Overview and Understanding Hair and Hair Growth

Hair is a complex structure and has important both socially and functionally. It not only plays a vital role in the appearance of both men and women but also helps to transmit sensory information.

Embryology of hair

By week 22 of the developing fetus the hair follicles have formed. By the second trimester of life there are approximately 5 million hair follicles on the fetuses body, with approximately one million follicles on the head, with about one hundred thousand of those follicles located on the scalp.
This is the largest total number of hair follicles a human will ever have. Specifically we do not generate, reproduce or create any new hair follicles anytime during the course of our lives.

HAIR STRUCTURE

Hair has two distinct structures and several associated structures:
– the follicle which is found within the skin and is a tubular like segment surrounded by the most superficial part of the skin: the epidermis lines tubular tunnel down into the dermis. The hair follicle contains several layers that all have separate functions.
1) At the base of the follicle is the papilla, which contain small blood vessels called capillaries that nourish the cells. In addition a plexus of nerves .
2) The hair bulb forms the base of the hair follicle. In the hair bulb, living cells divide and grow to build the hair shaft. Blood vessels nourish the cells in the hair bulb, and deliver hormones that modify hair growth and structure at different times of life. The bulb is the living part of the hair and is located at the very bottom of the follicle surrounded by the papilla. The cells of the bulb divide every 23 to 72 hours, remarkably faster than any other cell in the body.
-the shaft -which is what is visible above the scalp contains two sheaths, an inner and outer sheath, surround the follicle. These structures protect and form the growing hair shaft.
-The inner sheath follows the hair shaft and ends below the opening of a sebaceous (oil) gland, and sometimes an apocrine (scent) gland.
-The outer sheath continues all the way up to the gland. A muscle called an erector pili muscle attaches below the gland to a fibrous layer around the outer sheath. When this muscle contracts, it causes the hair to stand up which also causes the sebaceous gland to secrete oil.

ASSOCIATED GLANDS OF THE HAIR UNIT

The sebaceous gland and oil glands, which are located toward the top of the cutaneous portion of the hair shaft is vital component of the hair unit because it produces sebum and oils , which conditions and moisturizes the hair and skin. After puberty our body produces more oils and sebum but as we age we gradually make less sebum and oils. Women as they age and usually have less sebum and oil production.

ASSOCIATED HAIR MUSCLES OF THE HAIR UNIT

The arrector pili muscle is a tiny thin muscle that attaches at the base of the hair follicle and dermal tissue. When the arrector pili muscles contracts it causes the hair shaft to “stand up straight”.

ASSOCIATED HAIR NERVES OF THE HAIR UNIT

Around each hair a network or a plexus of nerve endings that surround each and separate hair follicle. Each nerve is a “receptor”, which means it can send and receive a nerve impulses to and from the brain when the hair moves. These nerves convey the touch sensation.

HAIR COMPOSITION

Hair is composed of a durable and hard protein called keratin and is made in three layers. This layer of protein is actually dead, so the hair that you see is not a living structure.
-The inner layer is called the medulla.
-The second layer is the cortex and makes up the majority of the hair shaft
-The outer layer is the cuticle and is a tightly formed structure resembling shingles.

HAIR GROWTH CYCLES

Hair on the body grows at different rates. On average on the scalp hair growth is 1/32 of a inch per day or about 6 inches per year. Unlike other mammals, human hair growth and shedding is a random event and is not seasonal. At any given time, a random number of hairs will be in one of three cycles/phases of growth, resting and shedding: anagen, catagen, and telogen.

Hair growth occurs in overlapping cycles consisting of three phases:

Anagen (growth phase):
Most hair is growing at this cycle time and is the active phase of the hair growth. The cells in the hair bulb are dividing rapidly. Also any new hair that is formed and pushes the old hair (a hair that has stopped growing or is no longer in the anagen phase) up the follicle and eventually sheds it. 
During this phase the average hair grows is about 1/2 inch every month. Scalp hair often stay in this anagen phase of growth for two to six years.
Interesting the length of hair is proportional to the length of time the hair is in the anagen phase. Thus people with very long hair have a long active phase of growth. In contrast hair on the eyelashes, arms, legs and eyebrows have a shorter active growth phase of about 30 to 45 days. Thus explaining why we have different length of hair with the scalp hair having the longest length.

Catagen (transitional phase):
During this phase, hair growth slows and the hair follicle shrinks. The catagen phase is a transitional stage and about 2-5% of all hairs are in this phase at any time. This phase lasts on average two to three weekgrowth stops, the outer root sheath shrinks and attaches to the root of the hair. This is the formation of what is known as a club hair.

Telogen (resting phase):
During this phase hair growth continues to markedly slows and then stops. The hair follicle is at rest. During this phase hair shaft detaches from the hair follicle. A new hair begins the anagen growth phase then pushes the old hair out. This phase lasts for about 100 days for hairs on the scalp and longer for hairs on the eyebrow, eyelash, arm, and leg. Approximately 25 to 100 telogen hairs are shed normally each day.

HAIR GROWTH RATES

As in skin color and height, likewise hair grows at different rates in different people and in different parts of the body. However the average hair growth length is approximately one-half inch per month.

HAIR COLOR
Hair color is created by melanin cells producing pigment in the hair follicle . It is both the cortex and the medulla of the hair that retains the hair’s pigment, giving it its color.
With aging, trauma, or stress the melanin producing pigment cells die, and thus hair turns lighter from gray to absence of pigment: white.

HAIR DENSITY
Hair density is genetic ie, it is a inherited factor.
In general most individuals will notice that the density of scalp hair is reduced as they grow from childhood to adulthood. One reason: Our skull continues grow in infancy through child hood and into adulthood thus hairs per square inch lessen.
While later into life preprogrammed genetic and hormonal influence come in to play.

SUMMARY

The hair unit consists is a complex structure with a combination living and non living components.
Hairs not only provide beauty, emanates vitality, have different thickness/density and color. In particular the scalp hair life cycle is often governed by pre programmed genetics that only be modestly and non permanently manipulated. The only permanent solution for hair restoration is by hair transplantation.

COSTS AND FEES

The fees are based on the anesthesia used (local vs sedation or general anesthesia), the facility (minor surgical suite, outpatient operating room or hospital setting) and if combined with other procedures. All pre and post operative care is included. Some preoperative laboratory analysis may be required (usually covered by your medical insurance).

CONCLUSIONS

The most important factor to consider is seeking the opinion and services of a skilled, experienced and Board Certified Plastic Surgeon who are experts in
automated follicular extraction (FUE) and translation techniques. The Imagine Plastic Surgery team uniquely provides not only a track record of success based on the full array of both non surgical and surgical alternatives and hair rejuvenation thus filling our motto of “One Goal, Many Options”. For more information, call and schedule a consultation.

Since 2003 the Staff of Imagine Plastic Surgery has provided comprehensive Cosmetic Plastic Surgery services and procedures for the many communities of the greater Inland Empire, California including but limited to Riverside, Redlands, Rancho Cucamonga, Ontario, Corona, Upland, Chino Hills, Temecula, Murrieta, Clairemont, the High Desert Cities of Victorville and Apple Valley.

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