L43 Embryology 2 Flashcards
What do Sertoli cells develop from?
n males, once the primordial germs cells reach the primitive sex cords, made up of sematic support cells, it causes them to differentiate. The sematic support cells, in the presence of the primordial germ cells, to differentiate into Sertoli cells.
What do seminiferous tubules develop from?
The primordial germ cells are invested by the Sertoli cells and elongate to form solid testes cords. The solid testes cords develop further and separate from the overlying epithelium. As they continue to develop they make the seminiferous tubules which are solid until puberty. At puberty the tubules canalise, so that male can produce sperm and eject them into the tubules
Which cells secrete AMH?
Sertoli cells also secrete Anti-Mullerian hormone (AMH). This actively causes the breakdown of the Mullerian ducts (Paramesonephric duct). It also stimulates the mesenchyme around it to differentiate.
How do Leydig cells arise?
The Sertoli cells in the sex cords stimulate the cells around it to differentiate into Leydig cells (produce testosterone). Testosterone cats as a signalling factor to all the structures to allow male develop to progress (elongate genital tubule and causes external genitalia to develop etc.)
When does the paramesonephric duct arise?
Week 6
What are the derivatives of the mesonephric duct?
On the medial side of the developing kidney is the developing gonad. The mesonephros has a region that has an excretory function for a short period of time. It functions as a primitive kidney emptying into the mesonephric duct. As we develop the metanephros, the mesonephros breaks down. In male development, TDF and testosterone allows us to maintain a couple of the excretory ducts of the mesonephros. The excretory ducts connect to the developing gonad. The mesonephric duct connects to the developing bladder. Later with development of the bladder it will connect to the prostatic urethra (where sperm enters). Development of the mesonephric duct and the excretory tubules, forms a connection with the urethra. The excretory tubules form efferent ductulus. Sperm is made in the seminiferous tubule, where they are passed to Retes for maturation, where it is passed to the efferent ductulus and epididymis - maturation occurs. During ejaculation sperm is passed through the duct system and into the prostatic urethra.
The vas deferens develops from the mesonephric duct - also the efferent ductulus and epididymis and the seminal vesicle.
What are the remnants of the paramesonephric duct in the male?
Since AMH is made, we break down the paramesonephric ducts (Mullerian ducts). There are still some remnants - the appendix testes and the utriculus prostaticus.
What are the derivatives of the paramesonephric duct?
There is no AMH and so the paramesonephric duct system is free to develop. Without testosterone, the mesonephric duct system is not maintained. The paramesonephric duct system towards the caudal region, the caudal tips fuse together - where they fuse together they form the uterus. The uterus is formed by the caudal tips of the duct system fusing together. The cranial part of the duct system forms the uterine tubes.
What are the remnants of the mesonephric duct in the female?
The break down of the mesonephric duct system leaves embryological remnants - Epophoron and the Paroophpon and the Gartner’s cyst near the vagina.
How does the vagina and uterus form?
The caudal parts of the paramesonephric duct fuse together to form the uterus. Once the two tubes fuses together, the septum separating them breaks down. There is a single uterine cavity. From development, the cloaca is where the hindgut empties and where the bladder develops from. The anorectal septum develops to separate the cranial (urogenital sinus) and caudal part (posteriorly the anal canal).
The urogenital sinus develops sinvoaginal bulbs (a thickening of endoderm either side) that fuse with the caudal tips of the paramesonephric ducts to form the vagina. The thickening grows towards the developing uterus cranially very quickly. As it grows cranially it pushes the uterus away from the developing bladder.
The distal vagina is formed from endoderm, the sinovaginal bulbs. The upper vaginal anal is formed from the paramesonephric duct, from mesoderm.
The hymen is a thin membrane. The sinovaginal bulbs form and develop very quickly. They flatten to form a plate. The plate then canalises to form a tube. Where the two meet is where the hymen forms.
How can abnormalities of the uterus form?
Development of the paramesonephric duct system fail to develop properly.
1. The left and right paramesonephric duct can fail to fuses there can be two reproductive canals - two vaginal canals.
2. With a double uterus, the paramesonephric ducts fuse only at the tips
3. If they fuse at the wrong point we can get a bi-cornered uterus
4. If the very caudal tips only just meet, can get a very thin cervix - clerical atresia
5. Unicornate uterus - one of the paramesonephric ducts does not develop properly
Septate uterus - they have fused together but the septa between the paramesonephric duct has not broken down.
What is Persistent Mullerian duct Syndrome?
No AMH production – paramesonephric ducts persist. Both mesonephric and paramesonephric duct derivatives develop. Normal male external genitalia but associated with cryptorchidism (undescended testes). There is a genetic male with testes producing testosterone which leads to external genetic genitalia. Due to the persistent Mullerian duct, a uterus develops inside. Two duct system develop. The testes must descent into the scrotum. This can causes issues here.
What is the indifferent stage of the development of the external genitalia?
Development of external genitalia
Up until 13 weeks of development, there is an indifferent external genitalia. Just either side of the urogenital sinus, mesoderm cells migrate around the cloaca membrane. They migrate to form elevations cloacal folds. Cranially the cloacal folds fuse to form a genital tubercle. Caudally they will go onto form an anal fold. They are separated when we develop a anorectal septum (sperate the cloacal fold and the anal fold).
The genital tubercle will go onto form the penis or the clitoris - this is due to the presence of testosterone. Next to the cloacal folds is the genital swellings which wither side of the cloacal folds (labia-scrotal swellings) go onto form the labia majora or the scrotum. They are homologues - in the male the skin is fused and the testes has descended into them.
What is development of male genitalia dependent on?
Testosterone
How does male genitalia develop?
Due to testosterone, elongation of the genital tubercle is driven to form the Phallus to form the penis. As the genital tubercle develops rapidly, it pulls the urethral groove with it.
As it develops it falls back on itself. In the supine position, if the penis is flattened you are looking at the dorsal surface. In the anatomical position, the penis is in the erect position. In an adult you need to lift it to see the ventral surface.
