Download Chapter 16_17_Urogenital - V14-Study

Chapters 16, 17: Urinary and Reproductive Sections- LO
1. What is the relationship of the intermediate mesoderm to the paraxial mesoderm during
early development? Where are these tissues located relative to the coelom?
The paraxial mesoderm is a solid bar of mesenchyme on either side of the neural tube, while the
intermediate mesoderm (forms the urogenital system) lies between it and the lateral plate
mesoderm (layers surrounding the coelom). The intermediate mesoderm is able to form a kidney
under the inductive influences of the paraxial mesoderm.
2. What is the functional unit of the kidney? Nephron (nephric tubule)
3. The specific part of the urogenital ridge that forms the urinary system is the nephrogenic
ridge. The specific part of the urogenital ridge that forms the genital system is the gonadal
ridge.
4. Describe how these specific parts of the pronephric kidney relate to the mesonephric kidney.
Only in lower vertebrates, the intermediate mesoderm divides into nephrotomoes that have a
nephrocoele (cavity) and nephrostome (peritoneal funnel), which connects the nephrocoele
with the intraembryonic coelom. These structures form the pronephric tubules and ducts.
Pronephric tubule – mesonephric tubule (consider location)
The pronephric tubules are evaginations of the nephrotome in the cephalic region, while
mesonephric tubules are more advanced tubules (each has individual internal glomerulus)
formed in the trunk region from the mesonephric ridge.
Pronephric duct – mesonephric duct
Lateral ends of the pronephric tubules bend and fuse to form a pronephric duct, which services
the mesonephric tubules. The mesonephric duct induces the mesonephric kidney.
5. Does the pronephric kidney function during development in most mammals?
Yes
No (only functional in lower vertebrates)
6. What structure forms from the caudal pronephric duct?
7. Does the mesonephric kidney function during any stage of development?
Yes (during embryonic life)
No
Is urine formed?
Yes (may function to form urine briefly in some mammalian embryos)
No
8. From what specific tissue do the mesonephric tubules form?
Form from the mesonephric ridge, which consists of intermediate mesoderm on the cranial part
of the nephrogenic ridge.
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9. What is a glomerular (Bowman’s) capsule (what is its derivation) in both the
mesonephric and metanephric kidney?
Structures of the mesonephric tubules that filter blood.
10. In mammals what do the mesonephric duct and mesonephric tubules ultimately form in the
male and female?
Male
The cranial mesonephric tubule forms the efferent ductules (testis) and the lobules of the head
of the epididymus
The caudal mesonephric tubules form the paradidymus (remnant)
The mesonephric duct forms the epididymus, ductus deferens, and the ejaculatory duct (urethra)
Female
The cranial mesonephric tubules form the tubules of the epoophoron (remnant)
The caudal mesonephric tubules form the paroophron (remnant)
11. What is the origin of the peritoneum? What is the difference between parietal and visceral
peritoneum?
Peritoneum is the lining of the coelom derived from mesodermal folds. The parietal
peritoneum lines the walls of the coelom, while the visceral peritoneum covers any organs that
projects into the coelom.
12. What is the origin of the genital folds?
Left and right mesonephric ducts move closer together, which results in the fusion of the
mesodermal folds. The fused structures suspending the mesonephric ducts are called the genital
folds (between the bladder and the rectum).
13. What are the two separate primordia that form the metanephric kidney? From what specific
tissues are they both derived?
Metanephric diverticulum (ureteric bud) is an outgrowth of mesonephric duct near its entrance
into the cloaca and the metanephrogenic blastema is derived from the condensation of
intermediate mesoderm in the trunk region of the embryo (caudal part of the nephrogenic ridge).
14. The metanephric diverticulum (ureteric bud) is the primordium of what adult structures?
Ureter, renal pelvis, and collecting tubules.
15. From what structure is the metanephric tubule formed, and what does this tubule eventually
form?
The metanephric tubule (renal tubule) forms from the metanephrogenic blastema, eventually
destined to become the nephron.
16. What are the parts of the renal corpuscle? Where are the renal corpuscles located?
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The renal corpuscle is the glomerulus covered by the glomerular capsule (Bowman’s capsule)
of the nephron. It is located in the outer cortical region of the kidney.
17. Describe the migration of the kidneys and the change in kidney orientation. Why is this
clinically important?
The kidney originally lies in the pelvic cavity the embryo, where the renal pelvis and ureters are
at the renal caudal pole and the paired external iliac arteries are located cranially. Cranial kidney
migration occurs as the same time as the regression of the mesonephric “kidneys”, so that they
ultimately lie more cranially in the sublumbar region, become in contact with the adrenal glands,
and the renal pelvis and ureters face the body midline. Their entire migration is made in the
retroperitoneal position.
18. Describe the pattern of branching of the blood vessels within the metanephric kidney.
Each blood vessel that runs into the metanephrogenic blastema immediately branches into a
number of arteries. The major branches of the renal artery are called the interlobar arteries.
Each interlobar artery terminates as the arcuate artery at the cortico-medullary junction of the
developing metanephric kidney. Each arcuate artery branches into interlobar and afferent
arterioles that form the glomerulus.
19. Describe the shape of the embryonic kidney. What animals exhibit this embryonic
configuration as an adult?
In all species, the branching of the ureteric bud follows the vascular branching pattern, ultimately
resulting in the embryonic kidney resembling a bunch of grapes (many lobes). The adult kidney
of the cow resembles an embryonic kidney.
20. Describe the parts of a renal “lobe” and its relationship to the developing uteric bud.
Each lobe (grape) is serviced by a branch of the ureteric bud. Each lobe has an outer cortex and
inner medulla. The medullary region of each lobe is tapered, forming a renal papilla, each of
which is cupped by a branch of the ureteric bud, forming a minor calyx.
21. What is a renal calyx? Do the kidneys of all domestic species exhibit calyces?
As the kidney matures, varying degrees of fusion of the lobes takes place (also involves the
fusion of associated ureteric bud branches and blood vessels). The fusion of these lobes results in
the renal calyx.
22. Do the kidneys of animals that have calyces function differently from kidneys that have a
renal crest? (I am asking about basic kidney function – making urine)
Yes No (Fusion of lobes has no effect on the basic function of the kidney)
23. For these species (cow, pig, horse, small ruminants, carnivores) answer the following
questions.
Cow
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Lobated, multipyramidal
2 major calyces and minor calyces
NO renal pelvis
Pig
Kidney is multipyramidal
Cortex fused
Medullary regions partially fused
Calyces and renal pelvis
Horse, small ruminants, carnivores
Kidney is unipyramidal
Cortex and medulla fused
Fused renal papillae form renal crest
Renal pelvis only (no calyces)
24. In what species is it common to find double renal arteries, and developmentally, how does
this happen? Why is this clinically important?
Because the lobes and branches of the ureteric bud fuse in carnivores (followed by the primary
branches of the renal artery), it is common to see double renal arteries. This is surgically
important if a nephrectomy and/or kidney transplant is planned.
25. What dilates to form the cloaca, and what opens into it? At this early stage is the cloaca
open or blind-ended?
The gut caudal to the point of origin of the allantois dilates to form the cloaca, into which open
the mesonephric tubules. At this stage, the cloaca is blind-ended.
26. What is the difference between the anorectal canal and the urogenital sinus, and how do they
form? What is the relationship of the perineal body to these two structures?
The cloaca divides into a dorsal part, which eventually forms the anorectal canal, and a ventral
part called the urogenital sinus. This division results from the growth of a crescent-shaped fold
called the urorectal septum. Eventually separation between the anorectal canal (anus) and
urogenital sinus is comprised on a remnant of mesodermal tissue known as the perineal body.
27. What are the 3 parts of the urogenital sinus and what do they eventually form?
A. Cranial vesicular part that is continuous with the allantois and will form the urinary bladder
B. Middle pelvic part that forms the pelvic urethra
C. Caudal phallic part that associates with the genital tubercle
28. What is the urachus?
In the early stages of bladder formation, the vesicular part of the urogenital sinus is continuous
with the allantois. The allantoic stalk gradually degenerates, leaving behind a fibrous cord called
the urachus, which extends from the apex of the developing urinary bladder to the umbilicus.
29. What is the trigone of the bladder and how does it develop (from what tissue is it formed)?
The triangular region on the dorsal wall of the adult bladder is called the trigone, which is the
result of the mesonephric ducts being incorporated into the dorsal bladder as it expanded. The
trigone is from mesoderm, while the rest of the bladder is from endoderm.
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30. What is the major developmental problem associated with Kidney anomalies?
Are there obvious symptoms related to each anomaly, and if so what are they?
Hydronephrosis (atrophy of kidney tissue), cystic kidney (small cysts, renal insufficiency),
renal cortical hypoplasia (renal insufficiency), congenital nephromas (highly malignant
cancer), patent urachus (dribbling of urine)
What anomalies are asymptomatic?
Pelvic and horseshoe kidney, unilateral renal agenesis
What anomalies have different symptoms in the male versus the female?
Ectopic ureter results in incontinence only in females
Are there differences if the problem is unilateral versus bilateral?
In renal agenesis, bilateral agenesis is lethal, while unilateral agenesis is asymptomatic (due to
compensatory hypertrophy of unaffected kidney)
31. Developmentally, what are the 3 sources of the gonad?
Primordial germ cells, mesenchyme of the gonadal ridge, mesothelium lining the intraembryonic
coelom
32. Describe the path of the primordial germ cells from the yolk sac to the gonads in mammals.
How does this migration differ in the chicken? Include important inductive factors, and how
these cells can be characterized.
The primordial germ cells are derived from the yolk sac endoderm and are transformed into
future primordial germ cells by inductive factors (BMP-4). At this point, the cells are large and
have a high content of alkaline phosphatase. They aggregate into a small cluster in the yolk sac
mesoderm and begin to migrate to the wall of the hindgut via the allantoic stalk. Then, they
travel through the dorsal mesentery via amoeboid movement to the gonadal ridges, which
secrete chemotactic substances that attract primordial cells. Leukemia inhibitory factor
promotes cells to undergo mitosis throughout their journey (~2000 reach each gonadal ridge).
In birds, germ cells can migrate via the vascular system.
33. What is a teratoma?
Abnormal migration of primordial germ cells results in ectopic embryogenesis of teratomas,
neoplasms composed of many tissue types, including hair, bone, teeth, muscle, and nerve tissues.
34. What is the indifferent stage of gonadal development?
The stage at which both male and female gonads exhibit similar morphological features.
35. What is the cranial pole of the gonadal ridge called, and what structure does it form? What
are the two cell types form the cortex and medulla in this structure?
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The mesenchyme of the cranial pole of the gonadal ridge is called the adrenocortical
primordium and forms the adrenal cortex, while the adrenal medulla is formed from neural
crest cells.
36. Are gonads formed if the primordial germ cells fail to reach the gonadal ridges?
Yes
No
37. Describe the formation of the primitive sex cords. What eventually happens to these cords
in the male versus the female?
At the time the primordial germ cells invade the gonadal ridge, the epithelium proliferates and
penetrates the underlying mesenchyme to form irregularly-shaped primitive sex cords that
surround germ cells during infiltration (in both sexes). Under the influence of TDF, the sex cords
develop into seminiferous tubules. In the female, they disintigrate, leaving behind a vascular
stroma called the ovarian medulla.
38. Describe the formation of the paramesonephric duct. What eventually happens to this
structure in the male versus the female?
In both sexes, a new pair of paramesonephric ducts develop lateral to the mesonephric ducts.
They extend from the thoracic region to the urogenital sinus and fuse at their junction with the
urogenital sinus.
39. What is the relationship of the paramesonephric duct to the coelom. As a result of this
relationship, what would happen to sperm in the female tract (specifically at the cranial end
– the answer is not in the text, see if you can derive the answer).
Cranially, the paramesonephric duct opens into the coelomic cavity.
40. For sex determination understand the following:
The sperm bears either an X or Y chromosome, while the ovum contains an X chromosome.
Fertilization of the ovum with a sperm carrying an X chromosome results in a genetic female
(XX), while fertilization with a Y-carrying sperm results in a genetic male (XY). In birds, the
male is ZZ, the female ZW, though the mechanism is not understood.
The gonad has an inherent tendency to develop an ovary, unless driven by specific genes on the
Y-chromosome. The testis-determining gene on the Y-chromosome is called SRY (member of
the SOX family), which expresses testis determining factor (TDF).
TDF triggers testis formation by inhibiting DAX1, which is X-linked and expressed in the
indifferent gonad. If DAX1 is not inhibited, the indifferent gonad forms an ovary.
41. In mammals, what determines secondary sexual characteristics?
The development of the mesonephric/paramesonephric duct systems and external genitalia (2°
sex characteristics) is determined by endocrine factors (estrogens and androgens).
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42. In some reptiles how does temperature affect the development of males versus females.
How does the hypothesis of aromatase involvement in this mechanism relate to concerns
about environmental pollutants that act as synthetic estrogens?
Aromatase converts testosterone to estrogen (needed for ovarian development). At low
temperatures, there is low aromatase activity, and a greater likelihood of forming males.
43. How does the tunica albuginea of the testes develop?
The tunica albuginea, capsule of the testis, is formed by increased mesenchymal condensation
underneath the coelomic epithelium. This thickening layer isolates the sex cords, in which lie
primordial germ cells, from surface epithelium.
44. From what are the seminiferous tubules and rete derived?
The cells of the sex cords proliferate by mitosis, and the outer portion forms elongated
horseshoe-shaped cords that extend towards the surface epithelium, but do not contact the tunica
albuginea. As this point, the sex cords are now called testis (medullary) cords. The inner
portions of testis cordis extend deep into the mesenchyme of the gonadal ridge and are
forerunners of the seminiferous tubules. The free limbs of the horseshoe-shaped testis cords
form a plexus called the rete testis.
45. What structures do the mesonephric tubes form? How does this development relate to the
developing seminiferous tubules?
The mesonephric tubules mostly degenerate. The remnants loose their glomerular end and attach
to the rete testis to form the efferent tubules. The mesonephric duct will become the
epididymus and ductus deferens (vas deferens)
46. What is the derivation of the Sertoli (sustentacular cells) and the Leydig (interstitial cells).
What cells are homologous in the female?
Original epithelial cells of the coelomic membrane, after forming the testis cords, form Sertoli
(sustentacular) cells. The mesenchymal cells of the gonadal ridge form Leydig (interstitial) cells.
The follicular cells of the female are homologous to the Sertoli cells.
47. In the male, how is the paramesonephric duct prevented from developing?
Once the Sertoli cells differentiate, they secrete a glycoprotein hormone, anti-Mullerian
hormone (AMH), which suppresses development of the paramesonephric duct. A remnant of the
duct may remain within the genital fold as the uterus masculinus.
48. What happens to the initial set of sex cords in the ovary?
The primitive sex cords of the female disintegrate, leaving behind primitive germ cells and a
vascular stroma that is later dubbed the ovarian medulla.
49. Why do secondary sex cords form in the ovary, but not in the testicle?
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Because the female fails to develop the tunica albuginea, the primary sex cords disintegrate. The
continual proliferation of the surface epithelium at the gonadal ridge gives rise to secondary sex
cords.
50. In what layer of the ovary are the primordial germ cells located in most mammals?
Cortex
Medulla
51. Describe follicularization. Why is this important?
Primordial follicles form when surface epithelium (germinal epithelium) forms follicular cells
and the germ cells they contain develop into oogonia. These oogonia arrest in the late prophase I
of meiosis until maturity. The delay if this meiosis enables the germ cells to be encapsulated by
follicular cells (follicularization), a process that ensures their survival.
52. Why does the mesonephric duct system regress in the female?
The mesonephric duct system regresses in the absence of testosterone and the paramesonephric
duct system develops in absence of AMH.
53. Describe the transformation of the paramesonephric duct in the female. What are the results
of differential fusion?
The paramesonephric ducts form the major portion of the female genital tract. Cranially, these
ducts form the oviducts. They are open to the coelomic cavity via a funnel-shaped expansion,
which will develop into the infundibulum of the oviduct. Caudally, the ducts fuseto form the
body of the uterus, cervix, and cranial vagina. The coelomic membrane (pre-peritoneum) with
which they associate suspends the ducts, eventually developing into the broad ligament of the
uterus (the genital fold in the male).
There is a variety of the degree of fusion of the paramesonephric ducts. No fusion results in
vagina duplex-uterus duplex, seen in marsupials, bats, and some rodents. Fusion of all but the
oviducts results in vagina simplex, seen in primates.
54. Developmentally describe the difference in the cranial and caudal vagina.
The cranial vagina develops from the fusion of the caudal paramesonephric ducts. The caudal
vagina forms from the urogenital sinus.
55. What happens to the cranial gonadal ligament in the male versus the female and what is its
relative importance in each sex?
The cranial gonadal ligament forms from mesenchymal condensation at the cranial pole of the
indifferent gonad. Because the mesonephros is retained in the male, this ligament is not welldefined and is transient at best. In the female (carnivores), this ligament is retained as the
suspensory ligament of the ovary.
56. What happens to the caudal gonadal ligament in the male versus the female?
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The caudal gonadal ligament forms from mesenchymal condensation at the caudal pole of the
indifferent gonad. In the male, this ligament is called the gubernaculum, which during the
indifferent stage extends from the caudal pole to the genital swelling. The gubernaculum forms
the proper ligament of the testis and the ligament of the tail of the epididymus. In the female,
the caudal gonadal ligament forms the proper ligament of the ovary and the round ligament of
the uterus.
57. What forms the broad ligament in the female, and what structures are associated with it?
Cranially, the paramesonephric ducts form the oviducts and are open to the coelomic cavity via a
funnel-shaped expansion. Caudally, the ducts fuse to form the body of the uterus, cervix, and
cranial vagina. The coelomic membrane (pre-peritoneum) with which the ducts associate
suspends the ducts and eventually develops into the broad ligament of the uterus. The part of
the broad ligament attaching to the ovary is the mesovarium. The part of the broad ligament
suspending the cranial part of the paramesonephric duct forms the mesosalphinx.
58. Describe the 3 phases of descent of the testes. Understand the following terms relative to
this descent.
Both ovaries and testes assume a position caudal to their site of origin. Their change of position
is called the descent of the gonads. In the male, the testes descend to the scrotum. In the females,
the ovaries move toward the pelvis within the abdomen. Phase I of the descent of the testes
involves regression of the cranial gonadal ligament. This is initiated by androgens from
interstitial cells and permits caudal migration of the testis (and mesonephric kidney). Phase II
involves transabdominal descent of the testis to the level of the deep inguinal ring. A insulin-like
peptide (product of INSL3 gene) of testicular interstitial cells may be involved in the migration.
Phase III consists of transinguinal descent and involves testosterone and the gubernaculum. The
gubernaculums swells, causing the inguinal canal to enlarge, facilitating testis descent. The
process of descent is passive and related to the shortening of the gubernaculum. The testis enter
the scrotum. The inside of the scrotum is lined by parietal peritoneum and the testis covered by
visceral peritoneum. Failure of normal descent of the testis into scrotum (testis may reside in
abdomen or inguinal canal) is called cryptorchidism. Unilaterally, male can be fertile.
Bilaterally, this condition results in sterility.
59. Into what structures do the three parts of the urogenital sinus develop?
A. Cranial vesicular part is continuous with the allantois and will form the urinary bladder
B. Middle pelvic part forms the pelvic urethra (the urethral endoderm forms the prostate and
bulbourethral glands in the male, but the urethra and caudal vagina in the female)
C. Caudal phallic part associates with the genital tubercle
60. From what are the round ligaments of the bladder derived?
In large animals, the fibrosed umbilical arteries form the round ligament of the bladder, and
are enclosed in lateral vesical ligaments.
61. What does the caudal part of the urogenital sinus form in the female?
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The caudal part of the urogenital sinus retains its embryonic form as the vestibule, from which
arise the vestibular glands.
62. What is formed where the ventral cloacal folds unite? What does this structure form in the
male versus the female?
The cloacal folds unite ventrally to form a genital tubercle (phallus). In the male, the genital
tubercle elongates to form the glans penis. In the female, the genital tubercle forms the clitoris.
63. As the urorectal septum grows, the cloacal folds are split into what two folds? What comes
to eventually lie between these two sets of folds?
The cloacal folds are split into urogenital folds and anal folds. Between these two folds, the
remnant of cloacal folds fuse along the midline forming the perineal raphe.
64. What do the genital or labioscrotal swellings form in the male versus the female?
In the male, these swellings fuse to form the raphe of the scrotum. In the female, these swellings
do not fuse, but form the labia (in domestic animals) or labia majora (in primates).
65. Describe the formation of the urethra in the male phallus. What hormone controls this
development? What anomalies can result if this development does not occur properly?
The external genital development in the male is controlled by dihydrotestosterone (DHT).
Under its influence, the genital tubercle elongates and forms the glans penis while the urethral
folds fuse to enclose the penile urethra.
66. From what tissue are the corpus cavernosum, corpus spongiosum, and os penis formed?
Blood sinuses form in the mesenchyme of the penis to form the corpus cavernosum, and around
the penile urethra to form the corpus spongiosum. These spongy tissues do not reach maximal
growth until sexual maturity. In dogs, rodents, and marine mammals, mesenchyme ossification
results in formation of an os penis.
67. Describe three things that happen during development of the female external genitalia that
do not happen during development of the male genitalia.
In the female, the perineum does not lengthen, the phallus does not elongate and the urethral
folds and labioscrotal swellings do not fuse.
68. From what tissues do mammary glands develop?
Mammary glands are modified cutaneous glands. Their primordial develop as two linear
ectodermal thickenings (mammary ridges) on the ventrolateral surface of the trunk, extending
from thoracic to pelvic limb buds.
69. How does the development of the mammary glands differ in their distribution among the
primates, carnivores, and ruminants?
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In carnivores and pigs, the mammary ridges remain distinct, extending from the axillary space to
the inguinal space. In ruminant and horses, the cranial part of the mammary ridges disappear,
limiting the ridges to the inguinal region.
70. What forms the lactiferous ducts, and is the formation identical in all mammals?
Focal condensation of ectoderm occurs at specific points along the mammary ridge in the. At
these sites, the ectoderm proliferates and invaginates into the underlying somatic mesoderm,
forming lactiferous ducts. The number of lactiferous ducts that form at each site are species
specific, ranging from 1 (cow, ewe, doe), 2 (mare, sow), or several (carnivores).
71. How do supernumerary teats occur?
At the site of invagination, the ectoderm and underlying mesoderm proliferate to form a teat, on
which the lactiferous ducts open (by invagination). Supernumerary teats are common, and
develop when mammary ridge remnants remain.
72. What is a true hermaphrodite?
True hermaphrodites are rare, and have both testicular and ovarian tissues. The external
genitalia may phenotypically appear male, female, or a combination of both. Intersex animals
(pseudohermaphrodites) are more common, where the animal has the gonads of one sex and the
phenotype of another.
73. What kinds of anomalies can result from defective separation of the urogenital sinus from
the anorectal canal?
Anomalies result in the formation of various types of fistulas. These problems include
imperporate anus, rectal atresia with urinary fistula, and rectal atresia with vaginal fistula.
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