Development of Accessory Sex Organs and External Genitalia

In addition to testes and ovaries, various internal accessory sex organs are needed for reproductive function. Most of these are derived from two systems of embryonic ducts. Male accessory organs are derived from the wolffian (mesonephric) ducts, and female accessory organs are derived from the mullerian (paramesonephric) ducts (fig. 20.5). Interestingly, the two duct systems are present in both male and female embryos between day 25 and day 50, and so embryos of both sexes have the potential to form the accessory organs characteristic of either sex.

Experimental removal of the testes (castration) from male embryonic animals results in regression of the wolffian ducts and development of the mullerian ducts into female accessory organs: the uterus and uterine (fallopian) tubes. Female accessory sex organs, therefore, develop as a result of the absence of testes rather than as a result of the presence of ovaries.

In a male, the Sertoli cells of the seminiferous tubules secrete mullerian inhibition factor (MIF), a polypeptide that causes regression of the mullerian ducts beginning at about day 60. The secretion of testosterone by the Leydig cells of the testes subsequently causes growth and development of the wolf-fian ducts into male accessory sex organs: the epididymis, ductus (vas) deferens, seminal vesicles, and ejaculatory duct.

The external genitalia of males and females are essentially identical during the first 6 weeks of development, sharing in common a urogenital sinus, genital tubercle, urethral folds, and a pair of labioscrotal swellings. The secretions of the testes masculinize these structures to form the penis and spongy (penile) urethra, prostate, and scrotum. In the absence of secreted testosterone, the genital tubercle that forms the penis in a male will become the clitoris in a female. The penis and clitoris are thus said to be homologous structures. Similarly, the labioscrotal swellings form the scrotum in a male or the labia majora in a female; these structures are therefore homologous also (fig. 20.6).

Labioscrotal

Labioscrotal swelling

Genital tubercle

Urethral folds

Labioscrotal swellings

Male

Developing ! penis

Glans penis

Scrotum

Scrotal raphe

Glans

Phallus

Glans

Phallus

Glans penis

Labia Majora And Labia Minora Disease

Developing glans clitoris

Labia minora Labia majora

Glans clitoris Hymen

Vaginal orifice

Female

Developing glans clitoris

Labia minora Labia majora

Glans clitoris Hymen

Vaginal orifice

■ Figure 20.6 The development of the external genitalia in the male and female. (a [ai, sagittal view]) At 6 weeks, the urethral fold and labioscrotal swelling have differentiated from the genital tubercle. (b) At 8 weeks, a distinct phallus is present during the indifferent stage. By week 12, the genitalia have become distinctly male (c) or female (d), being derived from homologous structures. (e, f) At 16 weeks, the genitalia are formed.

Masculinization of the embryonic structures described occurs as a result of testosterone secreted by the embryonic testes. Testosterone itself, however, is not the active agent within all of the target organs. Once inside particular target cells, testosterone is converted by the enzyme 5a-reductase into the active hormone known as dihydrotestosterone (DHT) (fig. 20.7). DHT is needed for the development and maintenance of the penis, spongy urethra, scrotum, and prostate. Evidence suggests that testosterone itself directly stimulates the wolffian duct derivatives—epididymis, ductus deferens, ejaculatory duct, and seminal vesicles.

In summary, the genetic sex is determined by whether a Y-bearing or an X-bearing sperm cell fertilizes the ovum; the

Reproduction presence or absence of a Y chromosome in turn determines whether the gonads of the embryo will be testes or ovaries; the presence or absence of testes, finally, determines whether the accessory sex organs and external genitalia will be male or female (table 20.1). This regulatory pattern of sex determina-

tion makes sense in light of the fact that both male and female embryos develop within an environment high in estrogen, which is secreted by the mother's ovaries and the placenta. If the secretions of the ovaries determined the sex, all embryos would be female.

Accessory Sex OrgansDht Vagina

■ Figure 20.7 The formation of DHT. Testosterone, secreted by the interstitial (Leydig) cells of the testes, is converted into dihydrotestosterone (DHT) within the target cells. This reaction involves the addition of a hydrogen (and the removal of the double carbon bond) in the first (A) ring of the steroid.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook


Responses

  • lexie
    Is the clitoris a female accessory sex organ?
    5 years ago
  • WISEMAN
    What is hymen in female?
    5 years ago
  • Sarama
    How to have sex with labia majora?
    5 years ago
  • Reagan Allan
    Is female anatomy derived from penis?
    5 years ago
  • fnan
    How to develop glans?
    5 years ago
  • kirstie
    What causes growth of the clitoris?
    5 years ago
  • luam
    Where is the raphe in the scrotum?
    5 years ago
  • kaija matinsalo
    How to determine visually if hymen is present?
    5 years ago
  • ermias selam
    How the penis of boys will be during first sex?
    5 years ago
  • Sinit
    What is the key enzyme in the development of the accessory sex glands and the external genitalia?
    5 years ago
  • Belinda Smallburrow
    How do sex organs development?
    5 years ago
  • john
    What determines external genitalia?
    5 years ago
  • genoveffa marino
    Why is the clitoria homologous?
    5 years ago
  • Judith Malone
    How are the scrotum and labia majora similar?
    5 years ago
  • fethawi
    What is a clitoris and labia?
    5 years ago
  • chelsea
    How to develop glans penis videos?
    5 years ago
  • greg
    How do human genitalia form?
    5 years ago
  • melanie
    Is penis accessory sex organ?
    5 years ago
  • elanor
    What male structure is homologous to the labia minora?
    5 years ago
  • poppy
    Which structures arise from the embryonic genital tubercle?
    5 years ago
  • john
    Where is a female labia on the vagina?
    5 years ago
  • Tommy
    What are penile or labial adhesions?
    5 years ago
  • mirin
    How to Stimulate the Clitoris With Your Fingers tube?
    5 years ago
  • Blanco
    Have sex clitoris or vagianl?
    5 years ago
  • kristian
    What is the raphe on a male body?
    5 years ago
  • iggi
    What is male clitoris?
    5 years ago
  • maunu mikkola
    What are the accessory sex organs of human female?
    5 years ago
  • Anu Heinonen
    Can a penis go through the vagina and urethra?
    5 years ago
  • clizia
    Is the clit a non developed penis and the labia a non developed scrotum?
    5 years ago
  • aatifa
    What are present in female external genitalia?
    5 years ago
  • michelle
    When does the genital tubercle form?
    5 years ago
  • Aki
    What are the accessory organs forming the male duct system?
    5 years ago
  • richard
    What causes the growth of the external genitalia in males?
    5 years ago
  • kyle
    Which accessory organ of the male duct system?
    5 years ago
  • Linda
    How to turn a vagina into a penis?
    5 years ago
  • mario pfeiffer
    Is a female clirtoris a penis?
    5 years ago
  • jose acree
    How to finger a clitoris?
    5 years ago
  • gilda bellucci
    What are the internal or accessory sex organs of the female?
    5 years ago
  • Girma
    What causes a swollen clitorus?
    5 years ago
  • aamos
    What hymen look like flower?
    5 years ago
  • RUSSELL
    Where is the clitrious in womens vagina with real pictures?
    5 years ago
  • Arcangelo
    What is accessory sex organ regression?
    5 years ago
  • Rowan
    What is the function of clitoris in female?
    5 years ago
  • rufina
    How is the clit stimulated during intercourse?
    5 years ago
  • Stewart Mackay
    How to convert a penis into a vagina surgery?
    5 years ago
  • raino
    Where is you hymen in the vagina?
    5 years ago
  • Lydia
    Why the clit enlargement?
    5 years ago
  • phillipp
    How do they turn a penis into a clit?
    5 years ago
  • Mhret
    What hormone is responsible for development of the external genitalia and accessory structures?
    5 years ago
  • gabriel
    How to stimulate the clitorus?
    5 years ago
  • Melba
    Where to put dick in vagina for sex?
    5 years ago
  • wolfgang
    What is the role of clitoris during sex?
    5 years ago
  • furuta
    How to turn a mans "penis into a clit"?
    5 years ago
  • Klaudia
    What does the genital tubercle form in female?
    4 years ago
  • elsie
    What is stage of vagina to penis?
    4 years ago
  • Agnese
    What part of the male sex organ is homologous to the clirtoris?
    4 years ago
  • temesgen
    Why are the external genitalia of males and females are homologous.?
    4 years ago
  • Mirella
    What causes a swollen labia?
    4 years ago
  • Fethawit Hamid
    Where are vaginal lymph nodes?
    4 years ago
  • Charles Dean
    What stimulates development of female genitalia?
    4 years ago
  • CARAMELLA
    Where is the clotoris?
    4 years ago
  • emma
    Are clitoris covered with a membrane?
    4 years ago
  • Leigha
    What are the accessory female sex prgans?
    4 years ago
  • cynthia burton
    What is responsible for producing and developing the external genitalia?
    4 years ago
  • nea
    Which hormone is directly responsible for female genitals?
    4 years ago
  • ausonia
    Where is the Glans clitoris developed?
    4 years ago
  • harris
    Is the vagina an accessory sex organ?
    4 years ago
  • veera
    What are the function of the accessory sex organs in the human for?
    4 years ago
  • Liisi Hintikka
    Can swollen clitoris look like a penis at 16 weeks sono?
    4 years ago
  • adalgisa
    What stimulates development of male and female sex organs?
    4 years ago
  • louis
    What is responsible for male sex organ developement and growth?
    4 years ago
  • SAKARI
    What stimulates genital formation in males?
    4 years ago
  • Katja
    What is the difference of internal vs. external accessory organs of human body reproductive system?
    4 years ago
  • saare
    How is the scrotum converted to a vagina?
    3 years ago
  • ELLA
    Does testosterone formation and maintenance of penis, scrotum and accessory organ?
    3 years ago
  • niklas
    What a labia looks like after testosterone?
    2 years ago
  • PANSY
    What happened in clitoria doring sex?
    2 years ago
  • amethyst
    Where is the male clit?
    2 years ago
  • Santeri
    What are the diseases of labia majora & labia minora?
    2 years ago
  • ismo lehtim
    Where is the phallus glans of male?
    2 years ago
  • abraham
    What happens to labians during an intercourse?
    2 years ago
  • piotr aitken
    When clittoris develop?
    2 years ago
  • Taina
    What makes swelling between labia minora?
    2 years ago
  • Mauri
    Which structure of female external genitilia is homologous to glans penis and scrotum of the male?
    2 years ago
  • tammy
    Why my vagina lips dont cover my clitorisis?
    1 year ago
  • shirley mosley
    How to stimulate the clirtoris?
    1 year ago
  • renzo siciliani
    Where is clitoric on pussy?
    1 year ago
  • marley
    What is function of pussy clitoric?
    1 year ago
  • burtuka
    Why does clitoral glans looks like penises?
    1 year ago
  • LATOYA
    What is the function of clitors?
    1 year ago
  • kaija
    Where is the cliturous?
    1 year ago
  • maik
    What does an engorged clitorus look like?
    1 year ago
  • ADAMO
    Where is clitrious in woman and how to identify it?
    1 year ago
  • herbert
    How big can a clitrious in a woman grow?
    1 year ago
  • TOM
    How clitoris penis is formed?
    1 year ago
  • Jakub Dickson
    Why would i have a growth like penis on vagina?
    1 year ago
  • Joseph Killian
    What causes labia minora to swell?
    1 year ago
  • crispino
    What happens to clitorsis after sex?
    1 year ago
  • TONY H
    How to turn a penis to a virgina?
    1 year ago
  • darius
    How to increase penile in a pussy?
    1 year ago
  • folcard
    What between clitorics and vigana with real images?
    1 year ago
  • Asmeret
    How genital tubercle become male or female genital?
    1 year ago
  • Stephen Cunningham
    Where the men clitrious present?
    12 months ago
  • Peter
    How the female sex organ develope?
    12 months ago
  • kayla
    How to avoid smell in clitorsis?
    11 months ago
  • nils
    How big can a clit grow on testosterone?
    11 months ago
  • ponto
    How to grow human sex organ?
    11 months ago
  • roderic galbassi
    What does a clitoris look like in real life?
    10 months ago
  • topi
    How to decrease glans clits?
    10 months ago
  • Maria
    Which hormone is responsible for stimulating the genital tubercle to develop into a clitoris?
    9 months ago
  • Hayden
    How to develop sex organs?
    8 months ago
  • GIADA
    What is male and female accessory organ?
    8 months ago
  • rezene
    How to find clitrious?
    7 months ago
  • asmara
    How do the labia majora and clitolis form scrotum and penis?
    6 months ago
  • lyle
    What causes the labia majora to swell?
    6 months ago
  • Ranugad Boffin
    What is responsible for the development of female sex organs?
    5 months ago
  • ann
    How large is a woman's cliturus?
    5 months ago
  • Anita
    How to put finger on clitorics?
    4 months ago
  • Antonio
    What are devlopment of accessory sex organs in female?
    4 months ago
  • Tommaso
    Where is the cliturous located on the vagina?
    4 months ago
  • leea pohjonen
    What is the function of big labias in sex?
    4 months ago
  • egidio napolitano
    Where is the cliturous located on a woman?
    3 months ago
  • Alan
    How does the labia receive the penis?
    2 months ago
  • antje freitag
    What is female accessory reproductive organs?
    2 months ago
  • Caterina
    What does labia majora help during intercourse?
    2 months ago

Post a comment