So let's talk a little bit about some
of the accessory structures of the skin.
The hair is found all over the body.
And the only place you don't find hair is on the
palms of your hands and the soles of your feet.
The hair is composed of
dead keratinized epidermal cells
very similar to the stratum
corneum layer of the epidermis
And there are lots of different
influences that determine the thickness
and the distribution of our hair including
genetic influences and hormonal influences.
There are multiple parts of the hair.
The part that you see or the part that is above
the skin surface is referred to as the hair shaft.
Below the level of the
skin, you have the hair root.
The hair root is surrounded by the
structure known as the hair follicle.
The hair follicle itself is made
of two sheaths or coverings.
The first sheath, the epithelial root
sheath is an extension of the epidermis.
The dermal root sheath is the part of the
dermis that is going to surround the follicle.
Also on the hair, you have three major
structures that are very important for hair growth.
You have the hair bulb which is shaped
like an onion or like the bulb at the hair root.
The second structure in this
bulb is going to be the hair matrix.
The hair matrix is actually
dervived from the same cells
that make up the stratum
basale in the epidermis
and therefore consist of
growing cells or stem cells
So it is this part of the hair
that is responsible for hair growth.
Hair growth cannot occur
without the presence of nutrients
and so we need a way to get blood toward
the bottom of the hair or the root of the hair
so that the hair can grow.
And for this, we have the hair papillae.
This is an indentation
in the bulb of the hair
where the blood vessels are able
to come in and nourish the matrix
so that your hair is able to grow.
Speaking of hair growth, our
hair actually grows in stages.
So starting with the growth stage, hair
from the matrix is going to start to grow
from that matrix out toward
the surface of the skin.
Ultimately over time, the regression
stage occurs where the matrix stops dividing
and the hair follicle begins to atrophy.
After this stage, there's a
stage of rest or a period of rest
where the follicle is not active at all.
Shortly after this, the growth
stage is going to begin again
and the hair matrix is
going to be reactivated
This new hair is going to then push the resting
hair out of the way as a new strand of hair grows.
Interestingly, all of the hair all over
your head is in different points of this cycle
and that is a good thing because if it
wasn't that way, then what we would do
is our hair would grow then it would
fall out and then new hair will grow
so we will go through periods of
having hair and then going bald.
But fortunately, that's not the
way it is but at any given point,
multiple hair follicles are going through
one of these stages of hair growth.
So along with the different stages of
hair there's also different types of hair.
First, in the fetus, you have lanugo.
Lanugo is a type of a very
fine pigmentless layer of hair
on the fetus and is also
present just as the baby is born.
Terminal hair is probably the
hair that you think most about
as that's the kind of hair
that you find on your head.
Covering the remainder
of your body is vellus hair.
Vellus hair are the short, fine pale hairs
found all over all of the surfaces of your skin
minus the areas where you have thick skin such as
the palms of your hands and the soles of your feet.
The interesting thing about vellus hair
is, it is actually in the place of lanugo hair
so it replaces lanugo hair as you grow.
Just like our skin, our
hair is also pigmented.
And just like our skin, the pigment that
is responsible for hair color is melanin.
There are two types of
melanin that are found in hair.
For people who have dark har,
they have an abundance of eumelanin
which is the black or brownish pigment.
For those who have more blonde hair or red
hair, they have an abundance of pheomelanin
which gives off this reddish-brownish colour
As you age, you start to decrease
the production of melanin in your hair
and that is when your hair
begins to turn grey, like mine.
And then finally, when you have
white hair, this is due to a lack of melanin
as well as the presence of
air bubbles in the hair shaft.
Located in the dermis of the skin, you
have several different types of glands.
First, you have the sebaceous or oil glands
which are glands that are directly connected
to the hair follicles in the dermis.
You then have two different
types of sweat glands.
There are eccrine sweat glands, which are
the most numerous and found all over the body
and are not associated
with a hair follicle.
And then you have the apocrine sweat
glands which are associated with hair follicles.
Finally, in the ears, you have a modified
sweat gland known as a ceruminous glands.
Ceruminous glands produce
cerumen or what we refer to as earwax.