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What role does the gubernaculum play in male genital development?
Which structure regresses in males during the differentiation of the genital system?
What does the genital tubercle develop into in females?
During which week does the descent of the testes occur?
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How do the urogenital folds develop in males compared to females?
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What structure forms as the labioscrotal folds fuse in males?
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What is the primary role of the paraxial mesoderm in development?
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Which mesoderm type contributes to the formation of the urogenital system?
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What does the pronephros primarily represent during embryonic development?
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What structure does the pronephric ducts open into?
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Which mesoderm area closely follows the endoderm?
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What is the fate of the pronephros during embryonic development?
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What is the main function of the lateral plate mesoderm?
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Which structure is not part of the urinary system derived from the intermediate mesoderm?
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During which week of development does the pronephros appear?
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What is the primary function of the mesonephros during its existence?
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At what stage of development does the metanephros begin to function?
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Which structures are formed from the ureteric bud during kidney development?
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What change occurs to the mesonephros at the end of the first trimester?
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How many glomeruli approximately consist in the mesonephros?
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Which is correct regarding the fate of the mesonephric tubules in males?
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What constitutes the excretory system in metanephros development?
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Where do accessory renal arteries typically arise from during embryonic development?
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What is a common outcome related to accessory renal arteries in adults?
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What is a characteristic of bilateral renal agenesis?
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Which type of kidney malrotation involves the hilum facing laterally?
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What percentage of the population is affected by horseshoe kidney?
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What is the most common congenital condition associated with kidney development?
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What occurs due to failure of the ureteric bud to penetrate the metanephric blastema?
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What condition is characterized by a reduction of normal kidney function and is the most common cystic kidney disease?
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What is associated with a supernumerary kidney?
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Which of the following conditions usually maintains a normal blood supply despite the presence of renal fusion?
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What is typically not observed in a patient with unilateral renal agenesis?
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Which structure does NOT form part of the urogenital sinus?
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What embryonic layer contributes to the epithelium of the majority of the male urethra?
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In male development, which structure is associated with ectodermal cells?
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What condition is characterized by the protrusion of the mucosal surface of the posterior bladder?
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What is the fate of the allantois in the development of the urinary bladder?
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Which structure emerges from the medial aspect of the mesonephros during gonadal development?
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Failure of mesenchymal cell migration between ectoderm and endoderm is associated with which anomaly?
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What embryonic tissue forms the connective tissue and smooth muscle of the urethra?
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What are urachal cysts associated with during embryonic development?
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Which statement correctly identifies the caudal ends of the mesonephric ducts?
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Study Notes
Intraembryonic Mesoderm
- Fills the space between the endoderm and ectoderm.
- Differentiates into three regions: paraxial, intermediate, and lateral plate mesoderm.
- Paraxial mesoderm forms the dermatome, sclerotome, and myotome.
- Intermediate mesoderm contributes to the urogenital system.
- Lateral plate mesoderm is involved in the formation of body cavities.
- Splanchnic mesoderm follows the endoderm.
- Somatic mesoderm follows the ectoderm.
Urogenital System Development
- The urogenital ridge appears in the 4th week.
- Urogenital ridge develops into the urinary system and the genital system.
Urinary System
- The urinary system develops in three stages: pronephros, mesonephros, and metanephros.
Pronephros
- Rudimentary and nonfunctional.
- Appears early in the 4th week.
- Tubular cell clusters in the cervical region.
- Pronephric ducts run caudally and open into the cloaca.
- Pronephros degenerates.
- Duct system persists and is used by the mesonephros.
Mesonephros
- Appears late in the 4th week.
- Caudal to the degenerating pronephros.
- Functions as interim kidneys.
- Consists of around 40 glomeruli and mesonephric tubules.
- Tubules open into mesonephric ducts (previously pronephric ducts).
- The duct opens into the cloaca.
- Degenerate at the end of the first trimester (around 3 months).
- Function: create urine between weeks 6 – 10 until permanent kidneys begin to function.
- Tubules become efferent ductules of the testes.
- Regress in females.
Metanephros
- Primordia of permanent kidneys.
- Develops early in the 5th week.
- Begins to function early in the 9th week.
- Develops through reciprocal induction:
- Ureteric bud (metanephric diverticulum)
- Collecting system: ureter, renal pelvis, calices, collecting tubules and ducts.
- Metanephrogenic blastema (mesenchyme from the nephrogenic cord)
- Excretory system: renal corpuscles, proximal convoluted tubules, loops (of Henle), distal convoluted tubules.
- Ureteric bud (metanephric diverticulum)
Urinary System Positional Changes
- Kidneys initially develop in the pelvis and ascend to their final position in the abdomen.
Congenital Abnormalities
-
Accessory renal arteries:
- Blood supply to the kidneys changes during embryonic and early fetal life.
- Around 25% of adult kidneys have accessory renal arteries.
- Inferior pole: polar arteries can cause hydronephrosis.
-
Renal agenesis (absence of kidney):
- Unilateral:
- Occurs in around 0.1% of the population.
- Results in hypertrophy of the single kidney.
- Bilateral:
- Leads to oligohydramnios (reduction of amniotic fluid).
- Occurs in 1 in 3000 births (3x more common in males).
- Incomptabile with postnatal life.
- Also have pulmonary hypoplasia.
- Failure of the ureteric bud to penetrate the metanephric blastema leads to the absence of renal development (no nephrons are induced by the collecting tubules).
- Unilateral:
-
Cystic kidney disease:
- Autosomal dominant polycystic kidney disease (ADPKD)
- Most common
- Occurs in 1:500 individuals.
- Reduces normal kidney function.
-
Malrotation of kidneys:
- No rotation: hilum faces anteriorly.
- Over rotation: hilum faces posteriorly.
- Medial rotation: hilum faces laterally.
-
Ectopic kidneys: kidneys remain in the pelvis or inferior part of the abdomen.
-
Unilateral fused kidney: developing kidneys fuse while in the pelvis and move to normal position.
-
Horseshoe kidney:
- Most common renal fusion defect, usually inferior pole fusion.
- Occurs in 0.2% of the population.
- Usually located in the pelvic region.
- Function is preserved, normal blood supply and ureteric formation.
-
Duplication of the urinary tract:
- Supernumerary kidney: duplication of the ureteric bud.
- Bifid ureter: partial duplication of the ureter.
- Double kidney (bifid / separate ureter): complete duplication of the kidney and ureter.
Urinary Bladder
- Develops from the vesical part of the urogenital sinus.
- Trigone: is formed by the caudal ends of the mesonephric ducts.
- Allantois becomes the urachus which becomes the median umbilical ligament.
- Epithelium is derived from the endoderm.
- Walls are derived from splanchnic mesoderm.
Urethra
- Develops from the pelvic part of the urogenital sinus.
- Endoderm of the urogenital sinus forms the epithelium of most of the male urethra and the entire female urethra.
- Ectodermal cells form the distal part of the urethra in the glans penis.
- Splanchnic mesenchyme forms connective tissue and smooth muscle of the urethra.
- Surface ectoderm forms the epithelium of the terminal part of the urethra.
Urinary Bladder Abnormalities
-
Ectopic ureter: does not enter the urinary bladder, resulting in incontinence.
- Males: neck / prostatic utricle.
- Females: neck / urethra / vagina / vestibule.
-
Urachal anomalies:
- Urachal lumen persists, forming cysts, sinuses, or fistulas.
-
Exstrophy of bladder (epispadias):
- Occurs in 1 in 30,000 - 50,000 (females).
- Protrusion of the mucosal surface of the posterior bladder.
- Failure of mesenchymal cells to migrate between the ectoderm and endoderm (rupture of the cloacal membrane).
Genital System
- Gonadal development (5th week):
- Mesothelium (mesodermal epithelium) forms the medial aspect of mesonephros.
- With underlying mesenchyme, this becomes the gonadal ridge.
- Mesenchyme (embryonic connective tissue) forms gonadal cords.
- Primordial germ cells (earliest undifferentiated sex cells from the epiblast) migrate into gonadal cords. -Become oocytes (female) and sperm (male).
- Mesothelium (mesodermal epithelium) forms the medial aspect of mesonephros.
Indifferent Gonads
- Become external cortex and internal medulla.
- Males (XY): medulla develops into testis, cortex regresses.
- Females (XX): cortex develops into ovary, medulla regresses.
Relocation
-
Descent of the testes:
- 7th week to birth.
- Controlled by androgens (testosterone).
- Gubernaculum: guides the descent of the testes through the abdominal cavity into the scrotum.
- Pulls structures involved in reproduction, forming the spermatic cord with the processus vaginalis.
-
Descent of the ovaries:
- Descend from the lumbar region to the pelvis.
- Gubernaculum guides the ovaries and attaches from the uterus near the attachment of the uterine tube.
- Forms the ovarian and round ligaments.
External Genitalia
-
Males:
- Urogenital folds fuse, the genital tubercle elongates to form the shaft and glans of the penis.
- Fusion of the urethral folds encloses the phallic portion of the urogenital sinus to form the penile urethra.
- Labioscrotal folds fuse to form the scrotum.
-
Females:
- Genital tubercle bends inferiorly to form the clitoris.
- Urogenital folds remain separated to form the labia minora.
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Description
This quiz focuses on the development of intraembryonic mesoderm and its differentiation into the urogenital system. It covers the formation stages of the urinary system, including pronephros, mesonephros, and metanephros. Test your knowledge on the embryonic structures and their functionalities.
