MALE GENITAL SYSTEM

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MALE GENITAL SYSTEM

• Dr. Mujahid Khan

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Development of Gonads

• The gonads are derived from 3 sources
• The mesothelium (mesodermal epithelium) lining
  the posterior abdominal wall
• The underlying mesenchyme (embryonic connective
  tissue)
• The primordial germ cells

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Indifferent Gonads

• The initial stages of gonadal development occur
  during the fifth week
• A thickened area of mesothelium develops on the
  medial side of the mesonephros
• Proliferation of this epithelium and the
  underlying mesenchyme produces a bulge on the
  medial side of the mesonephros called Gonadal
  ridge

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Indifferent Gonads

• Finger like epithelial cords or Gonadal cords
  soon grow into the underlying mesenchyme
• The indifferent gonad now consists of an external
  cortex and an internal medulla
• In embryos with an XX sex chromosome complex, the
  cortex differentiates into an ovary and the
  medulla regresses
• In embryos with an XY sex chromosome complex, the
  medulla differentiates into a testis and the
  cortex regresses

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Primordial Germ Cells

• These large, spherical cells are visible early in
  the fourth week among the endodermal cells of the
  yolk sac near the allantois
• During folding of the embryo, the dorsal part of
  the yolk sac is incorporated into the embryo
• With this the primordial germ cells migrate along
  the dorsal mesentery of the hindgut to the
  gonadal ridges
• During the sixth week the primordial germ cells
  enter the underlying mesenchyme and are
  incorporated in the gonadal cords

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Sex Determination

• Chromosomal and genetic sex is determined at
  fertilization
• It depends upon whether an X-bearing sperm or a
  Y-bearing sperm fertilizes the X-bearing ovum
• The type of gonads develop is determined by the
  sex chromosome complex of the embryo (XX or XY)

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Sex Determination

• Before the seventh week, the gonads of the two
  sexes are identical in appearance called
  indifferent gonads
• Development of the male phenotype requires a Y
  chromosome
• The SRY gene for a testes-determining factor
  (TDF) has been localized in the sex-determining
  region of the Y chromosome
• Two X chromosomes are required for the
  development of the female phenotype

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Sex Determination

• The Y chromosome has a testes-determining effect
  on the medulla of the indifferent gonad
• The absence of a Y chromosome results in the
  formation of an ovary
• Testosterone, produced by the fetal testes,
  determines the maleness
• Primary female sexual differentiation in the
  fetus does not depend on hormones
• It occurs even if the ovaries are absent

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Development of Testes

• Embryos with a Y chromosome usually develop
  testes
• The SRY gene for TDF on the short arm of the Y
  chromosome acts as the switch that directs
  development of indifferent gonad into testes
• TDF induces the gonadal cords to condense and
  extend into the medulla of indifferent gonad,
  where they form rete testes

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Development of Testes

• The connection of gonadal cords or seminiferous
  cords with the surface epithelium is lost as
  tunica albuginea develops
• The development of a dense tunica albuginea is
  the characteristic feature of testicular
  development in a fetus

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Development of Testes

• The enlarging testis separates from the
  degenerating mesonephros and becomes suspended by
  its own mesentery called mesorchium
• The seminiferous cords develop into the
  seminiferous tubules, tubuli recti, and rete
  testis
• The seminiferous tubules are separated by
  mesenchyme that gives rise to the interstitial
  cell of Leydig

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Development of Testes

• By the eighth week, these cells begin to secrete
  testosterone and androstenedione
• These hormones induce masculine differentiation
  of the mesonephric ducts and external genitalia
• Testosterone production is stimulated by HCG
• Fetal testes also produces a glycoprotein called
  antimullerian hormone (AMH) or mullerian
  inhibiting substance (MIS)

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Development of Testes

• AMH is produced by sustentacular cells of Sertoli
• AMH suppresses development of the paramesonephric
  ducts
• Seminiferous tubules remain solid until puberty

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Development of Testes

• The walls of seminiferous tubules are composed of
  two kinds of cells
• Sertoli cells, supporting cells derived from the
  surface epithelium on the testis
• Spermatogonia, primordial sperm cells derived
  from the primordial germ cells

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Development of Testes

• The rete testis becomes continuous with 15 to 20
  mesonephric tubules that become efferent ductules
• These ductules are connected with the mesonephric
  duct
• It becomes the duct of the epididymis

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Development of Genital Ducts

• Both male and female embryos have two pairs of
  genital ducts
• The mesonephric ducts (wolffian ducts) play an
  important role in the development of the male
  reproductive system
• The paramesonephric ducts (mullerian ducts) have
  a leading role in the development of the female
  reproductive system
• Till the end of sixth week, the genital system is
  in an indifferent state, when both pairs of
  genital ducts are present

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Development of Male Genital Ducts

• Distal to the epididymis, the mesonephric duct
  acquires a thick investment of smooth muscle and
  becomes the ductus deferens
• A lateral outgrowth from the caudal end of each
  mesonephric duct gives rise to the seminal gland
  or vesicle
• The secretion from this pair of glands nourishes
  sperms
• The mesonephric duct between the duct of this
  gland and the urethra becomes the ejaculatory duct

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Prostate

• Multiple endodermal outgrowths arise from the
  prostatic part of the urethra
• Grow into surrounding mesenchyme
• The glandular epithelium of the prostate
  differentiates from these endodermal cells
• The associated mesenchyme differentiates into the
  dense stroma and smooth muscle of the prostate

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Development of External Genitalia

• Up to the seventh week of development the
  external genitalia are similar in both sexes
• Distinguishing sexual characteristics begin to
  appear during the ninth week
• External genitalia are not fully differentiated
  until the twelfth week

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Development of External Genitalia

• Early in the fourth week, proliferating
  mesenchyme produces a genital tubercle in both
  sexes at the cranial end of the cloacal membrane
• Labioscrotal swelling and urogenital folds soon
  develop on each side of the cloacal membrane
• The genital tubercle soon elongates to form a
  primordial phallus

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Development of External Genitalia

• When the urorectal septum fuses with the cloacal
  membrane, it divides it into a dorsal anal
  membrane and a ventral urogenital membrane
• The urogenital membrane lies in the floor of a
  median cleft, the urogenital groove, which is
  bounded by urogenital folds

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Development of Male External Genitalia

• Masculization of the indifferent external
  genitalia is induced by testosterone
• The phallus enlarges and elongates to become the
  penis
• The urogenital folds form the lateral walls of
  the urethral groove on the ventral surface of the
  penis to form the spongy urethra

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Development of Male External Genitalia

• The surface ectoderm fuses in the median plane of
  the penis, forming a penile raphe and enclosing
  the spongy urethra within the penis
• At the tip of the glans of the penis, an
  ectodermal ingrowth forms a cellular ectodermal
  cord
• It grows towards the root of the penis to meet
  the spongy urethra

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Development of Male External Genitalia

• This cord canalizes and joins the previously
  formed spongy urethra
• This completes the terminal part of the urethra
  and moves the external urethral orifice to the
  tip of the glans of the penis
• During the twelfth week, a circular ingrowth of
  ectoderm occurs at the periphery of the glans
  penis

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Development of Male External Genitalia

• When this ingrowth breaks down, it forms the
  prepuce (foreskin)
• It is adherent to the glans for some time
• Usually not easy to retract at birth
• Corpora cavernosa and corpus spongiosum of the
  penis develop from mesenchyme in the phallus

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Development of Male External Genitalia

• The labioscrotal swellings grow towards each
  other and fuse to form the scrotum
• The line of fusion of these folds is clearly
  visible as the scrotal raphe
• Agenesis of scrotum is an extremely rare anomally

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Development of Inguinal Canals

• Inguinal canals develop in both the sexes
• The gubernaculum passes obliquely through the
  developing anterior abdominal wall at the site of
  future inguinal canal
• The gubernaculum attaches caudally to the
  internal surface of the labioscrotal swellings

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Development of Inguinal Canals

• The processus vaginalis develops ventral to the
  gubernaculum and herniates through the abdominal
  wall along the path formed by the gubernaculum
• The vaginal process carries extensions of the
  layers of the abdominal wall before it, which
  form the walls of the inguinal canal

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Development of Inguinal Canals

• In males, these layers also form the coverings of
  the spermatic cord and testis
• The opening in the transversalis fascia produced
  by the vaginal process becomes the deep inguinal
  ring
• The opening created in the external oblique
  aponeurosis forms the superficial inguinal ring

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Descent of Testes

• Testicular descent is associated with
• Enlargement of the testes and atrophy of the
  mesonephroi, allow caudal movement of the testes
• Atrophy of paramesonephric ducts enables testes
  to move transabdominally to the deep inguinal
  rings
• Enlargement of processus vaginalis guides the
  testes through the inguinal canal into the scrotum

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Descent of Testes

• By 26 weeks the testes have descended
  retroperitoneally to the deep inguinal rings
• This change in position occurs as the fetal
  pelvis enlarges and the trunk of the embryo
  elongates
• Little is known about cause of testicular descent
• The process is controlled by androgens

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Descent of Testes

• Passage of testis through the inguinal canal may
  also be aided by the increase in intra-abdominal
  pressure resulting from growth of abdominal
  viscera
• Descent of testes through the inguinal canals
  into the scrotum usually begins during 26th week
• It takes 2 to 3 days

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Descent of Testes

• More than 97 of full-term newborn males have
  both testes in the scrotum
• During the first 3 months after birth, most
  undescended testes descend into the scrotum
• Spontaneous testicular descent does not occur
  after the age of one year
• When the testis descends, it carries its ductus
  deferens and vessels with it

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