Anatomy & Embryology Flashcards
What are the components of the external genitalia?
Vulva
- mons pubis: hair
- labia majora
- labia minora
- clitoris
- vestibule: opening of Bartholin gland & paraurethral glands
- frenulum anteriorly
- fourchette posteriorly
What is the epithelial lining of the external genitalia?
Keratinized stratified squamous epithelium
EXCEPT the medial part of the labia minora -> non-keratinized
What are the internal genital organs?
- 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
What are the structures that surround the vagina?
- 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
What is the normal pH & lining of the vagina?
PH -> 4.5
Lining -> stratified squamous non keratinized
Doderlin bacillus is normal
What are the characteristics of the uterus?
- inverted pear shape anteverted 90 degree to the axis of the vagina
- weight -> 70gm
- consists 3 layers -> peritoneum, myometrium, endometrium
- lining -> simple columnar epithelium
What are the characteristics of the cervix?
- 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
What are the characteristics of the ovaries?
- 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
When is the sex of the embryo determined?
Genetically -> at fertilization
Gonadal differentiation -> week 7
What is the embryological origin of gonadal differentiation?
- 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
What is the cause of testicular formation in males?
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
What is the importance of the male sex hormones in the development of the male sexual organs?
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
What are the embryological origins of the external male genitalia?
- Genital ridge -> penis
- Urogenital folds -> close ventrally & enclose urethra
- Labioscrotal fold -> fuse to form the scrotum
What is the physiology of female gonadal differentiation?
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
What is the number of primordial follicles in a female through her life?
- 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
What is the embryological origin of the vagina?
Dual origin
- upper part -> paramesonephric ducts
- lower part -> urogenital sinus as sinovaginal bulb
What is the importance of paramesonephric ducts (Mullerian) in the formation of the female genital system in utero?
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
What prevents the differentiation of sertoli & leydig cells in female embryos?
The DAX1 gene found on the short arm of chromosome X
What does the sinovaginal bulb give rise to?
Lower 2/3rd of the vagina
1- evaginations at urogenital sinus that form vaginal plate
2- by month 5 undergoes canalization
What separates the lumen of the vagina from the urogenital sinus?
The hymen
- epithelial lining of the sinus + vaginal cells
When are external female genital structures recognizable & what are their embryological origins?
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
What is the physiology of the embryological development of the external female genitalia?
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
