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Hair Anatomy Hair Structure

What is the Hair Anatomy and Physiology

Hair Anatomy – A hair follicle is a mammalian skin organ that produces hair Found below the skin, the hair root is contained in a tube like structure called the hair follicle. New cells are created in the hair root. As they enlarge and divide, they are pushed up and out, causing visible hair growth. The human hair follicle is an intriguing structure.

Hair is a complicated structure that comprises of the root (or follicle) and the shaft (the visible part of hair). The root is enclosed in the hair follicle, submerges into the skin in inclination and ends down to the bulb.

At the base of hair follicles lie dermal papilla cells, biological structures that are very important to the follicle, as they bear capillary vessels which send nutritive elements from blood to cells.

In dermal papilla also lie the androgens receptors and the fibroblasts, which have an active role in the hair growth cycle.

The hair follicle can be divided into 3 regions

The lower segment (bulb and suprabulb)

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 (isthmus)

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 (infundibulum)

The upper segment extends from the entrance of the sebaceous gland duct to the follicular orifice.

The Hair Shaft

Each strand of hair has two main components: the hair shaft and the root. The shaft is formed from the old cells that are pushed out as a result of new cell growth in the root.

Shaft is the visible dead part of hair and consists of 3 layers

The Cuticle

The cuticle, which consists of colorless, flat overlapping cells. Forming the outer layer, the cuticle is made up of hard, transparent cells that overlap each other like the scales of a fish. General hair condition is largely determined by the condition of the cuticle, since it is the layer giving elasticity and resiliency to the hair.

The Cortex

The cortex, which contains pigment (melanin) that defines hair color. The cortex defines hair texture (straight, curly etc), includes keratin and is responsible for the shaft growth. Forming the middle layer, the cortex is protected by the cuticle and consists of rope-like protein fibres. If the cuticle is damaged, the cortex becomes exposed, allowing for moisture loss. When this happens the cortex unravels, causing split ends and damaged hair.

The Medulla or the core

Τhe medulla, the ‘’heart’’ of the shaft, usually found in hairs of big diameter. Medulla is the supporting structure for a strand of hair. It is interesting to note that the medulla can be absent or interrupted without weakening the hair strand

In the human scalp, the anagen phase lasts approximately 3-4 years, while the catagen phase lasts about 2-3 weeks, and the telogen phase lasts approximately 3 months. Approximately 84% of scalp hairs are in the anagen phase, 1-2% are in the catagen phase, and 10-15% are in the telogen phase.

The Life Cycle of Hair

Anagen or growth phase

The anagen phase is the phase of active growth. This is a period of very rapid keratin (protein) production. The average rate of human hair growth is about 1/100 of an inch per day.

Catagen or transitional phase

The catagen phase marks follicular regression,This period lasts only a few weeks during which the follicle winds down its rapid metabolism, shrinks, wrinkles and contracts. At this point, it finally stops producing keratin.

Telegon or resting phase

The telogen phase represents a resting period. Occurs when the follicle stops shrinking. This period usually lasts from 3-4 months. During this time, the hair rests in the follicle until it is physically dislodged by brushing, washing, combing, or massaging. When a hair reaches the end of its life, it falls out and is replaced by a new hair which grows in the same follicle as the old one.

In the human scalp, the anagen phase lasts approximately 3-4 years, while the catagen phase lasts about 2-3 weeks, and the telogen phase lasts approximately 3 months. Approximately 84% of scalp hairs are in the anagen phase, 1-2% are in the catagen phase, and 10-15% are in the telogen phase.

Hair Physiology

The different layers of the visible part of hair (shaft) are due to the alterations in the morphology and structure of matrix cells of the bulb. In the matrix cells takes place protein synthesis -especially Keratin synthesis- which contributes to the strength and endurance of the hair shaft and to nail configuration as well. Keratin also lies in the skin. Keratin is a group of proteins that contain sulphur and is being produced in the keratogen zone of the root.

Hair consists of…

  • proteins (65% – 95%),
  • lipids(1% – 9%),
  • trace elements,
  • polysaccharides
  • water.

Hair grows at different rates in different people; the average rate is around one-half inch per month. Hair color is created by pigment cells producing melanin in the hair follicle. With aging, pigment cells die, and hair turns gray.