The development of the reproductive system is a part of the prenatal development, and concerns the sex organs. It is a part of the stages of sexual differentiation. Because its location to a large extent overlaps the urinary system, the development of them can also be described together as the development of the urinary and reproductive organs. Prenatal development is the process in which an embryo or fetus (or foetus) gestates during pregnancy, from the times of fertilization until birth. ... A sex organ, or primary sexual characteristic, narrowly defined, is any of those parts of the body (which are not always bodily organs according to the strict definition) which are involved in sexual reproduction and constitute the reproductive system in an complex organism; namely: Male: penis (notably the glans penis... Sexual differentiation is the process of development of the differences between males and females from an undifferentiated zygote (fertilized egg). ... In prenatal development, the urinary and reproductive organs are developed from the intermediate mesoderm. ...

The reproductive organs are developed from the intermediate mesoderm. The 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 the end of fetal life. These embryonic structures are the Wolffian and Müllerian ducts. The Wolffian duct remains as the duct in males, and the Müllerian as that of the female. Intermediate mesoderm is a type of mesoderm that is located between the paraxial mesoderm and the lateral plate. ... The Wolffian duct (also known as archinephric duct, Leydigs duct, mesonephric duct, or nephric duct) is a paired organ found in mammals including humans during embryogenesis. ... The Müllerian ducts are paired ducts of the embryo which empty into the cloaca, and which in the female develop into the upper vagina, cervix, uterus and oviducts; in the male they disappear except for the vestigial vagina masculina and the appendix testis. ...

Wolffian Duct

The Wolffian duct originates from a part of the pronephric duct. In the outer part of the intermediate cell-mass, immediately under the ectoderm, in the region from the fifth cervical to the third thoracic segments, a series of short evaginations from each segment grows dorsalward and extends caudalward, fusing successively from before backward to form the pronephric duct. ...

Origin

In the outer part of the intermediate mesoderm, immediately under the ectoderm, in the region from the fifth cervical segment to the third thoracic segment, a series of short evaginations from each segment grows dorsally and extends caudally, fusing successively from before backward to form the pronephric duct. This continues to grow caudalward until it opens into the ventral part of the cloaca; beyond the pronephros it is termed the Wolffian duct. Thus, the Wolffian duct is what remains of the pronephric duct after the atrophy of the pronephros. Intermediate mesoderm is a type of mesoderm that is located between the paraxial mesoderm and the lateral plate. ... In anatomy, the dorsum is the upper side of animals that typically run, fly or swim in a horizontal position, and the back side of animals (like humans) that walk upright. ... It has been suggested that Human Anatomical Terms be merged into this article or section. ... In the outer part of the intermediate cell-mass, immediately under the ectoderm, in the region from the fifth cervical to the third thoracic segments, a series of short evaginations from each segment grows dorsalward and extends caudalward, fusing successively from before backward to form the pronephric duct. ... In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, urinary, and genital tracts of certain animal species. ... The Wolffian duct (also known as archinephric duct, Leydigs duct, mesonephric duct, or nephric duct) is a paired organ found in mammals including humans during embryogenesis. ...

Development in male

In the male the Wolffian duct persists, and forms the tube of the epididymis, the ductus deferens and the ejaculatory duct, while the seminal vesicle arises during the third month as a lateral diverticulum from its hinder end. A large part of the head end of the mesonephros atrophies and disappears; of the remainder the anterior tubules form the efferent ducts of the testis; while the posterior tubules are represented by the ductuli aberrantes, and by the paradidymis, which is sometimes found in front of the spermatic cord above the head of the epididymis. The Wolffian duct (also known as archinephric duct, Leydigs duct, mesonephric duct, or nephric duct) is a paired organ found in mammals including humans during embryogenesis. ... Male Anatomy The epididymis is part of the human male reproductive system and is present in all male mammals. ... Male Anatomy The vas deferens, also called ductus deferens, (Latin: carrying-away vessel) is part of the human male anatomy. ... The Ejaculatory ducts are part of the human male anatomy, which cause the reflex action of ejaculation. ... The seminal vesicles are a pair of simple tubular glands posterinferior to the urinary bladder of males. ... Human male anatomy The testicles, known medically as testes (singular testis), are the male generative glands in animals. ... Ductuli Aberrantes. ... The term paradidymis (organ of Giraldés) is applied to a small collection of convoluted tubules, situated in front of the lower part of the cord above the head of the epididymis. ... Male Anatomy The spermatic cord is the name given to the cord-like structure formed by the vas deferens and surrounding tissue (veins, arteries, nerves, and lymphatic vessels) that run from the abdomen down to each testicle. ...

Atrophy in female

In the female the Wolffian bodies and ducts atrophy. The nonfunctional remains of the Wolffian tubules are represented by the epoophoron, and the paroöphoron, two small collections of rudimentary blind tubules which are situated in the mesosalpinx. The epoophoron , also called organ of Rosenmüller, is a remnant of the Wolffian duct that can be found next to the ovary and fallopian tube. ... The paroöphoron consists of a few scattered rudimentary tubules, best seen in the child, situated in the broad ligament between the epoöphoron and the uterus. ... The portion of the broad ligament which stretches from the uterine tube to the level of the ovary is known by the name of the mesosalpinx. ...

Remnants

Section of the fold in the mesonephros of a chick embryo of the fourth day.

The lower part of the Wolffian duct disappears, while the upper part persists as the longitudinal duct of the epoöphoron, called Gartner's duct. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... The epoophoron , also called organ of Rosenmüller or the parovarium is a remnant of the Wolffian duct that can be found next to the ovary and fallopian tube. ... Gartners duct is a potential embryological remnant in human female development of the mesonephric ducts. ...

There are also developments of other tissues from the Wolffian duct that persist, e.g. the development of the suspensory ligament of the ovary.

The Müllerian Duct

A.—Diagram of the primitive urogenital organs in the embryo previous to sexual distinction. The common genital cord is labeled with gc.
* 3. Ureter.
* 4. Urinary bladder.
* 5. Urachus.
* cl. Cloaca.
* cp. Elevation which becomes clitoris or penis.
* i. Lower part of the intestine.
* ls. Fold of integument from which the labia majora or scrotum are formed.
* m, m. Right and left Müllerian ducts uniting together and running with the Wolffian ducts in gc, the common genital cord.
* ot. The gonadal ridge from which either the ovary or testis is formed.
* ug. Sinus urogenitalis.
* W. Left Wolffian body.
* w, w. Right and left Wolffian ducts.

Shortly after the formation of the Wolffian ducts a second pair of ducts is developed; these are the Müllerian ducts. Each arises on the lateral aspect of the corresponding Wolffian duct as a tubular invagination of the cells lining the abdominal cavity. The orifice of the invagination remains open, and undergoes enlargement and modification to form the abdominal ostium of the fallopian tube. The 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. The Müllerian ducts end in an epithelial elevation, the Müllerian eminence, on the ventral part of the cloaca between the orifices of the Wolffian ducts. At a later stage the eminence opens in the middle, connecting the Müllerian ducts with the cloaca. The Müllerian ducts are paired ducts of the embryo which empty into the cloaca, and which in the female develop into the upper vagina, cervix, uterus and oviducts; in the male they disappear except for the vestigial vagina masculina and the appendix testis. ... The Müllerian ducts end in an epithelial elevation, the Müllerian eminence, on the ventral part of the cloaca between the orifices of the Wolffian ducts; at a later date they open into the cloaca in this situation. ...

Atrophy in males

In the male the Müllerian ducts atrophy, but traces of their anterior ends are represented by the appendices testis (hydatids of Morgagni of the male), while their terminal fused portions form the utriculus in the floor of the prostatic urethra. The appendix testis (or Hydatid of Morgagni) is a vestigial remnant of the Müllerian duct present on the upper testis attached to the tunica vaginalis, on the the upper pole of the testis. ... The Hydatid of Morgagni can refer to one of two closely related structures: Appendix testis (in the male) Vesicular appendages of epoophoron (in the female) Category: ... The prostatic urethra, the widest and most dilatable part of the canal, is about 3 cm. ...

Development in females

In the female the Müllerian ducts persist and undergo further development. The portions which lie in the genital cord fuse to form the uterus and vagina. This fusion of the Müllerian ducts begins in the third month, and the septum formed by their fused medial walls disappears from below upward. This article is about female reproductive anatomy. ... The vagina, (from Latin, literally sheath or scabbard ) is the tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. ...

The parts outside this cord remain separate, and each forms the corresponding Fallopian tube. The ostium of the fallopian tube remains from the anterior extremity of the original tubular invagination from the abdominal cavity. The Fallopian tubes, also known as oviducts, uterine tubes, and salpinges (singular salpinx) are two very fine tubes leading from the ovaries of female mammals into the uterus. ...

About the fifth month a ring-like constriction marks the position of the cervix of the uterus, and after the sixth month the walls of the uterus begin to thicken. For a time the vagina is represented by a solid rod of epithelial cells. A ring-like outgrowth of this epithelium occurs at the lower end of the uterus and marks the future vaginal fornix. At about the fifth or sixth month the lumen of the vagina is produced by the breaking down of the central cells of the epithelium. The hymen represents the remains of the Müllerian eminence ^[1]. The cervix (from Latin neck) is the lower, narrow portion of the uterus where it joins with the top end of the vagina. ... The fornices of the vagina are the deepest portions of the vagina, extending into the recesses created by the extension of the cervix into the vaginal space. ... artery anatomy, showing lumen The lumen (pl. ... For the Greek god of marriage, see Hymenaios. ...

Gonads

Main article: Development of the gonads

The gonads are the precursors of the testes in males and ovaries in females. They initially develop from the mesothelial layer of the peritoneum. Human male anatomy The testicles, known medically as testes (singular testis), are the male generative glands in animals. ... Human female internal reproductive anatomy Ovaries are a part of a female organism that produces eggs. ...

Ovaries

The ovary is differentiated into a central part, the medulla of ovary, covered by a surface layer, the germinal epithelium. The immature ova originate from cells from the dorsal endoderm of the yolk sac. Once they have reached the gonadal ridge they are called oogonia. Development proceeds and the oogonia become fully surrounded by a layer of connective tissue cells (pre-granulosa cells) In this way, the rudiments of the ovarian follicles are formed. The embryological origin of granulosa cells, on the other hand, remains controversial. Just as in the male, there is a gubernaculum in the female, which pulls it downward, albeit not as much as in males. The gubernaculum later becomes the proper ovarian ligament and the round ligament of the uterus. The endoderm, sometimes refered to as entoderm, is one of the three germ layers of the developing embryo, the other two being the ectoderm and the mesoderm. ... The yolk sac is the first element seen in the gestational sac during pregnancy, usually at 5 weeks gestation. ... A cell that arises from a primordial germ cell and differentiates into an oocyte in the ovary. ... Cells in culture, stained for keratin (red) and DNA (green) The cell is the structural and functional unit of all living organisms, and are sometimes called the building blocks of life. ... The gubernaculum is a fold of peritoneum which attaches to the caudal end of the testes. ... The ovarian ligament (also called the utero-ovarian ligament or proper ovarian ligament) is a fibrous ligament that connects the ovary to the lateral surface of the uterus. ...

Testes

The periphery of the testes are converted into the tunica albuginea. Cords of the central mass run together and form a network which becomes the rete testis, and another network, which develops the seminiferous tubules. Via the rete testis, the seminiferous tubules become connected with outgrowths from the mesonephros, which form the efferent ducts of the testis. The tunica albuginea is the tough fibrous covering of the testicles. ... Rete testis is an anastomosing network of delicate tubules located in the hilum of the testicle (mediastinum testis) that carries sperm from the seminiferous tubules to the vasa efferentia. ... Human male anatomy The testicles, known medically as testes (singular testis), are the male generative glands in animals. ...

In short, the descent of the testes consists of the opening of a connection from the testis to its final location at the anterior abdominal wall, followed by the development of the gubernaculum, which subsequently pulls and translocates the testis down into the developing scrotum. Ultimately, the passageway closes behind the testis. A failure in this process causes indirect inguinal hernia. An indirect inguinal hernia a inguinal hernia which results from the failure of embryonic closure of the internal inguinal ring after the testicle has passed through it. ...

Division of cloaca

Tail end of human embryo thirty-two to thirty-three days old. The entodermal cloaca is visible at center left, labeled in green

After the separation of the rectum from the dorsal part of the cloaca, the ventral part becomes the primary urogenital sinus^[2]. The urogenital sinus, in turn, divides into the superficial definitive urogenital sinus and the deeper anterior vesico-urethral portion. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ...

Definitive urogenital sinus

The definitive urogenital sinus sonsists of a caudal phallic portion and an intermediate narrow channel, the pelvic portion.

Vesico-urethral portion

The vesico-urethral portion is the deepest portion, continuous with the allantois. It 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 and part of the prostatic urethra. The 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, which later is obliterated and becomes the median umbilical ligament of the adult. The trigone is a smooth triangular region of the internal urinary bladder formed by the two ureteral orifices and the internal urethral orifice. ... The prostatic urethra, the widest and most dilatable part of the canal, is about 3 cm. ... The vesico-urethral portion of the urogenital sinus absorbs the ends of the Wolffian ducts and the associated ends of the renal diverticula, and these give rise to the trigone of the bladder and part of the prostatic urethra. ... The median umbilical ligament is a structure in human anatomy. ...

The Prostate

The prostate originally consists of two separate portions, each of which arises as a series of diverticular buds from the epithelial lining of the urogenital sinus and vesico-urethral part of the cloaca, between the third and fourth months. These buds become tubular, and form the glandular substance of the two lobes, which ultimately meet and fuse behind the urethra and also extend on to its ventral aspect. The median lobe of the prostate is formed as an extension of the lateral lobes between the common ejaculatory ducts and the bladder. The prostate is a compound tubuloalveolar exocrine gland of the male mammalian reproductive system. ...

Skene's glands in the female urethra are regarded as the homologues of the prostatic glands. In human anatomy, the Skenes glands (also known as the lesser vestibular or paraurethral glands) are glands located on the upper wall of the vagina, around the lower end of the urethra. ...

The bulbourethral glands in the male, and Bartholin's gland in the female, also arise as diverticula from the epithelial lining of the urogenital sinus. Male Anatomy In the anatomy of the male human body, the bulbourethral glands (or Cowpers glands) are two small, rounded, and somewhat lobulated bodies, of a yellow color, about the size of peas, placed behind and lateral to the membranous portion of the urethra, between the two layers of... The Bartholins glands (also called Bartholin glands or greater vestibular glands) are two glands located slightly below and to the left and right of the opening of the vagina in women. ...

External genitalia

The mesoderm extends to the midventral line

Until about the ninth week of gestational age^[3] the external genitalia of males and females look the same, and follow a common development. This includes the development of a genital tubercle and a membrane dorsally to it, covering the developing urogenital opening, and the development of labioscrotal folds. The urogenital opening is where waste products of the body and reproductive fluids are expelled to the environment outside of the body cavity. ...

Even after differentiation can be seen between the sexes, some stages are common, e.g. the disappearing of the membrane. On the other hand, sex-dependent development include further protrusion of the genital tubercle in the male to form the penis. Furthermore, the labioscrotal folds evolve into the scrotum in males, while they evolve into labia in females.

Common development

Before differentiation

Urogenital membrane

There is initially a cloacal membrane, composed of ectoderm and endoderm, reaching from the umbilical cord to the tail, separating the cloaca from the exterior. After the separation of the rectum from the dorsal part of the cloaca, the ventral part of the cloacal membrane becomes the urogenital membrane. The region at the hind end of the embryo where the ectoderm and endoderm come into apposition and form is called the cloacal membrane. ... In placental mammals, the umbilical cord is a tube that connects a developing embryo or fetus to the placenta. ...

Genital tubercle

Mesoderm extends to the midventral line for some distance behind the umbilical cord, and forms the lower part of the abdominal wall; it ends below in a prominent swelling, the cloacal tubercle, which after the separation of the rectum becomes the genital tubercle. Dorsally to this tubercle the sides aren't really fused. Rather, the urogenital part of the cloacal membrane separates the ingrowing sheets of mesoderm. A genital tubercle is a body of tissue which forms in the ventral, caudal region of mammalian embryos of both sexes, and eventually develops into a phallus. ...

Phallus

The genital tubercle develops into the phallus, the first rudiment of the penis or clitoris. ‹ The template below (Expand) is being considered for deletion. ...

The terminal part of the phallus, representing the future glans becomes solid. The remainder of the phallus, which remains hollow, is converted into a longitudinal groove by the absorption of the urogenital membrane.

The term genital tubercle, however, still remains, but only refers to the future glans ^[3]

Urogenital opening

In both sexes the phallic portion of the urogenital sinus extends on to the under surface of the cloacal tubercle as far forward as the apex. At the apex the walls of the phallic portion come together and fuse, obliterating the urogenital opening. Instead, a solid plate, the urethral plate, is formed. The remainder of the phallic portion is for a time tubular, and then, by the absorption of the urogenital membrane, it establishes a communication with the exterior. This opening is for a while the primitive urogenital opening, and it extends forward to the corona glandis. The urogenital sinus (also known as the persistent cloaca) is a part of the human body while it is an embryo. ... The urogenital opening is where waste products of the body and reproductive fluids are expelled to the environment outside of the body cavity. ...

After differentiation

Development of female external genitalia

The following developments occur in both males and females, although a difference in the development between the sexes already can be seen:

• The corpora cavernosa of the penis or clitoris and of the urethra arise from the mesodermal tissue in the phallus; they are at first dense structures, but later vascular spaces appear in them, and they gradually become cavernous.

• The prepuce in both sexes is formed by the growth of a solid plate of ectoderm into the superficial part of the phallus; on coronal section this plate presents the shape of a horseshoe. By the breaking down of its more centrally situated cells the plate is split into two lamellæ. Thus, a cutaneous fold, the prepuce, is liberated and forms a hood over the glans.

A corpus cavernosum is one of a pair of a sponge-like regions of erectile tissue which contain most of the blood in the male penis during erection. ... The prepuce is a retractable piece of skin which covers part of the genitals of primates and other mammals. ...

Female

In the female, a deep groove forms around the phallus. The sides of it grow dorsalward as the labioscrotal folds, which ultimately form the labia majora in females. The labia minora, in contrast, arise by the continued growth of the lips of the groove on the under surface of the phallus; the remainder of the phallus forms the clitoris. The immature glans becomes the clitoral glans. The labioscrotal folds (or labioscrotal swellings) are paired embryonic structures that represent the final stage of development of the caudal end of the external genitals before sexual differentiation. ... The clitoris (Greek ) is a sexual organ that is present in biologically female mammals. ... The Clitoral Glans is an external portion of the clitoris. ...

Male

Development of male external genitalia

In the male the pelvic portion of the cloaca undergoes much greater development, pushing before it the phallic portion.

The labioscrotal folds extend around between the pelvic portion and the anus, and form a scrotal area. During the changes associated with the descent of the testes this scrotal area is drawn out to form the scrotal sacs. The penis is developed from the phallus. The scrotum (human variant shown) is a thin extension of the abdomen that contains the testes and helps regulate their temperature. ...

As in the female, the urogenital membrane undergoes absorption, forming a channel on the under surface of the phallus; this channel extends only as far forward as the corona glandis. The glans penis is the sensitive tip of the penis. ...

Urogenital opening

In the male, by the greater growth of the pelvic portion of the cloaca, a longer urethra is formed, and the primitive opening is carried forward with the phallus, but it still ends at the corona glandis. Later, this opening, which is located on the dorsal ide of the penis^[3], closes from behind forward. Meanwhile, the urethral plate of the glans breaks down centrally to form a median groove continuous with the primitive ostium. This groove also closes from behind forward, leaving only a small pipe running in the middle of the penis. Thus, the urogenital opening is shifted forward to the end of the glans.

Diagram of internal differentiation

Diagrams to show the development of male and female generative organs from a common type.

A.—Diagram of the primitive urogenital organs in the embryo previous to sexual distinction. Image File history File links Size of this preview: 207 × 600 pixelsFull resolution (276 × 800 pixel, file size: 53 KB, MIME type: image/png) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Size of this preview: 207 × 600 pixelsFull resolution (276 × 800 pixel, file size: 53 KB, MIME type: image/png) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...

• 3. Ureter.
• 4. Urinary bladder.
• 5. Urachus.
• cl. Cloaca.
• cp. Elevation which becomes clitoris or penis.
• i. Lower part of the intestine.
• ls. Fold of integument from which the labia majora or scrotum are formed.
• m, m. Right and left Müllerian ducts uniting together and running with the Wolffian ducts in gc, the genital cord.
• ot. The genital ridge from which either the ovary or testis is formed.
• ug. Sinus urogenitalis.
• W. Left Wolffian body.
• w, w. Right and left Wolffian ducts.

B.—Diagram of the female type of sexual organs.

• C. Greater vestibular gland, and immediately above it the urethra.
• cc. Corpus cavernosum clitoridis.
• dG. Remains of the left Wolffian duct, such as give rise to the duct of Gärtner, represented by dotted lines; that of the right side is marked w.
• f. The abdominal opening of the left uterine tube.
• g. Round ligament, corresponding to gubernaculum.
• h. Situation of the hymen.
• i. Lower part of the intestine.
• l. Labium major.
• n. Labium minus.
• o. The left ovary.
• po. Epoophoron.
• sc. Corpus cavernosum urethrae.
• u. Uterus. The uterine tube of the right side is marked m.
• v. Vulva.
• va. Vagina.
• W. Scattered remains of Wolffian tubes near it (paroöphoron of Waldeyer).

C.—Diagram of the male type of sexual organs.

• C. Bulbo-urethral gland of one side.
• cp. Corpora cavernosa penis cut short.
• e. Caput epididymis.
• g. The gubernaculum.
• i. Lower part of the intestine.
• m. Müllerian duct, the upper part of which remains as the hydatid of Morgagni; the lower part, represented by a dotted line descending to the prostatic utricle, constitutes the occasionally existing cornu and tube of the uterus masculinus.
• pr. The prostate.
• s. Scrotum.
• sp. Corpus cavernosum urethrae.
• t. Testis in the place of its original formation.
• t’, together with the dotted lines above, indicates the direction in which the testis and epididymis descend from the abdomen into the scrotum.
• vd. Ductus deferens.
• vh. Ductus aberrans.
• vs. The vesicula seminalis.
• W. Scattered remains of the Wolffian body, constituting the organ of Giraldès, or the paradidymis of Waldeyer.

References

In-line

1. ^ 1918 Gray's Anatomy
2. ^ embryology.ch - In males: Differentiation of the urogenital sinus
3. ^ ^{a b c} The University of North Carolina at Chapel Hill - Embryo images nr 024

General

• http://www.bartleby.com/107/252.html Henry Gray (1821–1865). Anatomy of the Human Body. 1918.

3. The Urogenital Apparatus