Inner root sheath

Inner Root Sheath

The Inner Root Sheath (IRS) is a part of the hair follicle that plays a crucial role in the formation and growth of hair. It is located between the hair shaft and the outer root sheath, and is composed of three layers: Henle's layer, Huxley's layer, and the cuticle of the IRS.

Structure

Diagram of a hair follicle. The Inner Root Sheath is located between the hair shaft and the outer root sheath.

The Inner Root Sheath is made up of three layers:

• Henle's layer: This is the outermost layer of the IRS. It is a single layer of cells that are flat and contain keratin.
• Huxley's layer: This layer is located inside Henle's layer and consists of two layers of cells. These cells also contain keratin and are filled with a substance called trichohyalin which gives them a granular appearance.
• Cuticle of the IRS: This is the innermost layer of the IRS and is in direct contact with the hair shaft. The cells in this layer are very thin and flat, and they overlap like the tiles on a roof.

Function

The primary function of the Inner Root Sheath is to mold and guide the growing hair shaft. The cells of the IRS undergo a process called keratinization which hardens them and gives the hair shaft its shape. The IRS also protects the hair shaft by providing a barrier against physical damage and harmful substances.

Clinical Significance

Abnormalities in the Inner Root Sheath can lead to various hair disorders. For example, defects in the trichohyalin gene, which is crucial for the formation of Huxley's layer, can cause a condition called Uncombable hair syndrome. Similarly, mutations in the keratin genes can lead to Monilethrix, a condition characterized by beaded or moniliform hair.

See Also

• Hair follicle
• Hair shaft
• Outer root sheath
• Keratinization