Development of the Gonads

Question 1

What is established during gastrulation?

Answer 1

The primitive streak develops and establishes a right and left side of the developing embryo

Question 2

What happen during craniocaudal embryonic folding?

Answer 2

The cranial and caudal end of the embryo come into closer proximity due to the weight of the amniotic fluid pushing them closer together

Question 3

What happens during lateral embryonic folding?

Answer 3

The 2 lateral edges of the embryonic disc come into closer proximity and fuse together in the midline

Question 4

What is the exception of areas that fuse during lateral embryonic folding?

Answer 4

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

Question 5

Which gonad is involved in determining genetic sex?

Answer 5

The sperm

Question 6

What is meant by the indifferent stage of development?

Answer 6

The developing gonad is the same in males and females for the first 7 weeks

Question 7

When does genetic determination of sex occur?

Answer 7

At fertilisation

Sex is determined by whether the sperm carries an X or a Y chromosome

Question 8

What is the precise component of the Y chromosome that determines sex?

Answer 8

The SRY gene of the Y-chromosome

This initiates production of testis-determining factor (TDF)

Question 9

What happens at fertilisation when there is no Y chromosome?

Answer 9

There is no SRY region

This means that no TDF is produced and an ovary develops

Question 10

What is the reproductive system derived from?

Answer 10

Intermediate mesoderm

Question 11

What will the intermediate mesoderm go on to form?

Answer 11

The intermediate mesoderm forms the urogenital ridge

The gonads develop from the genital ridge of the urogenital ridge

Question 12

What else is formed from the urogenital ridge?

Answer 12

The urogenital ridge goes on to form the urinary system and the reproductive system

Question 13

During which weeks of development is the indifferent gonad present?

Answer 13

Weeks 5-6

Question 14

What happens to the indifferent gonad as the epithelium covering the urogenital ridge begins to proliferate?

Answer 14

The epithelium of the genital ridge proliferates and thickens

It encroaches into the underlying mesenchyme to form primitive sex cords

Question 15

What are primitive sex cords?

Answer 15

The proliferations of epithelium that project into the mesenchyme

Question 16

What happens during week 6 of development?

Answer 16

The primordial germ cells migrate from the yolk sac to the genital ridge

Question 17

How do the primordial germ cells arrive at the genital ridge?

Answer 17

They migrate through the yolk sac and the dorsal mesentery

Question 18

Developmentally, how can the indifferent gonad be split into 2 distinct regions?

Answer 18

1. outer cortex

2. inner medulla

Question 19

What determines the fate of the medullary and cortical regions?

Answer 19

Whether the medulla or the cortical region is developed depends on whether TDF is present

Developing the medulla = testes

Developing the cortex = ovaries

Question 20

What information is contained within the primordial germ cells?

Answer 20

The genetic information that determines whether a male or female will develop

44+XX or 44+XY

Question 21

If there is a Y chromosome and SRY gene present, what will and won’t develop?

Answer 21

1. primitive sex cords (medullary cords) continue to develop further
2. the tunica albuginea will develop
3. no cortical cords will develop

Question 22

If there is an X chromosome present, and no SRY gene, what will and won’t develop?

Answer 22

1. the medullary cords regress and cortical cords develop

2. the tunica albuginea does not develop

Question 23

What happens to the primordial germ cells?

Answer 23

The medullary (primitive sex cords) invest the primordial germ cells

They are invested by the somatic support cells within the cords

Question 24

Under the influence of TDF, what happens to the primitive sex cords?

Answer 24

The primitive sex cords continue to develop into medullary (testis) cords

Question 25

What do the medullary (testis) cords dorm as they go further in to the medulla?

Answer 25

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

Question 26

What is the tunica albuginea?

Answer 26

It is the connective tissue that develops around the testes

Question 27

What happens to the seminiferous tubules during puberty?

Answer 27

They are solid cords up until puberty A surge of hormones causes them to canalise and the male can make mature sperm

Question 28

What happens to the primitive sex cords if there is no TDF?

Answer 28

The medullary cords regress and they are broken down into small pieces

Question 29

What produces the cortical cords in the ovary? Where do they develop?

Answer 29

The surface epithelium continues to proliferate to produce cortical cords These develop within the cortex of the developing gonad

Question 30

What is the role of the cortical cords?

Answer 30

They invest the primordial germ cells They split and surround the oocytes

Question 31

What do the somatic support cells form in the ovary?

Answer 31

The somatic support cells invest the primordial germ cells and form follicular cells

Question 32

what is the role of the follicular cells?

Answer 32

They signal back to the primordial germ cell and cause them to undergo the first stage of meiosis This forms a primary oocyte

Question 33

What happens to a female at puberty?

Answer 33

Hormones allow the primary oocytes to mature and ovulation begins

Question 34

Whereabouts in the body do the male and female gonads develop?

Answer 34

The gonads develop on the posterior abdominal wall This is where the genital ridge is

Question 35

What pulls the testes towards the anterior abdominal wall? When does this occur?

Answer 35

The extraabdominal gubernaculum shortens and pulls the testes towards the AAW This happens during week 7-12

Question 36

Where does the gubernaculum pull the testes to?

Answer 36

The deep inguinal ring They remain here from the 3rd-7th month

Question 37

What is the inguinal canal formed from?

Answer 37

The processus vaginalis This is an invagination of the parietal peritoneum

Question 38

What happens to the testes after the 7th month?

Answer 38

The gubernaculum begins shortening again to pull the testes through the inguinal canal

Question 39

What is the gubernaculum?

Answer 39

It is a tendinous cord that attaches to the inferior pole of the gonad It initially extends out and attaches to the pelvis

Question 40

What else helps to aid the movement of the testes through the inguinal canal?

Answer 40

The abdominal organs as they increase the intraabdominal pressure

Question 41

When do the testes reach the scrotum?

Answer 41

By the 9th month of development

Question 42

What is the purpose of the processus vaginalis?

Answer 42

it makes the road through which the testis are pulled through

Question 43

What happens to the processus vaginalis after birth?

Answer 43

Within the 1st year, the processus vaginalis obliterates leaving a remnant around the testes This is the tunica vaginalis

Question 44

What happens if the processus vaginalis fails to close off during the first year?

Answer 44

This can lead to a hernia as other structures can pass through the patent processus vaginalis

Question 45

What must the testes pass through as they descend?

Answer 45

As the testes descend through the abdominal wall, they must pass through the 3 muscular layers and the relevant fascia

Question 46

What do the testes pick up as they pass through the deep inguinal ring?

Answer 46

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

Question 47

What is the external spermatic fascia formed from?

Answer 47

External oblique muscle

Question 48

What is the cremasteric fascia formed from?

Answer 48

Internal oblique muscle

Question 49

What is the internal spermatic fascia formed from?

Answer 49

Transversalis fascia

Question 50

What is the cremasteric reflex?

Answer 50

If you touch the inner aspect of the thigh, the cremasteric muscle contracts and pulls the testes towards the thigh

Question 51

What is the cremasteric reflex controlled by?

Answer 51

The genitofemoral nerve As the testes pass through the fascia, it takes some of the muscle fibres with it

Question 52

What happens in patent processus vaginalis?

Answer 52

Parts of the processus vaginalis may remain unfused leaving small cysts

Question 53

What happens if the cysts begin to produce fluid?

Answer 53

They swell and form fluid-filled cysts This is a hydrocele

Question 54

What happens if the processus vaginalis remains completely patent to the abdominal cavity?

Answer 54

INdirect inguinal hernia This occurs when the intestine protrude through the inguinal canal

Question 55

How can a hydrocele be distinguished from other solid tissues (e.g. tumour/hernia)?

Answer 55

Through transillumination Light will pass through the hydrocele but the solid tissue wou;ld block light

Question 56

How are hydroceles treated?

Answer 56

They are benign but may cause discomfort They are removed surgically

Question 57

How many people are affected by cryptorchidism?

Answer 57

1-4% of births Most spontaneously correct by 3 months of age

Question 58

What is a cryptorchidism?

Answer 58

The testes become stuck along their path of descent This is usually in the high scrotal region

Question 59

What happens in the cases of cryptorchidism that do not correct themselves?

Answer 59

Those that remain undescended are corrected surgically at 4-6 minutes

Question 60

What is cryptorchidism associated with?

Answer 60

an increased risk of testicular cancer and infertility

Question 61

What happens to the gubernaculum during descent of the ovaries?

Answer 61

It passes through the inguinal canal and inserts onto the labia majora

Question 62

Where to the ovaries descend to?

Answer 62

The level of the pelvic brim

Question 63

What does the gubernaculum form in a female adult?

Answer 63

The ovarian ligament proper and the round ligament of the uterus

Question 64

In a male, what will the somatic support cells change to become?

Answer 64

Sertoli cells These invest primordial germ cells migrating from the yolk sac

Question 65

What will the sertoli cells and the primordial germ cells form?

Answer 65

Testes cords The testes cords then develop into seminiferous tubules