{"history":[],"article":{"id":"f1626e5c-4d41-48a4-a5a5-5ead77acab77","title":"Development of the urinary system","slug":"development-of-the-urinary-system","content":":::summary\n:::\n\n# \nThe **development of the [urinary system](https://bliptext.com/articles/urinary-system)** begins during [prenatal development](https://bliptext.com/articles/prenatal-development), and relates to the development of the [urogenital system](https://bliptext.com/articles/urogenital-system) – both the organs of the [urinary system](https://bliptext.com/articles/urinary-system) and the [sex organs](https://bliptext.com/articles/sex-organ) of the [reproductive system](https://bliptext.com/articles/reproductive-system).\nThe development continues as a part of [sexual differentiation](https://bliptext.com/articles/sexual-differentiation).\nThe urinary and reproductive organs are developed from the [intermediate mesoderm](https://bliptext.com/articles/intermediate-mesoderm).\nThe permanent organs of the adult are preceded by a set of structures which are purely embryonic, and which with the exception of the ducts disappear almost entirely before birth.\nThese embryonic structures are on either side; the [pronephros](https://bliptext.com/articles/pronephros), the [mesonephros](https://bliptext.com/articles/mesonephros) and the [metanephros](https://bliptext.com/articles/metanephros) of the [kidney](https://bliptext.com/articles/kidney), and the [Wolffian](https://bliptext.com/articles/wolffian-duct) and [Müllerian ducts](https://bliptext.com/articles/m-llerian-duct) of the [sex organ](https://bliptext.com/articles/sex-organ).\nThe pronephros disappears very early; the structural elements of the mesonephros mostly degenerate, but the [gonad](https://bliptext.com/articles/gonad) is developed in their place, with which the Wolffian duct remains as the duct in males, and the Müllerian as that of the female.\nSome of the tubules of the mesonephros form part of the permanent kidney.\n\n# Pronephros and Wolffian duct\n\n## Wolffian duct\nIn the outer part of the [intermediate mesoderm](https://bliptext.com/articles/intermediate-mesoderm), immediately under the ectoderm, in the region from the fifth [cervical segment](https://bliptext.com/articles/cervical-segment) to the third [thoracic segment](https://bliptext.com/articles/thoracic-segment), a series of short [evaginations](https://bliptext.com/articles/evagination) from each segment grows [dorsally](https://bliptext.com/articles/dorsum-anatomy) and extends [caudally](https://bliptext.com/articles/caudally), fusing successively from before backward to form the [pronephric duct](https://bliptext.com/articles/pronephric-duct).\nThis continues to grow caudally until it opens into the ventral part of the [cloaca](https://bliptext.com/articles/cloaca-embryology); beyond the [pronephros](https://bliptext.com/articles/pronephros) it is termed the [Wolffian duct](https://bliptext.com/articles/wolffian-duct).\nThus, the Wolffian duct is what remains of the pronephric duct after the atrophy of the pronephros.\n\n## Pronephros\nThe original evaginations form a series of transverse tubules each of which communicates by means of a funnel-shaped ciliated opening with the [abdominal cavity](https://bliptext.com/articles/abdominal-cavity), and in the course of each duct a glomerulus also is developed.\nA secondary glomerulus is formed ventral to each of these, and the complete group constitutes the pronephros.\nIn humans, the pronephros is just rudimentary, and undergoes rapid atrophy and disappears.\n\n# Wolffian duct\n\n## Mesonephros\nOn the medial side of the Wolffian duct, from the sixth cervical to the third lumbar segments, a series of tubules, the [Wolffian tubules](https://bliptext.com/articles/mesonephros), develops.\nThey increase in number by outgrowths from the original tubules.\nThey change from solid masses of cells to instead become hollowed in the center.\nOne end grows toward and finally opens into the Wolffian duct, the other dilates and is invaginated by a tuft of capillary bloodvessels to form a glomerulus.\nThe tubules collectively constitute the [mesonephros](https://bliptext.com/articles/mesonephros).\nThe mesonephros persists and form the permanent kidneys in fish and amphibians, but in reptiles, birds, and mammals, it atrophies and for the most part disappears rapidly as the permanent kidney ([metanephros](https://bliptext.com/articles/metanephros)) develops beginning during the sixth or seventh week, so that by the beginning of the fifth month only the ducts and a few of the tubules of the mesonephros remain.\n\n## Development in male\nIn the male, the [Wolffian duct](https://bliptext.com/articles/wolffian-duct) persists, and forms for example the [epididymis](https://bliptext.com/articles/epididymis), the [ductus deferens](https://bliptext.com/articles/ductus-deferens), the [ejaculatory duct](https://bliptext.com/articles/ejaculatory-duct), [seminal vesicle](https://bliptext.com/articles/seminal-vesicle) and efferent ducts.\nIn the female, on the other hand, the Wolffian bodies and ducts atrophy, leaving behind only remnants in the adult, involving e.g. the [development of the suspensory ligament of the ovary](https://bliptext.com/articles/development-of-the-suspensory-ligament-of-the-ovary).\n\n# Müllerian duct\nShortly after the formation of the Wolffian ducts, a second pair of ducts is developed; these are the [Müllerian ducts](https://bliptext.com/articles/m-llerian-ducts).\nEach arises on the lateral aspect of the corresponding Wolffian duct as a tubular invagination of the cells lining the abdominal cavity.\nThe orifice of the invagination remains open, and undergoes enlargement and modification to form the abdominal [ostium of the fallopian tube](https://bliptext.com/articles/ostium-of-the-fallopian-tube).\nThe ducts pass backward lateral to the Wolffian ducts, but toward the posterior end of the embryo they cross to the medial side of these ducts, and thus come to lie side by side between and behind the latter—the four ducts forming what is termed the common genital cord, to distinguish it from the genital cords of the germinal epithelium seen later in this article.\nThe Müllerian ducts end in an epithelial elevation, the [Müllerian eminence](https://bliptext.com/articles/m-llerian-eminence), on the ventral part of the cloaca between the orifices of the Wolffian ducts.\nAt a later stage, the eminence opens in the middle, connecting the Müllerian ducts with the cloaca.\n# [A.—Diagram of the primitive urogenital organs in the embryo previous to sexual distinction. The common genital cord is labeled with gc.
* 3. Ureter. \n
* 4. Urinary bladder. \n
* 5. Urachus. \n
* cl. Cloaca. \n
* cp. Elevation which becomes clitoris or penis. \n
* i. Lower part of the intestine. \n
* ls. Fold of integument from which the labia majora or scrotum are formed. \n
* m, m. Right and left Müllerian ducts uniting together and running with the Wolffian ducts in gc, the common genital cord. \n
* ot. The gonadal ridge from which either the ovary or testis is formed. \n
* ug. Sinus urogenitalis. \n
* W. Left Wolffian body. \n
* w, w. Right and left Wolffian ducts. | upload.wikimedia.org/wikipedia/commons/f/f1/Gray1110-1.png]\n\n## Atrophy in males\nIn the male, the Müllerian ducts atrophy, but traces of their anterior ends are represented by the [appendices testis](https://bliptext.com/articles/appendices-testis) ([hydatids of Morgagni](https://bliptext.com/articles/hydatids-of-morgagni) of the male), while their terminal fused portions form the [utriculus](https://bliptext.com/articles/prostatic-utricle) in the floor of the [prostatic urethra](https://bliptext.com/articles/prostatic-urethra).\n\n## Development in females\nIn the female, the Müllerian ducts persist and undergo further development.\nThe portions which lie in the genital cord fuse to form the [uterus](https://bliptext.com/articles/uterus) and [vagina](https://bliptext.com/articles/vagina).\nThis fusion of the Müllerian ducts begins in the third month, and the septum formed by their fused medial walls disappears from below upward.\nThe parts outside this cord remain separate, and each forms the corresponding [fallopian tube](https://bliptext.com/articles/fallopian-tube).\nThe [ostium of the fallopian tube](https://bliptext.com/articles/ostium-of-the-fallopian-tube) remains from the anterior extremity of the original tubular invagination from the abdominal cavity.\nAround the fifth month, a ring-like constriction marks the position of the [cervix](https://bliptext.com/articles/cervix) of the uterus, and after the sixth month, the walls of the uterus begin to thicken.\nFor some time, the vagina is represented by a solid rod of epithelial cells.\nA ring-like outgrowth of this epithelium occurs at the lower end of the uterus and marks the future [vaginal fornix](https://bliptext.com/articles/vaginal-fornix).\nAt about the fifth or sixth month, the [lumen](https://bliptext.com/articles/lumen-anatomy) of the vagina is produced by the breaking down of the central cells of the epithelium.\nThe [hymen](https://bliptext.com/articles/hymen) represents the remains of the Müllerian eminence.\n\n# Metanephros and definitive kidney\nThe metanephros is the definite, permanent, but yet immature kidney.\nIt arises from two directions.\nOn one hand, the precursor of the ureter buds from the Wolffian duct, while on the other hand, the precursor of the renal tubules develop from the metanephrogenic blastema.\nThe ureteric bud subsequently grows into the latter mass, forming the parts of the nephron.\nOther changes include e.g. the translocation of the ureteric opening directly into the cloaca.\n\n## Ureteric bud\nThe rudiments of the permanent [kidneys](https://bliptext.com/articles/kidney) make their appearance about the end of the first or the beginning of the second month.\nEach kidney originates as a [ureteric bud](https://bliptext.com/articles/ureteric-bud) from the caudal end of the Wolffian duct, which, in turn, originates from [intermediate mesoderm](https://bliptext.com/articles/intermediate-mesoderm).\nThe ureteric bud starts close to where the Wolffian duct opens into the cloaca, and grows dorsalward and [rostralward](https://bliptext.com/articles/rostralward) along the posterior abdominal wall, where its blind extremity expands and subsequently divides into several buds, which form the rudiments of the [renal pelvis](https://bliptext.com/articles/renal-pelvis) and [renal calyces](https://bliptext.com/articles/renal-calyces); by continued growth and subdivision it gives rise to the [collecting duct system](https://bliptext.com/articles/collecting-duct-system) of the kidney.\nThe other, more superficial, portion of the diverticulum, on the other hand, becomes the ureter.\n\n## Metanephrogenic blastema\nThe [renal corpuscles](https://bliptext.com/articles/renal-corpuscle) and [renal tubules](https://bliptext.com/articles/renal-tubule), in contrast, are developed from the metanephrogenic blastema instead of from the ureteric bud.\nThe metanephrogenic blastema is moulded over the growing end of the latter, and becomes a part of the metanephros in this way.\nThe renal tubules of the metanephros, unlike those of the pronephros and mesonephros, do not open into the Wolffian duct.\nInstead, the tubules rapidly elongate to form the parts of the [nephron](https://bliptext.com/articles/nephron): the [proximal tubules](https://bliptext.com/articles/proximal-tubule), the [loops of Henle](https://bliptext.com/articles/loops-of-henle) and the [distal convoluted tubules](https://bliptext.com/articles/distal-convoluted-tubule).\nThese last join and establish communications with the collecting duct system derived from the ultimate ramifications of the ureteric bud.\nIn the other end, the renal tubules give rise to [Bowman's capsules](https://bliptext.com/articles/bowman-s-capsule) and [glomeruli](https://bliptext.com/articles/glomerulus-kidney).\n\n## Other changes\nThe mesoderm around the tubules becomes condensed to form the connective tissue of the kidney.\nThe ureter opens at first into the hind-end of the Wolffian duct; after the sixth week it separates from the Wolffian duct, and opens independently into the part of the cloaca which ultimately becomes the [urinary bladder](https://bliptext.com/articles/urinary-bladder).\nThe renal tubules become arranged into [renal pyramids](https://bliptext.com/articles/renal-pyramids), and the lobulated condition of the kidneys exists for some time after birth, while traces of it may be found even in the adult.\nThe kidney of the ox and many other animals, on the other hand, remains lobulated throughout life.\n\n# Urinary bladder\nThe [urinary bladder](https://bliptext.com/articles/urinary-bladder) is formed partly from the endodermal [cloaca](https://bliptext.com/articles/cloaca-embryology) and partly from the ends of the Wolffian ducts.\nIn other words, the [allantois](https://bliptext.com/articles/allantois) takes no share in its formation.\nAfter the separation of the rectum from the dorsal part of the cloaca, the ventral part becomes the primary [urogenital sinus](https://bliptext.com/articles/urogenital-sinus).\nThe urogenital sinus, in turn, divides into the superficial definitive urogenital sinus and the deeper anterior vesico-urethral portion.\n# [Tail end of human embryo thirty-two to thirty-three days old. The entodermal cloaca is visible at center left, labeled in green | upload.wikimedia.org/wikipedia/commons/a/a6/Gray1116.png]\n\n## Definitive urogenital sinus\nThe definitive urogenital sinus consists of a caudal phallic portion and an intermediate narrow channel, the pelvic portion.\n\n## Vesico-urethral portion\nThe vesico-urethral portion is the deepest, continuous with the allantois.\nIt absorbs the ends of the Wolffian ducts and the associated ends of the renal diverticula, and these give rise to the [trigone of urinary bladder](https://bliptext.com/articles/trigone-of-urinary-bladder) and part of the [prostatic urethra](https://bliptext.com/articles/prostatic-urethra).\nThe remainder of the vesico-urethral portion forms the body of the bladder and part of the prostatic urethra; its apex is prolonged to the umbilicus as a narrow canal, the [urachus](https://bliptext.com/articles/urachus), which later is obliterated and becomes the [median umbilical ligament](https://bliptext.com/articles/median-umbilical-ligament) of the adult.\n\n# Sex organs\nUntil about the ninth week of gestational age, the [sex organs](https://bliptext.com/articles/sex-organs) of males and females look the same, and follow a common development.\nThis includes the development of a genital tubercle and a membrane dorsally to it, covering the developing [urogenital opening](https://bliptext.com/articles/urogenital-opening), and the development of labioscrotal folds.\nEven after differentiation can be seen between the sexes, some stages are common, e.g. the disappearing of the membrane.\nOn the other hand, sex-dependent development include further protrusion of the genital tubercle in the male to form the penis.\nFurthermore, the labioscrotal folds evolve into the scrotum in males, while they evolve into labia in females.\n# [Development of external genitalia. A: common development. C, E: male development. B, D, F: female development | upload.wikimedia.org/wikipedia/commons/0/07/Development///of///external///sexual///organs///in///the///male///and///female///Gray1119.png]\n\n# Diagram of internal differentiation\nA.—Diagram of the primitive urogenital organs in the embryo previous to sexual distinction.\nB.—Diagram of the female type of sexual organs.\nC.—Diagram of the male type of sexual organs.\n# [Diagrams to show the development of male and female generative organs from a common type. | upload.wikimedia.org/wikipedia/commons/e/eb/Gray1110.png]\n\n# In-line\n\n## General","current_revision":null,"created_by":"kACnuQmH5k9Nr5VNVEpVeg7XpvUmMctD","created_at":"2025-01-25T21:28:21.371Z","updated_at":"2025-01-25T21:28:21.371Z","search_vector":"'develop':1 'system':5 'urinari':4","search_content":" \n \n\n# \nThe **development of the [urinary system](https://bliptext.com/articles/urinary-system)** begins during [prenatal development](https://bliptext.com/articles/prenatal-development), and relates to the development of the [urogenital system](https://bliptext.com/articles/urogenital-system) – both the organs of the [urinary system](https://bliptext.com/articles/urinary-system) and the [sex organs](https://bliptext.com/articles/sex-organ) of the [reproductive system](https://bliptext.com/articles/reproductive-system).\nThe development continues as a part of [sexual differentiation](https://bliptext.com/articles/sexual-differentiation).\nThe urinary and reproductive organs are developed from the [intermediate mesoderm](https://bliptext.com/articles/intermediate-mesoderm).\nThe permanent organs of the adult are preceded by a set of structures which are purely embryonic, and which with the exception of the ducts disappear almost entirely before birth.\nThese embryonic structures are on either side; the [pronephros](https://bliptext.com/articles/pronephros), the [mesonephros](https://bliptext.com/articles/mesonephros) and the [metanephros](https://bliptext.com/articles/metanephros) of the [kidney](https://bliptext.com/articles/kidney), and the [Wolffian](https://bliptext.com/articles/wolffian-duct) and [Müllerian ducts](https://bliptext.com/articles/m-llerian-duct) of the [sex organ](https://bliptext.com/articles/sex-organ).\nThe pronephros disappears very early; the structural elements of the mesonephros mostly degenerate, but the [gonad](https://bliptext.com/articles/gonad) is developed in their place, with which the Wolffian duct remains as the duct in males, and the Müllerian as that of the female.\nSome of the tubules of the mesonephros form part of the permanent kidney.\n\n# Pronephros and Wolffian duct\n\n## Wolffian duct\nIn the outer part of the [intermediate mesoderm](https://bliptext.com/articles/intermediate-mesoderm), immediately under the ectoderm, in the region from the fifth [cervical segment](https://bliptext.com/articles/cervical-segment) to the third [thoracic segment](https://bliptext.com/articles/thoracic-segment), a series of short [evaginations](https://bliptext.com/articles/evagination) from each segment grows [dorsally](https://bliptext.com/articles/dorsum-anatomy) and extends [caudally](https://bliptext.com/articles/caudally), fusing successively from before backward to form the [pronephric duct](https://bliptext.com/articles/pronephric-duct).\nThis continues to grow caudally until it opens into the ventral part of the [cloaca](https://bliptext.com/articles/cloaca-embryology); beyond the [pronephros](https://bliptext.com/articles/pronephros) it is termed the [Wolffian duct](https://bliptext.com/articles/wolffian-duct).\nThus, the Wolffian duct is what remains of the pronephric duct after the atrophy of the pronephros.\n\n## Pronephros\nThe original evaginations form a series of transverse tubules each of which communicates by means of a funnel-shaped ciliated opening with the [abdominal cavity](https://bliptext.com/articles/abdominal-cavity), and in the course of each duct a glomerulus also is developed.\nA secondary glomerulus is formed ventral to each of these, and the complete group constitutes the pronephros.\nIn humans, the pronephros is just rudimentary, and undergoes rapid atrophy and disappears.\n\n# Wolffian duct\n\n## Mesonephros\nOn the medial side of the Wolffian duct, from the sixth cervical to the third lumbar segments, a series of tubules, the [Wolffian tubules](https://bliptext.com/articles/mesonephros), develops.\nThey increase in number by outgrowths from the original tubules.\nThey change from solid masses of cells to instead become hollowed in the center.\nOne end grows toward and finally opens into the Wolffian duct, the other dilates and is invaginated by a tuft of capillary bloodvessels to form a glomerulus.\nThe tubules collectively constitute the [mesonephros](https://bliptext.com/articles/mesonephros).\nThe mesonephros persists and form the permanent kidneys in fish and amphibians, but in reptiles, birds, and mammals, it atrophies and for the most part disappears rapidly as the permanent kidney ([metanephros](https://bliptext.com/articles/metanephros)) develops beginning during the sixth or seventh week, so that by the beginning of the fifth month only the ducts and a few of the tubules of the mesonephros remain.\n\n## Development in male\nIn the male, the [Wolffian duct](https://bliptext.com/articles/wolffian-duct) persists, and forms for example the [epididymis](https://bliptext.com/articles/epididymis), the [ductus deferens](https://bliptext.com/articles/ductus-deferens), the [ejaculatory duct](https://bliptext.com/articles/ejaculatory-duct), [seminal vesicle](https://bliptext.com/articles/seminal-vesicle) and efferent ducts.\nIn the female, on the other hand, the Wolffian bodies and ducts atrophy, leaving behind only remnants in the adult, involving e.g. the [development of the suspensory ligament of the ovary](https://bliptext.com/articles/development-of-the-suspensory-ligament-of-the-ovary).\n\n# Müllerian duct\nShortly after the formation of the Wolffian ducts, a second pair of ducts is developed; these are the [Müllerian ducts](https://bliptext.com/articles/m-llerian-ducts).\nEach arises on the lateral aspect of the corresponding Wolffian duct as a tubular invagination of the cells lining the abdominal cavity.\nThe orifice of the invagination remains open, and undergoes enlargement and modification to form the abdominal [ostium of the fallopian tube](https://bliptext.com/articles/ostium-of-the-fallopian-tube).\nThe ducts pass backward lateral to the Wolffian ducts, but toward the posterior end of the embryo they cross to the medial side of these ducts, and thus come to lie side by side between and behind the latter—the four ducts forming what is termed the common genital cord, to distinguish it from the genital cords of the germinal epithelium seen later in this article.\nThe Müllerian ducts end in an epithelial elevation, the [Müllerian eminence](https://bliptext.com/articles/m-llerian-eminence), on the ventral part of the cloaca between the orifices of the Wolffian ducts.\nAt a later stage, the eminence opens in the middle, connecting the Müllerian ducts with the cloaca.\n# [A.—Diagram of the primitive urogenital organs in the embryo previous to sexual distinction. The common genital cord is labeled with gc. * 3. Ureter. \n * 4. Urinary bladder. \n * 5. Urachus. \n * cl. Cloaca. \n * cp. Elevation which becomes clitoris or penis. \n * i. Lower part of the intestine. \n * ls. Fold of integument from which the labia majora or scrotum are formed. \n * m, m. Right and left Müllerian ducts uniting together and running with the Wolffian ducts in gc, the common genital cord. \n * ot. The gonadal ridge from which either the ovary or testis is formed. \n * ug. Sinus urogenitalis. \n * W. Left Wolffian body. \n * w, w. Right and left Wolffian ducts. | upload.wikimedia.org/wikipedia/commons/f/f1/Gray1110-1.png]\n\n## Atrophy in males\nIn the male, the Müllerian ducts atrophy, but traces of their anterior ends are represented by the [appendices testis](https://bliptext.com/articles/appendices-testis) ([hydatids of Morgagni](https://bliptext.com/articles/hydatids-of-morgagni) of the male), while their terminal fused portions form the [utriculus](https://bliptext.com/articles/prostatic-utricle) in the floor of the [prostatic urethra](https://bliptext.com/articles/prostatic-urethra).\n\n## Development in females\nIn the female, the Müllerian ducts persist and undergo further development.\nThe portions which lie in the genital cord fuse to form the [uterus](https://bliptext.com/articles/uterus) and [vagina](https://bliptext.com/articles/vagina).\nThis fusion of the Müllerian ducts begins in the third month, and the septum formed by their fused medial walls disappears from below upward.\nThe parts outside this cord remain separate, and each forms the corresponding [fallopian tube](https://bliptext.com/articles/fallopian-tube).\nThe [ostium of the fallopian tube](https://bliptext.com/articles/ostium-of-the-fallopian-tube) remains from the anterior extremity of the original tubular invagination from the abdominal cavity.\nAround the fifth month, a ring-like constriction marks the position of the [cervix](https://bliptext.com/articles/cervix) of the uterus, and after the sixth month, the walls of the uterus begin to thicken.\nFor some time, the vagina is represented by a solid rod of epithelial cells.\nA ring-like outgrowth of this epithelium occurs at the lower end of the uterus and marks the future [vaginal fornix](https://bliptext.com/articles/vaginal-fornix).\nAt about the fifth or sixth month, the [lumen](https://bliptext.com/articles/lumen-anatomy) of the vagina is produced by the breaking down of the central cells of the epithelium.\nThe [hymen](https://bliptext.com/articles/hymen) represents the remains of the Müllerian eminence.\n\n# Metanephros and definitive kidney\nThe metanephros is the definite, permanent, but yet immature kidney.\nIt arises from two directions.\nOn one hand, the precursor of the ureter buds from the Wolffian duct, while on the other hand, the precursor of the renal tubules develop from the metanephrogenic blastema.\nThe ureteric bud subsequently grows into the latter mass, forming the parts of the nephron.\nOther changes include e.g. the translocation of the ureteric opening directly into the cloaca.\n\n## Ureteric bud\nThe rudiments of the permanent [kidneys](https://bliptext.com/articles/kidney) make their appearance about the end of the first or the beginning of the second month.\nEach kidney originates as a [ureteric bud](https://bliptext.com/articles/ureteric-bud) from the caudal end of the Wolffian duct, which, in turn, originates from [intermediate mesoderm](https://bliptext.com/articles/intermediate-mesoderm).\nThe ureteric bud starts close to where the Wolffian duct opens into the cloaca, and grows dorsalward and [rostralward](https://bliptext.com/articles/rostralward) along the posterior abdominal wall, where its blind extremity expands and subsequently divides into several buds, which form the rudiments of the [renal pelvis](https://bliptext.com/articles/renal-pelvis) and [renal calyces](https://bliptext.com/articles/renal-calyces); by continued growth and subdivision it gives rise to the [collecting duct system](https://bliptext.com/articles/collecting-duct-system) of the kidney.\nThe other, more superficial, portion of the diverticulum, on the other hand, becomes the ureter.\n\n## Metanephrogenic blastema\nThe [renal corpuscles](https://bliptext.com/articles/renal-corpuscle) and [renal tubules](https://bliptext.com/articles/renal-tubule), in contrast, are developed from the metanephrogenic blastema instead of from the ureteric bud.\nThe metanephrogenic blastema is moulded over the growing end of the latter, and becomes a part of the metanephros in this way.\nThe renal tubules of the metanephros, unlike those of the pronephros and mesonephros, do not open into the Wolffian duct.\nInstead, the tubules rapidly elongate to form the parts of the [nephron](https://bliptext.com/articles/nephron): the [proximal tubules](https://bliptext.com/articles/proximal-tubule), the [loops of Henle](https://bliptext.com/articles/loops-of-henle) and the [distal convoluted tubules](https://bliptext.com/articles/distal-convoluted-tubule).\nThese last join and establish communications with the collecting duct system derived from the ultimate ramifications of the ureteric bud.\nIn the other end, the renal tubules give rise to [Bowman's capsules](https://bliptext.com/articles/bowman-s-capsule) and [glomeruli](https://bliptext.com/articles/glomerulus-kidney).\n\n## Other changes\nThe mesoderm around the tubules becomes condensed to form the connective tissue of the kidney.\nThe ureter opens at first into the hind-end of the Wolffian duct; after the sixth week it separates from the Wolffian duct, and opens independently into the part of the cloaca which ultimately becomes the [urinary bladder](https://bliptext.com/articles/urinary-bladder).\nThe renal tubules become arranged into [renal pyramids](https://bliptext.com/articles/renal-pyramids), and the lobulated condition of the kidneys exists for some time after birth, while traces of it may be found even in the adult.\nThe kidney of the ox and many other animals, on the other hand, remains lobulated throughout life.\n\n# Urinary bladder\nThe [urinary bladder](https://bliptext.com/articles/urinary-bladder) is formed partly from the endodermal [cloaca](https://bliptext.com/articles/cloaca-embryology) and partly from the ends of the Wolffian ducts.\nIn other words, the [allantois](https://bliptext.com/articles/allantois) takes no share in its formation.\nAfter the separation of the rectum from the dorsal part of the cloaca, the ventral part becomes the primary [urogenital sinus](https://bliptext.com/articles/urogenital-sinus).\nThe urogenital sinus, in turn, divides into the superficial definitive urogenital sinus and the deeper anterior vesico-urethral portion.\n# [Tail end of human embryo thirty-two to thirty-three days old. The entodermal cloaca is visible at center left, labeled in green | upload.wikimedia.org/wikipedia/commons/a/a6/Gray1116.png]\n\n## Definitive urogenital sinus\nThe definitive urogenital sinus consists of a caudal phallic portion and an intermediate narrow channel, the pelvic portion.\n\n## Vesico-urethral portion\nThe vesico-urethral portion is the deepest, continuous with the allantois.\nIt absorbs the ends of the Wolffian ducts and the associated ends of the renal diverticula, and these give rise to the [trigone of urinary bladder](https://bliptext.com/articles/trigone-of-urinary-bladder) and part of the [prostatic urethra](https://bliptext.com/articles/prostatic-urethra).\nThe remainder of the vesico-urethral portion forms the body of the bladder and part of the prostatic urethra; its apex is prolonged to the umbilicus as a narrow canal, the [urachus](https://bliptext.com/articles/urachus), which later is obliterated and becomes the [median umbilical ligament](https://bliptext.com/articles/median-umbilical-ligament) of the adult.\n\n# Sex organs\nUntil about the ninth week of gestational age, the [sex organs](https://bliptext.com/articles/sex-organs) of males and females look the same, and follow a common development.\nThis includes the development of a genital tubercle and a membrane dorsally to it, covering the developing [urogenital opening](https://bliptext.com/articles/urogenital-opening), and the development of labioscrotal folds.\nEven after differentiation can be seen between the sexes, some stages are common, e.g. the disappearing of the membrane.\nOn the other hand, sex-dependent development include further protrusion of the genital tubercle in the male to form the penis.\nFurthermore, the labioscrotal folds evolve into the scrotum in males, while they evolve into labia in females.\n# [Development of external genitalia. A: common development. C, E: male development. B, D, F: female development | upload.wikimedia.org/wikipedia/commons/0/07/Development///of///external///sexual///organs///in///the///male///and///female///Gray1119.png]\n\n# Diagram of internal differentiation\nA.—Diagram of the primitive urogenital organs in the embryo previous to sexual distinction.\nB.—Diagram of the female type of sexual organs.\nC.—Diagram of the male type of sexual organs.\n# [Diagrams to show the development of male and female generative organs from a common type. | upload.wikimedia.org/wikipedia/commons/e/eb/Gray1110.png]\n\n# In-line\n\n## General","revisionCount":0},"hasMore":false,"nextCursor":null}

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