The development of the urinary system and genital systems are closely linked. The urogenital system develops from intermediate mesoderm. A longitudinal elevation - the urogenital ridge - forms on each side of the dorsal aorta, with the nephrogenic cord leading to the urinary system and the gonadal ridge leading to the genital system.
The urogenital system develops from intermediate mesoderm. A longitudinal elevation - the urogenital ridge - forms on each side of the dorsal aorta, with the nephrogenic cord leading to the urinary system and the gonadal ridge leading to the genital system.
Three sets of kidneys develop in human embryos:
The ureteric bud/metanephric diverticulum is the beginning of the ureter, renal pelvis, calices, and collecting tubules.
Straight collecting tubules undergo repeated branching to form successive generations of tubules.
The end of each new collecting tubule induces clusters of mesenchymal cells to form small metanephric vesicles, which then elongate to form renal tubules and fuse with the collecting duct. The proximal ends are invaginated by glomeruli.
Each functional unit is therefore composed of two mesenchymal tissue types - the collecting duct from metanephric diverticulum and the nephron from metanephric mesoderm. Mesenchymal-to-epithelial transition is all over the place in the kidney.
Fetal kidneys are divided into lobes, which usually disappear as nephrons increase and grow. At term, each kidney contains 800,000 - 1,000,000 nephrons.
Metanephric kidneys begin close to each other in the pelvis. As the embryo grows, they come to lie in the abdomen and move into the abdomen, primarily due to the caudal end of the embryo growing away from the kidneys. During 'ascent' ,the kidneys' blood supply changes, with caudal branches undergoing involution. When the kidneys come into contact with the adrenal glands their ascent stops, and renal arteries become permanent.
The metanephric diverticulum, or ureteric bud, is the beginning of the ureter, renal pelvis, calices, and collecting tubules.
At the end of the 4th week, embryo folding produces the cloaca, or expanded hindgut. In the 5th week, the allantoic diverticulum and mesonephric ducts join the cloaca, while the urorectal septum (extraembryonic mesoderm) begins to divide the cloaca into the urogenital sinus and anorectum.
The urogenital sinus is then considered divided into the vesicourethral canal and the definitive urogenital sinus. The bladder is formed primarily from the vesicourethral canal, which also contributes to the urethra. The definitive urogenital sinus (the phallic part) forms portions of the genitalia.
The proximal mesonephric duct becomes incorporated into the dorsal wall of the urogenital sinus, forming the trigone. Mesonephric and metanephric ducts enter separately.
The urethra is derived from endoderm of the urigenital sinus
cloaca becomes separated to form urogenital sinus and anorectal canal (check these)
The mesenchymal gonadal ridge is soon joined by fingerlike epithelial cords, producing the indifferent gonad with a cortex and medulla. In females, the cortex differentiates into an ovary, while in males the medulla differentiates into the testes.
By the 6th week, the cloacal membrane forms the primary urethral groove, bounded by primary urethral (urogenital) folds. Genital (labioscrotal) swellings occur on either side and the genital tubercule ventral to it. Sexual differentiation of the external genitalia begins to occur in the 1oth week.
Primordial germ cells originate in the yolk sac and migrate through the gut to gonadal ridges during the 6th week.
The presence of a Y chromosome, with the SRY gene for testis-determining factor, induces male differentiation.
Absence of SRY gene and therefore testosterone and MIS leads to development of outer genitalia and Mullerian ducts and regression of Wolffian ducts.
The gonadal cord cortex forms folliculogenous cords, and primordial germ cells form oogonia. During the second trimester oogonia enter meiosis I and become surrounded by follicular cells, forming primordial ovarian follicles. Meiosis I completes during ovulation, while meiosis II occurs following fertilization.
Two Mullerian ducts form and fuse to form the uterus, cervix, and upper vagina, with proximal, unfused tubes becoming the uterine tubes.
in the presence of anti-Mullarian hormone/Mullerian inhibiting factor, produced by Sertoli cells, the paramesonephric ducts regress
The genital tubercle becomes the clitoris, the genital swellings become labia majora, and urethral folds become labia minora.
Under the influence of TDF, the gonadal ridge medulla differentiate into testicular cords containing prospermatogonia and future Sertoli cells. Interstitial Leydig cells begin secreting androgens early in the fetal period, leading to masculine differentiation of internal and external genitalia.
Mesonephric tissue grow into the medulla and form rete testis, while mesonephric tubules form efferent ductules connecting the rete testis to the duct of the epididymis.
Descent of the testes usually occurs during the third trimester and is androgen-dependent.
Mesonephric ducts develop in the 5th week, and in the presence of androgens, the epididymis, ductus deferens, seminal vesicle, and ejaculatory duct form. The mesonephric duct degenerates in females.
In the presence of androgens, the genital tubercule becomes the penis, the urethral folds form the ventral shaft, and the genital swellings fuse to form the scrotum.
- unilateral is 1:500 adults
both can be asymptomatic
Potter Syndrome - bilateral renal agenesis