Genital - Male Development

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Introduction

Urogenital male structures cartoon
Urogenital Male

The male and female reproductive systems develop initially "indifferently", it is the product of the Y chromosome SRY gene that makes the "difference". The mesonephric duct (Wolffian Duct) contributes the majority of male internal genital tract.


Embryonic gonad development leads to the mesonephric/paramesonephric duct changes, while the external genitaila remain indeterminate in appearance through to the fetal period.


Importantly its sex chromosome dependence, late embryonic/fetal differential development, complex morphogenic changes, long time-course, hormonal sensitivity and hormonal influences make it a system prone to many different abnormalities.


There are also currently separate pages describing Spermatozoa Development | Testis Development | Prostate Development.


Genital Links: genital | Lecture - Medicine | Lecture - Science | Lecture Movie | Medicine - Practical | primordial germ cell | meiosis | Female | X | ovary | corpus luteum | oocyte | uterus | vagina | reproductive cycles | menstrual cycle | Male | Y | SRY | testis | spermatozoa | ductus deferens | penis | prostate | endocrine gonad‎ | Genital Movies | genital abnormalities | Assisted Reproductive Technology | puberty | Category:Genital
Historic Embryology - Genital 
1887-88 Testis | 1901 Urinogenital Tract | 1902 The Uro-Genital System | 1904 Ovary and Testis | 1904 Leydig Cells | 1904 Hymen | 1905 Testis vascular | 1909 Prostate | 1912 Prostate | 1912 Urinogenital Organ Development | 1914 External Genitalia | 1914 Female | 1915 Cowper’s and Bartholin’s Glands | 1920 Wolffian tubules | 1921 Urogenital Development | 1921 External Genital | 1927 Female Foetus 15 cm | 1932 Postnatal Ovary | 1935 Prepuce | 1935 Wolffian Duct | 1942 Sex Cords | 1943 Testes Descent | 1953 Germ Cells | Historic Embryology Papers | Historic Disclaimer

Some Recent Findings

Male urogenital histology
Male urogenital development (week 8, stage 22)
  • Penile biometry on prenatal MR imaging [1]"Mean length values, including 95% confidence intervals and percentiles, were defined. Penile length as a function of gestational age was expressed by the regression equation: outer mean length= -5.514 + 0.622 *, and total mean length= -8.865 + 1.312 * (*= gestational weeks). The correlation coefficients were statistically significant (p < .001). The comparison between outer length on MRI and US data showed no significant differences, whereas total length on MRI and US data demonstrated significant differences (p< .001)."
  • Male reproductive tract abnormalities: More common after assisted reproduction?[2] "IVF and ICSI, by increasing the risks of prematurity, low birthweight, and multiple gestation, are indirect risk factors for developing male genital malformations. In infants with normal birhtweight or from singleton pregnancies, ICSI is a specific risk factor for hypospadias."
  • Temporal and spatial dissection of Shh signaling in genital tubercle development.[3] "Genital tubercle (GT) initiation and outgrowth involve coordinated morphogenesis of surface ectoderm, cloacal mesoderm and hindgut endoderm. GT development appears to mirror that of the limb. Although Shh is essential for the development of both appendages, its role in GT development is much less clear than in the limb. Here, by removing Shh at different stages during GT development in mice, we demonstrate a continuous requirement for Shh in GT initiation and subsequent androgen-independent GT growth."
  • Bmp7 expression and null phenotype in the urogenital system suggest a role in re-organization of the urethral epithelium. [4] "Signaling by Bone morphogenetic proteins (Bmps) has multiple and diverse roles in patterning and morphogenesis of the kidney, eye, limbs and the neural tube. ...Together, our analysis of Bmp7 expression and the null phenotype, indicates that Bmp7 may play an important role in re-organization of the epithelium during cloacal septation and morphogenesis of the genital tubercle."

Textbooks

Historic drawing of the testis
Historic drawing of the testis
  • Human Embryology (2nd ed.) Larson Chapter 10 p261-306
  • The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Chapter 13 p303-346
  • Before We Are Born (5th ed.) Moore and Persaud Chapter 14 p289-326
  • Essentials of Human Embryology, Larson Chapter 10 p173-205
  • Human Embryology, Fitzgerald and Fitzgerald Chapter 21-22 p134-152
  • Developmental Biology (6th ed.) Gilbert Chapter 14 Intermediate Mesoderm


Movies

Gonad-icon.jpg
 ‎‎Testis
Page | Play
Urogenital septum 001 icon.jpg
 ‎‎Urogenital Septum
Page | Play
Male external 001 icon.jpg
 ‎‎Male External
Page | Play
Testis 001 icon.jpg
 ‎‎Testis Descent
Page | Play
Gonad blood 01 icon.jpg
 ‎‎Gonad Vascular
Page | Play
Mouse Primordial Germ Cell Migration
Primordial germ cell 001 icon.jpg
 ‎‎Germ Cell E9.0
Page | Play
Primordial germ cell 002 icon.jpg
 ‎‎Germ Cell E9.5
Page | Play
Primordial germ cell 003 icon.jpg
 ‎‎Germ Cell E10.5
Page | Play

Development Overview

Three main stages during development, mesonephric/paramesonephric duct changes are one of the first male/female differences that occur in development, while external genitaila remain indeterminate in appearance for quite a while.

  1. Differentiation of gonad (Sex determination)
  2. Differentiation of internal genital organs
  3. Differentiation of external genital organs

The 2nd and 3rd stages dependent on endocrine gonad. Reproductive development has a long maturation timecourse, begining in the embryo and finishing in puberty. (More? Puberty Development)

Historic Images of Genital Changes

Urogenital Indifferent Urogenital Male Urogenital Female
Urogenital indifferent Urogenital male Urogenital female

Gonad - Testis

Links: Testis Development

Internal Genital

External Genital

Historic diagram of external development (male left)
  • external genitalia are initially identical and undergo male and female differentiation under the influence or absence of steroidal sex hormones.
  • Indifferent stage ‐ cloaca divided by proliferating mesenchyme forming the urorectal septum which separates the ventral urogenital sinus from the dorsal rectum.
  • Difference stage ‐ locally in this region the presence or absence of dihydrotestosterone (DHT), generated from testosterone, determines male/female development.
testosterone cartoon Dihydrotestosterone cartoon

Dihydrotestosterone (DHT)

Male presence of Dihydrotestosterone (DHT, 5α-dihydrotestosterone, androstanolone, 5α-androstan-17β-ol-3-one).
  • locally in this region leads to genital tubercle growth, form
  • genital folds (urethral) initial maintenance and then fusion, forming perineal and penile raphe.
  • labioscrotal swellings become the scrotum.
Testosterone metabolism
Links: Endocrinology - Diagram of the development of the external genitalia | image

Histology


Androgen and Digit ratio (2D:4D)

Androgen and Digit ratio (2D:4D

The ratio of 2nd and 4th finger (D, digit) length. This ratio has been suggested to relate to high fetal testosterone concentration (males have lower 2D:4D than females) and has been shown for several species.[5] Although a study in mice has not shown the same correlation.[6] There have been some suggestions that the ratio may also be an indicator of various neurological abnormalities.

To measure (2D:4D) - using your right hand palm up, measure the index finger (2) and ring finger (4) length from palm to tip. Dividing the index finger by the ring finger gives the 2D:4D ratio, average women ratio is 1, average men is 0.98.

Additional Images

References

  1. <pubmed>21484906</pubmed>
  2. <pubmed>20674196</pubmed>
  3. <pubmed>19906863</pubmed>
  4. <pubmed>19159697</pubmed>
  5. <pubmed>16504142</pubmed>
  6. <pubmed>19495421</pubmed>


Reviews

<pubmed>21397195</pubmed> <pubmed>20541146</pubmed> <pubmed>19845801</pubmed> <pubmed>17237341</pubmed> <pubmed>16522522</pubmed> <pubmed>12428197</pubmed> <pubmed>10715534</pubmed> <pubmed>10664515</pubmed>

Articles

<pubmed>21900680</pubmed> <pubmed>21791949</pubmed>


Search PubMed

Search Pubmed: Male Genital System Development | mesonephric duct

Terms

  • mesonephric duct - (Wollfian duct) An early developing urogenital paired duct system that initially runs the length of the embryo, that will differentiate and form the male reproductive duct system (ductus deferens). In females, this duct degenerates occasionally some remnants may remain associated in broad ligament.
  • Wolffian duct - (mesonephric duct, preferred terminology), A developmental duct that runs from the mesonephros to cloaca. The duct in male differentiates to form the ductus deferens and in female the same structure regresses. Historically named after Caspar Friedrich Wolff (1733-1794), a German scientist and early embryology researcher and is said to have established the doctrine of germ layers. (More? Caspar Friedrich Wolff)


Glossary Links

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Cite this page: Hill, M.A. (2019, November 14) Embryology Genital - Male Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Genital_-_Male_Development

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© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G