Development of the Urogenital System

The urogenital system is derived from intermediate mesoderm. The intermediate mesoderm differentiates into nephrogenic cords (which will go on to form the urinary system) and an adjacent area known as the gonadal ridge (which will go on to form the gonads). The nephrogenic cords elongate in a caudal direction and sequentially develop 3 different structures: the pronephros (rudimentary and nonfunctional), the mesonephros (forms the primitive urinary system), and the metanephros (forms the permanent kidney). Concurrently, the genital system develops in close association with the urinary system. Genital development depends on chromosomal sex, which determines whether the primitive gonads differentiate into testes or ovaries Ovaries Ovaries are the paired gonads of the female reproductive system that contain haploid gametes known as oocytes. The ovaries are located intraperitoneally in the pelvis, just posterior to the broad ligament, and are connected to the pelvic sidewall and to the uterus by ligaments. These organs function to secrete hormones (estrogen and progesterone) and to produce the female germ cells (oocytes). Ovaries. The gonads then secrete certain hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview, which direct further development of both the internal and external genital structures.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Early Embryonic Development

Bilaminar disc

Develops around week 2 of embryonic life: 

  • Layers:
    • Epiblast
    • Hypoblast
  • Undergoes a process called gastrulation Gastrulation Both gastrulation and neurulation are critical events that occur during the 3rd week of embryonic development. Gastrulation is the process by which the bilaminar disc differentiates into a trilaminar disc, made up of the 3 primary germ layers: the ectoderm, mesoderm, and endoderm. Gastrulation and Neurulation to form the trilaminar disc

Trilaminar disc

Layers:

  • Ectoderm
  • Mesoderm:
    • Paraxial mesoderm
    • Intermediate mesoderm
    • Lateral plate mesoderm (LPM): 
      • Somatic layer of the LPM
      • Splanchnic layer of the LPM
  • Endoderm (becomes the primitive gut tube)
Layers of the trilaminar disc

Layers of the trilaminar disc

Image by Lecturio.

Folding

  • The trilaminar disc folds in 2 directions:
    • Lateral folding creates a “cylindrical” structure surrounded by ectoderm.
    • Cranial-to-caudal folding
  • Key structures for urogenital development at this stage:
    • Intermediate mesoderm → develops into:
      • Nephrogenic cords → goes on to form the urinary system
      • Gonadal ridge (area adjacent to the nephrogenic cords) → goes on to form the stromal tissue of the gonads
    • Primordial germ cells:
      • Originate from epiblast cells
      • Cells migrate to the yolk sac
      • Will eventually migrate along the allantois to the gonadal ridge
      • Go on to become the spermatozoa or oocytes
Cross-sectional view of the early embryo

Cross-sectional view of the early embryo

Image by Lecturio.

Development of the Urinary System

The kidney develops from embryonic mesoderm in 3 successive forms from the nephrogenic cords as the cords elongate in a cranial-to-caudal direction.

Pronephros

  • Appears in week 4 as a cluster of a tubule and a few cells (nephrotomes) 
  • Develops in nephrogenic cords in the cervical region 
  • Rudimentary and nonfunctional 
  • Degenerates by the end of week 4 (persists < 1 week)
  • Purpose unclear, though may be a “scaffold” off which the next structure (the mesonephros) develops
Developmental location of the pronephros, mesonephros, and metanephros in the developing embryo

Developmental location of the pronephros, mesonephros, and metanephros in the developing embryo

Image by Lecturio.

Mesonephros

  • Begins to develop as pronephros regresses around week 5
  • Most of the mesonephros regresses by week 10.
  • Develops lower, in the thoracolumbar region
  • Connects with the cloaca at the caudal end of the primitive gut tube
  • Consists of:
    • A longitudinal mesonephric duct (also called the wolffian duct)
    • A series of tubules coming off that main duct, growing anteriorly toward the aorta 
  • Small glomerular vessels grow posteriorly off the aorta toward the mesonephric tubules, forming primitive renal corpuscles:
    • Mesonephric tubules grow around the glomerular capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries, forming Bowman capsules (though these will ultimately regress).
    • Forms the primitive urinary system
  • Filtration of blood begins: 
    • Blood flows down the aorta → glomerular capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries
    • Filtered through Bowman capsule 
    • Filtrate travels down the mesonephric tubule → mesonephric duct → cloaca → allantois
  • Mesonephros is present only from weeks 5–10 (at which time the permanent kidney formed from the metanephros takes over).
  • The mesonephric ducts persist in males and form part of the male reproductive system.
Graphical summary of the mesonephros

Graphical summary of the mesonephros:
Note that the nephrogenic cords (primary nephric ducts) elongate and join with the cloaca. Mesonephric tubules grow in a stepladder-like pattern and function as a primitive urinary system, while the definitive kidney develops from the metanephros further down in the growing pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 "hip" bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis.

Image by Lecturio.

Metanephros

The permanent kidney is formed from the metanephros.

  • Develops starting around the 5th week
  • Cells in the intermediate mesoderm in the pelvic region begin to differentiate into a structure called the metanephric blastema, which:
    • Ultimately becomes the cells making up the nephrons
    • Releases growth factors that stimulate the development of an outpouching off the caudal portion of the mesonephric duct called the ureteric buds
  • Ureteric buds grow toward and invade the metanephric blastema:
    • Elongating stalk of the ureteric bud develops into the ureter.
    • Within the metanephric blastema, the ureteric buds undergo a series of branchings to form the:
      • Renal pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 "hip" bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis
      • Major calyces
      • Minor calyces
      • Collecting tubules
  • Metanephric mesodermal cap: 
    • Mesoderm from the metanephric blastema sitting “on top of” the developing collecting ducts
    • Elongates, forming the tubular system The tubular system The kidneys regulate water and solute homeostasis through the processes of filtration, reabsorption, secretion, and excretion. After the filtration of blood through the glomeruli, the tubular system takes over and is responsible for adjusting the urine composition throughout the remainder of the nephron. The Tubular System of the nephrons → becomes known as the metanephric tubule
    • The metanephric tubule fuses with the collecting tubule, creating 1 continuous system.
  • Bowman capsule: forms off the growing end of the metanephric tubule
  • Glomerular capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries:
    • Develop off the common iliac arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries
    • Become associated with Bowman capsule at the end of the metanephric tubules → begin creating “urine” (Note: True waste products from the fetus are removed via the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity.)
  • Nephrons are formed until birth.
  • Nephron maturation continues after birth.

Position of the kidney and changes in vascularization

  • The kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys are initially located in the pelvic region.
  • As the caudal portion of the body grows downward, the relative location of the kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys “ascends” into the upper quadrants of the abdomen (failure to ascend results in a pelvic kidney).
  • As the kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys ascend, the original blood supply degenerates.
  • New vessels (higher up) develop off the aorta and invade the kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys, becoming the mature renal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries.
  • If the original vessels fail to regress, they may persist as additional renal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries or veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins.
Ascent of the kidneys and corresponding change in vascular supply

Ascent of the kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys and corresponding change in vascular supply

Image by Lecturio.

Development of the bladder and urethra

Between the 4th and 7th weeks of development, the cloaca divides into:

  • Urogenital sinus:
    • From the anterior portion of the cloaca
    • Connects to the ureters and mesonephric ducts
    • The urogenital sinus has 3 portions:
      • Proximal (largest) → urinary bladder 
      • Middle (narrow) → origin of prostate Prostate The prostate is a gland in the male reproductive system. The gland surrounds the bladder neck and a portion of the urethra. The prostate is an exocrine gland that produces a weakly acidic secretion, which accounts for roughly 20% of the seminal fluid. Prostate and other Male Reproductive Glands and prostatic and membranous urethra in males and the entire urethra in females
      • Distal → penile urethra in males
  • Anal canal:
    • From the posterior portion of the cloaca
    • Connects to the developing hindgut
  • Urorectal septum: 
    • Separates the urogenital sinus from the anal canal 
    • Starts at the superior/proximal portion of the cloaca → grows distally until it reaches the outside of the body, where it becomes the perineal body
    • Failure of the septum to form correctly can result in fistulas between the urogenital system and the anorectum.
  • The allantois (drains the cloaca through the umbilical cord) → ultimately turns into the median umbilical ligament

Early Embryologic Development of the Genital System

Overview of typical sex development

  • Chromosomal sex → determines gonadal sex → determines phenotypic sex
  • Up until 6 weeks of gestation, sex development is identical and nonbinary; developing structures include:
    • Nonbinary, bipotent, undifferentiated gonads
    • Mesonephric ducts (also known as wolffian ducts; also part of the primitive urinary system)
    • Paramesonephric ducts (also known as müllerian ducts) 
    • Urogenital sinus
    • The genital tubercle, genital swellings, and genital folds 
  • The genes present at fertilization Fertilization To undergo fertilization, the sperm enters the uterus, travels towards the ampulla of the fallopian tube, and encounters the oocyte. The zona pellucida (the outer layer of the oocyte) deteriorates along with the zygote, which travels towards the uterus and eventually forms a blastocyst, allowing for implantation to occur. Fertilization and First Week will determine how the developing bipotent gonads differentiate (e.g., into a testis or an ovary).
  • The developing gonads will then secrete hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview.
    • The presence and/or absence of specific hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview will determine how the remaining structures differentiate.
    • In general, female organs and structures are the “default” phenotype if specific genes and hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview are not present to stimulate male differentiation.
Sex differentiation

Sex differentiation from the mesonephric (wolffian) and paramesonephric (müllerian) ducts:
In females, the mesonephric ducts regress while the paramesonephric ducts persist. The paramesonephric ducts remain open to the intraembryonic coelom (the eventual peritoneal cavity) near the gonads, and the inferior/medial ends fuse into a common body in the midline, forming the uterus and upper vagina Vagina The vagina is the female genital canal, extending from the vulva externally to the cervix uteri internally. The structures have sexual, reproductive, and urinary functions and a rich blood supply, mainly arising from the internal iliac artery. Vagina, Vulva, and Pelvic Floor.
In males, the mesonephric ducts are closely associated with the gonads; they enter the urogenital sinus separately on each side becoming parts of the ejaculatory system, while the urogenital sinus becomes the bladder and prostate Prostate The prostate is a gland in the male reproductive system. The gland surrounds the bladder neck and a portion of the urethra. The prostate is an exocrine gland that produces a weakly acidic secretion, which accounts for roughly 20% of the seminal fluid. Prostate and other Male Reproductive Glands.

Image by Lecturio. License: CC BY-NC-SA 4.0

Embryologic development of the bipotent gonads

  • A portion of the intermediate mesoderm covering the anterior portion of the nephrogenic cords → known as the gonadal ridge
  • Epithelial cells in the gonadal ridge:
    • Proliferate and condense
    • Penetrate into the mesenchyme to form the primitive sex cords (still indifferent gonads)
    • These cells will become the stromal cells:
      • Sertoli and Leydig cells in males
      • Granulosa and theca cells in females
  • Primordial germ cells:
    • Will differentiate into spermatozoa or oocytes
    • Originate in the epiblast
    • Migrate to the yolk sac → through the allantois (umbilical cord) → along the dorsal mesentery of the hindgut → genital ridges
    • Germ cells invade the gonadal ridges by approximately 6 weeks
  • Developing sex cords associate with migrating primordial germ cells to form gonads.

Development of the Internal Male Genitalia

Overview of the adult male genital structures

Structures of the male reproductive system

Structures of the male reproductive system

Image: “Male Reproductive System” by OpenStax College. License: CC BY 4.0, cropped by Lecturio.

Development of the testes

  • Male development starts as a result of the presence of the sex-determining region of the Y chromosome gene (SRY gene):
    • Produces SRY protein (also known as testis-determining factor [TDF]) 
    • SRY/TDF stimulates the differentiation of the bipotent gonad into testes by stimulating stromal cells to differentiate into:
      • Leydig cells → secrete testosterone
      • Sertoli cells → secrete müllerian inhibitory factor (MIF) (also called antimüllerian hormone (AMH))
      • Seminiferous tubules
  • Testosterone:
    • Stimulates differentiation of the wolffian/mesonephric ducts into:
      • Epididymis
      • Vas deferens
      • Seminal vesicles
      • Ejaculatory ducts
    • Is converted to dihydrotestosterone (DHT) by 5α-reductase → stimulates development of:
      • The prostate Prostate The prostate is a gland in the male reproductive system. The gland surrounds the bladder neck and a portion of the urethra. The prostate is an exocrine gland that produces a weakly acidic secretion, which accounts for roughly 20% of the seminal fluid. Prostate and other Male Reproductive Glands from the urogenital sinus 
      • External male genitalia
  • MIF → causes regression of the müllerian/paramesonephric ducts (which develop into internal female structures)
  • Primordial germ cells differentiate into sperm.
  • The process of differentiation is largely completed by 12 weeks of gestation.

Development of the Internal Female Genitalia

Development of the ovaries Ovaries Ovaries are the paired gonads of the female reproductive system that contain haploid gametes known as oocytes. The ovaries are located intraperitoneally in the pelvis, just posterior to the broad ligament, and are connected to the pelvic sidewall and to the uterus by ligaments. These organs function to secrete hormones (estrogen and progesterone) and to produce the female germ cells (oocytes). Ovaries

  • Development of the ovary from the bipotent gonad requires:
    • Absence of the SRY gene (preventing differentiation into testes)
      • No testosterone → no development of the mesonephric ducts
      • No MIF → paramesonephric/müllerian ducts persist 
    • Presence of several genes found on chromosome 1
    • Begins around 10 weeks of development
  • Epithelial cells from the gonadal ridge → become follicular cells:
    • Cell types:
      • Granulosa cells 
      • Theca cells
    • Produce estrogen → stimulate the formation of the external female genitalia
  • Primordial germ cells:
    • Develop into oocytes
    • Associate with the follicular cells

Development of the fallopian tubes, uterus, and vagina Vagina The vagina is the female genital canal, extending from the vulva externally to the cervix uteri internally. The structures have sexual, reproductive, and urinary functions and a rich blood supply, mainly arising from the internal iliac artery. Vagina, Vulva, and Pelvic Floor

Step 1: Fusion of the paramesonephric ducts

  • The ducts fuse in the midline adjacent to the urogenital sinus.
  • Fused paramesonephric ducts differentiate into:
    • Uterus
    • Cervix
    • Upper vagina Vagina The vagina is the female genital canal, extending from the vulva externally to the cervix uteri internally. The structures have sexual, reproductive, and urinary functions and a rich blood supply, mainly arising from the internal iliac artery. Vagina, Vulva, and Pelvic Floor
  • The medial walls of the ducts initially form a longitudinal midline septum.
    • This septum normally fully regresses, creating a single cavity.
    • The septum can persist, resulting in a longitudinal uterine, cervical, and/or vaginal septum.
  • The lateral ends of the paramesonephric ducts remain “unfused” → these will differentiate into the fallopian tubes

Step 2: Connection of the fused paramesonephric ducts to the urogenital sinus

  • A thickening grows out of the superior portion of the urogenital sinus called the sinovaginal bulbs.
  • Sinovaginal bulbs:
    • Located between the fused paramesonephric ducts and the urogenital sinus
    • Thicken and grow into a solid structure called the vaginal plate
  • Vaginal plate:
    • Elongates
    • Connects the developing uterus (from the paramesonephric ducts) to the vestibule (opening to outside the body, originating from the urogenital sinus)
    • Lumen develops within the vaginal plate, creating the vagina Vagina The vagina is the female genital canal, extending from the vulva externally to the cervix uteri internally. The structures have sexual, reproductive, and urinary functions and a rich blood supply, mainly arising from the internal iliac artery. Vagina, Vulva, and Pelvic Floor
    • Failure to canalize results in vaginal agenesis
    • Hymen: membrane where the vaginal plate meets the urogenital sinus

Development of External Genitalia

  • Up until 6 weeks of gestation, sex development is identical and nonbinary.
  • Early structures develop from folds in the cloaca and include:
    • Genital tubercle 
    • Genital folds
    • Genital swellings
  • Development of the external genitalia depends on the hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview present:
    • Testosterone/DHT → male structures
    • Estrogen → female structures
Table: Development of the external genitalia from early structures
Undifferentiated structure In the presence of testosterone Estrogen/lack of testosterone
Urogenital sinus
  • Prostatic urethra
  • Membranous urethra
  • Prostate gland
  • Bulbourethral glands
  • (Bladder*)
  • Female urethra
  • Bartholin glands
  • Skene glands
  • (Bladder*)
Genital tubercle (forms erectile tissue)
  • Glans penis Penis The penis is the male organ of copulation and micturition. The organ is composed of a root, body, and glans. The root is attached to the pubic bone by the crura penis. The body consists of the 2 parallel corpora cavernosa and the corpus spongiosum. The glans is ensheathed by the prepuce or foreskin. Penis
  • Corpus cavernosum
  • Corpus spongiosum
  • Glans clitoris
  • Vestibular bulbs
Genital folds
  • Shaft of the penis Penis The penis is the male organ of copulation and micturition. The organ is composed of a root, body, and glans. The root is attached to the pubic bone by the crura penis. The body consists of the 2 parallel corpora cavernosa and the corpus spongiosum. The glans is ensheathed by the prepuce or foreskin. Penis
  • Penile urethra
Labia minora
Genital swelling Scrotum Labia majora
*Development is independent of hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview.
Phenotypic differentiation of the external genitalia in male and female embryos

Phenotypic differentiation of the external genitalia in male and female embryos:
Both male and female external genitalia develop from the same starting structures but diverge as they are exposed to different levels of androgens Androgens Androgens are naturally occurring steroid hormones responsible for development and maintenance of the male sex characteristics, including penile, scrotal, and clitoral growth, development of sexual hair, deepening of the voice, and musculoskeletal growth. Androgens and Antiandrogens and estrogens.

Image by Lecturio. License: CC BY-NC-SA 4.0

Clinical Relevance

Disorders of urinary development

  • Horseshoe kidney: developmental defect of the kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys in which the inferior poles are fused together. As the kidney attempts to migrate superiorly during development, it is blocked by the superior mesenteric artery. The vascular supplies and collecting system of the kidney also tend to have various degrees of distortion. Individuals are typically asymptomatic, with incidental diagnosis made on imaging. Other presentations include infection, obstruction, hydronephrosis Hydronephrosis Hydronephrosis is dilation of the renal collecting system as a result of the obstruction of urine outflow. Hydronephrosis can be unilateral or bilateral. Nephrolithiasis is the most common cause of hydronephrosis in young adults, while prostatic hyperplasia and neoplasm are seen in older patients. Hydronephrosis, and calculi. 
  • Duplications of the collecting system: known as a “duplex system.” Duplications of the collecting system are the most common congenital anomaly of the urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract. In these cases, a kidney will have 2 separate pelvicaliceal systems and 2 ureters. Ureteral insertion into the bladder from the duplicated system is often abnormal as well. Most individuals are asymptomatic, though recurrent urinary tract infections Urinary tract infections Urinary tract infections (UTIs) represent a wide spectrum of diseases, from self-limiting simple cystitis to severe pyelonephritis that can result in sepsis and death. Urinary tract infections are most commonly caused by Escherichia coli, but may also be caused by other bacteria and fungi. Urinary Tract Infections (UTIs) or obstruction may occur.
  • Renal agenesis: congenital absence of a kidney, specifically, renal parenchymal tissue. This absence results from disruption of metanephric development. Most individuals are asymptomatic (because they have another normally functioning kidney) and are diagnosed incidentally on imaging. Renal agenesis is often associated with additional congenital anomalies.
  • Posterior urethral valves: persistence of the urogenital membrane, resulting in urethral obstruction in males. Affected infants often present in utero with severe bilateral hydronephrosis Hydronephrosis Hydronephrosis is dilation of the renal collecting system as a result of the obstruction of urine outflow. Hydronephrosis can be unilateral or bilateral. Nephrolithiasis is the most common cause of hydronephrosis in young adults, while prostatic hyperplasia and neoplasm are seen in older patients. Hydronephrosis seen on ultrasonography that causes pressure necrosis of renal tissue and CKD CKD Chronic kidney disease (CKD) is kidney impairment that lasts for ≥ 3 months, implying that it is irreversible. Hypertension and diabetes are the most common causes; however, there are a multitude of other etiologies. In the early to moderate stages, CKD is usually asymptomatic and is primarily diagnosed by laboratory abnormalities. Chronic Kidney Disease in these children. There is a high likelihood that renal transplantation will be necessary.
  • Urachal fistula: persistence of the urachus. The urachus is known as the allantois earlier in development, and it connects to the bladder. Babies with a urachal fistula may leak urine from their umbilicus at birth.

Congenital anomalies of the reproductive system

  • Gartner duct cysts: benign cysts that can be seen on either side of female reproductive organs (typically the upper vagina Vagina The vagina is the female genital canal, extending from the vulva externally to the cervix uteri internally. The structures have sexual, reproductive, and urinary functions and a rich blood supply, mainly arising from the internal iliac artery. Vagina, Vulva, and Pelvic Floor). These cysts represent remnants of the mesonephric ducts and are usually asymptomatic.
  • Müllerian anomalies: abnormal fusion of the müllerian/paramesonephric ducts can result in a variety of uterine, cervical, and vaginal anomalies. Individuals are often asymptomatic, though they may present with infertility Infertility Infertility is the inability to conceive in the context of regular intercourse. The most common causes of infertility in women are related to ovulatory dysfunction or tubal obstruction, whereas, in men, abnormal sperm is a common cause. Infertility or issues related to menstruation.
Malformations of the uterus

Illustration showing types of congenital malformations of the uterus

Image by Lecturio. License: CC BY-NC-SA 4.0
  • Hymen anomalies: The hymen is the membrane where the vaginal plate met the urogenital sinus. Normally, the hymen ruptures prior to birth, however a number of anomalies are possible. An imperforate hymen will not allow efflux of any uterine fluid, and it typically presents with pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain at the onset of menses. Management is surgical.
Malformations of hymen

Normal parous hymen compared to common hymen malformations, including microperforate, septate, cribriform, and imperforate hymens

Image by Lecturio. License: CC BY-NC-SA 4.0
  • Hypospadias: congenital anomaly of the male urethra that is characterized by an abnormal location of the urethral meatus on the ventral surface of the penis Penis The penis is the male organ of copulation and micturition. The organ is composed of a root, body, and glans. The root is attached to the pubic bone by the crura penis. The body consists of the 2 parallel corpora cavernosa and the corpus spongiosum. The glans is ensheathed by the prepuce or foreskin. Penis. The meatus may be located anywhere on the glans, penile shaft, scrotum, or perineum.

Disorders of sexual development

Disorders of sexual development (DSDs) are a group of conditions characterized by atypical sexual development in an individual, which may involve abnormalities in the structure and/or function of the internal reproductive organs and/or external genitalia. 

  • Congenital adrenal hyperplasia Congenital adrenal hyperplasia Congenital adrenal hyperplasia (CAH) consists of a group of autosomal recessive disorders that cause a deficiency of an enzyme needed in cortisol, aldosterone, and androgen synthesis. The most common subform of CAH is 21-hydroxylase deficiency, followed by 11β-hydroxylase deficiency. Congenital Adrenal Hyperplasia: Increased formation of male sexual hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview ( androgens Androgens Androgens are naturally occurring steroid hormones responsible for development and maintenance of the male sex characteristics, including penile, scrotal, and clitoral growth, development of sexual hair, deepening of the voice, and musculoskeletal growth. Androgens and Antiandrogens) with virilization of the external female genitals. Characterized by low levels of cortisol, high levels of ACTH, and adrenal hyperplasia.
  • Androgen insensitivity syndrome Androgen insensitivity syndrome Androgen insensitivity syndrome (AIS) is an X-linked recessive condition in which a genetic mutation affects the function of androgen receptors, resulting in complete (CAIS), partial (PAIS), or mild (MAIS) resistance to testosterone. All individuals with AIS have a 46,XY karyotype; however, phenotypes vary and include phenotypic female, virilized female, undervirilized male, and phenotypic male individuals. Androgen Insensitivity Syndrome (AIS): Mutations in the androgen receptors cause partial or complete resistance to testosterone. Genotypically, affected individuals have a 46,XY karyotype and testes present internally. Testosterone levels are elevated, and some of this testosterone is converted to estrogen peripherally. Clinically, individuals with complete AIS will present with no sexual hair and have normal-appearing external female genitalia. Individuals are usually assigned female gender at birth and will present at puberty Puberty Puberty is a complex series of physical, psychosocial, and cognitive transitions usually experienced by adolescents (11-19 years of age). Puberty is marked by a growth in stature and the development of secondary sexual characteristics, achievement of fertility, and changes in most body systems. Puberty with amenorrhea.
  • Aromatase deficiency Aromatase deficiency Aromatase deficiency is a very rare genetic condition with autosomal recessive inheritance. Aromatase deficiency is characterized by congenital estrogen deprivation with increased levels of testosterone due to decreased levels of the aromatase enzyme. Aromatase Deficiencyresults in an inability to convert testosterone to estrogen, primarily causing virilization of the external genitalia in females.
  • 5α-reductase deficiency:  autosomal recessive Autosomal recessive Autosomal inheritance, both dominant and recessive, refers to the transmission of genes from the 22 autosomal chromosomes. Autosomal recessive diseases are only expressed when 2 copies of the recessive allele are inherited. Autosomal Recessive and Autosomal Dominant Inheritancedisorder that impairs conversion of testosterone to DHT, preventing full development of the external genitalia in males. This disorder results in ambiguous genitalia in 46,XY individuals at birth. 
  • Pure gonadal dysgenesis: results in nonfunctional gonads. In 46,XX individuals, pure gonadal dysgenesis presents with premature ovarian insufficiency (i.e., premature menopause Menopause Menopause is a physiologic process in women characterized by the permanent cessation of menstruation that occurs after the loss of ovarian activity. Menopause can only be diagnosed retrospectively, after 12 months without menstrual bleeding. Menopause) in otherwise normal-appearing females. In 46,XY individuals, the condition is known as Swyer syndrome Swyer syndrome Swyer syndrome is a disorder of sex development caused by a defect in the SRY gene on chromosome Y. The syndrome is characterized by complete testicular dysgenesis in an individual who has a 46,XY karyotype and is phenotypically female. Swyer Syndrome; without functional testes, testosterone and MIF are not produced, so individuals have external female genitalia and normal müllerian structures. Affected individuals present in adolescence with primary amenorrhea Primary Amenorrhea Primary amenorrhea is defined as the absence of menstruation in a girl by age 13 years in the absence of secondary sex characteristics or by the age of 15 years with the presence of secondary sex characteristics. Etiologies can originate in the hypothalamic-pituitary-ovarian (HPO) axis or from anatomic abnormalities in the uterus or vagina. Primary Amenorrhea and lack of all secondary sex characteristics.  
  • Klinefelter syndrome Klinefelter syndrome Klinefelter syndrome is a chromosomal aneuploidy characterized by the presence of 1 or more extra X chromosomes in a male karyotype, most commonly leading to karyotype 47,XXY. Klinefelter syndrome is associated with decreased levels of testosterone and is the most common cause of congenital hypogonadism. Klinefelter Syndrome: Chromosomal aneuploidy characterized by the existence of ≥ 1 extra X chromosomes in a male karyotype (e.g., 47,XXY or 48,XXXY). Symptoms are not usually observed during childhood. During adulthood, individuals are typically tall males who present with gynecomastia Gynecomastia Gynecomastia is a benign proliferation of male breast glandular ductal tissue, usually bilateral, caused by increased estrogen activity, decreased testosterone activity, or medications. The condition is common and physiological in neonates, adolescent boys, and elderly men. Gynecomastia and infertility Infertility Infertility is the inability to conceive in the context of regular intercourse. The most common causes of infertility in women are related to ovulatory dysfunction or tubal obstruction, whereas, in men, abnormal sperm is a common cause. Infertility related to hypogonadism Hypogonadism Hypogonadism is a condition characterized by reduced or no sex hormone production by the testes or ovaries. Hypogonadism can result from primary (hypergonadotropic) or secondary (hypogonadotropic) failure. Symptoms include infertility, increased risk of osteoporosis, erectile dysfunction, decreased libido, and regression (or absence) of secondary sexual characteristics. Hypogonadism. Educational difficulties are also common.
  • Turner syndrome Turner syndrome Turner syndrome is a genetic condition affecting women, in which 1 X chromosome is partly or completely missing. The classic result is the karyotype 45,XO with a female phenotype. Turner syndrome is associated with decreased sex hormone levels and is the most common cause of primary amenorrhea. Turner Syndromechromosomal aneuploidy characterized by the absence of an X chromosome in a female karyotype (e.g., 45,X0). Clinical manifestations include a characteristic phenotype (short stature, webbed neck, widely spaced nipples) and multiple anomalies usually involving the cardiac, renal, reproductive, skeletal, and lymphatic systems. Gonadal dysgenesis and infertility Infertility Infertility is the inability to conceive in the context of regular intercourse. The most common causes of infertility in women are related to ovulatory dysfunction or tubal obstruction, whereas, in men, abnormal sperm is a common cause. Infertility are likely.
  • True hermaphroditism True hermaphroditism True hermaphroditism, or ovotesticular disorder of sexual development (ODSD), is characterized by the presence of an ovotesticular gonad that contains both ovarian and testicular elements. Individuals are usually born with ambiguous genitalia, but the diagnosis is rarely confirmed before puberty. The most common karyotype is 46,XX, and less often, 46,XY can be identified. True Hermaphroditism: presence of an ovotesticular gonad that contains both ovarian and testicular elements. Affected individuals are usually born with ambiguous genitalia, and the internal structures depend on the adjacent gonadal tissue. The most common karyotype is 46,XX.

References

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