Development of the Gonads Flashcards
What is established during gastrulation?
The primitive streak develops and establishes a right and left side of the developing embryo
What happen during craniocaudal embryonic folding?
The cranial and caudal end of the embryo come into closer proximity due to the weight of the amniotic fluid pushing them closer together
What happens during lateral embryonic folding?
The 2 lateral edges of the embryonic disc come into closer proximity and fuse together in the midline
What is the exception of areas that fuse during lateral embryonic folding?
The lateral edges fuse everywhere except at the level of the midgut
This is at the level of the vitelline duct - which connects to the yolk sac
Which gonad is involved in determining genetic sex?
The sperm
What is meant by the indifferent stage of development?
The developing gonad is the same in males and females for the first 7 weeks
When does genetic determination of sex occur?
At fertilisation
Sex is determined by whether the sperm carries an X or a Y chromosome
What is the precise component of the Y chromosome that determines sex?
The SRY gene of the Y-chromosome
This initiates production of testis-determining factor (TDF)
What happens at fertilisation when there is no Y chromosome?
There is no SRY region
This means that no TDF is produced and an ovary develops
What is the reproductive system derived from?
Intermediate mesoderm
What will the intermediate mesoderm go on to form?
The intermediate mesoderm forms the urogenital ridge
The gonads develop from the genital ridge of the urogenital ridge
What else is formed from the urogenital ridge?
The urogenital ridge goes on to form the urinary system and the reproductive system
During which weeks of development is the indifferent gonad present?
Weeks 5-6
What happens to the indifferent gonad as the epithelium covering the urogenital ridge begins to proliferate?
The epithelium of the genital ridge proliferates and thickens
It encroaches into the underlying mesenchyme to form primitive sex cords
What are primitive sex cords?
The proliferations of epithelium that project into the mesenchyme
What happens during week 6 of development?
The primordial germ cells migrate from the yolk sac to the genital ridge
How do the primordial germ cells arrive at the genital ridge?
They migrate through the yolk sac and the dorsal mesentery
Developmentally, how can the indifferent gonad be split into 2 distinct regions?
- outer cortex
2. inner medulla
What determines the fate of the medullary and cortical regions?
Whether the medulla or the cortical region is developed depends on whether TDF is present
Developing the medulla = testes
Developing the cortex = ovaries
What information is contained within the primordial germ cells?
The genetic information that determines whether a male or female will develop
44+XX or 44+XY
If there is a Y chromosome and SRY gene present, what will and won’t develop?
- primitive sex cords (medullary cords) continue to develop further
- the tunica albuginea will develop
- no cortical cords will develop
If there is an X chromosome present, and no SRY gene, what will and won’t develop?
- the medullary cords regress and cortical cords develop
2. the tunica albuginea does not develop
What happens to the primordial germ cells?
The medullary (primitive sex cords) invest the primordial germ cells
They are invested by the somatic support cells within the cords
Under the influence of TDF, what happens to the primitive sex cords?
The primitive sex cords continue to develop into medullary (testis) cords
What do the medullary (testis) cords dorm as they go further in to the medulla?
Going further into the medulla, the cords begin to break up and form rete testis
The testis cords develop to form C-shaped tubules called seminiferous tubules
What is the tunica albuginea?
It is the connective tissue that develops around the testes
What happens to the seminiferous tubules during puberty?
They are solid cords up until puberty
A surge of hormones causes them to canalise and the male can make mature sperm
What happens to the primitive sex cords if there is no TDF?
The medullary cords regress and they are broken down into small pieces
What produces the cortical cords in the ovary?
Where do they develop?
The surface epithelium continues to proliferate to produce cortical cords
These develop within the cortex of the developing gonad
What is the role of the cortical cords?
They invest the primordial germ cells
They split and surround the oocytes
What do the somatic support cells form in the ovary?
The somatic support cells invest the primordial germ cells and form follicular cells
what is the role of the follicular cells?
They signal back to the primordial germ cell and cause them to undergo the first stage of meiosis
This forms a primary oocyte
What happens to a female at puberty?
Hormones allow the primary oocytes to mature and ovulation begins
Whereabouts in the body do the male and female gonads develop?
The gonads develop on the posterior abdominal wall
This is where the genital ridge is
What pulls the testes towards the anterior abdominal wall?
When does this occur?
The extraabdominal gubernaculum shortens and pulls the testes towards the AAW
This happens during week 7-12
Where does the gubernaculum pull the testes to?
The deep inguinal ring
They remain here from the 3rd-7th month
What is the inguinal canal formed from?
The processus vaginalis
This is an invagination of the parietal peritoneum
What happens to the testes after the 7th month?
The gubernaculum begins shortening again to pull the testes through the inguinal canal
What is the gubernaculum?
It is a tendinous cord that attaches to the inferior pole of the gonad
It initially extends out and attaches to the pelvis
What else helps to aid the movement of the testes through the inguinal canal?
The abdominal organs as they increase the intraabdominal pressure
When do the testes reach the scrotum?
By the 9th month of development
What is the purpose of the processus vaginalis?
it makes the road through which the testis are pulled through
What happens to the processus vaginalis after birth?
Within the 1st year, the processus vaginalis obliterates leaving a remnant around the testes
This is the tunica vaginalis
What happens if the processus vaginalis fails to close off during the first year?
This can lead to a hernia as other structures can pass through the patent processus vaginalis
What must the testes pass through as they descend?
As the testes descend through the abdominal wall, they must pass through the 3 muscular layers and the relevant fascia
What do the testes pick up as they pass through the deep inguinal ring?
As they pass through the inguinal canal they are accompanied by a part of the peritoneal lining of the abdominal cavity
This is the processus vaginalis
What is the external spermatic fascia formed from?
External oblique muscle
What is the cremasteric fascia formed from?
Internal oblique muscle
What is the internal spermatic fascia formed from?
Transversalis fascia
What is the cremasteric reflex?
If you touch the inner aspect of the thigh, the cremasteric muscle contracts and pulls the testes towards the thigh
What is the cremasteric reflex controlled by?
The genitofemoral nerve
As the testes pass through the fascia, it takes some of the muscle fibres with it
What happens in patent processus vaginalis?
Parts of the processus vaginalis may remain unfused leaving small cysts
What happens if the cysts begin to produce fluid?
They swell and form fluid-filled cysts
This is a hydrocele
What happens if the processus vaginalis remains completely patent to the abdominal cavity?
INdirect inguinal hernia
This occurs when the intestine protrude through the inguinal canal
How can a hydrocele be distinguished from other solid tissues (e.g. tumour/hernia)?
Through transillumination
Light will pass through the hydrocele but the solid tissue wou;ld block light
How are hydroceles treated?
They are benign but may cause discomfort
They are removed surgically
How many people are affected by cryptorchidism?
1-4% of births
Most spontaneously correct by 3 months of age
What is a cryptorchidism?
The testes become stuck along their path of descent
This is usually in the high scrotal region
What happens in the cases of cryptorchidism that do not correct themselves?
Those that remain undescended are corrected surgically at 4-6 minutes
What is cryptorchidism associated with?
an increased risk of testicular cancer and infertility
What happens to the gubernaculum during descent of the ovaries?
It passes through the inguinal canal and inserts onto the labia majora
Where to the ovaries descend to?
The level of the pelvic brim
What does the gubernaculum form in a female adult?
The ovarian ligament proper and the round ligament of the uterus
In a male, what will the somatic support cells change to become?
Sertoli cells
These invest primordial germ cells migrating from the yolk sac
What will the sertoli cells and the primordial germ cells form?
Testes cords
The testes cords then develop into seminiferous tubules
