Integumentary Investigation

As we learn about the integumentary system I quickly learned that there is much more to the system than merely skin. The hair on our heads and the nails on our fingers all share some of the same characteristics. We briefly talked about the anatomy of the hair follicle and its function but I decided to investigate a bit more on the topic. One distinguishing feature between the skin and the hair follicle is that unlike the skin, hair growth is not a continuous process. Instead, there is a period of growth (anagen) and a period where growth stops (catagen). Furthermore, after the catagen period is a period of rest termed telogen. These periods proceed in a sequential fashion and explains why sometimes hair takes a while to grow out. The anagen period is when new hair develops. When the catagen period begins this new hair follicle goes through atrophy, which causes the hair to eventually be lost. During the hair growth cycle mature hairs periodically experience apoptosis and initiate the catagen stage. This also explains why we shed so much hair on a daily basis. Hair loss can be explained by the catagen period, for this is the period when the entire follicle retracts toward the epidermal layer. When the bulge of the follicle is retracted it can no longer be supported by the nutrient-rich anagen bulb. Therefore, it is ejected from the resting telogen follicle.

            When a hair follicle remains attached in the telogen phase for several months, it is now referred to as a club hair. There are two main types of hairs that can easily be distinguished by looking at your own skin. The hair on your forearms is much thinner than the hair on your scalp (hopefully)J. The coarse hair of the scalp is termed terminal hairs. These may reach a meter or more in length. On the other hand vellus hair which includes the hairs of your forearm and hands may only be seen with the aid of a microscope.  This is because terminal hairs are produced by large-diameter, long follicles. On the other hand vellus hairs are produced by small follicles. A person who is becoming bald has terminal follicles that are gradually converting into vellus follicles. Eventually the vellus follicles outnumber the terminal follicles which increases the baldness. Interestingly, a “completely bald” person is actually not hairless but instead they have accumulated many vellus follicles that produce fine hairs and remain in telogen for long periods.

Ross, Michael H., and Wojciech Pawlina. Histology a Text and Atlas. Wolters Kluwer/Lippincott Williams & Wilkins Health, 2015.