The Origin
of Hair

Topic 1: Structures of
the Hair

Topic 1 Activity

Topic 1 Summary

Topic 2: The Layers of the Hair

Topic 2 Activities

Topic 2 Summary

Topic 3: Chemical Composition of Hair

Topic 3 Activities

Topic 3 Summary

Module Assessment

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Topic 1: Structures of the Hair

Formation of the Hair Bulb
While a baby is a fetus, the hair follicle is formed in the upper layer of the skin from a cluster of cells. These cells are called the primitive hair germ. Primitive hair germ cells get their nourishment by working their way down into the dermal layer of the skin. This cluster of cells creates a follicle as they pull the upper layer down in their search for nourishment, thereby creating a pocket known as the root sheath. Out of this sheath the hair will grow. Hair grows from stem cells. These cells grow directly under the oil (sebaceous) glands. As the cells continue to grow, the nucleus of the cells disappears and the cells become keratinized.

What Gives Hair its Shape 
The shape of the hair shaft is determined by the shape of the hair follicle. People with straight or wavy hair have typically round or oval shaped hair follicles. The hair follicle of hair that is curly or overly curly is elliptical in shape.

Structures of the Hair

Sebaceous Glands
Other changes take place in the hair follicle. Small, sac-like glands appear on the upper part of the follicle. One of the glands is the sebaceous gland. The function of these glands is to produce a substance called sebum. This substance is secreted into the hair follicle to lubricate and condition the hair and the skin. Sebum is a mixture of fats, proteins, cholesterol, alcohol and salts. When sebum mixes with the perspiration on your skin, it forms what is called the "acid mantle". This acid mantle is what protects your skin from bacteria and infections.

Arrector Pili Muscle
Just below the sebaceous gland, in the follicle is the arrector pili muscle. This is the muscle that causes you to have "goose bumps" or causes your hair to stand on end when you are cold or scared.

Dermal Papilla
A small cone-shaped elevation is located at the base of the hair follicle. This is the dermal papilla. The dermal papilla fits into the hair bulb and contains the blood and nerve supply, which nourish the cells around the hair bulb for growth. These cells are the germinal matrix cells. The germinal matrix area is where mitosis takes place and produces the keratin, which forms the three layers of the hair.

Growth Cycles of the Hair
Hair, like most living things goes through  cycles of growth. Hair goes through three cycles which are repeated over and over. The three cycles are the anagen, catagen and telogen phase. The gowth phase of hair is known as the anagen phase. In this stage  the stem cells manufacture new keratinized cells and the hair grows faster than any other time. This stage lasts about four years. In the catagen phase of growth the follice goes through many changes. During this stage, the follicle canal shrinks,the hair bulb disappears and the hair root becomes rounded.  The melanocytes stop producing color pigments and the dermal papilla shrinks. During this phase the follicle is preparing for new growth. This stage lasts from two to three weeks. The resting stage of hair growth is called the telogen phase. It is during this stage that the old hair shaft is shed. Often the hair bulb is still anchored to the follicle walls. When this happens the hair remains in place until the anagen stage and then it is pushed out. This resting phase last for approximately one hundred days. The cycle repeats itself over and over every four to five years.

Glossary of Terms

Arrector Pili Muscle - small involuntary muscle fibers in the skin attached to the base of the hair follicle.

Dermal Papilla - an elevation of the projecting corium into the overlying epidermis.

Follicle - a small secretory cavity or sac; the depression in the skin containing the hair root.

Germinal matrix - an area of reproducing cells situated around the papilla at the base of the hair bulb.

Hair bulb - the lower extremity of the hair.

Sebaceous glands - oil glands of the skin connected to hair follicles