[EMB] 16: DEVELOPMENT OF THE EXTERNAL GENITALIA

3rd week

When does cloacal fold form?

Cloacal Folds

In the 3rd week of development, mesenchyme cells originating from the region of the primitive streak migrate around the cloacal membrane to form what?

Genital Tubercle

Union of folds cranial to the cloacal membrane

Urethral Folds

What is the anterior cloacal fold called?

Anal Folds

What is the posterior cloacal fold called?

Genital Swellings

Pair of elevations visible on each side of the urethral folds

Male: Scrotal swelling & Female: Labia majora

What becomes of Genital Swellings?

6th week,

At the end of what week does it becomes impossible to differentiate between the 2 sexes, hence the term, “indifferent stage?

ANDROGENS

What influences the development of external genitalia in males?

phallus

Male external genitalia is haracterized by rapid elongation of the genital tubercle called?

Urethral groove

During elongation, the phallus pulls the urethral folds forward, forming the lateral walls of what?

F. DOES NOT

(T/F) Urethral groove extends along the ventral aspect of the elongated phallus and reaches the most distal part

Glans penis

What is the most distal part of the phallus?

Urethral Plate

This is the Epithelial lining of the groove

endodermal origin

What is the embryonic origin of the urethral plate?

Penile Urethra

Formed when 2 urethral folds close over the urethral plate

End of the 3rd Month

When is the Penile Urethra formed?

True

(T/F) In penile urethra formation, the Canal does not extend to the tip of the phallus

4th Month

When does the formation of the most distal portion of the urethra happen?

Ectodermal

At 4th Month, what cells from the tip of the glans penetrate inward and form a short epithelial cord?

External urethral meatus

What is the lumen of the penile urethra?

the inguinal region

Where does the scrotal swellings in the male arise in and with further development, they move caudally?

scrotal septum

What separates each scrotal swellinh the forms each half of teh scrotum?

Testes

These develop retroperitoneally in the abdominal region, move caudally and pass through the abdominal wall via the inguinal canal via the scrotum

Inguinal Canal

This lies superiorly to the medial half of the inguinal ligament

Deep (internal) inguinal ring

Where is the entry of the inguinal canal?

Superficial (external) inguinal ring (near pubic tubercle)

Where is the exit of the inguinal canal?

urogenital mesentery

At the end of the 2nd month, the this attaches the testis and mesonephros to the posterior abdominal wall.

caudal genital ligament.

Degeneration of the mesonephros leaves an attachment that functions as a mesentery for the gonad and later becomes the _________________

Gubernaculum

These are mesenchymal condensation rich in extracellular matrices extending from the caudal pole of the testis.

inguinal region

Prior to the descent of testis, gubernaculum terminates in this specific area between the differentiating internal and external abdominal oblique muscles

the inguinal region toward the scrotal swellings

As the testis begins to descend toward the internal inguinal ring, an extra-abdominal portion of the gubernaculum forms and grows from _______________ and towards ____________

scrotal floor

When the testis passes through the inguinal canal, the extra-abdominal portion of thegubernaculum contacts what?

F. The gubernaculum also forms in the females but remains rudimentary, normally

(T/F) Females do not form gunarnaculum

12 weeks

At what week will the testis reach the inguinal region?

28 weeks

At what week will the testis migrate through the inguinal canal?

33 weeks

At what week will the testis reach the scrotum?

Androgens, Müllerian Inhibiting substance (MIS)

What hormones influence teh descent of the testis?

True

(T?F) The testis retains its blood supply from the aorta, with the testicular vessels extending from their original lumbar position down to the testis in the scrotum.

Processus vaginalis

This is the evagination of the peritoneum of the abdominal cavity on each side of the midline into the ventral abdominal wall, independently to the descent of the testis

gubernaculum testis

What course does the processus vaginalis follow into the scrotal swellings?

INGUINAL CANAL

Processus vaginalis is accompanied by the muscular and fascial layers of the body wall, invaginates into the scrotal swelling forming the _____________.

visceral layer of the tunica vaginalis.

The peritoneal layer covering the testis is the _________________

parietal layer of the tunica vaginalis.

The remainder of the peritoneal sac forms the ___________________________

Transversalis fascia

What is the abdominal wall origin of the forms the Internal spermatic fascia?

Internal abdominal oblique muscle

What is the abdominal wall origin that gives rise to the cremasteric fascia and muscle?

External abdominal oblique muscles

What is the abdominal wall origin that forms the external spermatic fascia.?

Transversus abdominus muscle

What abdominal wall constituent does not contribute a layer in testis coverings?.

ESTROGENS

What stimulate sthe formation of external genitalia in females?

Clitoris

What becomes of the genital tubercle in females?

F. There can be a mistake as the male genital tubercle can be of similar size to female in these months

(T/F) Using the length of tubercle is an accurate method of identifying sexes in 3rd and 4th month of gestation

Labia minora

What becomes of the urthral folds in females?

Labia majora

What becomes of the genital swellings in females?

vestibule

What becomes of the urogenital groove in females?

below the rim of the true pelvis

Where does the ovary settle?

Cranial genital ligament

What is the embryonic origin of the cranial genital ligament in females?

Caudal genital ligament

What is the embryonic origin of the Ligament of ovary proper ○and round ligament of the uterus in females?

labia majora

Round ligament of the uterus extends into the ______________

Hypospadia

This is a common congenital birth defect (approx. 1 in 200 boys) where the urethral opening forms on the underside of the penis rather than at the tip

Incomplete fusion of the urethral folds r

This (type of hypospadias) results in abnormal urethral openings along the ventral penis (near the glans, shaft, or base), and in rare cases, the urethral meatus may extend along the scrotal raphe.

Complete failure of fusion

This (type of hypospadias) results in a wide sagittal slit along the entire length of the penis and scrotum, with the two scrotal swellings resembling the labia majora.

3–5 per 1000 births

Hypospadias occurs in about _______________, may be linked to increased exposure to environmental estrogens, although the exact cause remains unknown

Epispadias

This is a rare defect where the Urethral meatus is at dorsum of the penis

1 in 30,000 births

Epispadias occur in ________________

Exstrophy of the bladder & Abnormal closure of the ventral body wall

Epispadias can occur as an isolated defect, but isost often associated with:

micropenis

This is when there is an insufficient androgen stimulation for growth of external genitalia

Primary hypogonadism & Hypothalamic or Pituitary Dysfunction

micropenis is usually caused by

2.5 SD

At what SD below mean length when measured along the dorsal surface from pubis to the tip, with the penis stretched to resistance?

BIFID PENIS/ DOUBLE PENIS

Occurs when Genital tubercle splits

Ambiguous Genitalia

This is when there is a typically female appearance with a large clitoris (clitoral hypertrophy)

Ambiguous Genitalia

This is when there is a typically male with a small penis that is open on its ventral surface (hypospadias)

(hermaphrodites)

Ambiguous Genitalia results in individuals with characteristics of both sexes commonly known as

True hermaphrodism”

Ovotesticular Disorders of Sex Development “ is formerly called____________________, where both ovarian and testicular tissues are present

combination of ovary, testis, or ovotestis

What comprises the gonadal tissue in True hermaphrodism that is present in ⅔ of cases?

46, XX in 70% of cases (genotypically female)

What is the genotype of True hermaphrodism?

Bilateral gynaecomastia, small penis, empty scrotum and female hair distribution

What are the Manifestations of Ovotesticular Disorder>?

exposed to excessive amounts of androgen

What causes a Genetically female (46, XX) that causes the masculinizion the external genitalia?

Congenital adrenal hyperplasia –

This is the most common cause of ambiguous genitalia and accounts for 60% of these cases

Excessive androstenedione produced by the adrenal gland

What causes Congenital adrenal hyperplasia?

Phallic enlargement, degree of urethral fold fusion and Size and opening of the vagina

What cane be seen in Congenital adrenal hyperplasia?

Isolated Deficiency of Mullerian Inhibiting Substance (MIS)

Rare disorder wherein there is no production of MIS which results in the genitalia being normal for male, but with varying degrees of remnants of Mullerian system (uterus, uterine tubes)?

46, XY (male)

What is the genotype of Isolated Deficiency of Mullerian Inhibiting Substance (MIS) ?

Androgen Insensitivity Syndrome (AIS)

This is when there is a lack of androgen receptors or failure of tissues to respond to receptor-dihydrotestosterone complexes

Complete Androgen Insensitivity syndrome (CAIS)

This is when there is a short or poorly-developed vagina, or testes in the inguinal or labial region, but no spermatogenesis

Complete Androgen Insensitivity syndrome (CAIS)

This disorder increases the risk for testicular tumors , where 33% develop malignancies prior to age 50

Mild androgen insensitivity syndrome (MAIS)

This is when there is a virilization of varying degrees

Partial androgen insensitivity syndrome (PAIS)

This is when there may be an ambiguous genitalia present (clitoromegaly, small penis with hypospadias) but testes are usually undescended

5-ɑ-reductase deficiency

Inability to convert testosterone to dihydrotestosterone because of a lack of reductase enzyme

as underdeveloped genitalia with hypospadias

5-α-reductase deficiency causes abnormal external genital development, presenting in males as what

as clitoromegaly.

5-α-reductase deficiency causes abnormal external genital development, presenting in females as what?

Klinefelter syndrome

This is the most common sex chromosome disorder, presents with decreased fertility, small testes, low testosterone levels, and gynecomastia in approximately 33% of affected individuals.

47, XXY (other variants, e.g. XXXY)

Klinefelter syndrome, karyotype

Nondisjunction of the XX homologues

Klinefelter syndrome what is teh common causative factor?

Lower IQ than sibs, Tall stature, Poor muscle tone, Reduced secondary sexual characteristics, Gynecomastia (male breasts), Small testes / infertility

What can be seen in patients with klinefeter syndrome?

Gonadal dysgenesis

This is characterized by streak gonads with absent oocytes, resulting in underdeveloped ovaries.

female

Gonadal dysgenesis affected individuals typically lack secondary sexual characteristics at puberty and are phenotypically __________ but may have various chromosomal complements, including XY

Do not menstruate

Primary manifestation of Gonadal dysgenesis