11/20 Development Of Genitalia Flashcards
In what weeks do genitoreproductive structures differentiate?
Weeks 7-20
In what week are Genitoreproductive structures identifiable as male or female?
Week 12
What is the urogenital ridge (and what primordial tissue) and what does it contain?
Elevated intermediate mesoderm on either side of the dorsal aorta, along the posterior abdominal wall
Nephrogenic cord
Gonadal ridge
What is the mesothelium of genitoreproductive tissues? What does it give rise to?
Somatic mesoderm lining the gonadal ridge
Gives rise to gonadal cords, which will become the cortex and medulla of gonads
Where is endoderm found in genitoreproductive tissue? What does it form?
Primordial germ cells found in endoderm of umbilical vesicle and allantois
Form reproductive glands and epithelium of vagina
What is the development of the primordial germ cells (precursors to gametes) like in week 2, weeks 3-4, week 5, and week 6?
Week 2: arise from epiblast
Weeks 3-4: migrate through primitive streak to reside in
umbilical vesicle and allantois
Week 5: migrate back into body
Week 6: migrate into primary sex cords via dorsal mesentery
Why do primordial germ cells migrate through primitive streak?
to avoid all the signals within embryonic body
What do primordial germ cells proliferate into?
type A spermatogonia or into oogonia
When does proliferation into type A spermatogonia start in males?
Puberty
When does proliferation into oogonia start in females?
In utero
Genotypic sex (46XY or 46XX) is determined when?
At fertilization
How is phenotypic sex determined?
by embryonic/fetal development due to a complex genetic network
Embryonic genitoreproductive structures are identical until week _____, when they start differentiating
Will not be visibly recognizable until week ______
Week 7
Week 12
What are the genitoreproductive structures?
Gonads, genital tracts, external genitalia
What do gonads become?
Testes or ovaries
What do genital tracts become?
Vas deferens and epididymis
Uterine tube
What do the external genitalia become?
Scrotum and penis
Labia and clitoris
Sex differentiation in week 7-20 is sequential in this order from the start
Gonads
Genital ducts
External genitalia
What is the central event of sex differentiation?
Differentiation of testes
What is the differentiation of testes determined by?
SRY gene (on chromosome Yp11.3), which encodes for testes-determining factor (TDF)
What are the secondary events of sex determination?
Hormone production by gonads
What happens during sex differentiation hormone production by gonads?
Supporting cells for the gametes develop and secrete hormones to direct the indifferent embryo to a male or female phenotype
If SRY is present, what will happen?
TDF will be present
If SRY is not present, what will happen?
No TDF will be present
If TDF is present, what supporting cells for sex-specific gametes develop?
Interstitial cells, sustentacular cells
If interstitial cells and sustentacular cells are created, what hormones are secreted?
Interstitial cells: (high) Testosterone
Sustentacular cells: Anti-Müllerian hormone (AMH)
What does (high) testosterone from interstitial cells and Anti-Müllerian hormone (AMH) do to the duct systems? What does this mean?
(High) Testosterone: Mesonephric ducts persist
Anti-Müllerian hormone (AMH): paramesonephric ducts degenerate
Male phenotype
If TDF is not present, what supporting cells for sex-specific gametes develop?
Thecal cells, follicle cells
If thecal cells and follicle cells are created, what hormones are secreted?
Thecal: no (low) testosterone
Follicle: No anti-Müllerian hormone (AMH)
What does no (low) testosterone from thecal cells and no Anti-Müllerian hormone (AMH) do to the duct systems? What does this mean?
No (low) testosterone: mesonephric ducts degenerate
No anti-Müllerian hormone (AMH): paramesonephric ducts persist
Female phenotype
What are the steps to development of the indifferent gonads?
Week 5, Gonadal ridge develops medial to mesonephros
Week 6, primordial germ cells migrate into gonadal ridges
Indifferent gonads have both cortex and medulla, and these either develop or degenerate depending on sex
-primary sex cords and secondary sex cords
In development of gonads, what is the gonadal ridge made of? What does this develop?
Made of coelomic epithelium and urogenital ridge
Develops primary and secondary sex cords
Where do the primary sex cords extend?
extend into medulla of indifferent gonads
What are the secondary sex cords?
Cortex of indifferent gonads
In the development of the testes, what do the primary sex cords form?
thick tunica albuginea
seminiferous cords (contains primordial germ cells and
sustentacular cells), tubuli recti, rete testes
In the development of the testes, what do the secondary sex cords form?
Nothing
When do the testes descend?
Later in development, they descend to their final positions within the scrotum
What do the seminiferous cords become? When does this happen?
Tubules
At puberty
In the development of the ovaries, what do the primary sex cords form?
Extend into the medulla and form rete ovarii, which eventually degenerates
What happens to the rete ovarii
Eventually degenerates
In the development of the ovaries, what do the secondary sex cords form?
Forms a thin tunica albuginea
Form primordial follicles, which contain primary oocytes
What do primordial follicles contain?
Primary oocytes
What do connective tissue and similar tissues in ovaries form from?
Mesoderm
When do the ovaries descend?
Later in development, they descend to their final pelvic positions
What are the types of genital ducts that begin undifferentiated?
Mesonephric (Wolffian) ducts, paramesonephric (Müllerian) ducts
What are the mesonephric (Wolffian) ducts? What do they develop? How is this different in males/females?
Tubes from mesonephroi to cloaca
primarily for urinary development
in males there are places where the urinary and reproductive systems share structures and pathways
What are the paramesonephric (Müllerian) ducts?
Mesodermal invaginations on lateral urogenital ridge
What do the mesonephric ducts form in the male?
Form epididymis, vas deferens, seminal vesicle, and ejaculatory duct
Forms efferent ductules of testes
What do the paramesonephric ducts form in the male?
Caudally, fuse in midline to form uterovaginal primordium
Due to AMH, this all degenerates
What do the prostate and bulbourethral glands form from?
Endoderm of the urogenital sinus
What can you find vestigial remnants of in the adult male?
mesonephric duct, mesonephric tubules, and paramesonephric ducts
What do the mesonephric ducts become in the female?
Degenerate after mesonephroi form
What do the paramesonephric ducts become in the female?
Cranially, develop into uterine tubes
Caudally, fuse in midline to form uterovaginal primordium
Project into dorsal cloaca and form sinovaginal bulbs
What do the urethral, paraurethral, and greater vestibular glands form form?
Endoderm of the urogenital sinus
What are the steps for development of the uterus and vagina? (Long)
Uterovaginal primordium contacts the urogenital sinus and forms the sinus tubercle
Sinus tubercle induces growth of sinovaginal bulbs
Sinovaginal bulbs fuse to form vaginal plate
Vaginal plate canalizes to form lumen of vagina
Distal lumen partially covered by hymen, formed by a posterior invagination of the wall of the urogenital sinus
What is the development of the uterus and vagina? (Short)
Uterovaginal primordium contacts urogenital sinus = sinus tubercle -> sinovaginal bulbs fuse-> vaginal plate canalizes -> lumen of vagina -> hymen
What tissue does sinovaginal bulb grow from?
Endoderm
Superior 1/3 of vagina is from ______; inferior 2/3 of vagina is from ______
Uterovaginal primordium
Vaginal plate
Epithelial lining of entire vagina is from this tissue
Endoderm
What are the examples of class I congenital uterine anomaly, Müllerian hypoplasia or agenesis?
lower vaginal agenesis, cervical agenesis, uterine hypoplasia
What happens in class II congenital uterine anomaly with unicorneate uterus?
One paramesonephric duct fails to form
What are the types of congenital uterine anomalies?
Müllerian hypoplasia or agenesis
Unicorneate uterus
Double uterus (uterus didelphys)
Bicorneate uterus
Septate uterus
What happens in class III congenital uterine anomaly, double uterus? How does this present?
Paramesonephric ducts fail to fuse
Two halves of uterus, may or may not have septum in vagina
What happens in class IV congenital uterine anomaly, bicorneate uterus? How does this present?
Paramesonephric ducts fuse only partially
Partially split with indented fundus (looks like heart or horns)
What happens in class V congenital uterine anomaly, septate uterus? How does this present?
Medial walls of caudal paramesonephric ducts fails to resorb
Septum in uterus, looks normal externally
What is the hymen?
stretchy, flexible region of tissue surrounding the vaginal orifice
Does the hymen have a purpose?
no proven medical or physiological purpose
Is there anatomic variation in hymens?
Anatomic variation (shape, size, thickness) is normal, to a degree
Typically annular, crescenteric
How can an intact hymen be disrupted?
May be disrupted by physical activity, injury, medical exam, etc
What does an intact hymen indicate about sexual activity?
An intact hymen does not indicate anything about an individual’s sexual activity
What is the most common anomaly of the female reproductive tract that results in obstruction?
Imperforate hymen
What causes an imperforate hymen?
Incomplete canalization of vaginal plate
Why would an imperforate hymen require a minor surgical intervention if not self-corrected by puberty?
Need menstrual fluids to exit
What is the status of development of external genitalia of an indifferent embryo in week 4?
Genital tubercle
Labioscrotal folds x2
Urogenital folds x2
Urethral groove and membrane
What is the status of development of external genitalia of an indifferent embryo in weeks 7-8?
Cloacal and urogenital membranes rupture, therefore opening anal and urogenital orifices
What is the status of development of external genitalia of an indifferent embryo in weeks 9-12?
Differentiation of external genitalia
What is the anatomical position of the penis?
Erect
What is the first step in development of external genitalia that is undifferentiated between males/females before it is differentiated?
Genital tubercle elongates to form primordial phallus
What happens in development of male external genitalia after the genital tubercle elongates to form primordial phallus?
Primordial phallus enlarges/elongates -> glans penis
Urogenital folds fuse along ventral penis -> shaft of penis, penile raphe, and most of spongy urethra
What happens in development of male external genitalia after urogenital folds fuse along ventral penis? What primordial tissues are involved and what do they become?
At tip of glans, solid cord of ectoderm grows in to meet spongy urethra -> distal spongy urethra (navicular fossa) and external urethral orifice
Week 12, ingrowth of ectoderm at periphery of glans breaks down -> prepuce (foreskin) of penis
Mesenchyme in penis -> corpora cavernosa and corpus spongiosum
What is the final step of development of male external genitalia after the ectoderm breaks down and mesenchyme differentiate?
Labioscrotal swellings fuse -> scrotum and scrotal raphe
What happens in development of female external genitalia after the genital tubercle elongates to form primordial phallus?
Growth of primordial phallus decreases -> glans clitoris
Clitoris develops the same way as penis, except the urogenital folds only fuse posteriorly -> frenulum of labia minora
-Unfused part -> labia minora x 2
Labioscrotal folds fuse posteriorly and anteriorly, but mostly remain unfused -> posterior and anterior labial commissures, labia majora x 2, mons pubis
What is the most common penile anomaly in males?
Hypospadias
What is hypospadias? How is it named?
Urethral orifice is on ventral surface of penis
Naming depends on location (glandular most common)
What does hypospadias often occur with?
ventral chordee (poorly developed penis that curves ventrally)
What is the cause of hypospadias?
Cause: Urogenital folds fail to fuse completely
What are some problems one with hypospadias may have?
May have issues with urination, erection, ejaculation, fertility
What is epispadias? How is it named?
Urethral orifice is on dorsal surface of penis
Naming depends on location (glandular most common)
What does epispadias often occur with?
Often occurs with dorsal chordee (poorly developed penis that curves dorsally)
Often associated with exstrophy of the bladder or issues of neck of bladder
What is the cause of epispadias?
Hypothesized to involve issues with cloacal membrane and/or genital tubercle
What are some problems one with epispadias may have?
Females may have issues with urination/incontinence
Males may have issues with urination/incontinence, erection, ejaculation, fertility
What kinds of tissues make up the gonadal ridge?
Intermediate mesoderm
Somatic mesoderm (lining)
What are some of the hymen variations? Which are normal/abnormal?
Normal: annular hymen, normal parous introitos (hymen absent)
Abnormal: cribriform hymen, septate hymen, imperforate hymen
What is the final structure in males and females from the embryological structure of the gonads?
Male: testes
Female: ovaries
What is the final structure in males and females from the embryological structure of the genital tubercle?
Male: glans penis
Female: glans clitoris
What is the final structure in males and females from the embryological structure of the labioscrotal folds?
Male: scrotum
Female: labia majora
What is the final structure in males and females from the embryological structure of the urogenital folds?
Male: shaft of penis, some spongy urethra
Female: labia minora
How can you determine the sex using sonography in the 1st trimester (week 11)?
By observing the direction of the genital tubercle and sagittal sign (midline sagittal view of genital area)
How can you determine the sex using sonography in the 2nd and 3rd trimesters?
By observing genital anatomy
When using sonographic identification of sex in the 1st trimester, what determines a female fetus?
Downward tubercle, caudal notch
When using sonographic identification of sex in the 1st trimester, what determines a male fetus?
Upward tubercle, cranial notch
When using sonographic identification of sex in the 1st trimester, what does a downward tubercle typically indicate?
Female fetus
When using sonographic identification of sex in the 1st trimester, what does a upward tubercle typically indicate?
Male fetus
When using sonographic identification of sex in the 1st trimester, what does a caudal notch typically indicate?
Female fetus
When using sonographic identification of sex in the 1st trimester, what does a cranial notch typically indicate?
Male fetus
What are some factors that can interfere with sonographic identification of sex in the 1st trimester?
operator skill and equipment, maternal factors (bowel gas, obesity), fetal position (crossed legs, hyperactivity)
