Development of the Reproductive Tract Flashcards
Describe the male internal and external genitalia
Male Internal Genitalia contains: Testis, ducts system (epididymis, vas deferens, urethra), seminal vesicles, prostate gland and bulbourethral glands.
Male external genitalia contain the penis and scrotum.
Describe the female internal and external genitalia
Female internal genitalia contain: Ovaries and a duct system containing (fallopian tube, uterus, cervix, vagina).
Female external genitalia contain the vagina, vestibule, labia minora, labia majora and clitoris.
Does the embryo develop as male/female from the beginning?
Indifferent stage (gonad and duct system) up until a certain point at which we differ into male and female - developmental cross roads regulated by genetic sex
- Structural development occurs in utero
- Functional development and maturation continues after birth
What are secondary sexual characteristics - give examples
In the functional development stage children become sexually mature through puberty by developing secondary sexual characteristics this is known as sexual maturation.
Male secondary sexual characteristics: Increase body size relative to females, decrease fat composition and increase muscle, pubic hair grown and skin becomes more oily, male baldness may occur, smell changes and penis enlargement.
Female secondary sexual characteristics: decrease body size relative to males, increase subcutaneous fat and decrease muscle, pubic hair and breast development.
What is the urogenital ridge?
The Urogenital ridge is a region of intermediate mesoderm giving rise to both the embryonic kidney and the gonad. The indifferent Gonad is derived from intermediate mesoderm plus primordial germ cells (extragonadal).
What are primordial germ cells - where do they come from and where do they go?
Primordial germ cells are a special population of cells that arise in the yolk sac and migrate into the retroperitoneum, through the umbilicus and along the dorsal mesentery. They are separated out and protected from other somatic signals in the embryo.
What happens if the primordial germ cells don’t make it?
If these primordial germ cells get lost along the way they can die or sometimes they remain and lead to germ cell tumours.
What causes a foetus to develop into a male? What happens to the primordial germ cells if you are XY
Male gamete carries a Y chromosome so overall becomes XY
Expression of the SRY gene drives development of the male through formation of the gonad into a testis, internal and external genitalia form a male duct system. Colonisation of the medulla of the gonad and degeneration of the cortex and a thick tunica albuginea.
What happens to the primordial germ cells if you are XX
Male gamete carrying X chromosome so overall foetal cells are XX. Absence of the Y chromosome leads to development of female – gonad forms into ovaries, internal and external genitalia form a female duct system. Colonisation of the cortex of the gonad and degeneration of the medullary cords and no tunica albuginea.
Absence of a Y causes the development of a female.
What is the function of the mesonephric duct and in what direction does it run to?
Mesonephric tubules perform a primitive renal function. Mesonephric tubules and mesonephric duct = embryonic kidney. Mesonephric duct (Wolffian duct) runs caudally to contact the cloaca.
Describe the paramesonephric duct
Paramesonephric duct (mullerian duct) appear as invaginations of the epithelium of the urogenital ridge. Caudally contact the cloaca (urogenital sinus) and cranially open into the abdominal cavity.
What is the cloaca?
Cloaca is present early on in development and is where the genital, GI and urinary tract all merge and empty into the cloaca. Urogenital Sinus is formed after the urorectal septum separates the cloaca into urogenital sinus and rectum.
What happens to the paramesonephric duct in a female?
Initially the paramesonephric duct push out into the abdominal cavity and meet each other in the midline and fuse. This fusing of the ducts forms the uterus.
Vagina has contribution from endoderm (urogenital sinus) and mesoderm
Describe how one of the ducts become redundant in males
XY - embryo produces Testis. Testis produce androgens which supports the mesonephric duct (without signal it degenerates). Testis secretes mullerian inhibiting substance and so paramesonephric duct degenerates.
Describe how one of the ducts become redundant in females
XX - embryo ovary develops. No androgen so mesonephric duct degenerates. No testis so no MIS and so paramesonephric duct forms.
What does the wolffian duct form in males?
Wolffian Duct forms the Vas deferens, seminal vesicles, ejaculatory duct and epididymis
What does the mullerian duct form in females?
Mullerian duct forms the fallopian tubes, Uterus, cervix and upper portion of the vagina.
What are the 4 main structures that develop into the external genitalia
Indifferent stage – basic components: genital tubercle, genital folds, urogenital sinus and genital swellings.
Describe the formation of male external genitalia
In the male, the genital tubercle elongates and the genital folds fuse to form the spongy urethra. This occurs under the influence of testis-derived androgen hormones – dihydrotestosterone.
Genital fold – spongy urethra and ventral surface of the penis, genital swelling - scrotum, genital tubercle – glans penis and the urogenital sinus – urethral groove.
Describe the formation of the female external genitalia
In the female, no fusion occurs and urethra opens into the vestibule due to lack of androgen.
Genital fold – the labia minora, genital swelling – labia majora, genital tubercle clitoris and urogenital sinus - the urethral orifice.
Describe the descent of the testis
In males, testis descend between 7th - 8th months. The gubernaculum is a condensed band of mesenchyme that links inferior portion of testis (gonad) to labioscrotal swelling. It drags the testicle to where it need to go and the testicle brings with it it’s blood supply. The testicle is a retroperitoneal structure. The processus vaginalis which is a pouch of peritoneum invaginates ahead of the descending testicle into the scrotum.
As the testicle continues to descend it begins to be surrounded by the layers of the abdominal wall (no transversalis abdominis here) and eventually the processus vaginalis obliterates away from the main peritoneal cavity leaving a small amount of it attached to a portion of the testicle and becomes known as the tunica vaginalis. The abdominal wall layers surrounding the testicle eventually form into the layers surrounding the spermatic chord.
Describe the descent of the ovaries
Gubernaculum attaches ovary inferiorly to labio-scrotal folds. Ovary descends to the pelvis. The round ligament of the uterus is in the inguinal canal and comes off the uterus whilst the ligament of ovary proper supports the to the uterus.
The development of the uterus acts as a blockade preventing the movement of the ovary as far down as the testis go.
Describe the most common two genetic gender defects
Kleinfelter’s syndrome – XXY genetically Male but infertile
Turner’s Syndrome – partly or completely missing an X chromsome
Describe two common cloacal partitioning defects
Hypospadias
Uterine structural defects – bicorunate uterus – two conjoined cavities
