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Questions and Answers
From which embryonic tissue does the metanephros develop?
From which embryonic tissue does the metanephros develop?
Which of the following is the first set of excretory organs to develop in the embryo?
Which of the following is the first set of excretory organs to develop in the embryo?
What is the origin of the collecting system of the permanent kidney?
What is the origin of the collecting system of the permanent kidney?
When does the metanephros, the permanent kidney, appear in the embryo?
When does the metanephros, the permanent kidney, appear in the embryo?
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Which of these structures is derived from the mesonephric duct?
Which of these structures is derived from the mesonephric duct?
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What happens to the pronephric system by the end of the fourth week of development?
What happens to the pronephric system by the end of the fourth week of development?
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Which structure dilates to form the primitive renal pelvis?
Which structure dilates to form the primitive renal pelvis?
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What is a key characteristic of the mesonephros?
What is a key characteristic of the mesonephros?
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The minor calyces of the renal pelvis are formed through the enlargement and absorption of which generation of tubules?
The minor calyces of the renal pelvis are formed through the enlargement and absorption of which generation of tubules?
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Which structure does NOT originate from the ureteric bud?
Which structure does NOT originate from the ureteric bud?
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What forms the renal vesicles?
What forms the renal vesicles?
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Which of the following structures is formed by the proximal end of each nephron?
Which of the following structures is formed by the proximal end of each nephron?
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What does the distal end of the nephron establish a passageway to?
What does the distal end of the nephron establish a passageway to?
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When do the kidneys typically reach their maximum number of nephrons?
When do the kidneys typically reach their maximum number of nephrons?
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Around what time does urine production begin in gestation?
Around what time does urine production begin in gestation?
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In multicystic dysplastic kidney, which condition occurs?
In multicystic dysplastic kidney, which condition occurs?
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What is the term for a kidney that remains in the pelvis, close to the common iliac artery, after failing to ascend properly?
What is the term for a kidney that remains in the pelvis, close to the common iliac artery, after failing to ascend properly?
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The ascent of a horseshoe kidney is typically prevented by which of the following structures?
The ascent of a horseshoe kidney is typically prevented by which of the following structures?
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When does the definitive kidney formed from the metanephros typically become functional?
When does the definitive kidney formed from the metanephros typically become functional?
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During fetal life, which organ is primarily responsible for the excretion of waste products?
During fetal life, which organ is primarily responsible for the excretion of waste products?
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The cloaca divides into which two main structures during the 4th-7th weeks of development?
The cloaca divides into which two main structures during the 4th-7th weeks of development?
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What structure does the urorectal septum form the tip of?
What structure does the urorectal septum form the tip of?
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Which of the following is derived from the pelvic part of the urogenital sinus in males?
Which of the following is derived from the pelvic part of the urogenital sinus in males?
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What is the origin of the ureter?
What is the origin of the ureter?
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What is the incidence of unilateral renal agenesis?
What is the incidence of unilateral renal agenesis?
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Which sequence of symptoms is characteristic of bilateral renal agenesis?
Which sequence of symptoms is characteristic of bilateral renal agenesis?
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In which polycystic kidney disease is renal failure most likely to occur in infancy or childhood?
In which polycystic kidney disease is renal failure most likely to occur in infancy or childhood?
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What is a possible cause of congenital polycystic kidney disease?
What is a possible cause of congenital polycystic kidney disease?
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What anatomical change occurs as a kidney ascends from the pelvic region to the abdomen?
What anatomical change occurs as a kidney ascends from the pelvic region to the abdomen?
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What is the most common cause for duplication of the ureter?
What is the most common cause for duplication of the ureter?
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What condition occurs in approximately 1 in 10,000 births and results in renal failure?
What condition occurs in approximately 1 in 10,000 births and results in renal failure?
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The ascent of the kidney during migration is primarily caused by which of the following?
The ascent of the kidney during migration is primarily caused by which of the following?
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During the ascent of the kidneys, what is the fate of the mesonephric duct orifices in males?
During the ascent of the kidneys, what is the fate of the mesonephric duct orifices in males?
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What is the final origin of the epithelium lining the inside of the bladder?
What is the final origin of the epithelium lining the inside of the bladder?
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From which embryonic tissue does the epithelium of the urethra originate in both sexes?
From which embryonic tissue does the epithelium of the urethra originate in both sexes?
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In males, the proliferation of the epithelium of the prostatic urethra leads to the formation of which structure?
In males, the proliferation of the epithelium of the prostatic urethra leads to the formation of which structure?
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What is the underlying cause of exstrophy of the bladder?
What is the underlying cause of exstrophy of the bladder?
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Study Notes
Development of the Urinary System
- The urinary and genital systems develop from a common mesodermal ridge, specifically the intermediate mesoderm.
- The pronephros is the first excretory system, rudimentary and non-functional.
- The mesonephros, the second system, may function briefly in early fetal development.
- The metanephros, the third system, develops into the permanent kidney.
Kidney Systems
- Pronephros: Rudimentary, non-functional, early in development.
- Mesonephros: May function for a short time during fetal development.
- Metanephros: Forms the permanent kidney.
Pronephros
- Early in the fourth week, the pronephros consists of 7 to 10 solid cell groups in the cervical region.
- These groups form rudimentary excretory units (nephrotomes).
- The pronephric system disappears by the end of the fourth week.
Mesonephros
- Forms in the thorax and lumbar regions; large excretory units (nephrons).
- Forms its own collecting duct, the mesonephric (or Wolffian) duct.
- In males, few caudal tubules persist and participate in genital system development; in females, these structures disappear.
Metanephros (Definitive Kidney)
- The third urinary organ, the metanephros appears in the fifth week.
- Its excretory units come from metanephric mesoderm.
Collecting System
- Collecting tubules develop from the ureteric bud, an outgrowth of the mesonephric duct, inside the metanephric tissue.
- The bud penetrates the tissue, resulting in dilation of that portion to form the primitive renal pelvis.
- The collecting system further develops to include major and minor calyces.
- Tubules proliferate until the end of the fifth month.
- Third-, second-, and first-order tubules enlarge and absorb those of lower orders, to form the minor calyces of the renal pelvis.
- The collecting tubules of later generations elongate considerably, converge on the minor calyx, and form renal pyramids.
Nephrons
- Glomeruli form in the pockets at one end of the S-shaped tubules.
- Renal vesicles form small S-shaped tubules, where the metanephric tissue cap forms these.
- The proximal end of each nephron develops Bowman's capsule, indented by a glomerulus.
- The distal end of the tubules establishes a connection with a collecting tubule.
- The kidney develops from two sources:
- Metanephric mesoderm (excretory units)
- Ureteric bud (collecting system)
- Nephrons are formed until birth, resulting in approximately 1 million nephrons per kidney.
Urine Production
- Urine production begins early in gestation, after glomerular capillaries start forming around the 10th week.
Kidney Appearance at Birth
- At birth, kidneys have a lobulate appearance.
- This lobulation disappears during infancy due to further nephron growth, although the number of nephrons does not increase.
Renal Dysplasia and Agenesis
- Renal dysplasia and agenesis represent a spectrum of severe malformations in the kidneys.
- These malformations often require dialysis and transplantation in early years of life.
- Multicystic dysplastic kidney is a common example, where many ducts are surrounded by undifferentiated cells, preventing normal nephron development.
- Renal agenesis may be unilateral or bilateral, resulting in renal failure. Other severe defects (vagina, uterus, vas deferens, seminal vesicles) are often seen accompanying this condition.
Congenital Polycystic Kidney Disease
- Numerous cysts develop within the kidneys, inherited as autosomal recessive or dominant diseases.
- Autosomal recessive polycystic kidney disease occurs in 1/5000 births. This condition leads to progressive disease with renal failure in infancy or childhood.
- Autosomal dominant polycystic kidney disease is more prevalent (1/500-1/1000 births) but less progressive; renal failure is typically not seen until adulthood due to slower, lower levels of cyst formation, compared to recessive disease.
Duplication of the Ureter
- Results from early splitting of the ureteric bud.
- This splitting may be partial or complete, resulting in metanephric tissues separated into two or more parts.
- In rare cases, one ureter connects to the bladder and the other is ectopic, entering the vagina, urethra or vestibule
Position of the Kidney
- Kidneys initially located in the pelvis, later shifting to the abdominal region.
- Movement (ascent) involves crania shifting and lateral moving/meeting up with adrenal glands. A rotation also occurs that places the renal pelvis facing the midline.
- Factors motivating the rise of kidneys involve body curvature and growth in lumbar and sacral regions.
- The metanephros receives arterial supply from a pelvic branch of the aorta during its ascent.
Clinical Correlates: Abnormal Location of the Kidneys
- Occasionally, during kidney ascent, one kidney fails to pass through umbilical arteries and remains in the pelvis close to the common iliac artery as a pelvic kidney.
- Sometimes, kidneys are pushed together during ascent, causing fusion of the lower poles of the kidneys to form a horseshoe kidney.
- Usually located at the level of the lower lumbar vertebrae; blocked from moving upward by inferior mesenteric artery.
- Approximately 1/600 people have a horseshoe kidney. Renal arteries arise commonly from the aorta to supply kidneys.
Function of the Kidney
- The metanephros-formed definitive kidney becomes functional near the 12th week of gestation.
- Urine is passed into the amniotic cavity and mixes with amniotic fluid.
- The fluid is swallowed by the fetus, and recycled through the kidneys.
- In fetal development, the placenta handles waste product excretion, not the kidneys.
Bladder and Urethra
- The cloaca divides to form the urogenital sinus (anterior) and anal canal (posterior) during development weeks 4-7.
- The urorectal septum is a mesodermal layer separating the primitive anal canal from the urogenital sinus. It forms the perineal body.
- The urogenital sinus is divided into three portions:
- The upper/largest part is the urinary bladder.
- The second is the pelvic part of urogenital sinus that forms the prostatic and membranous portions of the urethra in males.
- The third part forms the phallic portion of the genital urethra. This part's development differs significantly between sexes.
Ureters
- The caudal portions of the mesonephric ducts are incorporated into the bladder wall, forming the ureters.
- During kidney ascent, the openings of the ureters move upward.
- The mesonephric ducts' openings approach each other and become the ejaculatory ducts in males.
- The mesodermal lining of the bladder trigone is gradually replaced by endodermal epithelium. This leads to the bladder's complete endodermal lining.
Urethra
- Both sexes' urethral epithelium originates in endoderm.
- The connective and smooth muscle tissue comes from visceral mesoderm.
- In males, prostatic urethra epithelium proliferates to form the prostate gland by the third month.
- In females, the cranial portion of the urethra gives rise to urethral and paraurethral glands.
Clinical Correlates: Bladder Defects
- Urachal fistula: Occurs when the intraembryonic portion of the allantois persists, causing urine to drain from the umbilicus.
- Urachal cyst: A local area of the allantois persists, leading to cystic dilation due to secretory activity.
- Urachal sinus: Upper portion of the allantois persists, resulting in a sinus usually connected to the urinary bladder.
Exstrophy of the Bladder
- A ventral body wall defect exposing the bladder mucosa.
- Likely due to failure of the lateral body wall folds to close in the midline in the pelvic region.
- A rare anomaly, occurring in approximately 2/100,000 live births.
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Description
Test your knowledge on the development of the metanephros and the origins of various components of the urinary system. This quiz covers key stages in embryonic kidney formation and essential structures involved in renal development. Perfect for students focusing on embryology and human anatomy.
