7.3 Lesson 3: Hair Growth: Keratin
- The dermal papilla, situated at the root of the hair follicle is nourished by a profuse system of blood vessels.
- The hair shaft is formed when epithelial cells lying over the papilla reproduce, move up the hair follicle and eventually keratinize (turn into keratin protein).
- The keratin molecules, which harden as the hair grows, are formed by peptide chains created by amino acids.
- Amino acids that contain sulfur (mainly cysteine and cystine) are primary to the synthesis of the keratin proteins in the hair follicle.
- The keratin filaments are inserted at the desmosome junctions that bind the cells to each other.
- Between adjacent cells there are open channels that allow nutrients to diffuse freely through the metabolically active layers of the epidermis.
- As long as the cells in the papilla remain alive, hair will continue to grow even when the hair is cut.
- There are two main subtypes of keratin proteins, "soft" keratins and "hard" keratins. Soft keratins are found in the skin and are relatively easy to break down whereas hard keratins are very resistant to degradation. The hair fiber is mostly made from hard keratin proteins.
