Development And Clinical Embryology Of The Urinary System

Question 1

What does the urinary system develop from?

Answer 1

Most of the urinaary system develops from the intermediate mesoderm& urogenital sinus (endodermal-part of cloaca)

Intermediate mesoderm: between paraxial and lateral mesoderm; extends along dorsal body wall of embryo

Question 2

Summarize development of urinary system

Answer 2

• Development of the kidneys and ureters are closely related to that of the Genital system
• Begins as a longitudinal elevation of intermediate mesoderm on the dorsal wall of the embryo

Urogenital ridge

• One position, the nephronic cord, gives rise to urinary system components
• The other portion, the gonadal ridge, gives rise to Genital system components

Question 3

What sequential systems do the urinary system develop into?

Answer 3

Pronephros- rudimentary non functional

Mesonephros- functions very briefly during the early fetal period

Metaneohros- will form the permanent kidney

Question 4

What is pronephros?

Answer 4

Beginning of week 4

• 7-10 cell groups in the cervical region
• Forms vestigial excretory units= neohrotomdd
• Regress before the next system is formed more caudally

Disappears by the end of week 4

Question 5

Explain the development of the mesonephros

Answer 5

Starts by week 4 simultaneous with pronephros regression

Excretory (mesonephric) tubules appear

• Gradually lengthen to form an S-shaped loop
• Acquire a tuft of blood to form primitive glomerulus
• The tubules elongate laterally and join with longitudinal collecting duct (mesonephric duct)
• The mesophrenic duct opens into the cloaca

Mesophrenic degenerates by the end of 1st trimester, but their excretory tubules and duct become the ductus deferens, duct of epididymis and efferent ductules

Question 6

Explain the development of metaneohros

Answer 6

Appears in the 5th week

Excretory ducts develop from the metanephric mesoderm in the same manner as did the mesonephros

Ureteric bud an outgrowth from the mesonephric duct close to its attachment to the cloaca

The bud penetrates the metaneohric tissue which is molded over by a cap from the surrounding mesoderm (metanephric blastema)

Question 7

Explain the development of the permanent kidneys-collecting tubules

Answer 7

the bud dilates to form the primitive renal pelvis and splits into a caudal stalk (ureter) and cranial portion (collecting tubules)

The metanephric diverticulum (ureteric bud) in its cranial part undergoes successive branching

First divides into two to form the major calyces

Continues to divide to form the minor calyces and collecting tubules

Question 8

Explain development of the permanent kidneys- nephron

Answer 8

The end of each collecting tubules divides and become arched
-The collecting tubules induce clusters of mesenchymal cells from metaphrenic blastema to form small metanephric vesicles

• These vesicles elongate to form S-shaped metanephric (renal) tubules
• The proximal ends of the renal tubules are invaginated by glomeruli (tuft of capillaries)

The tubules differentiate into structures firming the nephron

Question 9

When is development of the nephron complete?

Answer 9

Nephron formation is complete at birth, with 1-2 million nephrons in each kidney

-Excretory part-Bowman’s capsule, Proximal Convulited tubules (PCT), loop of henle and Distal Convuluted tubules(DCT)- develop from the ureteric bud

Question 10

What do metanephric tubules do in development in the nephron?

Answer 10

Metaneohric tubules become continuous with the ends of arched collecting tubules to form functional uriniferous tubules(nephron + collecting tubules)

-Glomeruli invaginate into the tubules

Question 11

Explain the renal “ascent “ and rotation

Answer 11

• The kidneys (permanent) are initially located in the pelvis
• Growth of abdomen and pelvis allows kidneys to ascend
• Initially, the hilum faces ventrally and receive branches from the common iliac arteries
• As the caudal parts of the embryo grow away from the kidneys they come to lie higher and higher in the abdomen (“ascent”)
• The kidneys rotate medially almost 90 degrees and lie lateral to the aorta during their upward migration

Question 12

Explain further ascent of the kidneys and arterial supply

Answer 12

• Successively higher and higher branches from the aorta supply the kidneys as they ascend
• Normally the primordial caudal branches disappear and only the final renal arteries persist
• By week 9, the kidneys are in contact with the suprarenal glands and reach their adult position

Question 13

Explain the functioning of the accessory renal arteries

Answer 13

• Approximately 25% of adult kidneys have 2-4 renal arteries
• Arise (from aorta) above or below the main renal artery
• Accessory arteries that enter the lower pole may cross anterior to the ureter and can cause obstruction-leading ti hydrophenophrosis (distension of the renal pelvis abd calices)
• Renal segmental arteries are end arteries, so injury or ligation of an accessory artery leads to ischemia of the segment of the kidney supplued

Question 14

How would failure of kidneys to rotate present itself?

Answer 14

Failure to rotate- hilum faces anteriorly (fetal kidney retains its embryonic position)

Excessive rotation- hilum faces posteriorly (rotation proceeded to far)

Lateral rotation - hilum faces laterally

-Malnutrition is often associaated with ectopic kidneys

Question 15

What is an ectopic kidney?

Answer 15

• Failure of ascent of one of both kidneys
• Most located in the pelvis
• Pelvic kidneys are close to each their and usually fused to form a discoid kidney
  
  • Receive blood supply from vessels near them e.g. internal or external iliac
• Crossed renal ectopia
  
  • Kidney crosses to other side
  • 90% are fused

Question 16

What is renal agenesis? What are the types?

Answer 16

Early degradation or failure of formation of the ureteric bud

Unilateral:
More common in boys
L kidney usually the one absent
Asymptomatic if other kidney is normal(compensatory hypertrophy)

Bilateral can result in:
Oligohydramnios
-Pulmonary hypoplasia
-POTTER Sequence
-Incompatible with post-natal life

Question 17

What is bifida ureter?

Answer 17

Early incomplete division of ureteric bud

Question 18

What causes a double kidney ?

Answer 18

Early complete division of the ureteric bud inducing the formation of two kidneys

Question 19

What causes supernumerary (extra kidneys) kidneys are rare?

Answer 19

Two separate ureteric buds developed on that side resulting in 2 separate kidneys.

When there are separate ureters, one may have a fistulous opening into urethra, vagina or vestibule

Question 20

Give the clinical details of horseshoe kidney

Answer 20

1:500 births

Fusion of lower poles while still in pelvis

Ascent interrupted by the inferior mesentric artery

Question 21

What are the inheritance methods for Poly cystic kidneys?

Answer 21

Inherited
Autosomal dominant (more common )
-cysts from all segments of the nephron renal failure is usuallly only until adulthood
-renal failure is usually only until adulthood

Autosomal recessive

• Cysts progressively form from the collecting ducts
• Kidneys become large and renal failure occurs in infancy or childhood

Question 22

What are suprarenal glands? What are the effects?

Answer 22

-Lie on superoxide-medial pole of each kidney surrounded by renal fascia

Embryology of Medulla- Neural crest cells migrate toward the coelemic cavity wall and form the adrenal medulla. They are called chromaffin (chromaphil) cells due to their staining (yellow) with chromium salts

Embryology of Cortex- Week 4 celomic epithelium (mesothelium) cells proliferate initially forming small buds that separate from the epithelium. Week 6 these now mesenchymal cells first form the fetal adrenal cortex which will later replace the adult cortex

Question 23

What does urorectal septum do?

Answer 23

Divides the cloaca into—>
-ventral primitive urogenital sinus

-dorsal primitive septum

Question 24

Describe bladder development in detail week 4-7

Answer 24

The cloaca divides into the urogenital sinus anteriorly and the anal canal posteriorly by the urorectal septum

Urogenital sinus has three portions

• Upper portion (vesicle part)-largest forms the bladder
  
  • Continuous it’s the allantois which becomes the ligamentous urachus which persist in the adult as the median umbilical ligament

- Middle portion is a thin pelvic part which will give rise to the urethra at the neck of bladder, prostatic and membranous portions of the male urethra and the entire female urethra     - The final portion is the phallic part firms most of the penile urethra in males

Question 25

What are congenital urachal anomalies ?

Answer 25

The urachus connects bladder to the umbilical cord during fetal life and is located anterior to the peritoneum

By-birth, the urachus is obliterated and converts into a structure known as the median umbilical ligament

In the absence kf complete obliteration, the urachus persists abd can lead to either urachal cyst, sinuses or fistulas

Question 26

When urachal cysts form?

Answer 26

Urachal cysts form when both the umbilical and bladder ends of the urachal lumen close, while a portion remains patent and fluid-filled

Question 27

What is an umbilical- urachal sinus?

Answer 27

What is the umbilical- urachal sinus represents a non-communicating dilatation of the urachus at the umbilical end

Question 28

What is urachal fistula?

Answer 28

Urachal fistula firms when there is an open channel between the bladder and the umbilicus