Anatomy & Embryology

Question 1

What are the components of the external genitalia?

Answer 1

Vulva
- mons pubis: hair
- labia majora
- labia minora
- clitoris
- vestibule: opening of Bartholin gland & paraurethral glands
- frenulum anteriorly
- fourchette posteriorly

Question 2

What is the epithelial lining of the external genitalia?

Answer 2

Keratinized stratified squamous epithelium
EXCEPT the medial part of the labia minora -> non-keratinized

Question 3

What are the internal genital organs?

Answer 3

• vagina -> 9-10cm long
• uterus -> 7.5cm long, 5cm wide, 3cm thick
• cervix -> 2.5cm long
• Fallopian tube
• ovaries -> 2.5-5cm long, 1-3cm wide

Question 4

What are the structures that surround the vagina?

Answer 4

• anteriorly -> vesicovaginal connective tissue then bladder
• posteriorly -> rectovaginal connective tissue then rectum
• the cervix divides the vault of the vagina into 4 fornixes -> anterior, posterior, & lateral fornixes

Question 5

What is the normal pH & lining of the vagina?

Answer 5

PH -> 4.5
Lining -> stratified squamous non keratinized

Doderlin bacillus is normal

Question 6

What are the characteristics of the uterus?

Answer 6

• inverted pear shape anteverted 90 degree to the axis of the vagina
• weight -> 70gm
• consists 3 layers -> peritoneum, myometrium, endometrium
• lining -> simple columnar epithelium

Question 7

What are the characteristics of the cervix?

Answer 7

• upper part is involuntary muscle
• lower part is connective tissue
• contains glands that contribute to discharge
• epithelium -> columnar is upper part & stratified squamous in the external os
  -> squamocolumnar junction between them

Question 8

What are the characteristics of the ovaries?

Answer 8

• outer cortex & inner medulla
  -> cortex lined by single layer of cuboidal epithelium supported by tunica albuginea
  -> medulla is composed of connective tissue & blood vessels
• cortex contains oocytes & developing follicles

Question 9

When is the sex of the embryo determined?

Answer 9

Genetically -> at fertilization
Gonadal differentiation -> week 7

Question 10

What is the embryological origin of gonadal differentiation?

Answer 10

• WEEK 4 -> genital ridge appears in the embryonic kidney in the intermediate mesoderm
• WEEK 5 -> germ cells migrate from endodermal cells of the yolk sac close to allantois to genital ridge
• WEEK 6 -> invasion of genital ridge
• WEEK 7 -> sexual differentiation only if germ cells arrive at bipotential gonads
• epithelial cells proliferate & invade mesenchyme to give rise to primitive sex cord

Question 11

What is the cause of testicular formation in males?

Answer 11

Activity of SRY gene (testis determining factor on the Y chromosome)
- gonads differentiate into 2 types of cells
-> Sertoli cells (from superficial epithelium of gonads) -> produces Anti-Mullerian Hormone
-> Leydig cells (from mesenchymal cells of genital ridge) -> produce testosterone by week 8

Question 12

What is the importance of the male sex hormones in the development of the male sexual organs?

Answer 12

1- Anti-Mullerian hormone -> Mullerian system regression
2- testosterone -> stimulates Wolffian ducts to form vas deferens, epididymis, & seminal vesicles
3- testosterone is converted to dihydrotestosterone in the external genital skin -> causes differentiation of external genitalia by 5 alpha reductive enzyme

Question 13

What are the embryological origins of the external male genitalia?

Answer 13

• Genital ridge -> penis
• Urogenital folds -> close ventrally & enclose urethra
• Labioscrotal fold -> fuse to form the scrotum

Question 14

What is the physiology of female gonadal differentiation?

Answer 14

1- Absence of SRY gene -> primitive sex cords dissociate into clusters of germ cells -> replaced by medulla of the ovary
2- surface epithelium of gonads continue to proliferate to give rise to cortical cords -> later split to isolated cell cluster
3- germ cell gives rise to oogonia
4- granulosa cells develop from proliferating coelomic epithelium -> surround germ cells & form primordial follicle
5- theca cells develop from proliferating coelomic epi separated from the granulosa cell by basal layer

Question 15

What is the number of primordial follicles in a female through her life?

Answer 15

• at 20 weeks gestation -> 6-7 million
• at birth -> 1-2 million
• puberty -> 300 000 - 400 000

Primordial follicles start meitotic division in utero -> then arrest in prophase till puberty

Question 16

What is the embryological origin of the vagina?

Answer 16

Dual origin
- upper part -> paramesonephric ducts
- lower part -> urogenital sinus as sinovaginal bulb

Question 17

What is the importance of paramesonephric ducts (Mullerian) in the formation of the female genital system in utero?

Answer 17

1- Longitudinal invaginations in the epithelium of genital ridges -> caudally open in the abdominal cavity
2- they bilaterally cross midline caudally to lie adjacent to each other
3- caudal ends open in urogenital sinus & form the Mullerian tubercle
4- cranial & horizontal parts develop into uterine tubes, but caudal give rise to uterine canal
5- fused ducts give rise to corpus & cervix surrounded by mesenchyme which gives rise to myometrium & peritoneum

Question 18

What prevents the differentiation of sertoli & leydig cells in female embryos?

Answer 18

The DAX1 gene found on the short arm of chromosome X

Question 19

What does the sinovaginal bulb give rise to?

Answer 19

Lower 2/3rd of the vagina
1- evaginations at urogenital sinus that form vaginal plate
2- by month 5 undergoes canalization

Question 20

What separates the lumen of the vagina from the urogenital sinus?

Answer 20

The hymen
- epithelial lining of the sinus + vaginal cells

Question 21

When are external female genital structures recognizable & what are their embryological origins?

Answer 21

Recognizable by week 12
- genital tubercle -> clitoris
- urethral folds -> labia minora
- labioscrotal folds (genital swelling) -> labia majora
- urogenital groove -> vestibule

Absence of testosterone will not virility the genital structures

Question 22

What is the physiology of the embryological development of the external female genitalia?

Answer 22

1- mesenchyme cells migrate along cloacal membrane to form cloacal folds -> urethral fold -> labia minora
2- cloacal folds anteriorly unite -> genital tubercle -> clitoris
3- cloacal fold caudally unite -> urethral fold anteriorly & anal folds posteriorly
4- genital swelling lateral to urethral folds -> labia majora