Pelvis 2 - Pelvic Muscles, Vessels, and Nerves

Venous drainage of the pelvic organs is generally via tributaries of the ___________ ___________ vein that have the same names as the arteries. What do these tributaries form near the organs? What do they converge to form? (generally speaking as there are several exceptions)

Venous drainage of the pelvic organs is generally via tributaries of the internal iliac vein that have the same names as the arteries. These tributaries may form venous plexuses near the organs (e.g. vesical venous plexus, prostatic venous plexus) before converging to form single veins that drain into the internal iliac vein. For example, in this image you can see the prostatic plexus of veins merging to form the inferior vesical vein. There are several exceptions to this general concept of venous drainage in the next few slides.

What do the visceral afferents travel with? What do they mediate? What do pain afferents from pelvic viscera travel with? (unlike other areas of the body)

Visceral afferents travel with the splanchnics mentioned previously; they mediate sensations such as distension, cramps or pain. Unlike other areas of the body, pain afferents from pelvic viscera travel with both sympathetics and parasympathetics.

What type of fibers innervate the skin of the perineum and the striated muscles of the pelvis? Through what branches? r

When thinking about innervation, it is useful to divide the "targets" in the pelvis into somatic and visceral categories. The skin of the perineum and the striated muscles of the pelvis receive somatic fibers through branches of the lumbar and sacral plexuses. Somatic components of spinal nerves mediate skin sensation and proprioception (position sense) for the body wall and limbs, as well as motor innervation to skeletal (striated or "voluntary") muscle. Your intuition will tell you, however, that there must also be nerves which are capable of relaying sensory information (particularly pain or stretch) from the internal organs or VISCERA, and of conveying motor outflow to glands, smooth muscle in viscera and blood vessels, or to the (cardiac) muscle of the heart. These are the visceral components of spinal nerves.

A few lymphatics from deep structures of the perineum travel with the _________ _______________ veins to the ______________ ________ nodes.

A few lymphatics from deep structures of the perineum travel with the internal pudendal veins to the internal iliac nodes. Once again there are a few exceptions to the general route of drainage on the next few slides.

After branching from the common iliac artery, where does the internal iliac course? What does it divide into?

After branching from the common iliac artery, the internal iliac courses inferiorly into the pelvic cavity where it divides into posterior and anterior divisions. The posterior division has been colored red on the left side of the image.

What is the iliolumbar artery? Where does it course? What does it supply?

Branch of the posterior division. The iliolumbar artery courses superiorly and laterally to supply muscles of the posterior abdominal wall.

What is the lateral sacral artery? Where does it course? What does it supply? Where does it send branches?

Branch of the posterior division. The lateral sacral artery courses inferiorly on the anterior surface of piriformis and the sacrum. It supplies the piriformis and sends branches through the anterior sacral foramina that supply the contents of the sacral canal.

What is the superior gluteal? Where does it exit the pelvic cavity and where does it enter? What does it supply?

Branch of the posterior division. The superior gluteal artery exits the pelvic cavity through the greater sciatic foramen in a position superior to piriformis. It enters the gluteal region and supplies muscles in that area.

What is the Coccygeus? Where does it originate? Where does it insert? What is it innervated by?

Coccygeus originates from the ischial spine and sacrospinous ligament, and inserts on the inferior part of the sacrum and the coccyx. It is innervated by a branch from the sacral plexus (n. to coccygeus).

What are the effects of the contraction of the pelvic diaphragm?

Contraction of the pelvic diaphragm causes it to rise, which provides support for the pelvic viscera. It also provides resistance to changes in intrapelvic pressure during contraction of abdominal muscles (e.g. during defecation), and aids with voluntary control of micturition.

Where do the fibers that leave through the lower part of lumbar splanchnics enter? Where do they synapse? Within what? How do they travel?

Fibers that leave through lower lumbar ganglia enter the hypogastric nerves or pelvic plexuses directly. These fibers synapse in sympathetic pelvic ganglia within the pelvic plexus (or its subsidiary plexuses) and follow vessels to their destination.

Where does the inferior gluteal artery exit the pelvic cavity? What is its source and what does it supply?

Finally, the inferior gluteal artery exits the pelvic cavity through the greater sciatic foramen (in a position inferior to piriformis), and enters the gluteal region. Source: Anterior divison of internal iliac artery Supplies: Gluteus maximus, piriformis and quadratus femoris muscles

What is the inferior vesical artery in females a branch of?

In females the inferior vesical artery is typically a branch of the middle rectal artery.

What is the uterine artery a branch of? How does it travel and where? What does it supply?

In the female there are several variations to the pattern just described. The uterine artery is typically the third branch of the anterior division of interior iliac artery (recall it was inferior vesical in males). The uterine artery courses medially within the transverse cervical ligament to the lateral side of the uterus (supplies the uterus and uterine tubes, and portions of the ovary and vagina).

What is the puborectalis?

In this view the inferior aspect of the pelvic diaphragm is shown, thus puborectalis is now visible. Note the openings in the midline that allow communication between the pelvic cavity and perineum.

In 20% of the population, what does the obturatory artery arise from and what does it reach? What is this known as (type)?

In ~20% of the population, the obturator artery arises from the external iliac or inferior epigastric arteries, and then descends over the pelvic brim to reach the obturator canal; this variation is called the accessory obturator artery. This image shows BOTH variations of the obturator artery. Typically you would only have one or the other.

What is the fibrous portion of the umbilical artery? What is it also known as?

It travels along the lateral wall of the true pelvis, gives off the artery of the ductus deferens (male only) and superior vesical arteries, and then becomes fibrous (not patent). The fibrous portion is the medial umbilical ligament that you have seen previously on the anterior abdominal wall.

What do lateral sacral veins communicate with in the epidural space? Through what? What conditions is this a possible route for the spread of? (name 2)

Lateral sacral veins communicate with the vertebral venous plexus (in the epidural space) through the sacral foramina. This is a possible route for the spread of infection from the pelvis to the vertebral canal. Clinical Note: Prostatic cancer often metastasizes to the sacrum or vertebral column via the route described above.

What is the Levator ani? What are its parts and what is their function? Where does it originate? Where does it insert and how? What is it innervated by?

Levator ani has three parts (pubococcygeus, iliococcygeus and puborectalis) that support the pelvic organs like a hammock. Its origin is the pubis, tendinous arch (a thickening of pelvic fascia on the internal surface of obturator internus) and the ischial spine. The muscle fibers insert by blending with fibers from the opposite side in the midline. It is innervated by a branch of the sacral plexus (n. to levator ani). Note that the puborectalis is not visible in this image as it is deep to the other two muscles.

What type of fibers are lumbar splanchnics? Where do they leave the sympathetic trunk? Where do the fibers that leave through the upper part enter? How do they travel? What do they reach?

Lumbar splanchnics are sympathetic preganglionic fibers that leave the sympathetic trunk through lumbar chain ganglia. Fibers that leave through the upper lumbar ganglia enter the aortic plexus and travel inferiorly through the superior hypogastric plexus/nerves to reach the pelvic plexuses.

Where do lymphatics of the pelvic organs initially drain? What do most perineal structures send their lymphatics along?

Lymphatics of the pelvic organs generally drain initially to the external iliac, internal iliac, and sacral lymph nodes. Most perineal structures send their lymphatics along branches of the external pudendal veins to the superficial and deep inguinal nodes.

Lymphatics of the superior part of the rectum travel with the ________ ________________ vein, and therefore drain to the __________ ________________ nodes on the _____________ __________.

Lymphatics of the superior part of the rectum travel with the inferior mesenteric vein, and therefore drain to the inferior mesenteric nodes on the abdominal aorta.

Lymphatics of the testis/ovary travel with the _____________ veins, and therefore drain directly to the __________ ________ (________) nodes in the posterior abdominal region.

Lymphatics of the testis/ovary travel with the gonadal veins, and therefore drain directly to the lateral aortic (lumbar) nodes in the posterior abdominal region.

What are the major effects of parasympathetic innervation in the female (3)?

Major effects of parasympathetic innervation in the female: cause contraction of the detrusor muscle and relaxation of the internal urethral sphincter during micturition; cause peristalsis in the rectum and relaxation of the internal anal sphincter during defecation; cause erection of the clitoris by dilating the vessels that supply these tissues (branches of internal pudendal artery), thus allowing the erectile tissue to fill with blood

What are the major effects of parasympathetic innervation in the male?

Major effects of parasympathetic innervation in the male: cause contraction of the detrusor muscle and relaxation of the internal urethral sphincter during micturition; cause peristalsis in the rectum and relaxation of the internal anal sphincter during defecation; cause erection of the penis by dilating the vessels that supply these tissues (branches of internal pudendal artery), thus allowing the erectile tissue to fill with blood

What are the major effects of sympathetic innervation in the female (3)?

Major effects of sympathetic innervation in the female: mediate vessel diameter; cause contraction of the internal urethral sphincter; cause contraction of the internal anal sphincter

What are the major effects of sympathetic innervation in the male?

Major effects of sympathetic innervation in the male: mediate vessel diameter; cause contraction of smooth muscle in the ductus (vas) deferens, seminal vesicles, ejaculatory ducts and prostate for emission of semen into the prostatic urethra; cause contraction of the internal urethral sphincter during ejaculation to prevent retrograde movement of sperm into the bladder; cause contraction of the internal anal sphincter

What is the pudendal nerve? What type of fibers does it carry?

Many of the branches of the sacral plexus are destined for the lower limb; five supply the pelvis or perineum: The pudendal nerve (S2-S4) is the major nerve of the perineum (sensory and motor).

what supplies most of the blood to the pelvis and perineum? What supplies the lower extremity?

Most of the blood supply to the pelvis and perineum is from the internal iliac artery. The external iliac artery supplies the lower extremity.

What is the obturator internus? Where is it found? Where does it originate? Where does it exit? Where does it insert as it exits the pelvic cavity?

Obturator internus is a fan-shaped muscle found on the lateral wall of the pelvic cavity. It originates from the obturator membrane and the bone surrounding it. The muscle fibers converge towards the ischial spine, and obturator internus exits the pelvic cavity through the lesser sciatic foramen. At this point the muscle fibers turn ~ 90° to insert on the greater trochanter of the femur.

Parasympathetics to the pelvic organs come from the __________ __________________.

Parasympathetics to the pelvic organs come from the pelvic splanchnics.

What type of fibers are pelvic splanchnics? What regions of the spinal cord do they arise from? How do they exit the spinal cord? What do they enter? What do they innervate?

Parasympathetics to the pelvic organs come from the pelvic splanchnics. Pelvic splanchnics are preganglionic parasympathetic fibers that arise from the S2-S4 regions of the spinal cord. They exit the spinal cord through the S2-S4 ventral roots, travel in the spinal nerves and ventral rami, and then leave the ventral rami (not by any particular branch) to enter the pelvic plexus. These nerves are the only parasympathetic supply to the pelvic organs. Recall from the abdomen unit that they also innervate the hindgut organs.

What causes stress urinary incontinence? What is it? What can patients be advised to do to reduce it?

Patients who suffer from stress urinary incontinence experience leakage of urine during events that increase intra-abdominal pressure (e.g. coughing, laughing, etc.). One cause of this problem is weak pelvic floor muscles that don't effectively close the urethra. Patients are advised to strengthen these muscles with exercises (e.g. Kegel exercises).

What innervate pelvic viscera? What type of fibers do they convey?

Pelvic viscera are innervated via autonomic plexuses which convey sympathetic, parasympathetic and visceral afferent fibers.

What type of nerves innervate pelvic viscera (autonomic or somatic)? What do these nerves form plexuses associated with?

Pelvic viscera receive innervation from autonomic nerves. As we have seen previously, the autonomic nerves form plexuses typically associated with vessels in the region.

What is the piriformis? Where is it found? Where does it originate? Where does it exit? Where does it insert as it exits the pelvic cavity?

Piriformis is found on the posterolateral wall. It originates from the anterior aspect of the sacrum and exits the pelvic cavity through the greater sciatic foramen; it inserts on the greater trochanter of femur.

What is the anorectal angle? What maintains it? Why is this important?

Puborectalis has the additional function of maintaining the anorectal angle, which is important for fecal continence. This is the "mid-axial longitudinal axis of the rectum and the anal canal", created by the anterior pull of the puborectalis sling at the level of the anorectal junction. At rest, it is held at 90 - 100°.

What type of fibers are sacral splanchnics? How do they enter the pelvic plexus? How do they synapse?

Sacral splanchnics are sympathetic preganglionic fibers that leave the sympathetic trunk through the sacral chain ganglia. They enter the pelvic plexus directly, and synapse in the same manner as the lumbar splanchnics. These fibers synapse in sympathetic pelvic ganglia within the pelvic plexus (or its subsidiary plexuses) and follow vessels to their destination.

Where do sympathetics to the pelvic organs arise (what levels of sympathetic chain)? What are they called?

Sympathetics to the pelvic organs arise from both lumbar and sacral levels of the sympathetic chain, and are logically called lumbar and sacral splanchnics.

Where are the arteries to the pelvic viscera found? What level does the aorta bifurcate into the common iliac arteries? What do these bifurcate into?

The arteries to the pelvic viscera are found deep to the peritoneum within the endopelvic fascia. Recall that the aorta bifurcates at the L4 vertebral level into the common iliac arteries. The common iliac arteries then bifurcate into internal and external branches.

What is the umbilical artery a branch of? Which branch is it? Where does it travel and what does it give off?

The branches of the anterior division are highly variable. The umbilical artery is usually the first branch. It travels along the lateral wall of the true pelvis, gives off the artery of the ductus deferens (male only) and superior vesical arteries, and then becomes fibrous (not patent).

What is the internal pudendal artery? How does it travel? Where does it leave the pelvic cavity? What is its convoluted course? What does it supply?

The internal pudendal artery courses inferiorly on the anterior surface of piriformis. It leaves the pelvic cavity through the greater sciatic foramen (inferior to piriformis), winds around the ischial spine, passes through the lesser sciatic foramen and enters the pudendal canal (this convoluted course allows it to exit the true pelvic cavity and enter the perineum). The internal pudendal is the major blood supply to the structures in the perineum. Source: anterior division of internal iliac artery Supplies: external genitalia, perineum

What is the lumbar plexus formed from? Which two branches provide innervation to the pelvis? What do they innervate? What type of fibers do they convey?

The lumbar plexus was discussed in the abdomen unit (plexus formed from L1-L4 ventral rami). Two of its branches provide innervation to the pelvis: the ilioinguinal nerve and genital branch of the genitofemoral nerve provide cutaneous innervation to the anterior part of the labia or scrotum (anterior scrotal and labial nerves). In human anatomy, cutaneous nerves are responsible for providing sensory innervation to the skin. They are generally thought of as sensory-only nerves, but they may provide motor innervation to structures in the skin, e.g. sweat glands.

Where does the middle rectal artery enter the rectum? What does it supply?

The middle rectal artery enters the rectum just superior to the pelvic floor, and supplies its muscular wall. The internal pudendal is the major blood supply to the structures in the perineum. Source: anterior internal iliac Supplies: Rectum, seminal vesicle, vagina

What is the inferior vesical artery? Is it found in males or females? what does it supply? Where is it located?

The next artery in the male is the inferior vesical artery (supplies the inferior aspect of the urinary bladder, prostate and seminal vesicles). The dotted lines indicate the position of the bladder and prostate. Source: Anterior Internal iliac artery Supplies: Prostate, seminal vesicle, urinary bladder, vas deferens

How does the obturatory artery travel and exit the pelvic cavity? What does it supply in the pelvis?

The obturator artery courses anteriorly along the lateral pelvic wall, and then exits the pelvic cavity through the obturator foramen (it does not supply anything in the pelvis). Source: anterior internal iliac Supplies: Obturator externus muscle, medial compartment of thigh, femur

What muscles comprise the pelvic diaphragm?

The pelvic diaphragm is comprised of two striated muscles, coccygeus and levator ani. Coccygeus

What is the pelvic diaphragm/floor? What does it separate? What does it cover? What is it covered by?

The pelvic floor or diaphragm is a funnel-shaped structure that separates the true pelvic cavity from the perineum. It partially covers the obturator internus muscle (see small inset with the pelvic floor removed). In the larger image the obturator internus muscle is shown covered by parietal pelvic fascia (obturator fascia).

The pelvic plexuses are located ____________ to the rectum and are associated with branches of the ________ ____________ artery (the vessels are not shown in this diagram).

The pelvic plexuses are located lateral to the rectum and are associated with branches of the internal iliac artery (the vessels are not shown in this diagram). The pelvic plexuses give off 'subsidiary plexuses' that accompany vessels of the same name to the viscera (e.g. vesical plexus, prostatic plexus, uterovaginal plexus, etc.).

What do the pelvic plexuses give off? What structures do they accompany?

The pelvic plexuses give off 'subsidiary plexuses' that accompany vessels of the same name to the viscera (e.g. vesical plexus, prostatic plexus, uterovaginal plexus, etc.).

What are the 3 branches of the posterior division? (name them)

The posterior division has three branches (mnemonic is "PILS", P=posterior). I: Iliolumbar artery L: Lateral sacral artery S: superior gluteal artery

The prevertebral (aortic) plexus from the abdomen travels ________ to the aortic bifurcation as the ____________ ___________________ plexus. What does this plexus bifurcate into? Where do these extend and what do they form?

The prevertebral (aortic) plexus from the abdomen travels anterior to the aortic bifurcation as the superior hypogastric plexus. This plexus bifurcates into two hypogastric 'nerves' (they are really plexuses) which extend inferiorly into the pelvis to form the inferior hypogastric (pelvic) plexuses.

What is the sacral plexus formed by the confluence of? Where is this plexus located and how does it travel into the gluteal region? What does it travel through to get there?

The sacral plexus is formed by the confluence of the lumbosacral trunk (ventral rami of L4, L5) with the ventral rami of S1-S4. The plexus is located on the anterior surface of the piriformis muscle and courses inferolaterally into the gluteal region via the greater sciatic foramen.

The sacral plexus supplies the muscles of the wall and floor via branches that are named by the _______. Where does the posterior femoral cutaneous nerve exit the pelvis? What does it give off? What does it innervate?

The sacral plexus supplies the muscles of the wall and floor via branches that are named by the nerve (e.g. nerve to levator ani). The posterior femoral cutaneous nerve exits the pelvis inferior to piriformis and gives off a perineal branch (to lateral skin of perineum); its main role is to provide cutaneous innervation to the posterior thigh (it is not shown in the diagram).

Where are the striated muscles of the pelvic cavity found? What are the two muscles that are found in each location and what is their general location?

The striated muscles of the pelvic cavity are found in two locations: the walls of the cavity and the floor of the cavity. Two muscles are found on the walls of the cavity (obturator internus and piriformis) and these muscles do not affect pelvic function (they move the lower extremity). Two muscles form the muscular "floor" of the pelvic cavity (aka. pelvic diaphragm) that supports the pelvic organs. These muscles are the levator ani and coccygeus.

What does the superior vesical artery emerge from? What does it supply?

The superior vesical artery supplies the superior surface of the bladder. Source: umbilical artery, or anterior trunk of internal iliac artery Supplies: Urinary bladder, ureter

The sympathetic trunks extend into the pelvis on the ______________ surface of the __________; they unite at the ___________.

The sympathetic trunks extend into the pelvis on the anterior surface of the sacrum; they unite at the coccyx.

Why is the umbilical vein an exception of the typical arrangement of venous drainage of pelvic organs.

The umbilical vein is one "exception" of the typical arrangement because it is not traveling with its corresponding arteries.

What does the vaginal artery branch from? What does it supply? What is the relationship between the uterine artery and ureter? How does this impact risk during a hysterectomy?

The vaginal artery in females may branch from the uterine artery or independently from the anterior division; it supplies the vagina, inferior surface of the bladder, and rectum. Note once again the close relationship of the uterine artery and the ureter. This relationship is clinically important as the ureter is at risk during a hysterectomy.

What is the superior rectal vein a tributary of? What are the middle and inferior rectal veins tributaries of? Why can portal hypertension cause a reversal of normal drainage? What could this result in?

The veins of the rectum are unique because the superior rectal vein is a tributary of the portal vein, while the middle and inferior rectal veins are tributaries of the internal iliac vein. Anastomoses exist between these veins, and portal hypertension may cause a reversal of the normal drainage; blood from the superior rectal vein may pass into the middle and inferior rectal veins causing them to dilate (hemorrhoids).

Where do the urethra and anus pass from the pelvic cavity into the perineum in the male?

This image is from the male. The openings in the pelvic diagram that you observed in the previous slide allow the anus and urethra to pass from the true pelvic cavity into the perineum.

Where do the urethra, anus, and vagina pass from the pelvic cavity into the perineum in the female?

This image shows the organs in the female. Once again, openings in the pelvic diagram allow the anus, vagina and urethra to pass from the true pelvic cavity into the perineum

Image: sagittal view of the right common iliac artery and its branches

This is a sagittal view of the right common iliac artery and its branches. This view will be used to examine the branches of the internal iliac artery in the subsequent slides. Note: Be aware that there is a lot of variation in the branching pattern of the internal iliac artery. If you don't see the typical pattern, you should name an artery by its destination (target) not its origin.

Where do the piriformis and obturator internus leave the pelvic cavity? Where do they insert as they exit? How do they affect the thigh? What are they innervated by?

This posterior view shows how the piriformis and obturator internus leave the pelvic cavity through the greater and lesser sciatic foramina, respectively, and insert on the greater trochanter of the femur. Both of the above muscles laterally rotate the thigh (will discuss more in the lower limb unit). They are innervated by branches of the sacral plexus (n. to obturator internus, n. to piriformis - see section on innervation).