Download 10th-12th week

Renal System Development
10th week
~12 weeks
Development of Three Nephric Systems
Cervical Nephrotomes & Mesonephroi
Upper thoracic
region to the
third lumbar
region
Development of Three Nephric Systems
Cervical Nephrotomes & Mesonephroi
Renal Corpuscle:
Glomerulus &
Bowman’s capsule
Mesonephric
excretory unit:
Renal corpuscle &
Nephric tubule
26 Days~22 days
6-10weeks-func
>10-regress.
Mesonephric
ducts in females
regress and in
males they persist
to form parts of
male genital duct
system.
Development of Three Nephric Systems.
Mesonephroi & Metanephroi
Regress to
the 1st three
lumbar levels
Sacral
Region
Reciprocal
induction
~22 days
Mesonephric
duct forming
Collecting Duct System of the Metanephroi
Sequence of bifurcations.
Sequence of bifurcations
~22 days
Sequence of bifurcations.
11 additional
generations of
bifurcations-->
1-3 mil branches.
~22 days
32nd Week
8 months
Nephron Development
Contains neural crest derived neurons. They play a role in
nephron induction. The neurons regulate blood flow and
secretory function.
~22 days
9th week
Nephron Development
10th week
10weeks+-->func: gl. filtrate to urine,
but main func to produce amniotic fl.
Definitive Kidney Architecture
Minor calyx
Major calyx
Pelvis
Contains the nephrons.
5th-15th weeks Renal Pyramid (inner medulla)
Contains the loops of Henle
and collecting ducts .
Kidneys ascend from a sacral to lumbar
location
~22 days
Movement of the Kidneys
~22 days
Figure 8-6
Anomalies during kidney ascent
Inferior
mesenteric
artery
~22 days
The remainder of the urinary tract develops
from the hingut endoderm
Cloacal expansion and partition
4th week
Female
Male
Vestibule of
vagina
Penile
urethra
Membranous
urethra
membranous
& prostatic
urethra
6th week
Exstrophy of the mesonephric ducts and
ureteric buds.
4-6 weeks
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-Endoderm grows over trigone
-Splanchnopleuric mesoderm associated
with the hindgut forms the smooth
muscle of the bladder wall.
Ureteric bud or metanephros induction defects
Renal agenesis
A. Defects in the inductive interaction between the ureteric bud and
metanephric blastema may cause renal agenesis.
B. Bilateral renal agenesis results in death. Unilateral renal agenesis
results in hypertrophic kidney.
C. 75% of the cases involving renal agenesis occur in males.
D. Bilateral renal agenesis can also result in oligohydramnios, causing
Potter’s syndrome (deformed limbs and facial defects.
E. Unilateral renal agenesis is usually associated with heart defects
and constrictions of the gastrointestinal tract.
Genital System Development
4-6 weeks
~12 weeks
The genital and urinary systems develop in
close conjunction
Primitive sex cord & Paramesonephric duct
development
(mullerian)
5-6 weeks
Third thoracic segment
caudally to the posterior
wall of the urogenital sinus
Virtually identical male and female genital
systems.
6th week
At this point the sex
cords have both a
cortical and medullary
region. After the
6th week these regions
pursue different fates in
the male and female.
Basis of sex differentiation
Autosomes and Sex Chromosomes
1. There is a total complement of 46 chromosomes, 22 pairs consist of matching
homologous chromosomes called autosomes. The 23rd pair are called the sex
chromosomes because they determine the sex of the individual.
2. XX individuals are genetically female.
XY individuals are genetically male.
Subsequent phases of sexual development are controlled by both the sex
chromosome genes and by the hormones and factors encoded by the
autosomes.
3. The sex-determining region of the Y chromosome (SRY) encodes a
transcription factor that controls the choice between the male and female
developmental paths.
Basis of sex differentiation
Autosomes and Sex Chromosomes
4. Male development is triggered when SRY is expressed in the sex cords
during the indifferent phase.
5. Thus the male pathway is actively
induced.
Figure 10-13
Male genital (internal) Development
Sertoli cell differentiation in the medullary
sex cords
~7th week
Male genital (internal) Development
Anti-Mullerian hormone (AMH) secretion
by Sertoli cells
(reminant of
~8-12th week
cranial end
of mesonephric duct)
Sertoli
Cells
Ductuli efferentes
(reminant of inferior
mesonephric tubules)
Male genital (internal) Development
Differentiation of the mesonephric ducts of
the male
~10th-12th week
Male genital (internal) Development
Differentiation of the accessory glands of
the male urethra
~10th-12th weeks
Female genital (internal) development
Absence of a Y chromosome
Female genital (internal) development
Absence of AMH in the female embryo
Female genital (internal) development
Absence of AMH in the female embryo
Female genital (internal) development
Absence of AMH in the female embryo
External genitalia development
Male and Female external genitalia develop
from the same primordia
or urethral fold
External genitalia is
similar in male and
female embryos
through the
12th week.
External genitalia development.
Male external genitalia.
12 weeks
14
weeks
External genitalia development
Female external genitalia
7th week
3rd month
The gubernaculum controls the descent of
the testes and ovaries
The descent of the testes
The gubernaculum controls the descent of
the testes and ovaries
The descent of the testes
The gubernaculum controls the descent of
the testes and ovaries
The descent of the testes
The gubernaculum controls the descent of
the testes and ovarie
The descent of the ovaries
Abnormal dev of the genital system
Testicular Feminization Syndrome--> the androgen
receptors are abnormal or lacking, resulting in the formation
of a blind-ending vagina (Male genotype, Female external
phenotype, no ovaries). Since the testes are still present and
AMH is produced, the paramesonephric ducts regress (Thus
no superior vagina, uterus, or fallopian tubes).
Abnormal dev of the genital system
True hermaphrodites--> have both ovarian and testicular
tissue. The gonads are usually a composite ovotestes
containing both seminiferous tubules and follicles.
Or an individual may have an ovary on one side and a testes
on the other side.
Most true hermaphrodites are reared as
males since a phallus is usually present at birth.