The clitoris is the human female's most sensitive erogenous zone and generally the primary anatomical source of human female sexual pleasure.
In humans it develops from an outgrowth in the embryo called the genital tubercle. Initially undifferentiated, the tubercle develops into either a penis or a clitoris, depending on exposure to androgens (primarily male hormones):
- If exposed to testosterone, the genital tubercle elongates to form the penis. By fusion of the urogenital folds – elongated spindle-shaped structures that contribute to the formation of the urethral groove on the belly aspect of the genital tubercle – the urogenital sinus closes completely and forms the spongy urethra, and the labioscrotal swellings unite to form the scrotum.
- In the absence of testosterone, the genital tubercle allows for formation of the clitoris; the initially rapid growth of the phallus gradually slows and the clitoris is formed (Pic. 1). The urogenital sinus persists as the vestibule of the vagina, the two urogenital folds form the labia minora, and the labioscrotal swellings enlarge to form the labia majora, completing the
female genitalia (Pic. 2).
The clitoris is a complex structure, containing external and internal components (Pic. 3). It consists of:
glans (including the frenulum clitoridis) - a frenulum on the under-surface of the glans and is created by the two medial parts of the labia minora
clitoral body - forms a wishbone-shaped structure containing the corpora cavernosa (a pair of sponge like regions of erectile tissue which contain most of the blood in the clitoris during clitoral erection)
clitoral hood - formed by the labia minora
vestibular or clitoral bulbs - aggregations of erectile tissue that are an internal part of the clitoris
The clitoris, vestibular bulbs, labia minora, and urethra involve two histologically distinct types of vascular tissue (tissue related to blood vessels):
Erectile tissue (trabeculated) - has a spongy appearance; along with blood, it fills the large, dilated vascular spaces of the clitoris and the bulbs. Beneath the epithelium of the vascular areas is smooth muscle. It may also be that the urethral lumen (the inner open space or cavity of the urethra), which is surrounded by spongy tissue, has tissue that "is grossly distinct from the vascular tissue of the clitoris and bulbs, and on macroscopic observation, is paler than the dark tissue" of the clitoris and bulbs.
Non – erectile tissue - the clitoral body becomes engorged with blood upon sexual arousal, erecting the clitoral glans, some sources describe the clitoral glans and labia minora as composed of non-erectile tissue; this is especially the case for the glans. They state that the clitoral glans and labia minora have blood vessels that are dispersed within a fibrous matrix and have only a minimal amount of smooth muscle, or that the clitoral glans is "a midline, densely neural, non-erectile structure". Other sources state that the glans is composed of erectile tissue and that erectile tissue is present within the labia minora; adipose tissue is absent in the labia minora, but the organ may be described as being made up of dense connective tissue, erectile tissue and elastic fibers.
Highly innervated, the glans exists at the tip of the clitoral body as a fibro-vascular cap, and is usually the size and shape of a pea, although it is sometimes much larger or smaller. While whether or not the glans is composed of erectile or non-erectile tissue is subject to debate. The entire clitoris, is estimated to have 8,000 or more sensory nerve endings.