What 2 things does completion of lateral folding result in?
During this time, where are precursors to the urinary and reproductive systems found? How does this relate to their adult locations?
Completion of these lateral folds results in the formation of the gut tube and the definition of the peritoneal cavity. The precursors of the urinary and reproductive systems can be found adjacent to each other and up against the posterior abdominal wall (see figure below). The adult location of organs and various tracts leading to/from these systems are a result of this position in the fetus. For example, the kidneys and ureters are located in a retroperitoneal position.
What embryonic layer do the urinary and reproductive systems develop from? Name the specific part of this embryonic layer they originate from.
The intermediate mesoderm produces the ____ ____. The ____ ____ (same as before) has 2 parts: the ____ ___ and the ___ ____.
The urinary and reproductive systems develop from the intermediate mesoderm. The intermediate mesoderm produces the urogenital ridge. The urogenital ridge has 2 parts: the nephrogenic cord (ridge) producing the urinary system and the gonadal ridge producing the reproductive system.
List the 3 consecutive sets of kidneys that develop in human embryos.
Where are pronephric kidneys located? Do they function as kidneys in the embryo? What ultimately happens to this set of kidneys?
Pronephric Kidneys – these are located in the neck (cervical) region and are nonfunctional. These kidneys degenerate.
Do the mesonephric kidneys function as kidnyes?
What is the mesonephric duct? What structure does it dump into? What does it give off?
What do the mesonephric tubules become in males? In females?
• second set of kidneys.
• large and elongated; have glomeruli; mesonephric tubules associate with capillaries.
• briefly functional .
Mesonephric Duct :
• extends to the cloaca
• gives rise to the metanephric diverticulum (a.k.a. ureteric bud).
Mesonephric Tubules become:
• In MALES - efferent ductules of the testes
• In FEMALES - mesonephric ducts degenerate.
What are the 2 parts of the metanephric kidneys? What structures do they each form?
The metanephric kidneys for the permanent kidneys which consist of 2 parts:
• the metanephric diverticulum (ureteric bud ) forms the collecting tubules (Collecting tubules and ducts, Minor and major calyces, Ureters)
• the metanephric mesoderm forms the nephrons.
What is the original position of the kidneys? How does the positioning of the kidneys change? How does its vascular supply change along with it?
Positional changes of the kidneys
• initially lie ventral to the sacrum
• As the body lengthens the kidneys “ascend” into the abdomen and establish “new” renal vessels and discard “old, lower” renal vessels. The kidneys do not really ascend-embryo just grows longer.
What is Horseshoe kidney? Explain the embryology behind it.
What is the typical clinical presentation of Horseshoe kidney?
What are the kidneys more susceptible to in this condition?
What is the treatment for Horseshoe kidney?
• most common type of renal fusion anomaly
• render the kidneys susceptible to trauma, renal calculi and cancer.
• found in 1 in 400-500 adults
• more frequently in males (M:F 2:1)
• usually identified incidentally
• formed by fusion across the midline of 2 developing kidneys
• fusion is between the lower poles
• normal ascent of the kidneys is impaired by the inferior mesenteric artery
• renal vascular anomalies are common
Treatment and prognosis
• do not require any treatment
The cloaca is divided by the ____ ____ to form what 2 organs?
The cloaca (means “sewer”) is divided by the urorectal septum to form the urinary bladder and the rectum.
The bladder begins as the cloaca which combines the dorsal rectum/ventral urogenital sinus. Eventually the urogenital sinus is partitioned separating it from the rectum.
What is the adult remnant of the allantois? What is the consequence if the allantois remains patent?
Allantois becomes the urachus; if the urachus remains open urine can leak out of the umbilicus
Explain the 2 step development of gonads.
In the early period of sexual development, what are gonads referred to and why?
The development of the gonads is a 2-step process.
1. Epithelium lining the posterior abdominal wall and the underlying mesenchyme form primitive sex cords.
2. Primordial Germ Cells are initially located in the lining of the yolk sac. During weeks 4-6 these primordial germ cells migrate from the yolk sac to the gonadal ridges . These primordial germ cells enter the underlying mesenchyme and are incorporated in the primary sex cords.
In the early period of sexual development the gonads are referred to as “indifferent gonads” since at this stage you cannot you cannot tell male from female.
What do primitive sex cords form in males? What do they become in females?
• The primordial germ cells become closely associated with the sex cords.
• If the sex becomes male then the sex cords become the seminiferous tubules.
• If the sex becomes female, then the sex cords wrap around the primitive oogonia. (CT support)
In females, which duct (mesonephric or paramesonephric) persists to form female genitalia?
What reproductive structures are formed from this persisting duct?
What hormone stimulates formation of the female reproductive tract?
In males, which duct persists (paramesonephric or mesonephric)?
What hormone is secreted to suppress the formation of the unneeded duct? What cells secrete it?
Under the influence of what hormone does the male reproductive tract form? What cells secrete it?
What structures does the remaining duct form?
What is the relationship of the paramesonephric duct (Mullerian) to the mesonephric duct (Wolffian)?
What is the anatomical location of the cranial ends of teh Mullerian ducts in females?
What do the caudal ends of paramesonephric/Mullerian ducts form?
- Mesonephric ducts degenerate.
- Paramesonephric (Müllerian) ducts lie lateral to the mesonephric ducts.
- The cranial ends open into the peritoneal cavity (future fimbriae).
- The caudal ends fuse to form a uterovaginal primordium.
- Summary: As the mesonephric ducts degenerate the paramesonephric ducts form the uterine tubes (cranially) and fuse (distally) to form uterovaginal primordium.
The vagina develops partly from the _____ ____ and the ____ ____.
The vagina develops partly from the paramesonephric ducts and the vaginal epithelium (ectoderm).
What do the urogenital folds form in females?
What do the labioscrotal folds form in females?
Development of female external genitalia
The feminization of the indifferent external genitalia is not clearly understood. Growth of the phallus (clitoris) gradually ceases but the urogenital folds do not fuse. Unfused parts of the urogenital folds form the labia minora. The labioscrotal folds fuse cranially to form the labia majora (homologous to the scrotum).
see pg 513 of first aid
What male structures do Wolffian/mesonephric ducts form?
Under the influence of what hormone?
• Sertoli cells of the testes produce mullerian inhibiting substance (MIS).
• MIS causes the paramesonephric ducts to disappear.
• Interstitial cells produce testosterone.
• Testosterone acts on the mesonephric ducts to form the male genital ducts.
What is the original location of the testes?
What 2 structures play a rolein moving the testes to their final location?
Explain how the vasculature travels with the testes on the way to their final location.
The testes begin in the posterior abdominal wall and are drawn down through the inguinal canal and into the scrotum by the gubernaculum.
2 structures play a role in moving the testes from the posterior abdominal wall to the scrotum.
1. Gubernaculum – attached to the inferior pole of the testes and the inferior aspect of the scrotal swellings forms a guidance mechanism.
2. Processus Vaginalis – a double walled sac of peritoneum surrounding each testis. Is formed when the testes go through the deep inguinal ring
The testes reach the scrotum by 33 weeks. During descent, blood supply to the testis from the aorta is “pulled along” and ends up within the spermatic cord along with the venous return and vas deferens. Intra-abdominal pressure forces the testes through the inguinal canal.
Development of male external genitalia
Proliferating mesenchyme produces a genital tubercle which forms a ____.
As the phallus enlarges and elongates the ____ ____ form urethral groove/spongy urethra which eventually closes to form the penile urethra within the bulbospongiosum.
Proliferating mesenchyme produces a genital tubercle which forms a phallus.
As the phallus enlarges and elongates the urogenital folds form urethral groove/spongy urethra which eventually closes to form the penile urethra within the bulbus spongiosum.
What is hypospadias? What causes hypospadias?
• congenital malformation affecting the male external genitalia.
• 0.2 - 4.1 per 1000 live births.
• urethral meatus is abnormally positioned proximally and ventrally to its normal position.
• due to failure of fusion of the urethral groove secondary to either testosterone deficiency/insensitivity.
Associated anomalies: congenital vesico-ureteral reflux