CHAPTER 10: UROGENITAL 2 Flashcards
Describe the embryology of the sexual organs
Prior to the 6th week of gestation the embryo is sexually indeterminate
Basic foetal model is female
SRY gene - present on Y-Chromosome → testes → Leydig cells (testosterone - male genitalia development) and Sertoli cells (removal of upper vagina and uterus)
If not → ovary
Virilization at 6-19 weeks gestation
After the 6th week the gonads arise from the genital ridges and differentiate into ♂+♀
The internal sexual organs form from the paramesonephric and mesonephric ducts.
The Paramesonephric duct (Müllerian duct)
- ♀ = fallopian tubes, uterus, cervix and upper vagina
- ♂ = degenerates to form the appendix testis
- Sertoli cells within the gonad secrete a testosterone analogue that acts as a Müllerian-inhibiting factor.
The mesonephric duct (Wolffian duct)
- ♂ = epididymis, ductus deferens, seminal vesicles, ejaculatory ducts
- Leydig cells secrete testosterone which stimulates development of mesonephric duct and genital tubercle.
How do the external genital organs form?
Until when are they sexually indistinct?
wk3
- cloacal membrane forms, fuses and forms genital tubercle
wk6
- cloacal membrane divides into urogenital and anal membranes
- cloacal folds divide into urethral and anal folds, with genital swellings laterally
wk 11
- o Central urethral groove
- o Urethral folds on either side of the urethral groove.
- o Labioscrotal swellings on either side of the urethral folds.
- o The genital tubercle anteriorly
- sexually indistinct up to this point
How does the male external genitalia form?
The genital tubercle elongates → penis
urethral groove grows distally down the genital tubercle, forming endoderm of the penile urethra almost to tip
Distal part of the urethra is initially formed by urethral plate (endoderm) & later replaced by ectodermal ingrowth from surface of glans penis canalising the glandular urethra and forming the external urethral meatus.
12th week → urethral folds fuse over the urethral groove, → tubed urethra from proximal-to distal.
labioscrotal swellings → scrotum, separated by scrotal septum.
7mths Testes usually descend into the scrotum
How does the female external genitalia form?
- Genital tubercle → clitoris urethral groove does not extend into the genital tubercle.
- he urethral folds do not fuse over urethral groove. Instead they form a hood over clitoris and labia minora.
- The labioscrotal swellings form the labia majora.
What is the anatomy of the penis?
- Root
- Body
- Glans
ROOT
- Bulb → corpus spongiosum
- bulbospongiosus muscle
- attaches to perineal body
- empties semen and urine
- contains urethra
- Lateral crurae (2) → corpus cavernosum
- ischiocavernosus muscle
- causes erection
- attaches to perineal memebrane
- Bulbourethral glands
What are the layers of the penis at the body?
Skin
Dartos fascia
- superficial dorsal vein
Bucks fascia
- deep dorsal vein
- dorsal artery
- dorsal nerve
Tunica albuginea
- corpus cavernosum - deep artery
- corpus spongiosum - artery to urethral bulb
What is the blood supply of the penis?
ARTERIES
- Internal iliac
- Internal pudendal
- Artery to urethral bulb
- Dorsal artery - supplies CC, skin, fascia, glans
- Deep artery (cavernosal artery - erectile)
VEINS
- deep dorsal vein → prostatic venous plexus
- venae comitantes → internal pudendal
- superficial dorsal vein → superficial external pudendal and great saphenous
What is the lymphatic drainage of the penis?
Superficial dorsal vein (skin) → superficial inguinal nodes
Glans and corpora → deep inguinal nodes → internal iliac nodes
What is the nerve supply to the penis?
Skin → posterior scrotal and dorsal br of pudendal
Glans skin → dorsal nerves
Ischiocavernosus and bulbospongiosus muscle → perineal branch of pudendal
Ejaculation → sympathetics(L1) sup&inf hypogastric plexi
Erection → parasympathetic pelvic splanchnic nerves to corpus cavernosum
What is the anatomy of the urethra?
3 parts
- prostatic
- membranous
- penile
transitional epithelium except part proximal to external meatus (stratified squamous)
external meatus → vertical split
3 constrictions
- internal meatus (bladder neck)
- prox end of navicular fossa
- external meatus
What are the fascial layers of the penis?
Colles fascia becomes Dartos and Bucks
Dartos
Bucks
Tunica albuginea (tightly binds corpus cavernosum and corpus spongiosum)
What is hypospadias?
Hypospadias is a congenital condition of the penis characterised by:
- ventral meatus
- dorsal hood = hooded prepuce
- chordee = ventral curvature
May be associated with
- paraurethral sinuses
- urethral valves
- flattened glans penis
- deficient central skin
- clefting of glans
- scrotal bipartition
What are the embryological theories of hypospadias?
- Failure of urethral folds coalesing in midline from base to tip (but what about glans?)
- Baskin (2000) urethral folds fuse → seam of epithelium → canalises by apoptosis. Similar canalisation by apoptosis of glans
- Prepuce - formed by growth of ridge of skin from corona. In hypospadias, urethral folds fail to fuse so prepuce is hooded
- Chordee - dorsal tissue grows normally, ventral urethra and associated tissues are attenuated
What is the epidemiology of hypospadias?
1 in 300 live male births
Distal - no assocs
Proximal - assoc w
- inguinal hernias (50%)
- other GU tract (25%)
- undescended testes (5% of all hypospadias, 31% of prox)
- open processus vag 9%
- upper GU tract abn 3%
- FHx - 4-10%
- IVF (4x more common)
What is the aetiology of hypospadias?
Environmental (increased oestrogens / plant oestrogens)
Androgen hyposensitivity
Genetic - father son 8%, sibling 14%
Androgen receptor deficiency