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Urogenital System
Kidney Systems
Three slightly overlapping kidney systems are formed in a cranial to caudal sequence: the
pronephros, mesonephros, and metanephros.
Pronephros
The pronephros is the type of kidney found only in the lowest of vertebrates. In humans
the first evidence of a urinary system consists of the pronephros, a few segmentally
arranged set of epithelial cords that differentiate from the anterior intermediate
mesoderm at about 22 days gestation. These sets cords in the cervical region are called
nephrotomes: a set on each side of the embryo. The nephrotomes connect laterally with
a pair of primary nephric (pronephric) ducts which grow toward the cloaca.
As the primary nephric ducts extend caudally, they stimulate the intermediate
mesoderm to form additional segmental sets of tubules: mesonephric tubules.
Mesonephros
From the upper thoracic to the upper lumbar region the mesonephros appears, while the
cervical pronephric system regresses. A typical mesonephric unit consists of a vascular
glomerulus surrounded by an epithelial glomerular capsule. Each mesonephric tubule
empties separately into the continuation of the primary nephric duct (from the
pronephros), which becomes the mesonephric (wolffian) duct.
The formation of mesonephric tubules occurs in a cranial to caudal direction. By the
end of the fourth week the mesonephric ducts attach to the cloaca. Very near its
attachment to the cloaca, the mesonephric duct develops an epithelial outgrowth called
the ureteric bud. Early in the fifth week the ureteric bud begins to grow into the most
posterior region the intermediate mesoderm. It then sets up a series of continuous
inductive interactions leading to the formation of the definitive kidney, the metanephros.
Urine formation in the mesonephros begins with a filtrate of blood from the
glomerulus into the glomerular capsule. This filtrate then flows into the tubular portion
of the mesonephros where there is selective resorption of ions and other substances.
The mesonephros does not develop into a sophisticated system for concentrating urine
as in the adult kidney. Its principal functions are to remove waste and there is no need to
conserve water.
Although most of the mesonephric tubules rapidly degenerate after the metanephric
kidneys become functional, the mesonephric ducts persist in the male. The ducts and a
few caudal tubules become incorporated as integral parts of the male genital system. In
the female, they all disappear.
Medial to the mesonephros a gonad is developing. The gonad and the mesonephros
form an elevation on both sides of the embryo called the urogenital ridge.
Metanephros
Development of the metanephros begins in the fifth week when the ureteric bud
(metanephric diverticulum) expands into the posterior portion of the intermediate
mesoderm. Mesenchymal cells of the intermediate mesoderm condense around the
metanephric diverticulum to form the metanephric blastema.
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The morphological basis for the development of the metanephric kidney is (1) the
elongation and branching (up to 15 times) of the ureteric bud, which becomes the
collecting (metanephric) duct system of the metanephros, and (2) the formation of
renal (excretory) tubules from mesenchymal condensations of the metanephric blastema
at the tips of the branching collecting system.
The formation of individual tubules (nephrons) in the developing metanephros
involves three mesodermal cell types: (1) epithelial cells of the ureteric bud, (2)
mesenchymal cells of the metanephric (metanephrogenic) blastema, and (3) ingrowing
vascular cells.
The earliest stage is the condensation of mesenchymal blastemal cells (metanephric
tissue cap) around the terminal parts (collecting tubules) of the ureteric bud. Influenced
by the collecting tubule, cells of the tissue cap form small vesicles, the renal vesicles,
which give rise to small S – shaped tubules. Capillaries will grow into the pocket of one
end of the S [like in the lower pocket here for example > S] and differentiate into
glomeruli. The renal tubules, together with their glomeruli, form nephrons (the
excretory units). The proximal end of each nephron (the pocket) forms Bowman's
capsule and the distal end forms an open connection with the collecting tubule, which
was derived from the ureteric bud. During differentiation of the nephron, a portion of the
renal tubule develops and elongated hairpin loop that extends into the medulla of the
kidney as the loop of Henle.
There are about 15 successive generations of nephrons in the peripheral (cortical) zone
of the kidney. While many sets of nephrons are differentiating, the kidney becomes
progressively larger. The branched system of ducts also becomes much larger and more
complex forming the pelvis and the calyces.
Hence, the kidney develops from two sources of intermediate mesoderm. (1) The
ureteric bud (off the mesonephric duct) forms the renal pelvis, major and minor calyces,
and
1 million to 3 million collecting tubules. (2) the metanephric blastema provides for the
excretory units that include Bowman's capsule [parietal and visceral (podocytes)
epithelium] plus the proximal and distal convoluting tubules. Mesangial cells are
derived from the mononuclear phagocyte system that differentiated from hematopoietic
cells (mesoderm). The basement membrane is derived from secretions of both
podocytes and adjacent endothelial cells of the glomeruli.
Urine production begins by the 10th week with about 1 million functional nephrons in
each kidney.
Positioning of the Kidney
Initially, the metanephric kidneys are located deep in the pelvic region. During the late
embryonic and early fetal period, they undergo a shift in position that moves them into
the abdominal cavity. There are two components to their migration. One is caudocranial
shift from the 4th lumbar to the 1st lumbar vertebrae. The other is a lateral displacement.
Both changes of positions bring the kidneys in contact with the adrenal glands. During
their migration, the kidneys also undergo a 90-degree rotation, with the pelvis ultimately
facing the midline. As they are migrating out of the pelvic cavity, the kidneys slide over
the large umbilical arteries. These changes occur behind the peritoneum, thus the
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kidneys are retroperitoneal. During the migration, the mesonephric kidneys regress. The
mesonephric ducts are retained for the developing gonads.
Formation of the Urinary Bladder
The cloaca is divided into a urogenital sinus and rectum is by means of the urorectal
septum. The urogenital sinus is continuous with the allantois, which has a tubular
process extending into the body stalk or umbilical cord. The dilated upper part of the
urogenital sinus forms the urinary bladder and superior to it, the distal end of the
allantois solidifies as the cordlike urachus. The urachus forms the median umbilical
ligament. The next lower part of the urogenital sinus (below the bladder) is narrow and
forms the pelvic part of the urogenital sinus. Here, the prostatic and membranous
parts of the urethra are formed in the male. In the female there is a membranous part of
the urethra.
As the bladder grows, it incorporates the mesonephric ducts and ureteric buds. The
result is that these structures open separately into the posterior wall of the bladder. The
mesonephric ducts enter into the prostatic urethra close together as the ejaculatory
ducts. The region bounded by the ureters and the ejaculatory ducts is the trigone of the
bladder.
Problems In Renal Formation
Anomalies of the urinary system are relatively common (3% - 4% of live births).
Renal Agenesis
Renal agenesis is the unilateral or bilateral absence of any trace of kidney tissue.
Unilateral agenesis is seen in about 0.1% of adults. Bilateral agenesis occurs in roughly
1/3500 newborns. The ureter may be present. Individuals with unilateral renal agenesis
are often asymptomatic and the single kidney undergoes compensatory hypertrophy.
An infant born with bilateral renal agenesis dies in a few days. Because of a lack of
urine output, reduction in the volume of amniotic fluid (oligohydramnios) during
pregnancy is often an associated feature. Infants born with bilateral renal agenesis
characteristically exhibit Potter facies, consisting of a flattened nose, receding chin, wide
interpupillary space, and large, low set ears. This problem is due to mechanical pressure
of the uterus on the fetus.
Renal Hypoplasia
This is an intermediate renal agenesis and a normal kidney, where one kidney or both are
substantially smaller than normal. A certain degree of normal function is maintained. If
one kidney is affected, the other will undergo compensatory hypertrophy.
Renal Duplications
Renal duplications range from a simple duplication of the renal pelvis to a completely
separate supernumerary kidney.
Anomalies of Renal Migration and Rotation
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The most common disturbance of renal migration is its failure to depart from the pelvis.
This is usually associated with malrotation of the kidney as well, so the hilus of the
pelvic kidney faces anteriorly instead of toward the midline. Another category of
defective migration is crossed ectopia, where one kidney and its associated ureter are on
the same side of the body as the other kidney.
The horseshoe kidney occurs in as many a 1 / 400 individuals, where the kidneys are
fused at their inferior poles. Horseshoe kidneys cannot migrate out of the pelvic cavity
because the inferior mesenteric artery blocks them. In most cases, the horseshoe kidney
is asymptomatic, but occasionally pain or obstruction of the ureters may occur.
Anomalies of the Renal Arteries
Duplication of the renal arteries is common.
Polycystic Disease of the Kidney
Congenital polycystic disease of the kidney, an autosomal recessive condition of
infants, is manifest by a large number of cysts in the kidney. Here, the pathogenesis has
not been ascertained. In adults, an autosomal dominant form of the disease results from
mutations in two genes encoding the transcription factors, ADPKD-1 and ADPKD-2
(autosomal dominant polycystic kidney disease), which produce the proteins
polycystin -1 and polycystin 2. Cysts occur in other organs, especially the liver and
pancreas.
Cysts, Sinuses, and Fistulas of the Urachus
If parts of the lumen of the allantois fail to obliterate, urachal cysts, sinuses, or fistulas
can form. In the urachal cyst, urine seeps from the umbilicus.
Exstrophy of the Bladder
Exstrophy of the bladder is a major defect where the urinary bladder opens broadly onto
the abdominal wall. Rather than being a primary defect of the urinary system, it is
commonly attributed to an insufficiency of tissue in the ventral abdominal wall. In males,
exstrophy of the bladder commonly involves the phallus and a condition called
epispadius.
--------------------------------------------------------------------------------------------------------------Genital System and Gonads
Sexual determination begins at fertilization, when a Y chromosome or an additional X
chromosome is joined to the X chromosome already in the egg. Although genetic gender
is determined at fertilization, the gross phenotypic gender is not manifested until the 7th
week of development. During this morphologically indifferent stage of sexual
development, the gametes migrate into the gonadal promordia from the yolk sac. The
female phenotype is the baseline, or default condition, that must be acted on by male
influences to produce a male phenotype.
Genetic Determination of Gender
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The testes determining gene is at the SRY (sex-determining region on Y) gene. The
SRY gene on the Y chromosome is located on its short arm. The SRY protein made by
the gene determines if there will be male or female development.
Migration of Germ Cells into the Gonads
Experimental studies have shown that primordial germ cells can be demonstrated in the
epiblast of the mouse. These cells pass through the early primitive streak and are located
as a small cluster of cells in the extraembryonic mesoderm near the base of the allantois.
They become associated with the endoderm of the posterior wall of the yolk sac. During
the 3rd week, human primordial germ cells can be observed in the yolk sac. In the
embryo, primordial germ cells migrate from the posterior wall of the yolk sac along the
wall of the hindgut and through the dorsal mesentery until they reach the region of the
genital ridges. As the germ cells approach the genital ridges late in the 5th week, they
may be influenced by chemotactic factors secreted by the newly forming gonads. About
1000 to 2000 primordial germ cells enter the genital ridges.
Once the primordial germ cells have penetrated the genital ridges, their migration
ceases. Some germ cells inappropriately migrate to extragonadal sites and they
degenerate. In rare instances they may persist, such as in the mediastinum and give rise
to teratomas (a tumor containing the three primary embryonic germ layers).
Origin of the Gonads
The gonads arise from an elongated region of mesoderm along the ventromedial border
of the mesonephros. Cells in the cranial part of this region condense to form the
adrenocortical primordia, and those in the caudal part become the genital ridges. The
genital ridges are identifiable midway through the 5th week. The early genital ridges are
composed of two cell populations: (1) cells from coelomic epithelium and (2) cells
arising from the mesonephric ridge.
Differentiation of the Testes
When the genital ridges first appear, those of males and females are indistinguishable or
indifferent gonads. The principle foundation for gonadal differentiation is the
influence of the SRY gene and its elaboration of testes-determining factor on the
gonads to have them develop into testes. In its absence, the gonads differentiate into
ovaries.
Neither the expression of SRY nor later differentiation of testes depends on the
presence of primordial germ cells. The sex-determining genes act on the somatic
portion of the testes and not the germ cells.
Testis develop more rapidly than the ovary. Precursors of supporting or Sertoli cells
(sustentacular cells) must be prepared to receive genetic signals for testicular
differentiation by a certain time. If not, the primordial germ cells begin to undergo
meiosis and the gonad differentiates into an ovary. Supporting cells are derived from
surface epithelium of the gonad as are the follicular cells of the ovary.
Evidence shows that the genital ridges first appear midway in the 5th week through the
proliferation of coelomic epithelial cells along the medial border of the mesonephros.
Later in the 5th week the primordial germ cells enter the early genital ridge and the
coelomic epithelium sends short epithelial pillars toward the interior or medullary portion
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of the gonad. Early in the 6th week a set of primitive sex cords takes shape in the genital
ridge, and the primordial germ cells migrate into the primitive sex cords.
Late in the 6th week the testes shows evidence of differentiation. The primitive sex
cords (derived from surface epithelium) enlarge, get better defined, forming the Sertoli
cells. As the sex cords differentiate, they are separated from the surface of the surface
epithelium (germinal epithelium) by a dense layer of tissue called the tunica albuginea.
The deepest portions of the testicular sex cords are in contact with the fifth to twelfth sets
of mesonephric nephrons. The outer portions of the testicular sex cords form the
seminiferous tubules, and the inner portions become the mesh-like rete testis. The rete
testis ultimately joins the efferent ductules, which are derived from the mesonephric
tubules.
Leydig cells do not appear until the 8th week and soon begin to synthesize androgenic
hormones (testosterone and androstenedione) and have receptors for luteinizing
hormone (LH) produced by the pituitary gland. The interstitial cells of Leydig are
derived from the original mesenchyme of the gonadal ridge. Fetal Leydig cells secrete
their hormones during the ninth to fourteenth weeks while the genital ducts differentiate.
Soon after, they involute and do not reappear until puberty as an adult isoform. By 8
weeks the embryonic Sertoli cells produce müllerian inhibiting substance, which
causes involution of the precursors of the female genital duct system, the müllerian or
paramesonephric ducts. Sertoli cells have receptors for follicle stimulating hormone
(FSH), from the pituitary gland to make androgen-binding protein.
During the late embryonic and fetal periods and after birth, the primordial germ cells
divide slowly by mitosis.
Differentiation of the Ovaries
In contrast to the testes, the presence of viable germ cells is essential for ovarian
differentiation. If primordial germ cells fail to reach the genital ridges or if they are
abnormal (e.g., XO) or degenerate, the gonad regresses and streak ovaries (vestigial
ovaries) result.
After the primordial germ cells have entered the genital ridges, they remain in the outer
cortical or near the corticomedullary region of the future ovary. Ovarian sex cords in the
medullary part of the ovary do not develop as well as those in the testes. The origin of
the follicular epithelial cells that surround the primordial germ cells appears to come
from coelomic epithelium. In the case of the ovary, coelomic epithelium continues to
proliferate and produces secondary sex cords that in contrast to the testes, remains in the
cortex of the gonad. These cells then surround the primordial germ cells (now called
oogonia).
The oogonia proliferate by mitosis from the time they enter the gonad until the start of
the 4th month. At that time, some of the oogonia enter prophase of the 1st meiotic
division. The meiotic oogonia are now called primary oocytes and with their
surrounding follicular cells they form primordial follicles. The oocytes continue in
meiosis until they reach the diplotene stage of prophase I. Meiosis is arrested at this
stage and the oocytes remain at this point until the block is removed. In the adult,
meiosis continues just before ovulation.
In the fetal ovary an inconspicuous tunica albuginea forms at the corticomedullary
junction, with the gametes external to it. The cortex of the ovary is the dominant
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component and contains the majority of oocytes. The medulla is filled with connective
tissue and blood vessels derived from the mesonephros. On the other hand, the medullary
region of the testes is the major gamete producing area, surrounded by the tunica
albuginea.
The Sexual Duct System
Like the gonads, the sexual ducts pass through an early indifferent stage. In males,
testicular secretory products develop the male duct system. In females, absence of
testicular products results in the preservation of the default female structures and
regression of the male structures.
Indifferent Sexual Duct System
The indifferent sexual duct system consists of the mesonephric (wolffian) ducts and the
paramesonephric (müllerian) ducts. The paramesonephric ducts arise from
longitudinal invaginations of the surface epithelium on the anterolateral surface of the
urogenital ridge. The invaginations soon become epithelial cords, which grow caudally
and terminate on the urogenital sinus between the ends of the mesonephric ducts without
breaking into the sinus. These cords develop a lumen. The cranial end of each
paramesonephric duct opens into the coelomic cavity as a funnel-shaped structure. Their
fates depend on the gender of the gonad.
Sexual Duct System if Males
Development of the sexual duct system in the male depends on secretions from the testes.
Under the influence of müllerian inhibiting substance (MIS), secreted by the Sertoli
cells at eight weeks gestation, the paramesonephric ducts degenerate leaving only their
remnants at their cranial and caudal ends. This "antimüllerian hormone" influences the
surrounding mesenchyme to instruct the epithelial cells to regress.
Under the influence of testosterone, secreted by the Leydig cells, the mesonephric
ducts continue to develop. The mesonephric ducts differentiate into the paired ductus
deferens, which transports sperm from the testis to the urethra. The most cranial portion
of the mesonephric ducts regress, except for a vestige known as the appendix
epididymus. Portions of the degenerating excretory mesonephric tubules (paragenital
tubules) may persist near the caudal pole of the testis as the paradidymus. A few
intermediately situated mesonephric excretory tubules will form the efferent ductules of
the testis that join the rete testes (from seminiferous tubules). The efferent tubules merge
into a highly convoluted (ductus) epididymus that continues as the vas (ductus)
deferens, ultimately draining into the prostatic urethra as the ejaculatory ducts.
Associated with the male genital tract is formation of the male accessory sex glands:
the seminal vesicles, the prostate, and the bulbourethral (Cowper's) glands. These
glands arise as epithelial outgrowths from their associated duct systems. The seminal
vesicles arise from the ductus deferens. The prostate and bulbourethral glands derive
from the urogenital sinus. These glands depend on androgenic stimulation for
development. Below the bladder, mesenchymal cells develop intracellular receptors for
circulating androgens (dihydrotestosterone, DHT). Incomplete masculinization occurs
when testosterone fails to convert to DHT or when DHT fails to act within the cytoplasm
or nucleus of the cells of the external genitalia and urogenital sinus. Actually, the
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mesonephric duct and its derivatives need testosterone to develop, while the accessory
glands and external male genitalia need dihydrotestosterone.
Mesodermal cells having the enzyme 5α – reductase, convert testosterone into
dihydrotestosterone. If intracellular androgen receptors are not present or if tissues lack
receptors for DHT complexes, then external male differentiation fails to take place. Such
is the case of males (46, XY) with androgen insensitivity syndrome (AIS) or testicular
feminization syndrome. Because, müllerian inhibitory factor is produced by the Sertoli
cells, the uterus and upper part of the vagina do not form. Here, the male has the
appearance of a normal female due there is unresponsiveness to androgens. The basic
etiology of the (AIS) is a loss-of-function mutation in the androgen receptor (AR) gene.
Sexual Duct System of Females
If either the ovaries are present or the gonads are absent or defective, the sexual duct
system differentiates into a female phenotype. In the absence of testosterone the
mesonephric ducts regress, leaving only rudimentary structures. In the absence müllerian
inhibitory substance the paramesonephric (müllerian) ducts continue to develop into the
major structures of the female genital tract.
The cranial portions of the paramesonephric ducts become the uterine tubes, with
their cranial parts opening into the coelomic cavity. Fimbria are located at their
intraperitoneal terminations. Toward their caudal ends the paramesonephric ducts begin
to approach the midline and cross the mesonephric ducts ventrally. This crossing and
ultimate meeting in the midline are caused by the medial swinging of the entire urogenital
ridge. The region of midline fusion of the paramesonephric ducts ultimately becomes the
uterus, and the ridge of tissue that is carried with the paramesonephric ducts forms the
broad ligament of the uterus. The fused paramesonephric ducts give rise to the both the
corpus and cervix of the uterus.
Shortly after the paramesonephric ducts reach the urogenital sinus, two solid
evaginations grow out from that part of the urogenital sinus. These evaginations
(sinovaginal bulbs) proliferate and form a solid vaginal plate (uterovaginal plate). At
the cranial end of the plate there is proliferation of tissue that elongates the potential
vagina. This increases the distance between urogenital sinus and its cranial end united to
the caudal paramesonephric ducts. In the 5th month the solid vagina is canalized. Thus,
the vagina has two origins: (1) the upper portion that has the fornices around the cervix,
both derived from the paramesonephric ducts, and (2) the lower portion derived from the
urogenital sinus.
The lumen of the vagina is separated from the urogenital sinus by a thin tissue called
the hymen, usually with a small opening in it around birth.
Remnants of the cranial excretory tubules (mesonephros) may be retained in the
mesovarium (peritoneal folds containing the ovary). These remnants are the
epoöphoron and paroöphoron. Occasionally, a small portion of the mesonephric duct
may be found in the wall of the uterus or vagina that later forms a Gartner's cyst, which
feels like a round hard bump.
Descent of the Testicles
The testicles are retroperitoneal and they descend behind the peritoneal epithelium.
Before descending, their cranial parts are anchored to the diaphragmatic (cranial)
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suspensory ligament of the mesonephros and caudally to the inguinal (caudal)
ligament of the mesonephros: the gubernaculum.
First, under the influence of androgens acting through androgen receptors in the
cranial suspensory ligament, the ligament regresses, releasing its attachment to the testes.
Secondly, the testes then make a transabdominal descent down to the inguinal ring. In a
third phase, the transinguinal descent, the testes are brought into the scrotum. This
phase involves both the action of testosterone and the guidance of the inguinal ligament
of the mesonephros. Testicular descent begins in the 7th month and descent may not be
completed until birth. As it descends into the scrotum, the testes slide behind an
extension of the peritoneal cavity, the vaginal process. This is a potential weak point,
prone to intestinal herniation into the scrotum.
Descent of the Ovaries
While the paramesonephric ducts cross over medially, the ovaries move laterally. Their
positions are stabilized by two ligaments, both remnants of the mesonephros. Cranially,
the diaphragmatic ligament of the mesonephros becomes the suspensory ligament of
the ovary (containing the ovarian vessels). The superior portion of the inguinal ligament
of the mesonephros develops into the round ligament of the ovary, and its inferior
portion becomes the round ligament of the uterus. The round ligament of the uterus
terminates in the labia majora.
External Genitalia
Indifferent Stage
A very early midline elevation called the genital eminence is situated just cephalic to the
proctodeal depression. This structure soon develops into a prominent genital tubercle,
which is flanked by a pair of genital (urethral) folds extending to the proctodeum (an
ectodermal depression that will form the anal canal when ruptured). Between the genital
folds is the urogenital sinus. [The urogenital sinus area will become the urethral groove
in the male, and the vestibule in the female.] Somewhat lateral to the genital folds are
paired genital swellings. When the original cloacal membrane breaks down during the
8th week, the urogenital sinus opens up to the outside between the genital folds. An
endodermal urethral plate lines much of the open genital sinus. During the indifferent
stage, these structures are virtually identical in male and female embryos.
External Genitalia of Males
Under the influence of dihydrotestosterone (DHT), the genital tubercle undergoes a
second phase of elongation to form the penis or phallus, and the genital swellings enlarge
to form the scrotal pouches. During this elongation, the phallus pulls the urethral
(genital) folds forward so that they form the lateral walls of the urethral groove. The
epithelial lining of the groove, which is endodermal, forms the urethral plate. The male
urethra forms in a proximodistal direction by ventral folding and midline fusion of the
urethral folds. At the end of the 3rd month the folds close over the urethral plate,
forming the penile urethra. The most distal part of the urethra is formed in the 4th
month when ectodermal cells penetrate its tip, thus forming the external urethral
meatus. After the urethra has formed, the line of fusion of the urethral folds is marked
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by the persistence of a ventral raphe that passes between the scrotal swellings. The
scrotal swellings are separated by a scrotal septum.
External Genitalia of Females
In females the pattern of external genitalia is similar to the indifferent stage. The genital
tubercle becomes the clitoris and the genital folds, which do not fuse, become the labia
minora. The genital swellings become the labia majora. As mentioned earlier, the
urogenital groove in the female is open and forms the vestibule. The female urethra,
developing from the more cranial part of the urogenital sinus, is equivalent to the
prostatic urethra of the male.
Fetal sex determination can usually be done accurately at 16 weeks or later with
expert ultrasound.
Abnormalities of Sexual Differentiation
Turner's syndrome – Turner's syndrome (gonadal dysgenesis) results form a
chromosomal anomaly (45, XO). Individuals with this syndrome, which are
phenotypically female, possess primordial germ cells that degenerate shortly after
reaching the gonads. Differentiation of the gonad fails to occur, leading to the formation
of a streak gonad. These people have short stature, high arched palates, webbed neck,
shieldlike chest, renal abnormalities, and inverted nipples.
Klinefelter syndrome - Klinefelter syndrome people have a karyotype of 47,XXY or
variants of XXXY. Its occurrence is 1/500 males. Patients are characterized by
infertility, gynecomastia, and varying degrees of impaired sexual maturation.
Nondisjunction of the XX homologues is the most causative factor.
True hermaphroditism – Individuals with true hermaphroditism, which is extremely
rare, possess both testicular and ovarian tissue, Most cases are genetic mosaics. In some
case the gonad is both ovary and testis (ovotestis). Most are 46,XX and reared as
females.
Female pseudohermaphroditism – The people are genetically female (46,XX) and are
sex chromatin positive. The internal genitalia are female, but the external genitalia are
masculinized. These cases occur to either an excessive production of androgen hormones
from the adrenal cortex (congenital virulizing adrenal hyperplasia) or form
inappropriate hormonal treatment of pregnant women.
Male pseudohermaphroditism – These persons are sex chromatin negative or 46,XY.
Because this condition commonly results from inadequate hormone production by the
fetal testes, the phenotype can vary (i.e., internal and external parts vary as to male or
female).
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Testicular feminization (androgen insensitivity) syndrome – Here, individuals are
genetic males (46, XY), possess internal testes, but have a normal female external
phenotype, this they are raised as females. Often, this is not discovered until the person
seeks treatment for amenorrhea or is tested for sex chromatin before athletic events. The
testes produce testosterone, but there is a gene mutation on the X chromosome that
manufactures androgen receptors.
Questions
1. Which of the embryonic excretory systems is the first to regress and stop
functioning?
a. pronephros
b. mesonephros
c. metanephros
d. metanephric blastema
2.
The ureteric bud is an outgrowth of the ___________.
a. paramesonephric duct
b. metanephric blastema
c. mesonephric duct
d. cloaca
3. Several ____________ tubules will be incorporated into the metanephric blastema
and
become part of the adult kidney.
a. pronephros
b. mesonephros
c. metanephros
d. cloaca
4. The excretory units (glomeruli, tubules) of the kidney are derived from the
__________.
a. mononuclear phagocyte system
b. metanephric blastema
c. mesonephric duct
d. urogenital sinus
5.
The distal end of the __________ will form the urachus.
a. urogenital sinus
b. mesonephric duct
c. metanephric blastema
d. allantois
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6.
The solidified urachus will for the __________ ligament in the adult.
a. median umbilical
b. medial umbilical
c. lateral umbilical
d. falciform
7.
The wolffian duct is the alternative name for the ___________.
a. paramesonephric duct
b. urogenital sinus
c. mesonephric duct
d. allantois
8. The area flanked where the ureteric buds enter the bladder, and the mesonephric
ducts
also enter the bladder, but at a lower and more medial position, is called the
________.
a. cloaca
b. trigone
c. urachus
d. allantois
9.
_____________ can result in oligohydramnios and Potter facies.
a. renal agenesis
b. horseshoe kidney
c. exstrophy of the bladder
d. adult polycystic kidney disease
10. Defects in the production of polycystin proteins are seen in _______________.
a. renal agenesis
b. horseshoe kidney
c. exstrophy of the bladder
d. adult polycystic kidney disease
-------------------------------------------------------------------------------------------------------------11. In the female, sex chromatin results in the creation of a _________ due to extra Xchromosomal DNA not needed.
a. Sry gene
b. Y chromosome
c. Barr bodies
d. antimüllerian protein
12. The testes-determining factor gene is located on the _____________ chromosome.
1
3
a.
b.
c.
d.
long arm of the X
long arm of the Y
short arm of the X
short arm of the Y
13. Gender is determined when __________.
a. fertilization occurs
b. primordial cells migrate from the epiblast
c. primordial germ cells are in the yolk sac
d. oogonia are formed in the indifferent gonads
14. Sertoli cells (males) and the sex cords (male and female) are derived from
__________.
a. mesenchyme of the gonadal ridge
b. genital ridge surface (coelomic) epithelium
c. differentiated germ cells
d. mesonephric ducts
15. Interstitial cells of Leydig are derived from _______________.
a. mesenchyme of the gonadal ridge
b. genital ridge surface (coelomic) epithelium
c. differentiated germ cells
d. mesonephric ducts
16. Müllerian inhibiting substance is secreted by ___________.
a. Leydig cells
b. oogonia
c. Sertoli cells
d. thecal cells
17. In the female, follicular cells appear to be derived from __________
a. mesenchyme of the gonadal ridge
b. genital ridge surface (coelomic) epithelium
c. differentiated germ cells
d. mesonephric ducts
18. If the gender permits, the ___________ develop into the female genital duct system.
a. wolffian ducts
b. ureteric bud
c. urogenital sinus
d. müllerian ducts
19. In the male, the epididymus and vas deferens need _________ to develop and the
external genitalia need __________ to develop.
1
4
a.
b.
c.
d.
dihydrotestosterone / testosterone
estrogen / dihydrotestosterone
testosterone / dihydrotestosterone
testosterone / diethylstilbestrol
20. Androgen insensitivity syndrome is, mostly in part, due to lack of ___________.
a. testosterone receptors that help develop the vas deferens
b. androgen receptors in mesoderm that form the external male genitalia
c. estrogen receptors that form the external female genitalia
d. testes determining factor that form the testes
21. The vagina is formed from tissue of both the _________ and the ___________.
a. paramesonephric ducts / urogenital sinus
b. paramesonephric ducts / cloaca
c. mesonephric ducts / urogenital sinus
d. mesonephric ducts / cloaca
22. A Gartner's cyst in the uterus or vagina is a remnant of the ____________.
a. müllerian duct
b. peritoneum
c. wolffian duct
d. ureteric bud
23. Which of the following forms the clitoris in the female?
a. genital swellings
b. urethral folds
c. genital tubercle
d. urethral plate
24. Which of the following is 45, XO?
a. Turner's syndrome
b. Klinefelter's syndrome
c. true hermaphroditism
d. testicular feminization
25. Which of the following is 47, XXY or 48, XXXY?
a. Turner's syndrome
b. Klinefelter's syndrome
c. true hermaphroditism
d. testicular feminization