Structure of the Hair Flashcards
What are the three areas of the hair?
The shaft - lies above the skin but also runs through the surface of the hair.
The root - lies underneath the skin, inside the follicle
the bulb - large base at the bottom of the root and encase the dermal papilla. The matrix is the lower region of the bulb where the cells divide rapidly to produce the new hair and follicle structure.
What is the cuticle?
Protective outer layer of scale like keratinised cells with each scale overlapping another towards the tip of the hair. This layer contains no pigment, it is translucent and allows the colour to show from below.
What is the Cortex?
Main part of hair, contains elongated cells which are keratinised and cemented together. The pigment granules (melanin for black/brown and pheomelanin for red/yellow) are present here. How the cells are held together determines the strength, thickness and elasticity of the hair.
What is the medulla?
Middle, soft and spongy core of the hair. Contains large, loosely connected keratinised cells, which may or may not be continuous. this results in air spaces which determine the sheen and colour tones by influencing the reflection of light. The medulla is often not present in fine terminal and vellus hairs
What is the hair follicle?
An indentation of the epidermis with the walls of the follicle being formed from a continuation of the cellular layer of the skins surface. It has three sheaths.
Describe the inner root sheath
Layer closest to the hair and has scale like cells that interlock with the cuticle to hold the hair firmly in place. The hair and the inner root sheath grow upwards together. .
What are the three layers of the inner root sheath called?
Cuticle of inner root sheath, henle’s layer and huxley’s layer.
What is the outer root sheath?
follicle wall, it does not grow upwards but remains stationary in one place.
What is the connective tissue sheath?
Surrounds the rest of the follicle and the sebaceous gland. An extension of the papillary layer of the dermis and provides a sensory nerve and blood supply
Three stages of hair growth
Anagen - active
Catogen - changing
Telogen - tired (resting)
What is anagen?
Active phase of growth hair is receiving nourishment in the form of food and oxygen from the blood supply via the dermal papilla. The hair cells divide by mitosis in the matrix to produce a new hair. This hair grows upwards and outwards and eventually out of the skins surface. For successful electrical epilation the hair needs to be treated at this stage. A terminal hair removed at this stage will have a dark bulb and an inner root sheath which is like a jelly coating.
What is catagen?
changing/transitional stage. Dermal papilla separates from the hair but still receives a small amount of nourishment from the follicle walls. During this stage the follicle shrinks by a third and no mitosis occurs in the matrix. The dermal cord forms at this stage. The hair gradually becomes drier and starts to lose its colour pigment as it continues to move upwards to just below the sebaceous gland where it will easily fall out.
Hair removed at this point is limp with a straggly end
what is telogen?
Resting phase, dead hair lies in follicle waiting to fall out or for new hair to push it out. Receives no nourishment. the follicle rests until it is stimulated by hormones to return to anagen phase.
Hair removed at this stage will have a straggly brush like end club ended.
What is lanugo hair?
found on unborn baby and first result of cellular activity within the skin. This is usually discarded before or soon after birth and replaced by slightly coarser hair.
What is vellus hair?
Soft downy hair found on the cheeks and all over the body. Usually lacking in pigmentation and grow from a shallow depth at about sebaceous level. These hairs rarely grow longer than 2cm in length and are usually straight due to the fact that they have shallow follicles. They don’t become terminal unless they are stimulated by a topical systemic cause. If this occurred they would then start to grow deeper developing a bulb pick up a blood supply from the dermis and become a shallow terminal hair.
