[Anatomy] Perineum

Front 1

boundaries of perineum

Back 1

- The perineum is a diamond shaped region located inferior to the pelvic diaphragm (levator ani plus coccygeus)
- Bounded by the pubic symphysis anteriorly, the coccyx posteriorly, and the left and right ischial tuberosities laterally

Front 2

division of perineum

Back 2

- A line drawn between the ischial tuberosities divides the perineum into two triangles
o Anal Triangle (posterior to the line)
o Urogenital (UG) Triangle (anterior to the line)

Front 3

anal triangle

Back 3

posterior to line between ischila tuberosities; contains ischioanal fossae, anal canal

Front 4

ischioanal (ischiorectal) fossae

Back 4

o Fat filled spaces on either side of the anal canal
o Allows for dilation of the anal canal
o The lateral wall of each fossa is formed by obturator internus and the ischial tuberosity
o The medial wall of each fossa is formed by the levator ani and the anal canal
o Each fossa projects anteriorly into the UG triangle, forming an anterior recess
o The fossae communicate with one another posterior to the anal canal

Front 5

anal canal

Back 5

posterior to line between ischial tuberosities; begins at anorectal flexure and ends at anus; includes anal columns, anal valves, pectinate line, internal and external anal sphincter

Front 6

anal columns

Back 6

vertical folds in the mucosal lining

Front 7

anal valves

Back 7

crescent shaped folds that unite the anal columns inferiorly

Front 8

pectinate line

Back 8

irregular line at the level of the anal valves

Front 9

superior to the pectinate line

Back 9

• Anal canal is derived from the hindgut (endoderm)
• Supplied by superior rectal vessels (origin: inferior mesenteric vessels) (minor supply/drainage via the middle rectal vessels (origin: internal iliac vessels))
• Site of internal hemorrhoids
• Lymph drains to the internal iliac lymph nodes
• Parasympathetic and sympathetic innervation similar to the hindgut; sensitive to stretch but not pain/temp/touch

Front 10

inferior to the pectinate line

Back 10

• Anal canal is derived from ectoderm
• Supplied by inferior rectal vessels (origin: internal pudendal vessels from internal iliac)
• Site of external hemorrhoids
• Lymph drains to the superficial inguinal lymph nodes
• Somatic innervation via the inferior rectal nerve (branch of the pudendal nerve); very sensitive to pain/temp/touch

Front 11

internal anal sphincter

Back 11

(involuntary)
• Smooth muscle sphincter
• Thickening of the superior 2/3 of the anal canal
• Sympathetic innervation stimulates its contraction (preventing defecation)
• Parasympathetic innervation relaxes the sphincter (allowing defecation to occur)

Front 12

external anal sphincter

Back 12

(voluntary)
• Skeletal muscle sphincter surrounding the inferior 2/3 of the anal canal
• Somatic innervation (inferior rectal nerve) stimulates its contraction (‘potty’ training involves learning how to control this sphincter)

Front 13

urogenital triangle

Back 13

includes superficial perineal fascia, deep perineal fascia, perineal membrane, perineal body, external genitalia, muscles, glands

Front 14

superficial perineal fascia

Back 14

o Superficial fatty layer
• Continuous with Camper fascia of the abdomen
o Deep membranous layer (Colles fascia)
• Continuous with Scarpa fascia of the abdomen
• In males, also continuous with dartos fascia

Front 15

deep perineal fascia

Back 15

o Invests the muscles of the perineum

Front 16

perineal membrane

Back 16

o Facial layer that divides the UG triangle into a superficial perineal pouch and a deep perineal pouch
o Provides attachment for the erectile tissue and muscles of the UG triangle
o The urethra passes through the perineal membrane as it courses from the pelvic cavity to the perineum
o In female, the vagina also passes through the perineal membrane posterior to the urethral hiatus

Front 17

superficial perineal pouch

Back 17

located between the perineal membrane and the membranous layer of the superficial fascia (Colles’ fascia)

Front 18

deep perineal pouch

Back 18

located between the perineal membrane and the levator ani

Front 19

perineal body

Back 19

o Midline thickening of the posterior border of the perineal membrane
o Muscles of the pelvic floor and the perineum insert into the perineal body, so it is an important in maintaining the integrity of the pelvic floor and perineum
o Weakening of the perineal body can result in vaginal prolapse

Front 20

female external genitalia

Back 20

collectively known as vulva or pudendum; mons pubis, labia majora, labia minora, vestibule, clitoris, bulbs of vestibule

Front 21

episiotomy

Back 21

o During childbirth, the perineal body may be stretched or torn; to avoid a ragged tear, an incision (episiotomy) can be made either through the perineal body, or lateral to it to allow for passage of the baby’s head

Front 22

mons pubis

Back 22

- Fat and connective tissue located anterior to the pubic symphysis
- Covered with pubic hair

Front 23

labia majora

Back 23

• Fat filled folds containing the round ligament of the uterus
• Covered with pubic hair
• Correspond to the scrotum in males

Front 24

labia minora

Back 24

• Thin folds (no fat, no hair) located on either side of the midline
• The labia minora join together superior to the clitoris to form the prepuce

Front 25

vestibule

Back 25

• Space between the labia minora
• Contains the openings of the urethra and vagina (hymen is a mucous membrane that spans the vaginal orifice)

Front 26

erectile tissues

Back 26

female: clitoris (corpora cavernosa), bulbs of vestibule; male: penis

Front 27

clitoris

Back 27

• The root of the clitoris is formed by the crura (proximal ends of the corpora cavernosa)
• The body of the clitoris is formed by the distal ends of the corpora cavernosa
• The clitoris is supported by the suspensory ligament, an extension of the deep fascia that attaches to the pubic symphysis

Front 28

corposa cavernosa of clitoris

Back 28

(paired structures)
o Proximal ends attached firmly to the pubic arch, forming the crura (singular: crus) of the clitoris
o Distal ends form the body of the clitoris and its terminal expansion, the glans clitoris

Front 29

bulbs of vestibule

Back 29

(paired structures)
• Located on either side of the vaginal opening
• Do not contribute to the clitoris
• Correspond to the bulb of the penis (proximal part of the corpus spongiosum) in males

Front 30

corpora cavernosa of penis

Back 30

(paired structures)
o Proximal ends attached firmly to the pubic arch, forming the crura of the penis
o Distal ends form the posterior parts of the body of the penis

Front 31

corpus spongiosum

Back 31

(unpaired structure)
o Forms the bulb of the penis
o Distal end forms the anterior part of the body of the penis and its terminal expansion, the glans penis
o Encloses the penile (spongy) urethra

Front 32

penis

Back 32

• The root is composed ofthe crura (proximal ends of the corpora cavernosa), and the bulb of the penis (proximal part of the corpus spongiosum)
• The body is composed of the distal ends of the corpora cavernosa posteriorly and the corpus spongiosum anteriorly
• Distally the skin of the penis is loosely attached and forms the prepuce (foreskin) covering the glans
• The penis is supported by the suspensory ligament, an extension of the deep fascia that attaches to the pubic symphysis

Front 33

muscles of UG triangle

Back 33

ischiocavernosus, bulbospongiosus, superficial transverse perineal muscles, urogenital diaphragm (deep transverse perineal muscles, external urethral sphincter)

Front 34

ischiocavernosus

Back 34

(in superficial perineal pouch)
• Paired muscles covering the crura of the clitoris and penis
• Aid in erection (compress veins of the corpora cavernosa, maintaining blood within these tissues)

Front 35

bulbospongiosus

Back 35

(in superficial perineal pouch)
• Paired muscles associated with the bulbs of the vestibule in females and the bulb of the penis in males
• Attached to the perineal body

Front 36

superficial transverse perineal muscles

Back 36

(in superficial perineal pouch)
• Paired muscles attached to the ischial tuberosities laterally and the perineal body medially
• Help stabilize the perineal body

Front 37

urogenital diaphragm

Back 37

(in deep perineal pouch); include deep transverse perineal muscles and external urethral sphincter

Front 38

deep transverse perineal muscles

Back 38

• Paired muscles attached to the ischial tuberosities laterally and the perineal body medially
• Help stabilize the perineal body

Front 39

external urethral sphincter

Back 39

• In males, the external urethral sphincter surrounds the membranous urethra

Front 40

bulbospongiosus (male vs. female)

Back 40

• In males, the right and left muscles unite in the midline to surround the bulb of the penis; compress the veins in the bulb to aid in erection and expel semen (during ejaculation) or residual urine
• In females, right and left muscles do not unite in the midline

Front 41

glands of the UG triangle

Back 41

o Greater vestibular (Bartholin) glands in the female
• Located just posterior to the bulbs of the vestibule
• Ducts open into the vagina and secrete mucus
• Infection and formation of cysts common
o Bulbourethral (Cowper) glands in the male
• Located just lateral to the external urethral sphincter
• Ducts empty into the penile urethra and contribute to the semen

Front 42

membranous urethra

Back 42

• Shortest part of the urethra (which has prostatic, membranous, and penile parts)
• Thin walls can be ruptured (e.g., when inserting catheters)

Front 43

nerves of the perineum

Back 43

pudendal nerve (S2-S4); branches into inferior rectal nerves, perineal nerves, dorsal nerve of penis or clitoris

Front 44

pudendal nerve

Back 44

(S2-S4)
o Leaves the pelvic cavity through the greater sciatic foramen, inferior to piriformis, courses around the ischial spine, and enters the perineum through the lesser sciatic foramen
o After passing through the lesser sciatic foramen, the pudendal nerve enters the pudendal (Alcock) canal on the lateral wall of the ischioanal fossa

Front 45

pudendal nerve block

Back 45

can be performed to anesthetize the perineum; the needle is directed towards the ischial spine

Front 46

inferior rectal nerves

Back 46

• branch of pudendal nerve
• Course medially across the ischioanal fossa
• Innervate the external anal sphincter and the skin of the anal triangle

Front 47

perineal nerves

Back 47

Innervate the muscles and skin of the UG triangle

Front 48

dorsal nerve of penis or clitoris

Back 48

Innervates skin of the penis/clitoris, particularly the glans

Front 49

internal pudendal artery

Back 49

o Primary source of blood to the perineum
o Branch of the internal iliac artery
o Accompanies the pudendal nerve (leaves the pelvis through the greater sciatic foramen, inferior to piriformis, courses around the ischial spine, passes through the lesser sciatic foramen and enters the pudendal canal)

Front 50

branches of pudendal artery

Back 50

• Inferior rectal artery
• Perineal arteries
• Dorsal artery of the penis or clitoris
• Deep artery of the penis or clitoris

Front 51

veins of perineum

Back 51

accompany the arteries and share the same names
o Exceptions: superficial and deep dorsal veins of the penis

Front 52

lymphatic drainage of perineum

Back 52

o Deep perineal tissues > lymphatic vessels accompany the internal pudendal vessels and drain into internal iliac nodes
o Superficial perineal tissues > lymphatic vessels drain to the superficial inguinal nodes
o Remember: lymph from the testes drains to the lumbar nodes (alongside the abdominal aorta)

Front 53

divisions of the lower extremity

Back 53

- The lower extremity includes the gluteal region and all structures inferior to it
- Divisions of the lower extremity:
o Gluteal region
o Thigh (hip to knee)
o Popliteal fossa (posterior aspect of knee)
o Leg (knee to ankle)
o Foot (dorsal and plantar aspects)

Front 54

bones of the lower extremity

Back 54

- Bones of the lower extremity: hip bones (see Pelvis I notes), femur, patella, tibia (medial bone of leg), fibula (lateral bone of leg), 7 tarsals (calcaneus, talus, navicular, cuboid, medial, intermediate, and lateral cuneiforms), 5 metatarsals (proximal part is the base, distal part is the head), 14 phalanges (proximal, middle, distal; the hallux (big toe) has a proximal and distal phalanx only)

Front 55

femur

Back 55

o Head
o Neck
o Shaft (body) with linea aspera (on posterior surface)
o Medial and lateral femoral condyles (distal)

Front 56

tibia

Back 56

o Medial and lateral tibial condyles (proximal)
o Shaft (body)
o Medial malleolus is the distal protuberance on medial side of the ankle

Front 57

fibula

Back 57

o Head (proximal protuberance)
o Shaft (body)
o Lateral malleolus is the distal protuberance on lateral side of the ankle

Front 58

hip joint

Back 58

o Acetabulum of the hip bone articulates with the femoral head
o Ball and socket synovial joint
o Flexion reduces the angle between the thigh and trunk anteriorly
o Extension increases the angle between the thigh and trunk anteriorly
o Abduction draws the thigh away from the midline of the body
o Adduction draws the thigh towards the midline of the body
o Medial rotation femur rotates medially along its long axis
o Lateral rotation femur rotates laterally along it long axis

Front 59

knee joint

Back 59

o Femoral condyles articulate with the tibial condyles
o Hinge synovial joint
o Flexion brings the leg closer to the posterior aspect of the thigh
o Extension draws the leg away from the posterior aspect of the thigh

Front 60

ankle (talocrural) joint

Back 60

o Talus articulates with distal tibia and lateral malleolus of the fibula
o Hinge synovial joint
o Dorsiflexion brings the foot closer to the anterior aspect of the leg (directs toes superiorly)
o Plantarflexion draws the foot away from the anterior aspect of the leg (directs toes inferiorly)

Front 61

subtalar joint

Back 61

o Synovial joint between the talus and the calcaneus
o Eversion causes the sole to face laterally
o Inversion causes the sole to face medially

Front 62

metatarsophalangeal (MTP) joints

Back 62

o Synovial joints between the metatarsals and the proximal phalanges
o Flexion of toes (towards the ground)
o Extension of toes (away from the ground)
o Abduction (movement away from the second digit)
o Adduction (movement towards the second digit)