Anatomy of Hair Follicle

A hair mainly consists of the hair shaft and hair root, pigment cells that determine the color of the hair and provides nourishment to them via blood vessels. The sebaceous gland along with arrectorpili muscle constitute the hair follicle. Anatomy of Hair Follicle  The anatomy of a human hair is pretty complex and a lot still needs to be discovered about it. Its anatomy is basically divided into 3 regions:

  1. The lower segment; which consists of the bulb and suprabulb. This region begins from the base of the hair follicle and ends at the insertion point of the arrectorpilimuscle.
  2. The middle segment also known as the isthmus. This segment beginsat the insertion point of erector pili muscle and extends to the entrance of the sebaceous gland duct.
  3. The upper segment that comprises of the infundibulum. This starts from the entrance of the sebaceous gland duct and ends at the follicular orifice.

Hair Shaft It’s basically a thin strand of hardened cells that is visible above the scalp. The thickness of a hair is varies something in-between 0.04-0.12mm. Studies have revealed that light colored hair are finer than dark or red ones. A cross section of a hair may have various forms but mostly they are round to oval. Cuticle Layer It’s the outermost layer of the hair and protects the inner layers from harm. It has a tough and dense structure. It’s colorless in nature and allows light to shine through it. Around 10% of the hair diameter consists of the cuticle layer. It’s known to provide shine and elasticity to the hair. Cortex Layer It’s the thickest layer of the hair and constitutes around 80-90% of the hair’s diameter. It contains numerous hardened fibrous cells which are made up of various protein molecules. These cells are arranged together in bundles surrounded by keratins. It’s also known to contain the pigment, Melanin giving the hair its natural color. Medulla Layer It’s the core of the hair. Its thickness ranges according to the thickness of the hair. Medulla’s presence in a hair determines its stiffness and thickness. It’s not at all present in fine hairs. Hair Bulb It’s the source of all biological processes and is located in a tight tube of skin called the hair follicle. Hair bulb’s shape is pretty similar to that of an onion. It’s connected with papilla from below. Two types of cells surround the papilla namely the matrix cells (keratinocytes) and pigment cells (melanocytes). This constitutes the living part of the hair. Very intricate blood vessels (capillaries) grow near these cells. The hair’s life cycle, cell metabolism and growth of the hair all depend on blood circulation within these capillaries. Anatomy of hairs varies considerably at different locations found on the human body. Anatomy of large terminal hairs found on the scalp varies immensely from those found on our skin (vellus hairs). Hormonal changes that occur in males during puberty lead to vellus hair (beard) found on their face to become more thick and darker. Though there are more vellus hair found on human body than terminal hair, yet terminal hair are of more prominence. A terminal hair found on the scalp goes through a number of stages during its life cycle. These stages are namely anagen, catagen, and telogen. During the anagen stage the hair grows in length and thickness and this period lasts for 3-4 years, within the catagen stage the growth of the hair regresses and this period usually lasts for 2-3 weeks, and during the telogen stage the hair rests which lasts for around 3 months. Around 84% of the hair found on scalp are within the anagen stage, 1-2% are within the catagen stage and 10-15% are within the thetelogen stage.