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1. List & identify the named branches of the lumbar plexus as seen in the abdomen, and describe innervation patterns for specific branches.
1. List & identify the named branches of the lumbar plexus as seen in the abdomen, and describe innervation patterns for specific branches.
The lumbar plexus is a somatic nervous plexus (somatic afferent & efferent fibers) - not an autonomic nerve plexus like many of the other nerve plexuses we have and will discuss. This plexus is derived from the VPR of spinal nerves L1-L4.
The psoas major mm. are very important landmarks for identifying the lumbar plexus nerves.
There are 6 main nerve branches of the lumbar plexus. We will understand where these branch in relation to the psoas major m. We will then focus on the first three here, as the lateral femoral cutaneous, obturator, and femoral nerves will be discussed in more detail during the musculoskeletal content as they play a bigger role in the lower limb.
Iliohypogastric nn. (superolateral border of psoas major m.)
Ilio-inguinal nn. (lateral border of psoas major, just inferior to iliohypogastric n.)
Genitofemoral nn. (formed deep to psoas major m. and will then pierce the muscle)
Lateral femoral cutaneous nn. (lateral border of psoas major m.)
Obturator nn. (inferomedial border of psoas major m.; typically 2nd largest lumbar plexus n.)
Femoral nn. (inferolateral border of psoas major m.; largest lumbar plexus branch)
2. Diagram the major features of the pelvic girdle.
2. Diagram the major features of the pelvic girdle.
The pelvic girdle connects the lower back (i.e. lumbar vertebrae & sacrum) to the lower limbs (i.e. femurs and beyond).
The bony pelvis is composed of a pair of coxal (hip) bones. They form 2 sacro-iliac (SI) joints with the sacrum, and the coxal bones meet anteriorly at the pubic symphysis, a cartilaginous joint.
The coxal bones are each a set of 3 fused bones:
Ilium: superior and fan-shaped
Ischium: more posteriorly-placed
Pubis: anteriorly-placed
These parts of the bone all meet and fuse within the acetabulum (where the femoral head articulates with the coxal bone).
When discussing the pelvic girdle, it is sometimes useful to delimit the true (lesser) pelvis from the false (greater) pelvis. These are divided by the pelvic brim.
Pelvic brim: bony elements that define the pelvic inlet
Connects the sacral promontory (the anterior projecting edge of the body of the S1 vertebrae), around the ilium, to the superior portions of the pubis bones
False (greater) pelvis: lies superior to the pelvic brim
Predominantly occupied by abdominal viscera
True (lesser) pelvis: lies inferior to the pelvic brim and superior to the pelvic outlet
Will include organs of the pelvic cavity and deepest portions of the perineum
3. Describe the spatial relationships of the viscera and peritoneum of the pelvic cavity.
3. Describe the spatial relationships of the viscera and peritoneum of the pelvic cavity.
The pelvis contains viscera of the GI, urinary, and reproductive (and associated endocrine) systems.
Gastrointestinal
The pelvis transmits the distalmost portions of the digestive system: the distal sigmoid colon, rectum, and anal canal. The rectum is found in the posterior aspect of the pelvic cavity.
Reproductive
When present in the pelvis, reproductive organs are typically situated anterior to the rectum, and posterior, lateral, superior, or inferior to the urinary bladder depending on the organ.
Reproductive (or associated endocrine) organs potentially located in the pelvic cavity include:
Uterus
Uterine (Fallopian) tubes
Ovaries
Vagina
Prostate gland
Seminal vesicles (glands)
Ductus (vas) deferens
Bulbo-urethral glands
Urinary
The pelvis contains the urinary bladder, and transmits the distal ureters to the urinary bladder. The ureters enter the pelvic cavity adjacent to the bifurcation of the common iliac aa., and connect to the posterior aspect of the urinary bladder. The urinary bladder is found in the anterior aspect of the pelvic cavity, closely associated with the pubic symphysis.
Peritoneum
The pelvic viscera are variably covered with peritoneum. Depending on their relationship to the peritoneum, these structures may be intra-, retro-, or subperitoneal.
Assigned Female At Birth (AFAB) Peritoneum/Pelvic Cavity Relationships
The peritoneum contacts the anterior abdominal wall, covers the posterior portion of the bladder, reflects superiorly to cover the anterior surface of the uterus (if present), traverses over the fundus of the uterus, and covers the posterior surface of the uterus.
At about the level of the internal os of the cervix, the peritoneum reflects onto the rectum and continues up the posterior wall. This leaves the vagina and bottom third of the rectum devoid of any peritoneum covering.
Areas where the peritoneum reflects from one portion of viscera to another create pouches, or are simply referred to as reflections.
There are typically two pouches in individuals assigned female at birth:
Vesico-uterine pouch/Bladder reflection/Anterior cul-de-sac
Created by the reflection between the urinary bladder and uterus
Recto-uterine pouch/pouch of Douglas/Posterior cul-de-sac
Created by the reflection between the uterus and rectum
Most inferior extension of the peritoneum
Close relationship with the posterior vaginal fornix
As gravity may guide fluid inferiorly, materials (blood, exudate, etc.) may accumulate in the recto-uterine pouch. This area may be accessed with a hypodermic needle via the posterior vaginal fornix in a procedure called culdocentesis.
Assigned Male At Birth (AMAB) Peritoneum/Pelvic Cavity Relationships
The peritoneum contacts the anterior abdominal wall, covers the posterior portion of the bladder and reflects superiorly onto the rectum, and continues to the posterior wall. This leaves the prostate, seminal vesicles, and the bottom third of the rectum devoid of any peritoneal covering.
The area where the peritoneum reflects from the bladder to the rectum is called the recto-vesical pouch.
Inferior to the pelvic viscera is the muscular floor of the pelvic cavity, the pelvic diaphragm. The pelvic diaphragm separates the pelvic cavity from the perineum, which will be discussed in the following session.
4. Describe the location and structure of the portions of the urinary system in the pelvic cavity.
4. Describe the location and structure of the portions of the urinary system in the pelvic cavity.
Ureters
Urine from the kidneys is conducted via the ureters to the urinary bladder. There are 3 parts of the ureter:
Abdominal part: retroperitoneal
Adjacent to the psoas major m. and crosses anterior to the genitofemoral n.
Crossed by gonadal vessels
Crosses over the bifurcation of the common iliac a. and enters the pelvic cavity
Pelvic part: retroperitoneal and then subperitoneal
Will have close relationships in certain areas with the uterine a. or ductus (vas) deferens
Intramural part: contained within the wall of the base of the urinary bladder
Urinary bladder
The urinary bladder is a distensible, urine-storing, subperitoneal organ.
There are multiple parts and surfaces of the urinary bladder. Three of the most clinically relevant areas include:
Apex: superoposterior relative to the superior portion of the pubic symphysis
The apex is connected to the umbilicus by the median umbilical ligament, the peritoneal fold containing the urachus.
Base/Fundus: posterior-most wall (opposite the apex)
May be closely associated with the vagina or the rectum dependent on viscera present
The wall of the base contains the intramural parts of the ureters, which open into the lumen of the bladder via the ureteric orifices
Neck: inferior-most portion of the bladder and contains the internal urethral meatus
The neck may be adjacent to the vagina or the prostate gland
The triangular space is formed by the ureteric orifices and the internal urethral meatus in the internal bladder is called the trigone.
The urinary bladder voids urine to the external environment through the urethra. The urethra is substantially sexually polymorphic.
Urethra
Typical urethral anatomy of an Assigned Female at Birth (AFAB) individual
The urethra begins at the internal urethral meatus, travels anteroinferiorly between the pubic symphysis and vagina, and terminates in the external urethral meatus. The external urethral meatus is typically found in the vestibule of the vagina between the glans clitoris and the opening of the vagina.
Typical urethral anatomy of an Assigned Male at Birth (AMAB) individual
Typically, there are 3 major parts of the AMAB urethra:
Prostatic part: begins at the internal urethral meatus, traverses the prostate gland, where it receives secretions of the prostate as well as from the ejaculatory ducts
This is the point of entry of semen into the urethra
Membranous part: traverses the pelvic diaphragm
Spongy/penile part: traverses the corpus spongiosum of the penis
Ends in the external urethral meatus on the distal ventral portion of the glans penis
5. Describe the gross anatomy and anatomical relationships of the AFAB pelvic reproductive viscera & genital tract. List associated fascial & peritoneal specializations and neurovasculature.
5. Describe the gross anatomy and anatomical relationships of the AFAB pelvic reproductive viscera & genital tract. List associated fascial & peritoneal specializations and neurovasculature.
An Assigned Female At Birth (AFAB) individual will typically have the following viscera: uterus, uterine (Fallopian) tubes, ovaries, vagina, and associated mesenteries and ligaments.
Uterine (Fallopian) tubes
The uterine (Fallopian) tubes are laterally continuous with the body of the uterus, and serve as a pathway for oocytes (and their ontogenetic derivatives) from the ovary to the uterine cavity. The uterine tubes are intraperitoneal.
Four major parts of the tubes (lateral to medial):
Infundibulum: most distal portion of the uterine tube which opens into the peritoneal cavity via the abdominal ostium
Have fringed processes, fimbriae, at distal-most end that are in close proximity to the ovary
Ampulla: longest and widest portion of uterine tube
Fertilization of the oocyte most typically occurs in this part
Isthmus: narrowest portion
Uterine part: leads into the uterine cavity
Tubal ligation (‘tubes tied’) is a surgery where the uterine tubes are ligated, incised, clamped, or occluded to prevent the passage of oocytes to the uterus.
Ovaries
The typically paired ovaries are gonads in which oocytes (gamete or germ cell) develop as well as an endocrine function with production of specific hormones.
Oophorectomy is the surgical removal of an ovary.
Uterus
The uterus is a pyriform (pear-shaped), distensible organ which may host a developing embryo & fetus until parturition.
It is structurally composed of 2 parts:
Body: muscular, ‘upper’ two-thirds
Fundus: portion of the body of the uterus superior to the uterine ostia (where the uterine tubes enter the uterus)
Cervix: lower, fibrous third
Hysterectomy is the surgical removal of the uterus.
Vagina
The vagina is a muscular passage from the cervix of the uterus to the vestibule of the vagina. It is posteriorly adjacent to the base of the urinary bladder and urethra, and is anteriorly adjacent to the rectum.
Proximally, the vaginal fornix surrounds the protrusion of the cervix into the vagina. The vaginal fornix may be conceptually divided into anterior, lateral, and posterior parts, with the posterior vaginal fornix being most clinically significant, as it offers access to the recto-uterine pouch to enter the peritoneal cavity.
Peritoneal & Endopelvic Fascial Ligaments
Broad ligament of uterus
The broad ligament of the uterus is composed of two layers of peritoneum and serves to divide the true pelvis into an anterior part (containing the bladder) and a posterior part (containing the rectum), in addition to attaching the uterus to the lateral pelvic walls.
Components of the broad ligament:
Mesometrium: covers the body of the uterus
Mesosalpinx: covers the uterine tube
Mesovarium: covers the ovaries
Suspensory (Infundibulopelvic/IP) ligament of ovary
This ligament attaches the aorta and inferior vena cava to the lateral pole of the ovary, and conducts the gonadal a. & v. This ligament is continuous with the mesovarium.
Ovarian ligament
The ovarian ligament connects the ovary and the uterus, and is a remnant of the gubernaculum.
Round ligament of uterus
The round ligament of the uterus extends from the uterus to the labium majus. The round ligament is a remnant of the gubernaculum and will traverse the inguinal canal. This ligament is closely associated with the artery of (Sampson) the round ligament.
Transverse cervical (cardinal) ligament
The transverse cervical (cardinal) ligament extends from the cervix to lateral pelvic wall, and transmits the uterine a. adjacent to the base of the broad ligament. It is in this location that the ureter travels in close approximation and inferior to the uterine a.
6. Describe structures of the vulva (external AFAB genitalia).
6. Describe structures of the vulva (external AFAB genitalia).
The vulva (AFAB external genitalia) is typically inclusive of:
Mons pubis: mound of subcutaneous tissue and skin with dense hair anterosuperiorly adjacent to the labia majora
Anterior (and superficial) to the pubic symphysis
Labia majora: protuberant cutaneous folds forming the lateral-most borders of the vulva
Singular = labium majus
Connect the mons pubis posteriorly to the perineum
Labia minora: medial and parallel to the labia majora
Extends posteriorly from the clitoris to encircle the vestibule
The anterior region of each labium minus diverges to form 2 structures:
Prepuce of clitoris: anterior & superficial to the clitoris
Frenulum of the clitoris: posterior
Vestibule of the vagina
The labia minora surround the vestibule, a medial cavity
Contains the external urethral meatus (the final anatomical point of the urine conducting pathway), the vaginal orifice (the external opening of the vagina), and the meatuses of the great vestibular (Bartholin’s) glands
Clitoris
Composed of erectile tissues
Crura of the clitoris: composed of corpora cavernosa (erectile tissue)
Run adjacent to the inferior margins of the ischiopubic rami
Covered by the ischiocavernosus mm.
Body (shaft) of the clitoris: paired, yet separated termini of the corpora cavernosa
Glans clitoris (also known as the glans of clitoris, the glans, or colloquially - albeit incompletely - as the clitoris) is nestled beneath the prepuce of clitoris and supported by the frenulum of clitoris (both are of the labia minora)
Composed of corpus spongiosum
Sits atop the inferior portion of the body of the clitoris
Densely covered in sensory receptors and free nerve endings
Richly vascularized and innervated (particularly the glans) structure that is an important mediator of sexual response
Vestibular bulbs
Masses of erectile tissue (corpus spongiosum) flanking the vestibule of the vagina and attached to the perineal membrane
United anteriorly by a slight commissure, which is associated with the body of the clitoris
Covered by the bulbospongiosus mm.
Greater vestibular (Bartholin’s) glands
Associated with the posterior margin of each bulb of the vestibule
The ducts from the greater vestibular glands empty into the vestibule, as these glands play an important role in lubricating this area
May become blocked, resulting in a Bartholin’s cyst
7. Describe the gross anatomy of the AMAB reproductive tract, spermatic cord, scrotum, and penis.
7. Describe the gross anatomy of the AMAB reproductive tract, spermatic cord, scrotum, and penis.
Scrotum
The scrotum is a cutaneous expansion suspended from the perineum and inferior portion of the proximal body of the penis. The scrotum contains the testes, which are suspended by the spermatic cords. The layers of the scrotum and spermatic cord are homologous and contiguous with many of the layers of the anterior abdominal wall.
Testes
The testes are gonads that produce spermatozoa and specific hormones. Each testis is enveloped by the tunica vaginalis, a serous membrane derived from peritoneum, and tunica albuginea, a dense white fascial layer which surrounds and compartmentalizes segments of the seminiferous tubules.
Spermatozoa travel from the coiled seminiferous tubules through straight tubules into the rete testis. From the rete testis, spermatozoa move into the epididymis before traveling to the ductus (vas) deferens. The epididymis is composed of a head and body (which receive spermatozoa from the rete testis) and tail.
To review the pathway of spermatozoa:
Seminiferous tubules → Rete testis → Epididymis head → Epididymis body → Epididymis tail → Ductus deferens
Spermatic cord
The spermatic cord consists of 3 layers of tissues that envelop contents. These layers include (with associated homologs):
External spermatic fascia ( = external oblique m. fascia),
Cremaster m.. & fascia ( = internal oblique m. & fascia),
Internal spermatic fascia ( = transversalis fascia)
The major contents of the sheath are the:
Ductus (vas) deferens,
Testicular a.
Pampiniform plexus (of veins)
A dilation or enlargement of the pampiniform plexus (of veins) is known as a varicocele. This is more frequent on the left side due to draining into the L. renal v. versus directly into the IVC on right side).
Other contents include: artery of ductus deferens, cremasteric a., genital br. of genitofemoral n., autonomic fibers (sympathetics follow the arteries; parasympathetics follow ductus deferens), and lymphatics.
Ductus (vas) deferens
The ductus (vas) deferens conducts spermatozoa from the testis, through the spermatic cord (and through the inguinal canal) to the deep ring, and travels posteriorly to the bladder, superior to the ureter, ultimately joining the seminal vesicle to form the ejaculatory duct. The distalmost and dilated portion of the ductus deferens is referred to as the ampulla of ductus deferens.
The ligation or embolization of the ductus (vas) deferens is known as a vasectomy.
Seminal Glands (Vesicles)
The seminal glands (vesicles) are located near the prostate between the posterior bladder and anterior rectum. The seminal glands produce a fluid that is more alkaline and contains fructose, and will be a significant portion of semen. The ducts of the seminal gland will join with the ampulla of ductus deferens to form the ejaculatory duct. The ejaculatory ducts will run through the posterior prostate to reach the prostatic urethra.
Prostate Gland
The prostate gland sits inferior and in close approximation with the neck of the urinary bladder. It surrounds and conducts the prostatic urethra to the membranous urethra. The prostate gland receives the ejaculatory ducts.
With benign prostatic hyperplasia (BPH), glandular cells of the transitional (peri-urethral) zone may multiply, and exert pressure upon the prostatic urethra, which can make voiding the bladder difficult. A common treatment for BPH is transurethral resection of the prostate (TURP), a procedure involving the passing of a resectoscope through the urethra, and removing portions of the prostate gland in order to maintain patency of flow.
The prostate may be palpated through the anterior wall of the rectum.
Bulbo-urethral (Cowper’s) Glands
The bulbo-urethral (Cowper’s) glands are pea-shaped glands located posterolateral to the membranous portion of the urethra. The ducts for these glands will pass through the perineal membrane, and open into the spongy urethra located in the bulb of the penis.
Penis
The penis consists of a root (that anchors the penis to the perineum) and body (that serves the intromittent organ). The root of the penis consists of three masses of erectile tissue within the superficial perineal space (the crura and bulb of the penis).
Three tubes of erectile tissue internally traverse the penis: laterally paired corpora cavernosa and a single corpus spongiosum.
In standard anatomical position (SAP), the penis is in an erect state. The side of the penis in SAP may contact the anterior abdomen is the dorsum (dorsal surface) of the penis. Opposite from the dorsal surface is the urethral surface.
The distal end (tip) of the body is the glans penis, a bulbous, skin-covered elaboration of corpus spongiosum.
The spongy (penile) urethra is transmitted by the corpus spongiosum and terminates at the external urethral meatus of the glans penis.
8. Diagram the arterial supply of the gonads.
8. Diagram the arterial supply of the gonads.
Most pelvic viscera receive arterial supply from branches of the internal iliac aa. The gonads are an important exception, deriving blood supply from the gonadal aa. (ovarian and testicular aa.). These arteries are branches of the abdominal aorta (at approximately L2), branching just distal to the renal aa.
The ovarian aa. travel within the suspensory ligaments of ovaries (infundibulopelvic; IP ligament) to reach the ovaries. While predominantly supplying the ovaries, the ovarian aa. also sends branches to supply the uterine tubes and anastomose with the uterine aa.
The testicular aa. will enter the deep inguinal ring to travel within the spermatic cord to reach and supply the testes.
It is important to be mindful of the long, retroperitoneal course of the gonadal aa. and the ureters from the abdominal cavity into the pelvic cavity in cases of arterial ligation.
9. Diagram the muscular contents of the pelvic diaphragm.
9. Diagram the muscular contents of the pelvic diaphragm.
The pelvic diaphragm/floor is composed of skeletal muscles and associated investing fasciae, and fills the inferior-most aspect of the pelvic cavity.
The perineum is inferior/superficial to the pelvic diaphragm. There is an opening in the midline called the urogenital hiatus through which the pelvic viscera passes.
The function of the pelvic diaphragm is fairly complex, but it works primarily to resist intra-abdominal pressure and to provide support and stabilize the pelvic viscera.
Conceptually, the pelvic diaphragm is a continuous sheet of muscle except for the urogenital hiatus; however, it is divided into different components: levator ani mm. & (ischio)coccygeus mm.The levator ani mm. is often subdivided into 3 major parts: puborectalis mm., pubococcygeus mm., & iliococcygeus mm.
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