[EMB] 15: DEVELOPMENT OF THE INTERNAL GENITALIA

Sexual Dimorphism

This is the determination whether baby is male or female

Y chromosome

Sexual Dimorphism is dependent on what chromosome?

SRY protein

This is the sex determining region on Y chromosome

SRY protein

Without this protein, there will be no differentiation to male or female

intermediate mesoderm

Where does the gonads differentiate/come from

Both urinary and genital systems are closely related and both arose from the intermediate mesoderm

Why are gonads closely related to development of the kidneys?

at fertilization

When is genetic sex determined?

7th week

Morphologic internal genitalia is seen at what week?

Genital duct system and morphologic genitalia

What becomes evident at 7th week?

Hormones

These are necessary for genital duct development

Testosterone

What hormone is for the male duct?

Estrogen

What hormone is for the female duct?

SRY (sex-determining region on Y) gene

This is the testis determining factor

differentiation or development

SRY (sex-determining region on Y) gene determines the _________________ of the male internal reproductive system

regression

SRY (sex-determining region on Y) gene determines the _______________ of the female internal reproductive system

False. crucial

(T/F) SRY gene is not crucial for the differentiation of the indifferent gonad

male internal reproductive system

If the fetus has a Y chromosome then all of the structures will later on differentiate into what?

True

(T/F) In the absence of SRY protein there will be no differentiation of the male gonads/ductal system, and the female internal reproductive system pursues

diploid number (2n)

At fertilization, zygote acquires _______________ of chromosomes from haploid (n) maternal and paternal gametes

epiblasts

Primordial germ cells come from these embryonic cell

primitive streak

Primordial germ cells migrate from the epiblasts and travel through this structure

Primordial germ cells

These have an inductive influence on the development gonads into ovary or testis

third week

By this week, the primordial germ cells are present near the endodermal cells in the wall of the yolk sac, near the allantois

fourth week

By this week, primordial germ cells migrate along the dorsal mesentery of the hindgut

5th week

By this week, primordial germ cells arrive at the primitive gonads

sixth week

When do primordial germ cells start invading the genital ridges forming gonadal ridge?

gonadal ridge

Primordial germ cells invading the genital ridges results in the combination of epithelium (epiblast) and mesenchyme (from the endoderm cells) forming this structure

Without the migration of these PGCs to the gonadal ridge, sexual differentiation and development will not take place

What happens if there is no migration of the PGC?

Epithelial cells

Before arrival of PGCs these penetrate underlying mesenchyme to form primitive sex cords which are connected to the surface epithelium.

Primitive sex cords

These are an effect of the infiltration of the primordial germ cells

indifferent stages

At this stage, it is still unsure whether the gonads will differentiate into the male or female gonads

indifferent gonad/ bipotential gonad

The gonads during indifferent stages are called?

medulla of the gonadal ridge

primitive sex cords form/infiltrate this

rete testis

At the hilum, these primitive sex cords break and form what

tunica albuginea

As the testis cords separate from the cortex, this is formed

Tunica albuginea

This is the fibrous capsule surrounding the testis

16th week

At around the what week of development, these primitive sex cords become horseshoe in shape

primordial germ cells and sustentacular cells of Sertoli

At 16th week, Sex cords are now composed of what structures which are derived from the surface epithelium

anti-Mullerian hormones

Sertoli cells secrete what hormone and causes the paramesonephric duct to regress

interstitial cells of Leydig

In between the cords lie this which came from mesenchyme

8 th week

interstitial cells of Leydig start secreting testosterone in this week of gestation to influences the differentiation of the ductal system

seminiferous tubules

Testis cords remain solid and canalize during puberty, now called

primordial follicles

2nd generation cortical cords develop and break off into clusters forming this structure

Primordial follicles

These are brought about by pinching from the surface epithelium

primary oocyte (red dots in the figure) or primordial germ cells

Primordial follicles are formed by these structures and are encased by follicular cells that came from the cortex

True

(T/F) At birth, there are approximately 600,000 - 800,000 primary oocytes

F. Females. males will continue to be replenished after birth

(T/F) For males, no new primary oocytes will be formed after birth

40,000

Around puberty, only around _______________ oocytes remain

The development of the ovaries ensues, Medullary cords degenerate, Cortical cords develop and No tunica albuginea

What happens in the absence of Y chrmosome?

The indifferent gonad would develop into the testis, Medullary cords would develop, No cortical cords and Thick tunica albuginea will develop

What happens in the presence of Y chrmosome?

12th week

At what week will the testis go to the inguinal region?

28th week

At what week will the testis go to the inguinal canal?

33rd week

At what week will the testis go to the scrotum?

2nd month

Towards the end of this month, there is a urogenital mesentery that attaches the testis and the mesonephros to the posterior abdominal wall

urogenital mesentery

As the mesonephros degenerate, this becomes a mesentery from the gonads

caudal genital ligament

The urogenital mesentery caudally becomes ligamentous, called the ___________and is accompanied by the gubernaculum, which is a mesenchymal condensation

level of the inguinal region

Prior to the descent of the testis, the gubernaculum terminates around what level between the layers of the internal and external abdominal oblique muscles

scrotal swelling

As the testis start to descend, the extra-abdominal portion of the gubernaculum grows from the inguinal region until it reaches this area

extra-abdominal portion of the gubernaculum

The _________________________ with the increasing intra-abdominal pressure (by the developing organs of the abdominal cavity) pushes the testis to enter the inguinal cana

anti-Müllerian hormone or the Müllerian inhibiting substance

This hormone causes regression of the paramesonephric ducts which are important for female internal reproductive system development

Internal spermatic fascia

What is the corresponding layer covering the Testis of the Transversalis fascia?

No extension (it just arches over the area of the inguinal canal

What is the corresponding layer covering the Testis of the Transversus abdominis

Cremasteric fascia and muscle

What is the corresponding layer covering the Testis of the Internal abdominal oblique aponeurosis

External spermatic fascia

What is the corresponding layer covering the Testis of the External abdominal oblique aponeurosis

Extension of the Scarpa’s fascia

What is the corresponding layer covering the Testis of the Dartos

Label

True

(T/F) Descent occurs to a lesser extent in females compared to testes

2 nd part of paramesonephric ducts

These moves mediocaudal while genital ridges (remain) lie transversely

pelvic fold or broad ligament

As the paramesonephric ducts fuse in the middle, it brings with it a fold of peritoneum formation of ____________________________

Congenital indirect inguinal hernia

Descent of intestines into the scrotum because there is an open connection between the peritoneal cavity and processus vaginalis

1 st year after birth

Normally, the connection between the abdominal cavity and the scrotum obliterates at around the what age?

Hydrocele

This is the accumulation of fluid in the incompletely obliterated processus vaginalis

processus vaginalis

In hydrocele there is the irregular obliteration of the what that results in the development of cysts that secrete fluids

Cryptorchidism

There is incomplete or failure of the descent of the testes into the scrotum

ectopic testis

This is a rare congenital condition where a testicle descends outside the normal pathway and settles outside the scrotum, often in the groin, perineum, or thigh

Can be subjected to trauma, Can have torsion and compromise the blood supply and abnormal location results in a higher temperature than what is ideal for spermatogenesis

Possible dangers of ectopic or cryptorchid testes:

Gubernaculum

Mesenchymal condensation that appears to guide the descent of the gonads

gubernaculum testis

What is the male derivative of the gubernaculum?

suspensory ligament of the ovary

What is the female derivative of the gubernaculum cranially?

True ovarian ligament / round ligament of ovary and Round ligament of uterus

What is the female derivative of the gubernaculum caudally?

Paramesonephric duct or Mullerian duct

During the indifferent stage,These will eventually be suppressed/ disintegrate

Mullerian Inhibiting Substance (MIS) / anti-Mullerian hormone

The effects of these hormones produced by sertoli cells are inhibition of female characteristics, and suppression of paramesonephric ducts

Testosterone

The effects of these hormones produced by Leydig cells are stimulation of mesonephric ducts to differentiate Vas deferens, epididymis, seminal vesicle, ejaculatory duct

Dihydrotestosterone

This leads to the development of the External genitalia stimulated along with growth of penis, scrotum, & prostate

efferent tubules

Epigenital tubules that later develop into these tubules connected to the rete testis

paradidymis

The excretory tubules and the paragenital tubules at the caudal pole regress into this

mesonephric duct

Distally, the these elongates and later on would coil and form the epididymis, as well as the vas deferens, seminal vesicles and ejaculatory duct

utriculus prostaticus and the appendix testis

Paramesonephric duct - degenerates and what remains of it are these

Mesonephric tubules

What embryonic structures form the Efferent ductules

Mesonephric duct or Wolffian ducts

What embryonic structures form the epididymis, ductus/vas deferens, seminal vesiclesand ejaculatory duct

Mesonephric (Wolffian) -mAppendix epididymis

Paragenital tubules - Paradidymis

Paramesonephric (Mullerian) -Appendix testis and Utriculus prostaticus

What embryonic structures form the vestigial structures

Paragenital tubules

What forms the paradidymis

the uterine tubes/ fallopian tubes, uterus, and upper portion of vagina.

Presence of estrogen from the ovary stimulates the differentiation of the paramesonephric ducts into →

labia, clitoris, and lower portion of the vagina

Presence of estrogen from the ovary stimulates the differentiation of the external genitalia into →

Cranial vertical part

This part of the paramesonephric ducts opens into the abdominal cavityand develops into the uterine/fallopian tubes

Horizontal part

This part of the paramesonephric ducts crosses the mesonephric duct and forms part of the uterine tubes

Caudal vertical part

This part of the paramesonephric ducts fuses with its counterpart on the other side to form the uterine canal

True

(T/F) The regressing mesonephric ducts in females also have vestigial structures

Epoophoron

Epigenital tubules will become what, while the more caudal portion will become the Paroophoron