DHT, an androgen metabolite of testosterone which is secreted by the gonads, causes changes in the cartilages and musculature of the larynx when present in high enough concentrations, such as during an adolescent boy's puberty: The thyroid prominence appears, the vocal folds lengthen and become rounded, and the epithelium thickens with the formation of three distinct layers in the lamina propria.

They have a minimal role in normal phonation, but are often used to produce deep sonorous tones in Tibetan chant and Tuvan throat singing,[2] as well as in musical screaming and the death growl vocal style.

[citation needed] The vocal cords are composed of twin infoldings of 3 distinct tissues: an outer layer of flat cells that do not produce keratin (squamous epithelium).

While the fibrous components are sparse, making the lamina propria structure loose, the hyaluronic acid (HA) content is high.

HA is a bulky, negatively charged glycosaminoglycan, whose strong affinity with water procures hyaluronic acid its viscoelastic and shock absorbing properties essential to vocal biomechanics.

Chan, Gray and Titze, quantified the effect of hyaluronic acid on both the viscosity and the elasticity of vocal folds by comparing the properties of tissues with and without HA.

[4] The rough endoplasmic reticulum and Golgi apparatus, as shown by electron micrographs, are not well developed, indicating that the cells are in a resting phase.

Their rough endoplasmic reticulum and Golgi apparatus were still not well developed, indicating that despite the change in shape, the fibroblasts still remained mostly in a resting phase.

In females, androgens are secreted principally by the adrenal cortex and the ovaries and can have irreversible masculinizing effects if present in high enough concentration.

[8] These changes are also irreversible without surgery, albeit the thyroid/laryngeal prominence, also known as an Adam's apple can be potentially diminished via a tracheal shave or feminization laryngoplasty.

[10] In those two layers, which form what is known as the vocalis ligament, the elastic and collagenous fibers are densely packed as bundles that run almost parallel to the edge of the vocal fold.

[12] The extracellular matrix of the vocal cord LP is composed of fibrous proteins such as collagen and elastin, and interstitial molecules such as HA, a non-sulfated glycosaminoglycan.

Hirano et al. previously found that the newborns did not have a true lamina propria, but instead had cellular regions called maculae flavae, located at the anterior and posterior ends of the loose vocal fold tissue.

Even though the vocal cords seem to start organizing, this is not representative of the trilaminar structure seen in adult tissues, where the layer are defined by their differential elastin and collagen fiber compositions.

[18] The histological structure of the macula flava is unique, and Sato and Hirano speculated that it could play an important role in growth, development and aging of the vocal cords.

The viscoelastic properties of human vocal fold lamina propria are essential for their vibration, and depend on the composition and structure of their extracellular matrix.

The stellate cells synthesized fewer extracellular matrix molecules, and the cytoplasmic processes were shown to be short and shrinking, suggesting a decreased activity.

[20] The gene expression levels of extracellular matrix constituents such as fibronectin, MMP1, decorin, fibromodulin, hyaluronic acid synthase 2, and CD44 were altered.

In the end, cell-surface receptors close the loop by giving feedback on the surrounding extracellular matrix to the cells, affecting also their gene expression level.

Their effect is due to their ability to bind to intracellular receptors, modulating the gene expression, and subsequently regulating protein synthesis.

Hammond et al. observed that the hyaluronic acid content in the vocal fold lamina propria was significantly higher in males than in females.

Newman et al. found that hormone receptors are indeed present in the vocal cords, and show a statistical distribution difference with respect to age and gender.

Bentley et al. demonstrated that sex skin swelling seen in monkey was due to an increase in hyaluronic acid content, which was in fact mediated by estrogen receptors in dermal fibroblasts.

[29] Under the correct conditions, the energy transferred to the tissues is large enough to overcome losses by dissipation and the oscillation pattern will sustain itself.

[30] The perceived pitch of a person's voice is determined by a number of different factors, most importantly the fundamental frequency of the sound generated by the larynx.

This causes the vocal fold mucosa to appear floppy with excessive movement of the cover that has been described as looking like a loose sock.

Vocal fold injuries can have a number of causes including chronic overuse, chemical, thermal and mechanical trauma such as smoking, laryngeal cancer, and surgery.

[35] Any injury to human vocal folds elicits a wound healing process characterized by disorganized collagen deposition and, eventually, formation of scar tissue.

[36][37][38][39] Verdolini[40] and her group sought to detect and describe acute tissue response of injured rabbit vocal cord model.

[44] According to the Oxford English Corpus, a database of 21st-century texts that contains everything from academic journal articles to unedited writing and blog entries, contemporary writers opt for the nonstandard chords instead of cords 49% of the time.