Anatomy of Human Development 1

Question 1

What are the 3 main bones of the pelvis? Which bone are they joined to and via which joints?

Answer 1

The 3 main bones are the ilium, ischium and pubis, which are joined centrally to the sacrum via the sacroiliac joints.

Question 2

Why is plain radiograph/x-ray a good diagnostic tool for examining bony structures of the pelvis?

Answer 2

Many of these key bony features are also visible on plain radiographs (x-rays) of the the pelvis, making this a good diagnostic tool for examining the bony structures.

Question 3

What is the function of the pelvic inlet and what are its borders?

Answer 3

The pelvic inlet (also known as the pelvic brim) divides the abdominal cavity from the pelvic cavity.

The borders of the pelvic inlet include:

1. Sacral promontory and ala (posterior border)
2. Lines terminals (a combination of the arcuate line on inner surface of ilium and pectineal line on superior pubic ramus) (lateral border)
3. Pubic symphysis (anterior border)

Question 4

What is the pelvic outlet and what muscles are found within this region? What are the borders of the pelvic outlet?

Answer 4

The pelvis also has a region known as the pelvic outlet. The pelvic floor muscles are found within this region.

The borders of the pelvic outlet include:

1. Tip of the coccyx (posterior border)
2. Ischial tuberosities (lateral border)
3. Inferior border of the sacrotuberous ligament (posterolateral border)
4. Pubic arch (anterior border)

Question 5

What spinal level does the iliac crest lie at?

Answer 5

Typically lies at the level of L4.

Question 6

Where is the sacroiliac joint (SIJ) located?

Answer 6

Sacroiliac joint - between the sacrum and ilium.

Question 7

What and where is the pubic tubercle?

Answer 7

Attachment point for the inguinal ligament, it lies just lateral to the pubic crest.

Question 8

What is the obturator foramen and what passes through it?

Answer 8

An opening in between the superior and inferior pubic rami through which the obturator neurovasculature passes.

Question 9

How do you label the bone structures of the pelvis?

Answer 9

See a diagram to see the structures

Question 10

What are the functions of ligaments within the pelvis?

Answer 10

Ligaments within the pelvis are provide stability within the region and also contribute to outlets (foramen) through which key anatomical structures pass.

Question 11

Which ligament runs from the sacrum to the ischial tuberosity?

Answer 11

The sacrotuberous ligament runs from the sacrum to the ischial tuberosity.

Question 12

Which ligament runs from the sacrum to the ischial spine?

Answer 12

The sacrospinous ligament runs from the sacrum to the ischial spine.

Question 13

Which structures pass through the greater sciatic foramen?

Answer 13

Inferior gluteal nerve
Internal pudendal vessels
Piriformis
Pudendal nerve
Sciatic nerve
Superior gluteal nerve

Question 14

Which structures pass through the lesser sciatic foramen?

Answer 14

Internal pudendal vessels
Pudendal nerve
Tendon obturator internus

Question 15

Which artery does the blood supply in the pelvis predominantly come from? What is this a branch of?

Answer 15

The blood supply within the pelvis is predominantly from the internal iliac artery - this is a branch of the common iliac artery.

Four of these branches exit the pelvis, the rest supply organs and structures within the pelvis.

Question 16

Which organ does the superior vesicular artery supply?

Answer 16

Bladder

Question 17

Which organ does the inferior vesicular artery supply?

Answer 17

Prostate gland (male)

Question 18

Which organ does the uterine artery supply?

Answer 18

Uterus (female)

Question 19

Which organ does the middle rectal artery supply?

Answer 19

Rectum

Question 20

Where does the nerve supply in the pelvis predominantly come from? What does this set of nerves give rise to?

Answer 20

The nerve supply within the pelvis is predominantly from the sacral plexus. This set of nerves also gives rise to the sciatic nerve which supplies a large portion of the lower limb.

Return to the 3D model above and identify:
Superior and inferior gluteal nerves
Pudendal nerve
Obturator nerve
Sciatic nerve

Question 21

Which spinal levels innervate the skeletal muscles contained in the perineum and pelvic floor? Where does the somatic motor and sensory innervation of the perineum come from? Where does this nerve leave the pelvic cavity and where does it enter the perineum?

Answer 21

Most of the skeletal muscles contained in the perineum and pelvic floor, including the external anal sphincter and external urethral sphincter, are innervated by spinal cord levels S2-S4. Much of the somatic motor and sensory innervation of the perineum is provided by the pudendal nerve from spinal cord levels S2-S4. The pudendal nerve leaves the pelvic cavity through the greater sciatic foramen and then immediately enters the perineum inferiorly to the pelvic floor by passing around the ischial spine and through the lesser sciatic foramen.

Question 22

What special kind of nerve supply do the organs in the pelvis receive? Which nerves supply it with parasympathetic innervation and which spinal level do these come from?

Answer 22

The organs in the pelvis recieve autonomic nerve supply.

The parasympathetic supply in the pelvis is from preganglionic fibres which originate from S2,3 & 4 (pelvic splanchnic nerves).

Question 23

Where is the superior hypogastric plexus, what is it a continuation of and what does it contain? What does it divide to form?

Answer 23

The superior hypogastric plexus is anterior to the sacral promontory. It is a continuation of the aortic plexus and L3 and L4 sympathetic ganglia. It contains sympathetic, sacral parasympathetic (ascending) and visceral afferent fibres. The hypogastric plexus divides inferiorly to form the right and left hypogastric nerves.

Question 24

Where are the inferior hypogastric plexuses? What are they formed from?

Answer 24

The inferior hypogastric plexuses lie on either side of the rectum. Each plexus is formed by a hypogastric nerve (from the superior plexus) and from the pelvic splanchnic nerves.

Question 25

Where are all of the blood vessels supplying the pelvis located?

Answer 25

See a diagram

Question 26

Gluteus medius and minimus receive oxygenated blood from which vessel?

Answer 26

Gluteus medius and minimus receive oxygenated blood from the superior gluteal artery.

Question 27

What is the nerve supply to gluteus maximus?

Answer 27

Gluteus maximus is innervated by the inferior gluteal nerve.

Question 28

The rectum receives blood supply from three separate arteries. Where does each of these arteries originate?

Answer 28

Superior rectal artery - inferior mesenteric artery

Middle rectal artery - internal iliac artery

Inferior rectal artery - internal pudendal artery

Question 29

What bony landmark can be used to locate the pudendal nerve?

Answer 29

The ischial spine can be palpated to locate the pudendal nerve.

Question 30

Where does the ovarian/testicular arterial supply originate from?

Answer 30

The ovarian/testicular arteries originate from the abdominal aorta at the T12 vertebral level.

Question 31

What is the function of the pelvis floor muscles? What other muscles are in the pelvic region?

Answer 31

The pelvic floor plays an important role in continence. The diagram on the left details the pelvic floor muscles (levator ani and coccygeus) from an inferior view as well as a coronal section to show the orientation of the muscles.

It is also worth noting a couple of other muscles within this region: iliacus which sits deep to the ilium and merges with the psoas muscle to form iliopsoas - the main hip flexor; and also obturator internus.

Question 32

Which part of Levator ani plays a role in continence?

Answer 32

Puborectalis

Question 33

What is one of the main mechanisms to achieve continence (aside from internal and external sphincters)?

Answer 33

One of the main mechanisms to help to achieve continence, aside from the internal and external sphincters, is the puborectal sling. Contraction of puborectalis creates a more acute angle, meaning passage of stool cannot occur. As puborectalis relaxes, this increases the angle, making defecation possible.

Question 34

Which muscles make up the levator ani group?

Answer 34

The levator ani group is made up of three muscles:

1. Iliococcygeus
2. Pubococcygeus
3. Puborectalis

Coccygeus contribues to make the pelvic floor but is not part of the levator ani group.

Question 35

What organs are included in the pelvic viscera from anterior to posterior?

Answer 35

Here we can see a sagittal view of the pelvic viscera. From anterior to posterior, the organs include the bladder, the uterus and the rectum.

Question 36

The posterior wall of the vagina is longer than the anterior wall. True or false?

Answer 36

True, refer back to the diagram and see the vagina slopes posteriorly, terminating at the level of the anteriorly angled cervix. This means the posterior wall is longer than the anterior wall.

Question 37

Sort the organs from anterior to posterior: rectum, bladder, vagina?

Answer 37

Anterior = bladder
Middle = vagina
Posterior = rectum

Question 38

The urethra and vagina both open into the vestibule of the vagina - true or false?

Answer 38

True. The vestibule of the vagina is enclosed by the labia minora. Within this region are the external orifices of both the urethra and vagina.

Question 39

In which part of the Fallopian tube does fertilisation most commonly occur?

Answer 39

Fertilisation most commonly occurs in the ampulla.

Question 40

What are the pelvic viscera covered by? What is the name for the peritoneum that folds over the uterus? What ligaments support the pelvic viscera? What lies between the pelvic viscera? What is the clinical significance of these?

Answer 40

The pelvic viscera are covered by the peritoneum, which drapes over the top of them. The peritoneum which folds over the uterus is termed the broad ligament.

They are also supported by a variety of ligaments within the pelvis - such as the round ligament which can both be visualised on this image on the left (below); as well as the ovarian ligament which connects the ovary to the uterus. The suspensory ligament provides support also, and this carries the ovarian vasculature within it.

Between the pelvic viscera lie pouches - the vesicouterine pouch and the rectouterine pouch (see the image below). These have clinical significance as this may be the first location fluid accumulates within the abdomen/pelvis if there is pathology.

Question 41

What is the blood supply of the uterus? What about the vagina and the ovaries? How does this change during pregnancy?

Answer 41

The uterus receives its blood supply from the anterior trunk of the internal iliac artery, the uterine artery. The uterine artery also provides blood supply to the vagina, via the vaginal artery. The ovarian artery (gonadal artery) originates from the abdominal aorta and provides blood supply to the ovaries and anastamose with terminal branches of the uterine artery. On each side, they travel in the suspensory ligament of the ovary as they cross the pelvic inlet. During pregnancy the ovarian artery enlarges significantly to augment uterine blood supply.

Question 42

Which artery is providing blood supply to the Fallopian tube?

Answer 42

Both the ovarian and uterine arteries provide blood supply to the Fallopian tube.

Question 43

Where does the bladder lie in relation to the reproductive organs? What are its features?

Answer 43

The bladder lies anterior to the reproductive organs. This image depicts a coronal section through the bladder, and shows the region known as the trigone, a smooth walled area between the opening of the ureters and internal urethral orifice.

Question 44

Which spinal cord levels innervated most of the skeletal muscles in the perineum and pelvic floor? Where does the motor and sensory innervation of the perineum come from? Where does the pudenal nerve leave the pelvic cavity and where does it enter the perineum?

Answer 44

Most of the skeletal muscles contained in the perineum and pelvic floor, including the external anal sphincter and external urethral sphincter, are innervated by spinal cord levels S2-S4. Much of the somatic motor and sensory innervation of the perineum is provided by the pudendal nerve from spinal cord levels S2-S4. The pudendal nerve leaves the pelvic cavity through the greater sciatic foramen and then immediately enters the perineum inferiorly to the pelvic floor by passing around the ischial spine and through the lesser sciatic foramen.

Question 45

How is the normal position of the uterus described?

Answer 45

The normal position of the uterus is described as anteverted and anteflexed.

Question 46

Where does implantation occur in a normal pregnancy?

Answer 46

Usually implantation occurs in the uterus. If implantation occurs in any other location (such as the Fallopian tube, ovary or cervix) this is refer to as an ectopic pregnancy.

Question 47

Why is an ectopic pregnancy dangerous?

Answer 47

The main risk of ectopic pregnancies are that ectopic sites (usually the Fallopian tube) cannot expand to the same extent as the uterus, and the site ruptures, resulting in extensive haemorrhage.

Question 48

Cho’s ectopic pregnancy is implanted in the Fallopian tube. If this site ruptures, what arteries will be the source of the haemorrhage?

Answer 48

Uterine artery and ovarian artery
The Fallopian tube receives anastomotic blood supply from the ovarian and uterine arteries. Therefore the bleeding from a ruptured ectopic is substantial.

Question 49

What is the structure of the male bladder similar to? Where do the ureters enter the male bladder? What is the muscular component of the bladder wall, and what type of control is it under?

Answer 49

The male bladder is structurally very similar to the female bladder, although it is slightly larger. The ureters enter obliquely on the posterior surface, and filling is permitted while the bladder wall is relaxed and the urethral sphincters are closed.

The bladder wall has a muscular component, known as the detrusor muscle, which is under autonomic control.

Question 50

Sympathetic stimulation on the bladder results in what?

Answer 50

Relaxation

Question 51

How is the male urethra different to the female? What and where are its regions? What sphincters are present in the male bladder? What is the additional function of the male sphincters?

Answer 51

The male urethra is much longer than the female (about 20cm, compared to 4cm), and for this reason is commonly divided into different regions. The first of these, the preprostatic urethra, is the shortest and extends from the bladder neck to the prostate. Surrounding the urethra at this level is the internal urethral sphincter. The prostatic urethra is the region which passes through the prostate, and the ejaculatory and prostatic ducts drain into it at this level. The membranous urethra passes through the deep perineal pouch, and is encircled by the external urethral sphincter. Finally, the spongy urethra is the longest part, travelling through the corpus spongiosum of the penis and terminating at the external urethral meatus.

Note that there are two anatomical urethral sphincters in the male, as opposed to one in the female. The internal sphincter has the additional function of contracting during ejaculation to prevent retrograde ejaculation into the bladder.

Question 52

Put the parts of the urethra into order, proximal to distal.

Answer 52

1st - preprostatic
2nd - prostatic
3rd - membranous
4th - spongy

Question 53

What is the prostate and what is its function? Where is it located? How can it be divided?

Answer 53

The prostate is a walnut-sized gland located at the base of the bladder in males. Its secretions account for about 20% of the volume of ejaculate.

It sits between the internal and external urethral sphincters, and the urethra passes through, the ejaculatory and prostatic ducts opening into it.

The prostate can be divided into different zones, including central, peripheral, transitional (periurethral) and fibromuscular zones. The peripheral zone contains much of the glandular tissue of the prostate, and is the most common site of prostate cancer. The transitional zone, however, is most involved in benign prostate hyperplasia.

Question 54

Based on its anatomical location, which signs would you expect to be associated with benign prostatic hyperplasia?

Answer 54

Due to its position around the urethra BPH usually presents as lower urinary tract symptoms such as:

poor stream despite straining

hesitancy, frequency and incomplete emptying of the bladder

nocturia

Question 55

What is the vas deferens and what does it do? Where does it travel up to and where does it open into? What does the ejaculatory duct do?

Answer 55

The vas deferens is a muscular tube which carries sperm from the testes to the ejaculatory duct. It travels in the spermatic cord up into the pelvis, where it crosses the lateral wall to arrive at the posterior aspect of the bladder. It opens into the ejaculatory duct, where sperm are mixed with fluid from the seminal vesicles. This highly alkaline fluid is high in sugar to support the sperm.

The ejaculatory duct opens into the prostatic urethra so that sperm can be ejaculated via the external urethral meatus.

Question 56

What should be noted about the vas deferens?

Answer 56

Note how it is continuous with the tail of the epididymis and follow its course up into the pelvis to drain into the ejaculatory duct

Question 57

What should be noted about the male bladder?

Answer 57

Note the shape of the bladder, with the apex pointing anteriorly. It is held on the anterior wall by the median umbilical ligament, which can just about be made out here.

Question 58

Where is a vasectomy most usually performed?

Answer 58

Near the testis
This is the most common place to perform vasectomy. The vas deferens is easily accessible via a small incision in the scrotum and spermatic cord.