2a.) Development of Urinary System

Question 1

When concerning ourselves with development of urinary system we are concerned with development of what two specific components?

Answer 1

• Kidneys and ureters
• Bladder and urethras

Question 2

How many separate kidney sytems form in the process of creating the kidneys

Answer 2

Three separate kidney systems form sequentially; disappearance of one system marks onset of devlopmetn of another system

Question 3

From what germ layer does the kidney arise?

Answer 3

Intermediate mesoderm

Question 4

What is the first kidney system to develop and where does it develop?

Answer 4

• Pronephros
• Develops in the cervical region

Question 5

State the three kidney systems involved in development of definitive kidneys

Answer 5

Question 6

Given that the pronephros is non-functional, why do we consider it in the devlopment of the kidneys?

Answer 6

The pronephric duct drives the development of next stage

Question 7

When does the pronephros appear?

When does the pronephros disappear?

Answer 7

4th week

End of week 4

Question 8

Describe the strucurre of the pronephric duct, include:

• What it is made of
• Where it extends from and to

Answer 8

• Segmented divisions of intermediate mesoderm from nephrotomes (tubules)- 6-10 pairs
• Tubules join to form pronephric duct
• Duct extends from cervical region to cloaca

Question 9

Describe the development of the mesonephros

Answer 9

Mesonephros develop caudally to pronephros. Pronephric duct induces nearby intermediate mesoderm (in thoraco lumbar region) to form mesonephric tubules. Tubules receive capillaries from dorsal aorta allowing them to filter blood; the tubules then drain into the mesonephric duct (a continuation of the pronephric duct)

Question 10

Why do we need to continue devloping the urinary system after the mesonephros?

Answer 10

Mesonephros acts as primitive excretory system, as it can filter blood it receives from capillaries from the abdominal aorta, but it has no water conserving function hence we need to “upgrade it”

Question 11

What two components make up the embryonic kidney?

Answer 11

Mesonephric tubules + mesonephric duct

Question 12

What does the mesonephros sprout and why is this important?

Answer 12

Mesoneprhos sprouts uretericbud caudally; ureteric bud induces development of definitive kidney

Question 13

Why is the ureteric bud able to induce devlopment of the definitive kidney?

Answer 13

It has ability to drive development of undifferentiated intermediate mesoderm; it creates the metanephric blastema

Question 14

Which of the _____neprhos forms the definitive kidneys?

Answer 14

Metanephros

Question 15

When does the metanephros appear?

When is the metanephros functional by?

Answer 15

• Appears 5th week
• Functional by 12th week

Question 16

State the two components of the metanephric system which goes on to make definitive kidney

Answer 16

• Collecting system- derived from ureteric bud
• Excretory system- derived from metaneprhic blastema (intermediate mesoderm) under the influence of the ureteric bud

Question 17

Define blastema

Answer 17

. Blastema just means cells capable of growing or regenerating organs or body parts hence both the ureteric bud and the metanephric blastema may be referred to as blastema

Question 18

Where does the metaneprhic kidney first appear?

Which way must it move?

Describe the arterial supply as it moves

Answer 18

Metanephric kidney first appears in pelvic region so must then ascend into abdomen. When in pelvis, it receives it’s blood supply from pelvic branch of abdominal aorta and as it ascends new arteries from abdominal aorta supply the kidney and the other arteries including the pelvic arteries USUALLY regress. If they do not regress they will persist as accessory renal arteries.

• “Caudal to cranial shift”
• Crosses the arterial fork formed by vessels returning blood from fetus to placenta

Question 19

Describe how the ureteric bud develops into the collecting system

Answer 19

It dilates to form the ureter, renal pelvis, major and minor calyces and collecting tubes (terminating at the distal convulted tube)

Question 20

Describe how the metanphric blastema develops into the excretory system

Answer 20

• Collecting tubule formed
• Collecting tubules covered by metanephric cap which gives rise to excretory tubules which form the neprhon
• Proximal end of excretory tubules form Bowman’s capsule around a glomerulus and distal end elongated to form proximal convoluted tube, loop of Henle and distal convulted tube

Question 21

What is the cloaca?

Is it open or closed to outside environment?

Answer 21

• Terminal/end structure of hindgut that is a common chamber for GI and urinary waste
• Closed to outside environment by cloacal membrane

Question 22

The uro-rectal septum divides the cloaca into what two parts?

Answer 22

• Urogenital sinus (anterior)
• Anal canal (posteior)

Question 23

The urogential sinus is continuous with the umbilicus via what structure?

Answer 23

Urachus

Question 24

During what weeks is the cloaca divided into two parts by the uro-rectal septum?

Answer 24

4th - 7th weeks

Question 25

What is the uro-rectal septum?

Answer 25

Septum that divides cloaca into urogential sinus and anal canal

Question 26

The urogenital sinus is divided into three parts based on what each part becomes; describe the three divisions and what they differentiate into

Answer 26

* Superior part: bladder * Pelvic part: * Females: entire urethra and some of productive tract * Males: prostatic and membranous urethra * Caudal part: * Female: some of reproductive tract * Males: spongey urethra

Question 27

Describe how the bladder and ureters develop from the urogenital sinus

Answer 27

* Mesonephric ducts reach urogenital sinus * Caudal parts of mesoneprhic ducts are absorbed by urogenital sinus becoming the trigone of the bladder * Uretic buds sprout from mesoneprhic ducts and these become the ureters which enter the bladder at the base of the trigone

Question 28

Once the urogenital sinus has enlarged to become bladder, the caudal parts of mesonephric ducts have been absorbed to form trigone of bladder and ureteric buds have given rise to ureters which enter at base of trigone the development differs for females and males. Describe the next step for **females**

Answer 28

* As the kidneys ascend into abdomen the ureteric openings move cranially * Mesonephric ducts degenerate due to lack of testicular androgens * Urethra is formed from thepelvic part of the urogenital sinus

Question 29

Once the urogenital sinus has enlarged to become bladder, the caudal parts of mesonephric ducts have been absorbed to form trigone of bladder and ureteric buds have given rise to ureters which enter at base of trigone the development differs for females and males. Describe the next step for **males**

Answer 29

* As kidneys ascend into abdomen the ureteric openings move cranially * Mesonephric ducts move caudally and closer together and enter the/join the prostatic urethra (formed from inferior [or more specifically pelvic part] of the urethra) to become the ejaculatory ducts * Pre-prostatic, prostatic and membranous urethra is formed from the pelvic part of the urogential sinus * Spongey urethra formed from the caudal part of urogential sinus

Question 30

Describe how the spongey urethra forms in males

Answer 30

* Genital tubercle, genital folds and urogential sinus also elongate. * Genital folds fuse to become spongey urethra * Urogenital sinus forms urethral groove

Question 31

Describe formation of female genitalia

Answer 31

* Gential tubercle elongates slightly then retracts to form clitoris * Genital folds become labia minora * Genital swellings become labia majora

Question 32

What is responsible for differential development of external genitalia?

Answer 32

Presence of androgens (in particular dihydrotestosterone)

Question 33

What is hypospadias?

Answer 33

Defect in fusion of genital/urethral folds resulting in urethra opening on the ventral surface rather than the end of the glans penis

Question 34

Is the incidence of hypospadias increasing?

Answer 34

Yes

Question 35

Both the kidney and ureter form from intermediate mesoderm at??

Answer 35

Urogenital ridge

Question 36

When does the mesonephros appear and when does it regress?

Answer 36

* Appear end of week 4 * Regress end of week eight

Question 37

Describe the caudal to cranial shift, include: * Where shifts from and to * Displacement * Rotation

Answer 37

* From L4 to L1/L2 * Lateral displacement (meets with adrenal glands) * 90 degree rotation so renal pelvis faces midline

Question 38

Is there any mesoderm in the cloaca?

Answer 38

No

Question 39

What is the allantois?

Answer 39

Suproventral diverticulum of the hindgut and extends into the umbilical cord. Lumen becomes obliterated to become the urachus which is the median umbilical ligament in adults.

Question 40

State some examples of how the embryology/formation of urinary system can go wrong

Answer 40

* Uteric bud fails to interact with intermediate mesoderm resulting in renal agenesis * Migration goes wrong * Duplication defects * Ectopic ureter * Cystic disease

Question 41

What is meant by: * Pelvic kidney * Horseshoe kidney

Answer 41

* Pelvic kidney: one kidney didn't migrate * Horshoe kidney: as the kidneys ascent the caudal poles fuse

Question 42

What is the consequence of splitting of the uteric bud?

Answer 42

May get additional kidneys and ureters; ureters often have ectopic openings

Question 43

What is exstrophy of the bladder?

Answer 43

Skin over lower abdomen does not form properly so bladder is exposed on outside of abdomen

Question 44

What is the adult derivative of the urachus?

Answer 44

Median umbilical ligament

Question 45

What renal fetal abnormality might you suspet if you examined a pregnant patient and discovered there was abnormally low amount of amniotic fluid?

Answer 45

Renal agenesis; fetal urine makes up large proportion of amniotic fluid