Hair Follicle :- The human hair follicle is an intriguing structure, and much remains to be learned about hair anatomy and its growth. The hair follicle can be divided into 3 regions: the lower segment (bulb and suprabulb), the middle segment (isthmus), and the upper segment (infundibulum). The lower segment extends from the base of the follicle to the insertion of the erector pili muscle (also known as the arrector pili muscle). The middle segment is a short section that extends from the insertion of the erector pili muscle to the entrance of the sebaceous gland duct. The upper segment extends from the entrance of the sebaceous gland duct to the follicular orifice.