Hair follicle is the part from which hair root or the shaft arises outside. So, hair follicle is not visible outside. It is divided into three segments:
Infundibulum (upper part):
- This segment is from opening of the sebaceous gland duct to the epidermis.
- As this part is ending at the epidermis, it has the continuous epithelium which helps in regeneration of epidermis and replenish after the injury.
Isthmus (middle part):
- This segment includes the region from the bulge region of hair follicle (erector pili muscle) to the opening of sebaceous gland duct.
Inferior (lower part):
- It consists of stem and bulb.
- Stem is the above keratogenous zone up to the insertion of the erector pilorum.
- Bulb contains dermal papilla.
- Papilla is the main part of the structure that provides nutrients to grow the hair.
- The nutrients required for hair are sent from blood to the hair follicle through this papilla connected to blood vessels.
Types of hairs:
Hair types based on the thickness of the shaft:
They are thin, short, unmedullated and unpigmented. These hairs cover most of the body surface.
They are dark, thick, medullated, pigmented and long. They cover scalp, beard, moustache, axilla and pubis.
They cover the fetal skin and are shed at the age of 7-9 months. They are thin, unmedullated, light coloured but are longer than vellus hair.