Chapter 5. Anatomy and Embryology

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Chapter 5. Anatomy and Embryology

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Pelvic Viscera
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Embryonic development

• Female urinary and genital tract
• Closely related, anatomically and embryologically
• Embryologic urinary system important inductive
  influence on developing genital system
• Anomalies in one system are often mirrored by
  anomalies in another system

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Embryonic development

• Urinary system, internal reproductive organs and
  external genitalia
• Develop synchronously at an early embryologic
  age(table 5.6)

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Urinary system
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Kidney, Renal collecting system, Ureters

• Kidney, renal collecting system and ureters from
  longitudinal mass of mesoderm(nephrogenic cord)

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Mesonephric(Wolffian) duct

• Singular importance for the following reasons
• Grows caudally in developing embryo to open an
  excretory channel into the primitive cloaca and
  outside world
• Serves as starting point for development of the
  metanephros which becomes definitive kidney
• Differentiates into the sexual duct system in
  male
• Although regressing in female fetuses, inductive
  role in development of the paramesonephric or
  mullerian duct

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Metanephros

• Development of metanephros

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Bladder and Urethra

• Cloaca

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Genital system development
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Genital system

• In embryologic stage, early genital system
• Indistinguishable between two sexes
• Known as indifferent stage of genital
  development
• Mesodermal epithelium, mesenchyme and primordial
  germ cell

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Internal reproductive organs

• Primordial germ cells

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1. Mullerian duct

• Paramesonephric or mullerian ducts
• Form lateral to mesonephric ducts
• Grow caudally and then medially to fuse in
  midline
• Contact urogenital sinus in region of the post.
  urethra at slight thickening known as sinusal
  tubercle

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Male fetus

• TDF
• Results in degeneration of gonadal cortex and
  differentiation of the medullary region of the
  gonad into Sertoli cells
• Sertoli cells
• Secrete glycoprotein known as anti-mullerian
  hormone(AMH)
• Cause regression of paramesonephric duct system
  in male embryo
• Signal for differentiation of Leydig cells from
  the surrounding mesenchyme

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Male fetus

• Leydig cells
• Produce testosterone,dihydrotestosterone with
  5a-reductase
• Testosterone
• Responsible for evolution of mesonephric duct
  system into vas deferens, epididymis, ejaculatory
  ducts and seminal vesicle
• At puberty, leads to spermatogenesis and changes
  in primary and secondary sex characteristics
• DHT
• Results in development of the male external
  genitalia and prostate and bulbourethral glands

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Female fetus

• In the absence of TDF, medulla regresses and
  cortical sex cords break up into isolated cell
  clusters(primordial follicles)
• in the absence of AMH testosterone,
• Mesonephric duct system degenerates
• Then, paramesonephric duct system develops
• Inf. fused portion
• Uterovaginal canal -gt uterus and upper vagina
• Cranial unfused portions
• Open into celomic cavity(future peritoneal
  cavity)
• Fallopian tubes

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3. Accessory genital glands

• Female accessory genital glands
• Develop as outgrowths from urethra(paraurethral
  or Skene) and definitive urogenital sinus(greater
  vestibular or Bartholin)
• Ovaries first develop in the thoracic region, but
  arrive in pelvis by complicated process of
  descent
• This descent by differential growth under the
  control of a ligamentous cord called the
  gubernaculum

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Genital system 3. Accessory genital glands

• Gubernaculum

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External genitalia
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Genital system abnormalities

• Congenital defects in sexual development, usually
  arising from a variety of chromosomal
  abnormalities, tend to present clinically with
  ambiguous external genitalia
• Known as intersex conditions or hermaphroditism
• Classified according to the histologic appearance
  of the gonads

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(1) True hermaphroditism

• Individuals with true hermaphroditism
• Have both ovarian and testicular tissue
• Most commonly as composite ovotestes
• Occasionally with an ovary on one side and a
  testis on the other
• In the latter case, a fallopian tube and single
  uterine horn may develop on the side with the
  ovary
•      ? absence of local AMH
• Extremely rare condition

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(2) Pseudohermaphroditism

• In individuals with pseudohermaphroditism,
• Genetic sex indicates one gender
• External genitalia has characteristics of the
  other gender
• Caused either by abnormal levels of sex hormones
  or abnormalities in the sex hormone receptors

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(2) Pseudohermaphroditism

• Males with pseudohermaphroditism
• Genetic males with feminized external genitalia
• Hypospadias(urethral opening on the ventral
  surface of the penis)
• Incomplete fusion of the urogenital or
  labioscrotal folds m/c manifesting sx.
• Females with pseudohermaphroditism
• Genetic females with virilized external genitalia
• Clitoral hypertrophy
• Some degree of fusion of the urogenital or
  labioscrotal folds

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Genital Structures
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Vagina

• Hollow fibromuscular tube extending from the
  vulvar vestibule to the uterus
• In dorsal lithotomy, directed posteriorly toward
  the sacrum
• In upright position, almost horizontal
• Spaces between the cervix and vagina ant, post,
  and lateral vaginal fornices
• Post. vaginal wall about 3 cm longer than the
  ant. wall
•    ? vagina is attached at a higher point
  posteriorly than anteriorly

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Vagina

• Post. vaginal wall separated from post.
  cul-de-sac and peritoneal cavity by the vaginal
  wall and peritoneum
• This proximity clinically useful
• Culdocentesis
• Intraperitoneal hemorrhage, pus, other
  intraabdominal fluid
• Posterior colpotomy
• As an adjunct to laparoscopic excision of adnexal
  masses

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Cervix

• Endocervical canal
• About 2-3cm in length, opens proximally into the
  endometrial cavity at the internal os
• In early childhood, during pregnancy, or  with
  oral contraceptive use,
• Columnar epithelium may extend from the
  endocervical canal onto the exocervix -gt eversion
  or ectopy
• Cervical mucus production
• Under hormonal influence
• Around the time of ovulation - profuse, clear,
  thin
• In the postovulatory phase of the cycle scant
  and thick mucus

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Corpus

• At birth, cervix and corpus are about equal in
  size
• In adult women, corpus has grown to 2-3 times the
  size of the cervix
• Position flexion and version
• Flexion - angle between the long axis of the
  uterine corpus and cervix
• Version - angel of the junction of the uterus
  with the upper vagina

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Corpus

• Divided into several different regions
• Isthmus or lower uterine segment
• The area where the endocervical canal opens into
  the endometrial cavity
• Uterine cornu
• On each side of the upper uterine body,
  funnel-shaped area receives the insertion of the
  fallopian tubes
• Fundus
• Uterus above this area(cornu)

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Fallopian tubes

• Fallopian tubes and ovaries referred to as the
  adnexa
• Vary in length from 7 to 12 cm
• Function
• Ovum pickup
• Provision of physical environment for  conception
• Transport and nourishment of the fertilized ovum

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Fallopian tubes

• Divided into several regions
• Interstitial
• Narrowest portion of the tube, lies within the
  uterine wall and forms the tubal ostia at the
  endometrial cavity
• Isthmus
• Narrow segment closest to the uterine wall
• Ampulla
• Larger diameter segment lateral to the isthmus
• Fimbria(infundibulum)
• Funnel-shaped abdominal ostia of the tubes

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Ovaries

• Paired gonadal structures that lie suspended
  between the plevic wall and the uterus by the
  infundibulopelvic ligament laterally and
  uteroovarian ligament medially
• Varies in size with measurements up to 533cm
• Consists of a cortex and medulla
• Cortex - specialized stroma and follicles
• Medulla - primarily of fibromuscular tissue and
  blood vessels

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Urinary tract
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Ureters

• 25cm in length
• Totally retroperitoneal in location
• Pathway of lower half of each ureter
• Traverses the pelvis after crossing the common
  iliac vessels at their bifurcation, just medial
  to the ovarian vessels
• Descends into the pelvis adherent to the
  peritoneum of the lateral pelvic wall and the
  medial leaf of the broad ligament
• Enter the bladder base anterior to the upper
  vagina, traveling obliquely through  the bladder
  wall

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Bladder

• divided into two areas
• Base of the bladder
• Consists of the urinary trigone posteriorly and a
  thickened area of detrusor anteriorly
• Trigone - two ureteral orifices and opening of
  the urethra into the bladder
• Receives a-adrenergic sympathetic innervation
• Is the area responsible for maintaining
  continence
• Dome of the bladder
• Parasympathetic innervation
• Is responsible for micturition

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Urethra

• Female urethra about 3 to 4 cm in length
• Extends from the bladder to the vestibule,
  traveling just anterior to the vagina
• Lined by nonkeratinized squamous epithelium that
  is responsive to estrogen stimulation
• Contains as inner longitudinal layer and outer
  circular layer

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Abdominal Wall
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Abdominal wall

• 1. Skin
• 2. Muscles
• Five muscles and their aponeuroses(fig 5.16)

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3. Fascia (1) Superficial fascia

• Consists of two layers
• Camper fascia
• Most superficial layer, which contains a variable
  amount of fat
• Scarpa fascia
• Deeper membranous layer continuous in the
  perineum with colles fascia(superficial perineal
  fascia) and with deep fascia  of the thigh(fascia
  lata)

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3. Fascia (2) Rectus sheath

• Aponeuroses of the external and internal oblique
  and the transversus abdominis
• Combine to form a sheath for the rectus
  abdominis and pyramidalis, fusing medially in the
  midline at the linea alba and laterally at the
  semilunar line(fig 5.16)

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3. Fascia (3) Transversalis fascia and
endopelvic fascia

• Firm membranous sheet on the internal surface of
  the transversus abdominis muscle
• Like peritoneum, divided into a parietal and a
  visceral component
• Transversalis fascia
• Continues along blood vessels and other
  structures leaving and entering
  the abdominopelvic cavity
• Contributes to the formation of the visceral
  (endopelvic) pelvic fascia
• Pelvic fascia
• Invests the pelvic organs and attaches them to
  the pelvic side walls, thereby playing a critical
  role in pelvic support

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Perineum

• Situated at the lower end of the trunk between
  the buttocks
• Its bony boundaries
• Lower margin of the pubic symphysis anteriorly
• Tip of the coccyx posteriorly
• Ischial tuberosities laterally
• Diamond shape of the perineum
• Divided by imaginary line joining the ischial
  tuberosities immediately in front of the anus, at
  the level of the perineal body, into an ant.
  urogenital and a post. anal triangle(fig 5.18)

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