Development of the Genital System | B2, WK5 Flashcards
Which develops first: External or internal genitals?
Internal (External takes longer)
The urinary and genital systems are derived from _______________________-
intermediate mesoderm (intermediate mesenchyme)
Intermediate mesoderm forms a _______________ ________________ (2 words), which differentiates into what 2 structures?
Urogenital ridge
1. nephrogenic cord
2. genital ridge
T/F: Up until week 6, the genital system develops differently for Male/Female, regardless of chromosomal composition of the embryo
False
Up until week 6, the genital system develops similar for Male/Female, regardless of chromosomal composition of the embryo
What is genotypic sex?
Sex of individual based on chromosomes
46 XX, 46 XY
[don’t forget about 45X (turner syndrome) and 47 XXY [Klinfelter syndrome]
What is phenotypic sex?
Based on the appearance of internal/external genitalia (i.e., phenotype = physical)
How is phenotypic sex first determined? (list/describe the process)
Y chromosomes have SRY genes. These genes produce SRY protein (or testis determining factor)
1. SRY protein produced in developing gonad
2. SRY protein starts cascade of factors that initiate male-like phenotypic sex development
What happens (in terms of phenotypic sex) when an embryo has XX chromosomal pattern OR the Y chromosome does not contain the SRY gene
Female-like phenotypic sex will be produced
Genital (gonadal) ridges form _____________ to mesonephros and are initially at level of _______ vert.
Medial
T10
During the 5th-6th week, what cells migrate from the yolk sac to the genital ridges? What happens if these cells don’t migrate?
Primordial germ cells [oocytes/sperm]
If they don’t migrate - gonads will NOT form
What is the outer part of the gonad? inner part?
Outter: cortex
Inner: medulla
The ____________________________ (3 words) are found in the medulla of developing gonad.
Primitive (primary) sex cords
By the 6th week - What two duct systems form?
- Mesonephric (wolffian) ducts
- Paramesonephric
What are Mesonephric (wolffian) ducts?
Form most of the phenotypic-male duct system
What are Paramesonephric (Mullerian) ducts?
Form most of the phenotypic female duct system
SRY protein starts its work at week 7 - what does this do/mean?
Differentiation of genitalia during Wk 7 – SRY protein influences the gonad to become a testis
Under influence of SRY protein, medullary portions of _______________________ develop
Primitive sex cords (testis cords)
What does the testis cord form?
Seminiferous tubules & rete testis
What do sustentacular (sertoli) cells secrete?
Anti-mullerian hormone (AMH) [or Mullerian Inhibiting Substance (MIS)]
What does AMH (MIS) induce?
degeneration of paramesonephric ducts
The paramesonephric ducts degenerate, but what about the mesonephric duct?
This duct remains, will form most of the reproductive duct system associated w/ the testis
How does the prostate and bulbourethral glands form?
Form from endodermal ‘buds’ off of urethra
What pulls the testis down from its lumbar placement into the scrotum?
Gubernaculum!
3rd - 7th month of development - where are the testes located?
Testis at level of deep inguinal ring
9th month of development - where are the testes located?
Testis pulled into scrotum
What gets “pulled” with the testis as it descends?
Its innervation (T10/T11)
The kidneys _________________ while the testes start to ________________.
Kidneys: ascend
Testes: descend
T/F: The descent of the testes occurs throughout entire fetal period
TRUE
What is cryptorchidism?
“Hidden testis”
-Undescended testis
Why does cryptorchidism occur more commonly in preemies?
Born before 9th month, so it has not descended yet
What other increased risks are associated with cryptochidism?
Testicular cancer
Fertility problems (b/c of temp regulation that is needed)
What is testicular Hydrocele?
Fluid-build up in either tunica vaginalis or part of patent process vaginalis
T/F: Testicular hydrocele typically occurs in 3-5 yr olds and needs medical attention, as it will not regress on its own
FALSE:
typically occurs in 1 yr olds AND typically regresses on its own
(emphasis on typically)
Absence of the Y-chromosome and SRY gene will yield
Female-like development
During the 7th week, the testis cords of gonads degenerate and a secondary set of cords called ______________________ develop in the __________________
[differentiation of ovaries]
cortical cords ; cortex
Cortical cords form what?
Follicular cells of ovarian follice
Does the medulla of the ovary have sex cells? {Think about gross anatomy and histo}
NO
In female development, absence of AMH yields
-degeneration of mesonephric ducts
-development of paramesonephric ducts
What forms the uterus and superior part of the vagina?
Inferior (caudal) ends of paramesonephric ducts that fuse (during 2nd trimester)
What forms the uterine tubes?
Unfused superior forms of paramesonephric ducts
The inferior part of the vagina is formed from?
Sinovaginal bulbs (off of UG sinus) that fuse – OUTGROWTH of urethra
The vagina separates from the bladder when?
When the inferior part of the vagina forms
Where do the ovaries descend from?
T10 region –> to pelvic cavity
(posterior to broad ligament)
What are uterine malformations typically caused by?
Partial atresia of one of the paramesonephric ducts
(atresia: a body part that is tubular in nature does not have a normal opening, or lacks the ability to allow material to pass through it.)
What is uterus didelphys?
Double uterus & double cervix – fundus malformation
What does this pic show?
Bicornuate Uterus
Why are uterine malformations (such as uterus didelphys) harmful?
Causes issues for the development of offspring (i.e., uterus can’t expand as fetus grows)
What occurs when sinovaginal bulbs fail to form?
Vaginal Atresia
Vaginal atresia is when…
The superior vagina forms but the inferior part does not (so, no connection to the outside body)
External genitalia are undifferentiated until about week ____. They are phenotypically differentiated by about week _____.
12
20
What are the three sets of primordia (external genitalia) found at week 6?
- Urethral (urogenital folds)
- Labioscrotal swellings
- Gentical tubercle (phallus)
Under the influence of testosterone - what happens to the following?
-Genital tubercle
-Urethral folds
-Labioscrotal folds
-Genital tubercle: enlarges, forms the glans of penis
-Urethral folds: fuse to form the ventral surface of the penis (encloses penile urethra)
-Labioscrotal folds: fuse to form the scrotum
In the absence of testosterone (or lack of tissue response to testosterone), the embryonic folds remain
Unfused
Under NO influence of testosterone - what happens to the following?
-Genital tubercle
-Urethral folds
-Labioscrotal folds
-Genital tubercle: becomes clitoris
-Urethral folds: becomes labia minora
-Labioscrotal folds: labia majora
What is hypospadias?
Disorder where irethra found on inferior (ventral) surface of penis instead of glands
What causes hypospadias?
Incomplete fusion of urethral folds
What is epispadias?
Disorder when urethral opening is on the DORSUM of penis
What is epispadias usually associated with?
Bladder exstrophy (Ventral body defect - bladder inside out, sticks out of abdominal wall)
What is 46 XY DSD?
XY genotype w/ ambiguous external genitalia or variable phenotypic female-like external genitalia
Testicular tissue may be present
What usually causes 46 XY DSD?
A reduction in male hormones in development
OR
Tissues don’t respond to androgens (insensitivity)
What is 46 XX DSD?
XX genotype
Ambiguous or phenotypic male-like external genitalia
What are the phenotypic characteristics of 46 XX DSD?
Clitoris may be enlarged
Labia may be partially or completely fused
What is 46 XX DSD due to exposure of XX fetus to excessive androgens?
-Occurs when pregnant individuals produce or are exposed to abnormal amounts of androgens
What is Conginital adrenal hyperplasia (CAH)?
Fetal adrenal gland produces EXCESSIVE amounts of androgens (most common cause of 46 XX intersex)
