Glans

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I. Definition:
The glans is a vascular structure located at the tip of the penis in men or a homologous genital structure of the clitoris in women.


II. Development
In the development of the urinary and reproductive organs, the glans is derived from the genital tubercle.
III. Embryology of glans (mainly about ectoderm):
Male:

The genital tubercle is elongating and growing to form the penis.

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As the genital tubercle is elongating and growing to form the penis, the urogenital folds which lie on either side of the urogenital membrane begin to move towards each other forming a groove, this is known as the urethral groove. The urogenital folds fuse together on the ventral side of the developing penis, enclosing what will now become the spongy urethra. If the urogenital folds fail to close, hypospadias results.

The tip of the penis, which is now called the glans, then begins to form a cord of ectoderm which grows toward the spongy urethra. This cord is known as the urethral plate and when it canalizes, the end of the urethra (external urethral orifice) is at the tip of the penis.

The foreskin is formed in the twelfth week of development. A septum of ectoderm moves inward around the edges of the penis and then breaks down, leaving a thin layer of skin surrounding the penis. During this time, the penis is also developing its corpus cavernosa and spongiosa from proliferating mesenchyme within the genital tubercle.

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Female:
In the female, the tubercle remains small, as the clitoris; it does not contain the urethra. The urogenital folds remain unclosed as the lesser vulvar lips and are flanked by the unshifted and unfused genital swellings, or greater lips.


The head or glans of the clitoris is roughly the size and shape of a pea, although it can be significantly larger or smaller. The clitoral glans is highly sensitive, containing as many nerve endings as the analogous organ in males, the glans penis, making it particularly well-suited for sexual stimulation. During arousal, the glans becomes engorged with blood and protrudes from the clitoral hood.


Figure shows the abundance of nerve endings on the clitoral glans, causing it to be very sensitive to the touch.

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Introduction:
The ectoderm is the start of a tissue that covers the body surfaces. It emerges first and forms from the outermost of the germ layers.
Generally speaking, the ectoderm differentiates to form the nervous system, and the epidermis (the outer part of integument).
In vertebrates, the ectoderm has three parts: external ectoderm (also known as surface ectoderm), the neural crest, and neural tube. The latter two are known as neuroectoderm.

Ectoderm, Mesoderm and Endoderm:
During gastrulation, three major cell lineages are being established. They are the Ectoderm (shown in the diagram as blue), Mesoderm (red) and Endoderm (yellow). Following gastrulation, various cell lineages are derrived from these three primary cell types. For example, the Ectoderm gives rise to the epidermis and its derrivatives such as nails, hair and teeth. On the other hand, the Ectoderm also gives rise to the Central Nervous System.

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