EXCRETORY AND REPRODUCTIVE

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EXCRETORY AND REPRODUCTIVE SYSTEM DEVELOPMENT
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4. Degenerates by end of 4th week of
development. 5. In species with functional
pronephros, branch of aorta will form a
glomerulus either adjacent to nephrostome in
peritoneal coelom or adjacent to tubule
Human embryo 1. Evident at about 20 days after
fertilization 2. 7-10 pairs of rudimentary
tubules in segmented mesoderm 3. Non-functional
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Human embryo 1. Develops during second month 2.
35-49 pairs of functional mesonephric tubules in
unsegmented intermediate mesoderm 3. 3 - 4
tubules adjacent to each somite
4. Extends from 10th - 26th somite 5. Induction -
Mesonephric (pronephric) duct must be present. If
removed, mesonephric tubules will not form. 6.
Evocation - masked morphogen
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Metanephros
Human embryo 1. Development begins at end of 1st
month with formation of ureteric bud 2.
Development continues for next 2 months, but
metanephric kidney is not functional until the
3rd month
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• Metanephric diverticulum will form
• ureter, Medulla of kidney
• 2. pelvis of kidney
• 3. major and minor calyxes
• 4. papillary collecting ducts

Metanephrogenic blastema Cortex of kidney -
metanephric nephrons
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Papillary collecting ducts
Metanephric diverticulum will form 1. ureter 2.
pelvis of kidney Medulla of kidney 3. major and
minor calyxes 4. papillary collecting ducts
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• Metanephric diverticulum will form
• ureter, Medulla of kidney
• .
• 2. pelvis of kidney
• .
• 3. major and minor calyxes
• .
• 4. papillary collecting ducts

Metanephrogenic blastema Cortex of kidney -
metanephric nephrons
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Metanephrogenic blastema will form Cortex of
kidney - metanephric nephrons
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CLOACAL REGION - SEPARATION OF THE DIGESTIVE AND
EXCRETORY SYSTEMS
Human Development 4 weeks
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CLOACAL REGION - SEPARATION OF THE DIGESTIVE AND
EXCRETORY SYSTEMS
SEE LECTURE PACKET FOR FIGURES
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CLOACAL REGION - SEPARATION OF THE DIGESTIVE AND
EXCRETORY SYSTEMS
SEE LECTURE PACKET FOR FIGURES
As the Rathke and Tourneux folds meet and fuse,
the establish the urorectal septum and separate
the urinary and digestive tracts from each other.
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As the Rathke and Tourneux folds meet and fuse,
the establish the urorectal septum and separate
the urinary and digestive tracts from each other.
SEE LECTURE PACKET FOR FIGURES
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Rathke folds fail to form
These or similar sorts of defects occur in 1 in
every 4000 births in the U.S.
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1. Early in mammalian development, the primordial
germ cells (PGCs) are found in a cluster in
extraembryonic endoderm of the yolk sac. 2. Prior
to about 1990, they were considered to be
endodermally derived. 3. Subsequent research has
identified these cells during the primitive
streak stage in presumptive extraembryonic
mesoderm of the epiblast. 4. These cells can be
identified by endogenous alkaline phosphatase
activity that other cells of the early embryo
lack. 5. The alkaline phosphatase will react
with a substrate that produces a colored reaction
product. 6. The PGCs are now considered to be
mesodermally derived. 7. They then migrate to the
endoderm, and subsequently migrate to the
developing gonads.
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Human male reproductive tract
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Human Development
gonadal ridge genital ridge
4 weeks

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Primordial germ cells migrate from the yolk sac
endoderm to the genital ridges during the 5th
week of human development.
Human Development
5 weeks
Gonads start to form during the 5th week, but at
this point they are equivalent in males and
females - i.e. not yet testis or ovary.
Rete blastema forms from germinal epithelium of
genital ridge in both males and females. Cells of
rete blastema migrate closer to mesonephric ducts.
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In human female embryos, proliferation of the
primary sex cords stops by the end of the 6th
week.
Human Development
6-7 weeks
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Differentiation of the gonads (testis or ovary)
will begin during the 7th week of development
(tunica albuginea in males). The tissues of the
genital ridge will bulge into the peritoneal
cavity and eventually will hang from a mesentary
- mesorchium in male and mesovarium in female.
7 weeks
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(epididymis vas deferens)
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SEE LECTURE PACKET FOR FIGURES
5-6 weeks
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Male and female reproductive tract -
ductwork Fate of the mesonephric and Mullarian
ducts.
Text
(6 - 7 weeks)
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SEE LECTURE PACKET FOR FIGURES
5-6 weeks
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SEE LECTURE PACKET FOR FIGURES
In the male, the remnants of the Mullarian ducts
are the vagina masculina and appendix testis
The mesonephric tubules degenerate in female
leaving some non-functional remnants called the
epoophoron near the ovary. The mesonephric ducts
degenerate in females however, they sometimes
leave a small non-functional duct called the
canal of Gartner that extends from the epoophoron
to the vagina.
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Female
Female
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Uterovaginal plate
SEE LECTURE PACKET FOR FIGURES
Uterovaginal plate
Mullers tubercle
Vaginal plate
Uterovaginal plate, vaginal plate, Mullers
Tubercle - other names for the sinovaginal
bulb. Vestibule - the region surrounding the
vaginal opening that is bordered by the labia
minora. Bartholins glands - paired glands, one
on either side of the vaginal opening, with ducts
opening into the vestibule. Secrete a mucus that
lubricates the vestibular walls. Developmentally
homologous to Cowpers (bulbourethral) glands in
the male.
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MALE AND FEMALE EXTERNAL GENITAL DEVELOPMENT SEE
LECTURE PACKET FOR FIGURES
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MALE AND FEMALE EXTERNAL GENITAL DEVELOPMENT SEE
LECTURE PACKET FOR FIGURES
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