Urinary System Development

Describe how the Urinary & Genital systems are embryologically & anatomically interwoven

Both develop from common pair of intermediate mesoderm
elevations located on each side of the the median plane along the
embryonic posterior abdominal wall.

Describe the gross structures of the kidneys:

• Hilum

• Renal Sinus

• Renal Pelvis

• Major Calyces

• Minor Calyces

• Renal Cortext

• Renal Medula

• Renal Column

• Renal Pyramids

• Medullary rays

• Renal Papilla

Describe the two systems that the kidneys have and the components of each system

Filtration System: filter blood and produce urine

• Renal corpuscle: glomerulus (arterial
  capillaries)+ Bowman’s capsule

• Proximal convoluted tubule

• Henle’s loop (thick and thin limbs)

• Distal convoluted tubule

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Collecting System collect urine for transport to the bladder by the ureter

• Collecting tubules & ducts

• Minor calyces

• Major calyces

• Renal pelvis

• Ureter

What are the three stages of kidney development; Where and when do they appear?

• Pronephros (cranial, week 4)

• Mesonephros (thoracic & lumbar, week 4-8)

• Metanephros (pelvic, week 5-40)

***Three overlapping kidney systems develops in a cranial-caudal sequence during gestation***

1. Describe the Pronephros’ characteristics

2. What is the Pronephric Duct? What does it become and why is it important?

Pronephros

• non-functional excretory tubules: no glomeruli & no
  connection w/ pronephric duct

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Pronephric duct

• collecting duct runs caudally and opens into anterior portion of cloaca at the end of 4th week

• becomes mesonephric duct

• plays essential part as inductor of mesonephos

Describe the Mesonephros:

• How is it formed? Components?

• Describe how the Mesonephros can persist after the 8th week? Describe its excretory tubules

• Where is the Wolffian duct derived/open to? What does this structure form in the future?

Mesonephros Formation:

• During Growth/Folding of Embryo → intermediate
  mesoderm forms a bulge (urogenital ridge) that comprises:

  • Gonadal ridge

  • Mesonephros

  • Mesonephric duct

  • Paramesonephric duct

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Mesonephros:

• some caudal tubules of mesonephros becomes efferent ductules of testis

• Excretory Tubes:

  • Has Bowman’s Capsule surrounded by Arterial Glomerulus

  • No Loop of Henle

  • Opens into mesonephric ducts

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Mesonephric (wolffian) duct

• Derived from pronephric duct

• Opens into urogenital sinus (ventral derivative of cloaca)

• DEVELOPS INTO/GIVE RISE TO:

  • uretic bud of metanephros system (future ureter)

  • trigone region of the bladder (Caudal End of Duct)

  • Persists As

    • ductus deferent

    • seminal vesicles

    • (degenerate in female)

1. Describe the Metanephros

   • When does it produce urine?

   • What 2 sources develops into this?

2. Describe the metanephric diverticulum or ureteric bud

   • Where does this developed from?

   • How does it contribute to the adult Kidneys

3. Describe the metanephric mesoderm or metanephic blastema

   • How does it contribute to the adult kidneys

   • How does the kidney’s shape change from infancy to adult

Metanephros: permanent kidney

• Arrived by the 5th week, produces urine in the 10th

• Developed from ureteric bud & metanephric blastema

  • Both of intermediate mesodermal origin

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metanephric diverticulum or ureteric bud

• Developed from outgrowth of mesonephric duct near the cloaca

• Penetrates metanephric blastema → Subdivision → COLLECTING SYSTEM

  • Metanephric blastema induces branching of ureteric bud

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metanephric mesoderm or metanephic blastema:

• metanephric tissue caps induces Nephron (near collecting tubules) Development

  • Nephron develops Bowman’s Capsule, surrounded by glomerulus

    • Distal end of bowmans → Rest of nephron (PT, LOH, DT, etc)

• At birth, kidneys = lobulated appearance ;disappears as
  nephrons growth in size but not in number during infancy

1. Describe the Ascent & rotation of the kidneys

2. Describe the blood supply

Ascent & rotation of the kidneys:

• Moves from Pelvis to Abdomins → Reretroperitoneal on posterior abdominal wall by 9th week

• 90 ̊ medial rotation from facing anteriorly

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Blood Supply:

• supplied by arteries closest to them at higher levels while ascending

• Main Blood Supply:

  • caudal arteries = degenerate;

  • Cranial Branches from abdominal aorta = permanent renal arteries

• Accessory renal arteries:

  • persistence of embryonic vessels > enter
    superior or inferior pole of kidney

  • can obstruct ureter & enlarged renal pelvis

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Note: Prior to birth, the placenta is the primary remover of nitrogenous wastes from the fetus via the allantois. After birth,
the kidney takes on this role. The urachus (median umbilical ligament) is remnant of allantois.

Describe Renal Agenesis:

• How does this happen?

• Compare agenesis of one vs two kidneys

Renal Agenesis:

• Absence of kidney(s) when metanephric diverticulum (ureteric bud) fails to develop or degenerates early → no nephrons

• Unilateral Abscence:

  • relatively asymptomatic b/c remaining kidney can take up the slack

• Bilateral Absence:

  • Incompatible w/ postnatal life

  • results in oligohydramnios → (no micturition)

  • Potter sequence

    • (flattened face, hypoplastic lungs, limb deformities)

Describe Cystic Kidney Disease:

• Multicystic dysplastic disease

• Polycystic Kidney Disease

Multicystic dysplastic disease:

• Kidney consists of irregular cysts (bunch of grapes)

• Genetic factors & certain drugs

• Unilateral = Good outcome; Bilateral = fatal after birth

• associated with Potter sequence

• Abnormal Induction = Renal Agenesis

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Polycystic Kidney Disease:

• Kidneys contain multiple small to large cysts--severe renal insufficiency

• Autosomal recessive (childhood): Cysts develop from the collecting duct

  • death usually occurs after birth, but survival has increased due to hemodialysis and kidney transplants

  • Potter sequence

• Autosomal dominant (adult): mutation in ADPKD genes (polycystin 1& 2) that play a role in renal tubular development & function

  • cysts develop from parts of nephron

  • renal failure in adult, more common

1. Describe the types of Renal Ectopia/ Consequences

2. What is Malrotated Kidney/ Consequences

Renal Ectopia:

• Simple: one or both kidneys in an abnormal position

  • Usually more inferior than usual; failure to ascend

• discoid or pancake kidney: Pelvic kidneys may fuse to form a round mass; does not ascend

• Crossed: Developing Kidneys Fused, then ascend

• Consequences

  • urinary tract infections, kidneys stones, kidney failure b/c of blockage or vesicouretral reflux

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Malrotated:

• no rotation > face anteriorly; too far > face posteriorly; also can face laterally

• Usually asymptomatic but hydronephrosis and stone formation more frequent

1. What is a horseshoe Kidney

2. Which conditions increases risk of this

Horseshoe Kidney:

• results from fusion of poles of kidneys, usually inferior poles

• U-shaped kidney in hypogastrium, anterior to lumbar
  vertebrae because normal ascent prevented by the root
  of inferior mesenteric artery

• Asymptomatic

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Higher Risk of Horseshoe Kidney:

• Turner Syndrome (45,XO)

• Wilms‘ tumor (nephroblastoma)

• Increased risk of infection (pyelonephristis)

Describe the various ways duplication of the Urinary Tract can occur

Duplications of the Urinary Tract:

• result from division of one ureteric bud

  • incomplete division --> divided kidney with a bifid ureter (B)

  • complete division --> double kidney with bifid ureter (C)

• formation of 2 ureteric buds

  • supernumerary kidney with own ureter (F)

1. Describe the development of the bladder and urethra

2. What can abnormalities create?

Development of the bladder and urethra:

• Begin to develop w/ division of the cloaca by the urorectal septum into the urogenital sinus anteriorly and anorectal canal posteriorly

• Tip of urorectal septum forms perineal body

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Abnormalities:

• rectourethral & rectovaginal fistula where hindgut opens in urethra or vagina

What is the perineal body?

• Attachment point for many muscles and fascial structures of the pelvis and perineum

• Between anal aperture and vestibule (female) or bulb of penis (male)

Describe the three portions of the urogenital sinus

Urinary bladder (minus trigone) superiorly

Pelvic part:

• Male: prostatic & membranous parts of the urethra

• Female: Upper urethra

Phallic part:

• Male: penile (spongy) urethra

• Female: lower urethra with external urethral orifice opening in vestibule

Describe the Development of urinary bladder

Development of urinary bladder

• embryonic allantois → urachus

  • connects the apex of the bladder to the umbilicus and has peritoneum raised over it as the median umbilical fold.

  • forms a thick, fibrous cord, when its lumen is obliterated after birth.

    • If lumen of urachus persists → urachal fistula → drain urine from umbilicus of newborn

• caudal portions of the mesonephric ducts and proximal portions of the ureters (ureteric buds) absorbed into posterior wall of urinary bladder → trigone

• w/ time: mesoderm is replaced by endoderm so that the
  bladder is completely lined by endodermal epithelium.

• ***Rest of bladder origins from uroginal sinus that has an
  endodermic origin***

1. What is an Ectopic ureteral orifices

2. How can this happen

3. Consequences?

Ectopic ureteral orifices:

• ureters that open anywhere except into the urinary bladder

• results when ureter is not incorporated into the posterior part of the urinary bladder but is carried caudally into the developing prostatic urethra in males and the entire urethra in females

• incontinence common because urine does not enter the bladder but continually dribbles from the urethra in both genders and/or from vagina in females

1. Describe Bladder Exstrophy

2. Who is it more common in?

3. Consequence of this?

Bladder exstrophy

• ventral body wall defect due to incomplete body folding or a failure of mesodermal migration may expose the bladder to the surface

  • associated with defect in musculature of anterior abdominal wall.

• More Common In Males

  • associated with a urinary tract (urethra) open dorsally on the penis (epispadias)

  • In female, the vagina is not fully formed

• Consequences:

  • can’t store urine or function normally → incontinence

  • Defects in pelvic bones, rectum and anus can also occur

  • Reconstructive surgery is required