The dartos fascia or simply dartos is a layer of
connective tissue
Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tissue ...
found in the
penile shaft,
foreskin
In male human anatomy, the foreskin, also known as the prepuce, is the double-layered fold of skin, mucosal and muscular tissue at the distal end of the human penis that covers the glans and the urinary meatus. The foreskin is attached to ...
,
scrotum and
labia.
The penile portion is referred to as the superficial fascia of penis or the subcutaneous tissue of penis, while the scrotal part is the dartos proper. In addition to being continuous with itself between the scrotum and the penis, it is also continuous with
Colles fascia of the perineum and
Scarpa's fascia of the abdomen.
The dartos lies just below the skin, which places it just superficial to the external spermatic fascia in the scrotum and to
Buck's fascia in the penile shaft. In the scrotum, it consists mostly of
smooth muscle
Smooth muscle is an involuntary non- striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit ...
. The tone of this smooth muscle is responsible for the wrinkled (rugose) appearance of the scrotum.
In females, the same muscle fibers are less well developed and termed ''dartos muliebris,'' lying beneath the skin of the
labia majora. The dartos fascia receives innervation from
postganglionic sympathetic nerve fibers arriving via the
ilioinguinal nerve and the
posterior scrotal nerve.
Function
In the penis, the loose attachment of the dartos fascia to Buck's fascia is responsible for the high degree of mobility of the penile skin over the underlying tissue.
It is also responsible for carrying the blood supply of the penile skin, a longitudinally-coursing anastomotic network of vessels that arise from the external pudendal vessels.
In the scrotum, the tunica dartos acts to regulate the
temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied on ...
of the
testicles, which promotes
spermatogenesis
Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testis. This process starts with the mitotic division of the stem cells located close to the basement membrane of the t ...
. It does this by expanding or contracting to wrinkle the scrotal skin.
* Contraction reduces the
surface area
The surface area of a solid object is a measure of the total area that the surface of the object occupies. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of ...
available for heat loss, thus reducing
heat
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...
loss and warming the testicles.
* Conversely, expansion increases the surface area, promoting heat loss and thus cooling the testicles.
The dartos muscle works in conjunction with the
cremaster muscle to elevate the
testis but should not be confused with the
cremasteric reflex.
The dartos fascia keeps the foreskin close to the glans penis throughout life. In infancy, the dartos fascia operates as a one-way check valve at the tip of the foreskin, allowing urine to pass out, but prohibiting the entry of foreign matter and pathogens.
There is an increase in elastic fibers with increasing maturity that allows the foreskin to become retractable by adulthood and glide freely back and forth.
Related terms
Etymology:
: Derived from the Greek δέρνω/derno (beat, flog) and/or δέρμα/derma (skin), meaning "that which is skinned or flayed", possibly due to its appearance.
Some dartos-related terms:
: dartoic ''(dar·to·ic)'' (dahr-to'ik) of the nature of a dartos; having a slow, involuntary contractility like that of the dartos.
: dartoid ''(dar·toid)'' (dahr'toid) resembling the dartos.
Additional images
File:Gray1145.png, Transverse section through the left side of the scrotum and the left testis.
File:Slide9eee.JPG, Dartos
File:Penis_cross_section.svg
References
{{Authority control
Mammal reproductive system
Human reproduction
Fascia