    <p>To protect the clitoris and surrounding area</p> Signup and view all the answers

    What is the relationship between the blood supply, lymph drainage, and nerve supply of the clitoris and penis?

    <p>Identical patterns in both</p> Signup and view all the answers

    What is the location of the greater vestibular glands?

    <p>Between the labia minora</p> Signup and view all the answers

    What is the function of the superficial transverse perineal muscles?

    <p>To fix the perineal body in the center of the perineum</p> Signup and view all the answers

    Which arteries supply the scrotum?

    <p>All of the above</p> Signup and view all the answers

    What is the function of the perineal branch of the pudendal nerve?

    <p>To supply the skin and muscles of the scrotum</p> Signup and view all the answers

    Where do the contents of the scrotum (testis and epididymis) drain lymphatically?

    <p>Lumbar (paraaortic) lymph nodes at the level of the first lumbar vertebra</p> Signup and view all the answers

    What is the perineal body?

    <p>A small mass of fibrous tissue that attaches to the center of the perineum</p> Signup and view all the answers

    Which muscles attach to the perineal body?

    <p>External anal sphincter, superficial transverse perineal muscles, and bulbo cavernosus muscle</p> Signup and view all the answers

    What is the function of the arteriovenous anastomoses in the scrotum?

    <p>To promote heat loss and assist in the environmental control of the temperature of the testes</p> Signup and view all the answers

    What is the blood supply to the scrotum?

    <p>External pudendal branches of the femoral artery and ClOtal branches of the internal pudendal arteries</p> Signup and view all the answers

    What is the main reason for the higher incidence of cystida in females compared to males?

    <p>The shorter length of the female urethra</p> Signup and view all the answers

    What is the significance of the bluish discoloration of the vulva and vagina during pregnancy?

    <p>It is a result of venous congestion</p> Signup and view all the answers

    What is the characteristic of the epithelium lining the vagina?

    <p>It is squamous and stratified</p> Signup and view all the answers

    Why is catheterization easier in females compared to males?

    <p>The female urethra is shorter and wider</p> Signup and view all the answers

    What is the significance of digital examination of the vagina?

    <p>It provides valuable information about the health of the vaginal walls</p> Signup and view all the answers

    What is the consequence of repeated inflammation of the prepuce?

    <p>It can lead to phimosis</p> Signup and view all the answers

    What is the advantage of the acidic pH of the vagina?

    <p>It decreases the risk of infection</p> Signup and view all the answers

    What glands can become infected in the female reproductive system?

    <p>All of the above</p> Signup and view all the answers

    What is the primary cause of types 1 and 2 epispadias?

    <p>Failure of the bud of ectodermal cells to grow into the substance of the glans</p> Signup and view all the answers

    What is the name of the structure that forms the boundary of the anal triangle?

    <p>Puborectalis muscle</p> Signup and view all the answers

    What is the location of the meatal orifice in the penoscrotal variety of epispadias?

    <p>In the midline of the scrotum</p> Signup and view all the answers

    What is the name of the ligament that overlies the border of the gluteus maximus muscle?

    <p>Sacrotuberous ligament</p> Signup and view all the answers

    What is the direction of the anal canal from the rectal ampulla to the anus?

    <p>Inferiorly and posteriorly</p> Signup and view all the answers

    What is the name of the tissue that develops within the mesenchymal core of the penis?

    <p>Erectile tissue</p> Signup and view all the answers

    What is the term for the fluid that constitutes the spermatozoa and the secretions of the several accessory glands?

    <p>Semen</p> Signup and view all the answers

    What is the purpose of the frenulum?

    <p>To attach the skin to the ventral aspect of the root of the glans</p> Signup and view all the answers

    What is the narrowest part of the entire urethra?

    <p>Membranous urethra</p> Signup and view all the answers

    What is the result of the two genital folds fusing together progressively along the shaft of the phallus?

    <p>Formation of the penile urethra</p> Signup and view all the answers

    In which direction does the penile urethra open?

    <p>At the tip of the glans</p> Signup and view all the answers

    What is the name of the space that the internal pudendal artery enters after piercing the perineal membrane?

    <p>Pudendal canal</p> Signup and view all the answers

    What is the origin of the dorsal artery of the penis?

    <p>Internal pudendal artery</p> Signup and view all the answers

    What is the term for the condition where the penis is curved in a downward or ventral direction?

    <p>Chordee</p> Signup and view all the answers

    What is the possible consequence of repeated inflammation of the prepuce?

    <p>Phimosis</p> Signup and view all the answers

    What is the origin of the remainder of the urethra in the glans?

    <p>A bud of ectodermal cells from the tip of the glans</p> Signup and view all the answers

    What is the shape of the perineum when seen from below with the patient in the lithotomy position?

    <p>Diamond</p> Signup and view all the answers

    What is the name of the cartilaginous joint that lies in the midline between the bodies of the pubic bones?

    <p>Symphysis pubis</p> Signup and view all the answers

    What is the lower opening of the anal canal?

    <p>Anus</p> Signup and view all the answers

    What is the structure that contains the penis and the scrotum in males?

    <p>Male urogenital triangle</p> Signup and view all the answers

    What is the name of the muscle that supports the weight of the body in the sitting position?

    <p>Gluteus maximus</p> Signup and view all the answers

    What is the name of the bony structure that forms the posterior boundary of the perineum?

    <p>Coccyx</p> Signup and view all the answers

    What is the color of the anal margin in the living?

    <p>Reddish brown</p> Signup and view all the answers

    What is the structure that lies in the midline between the bodies of the pubic bones?

    <p>Symphysis pubis</p> Signup and view all the answers

    What is the characteristic of the pubic hair in the female?

    <p>Has an abrupt horizontal superior margin</p> Signup and view all the answers

    What is the location of the vaginal orifice?

    <p>In the vestibule, posterior to the external urethral meatus</p> Signup and view all the answers

    What is the function of the hymen in virgins?

    <p>Protects the vaginal orifice</p> Signup and view all the answers

    What is the boundary of the anal triangle?

    <p>Formed by the gluteus maximus muscle</p> Signup and view all the answers

    What is the shape of the vestibule?

    <p>Triangular</p> Signup and view all the answers

    What is the location of the fourchette?

    <p>At the base of the vestibule</p> Signup and view all the answers

    What is the characteristic of the labia majora?

    <p>Fat-filled folds of skin</p> Signup and view all the answers

    What is the result of the first coitus on the hymen?

    <p>It tears, usually posteriorly or posterolaterally</p> Signup and view all the answers

    Study Notes

    Anal Triangle

    • The anal triangle is the posterior half of the perineum.
    • Its boundaries are the ischial tuberosities, sacrotuberous ligaments, and the tip of the coccyx.

    Anal Canal

    • The anal canal is about 1.5 inches (4 cm) long and passes downward and backward from the rectal ampulla to the anus.
    • The levator ani muscles and the anal sphincters keep its lateral walls in apposition except during defecation.

    Structure of the Anal Canal

    • The mucous membrane of the upper half of the anal canal is derived from hindgut entoderm.
    • It is lined by columnar epithelium and is thrown into vertical folds called anal columns.
    • The mucous membrane of the lower half of the anal canal is derived from ectoderm and is lined by stratified squamous epithelium.

    Arterial Supply

    • The arterial supply is the superior rectal artery, a branch of the inferior mesenteric artery.
    • The inferior rectal artery, a branch of the internal pudendal artery, supplies the lower half of the anal canal.

    Venous Drainage

    • The venous drainage is mainly by the superior rectal vein, a tributary of the inferior mesenteric vein.
    • The inferior rectal vein, a tributary of the internal pudendal vein, also drains the lower half of the anal canal.

    Lymphatic Drainage

    • The lymphatic drainage is mainly upward along the superior rectal artery to the pararectal nodes and then eventually to the inferior mesenteric nodes.

    Innervation

    • The nerve supply is from the somatic inferior rectal nerve and the autonomic hypogastric plexuses.
    • The nerve supply is sensitive to pain, temperature, touch, and pressure.

    Ischioanal Fossa

    • The ischioanal fossa is a fat-filled space on each side of the anal canal.

    Perineal Body

    • The perineal body is a mass of fibrous tissue lying between the anal canal and the coccyx.
    • It is surrounded by the levator ani muscles and the external anal sphincter.

    Urogenital Triangle

    • The urogenital triangle is the anterior half of the perineum.
    • Its boundaries are the ischial tuberosities, the pubic symphysis, and the tip of the coccyx.

    Puborectalis

    • The puborectalis is a muscle that forms a sling around the junction of the rectum and anal canal.
    • It is a part of the levator ani muscle.

    Anococcygeal Body

    • The anococcygeal body is a mass of fibrous tissue lying between the anal canal and the coccyx.
    • It is posterior to the anal canal.

    Muscles of the Scrotum

    • The superficial transverse perineal muscles compress the crus penis and assist in the process of erection of the penis.
    • The function of these muscles is to fix the perineal body in the center of the perineum.

    Blood Supply

    • The external pudendal branches of the femoral and internal pudendal arteries supply the scrotum.
    • The veins accompany the corresponding arteries.

    Lymph Drainage

    • The wall of the scrotum drains into the medial group of superficial inguinal lymph nodes.
    • The contents of the scrotum (testis and epididymis) drain upward to the lumbar (paraaortic) lymph nodes at the level of the first lumbar vertebra.

    Perineal Body

    • A small mass of fibrous tissue that attaches to the center of the posterior margin of the perineal membrane.
    • It serves as a point of attachment for the external anal sphincter, bulbospongiosus muscle, and superficial transverse perineal muscles.

    Sphincter Urethrae Muscle

    • A complex structure composed of multiple parts.
    • The action of the lower part of the muscle on the urethra is somewhat uncertain.
    • The inferior part of the external sphincter (between the perineal membrane and the prostate) appears to form a true sphincter-like unit encircling the intermediate part of the urethra.

    Internal Pudendal Artery

    • Pierces the perineal membrane, enters the deep perineal space (pouch), and passes forward.
    • Gives rise to the artery to the bulb of the penis; the deep artery of the penis to the crus of the penis; and the dorsal artery of the penis, which supplies the skin and fascia of the penis.

    Male Urogenital Triangle

    • The urethra has three parts: prostatic, intermediate (membranous), and penile (spongy).
    • The prostatic urethra is about 1.25 in. (3 cm) long and passes through the prostate from the base to the apex.

    Catheterization

    • The external orifice at the glans penis is the narrowest part of the entire urethra.
    • The urethra dilates to form the fossa navicularis within the glans.

    Female Genitalia

    • The mons pubis, labia majora, labia minora, clitoris, vestibule, vestibular bulbs, and greater vestibular glands.
    • The epithelium of the glans has numerous sensory endings and is the most sensitive part of the clitoris.

    Pelvic Fractures and Infections

    • Shearing forces in pelvic fractures can damage the urethra as it emerges from the fixed perineal membrane.
    • The urethra, vagina, lesser vestibular glands, and sebaceous glands of the labia majora can become infected.
    • The vagina has no glands and is lined with stratified squamous epithelium, capable of resisting infection to a remarkable degree if pH is kept low.

    Catheterization

    • Female urethra is shorter, wider, and more dilatable, making catheterization easier than in males.
    • The urethra is straight, and only minor resistance is felt as the catheter passes through the external urethral sphincter.

    Vulva and Pregnancy

    • A bluish discoloration of the vulva and vagina appears at the 8th to 12th week of pregnancy due to venous congestion.
    • Digital examination of the vagina provides valuable information concerning the health of the vaginal walls, uterus, and surrounding structures.

    Urethral Infection

    • The short length of the female urethra predisposes to ascending infection, making cystitis more common in females than males.
    • Five degrees of severity can occur: glandular, coronal, penile, penoscrotal, and perineal.

    Development of the Penis

    • The penile urethra develops from the fusion of the two genital folds and the bud of ectodermal cells from the tip of the glans.
    • The prepuce (foreskin) is formed from a fold of skin at the base of the glans.
    • The erectile tissue develops within the mesenchymal core of the penis.

    Female Genitalia

    • The changes in the female are less extensive than those in the male.
    • Epispadias occurs when the genital folds fail to unite on the undersurface of the developing penis.

    Surface Anatomy

    • The perineum is diamond-shaped and bounded by the symphysis pubis, the tip of the coccyx, and the ischial tuberosities.
    • The male urogenital triangle contains the penis and scrotum.
    • The anus is the lower opening of the anal canal and lies in the midline.

    Radiographic Anatomy

    • The radiographic anatomy of the bones forming the boundaries of the perineum is shown in Chapter 9.

    Anal Triangle

    • The anus is surrounded by coarse hairs and has a reddish-brown color.
    • The anal margin is puckered by the contraction of the external anal sphincter.

    Male Urogenital Triangle

    • The penis consists of a root, a body, and a glans.
    • The symphysis pubis is a cartilaginous joint that lies in the midline between the bodies of the pubic bones.

    Female Genitalia

    • The labia majora are prominent, paired, fat-filled folds of skin extending posteriorly from the mons pubis.
    • The vestibule is a smooth triangular area bounded by the labia minora, with the clitoris at its apex and the fourchette at its base.
    • The vaginal orifice lies in the vestibule, posterior to the external urethral meatus.

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