Overview of the Pelvis Anatomy

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Questions and Answers

Which artery supplies the uterus?

Superior vesical artery

Superior rectal artery

Uterine artery (correct)

Inferior vesical artery

What is the anatomical position of the bladder relative to the rectus abdominus muscle?

Deep to the bladder

Anterior to the bladder

Posterior to the bladder (correct)

Superficial to the bladder

Which of the following arteries branches from the internal iliac artery?

Femoral artery

Inferior rectal artery (correct)

Inferior epigastric artery

Abdominal aorta

What is the position of the vaginal canal relative to the bladder?

Posterior to the bladder Signup and view all the answers

The abdominal aorta branches into the common iliac arteries at what level of the lumbar vertebrae?

L4 Signup and view all the answers

What distinguishes the true pelvis from the false pelvis?

The true pelvis contains the pelvic cavity, whereas the false pelvis is part of the abdominal cavity. Signup and view all the answers

Which muscles are primarily involved in forming the pelvic diaphragm?

Levator ani and coccygeus Signup and view all the answers

What structure serves as a bridge connecting the ischium and pubis?

Ischiopubic ramus Signup and view all the answers

Which part of the pelvis is primarily responsible for protecting pelvic organs such as the rectum and bladder?

Pelvic bowl Signup and view all the answers

Which bones fuse to form the ox coxae?

Ilium, pubis, and ischium Signup and view all the answers

What is the primary function of the bony pelvis in locomotion?

Providing a surface for lower limb articulation Signup and view all the answers

Which of the following correctly describes the sacrum?

It is made up of five fused vertebrae and distributes weight to the ilia. Signup and view all the answers

Which passageway is NOT associated with structures entering or leaving the pelvis?

Coccygeal canal Signup and view all the answers

Which muscle is primarily responsible for expelling urine from the bladder?

Detrusor Signup and view all the answers

What structure is located anteriorly in the female pelvis?

Urinary bladder Signup and view all the answers

What is the role of transitional epithelium in the urinary bladder?

To allow for extreme stretching Signup and view all the answers

Which structure is found passing through the greater sciatic foramen?

Pudendal nerve Signup and view all the answers

What separates the urinary bladder and the uterus in females?

Vesicouterine pouch Signup and view all the answers

What is the purpose of the external urethral sphincter in both genders?

To control urine flow Signup and view all the answers

Where does the urethra open in females?

Into the vestibule Signup and view all the answers

What anatomical feature is described as a smooth area known as trigone?

Region formed by ureter openings and urethra Signup and view all the answers

Which artery, vein, and nerve primarily pass through the obturator canal?

Obturator Signup and view all the answers

What is the relationship of the ureters to the uterine arteries and veins?

They run underneath Signup and view all the answers

Which nerve exits through the greater sciatic foramen, superior to the piriformis muscle?

Superior gluteal nerve Signup and view all the answers

What is the primary function of the pudendal nerve in the context of micturition?

Contract the external anal sphincter Signup and view all the answers

What type of muscle is the internal anal sphincter composed of?

Smooth muscle Signup and view all the answers

Which lymph nodes are primarily responsible for draining the external genitalia?

Superficial inguinal lymph nodes Signup and view all the answers

Which ligament is associated with the ovarian suspension in the female reproductive system?

Suspensory ligament Signup and view all the answers

How do parasympathetic nerves affect the detrusor muscle during micturition?

They contract the detrusor muscle Signup and view all the answers

Which of the following structures is likely to be affected by the contraction of the external urethral sphincter?

Internal urethral sphincter Signup and view all the answers

What characterizes cavernous erectile tissues compared to spongy erectile tissues?

Have a thicker connective tissue covering Signup and view all the answers

What is the anatomical orientation of the perineum relative to the pelvis?

Inferior Signup and view all the answers

What is the anatomical role of fascia in the perineum?

Forms a stable roof for external genitalia Signup and view all the answers

Which area receives the sympathetic nerves involved in pelvic organ innervation?

Superior aspect of pelvic inlet Signup and view all the answers

Which muscle is not directly involved in the maintenance of erection?

Transversus abdominis Signup and view all the answers

Which structure is NOT part of the male external genitalia?

Labia majora Signup and view all the answers

What causes a bulge in the anterior vaginal wall?

Prolapse due to damage of passive supports Signup and view all the answers

Which vessels supply the gonads and do not originate from the iliac vessels?

Gonadal arteries Signup and view all the answers

Why is it crucial to avoid damaging the ureter during a hysterectomy?

The ureter passes posterior to the uterine artery Signup and view all the answers

Which nerve and blood vessels travel through the obturator canal?

Obturator nerve, artery, and veins Signup and view all the answers

How does the obturator nerve become more susceptible to injury during childbirth?

It travels from the posterior to the anterior pelvis Signup and view all the answers

Which type of hysterectomy preserves the cervix?

Subtotal hysterectomy Signup and view all the answers

What is a potential complication of a hysterectomy related to nerve damage?

Urinary incontinence Signup and view all the answers

What is the significance of the plane of least dimensions during childbirth?

It is the site where labor frequently stalls or slows down Signup and view all the answers

What pelvic shape is most commonly found in women and is better suited for childbirth?

Gynaecoid Signup and view all the answers

Which levator ani muscle is specifically important in maintaining fecal continence?

Puborectalis Signup and view all the answers

What occurs to the sacroiliac joint during pregnancy?

It expands to facilitate childbirth Signup and view all the answers

What anatomical structure sits at the bottom of the pelvis and can cause dysfunction in childbirth?

Pubic symphysis Signup and view all the answers

Which pelvic shape is typically associated with a higher likelihood of C-section deliveries?

Platypelloid Signup and view all the answers

Study Notes

Overview of the Pelvis

The pelvis is the intersection of the abdomen and lower extremity, serving as a vital structure for locomotion, weight distribution, and organ protection.

Bony Pelvis Components

The bony pelvis is comprised of the two hip bones (ox coxae), the sacrum, and the coccyx.
Each hip bone is a fusion of the ilium, pubis, and ischium.
The ilium forms the superior portion of the hip bone with flaring wings (ala) and the iliac crest.
The pubis is located anteriorly and articulates with the opposite pubis.
The ischium is located posteriorly and provides support for sitting.
The greater and lesser sciatic notches allow for nerves, vessels, and muscles to leave the pelvis.
The obturator foramen is a hole beneath the acetabulum largely sealed by a fibrous membrane and muscles.

True vs False Pelvis

The bony pelvis can be divided into the false pelvis, which is the superior region above the pelvic brim, and the true pelvis, which is the inferior region below the pelvic brim.
The true pelvis houses the pelvic organs and is essential for childbirth.

Muscles of the Pelvis

The pelvic floor is composed of the pelvic diaphragm (levator ani and coccygeus), which supports the pelvic organs and aids in urinary and fecal continence.
The external anal sphincter lies deep to the perineal skin.

Passageways for Structures to Enter/Leave the Pelvis

These passageways include the:
- Inguinal canal: Contains the testicular vasculature and vas deferens in males, and the round ligament of the uterus in females.
- Femoral canal: Contains the femoral artery, vein, and nerve.
- Obturator canal: Contains the obturator artery, vein, and nerve.
- Greater sciatic foramen: Contains the gluteal artery, vein, and nerve, as well as the pudendal nerve and internal pudendal artery/vein.
- Urogenital hiatus: Forms the gap for the urinary and reproductive tract openings into the perineum.

Female Pelvic Viscera

The female pelvic viscera include:
- Urinary bladder and urethra: Anteriorly
- Uterus and adnexa: (ovaries, uterine tubes, ligaments)
- Rectum/anus: Most posteriorly

Positional Relationships of Pelvic Viscera

Important spaces between pelvic viscera include:
- Retropubic space: Between the pubis and bladder, filled with loose connective tissue.
- Vesicouterine pouch: Between the bladder and uterus.
- Rectouterine space: Between the uterus and rectum.

The Urinary Bladder

The urinary bladder is a highly textured organ with a complex smooth muscle arrangement called the detrusor muscle.
The bladder's lining, composed of transitional epithelium, allows for expansion and stretching during urine storage and excretion.
The ureters, traveling underneath the uterine arteries and veins, enter the posterior urinary bladder.

Coronal Section of the Urinary Bladder

The detrusor muscle forms the majority of the bladder wall.
The urethra opens inferiorly, connecting to the vestibule in the perineum.
The male internal urethral sphincter is more prominent than the female due to its potential role in sexual function.
The external urethral sphincter, present in both genders, allows for voluntary control of urination.
The trigone, a smooth area on the posterior side of the bladder, contains the two ureteral openings and the urethra.

Female Urethra

The female urethra is 4-6cm long and 6mm in diameter.
It lies anterior to the vagina.
Both the urethra and vagina open into the vestibule between the labia majora.

Paraurethral Glands (Skene's Gland)

These glands secrete mucus into the lesser vestibule, which is the area around the urethral opening.
They are homologous to the male prostate and may have antimicrobial function.

Nerves of the Pelvis

Superior gluteal nerve leaves the pelvis through the greater sciatic foramen, superior to piriformis muscle.
Inferior gluteal nerve exits the pelvis through the greater sciatic foramen inferior to piriformis muscle.
Internal pudendal nerve leaves through the lesser sciatic foramen, between the coccygeus and piriformis muscles
Obturator nerve leaves the pelvis through the obturator canal.

Autonomic Innervation of Pelvic Organs

Sympathetic nerves originate in the thoracolumbar region (T1 - L2/3).
Parasympathetic nerves originate in the craniosacral region (CN 3, 7, 9, 10, and S2-4).
Pelvic nerves originate in the lower lumbar and sacral area.
All of these nerves combine to form the hypogastric plexus which innervates the abdomen and pelvis.

Somatic Innervation of Micturition and Defecation

Pudendal nerve originates from S2-4 and innervates structures in the anal and urogenital triangles.
The pudendal nerve innervates the external urethral and external anal sphincters.

Micturition Reflex

The detrusor and internal urethral sphincter are smooth muscles.
Sympathetic stimulation relaxes the detrusor muscle and contracts the internal urethral sphincter, storing urine.
Parasympathetic stimulation contracts the detrusor and relaxes the internal urethral sphincter, stimulating urination.

Defecation Reflex

The rectum wall and internal anal sphincter are smooth muscles.
Sympathetic stimulation relaxes the rectum wall and contracts the internal anal sphincter, storing feces.
Parasympathetic stimulation contracts the rectum wall and relaxes the internal anal sphincter, stimulating defecation.

Lymphatics of Pelvis and Perineum

Pelvic lymph nodes drain structures within the pelvis.
Perineal lymph nodes drain structures within the perineum.
Important lymph nodes include:
- Internal iliac lymph nodes
- Inguinal lymph nodes
- Preaortic and lumbar nodes
- External iliac lymph nodes

Perineum and External Genitalia

The perineum is the space inferior to the pelvis, delineated from the pelvis by the levator ani muscle.
The perineum is diamond-shaped and divided into two triangles, the urogenital triangle and the anal triangle.
The perineal membrane is a thickened membrane inferior to the anterior extent of the levator ani.

Spaces and Fascia in the Perineum

The perineal membrane is a composite of many tissues.
Superficial perineal fascia (Colles' fascia) and Scarpa's fascia continue as the Dartos fascia in males and females.
The perineal body is a midline point where multiple fascial layers meet.
The superficial perineal pouch lies between Colles' fascia and the perineal membrane.
The deep perineal pouch lies superior to the perineal membrane, extending to the superior fascia layer.

Clinical Correlate: Extravasation of Urine

Extravasation of urine occurs when urine escapes into body cavities.
A perforation of spongy urethra allows urine to leak into the superficial perineal pouch.

External Genitalia: Female

Mons pubis: A rounded fatty eminence anterior to the pubic bone.
Labia majora Prominent folds protecting the labia minora and structures in the vestibule.
Labia minora: Fat-free folds of hairless skin containing erectile tissue.
Clitoris: An erectile organ with a visible glans and a hidden internal extent.
Vestibule: Space outlined by the labia minora, containing the external urethral and vaginal orifices.

Erectile Tissue: Female

Spongy Erectile Tissue: Less blood during erection, found near structures that need to remain open.
Cavernous Erectile Tissue: Holds more blood, found in areas where erection needs to be rigid.
Crus of clitoris: Cavernous tissue anchored to the ischiopubic rami, forming the body of the clitoris.
Bulb of vestibule: Spongy tissue found on both sides of the vaginal orifice.

Skeletal Muscles: Female

Ischiocavernosus muscle: Overlies the crus of the clitoris.
Bulbospongiosus muscle: Overlies the bulb of the vestibule.
Superficial and deep transverse perineal muscles: Support pelvic floor and maintain intra-abdominal pressure.

External Genitalia: Male

Body of penis: Visible part of the penis.
Glans penis: Distal expansion of the corpus spongiosum, contains the external urethral orifice.
Spermatic cord: Contains the vas deferens and testicular neurovasculature.
Scrotum: Fibromuscular sac that encloses the testes.
Epididymis: Arcs over the testes and stores sperm until it matures.

Testis: Male

Seminiferous tubules: produce sperm.
Rete testis: Where neurovasculature enters the testis.
Efferent tubules: Carry sperm to the epididymis.

Erectile Tissue: Male

Corpus cavernosum: Cavernous tissue, forms the body of the penis.
Bulb of the penis: Unique structure that merges with the corpus spongiosum, Unlike the female, there is only one bulb
Corpus spongiosum: Spongy tissue that surrounds the urethra.

Perineal Muscles: Male

Bulbospongiosus muscle: Overlies the bulb of the penis.
Ischiocavernosus muscle: Overlies the crus of the penis.

Blood Supply to the Perineum

Internal pudendal artery: Enters perineum through the lesser sciatic foramen and supplies the perineum.
Inferior rectal artery: Supplies the anus, external anal sphincter, and ischioanal fossa.
Perineal artery: Supplies muscles of the external genitalia and erectile tissues.
Dorsal genital artery: Supplies the dorsal clitoris or dorsal penis.

Innervation of the Perineum

Perineal nerve: Follows the same path as the internal pudendal artery and branches extensively throughout the perineum.
Pudendal nerve: Somatic nerve that innervates the external anal and urinary sphincters and assists in maintaining erections.

Autonomic Innervation of Erectile Tissue

Hypogastric plexus: Supplies the autonomic innervation of the erectile tissue of both genders.
Parasympathetic stimulation causes erection in both genders.
Sympathetic stimulation contributes to emission and ejaculation in males.

Female Reproductive Tract

Ovaries: Produce oocytes and hormones.
Uterine tube (fallopian tube): transports oocytes from the ovary to the uterus; site of fertilisation
Uterus: Muscular organ where a fertilized egg implants.
Endometrium: The inner lining of the uterus, undergoes cyclic changes in preparation for pregnancy

Erectile Tissues and Sexual Stimulation: Female

Parasympathetic stimulation relaxes smooth muscle in the crura, allowing blood to dilate the cavernous sinuses.
Somatic stimulation of the bulbospongiosus and ischiocavernosus muscles compresses veins, maintaining erection.
Greater vestibular glands: Secrete lubricating mucus during sexual arousal.

Cervix

Opens during puberty and is exposed to the acidic environment of the vagina.
Widens during reproduction to allow sperm to enter.

Ejaculation/Orgasm: Female

The role of female ejaculation and orgasm needs further investigation.

Learning Outcomes

Orient to the perineum, its subdivisions and fascia.
Compare erectile tissues of men and women.
Describe neurovasculature of perineum as it pertains to sexual reproduction.
Trace reproductive tract of males and females.
Describe the process of sexual differentiation from an early indifferent gonad stage.

Ultrasound of Pelvic Anatomy

Longitudinal ultrasound of the pelvis is not symmetrical, while transverse is
Rectus abdominus: Anterior to bladder
Bladder: Posterior to rectus abdominus, no echo
Vaginal canal: Posterior to bladder, collapsed potential space
Uterus: Long lumen, closer to the superior bladder aspect
Superior vesical artery: Branches from the umbilical artery
Inferior vesical artery: Branches from the anterior division of the internal iliac artery
Umbilical artery: Curves superiorly towards the obturator foramen

Pelvic Arteries

Inferior epigastric artery: Deep to the rectus muscle
Superficial epigastric artery: Superficial to the rectus muscle, in subcutaneous layers
Both arteries branch from the external iliac artery
Internal iliac artery: Branches into the anterior and posterior divisions
Anterior division (internal iliac): Supplies the inferior vesical, inferior gluteal and middle rectal arteries
Posterior division (internal iliac): Supplies the superior gluteal artery
External iliac artery: Becomes the femoral artery after passing under the inguinal ligament

Fecal and Urinary Incontinence

Levator ani muscles: Puborectalis, pubococcygeus and iliococcygeus
Puborectalis: Forms a sling around the lower rectum, important for fecal continence
Pubococcygeus: Important for urinary continence, supports vagina and prostate
Iliococcygeus: Anchoring point for the pelvic floor
Weakness in the pelvic diaphragm can lead to pelvic organ prolapse, fecal or urinary incontinence

Pelvic Organ Prolapse

Prolapse: Occurs when a pelvic organ falls out of its position
Can be caused by increased pressure in the abdomen, coughing or pregnancy
May involve the uterus, rectum or bladder
Anterior vaginal wall: Lies just posterior to the bladder and urethra
Damage to the ligaments and fascia of the anterior vaginal wall can lead to prolapse

Uterine Arteries and Hysterectomy

Uterine artery: Supplies the uterus, branches from the anterior division of the internal iliac artery
Ureter: Passes posterior to the uterine artery, "water under the bridge"

Pelvic Nerve and Vessel Structures

Obturator nerve, artery and veins: Pass through the obturator canal
Superior gluteal nerve and artery: Pass through the greater sciatic foramen, suprapiriformic section
Inferior gluteal nerve and artery: Pass through the greater sciatic foramen, infrapiriformic section
Obturator nerve: More susceptible to traction injury during childbirth due to its long journey through the pelvis
Sciatic nerve: Less susceptible because it only passes through the pelvis for a short time

Hysterectomy

Hysterectomy: Surgical procedure to remove the uterus
Types of hysterectomy:
- Simple hysterectomy: Removal of uterus and cervix, preserves vagina, parametrium, ovaries, and fallopian tubes.
- Total hysterectomy: Removal of uterus and cervix, preserves vagina and parametrium. Ovaries and fallopian tubes removed (bilateral salpingo-oophorectomy).
- Subtotal hysterectomy: Removal of uterus, preserving cervix.
Indications for hysterectomy: Uterine prolapse, endometriosis, uterine fibroids, abnormal bleeding
Procedure:
- Can be performed through abdominal, laparoscopic or vaginal approach.
- Surgeon ligates the uterine arteries.
- Surgeon carefully avoids damaging the ureters, bladder and blood vessels.

Prostatectomy

Prostatectomy: Surgical procedure to remove the prostate gland.
Types:
- Simple prostatectomy: Partial removal, through urethra.
- Radical prostatectomy: Full removal, through open incision.
  - Retropubic:
  - Suprapubic:
  - Perineal:
Complications: Urinary incontinence, erectile dysfunction, damage to nerves, arteries and lymph vessels.

Pelvic Inlet and Childbirth

Pelvic inlet: Opening at the top of the pelvis, shaped by the pelvic bones.
Important for childbirth: Determines the size and shape of the passage through which the baby’s head passes.
Types of pelvic inlet:
- Gynaecoid (40-50%): Rounded and broad, most favorable for childbirth.
- Android (common in men): Narrow and heart-shaped, less favorable for vaginal delivery.
- Platypelloid: Flat and wide, difficult for vaginal delivery, often requires C-section.
- Anthropoid (23.5%): Long and narrow, vaginal delivery is possible but more challenging than gynaecoid.

Pelvic Joint Relaxation and Childbirth

Sacroiliac joint: Expands during pregnancy, allowing for passage of the baby.
Parturition: The lumbar spine flattens, the base of the sacrum drops downwards and tilts forward, increasing pelvic dimensions.
Pubic symphysis: Joint that connects the two pubic bones, relaxes during pregnancy due to the hormone relaxin.
Plane of least dimensions: The narrowest point of the pelvis through which the baby's head must pass.
- Transverse: Between the ischial tuberosities.
- Anteroposterior: Pubis to sacrococcygeal joint.
Diagonal circumference: Must be over 11.5 cm for safe vaginal delivery.
Cephalopelvic disproportion (CPD): Baby's head is too large to descend through the pelvis.

Pelvic Diaphragm and Incontinence

Levator ani muscles: Forms the pelvic diaphragm, responsible for continence and supporting pelvic organs.
Puborectalis: Important for fecal continence, keeps the anal sphincter closed.
Pubococcygeus: Important for urinary continence, supports the vagina and prostate.
Iliococcygeus: Provides anchorage for the pelvic floor.
Pelvic organ prolapse: Occurs when a pelvic organ drops out of its position due to weakness in the pelvic diaphragm.
Pregnancy and childbirth: Contribute to strain on the pelvic diaphragm, potentially leading to prolapse.

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Description

This quiz explores the anatomy of the pelvis, detailing its crucial role in locomotion and weight distribution. It covers the components of the bony pelvis, including the hip bones, sacrum, and coccyx, as well as the distinction between the true and false pelvis. Test your knowledge on this fundamental aspect of human anatomy.