Development of the Urogenital System Part 1

Question 1

The urogenital system is derived from the ________

Answer 1

• Intermediate mesoderm

Question 2

The urogenital system is divided into the ______ _______ and the __________ _________

Answer 2

• Urinary system
• Genital system
  They are both studied together because of how closely related they are as they both develop from the intermediate mesoderm forming the longitudinal urogenital ridge

Question 3

What is in the urinary system?

Answer 3

• Kidneys to produce urine
• Ureters to transfer urine from the kidneys to the bladder
• Bladder to store urine
• Urethra excretes urine from the bladder

Question 4

What are nephrons?

Answer 4

• They are functional units of the kidney

Question 5

Explain the development of the kidneys

Answer 5

• pronephric ducts that hold the pronephric tubules
• The pronephroi degenerate but the ducts stay to be used in the next set of kidneys (mesonephroi)
• The pronephric ducts are now the mesonephric ducts that run caudally and open into the cloaca
• Cell clusters → vesicles → tubules of the mesonephroi which contact the ducts
• The metanephroi develop and function in the production of urine as the permanent kidney

Question 6

List the three sets of kidneys that form in human embryos and when they appear

Answer 6

-Pronephroi (non functional, early 4th week)
- Mesonephroi (functional for a short period, later 4th week)
- Metanephroi (forms the permanent kidney, 5th week)

Question 7

Where is the pronephroi in the body?

Answer 7

• At the pronephric tubules in the cervical region of the intermediate mesoderm

Question 8

What is the anatomy of the mesonephroi

Answer 8

• They consist of the glomeruli and tubules
• The tubules open into the bilateral mesonephric ducts that were originally the pronephric ducts
• The ducts open into the cloaca
• The mesophroi degenerate towards the end of the first trimester
• the tubules become the efferent ductule of the testes in males

Question 9

How is urine excreted from a fetus?

Answer 9

• The metanephroi produces urine and its excreted into the amniotic fluid which the fetus DRINKS (ew, but this is why the levels of amniotic fluid is important) the wastes are absorbed and removed via the placenta

Question 10

The metanephroi is developed from the _____ _______ and the ________ _______

Answer 10

• Metanephric diverticulum: an outgrowth from the ducts near the cloaca. gives rise to the ureter, renal pelvis, major and minor callices, collecting tubules and ducts (urine transport structures)
• Metanephric blastema: located in the caudal part of the nephrogenic cord. induce the mesoderm to form clusters → vesicles → tubules → nephrons

Question 11

How is the ureter formed?

Answer 11

• The stalk of the metanephric diverticulum becomes the ureter
• The cranial portion forms the collecting tubules of the metanephros (first 4 generation tubules become the major callices and the second 4 generations coalesce to form the minor callices

Question 12

where do the kidneys move to in the embryo

Answer 12

• The kidneys are originally forming in the pelvis (lateral to the cloaca) but then come to lie in the abdomen due ascending
• As the kidney ascends their blood supply changes
• Renal arteries appear in the 9th week

Question 13

Explain the development of nephrons

Answer 13

• The collecting tubules in the metanephrogenic blastema induce clusters of mesenchymal cells to condense to form metanephric vesicles
• growth factors are continuously released by the collecting tubule to allow the metanephric vesicle to elongate = tubules
• The metanephric tubules (now the distal convoluted tubule DCT) become continuous with the collecting tubules (from diverticulum) to form the uriniferous tubules
• The DCT continues to grow and there is a proximal convoluted tubule PCT.
• The PCT changes its configuration to form a cup-like structure Bowman’s capsule
• The common iliac arteries that make the glomeruli capillaries are found in the pelvis region
• The capillaries produced are interacting with the Bowman’s capsule → PCT → DCT → collecting tubule to make urine
• The mesoderm between the PCT and DCT grow downwards forming a “Loop of Henli”

Question 14

What is the difference between epithelial and mesenchymal cells?

Answer 14

• Epithelial cells are stationary
• Mesenchymal cells can move around because they’re linked by gap junctions and cell adhesion molecules
• Mesenchymal cells have a low expression of cell adhesion molecules

Question 15

Explain the reciprocal inductive effect between the metanephric diverticulum and the mesoderm

Answer 15

• The branching of the metanephric diverticulum depends on induction by the metanephric blastema
• They both interact and induce each others’ growth = reciprocal induction to form the permanent kidneys
• The differentiation of the nephrons depend on the inductive signals by the collecting tubules

Question 16

Explain the reciprocal induction pathway between the metanephric blastema and diverticulum

Answer 16

• The metanephrogenic blastema produces a transcription factor WT1 that regulates the expression of genes; GDNF (receptor is RET) and HGF (receptor is MET).
• When GDNF and HGF bind to their receptors that are found in the diverticulum it induces the branching of the diverticulum
• Because the diverticulum is invaginating into the blastema, this creates a tendency for the blastema to undergo apoptosis
• The diverticulum secretes FGF2 and BMP7 to prevent this
• As the diverticulum branches it releases Wnt9b and Wnt6
• These proteins act on the blastema to produce Pax2 and Wnt4
• Pax2 inducing the condensation of mesenchymal cells to form vesicles and tubules
• Wnt4 induces the epithelializing of the tubules

Question 17

What does GDNF and HGF stand for

Answer 17

• Glial Derived Neurotrophic Factor
• Hepatocyte Growth Factor

Question 18

What are the functions of FGF2 and BMP7

Answer 18

• To prevent the metanephrogenic cells from undergoing apoptosis
• Maintaining the synthesis of WT1 which helps blastema cells remain competent

Question 19

What are the two parts of the uriniferous tubule

Answer 19

• A nephron (from the metanephrogenic blastema)
• A collecting tubule (from the metanephric diverticulum)

Question 20

Explain the ascending of the kidneys and the change in blood supply

Answer 20

• Originally, the blood feeding into the kidneys are from the common iliac arteries which degenerate to cause the kidneys to move upwards
• When the kidneys move upwards, blood vessels from the top part of the aorta invade the kidneys = renal arteries

Question 21

What are the different abnormalities of the kidneys and ureters?

Answer 21

• Renal agenesis
• Ectopic kidneys
• Horseshoe kidneys
• Duplications of the upper urinary tract

Question 22

Describe the development of the bladder and urethra

Answer 22

• The urorectal septum divides the cloaca into the dorsal rectum and ventral urogenital sinus (gives rise to the bladder and urethra)
• As the bladder enlarges, the mesonephric ducts (later becoming ureters) are incorporated into its walls
• The allantois (functions in gas exchange) → urachus attached to bladder and umbilicus (later goes away after birth due to lack of function)
• Urethra develops from the caudal part of the UG sinus

Question 23

What causes exstrophy of the bladder

Answer 23

• Failure of the mesoderm to migrate
• improper formation of the anterior abdominal wall