A genital tubercle, phallic tubercle, or clitorophallic structure is a body of tissue present in the
development of the reproductive system
The development of the reproductive system is the part of embryonic growth that results in the sex organs and contributes to sexual differentiation. Due to its large overlap with development of the urinary system, the two systems are typicall ...
of
amniote
Amniotes are tetrapod vertebrate animals belonging to the clade Amniota, a large group that comprises the vast majority of living terrestrial animal, terrestrial and semiaquatic vertebrates. Amniotes evolution, evolved from amphibious Stem tet ...
s. It forms in the ventral, caudal region of
mammal
A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...
ian
embryo
An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...
s of both
sex
Sex is the biological trait that determines whether a sexually reproducing organism produces male or female gametes. During sexual reproduction, a male and a female gamete fuse to form a zygote, which develops into an offspring that inheri ...
es, and eventually develops into a
primordial phallus
In embryology, the primordial phallus refers to the clitoris of a female or the penis in the male, particularly during embryonic development of the urinary and reproductive organs, before sexual differentiation is evident. This is also the case ...
. In the human
fetus
A fetus or foetus (; : fetuses, foetuses, rarely feti or foeti) is the unborn offspring of a viviparous animal that develops from an embryo. Following the embryonic development, embryonic stage, the fetal stage of development takes place. Pren ...
, the genital tubercle develops around week four of
gestation
Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregn ...
, and by week nine, becomes recognizably either a
clitoris
In amniotes, the clitoris ( or ; : clitorises or clitorides) is a female sex organ. In humans, it is the vulva's most erogenous zone, erogenous area and generally the primary anatomical source of female Human sexuality, sexual pleasure. Th ...
or
penis
A penis (; : penises or penes) is a sex organ through which male and hermaphrodite animals expel semen during copulation (zoology), copulation, and through which male placental mammals and marsupials also Urination, urinate.
The term ''pen ...
. This should not be confused with the
sinus tubercle
Sinus tubercle (also known as sinual tubercle or Müllerian eminence) is the proliferation of endoderm induced by the paramesonephric ducts. It is located in the developing fetus between the orifices of the mesonephric ducts on the urogenital sin ...
which is a proliferation of
endoderm
Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gastr ...
induced by paramesonephric ducts. Even after the phallus is developed (either a
penile shaft or
clitoral shaft), the term genital tubercle remains, but only as the terminal end of it,
which develops into either the
glans penis
In male human anatomy, the glans penis or penile glans, commonly referred to as the glans, (; from Latin ''glans'' meaning "acorn") is the bulbous structure at the Anatomical terms of location#Proximal and distal, distal end of the human penis ...
or the
glans clitoridis
In amniotes, the clitoris ( or ; : clitorises or clitorides) is a female sex organ. In humans, it is the vulva's most erogenous area and generally the primary anatomical source of female sexual pleasure. The clitoris is a complex structu ...
.
In the development of the male fetus, the two sides of the tubercle approach ventrally forming a hollow tube that encloses the
male urethra
The urethra (: urethras or urethrae) is the tube that connects the urinary bladder to the urinary meatus, through which placental mammals urinate and ejaculate.
The external urethral sphincter is a striated muscle that allows voluntary contro ...
. The two glans wings merge in the midline forming the
septum glandis
The septum glandis, also septum of the glans, refers to the fibrous partition of the ventral aspect of the glans penis that separates the two glans wings in the ventral midline. The septum extends from the urethral meatus through the glanular ur ...
. In the female fetus, the tubercle is attached to the vestibular folds that remain unfused forming the
labia minora
The labia minora (Latin for 'smaller lips', : labium minus), also known as the inner labia, inner lips, or nymphae, are two flaps of skin that are part of the primate vulva, extending outwards from the inner Vagina#Vaginal opening and hymen, vagi ...
and the
vaginal vestibule in between.
The genital tubercle is sensitive to
dihydrotestosterone
Dihydrotestosterone (DHT, 5α-dihydrotestosterone, 5α-DHT, androstanolone or stanolone) is an endogenous androgen sex steroid and hormone primarily involved in the growth and repair of the prostate and the penis, as well as the production o ...
and rich in
5-alpha-reductase, so that the amount of fetal
testosterone
Testosterone is the primary male sex hormone and androgen in Male, males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testicles and prostate, as well as promoting se ...
present after the second month is a major determinant of phallus size at birth.
See also
*
Clitorophallus
Clitorophallus is a term used to refer to the penis or clitoris. It is typically used when the clitorophallus is of a size where it is not clear as to whether it is a penis or a clitoris ( ambiguous genitalia). Often it is a matter of size that ...
*
Sexual differentiation
Sexual differentiation is the process of development of the sex differences between males and females from an undifferentiated zygote. Sex differentiation is usually distinct from sex determination; sex determination is the designation of the de ...
References
External links
*
Overview at mcgill.ca
{{DEFAULTSORT:Genital Tubercle
Embryology of urogenital system