Perineum Flashcards
(40 cards)
1
Q
What are the Boundaries of the Perineum?
A
- Located inferior to the pelvic diaphragm (coccygeus + levator ani)
- Bounded by the inferior pelvic aperture (pelvic outlet)
- A line drawn between the ischial tuberosities divides the perineum into two triangles
1) Urogenital (UG) Triangle (anterior to the line)
2) Anal Triangle (posterior to the line)
2
Q
What makes up the Anal Triangle
A
- Ischioanal fossae
- Anal Canal
3
Q
Describe the Ischioanal fossae
A
- Fat filled spaces on either side of the anal canal; allow for dilation of anal canal
- Lateral wall of each fossa: formed by obturator internus and ischial tuberosity
- Medial wall of each fossa: formed by the levator ani and external anal sphincter
- Each fossa projects anteriorly into the UG triangle, forming anterior recesses, these recesses facilitate the spread of infection between the UG and anal triangles
- The fossae also communicate with one another posterior to the anal canal; this communication facilitates the spread of infection between the left and right sides of the anal triangle.
4
Q
Describe the Anal Canal
A
- Begins at anorectal flexure and ends at the anus
- Anal columns-vertical folds in the mucosal lining
- Anal valves-crescent shaped folds that unite the anal columns inferiorly
- Pectinate line-irregular line at the level of the anal valves
5
Q
Describe what is superior to the pectinate line
A
- Anal canal is derived from the hindgut (endoderm)
- Supplied/drained by superior rectal vessels (origin: inferior mesenteric vessels) with minor supply/drainage via the middle rectal vessels (origin: internal iliac vessels)
- Lymph drains to the internal iliac lymph nodes
- Parasympathetic and sympathetic innervation similar to the hindgut; visceral sensory innervation (sensitive to stretch/ischemia but not pain/temp/touch)
6
Q
Describe what is Inferior to the pectinate line
A
- Anal canal is derived from ectoderm
- Supplied/drained by inferior rectal vessels (origin: internal pudendal vessels from internal iliac)
- Lymph drains to the superficial inguinal lymph nodes
- Somatic innervation via the inferior rectal nerve (branch of the pudendal nerve); sensitive to pain/temp/touch
7
Q
Describe the Portal-caval anastomosis related to the rectum and anal canal
A
- Proximal drainage into the superior rectal vein (portal system)
- Distal drainage into the inferior rectal vein (caval system)
- In cases of portal hypertension, the increased volume of blood in the inferior rectal veins leads to external hemorrhoids (note: internal hemorrhoids occur most commonly in the absence of portal hypertension, and are thought to be related to a breakdown of the muscle walls of the anal canal, leading to prolapse).
8
Q
What are the anal sphincters?
A
Internal anal sphincter
External anal sphincter
9
Q
Describe the Internal anal sphincter
A
- Smooth muscle sphincter; thickening of the superior 2/3 of the anal canal
- Sympathetic innervation (via lumbar splanchnic nerves) stimulates its contraction (preventing defecation)
- Parasympathetic innervation (via pelvic splanchnic nerves) relaxes it (allowing defecation to occur)
10
Q
Describe the External anal sphincter
A
- Skeletal muscle sphincter surrounding the inferior 2/3 of the anal canal
- Somatic motor innervation (via inferior rectal nerve) stimulates its contraction (‘potty’ training involves learning how to control this sphincter)
11
Q
What makes up the female External genitalia
A
- Collectively, the female external genitalia are called the vulva or pudendum
1) Mons pubis
2) Labia majora
3) Labia minora
4) Vestibule
12
Q
Describe the Mons pubis
A
- Located anterior to the pubic symphysis
- Covered with pubic hair and filled with fat and connective tissue
13
Q
Describe the Labia majora
A
- Fat filled folds containing the round ligament of the uterus
- Covered with pubic hair
- Correspond to the scrotum in males
14
Q
Describe the Labia minora
A
- 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
15
Q
Describe the Vestibule
A
- Space between the labia minora
- Contains the openings of the urethra and vagina (hymen is a mucous membrane that spans the vaginal orifice)
16
Q
What are the Erectile tissues in the female
A
- Clitoris
- Bulbs of the Vestibule (paired structures)
17
Q
Describe what makes up the Clitoris
A
Corpora cavernosa (paired structures)
- Proximal ends attached to the pubic arch, forming the crura (singular: crus) of the clitoris
- Distal ends form the body of the clitoris and its terminal expansion, the glans clitoris
The clitoris is supported by the suspensory ligament of the clitoris, an extension of the deep fascia that attaches to the pubic symphysis
18
Q
Describe the Bulbs of the Vestibule (paired structures)
A
- 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
19
Q
Describe the Erectile tissues in the male penis
A
1) Corpora cavernosa (paired structures)
2) Corpus spongiosum (unpaired structure)
- 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 of the penis, an extension of the deep fascia that attaches to the pubic symphysis
20
Q
Describe the Corpora cavernosa (paired structures)
A
- Proximal ends attached to the pubic arch, forming the crura of the penis
- Distal ends form the dorsal parts of the body of the penis
21
Q
Describe the Corpus spongiosum (unpaired structure)
A
- Proximal end forms the bulb of the penis
- Distal end forms the ventral part of the body of the penis and its terminal expansion, the glans penis
- Encloses the penile (spongy) urethra
22
Q
What are the Skeletal muscles of the UG Triangle?
A
1) Ischiocavernosus
2) Bulbospongiosus
3) Superficial transverse perineal muscles
4) Urogenital (UG) diaphragm (in deep perineal pouch)
- Deep transverse perineal muscles
- External urethral sphincter
23
Q
Describe the Ischiocavernosus
A
- Paired muscles covering the crura of the clitoris and penis
- Aid in erection (compress veins of the corpora cavernosa, maintaining blood within these tissues)
24
Q
Describe the Bulbospongiosus
A
- Paired muscles covering the bulbs of the vestibule in females and the bulb of the penis in males
- Attached to the perineal body
25
What are the male and female differences in the bulbospongiosus?
- 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
26
Describe the Superficial transverse perineal muscles
- Paired muscles attached to the ischial tuberosities laterally and the perineal body medially
- Help stabilize the perineal body
27
Describe the Urogenital (UG) diaphragm (in deep perineal pouch)
1) Deep transverse perineal muscles
- Paired muscles attached to the ischial tuberosities laterally and the perineal body medially
- Help stabilize the perineal body
- Mix of smooth and skeletal muscle in females
2) External urethral sphincter
- Somatic motor innervation (via perineal nerves) stimulates its contraction, which may help prevent urination
28
What are the male and female differences in the External urethral sphincter
-In females, surrounds urethra (which is very short)
- In males, surrounds the membranous urethra
- Shortest part of the male urethra (which has prostatic, membranous, and penile parts)
- Thin walls of the membranous urethra can be ruptured (e.g., when inserting catheters)
29
What are the Glands of the UG Triangle
- Greater vestibular (Bartholin) glands in the female
| - Bulbourethral (Cowper) glands in the male
30
Describe the Greater vestibular (Bartholin) glands in the female
- Located just posterior to the bulbs of the vestibule
- Ducts open into the vestibule on each side of vaginal orifice and secrete mucus (for lubrication)
- Infection and formation of cysts can occur
31
Describe the Bulbourethral (Cowper) glands in the male
- Located just lateral to the external urethral sphincter
- Ducts empty into the penile urethra and secrete pre-ejaculate, which helps lubricate and neutralize the urethra for passage of sperm
32
What are the Nerves of the Perineum?
- Sacral Plexus (ventral rami L4-S4)
| - Pudendal nerve (S2-S4)
33
Describe the Sacral Plexus (ventral rami L4-S4)
-Lumbosacral trunk (ventral rami L4-L5)
• Descends from the abdomen to join the sacral ventral rami
-Ventral rami S1-S4 emerge from the anterior sacral foramina and travel through the piriformis muscle
-The sacral plexus can be compressed by pelvic tumors or the fetal head during childbirth
-A major branch of the sacral plexus is the pudendal nerve
34
Describe the Pudendal nerve (S2-S4)
- Exits 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
- After passing through the lesser sciatic foramen, the pudendal nerve enters the pudendal (Alcock) canal on the lateral wall of the ischioanal fossa
- A pudendal nerve block can be performed to anesthetize the perineum; the needle is directed towards the ischial spine
35
What are the branches of the Pudendal nerve (S2-S4)?
1) Inferior rectal nerves
- Course medially across the ischioanal fossa
- Innervate the external anal sphincter and the skin of the anal triangle
2) Perineal nerves
- Innervate the muscles and skin of the UG triangle
3) Dorsal nerve of the penis or clitoris
- Innervates skin of the penis/clitoris, particularly the glans
36
Describe Parasympathetic Autonomic control of sexual function
- Parasympathetic supply (via pelvic splanchnic nerves) helps achieve erection (e.g., by closing off arteriovenous anastomoses in the region so that blood pools in the sinuses of the erectile tissues)
- Note: some skeletal muscles (e.g., ischiocavernosus, bulbospongiosus) also play key roles in sexual function and they are innervated by somatic nerves; see notes above)
37
Describe sympathetic Autonomic control of sexual function
-Sympathetic supply (via lumbar splanchnic nerves) helps achieve emission (e.g., peristalsis of ductus deferens delivers sperm and glandular secretions to prostatic urethra) and contraction of internal urethra spinchter (which prevents sperm from entering the bladder)
38
What are the Blood Vessels of the Perineum?
Internal pudendal artery
- Primary source of blood to the perineum
- Branch of the internal iliac artery
- 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)
Veins of the perineum accompany the arteries and share the same names
-Exceptions: superficial and deep dorsal veins of the penis
39
What are the branches of the Internal pudendal artery?
- Inferior rectal artery
- Perineal arteries
- Dorsal artery of the penis or clitoris
- Deep artery of the penis or clitoris
40
Describe Lymphatic drainage of the Perineum
- Deep perineal tissues --> lymphatic vessels accompany the internal pudendal vessels and drain into internal iliac nodes
- Superficial perineal tissues --> lymphatic vessels drain into superficial inguinal nodes
