Development Of The Urogenital System

Question 1

What are the names of the three sets of kidney structures during development?

Answer 1

Pronephros -cervical region
Mesonephros - abdominal region
Metaneohros - pelvic region

Question 2

Describe the pronephros.

Answer 2

Develops first and regresses around week 4.
It’s rudimentary and non-functional.
It has 7-10 solid cell groups

Question 3

Describe the mesonephros.

Answer 3

This is first seen in week 4 after the pronephros regresses
The excretory tubules form first and drain into the mesonephric duct .
It contributes supporting cells to the genital ridge

Question 4

Describe the metanephros.

Answer 4

This is the definitive kidney.
It appears in week 5 and is functional by week 11
The excretory units develop from the metanephric mesoderm.
It’s made of two parts - ureteric bud
- metanephric cap

Question 5

When do the nephrons stop developing?

Answer 5

They continue developing until birth, but urine production starts early in gestation.

Question 6

How does the urorectal septum divide the cloaca, and when does this happen?

Answer 6

It’s fuses with the cloaca membrane to form the anterior urogenital sinus and the posterior rectal/anal canal
This happens between weeks 4 and 7

Question 7

What is the bladder eventually formed from?

Answer 7

The urogenital sinus and caudal parts of the mesonephric duct (trigone)

Question 8

What is the bladder lined with at this stage?

Answer 8

Endoderm

Question 9

What is the allantois?

Answer 9

Outpouching of the hindgut

It’s a sac like structure involved in nutrition and excretion.

Question 10

What is the urachus?

Answer 10

It’s a duct between the bladder and the yolk sac, formed form the allantois. It eventually becomes the medial umbilical ligament

Question 11

What is the cloaca?

Answer 11

A posterior orifice that serves as the only opening for the early stages of the intestinal, reproductive and urinary tracts.

Question 12

What is the ureteric bud?

Answer 12

A protrusion of the mesonephric duct. It allows drainage from the developing kidney.

Question 13

What is the difference between genetic sex and physiological sex?

Answer 13

Genetic sex is determined at fertilisation. Gonads only develop make or female characteristics around week 7.

Question 14

What three stages are there in the development of the reproductive tract?

Answer 14

1) Genital duct development (the indifferent stage)
2) Gonadal development
3) External genitalia development.

Question 15

What happens in the genital duct development stage?

Answer 15

Two pairs of genital ducts develop in weeks 5-6.
- the paramesonephric duct (female)
- the mesonephric duct (male)
The paramesonephric ducts are lateral to the mesonephric ducts

Question 16

What is the function of the mesonephric (male) ducts, and how do they develop?

Answer 16

Drain urine from the mesonephric kidney.
Play an essential role in development of the male reproductive system.
Under the influence of testosterone it forms the vas deferens and ejaculatory duct once the mesonephros regresses
In females the lack of testosterone allows the duct to disappear, leaving only a few non-functional remains.

Question 17

What is the function of the paramesonephric ducts and how do they develop?

Answer 17

They develop laterally to the gonads and mesonephric ducts
They form funnel shaped cranial ends that open into the peritoneal cavity
They migrate caudally, parallel to the mesonephric ducts until they reach the future pelvic region
They approach each other in the midline, with the cranial part forming uterine tubes and the caudal part forming the uterus and superior vagina (uterovaginal primordium)

Question 18

What happens to the paramesonephric ducts in males?

Answer 18

They degenerate due to the action of anti-mullerian hormone, a protein made by the serotoli cells of the testes.

Question 19

How do they gonads usually appear in week 5 in both of the sexes?

Answer 19

As longitudinal ridges. Also known as the urogenital or gonadal ridges.

Question 20

What forms the urogenital or gonadal ridges?

Answer 20

Projection of the mesoderm structure into the coelomic cavity

Question 21

Where do primordial germ cells originate from and how doe they get to the gonadal ridge?

Answer 21

They originate in the yolk sac and move to the gonadal ridge via the dorsal else try to form the primordial gonad.

Question 22

What happens if the primordial germ cells don’t reach the gonadal ridge by week 6?

Answer 22

The ridges can’t develop any further

Question 23

What happens to the primordial germ cells when they reach the gonadal ridge?

Answer 23

They form in a cord like structure to become the primitive sex cords

Question 24

What is the testis determining factor and what does it do?

Answer 24

If the embryo is genetically male, the Y chromosome encodes the testis determining factor SRY (sex determining region of Y chromosome)
This acts on somatic cells and allows proliferation of the sex cords

Question 25

Describe gonad differentiation in males.

Answer 25

The cords become horseshoe shaped, and then break up into tubules.
- the cords contain both somatic and primitive germ cells
Leidig cells begin to produce testosterone
Serotoli cells begin to produce AMH (anti-mullerian hormone)
Dense connective tissue forms
- tunica alberguinea
- this separates the cords from the surface epithelium

Question 26

Testis cords are solid until puberty, when what occurs?

Answer 26

They acquire a lumen to form seminiferous tubules
They join with the rete testes, which joins with the efferent ductlules
The rete testis and the mesonephric duct link to form the ductus deferens

Question 27

What is the active signal needed for the maintained of the paramesonephric ducts and thus female development?

Answer 27

Wnt4 - the ovary determining gene

Question 28

What hormone is needed for the development of the female gonads?

Answer 28

No hormones. Just the XX chromosome means SRY can’t be produced.

Question 29

What effects do the primordial germ cells have on the gonadal ridge in females?

Answer 29

It stimulates somatic cells to grow from the coelomic epithelium
Allows surface epithelium to continue to proliferate
They also divide by mitosis to form a pool of oogonia

Question 30

How do oogonia become oocytes?

Answer 30

They enter meiosis arrest at 4 months - now called oocytes

They then become associated with follicular cells and are called primordial follicles

Question 31

When does the development of the external genitalia begin?

Answer 31

Week 3

Question 32

How does the development of th external genitalia begin?

Answer 32

A pair of cloacal folds develop around the cloacal membrane, joining at the cranial end to form a genital tubercle

Question 33

In what ways are the cloacal folds then subdivided?

Answer 33

They form urethral folds in front (labia minora in females)
Anal folds behind
Genital swellings then appear in either side of the urethral folds
- form scrotal swellings in men
- form labia majora in females

Question 34

What forms the urethra?

Answer 34

The middle pelvic part of the urogenital sinus

Question 35

What causes the gentian tubercle to elongate into phallus in men?

Answer 35

Androgens from the fetal testis

Question 36

What happens when the genital tubercle elongates into a phallus in men?

Answer 36

The phallus pulls the urethral folds forward
These then form the lateral walls of the urethral groove and close over the urethral plate to form the penile urethra
The terminal part of the male urethra forms surface ectoderm

Question 37

What is the prostate gland derived from?

Answer 37

Outgrowths from the prostatic urethra

Question 38

What are the bulbourethral glands derived from?

Answer 38

Outgrowths of the penile urethra

Question 39

What is the lower part of the vagina formed from?

Answer 39

Two outgrowths of the urogenital sinus (sinovaginal bulbs) fuse to forms vaginal plate.
This then hollows to form a cavity

Question 40

Name some of the things that can go wrong in female development.

Answer 40

Double uterus - failure of fusion
Vaginal atresia - failed canalisation
Absense of vagina and uterus
- failure of sinovaginal bulbs means no vagina
- because the formation of these bulbs are normally induced by the uterus, it is normally absent as well.

Question 41

Name some of the possible developmental problems in males.

Answer 41

Hypospadias (penile, perineal)

Epispadias

Question 42

Name some of the possible intersex disorders

Answer 42

Klinefelter’s syndrome - XXY or XXXY
Testicular feminising syndrome - female external phenotype
Turners syndrome - X0
Dihyrdotestosterone- lack of gene for 5-alpha reductase

Question 43

Describe klinefelter’s syndrome

Answer 43

When a man has the chromosomes XXY or XXXY, causing the leidig cells to not produce enough steroids, causing low sperm production
(1 in 500 males)
Causes infertility, gynaecomastia and impaired sexual maturation

Question 44

Describe testicular feminising syndrome.

Answer 44

When someone is genetically male, but has female external phenotype, with internal testes.
The testes produce testosterone, but a mutation on the X chromosome causes a deficiency in androgen receptors so the testosterone can’t act in target tissue
The uterus and upper vagina is absent because they can still produce AMH

Question 45

Describe turners syndrome.

Answer 45

This is a woman with the chromosomes X0
It causes primordial germ cells to degenerate shortly after arriving at the gonadal ridge
This causes failure of gonadal development - infantile genitalia and mesonephric duct regression

Question 46

What happens when men don’t get dihydrotestosterone in utero?

Answer 46

This is caused by a lack of the gene that encodes for 5-alpha reductase
This enzyme normally converts testosterone to dihydrotestosterone
This means their penis doesn’t develop properly, they have an enlarger clitoris, they have a blind vaginal pouch and internal testis.
They look female
Suddenly grow a penis and normal secondary sex characteristics at puberty

Question 47

What part of the gastrula does the urogenital tract originate from?

Answer 47

The intermediate mesoderm