Pelvic Cavity
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Fall 1999 Moore, pp 332-388

Lecture 19 Dr. C. Dlugos

 

PELVIC CAVITY AND ORGANS

Overview: An understanding of the pelvis and the organs contained within it is essential in several medical disciplines such as gynecology, obstetrics, urology and gastroenterology. The functions of the pelvis include protection of the viscera, composition of the girdle by which the lower limb is attached to the axial skeleton, and an attachment site for the external genitalia. This lecture should provide the student with basic information concerning the pelvis, differences in the pelvis within the sexes, and a general knowledge of the anatomy of the pelvic organs in males and females.

 

Objectives

1. to learn the anatomy of the bony pelvis and what regions comprise the false and the true pelvis

2. to be aware of sexual differences in the pelvis

3. to understand the anatomy of the pelvic diaphragm in the male and the female

4. to understand the anatomy of the pelvic organs in the male and the female

 

Pelvis:(Latin for basin), region of transition where the trunk and the lower limbs meet, inferior portion of the trunk, contains pelvic cavity, the inferior portion of the abdominopelvic cavity, below the pelvic brim.

1. The pelvis is divided into two parts (Moore Fig. 3.1. pp332-333):

a. the greater pelvis or pelvis major (false pelvis), between iliac fossae, part of the abdominopelvic cavity proper

b. the lesser pelvis or pelvis minor (true pelvis), "obstetric pelvis", boundaries : anterior (pubic symphysis), posterior (sacrum and coccyx) and lateral (bodies of ischia).

2. Separation between the false and the true pelvis is the pelvic brim or inlet readily discernable because of the presence of the linea terminalis or iliopectineal line, an oblique ridge on the internal surface of the ilium which is continued on the pubis. Most of these terms are review from first block.

3. Bony and cartilaginous constituents of the pelvis: (Moore Fig.3.2., p334)

a os coxae or hip bones: three bones which fuse at age 16-17, ilium, pubis, and ischium.

b. sacrum: five sacral vertebrae fuse together

(1) anterior and posterior sacral foramina, meet with anterior and posterior rami of sacral nerves

(2) large articulating surface for joining with os coxae

c. Ligaments which prevent sacrum from rotating on the sacroiliac joints and demarcate the greater and lesser sciatic foramina

(1) sacrotuberous ligament : extends between sacrum and ischial tuberosity

(2) sacrospinous ligament: extends between sacrum and ischial spine

d. Coccyx: 3-5 fused vertebrae

(1) may fuse to sacrum late in life

(2) partially closes pelvic outlet and functions as an attachment for muscles which close pelvic diaphragm.

4. Pubic symphysis: fibrocartilage, unites two sides of pubic bones

5 . Acetabulum: head of the femur articulates with os coxae, point at which all three bones comprising the hip bone meet. (Moore, Fig.3.2., 3.3., pp334-335).

The false pelvis you have already studied, it lies between the iliac fossa at vertebral levels L5 and S1 and contains the ileum and the sigmoid colon. The true pelvis or pelvis minor is situated between the pelvic inlet and pelvic outlet and contains the pelvic organs such as the urinary bladder, rectum, and reproductive organs.

 

 

Regions of true pelvis:

Superior pelvic aperture (pelvic inlet): oval (female) or heart shaped (male) opening, larger in females than in males, periphery is demarcated by linea terminalis which separates the false from the true pelvis. The linea terminalis has a pubic portion (pectineal line) and an illial portion, (arcuate line). This boundaries of the inlet are; 1) anteriorly the pubic symphysis, 2) laterally, the linea terminalis and 3) posteriorly, the sacrum and the sacral promotory or the projection on the ventral portion of the sacrum where it is connected to the last lumbar vertebrae.

2. Pelvic cavity: contains rectum, bladder, and reproductive organs. The walls of the pelvic cavity are formed by the pubic symphysis anteriorly, the obturator internus muscle laterally and the piriformis muscle posteriorly.

3. Inferior pelvic aperture (pelvic outlet): bounded anteriorly by pubic symphysis, posteriorly by sacrum and coccyx, and laterally by ischial tuberosities, diamond shaped, partially closed because of coccyx. Pelvic diaphragm comprises this area.

Differences in the pelvis between sexes (Moore, Table p336).

1. In the female, the bones are more delicate, the female pelvis is less massive, and the muscular impressions are less marked.

2. In the female, the ilia flare more laterally and the anterior iliac spines are more widely separated causing a widening of the hips with respect to the male.

3. In the female, the superior aperture of the lesser pelvis is wider.

4. In the female, the subpubic angle (angle between the ischiopubic rami) is wider (usually greater than 90)

5. In the female, the sacrum is shorter, wider, and less curved

6. In the female, the acetabulum is smaller.

7. In the female, the pelvic inlet is round or oval with respect to the heart-shaped pelvic inlet in the male.

 

Pelvic diaphragm: funnel shaped fibromuscular diaphragm comprised of two levator ani and two coccygeus muscles. This diaphragm closes the pelvic outlet posteriorly . It is open anteriorly where the urethra, vagina, and anal canal exit (Moore 3.5, p342-343).

 

Muscles:(Moore, Fig. 3.6. p344-345)

1. Levator ani: broad muscle which forms the hammock-like floor of the pelvis and has several parts:

1. Pubococcygeus muscle:attaches on pubis, coccyx , and anococcygeal ligament (the region where the two halves of pubococcygeus meet behind the rectum), the main portion of the levator ani

2. Puborectalis muscle: lies deep to pubococcygeus and forms a supportive sling around the rectum (Fig. 3.6., p344 and Fig. 3.7., p345).

3. Iliococcygeus muscle: thin muscle which attaches to the obturator fascia, the ischial spine, the coccyx and anococcygeal ligament.

e. Innervation of the levator ani: branches of S3,4 supply the pelvic surface and the perineal nerve (S2,3,4,) supplies its perineal surface.

2. Coccygeus (ischiococcygeus): smaller and less important, dorsal to levator ani, attaches to ischial spine, sacrospinous ligament, and coccyx

Innervation:pudendal plexus from 4 and 5 sacral nerves

 

Functions of pelvic diaphragm (levator ani and coccygeus muscles):

1. supports pelvic viscera and closes pelvic outlet

a. In particular, a part of the diaphragm, the puborectal sling ( puborectalis muscle ) holds the front portion of the anorectal junction anteriorly. This action takes pressure from the external anal sphincter and supports the vagina and bladder in the female and the bladder, seminal vesicles, and prostate in the male.

2. Resists the inferior thrust of increases in abdominal pressure (ie. coughing, sneezing) for maintaining urinary continence.

3. Raises the pelvic floor and assists in urination and defecation.

4. Supports fetal head during uterine contractions during delivery.

 

Peritoneum: covers the superior portions of the pelvis (Moore, Fig. 3.15, p360, Table 3.5., p388).

1. In males the peritoneum passed from the anterior body wall, superior to the the pubic bone and covers the superior and part of the posterior surface of the urinary bladder and superior tips of the seminal vesicles. It invaginates between the bladder and the rectum as the rectovesicular pouch ,the most inferior extent of the peritoneum in the male. It attaches to the anterior aspect of the rectum.

2. In females, the peritoneum takes the same course except that it forms a shallow pouch between the bladder and the uterus, the vesicouterine pouch and the deeper rectouterine pouch between the rectum and the uterus. In the female, the rectouterine pouch is the most inferior extent of the peritoneum.

 

Fascia of the pelvis:

1. Visceral fascia:covers organs, binds the pelvic viscera to each other and to the parietal fascia

2. Parietal fascia: covers the pelvic surfaces of muscles and lines the pelvic cavity

a. superior parietal fascia is thickened at the neck of the urinary bladder to form the pubovesicular ligament (female) and the puboprostatic ligament (male), anchors neck of urinary bladder to the pubis. The pubovesicular ligament in the female, attaches to the vagina as well. (Moore,Fig. 3.16., ,p360-61).

 

Spaces within the fascia

1. retropubic space: fascial plane between bladder and pubic symphysis which allows for expansion of the bladder and access to the bladder and the prostate without entering the peritoneal cavity.

 

Pelvic organs

Bladder (vesica urinaria) (Moore, Fig.3.61., p361).

1. Location: In adults the bladder is located within the pelvis minor in back of the pubic symphysis. In infants, the bladder is located in the abdomen and descends into the pelvis major at about age 6. The bladder does not reside in the pelvis minor until after puberty.

2. Surfaces: superior (supports sigmoid colon and urethra), two inferiolateral (cover levator ani), and posterior surfaces (fundus of the bladder)

3. Angles: four angles (a duct is attached to each), anterior (urachus), posteriolateral angles (ureter), and inferior (urethra).

 

4. Anatomy

a. The smooth muscle of bladder is also called the detrusor muscle and consists of three layers. It is thickened to form the internal urethral sphincter

b. The urinary trigone is that part of the bladder which is not formed embryologically from the urogenital sinus. It consists of a triangular region demarcated by the entrance to the two ureters (united as the interureteric fold) (Moore, Fig.3.17, p363) and the exit of the internal urethral orifice which initiates the urethra.

5. Arterial Supply: In both sexes, the superior vesicular arteries, supply the anteriosuperior portion of the bladder. In females, the vaginal artery supplies the posterioinferior portion of the bladder whereas the inferior vesicular artery supplies this region in males.

6. Innervation: Parasympathetic by way of the pelvic splanchnics and sympathetic fibers.

 

Rectum: begins superior to level of third sacral vertebrae, extends from sigmoid colon to puborectalis muscle (Moore, Fig.3.30, pp386)

1. Peritoneal coverings: anterior and lateral surfaces of superior 1/3, anterior aspect of middle 1/3, none of distal 1/3

2. Flexures: The rectum has three sharp curves or flexures as it follows the sacrococcygeal curve - forms transverse rectal folds

3. Arterial Supply: The superior rectal artery( termination of inferior mesenteric artery) and the middle rectal artery (from internal iliac artery) supply most of the rectum. The inferior rectal artery supplies the anal canal.

4. Venous Drainage: Rectal venous plexus Two parts:

a. internal rectal venous plexus, drains mainly into superior rectal vein and enters portal system through the connection between the superior rectal vein and the inferior mesenteric vein. It communicates with the systemic system as well.

external rectal venous plexus drains into the superior rectal vein (portal system), and the middle and inferior rectal veins (systemic system).

 

Anal Canal: from puborectalis to anus

1. Embryology The anal canal is comprised of two embryological regions. At the pectinate line, (Sadler, Fig. 14.34 and 14.35) the hindgut (an endodermal derivative) meets the ectoderm of the proctadeum. The pectinate line is demarcated by the distal end of the anal valves and a transition in epithelial types from the simple columnar epithelium of the gut to the stratified squamous epithelium of the epidermis.

2. Anatomy

a. Anal columns: longitudinal columns on walls of rectum contain branches of superior rectal arteries

b. Anal valves: flaps below the columns

c. Anal sinuses: above valves, secrete mucus, help to expel feces

4. Sphincters:

a. internal, involuntary circular smooth muscle, superior 2/3 of anal canal

b. external, voluntary, inferior 2/3 of anal canal

5 Arterial Supply: The superior rectal artery supplies the area superior to pectinate line, and the inferior rectal artery supplies the area inferior to the pectinate line. The middle rectal artery form anastamoses between the two parts.

6. Venous supply: Above the pectinate line, drainage to superior rectal vein, below pectinate line, drainage into inferior rectal veins.

Two important factors in maintaining fecal continence are:

The support of the the 80 anorectal flexure by the puborectalis muscle

The relaxation of the terminal portion of the rectum or ampulla to accomadate fecal masses.

REPRODUCTIVE ORGANS:

Embryology: The ovaries and testes are the primary sex organs ard are derived from the genital or gonadal ridges in close association with the mesonephric kidneys. The mesonephric ducts detreriorate in the female and the uterine tubes and uterus in the female are derived from the parmesonephric ducts. In males, the vas deferens and epididymis is formed from the mesonephric ducts. (Sadler, Fig. 15.20., 15.21,15.23,15.14, pp286-296).

 

Ovaries: Almond shaped, oval bodies which produce ova (Moore, Fig.3.22, p370 and Fig. 3.27., p377).

1. Ligaments of ovary

a. suspensory ligament: conveys ovarian vessels

b. ligament of the ovary: part of gubernaculum, thick region of connective tissue attaching ovary to lateral wall of uterus

c. mesovarium: part of broad ligament attached to surface of ovary

2. Arterial Supply:ovarian artery with a strong anastamosis from the uterine artery.

 

Uterus: Usually anteverted (tipped anteriorly), pear-shaped muscular organ between bladder and rectum.(Moore,Fig.3.27., p377 , Fig. 3.22, p370 and Fig. 3.11.p 354).

 

Regions: The uterus consists of a 1)fundus, above the entry of the uterine tubes 2) body, 3) isthmus, transitional region between body and isthmus and 4)cervix, the cylindrical inferior 1/3

 

Openings :uterine tubes, internal os (within uterus) and external os (uterus to vagina).

 

Ligaments

1. Broad ligament connects uterus, oviduct, and ovary to lateral pelvic wall. Three distinct regions 1)mesosalpinx (covers oviduct), 2)mesovarium (suspends ovary), 3) broad ligament proper (suspends uterus).

2. Round ligament: connects uterus to labia majora, remnant of the gubernaculum (Moore, Fig.3.27., p377).

 

Arterial supply: uterine arteries, branch of internal iliac

 

Uterine Tubes: oviducts, no direct connection to ovary

 

Openings: The oviducts open laterally into the peritoneal cavity and medially into the uterus.

 

Regions: 1) isthmus (medial constricted 1/3, close to uterus), the ampulla (dilated portion which curves over ovary), and the infundibulum with fimbiae (abdominal opening)

 

Arterial Supply: uterine and ovarian arteries

 

Vagina: formed from the urogenital sinus, organ of copulation and birth, musculomembranous tube or sheath, extends from cervix of the uterus to the vestibule of the vagina, cleft between the labia minora. This organ passes through the urogenital diaphragm and the pelvic diaphragm.

1.Fornix :spaces between vagina and cervix can be considered to have anterior, posterior and lateral parts. The pulse of the uterine artery can be felt in the lateral fornix.

 

Arterial supply: Vaginal artery, uterine artery, internal pudendal artery and middle rectal artery.

 

Male Reproductive Organs of Pelvis: (Moore, Fig.3.21., p368).

 

Ductus Deferens: conducts sperm from epididymis, through inguinal ligament, to the posterior surface of bladder. Here the ductus expands as the ampulla.

 

Arterial supply: artery to the ductus

 

Seminal Vesicles: posterior surface of bladder, superior to prostate, does not store sperm but contributes to the semen. The duct of the seminal vesicle unites with the ductus deferens at the base of the prostate to form the ejaculatory duct.

 

Arterial Supply: artery to ductus deferens

 

Prostate: largest accessory gland of the reproductive system.

1. Prostatic utricle, region within urethra in the prostate which is homologous to female uterus . Near the utricle on the posterior wall of the urethra or urethral crest, the ejaculatory ducts open (Moore, Fig.3.17,p363.)

2. prostatic ducts, empty on prostatic sinuses on either end of urethral crest

3. Arterial supply: internal pudendal, inferior vesicular, and middle rectal

4. Venous drainage: prostatic venous plexus into internal iliac arteries

 

Arteries to pelvis

I. Aorta: ovarian and testicular arteries to gonads median sacral artery -supplies sacrum (Moore, Fig. 2.75, p303)

II Internal iliac artery (Moore,Fig.3.10.Fig. 3.4. and Table 3.4. p353)

 

A. Parietal branches

Dorsal parietal branches:

1. iliolumbar: iliacus, psoas, and quadratus lumborum

2. lateral sacral:skin and muscles on dorsum of sacrum

3. superior gluteal:all gluteal muscles

4. inferior gluteal: supplies gluteus maximus and pelvic diaphragm

Ventral parietal branches:

1. Internal pudendal: stuctures of the perineum (sometimes arises form inferior gluteal)

2. Obturator artery, may arise from external iliacs, supplies obturator muscles and adductor compartment of the thigh

 

B. Visceral Branches:

1. Middle rectal artery:rectum, seminal vesicle, vagina, and prostate

2. Uterine artery: only in females, supplies uterus and gives off vaginal branch (homologue to inferior vesicular artery in the male

a. vaginal artery: usually from uterine, female correlate to inferior vesicular artery, gives off branch to urinary bladder and to vagina, anastamoses with uterine artery

3. umbilical artery: superior portion of the urinary bladder as superior vesicular artery, , part is obliterated and forms medial umbilical ligaments.

4. inferior vesicular artery: only in males, posterioinferior portion of the urinary bladder, seminal vesicles, and prostate. The artery to the ductus deferens is a branch of the inferior vesicular artery.

 

Nerves of pelvis:(Table 3.3, p348)

1. Sacral plexus: formed by lumbosacral trunk (descending ventral rami of L4 and L5 and ventral rami of S1-4).

a. Sciatic nerve (ventral rami of L4,5,S1,2,3)-largest nerve in body

b. Pudendal nerve (ventral rami of S2,3,4)-muscles of perineum, external anal sphincter and is sensory to genitalia

c. Superior and Inferior gluteal nerves to gluteal region

d. nerves to the piriformis, pelvic diaphragm, and quadratus femoris

2. Coccygeal plexus-supplies parts of levator ani and coccygeus

3. Sympathetics-sympathetic chain ends at ganglion impar of coccyx

Parasympathetics-splanchnic nerves from S2,3,4