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Development of Urinary &
Male Genital System
M. Mansyur Romi
Introduction
• Urinary and genital systems are closely associated
• Both develop from intermediate mesoderm
– 7th- 28th somite level (3rd week)
– Nephrogenic mass (cord)
• Dorsal side of coelom, each cord produces a bulge
into the coelom called the urogenital ridge
• Urinogenital Ridge
– Form the urinary and genital structures
– Nephrogenic tissue from 7-14th somite breaks up into
segments called nephrotomes
Fig. 1 -
Transverse section and dorsal view of an embryo (trilaminar)
Transverse section of the three-layered embryo towards
the end of the 3rd week of development.
(ca. 21 days)
1.Paraxial mesoderm
2.Intermediate mesoderm
3.Lateral mesoderm
4.Notochord
5.Amnion
6.Intraembryonic coelom
7.Endoderm
8.Ectoderm
9.Somatopleural
(mesoderm and ectoderm)
10Splanchnopleural
(mesoderm and endoderm)
11.Neural groove
12.Neural ridge
Kidney Development:
Formation of 3 kidney systems
• Pronephros (simplest & most primitive)
– 7-10 solid or tubular arranged cell groups in the cervical
region (head kidney)
– It is seen in the late 3rd wk, gone by the end of the 4th wk
• Mesonephros (intermediate-more advanced)
– Appear during regression of pronephros, 10-26th somite
– It is transient, but serves as an excretory organ while the
metanephros begins its development
– It is seen at 24th day, dissapear by the 4th month
• Metanephros (permanent kidney)
– Begins to develop early in 5th wk, functions by the 11th
wk
Pronephros (forekidney): transitory structure
1.Nephrogenic cord
2.Mesonephric duct
(Wolff)
1+2.Mesonephros
3.Intestinal tube
4.Cloaca
5.Atrophying
nephrotomes
6.Yolk sac (umbilical
vesicle)
7.Allantois
8.Outflow of the
mesonephric duct into
the cloaca
Mesonephros
• Tubules develop from nephrogenic cord (NC)
– Opens into the excretory/mesonephric duct
– Gone by week 10 in females, in males some tubules
persist & become vas deferens
• Approximately 38 pairs of closed tubules
– S shaped bend
– Surrounds internal glomerulus
• Mesonephric duct develops laterally from NC &
extends from 8th somite to urinogenital sinus
Mesonephros: transitory kidney
1.Nephrogenic cord
2.Mesonephric duct
1+2.Mesonephros
3.Intestine
4.Cloaca
5.Atrophied
nephrotome
6.Yolk sac (umbilical
vesicle)
7.Allantois
8.Outflow of the
mesonephric duct
into the cloaca
9.Ureter bud (anlage)
Mesonephros enlargement point A
1.Neural tube
2.Notochord
3.Aorta dorsalis
4.Dorsal mesentery
5.Intestinal tube
6.Ectoderm
7.Somite
8.Inferior cardinal vein
9.Mesonephric duct
(Wolffian duct)
10.Mesonephric
tubule
11.Urogenital ridge
Mesonephros enlargement point A
1.Neural tube
2.Notochord
3.Aorta dorsalis
4.Dorsal mesentery
5.Intestinal tube
6.Ectoderm
7.Somite
8.Inferior cardinal vein
9.Mesonephric duct
(Wolffian duct)
10.Mesonephric
tubule
11.Urogenital ridge
Metanephros
• Nephrons/tubules develop from nephrogenic mass
(26th-28th somite level)
– Located lateral to mesonephric duct
– Internal dense layer which forms tubules/nephrons
– Outer loose layer forms connective tissue capsule
• Duct system derived from ureteric bud
– Ureter, renal pelvis, calyces, collecting ducts
– Ureteric bud elongates and makes contact with
nephrogenic mass which surrounds bud like a cap
• Tubules are closed (internal glomerulus)
• Migrate from pelvis to abdomen as fetus grows
– Blood supply from aorta changes as ascent occurs
• Becomes functional in second ½ of pregnancy
Metanephric outflow
1.Cloaca
2.Ureter anlage
3.Metanephric
blastema
2+3.Metanephros
4.Mesonephric duct
(Wolffian duct)
5.Nephrogenic cord
4+5.Mesonephros
Renal ascent
• Between the 6th – 9th
wks the kidney ascend
to a lumbar site just
below the adrenal
glands
• When the kidney falls
to ascend properly, its
location becomes
ectopic
Male Genital Development
• Development of gonads
• Development of genital ducts
• Development of external genital
Origin
• Gonads – intermedial
mesoderm of
mesonephros
• Primordial germ cells
– endoderm of yolk
sac
• External genitalia –
ectoderm and
mesoderm
Indiferent stage
• Both sexes has same first stage
– coelomic epithelium
• primary germ cords
– primordial germ cells
– mesonephric duct (Wollfian) and tubules
– paramesonephric duct
Genital Development
• Formation of genital ridges
– During the 5th week: primordial germ cells migrate from
yolk sac to populate the mesenchyme of the posterior
body wall near the 10th thoracic level
– The arrival serves as the signal to form a pair of genital
ridges, medial to the mesonephros
– During the 6th week: the cells of ridges invade the
mesenchyme to form primitive sex cords
– A new pair of paramesonephric (mullerian) ducts begins
to form lateral to the mesonephric ducts in both sexes
Genital Development
Genital Development
• Development of male genital structures
– Under the influence of SRY (sex-determining
region of Y) cells in medulla of primit. sex cords
differentiate into Sertoli cells; otherwise (no
SRY) into ovarian follicles
– During the 7th week: Sertoli cells organize to
form testis cords.
– Direct contact between developing sertoli cells
& primordial germ cells plays a key role in the
proper development of male gametes
Male gonads
• Y – chromosome: SRY (sex
determining regionY) TDF
(testes determining factor)
• if produced 
development of testis
– usually from 7th week
• if not produced 
development of ovarium
– usually from 12th week
– „waiting period“
Genital Development
Development of testis
• TDF stimulates proliferation of primary germ
cord  medullary cords
– origin of seminiferous tubules and rete testis
– origin of Sertoli cells
• intermedial mesenchyme
– origin of Leydig cells
• rest of coelomic epithelium changed to tunica
albuginea
Seminiferous tubules
• Spermatogonia – from primordial germ cells
• Sertoli cells
– surrounds spermatogonia
– secrete anti-müllerian hormone (AMH) / Müllerian
inhibiting hormone/substance (MIH/MIS)
• inhibition of paramesonephric duct (Müllerian)
• interstitial Leydig cells
– produce testosteron from 8th week
• no lumen till puberty
Genital ducts
• Connected medullar cords
– rete testis
• Mesonephric tubules
– Efferent ducts
• Mesonephric duct (Wollfian)
– Epididymal duct, ductus deferens, vesicular glands,
ductus ejaculatorius
– (ureter, pelvis, calices, collecting duct and tubules)
• Paramesonephric duct (Müllerian) disappear
Genital Development
• Development of male genital structures
– The sertoli cells begin to secrete mullerianinhibiting substance (MIS), which causes
mullerian ducts to regress rapidly 8th – 10th wks
– During 9th – 10th wks Leydig cells differentiate
from mesenchyme of the genital ridge in
response to SRY protein; these produce
testosteron
– Between 8th – 12th wks testosteron stimulates
mesonephric ducts to transform  vas
deferens
– The seminal vesicles sprout from the distal
mesonephric ducts
– The prostate and bulbourethral glands develop
from the urethra
• Development of female genital structures
– In the absence of SRY protein and Sertoli cells:
MIS synthesis, Leydig cells diff. & androgen
production do not occur
– The mesonephric (wolffian) ducts degenerate,
paramesonephric (mullerian) ducts give rise to
the fallopian tubes, the uterus, the upper 2/3rd
of the vagina.
Genital Development
Genital Development
• Development of external genitalia
– The early development is similar in both sexes
– In the 4th mth, the effects of dihydrotestosteron
(DHT) on the male external genital become
readily apparent
– In the absence of dihydrotestosteron  female:
the primitive perineum does not lengthen, and
the labioscrotal and urethal folds do not fuse
across the midline
– The penile urethra is enclosed by the 14th wk
Genital Development
External genitalia
• indiferent stage
• male genital
• genital tubercle
• urogenital folds
• labioscrotal folds
• penis
• spongious urethra
• scrotum
Gonadal descent
– In both sexes the initial descent depends on a
ligamentous cord: gubernaculum
– Testes descend through inguinal canal down to
the scrotum; ovaries remain within abdom.cvt
– Testicles descend to internal inguinal ring by the
3rd mth and complete their descent into the
scrotum by the 7th – 9th mth
Descensus of the testis
• from thoracolumbal area to scrotum
– AMH, testicular growth, elongation of body
– gubernaculum – connective cord between testis
and scrotum
• from 26th week
• mark of fetal maturity
• cryptorchism vs. ectopic testis
Descensus of the testis
Spermatogenesis
• Early in embryonic development, primordial germ cells enter
the testes and differentiate into spermatogonia
• Spermatogonia are diploid cells, each with 46 chromosomes
(23 pairs) located around the periphery of the seminiferous
tubules.
• At puberty, hormones stimulate these cells to begin dividing
by mitosis. Some remain at the periphery as spermatogonia.
• Others become primary spermatocytes. Because they are
produced by mitosis, primary spermatocytes are diploid and
have 46 chromosomes.
Spermatogenesis
• Each primary spermatocytes goes through the first meiotic
division, meiosis I, to produce two secondary spermatocytes,
each with 23 chromosomes (haploid). Just prior to this
division, the genetic material is replicated . During meiosis I,
one chromosome, goes to each secondary spermatocyte.
• In the second meiotic division, meiosis II, each secondary
spermatocyte divides to produce two spermatids. There is no
replication of genetic material in this division, but a singlestranded chromatid goes to each cell.
• As a result of the two meiotic divisions, each primary
spermatocyte produces four spermatids, each spermatid has
23 chromosomes (haploid), one from each pair in the original
primary spermatocyte.
Spermatogenesis
38
Spermatogenesis
• The final step in the development the spermatids formed
from spermatogenesis become mature spermatozoa, or
sperm.
• The mature sperm cell has a head, midpiece, and tail.
• The head, also called the nuclear region, contains the 23
chromosomes surrounded by a nuclear membrane. The tip of
the head is covered by an acrosome, which contains enzymes
that help the sperm penetrate the female gamete.
• The midpiece, metabolic region, contains mitochondria that
provide adenosine triphosphate (ATP).
• The tail, locomotor region, uses a typical flagellum for
locomotion.
Spermatogenesis
• The sperm are released into the lumen of the seminiferous
tubule and leave the testes. They then enter the epididymis
where they undergo their final maturation and become
capable of fertilizing a female gamete.
• Sperm production begins at puberty and continues
throughout the life of a male.
• The entire process, beginning with a primary spermatocyte,
takes about 74 days. After ejaculation, the sperm can live for
about 48 hours in the female reproductive tract.
Spermiogenesis:
Spermatids to Sperm
42
Pembuahan / fertilisasi / konsepsi