9. Urinary - Development of the Urinary System

Question 1

What are the three kidney systems formed resulting in the development of the kidneys?

Answer 1

1. Pronephros
2. Mesonephros
3. Metanephros

Question 2

Describe the development of the pronephros

Answer 2

1. Develops in the cervical region
2. Never functions but role is to make a duct running from the cervical region, through the abdomen and to the cloaca
3. The duct is called the pronephric duct (its formation drives the next system to develop - the mesonephros)

Question 3

What is the urogenital ridge?

Answer 3

1. Region of intermediate mesoderm
2. Gives rise to both the embryonic kidney and gonad

Question 4

Describe the development of the mesonephros

Answer 4

1. Mesonephric tubules develop caudal to the pronephric region
2. Mesonephric tubules + mesonephric duct = embryonic kidney
3. This system can filter, but no water conservation
4. Ureteric buds sprout from the mesonephric duct triggering next developmental stage (metanephros)
5. The remaining mesonephric duct has a role in the male reproductive system

Question 5

Describe the development of the metanephros

Answer 5

1. The ureteric bud induces development of the kidney within the intermediate mesoderm
2. It is called the metanephric blastema
3. As the ureteric bud contacts the metanephric blastema, the bud branches and expands

Question 6

What happens as the ureteric bud contacts the metanephric blastema?

Answer 6

1. Bud expands and branches
2. Differentiates the metanephric blastema

Question 7

What does the ureteric bud eventually become?

Answer 7

The collecting system is derived from the ureteric bud

Question 8

What is the excretory component derived from?

Answer 8

Intermediate mesoderm under the influence of the ureteric bud

Question 9

Describe the ascent of the kidneys

Answer 9

1. The metanephric kidney first appears in the pelvic region
2. Caudal –> Cranial shift, corssing the arterial fork (formed by vessels returning blood from the fetus to the placenta)
3. As the kidney ascends, new blood vessels sprout from the abdominal aorta. Old vessels regress as new ones form.

Note: Any which fail to regress = accessory/super numerary renal arteries

Note: look at the blood vessels connecting the kidney in the sequency of pictures attached

Question 10

What is renal agenesis and how does it happen?

Answer 10

1. Absence of a kidney
2. Ureteric bud fails to interact with intermediate mesoderm
3. Can be unilateral or bilateral
4. Can be detected by low amniotic fluid volume

Question 11

Describe some duplication defects of the kidney

Answer 11

1. Two pelvicalyceal systems draining a single renal parenchyma
2. One kidney, two ureters that drain separately into the bladder or genital tract
3. A duplex kidney draining into: a single ureter, bifid ureter, two separate ureteres entering bladder at different places

Note: two ureters - this could be due to splitting of the ureteric bud = partial or complete

Note: this could lead to ectopic ureter where the ureter enters the wrong place

Question 12

Describe some structural abnormalities related to migration

Answer 12

Question 13

Three body tracts share a common caudal opening. What are the three tracts and what is the shared opening called?

Answer 13

1. Urinary, GI, Reproductive tracts
2. Cloaca (dilated structure near the hindgut)
3. Closed to the outside by cloacal membrane

Question 14

How do we separate the cloaca into three different tracts?

Answer 14

1. Urorectal septum
2. Causes the hindgut to form the urogenital sinus (continuous with the umbilicus via the urachus). Note: this closes to become the median umbilical ligament which runs form the umbilicus to the apex of the bladder)
3. The urogenital sinus is divided into 3 parts - bladder, pelvic and phallic

Note: description isn’t great but the picture shows it well.

Question 15

Describe the urogenital sinus

Answer 15

1. Superior part connect to umbilicus
2. Majority differentiates to form the urinary bladder
3. Inferior part develops into the urethra (Note: sex differences in structural development of the urethra)

Question 16

The mesonephric duct reaches the urogenital sinus (UGS). What happens next in the female?

Answer 16

Question 17

The mesonephric duct reaches the urogenital sinus (UGS). What happens next in the male?

Answer 17

The mesonephric ducts become the vas deferens

Question 18

How is the female urethra formed?

Answer 18

1. Female: Pelvic part of urogenital sinus

Question 19

How is the male urethra formed?

Answer 19

Male urethra divided into 4 parts: Pre-prostatic, prostatic, membranous, spongy

Preprostatic, prostatic, membranous = pelvic part of urogenital sinus

Spongy = phallic part of urogenital sinus

Question 20

Discuss the development of the male and female external genitalia

Answer 20

1. Basic components = genital tubercle, genital folds, genital swellings
2. In males: The Genital tube elongates and genital folds fuse to form the spongy urethra
3. In females: no fusion of the genital folds and urethra opens into the vestibule

Question 21

Describe what goes wrong when a fistulae is formed on the bladder

Answer 21

the urorectal septum is not complete

Question 22

Describe Exstrophy of the bladder

Answer 22

Bladder opens onto the abdominal wall

Question 23

What is hypospadias?

Answer 23

1. Defect in fusion of urethral folds
2. This means that the urethra opens onto the ventral surface rather than at the end of the glans
3. Incidence of this is on the increase!