Module 6: Development of the Urinary and Genital Systems Flashcards
What does the urinary system consist of?
kidneys, bladders, ureters, and urethra
What is the urinary system responsible for?
production and elimination of urine
What does the genital system consist of?
external genitalia, internal organs, gamete/hormone producing gonads
What is the genital system responsible for?
reproductive activity, sexual satisfaction, hormone production
What are the 3 mesoderm divisions?
paraxial, intermediate, lateral
What does the paraxial mesoderm form?
muscle, CT, and somites
What does the intermediate mesoderm form?
kidneys and genitals
What does the lateral mesoderm form?
pharyngeal arches and limbs
When the development of the urinary and genital systems start?
around week 4
What are the urogenital ridges?
parallel ridges on either side of the midline of the embryo made out of intermediate mesoderm
What are the urogenital ridges divided into?
genital and nephrogenic ridges
What will the genital ridge develop into?
the genital system
What will the nephrogenic ridge develop into?
urinary tract
What type of cell does the kidney contain?
nephrons
What makes up the excretory portion of the kidney?
glomerulus, proximal convoluted tubule, loop of henle, distal convoluted tubule
What makes up the collecting portion of the kidney?
collecting ducts and tubules (minor and major calyces), renal pelvis, ureter
What 3 systems form within the nephrogenic ridge?
pronephros, mesonephros, metanephros
What is the pronephros?
- first and most cranial kidney system
- develops in the cervical region during the 4th week and regresses by the end of the week
- vesicles formed by intermediate mesoderm link together to form the pronephric duct
Where does the nephrogenic ridge start to appear?
opposite the cervical segments of the embryo
What does the pronephric duct open into?
caudal tip opens into the cloaca
During regression of the pronephros, what regresses and what remains?
pronephric part of the nephrogenic ridge and pronephric duct -> regresses, remainder is the mesonephric duct
What is the mesonephros?
- formed during the regression of the pronephros
- develops in the thoracic and lumbar regions
- functions as the primitive kidneys and urinary system for week 4-12
- regresses in females
- forms several structures of the male genital system
What are the 2 components of the mesonephros?
mesonephric tubules and mesonephric duct
What are the mesonephric tubules?
associated with the glomeruli and drain into the mesonephric duct
What do the lateral ends of the mesonephric tubules do?
fuse and open into the duct
What do the medial ends of the mesonephric tubules do?
associate with blood vessels by lengthening toward and around the glomeruli
What is the mesonephric duct?
attaches to the cloaca and forms a primitive excretion pattern
What is the metanephros?
- will eventually become the adult kidney
- appears during the 5th week in the lumbosacral region
- replaces the primitive urinary system of the mesonephros
What is the ureteric bud?
- epithelial outgrowth of the mesonephric duct
- grows into the metanephric tissue to form the metanephric system
What are the 2 components of the metanephric system?
the collecting and excretory systems
When does the metanephros system begin functioning?
week 12
When does the collecting system start developing?
week 6
What are the steps to collecting system development?
penetration - ureteric bud penetrates the metanephric tissue and dilates to form the primitive renal pelvis and major calyces
division - major calyx forms 2 new buds that subdivide until 12 generations of tubules have developed
formation - gens 2-4 form the minor calyces, gens 5-12 form the renal pyramids and the collecting tubules
What is a nephric vesicle?
induced to form the metanephric tissue on the tip of each collecting tubule; develop into the nephric tubules
What are nephrons made up of?
nephric tubules and glomeruli
How do the kidneys ascend?
- initially they lie close to each other on opposite sides of the sacral segments
- start to ascend to the posterior abdominal wall during week 6-9 and medially rotate so that hiluses face medially
What are the 3 portions of the urogenital sinus
urinary bladder, urethral portion, phallic portion
What does the urethral portion gives rise to?
the prostatic urethra in males and urethra in females
What does the phallic portion gives rise to ?
the clitoris and penis
What do the mesonephric ducts give rise to?
the ureters and the ejaculatory duct in males
What are the gonads responsible for?
producing gametes and sex hormones
What are the genital ducts responsible for?
transportation of the gametes through the genital system
What is the external genitalia responsible for?
protect the internal genital tract from infection, sensory tissues during sex, assist in urination
What are the gonads, genital ducts and external genitalia in females?
ovaries, fallopian tubes, uterus, vagina, vulva
What are the gonads, genital ducts and external genitalia in males?
testes, epididymis, vas deferens, and urethra, penis, and scrotum
When does gonad differentiation begin?
week 7
What induces gonad development?
primordial germ cells
Where do the primordial germ cells reside?
in the genital ridges during the indifferent stage
Where do primordial germ cells migrate from?
migrate through the primitive pit and reside in the wall of the yolk sac during week 3, migrate along the dorsal mesentery and invade the genital ridges during week 6
What happens before the arrival of the primordial germ layers?
epithelium proliferates to form primitive sex cords
What are the primitive sex cords?
predecessor to the cords in the testis and cortical cords
When gene determines which gonads develop?
SRY gene found on the Y chromosome
What happens in the presence of the SRY gene?
causes primitive sex cords to penetrate deep into the medulla of the genital ridge to form the testis cords
What are Sertoli cells?
develop from surface epithelium and produce AMH
What are Leydig cells?
develop from the genital ridge and produce testosterone
Why are testosterone and AMH important?
play roles in inducing the development of the genital ducts and external genitalia
What is the rete testis?
network of tubules formed from the testis cords
What is the tunica albuginea?
layer of CT that separates the rete testis from the surface epithelium
What happens in the absence of the SRY gene?
primitive sex cords dissociate into irregular cell clusters that contain primordial germ cells that reside in the ovarian medulla
What are cortical cords?
proliferations of the surface epithelium that split into isolated cell clusters
What are primordial follicles?
oogonium surrounded by cell clusters and follicular cells
How many pairs of genital ducts to embryos develop during week 4?
2 - Wolffian ducts (males), Mullerian ducts (females)
What happens to the genital ducts in males?
AMH causes the Mullerian ducts to regress and testosterone ensures the Wolffian ducts persist
What does the Wolffian duct differentiate into?
epididymis, vas deferens, seminal vesicles, ejaculatory duct
What are the efferent ductules?
joined seminiferous tubules and epigenital tubules that connect to the Wolffian duct
What is the paradidymis?
vestiges formed by the paragenital tubules
What is the epididymis?
convoluted structure below the entrance to the efferent ductules
What is the vas deferens?
portion of the Wolffian duct from the end of the epididymis to the seminal vesicles
What is the ejaculatory duct?
portion of the Wolffian duct beyond the seminal vesicle
What happens to the genital ducts in females?
absence of testosterone causes the Mullerian ducts to persist and the Wolffian ducts regresses without the presence of testosterone and AMH
What does the Mullerian duct differentiate into?
fallopian tubes, uterus, and upper portion of the vagina
What are the 3 portions the Mullerian ducts?
cranial, horizontal, caudal
How does the upper portion of the vagina and uterus form?
Mullerian duct fuses at the midline created the broad ligament of the uterus
How does the broad ligament divide the pelvis?
into utero-rectal and utero-vesical pouches
What are the steps to vagina/uterus development?
- fusion
- proliferation - sinovaginal bulbs grow out from the urogenital sinus and form the vaginal plate, the vaginal plate continues to proliferate to increase the distance between the uterus and the urogenital sinus
canalization
What separates the vagina and the urogenital sinus?
a hymen
What forms where the Mullerian ducts fused to the urogenital sinus?
vaginal fornices
What happens during the indifferent stage that contributes to external genitalia development?
mesenchymal cells migrate from the primitive streak to the cloacal membrane to form cloacal folds
What does the union of the cloacal folds form?
genital tubercle cranially and urethral and anal folds caudally
What forms on each side of the urethral folds?
genital swellings
How is the urethral groove formed?
phalus (formed from the genital tubercle) pulls the urethral folds forward forming the groove
How is the penile urethra formed?
urethral folds of the urethral groove fuse in the 3rd month
How is the external urethral meatus formed?
ectodermal cells from the tip of the gland penetrate inwards in the 4th month
How is the scrotum formed?
genital swellings become scrotal swellings, move caudally, and fuse to form the scrotum
What is the gubernaculum?
fibrous cord that connects the fetal testis with the bottom of the scrotum
How do the testis descend?
as the gubernaculum shortens, the testis travel through the inguinal canal to the scrotum; they enter via the deep inguinal ring and exit via the superficial inguinal ring
What are the coverings of the testis from superficial to deep?
external abdominal oblique, internal abdominal oblique, transversus abdominis, transversalis fascia
What does the external abdominal oblique muscle form?
external spermatic fascia
What does the internal abdominal oblique muscle form?
cremaster muscle
What does the transversalis fascia form?
internal spermatic fascia
How is the clitoris formed?
genital tubercle elongates to form the clitoris
How is the urethral groove formed (female)?
clitoris is pulled forward to form the groove
How is the vestibule formed?
the urethral groove extends along the elongated tubercle and forms the vestibule
How is the labia minora formed?
urethral folds do not fuse in females to form the labia minora
How do the ovaries descend?
along the ovarian and round ligaments
What does the ovarian ligament connect?
ovary to the uterus
What does the round ligament connect?
uterus to labia majora
What other ligaments support the descent of the ovaries?
suspensory ligament and broad ligament
What does the suspensory ligament connect?
the ovary to the wall of the pelvis
What is the role of the broad ligament?
envelops the genital organs
When is the indifferent phase?
week 4-6
When does gonadal differentiation take place?
week 7
When does ductal differentiation take place?
week 9-11
When does external genitalia differentiation take place?
week 10-12
