Next up, we're gonna talk about alopecia,
or colloquially known as "hair loss"
First off, before we start talking about the
different things that can cause hair loss,
we should discuss the life cycle of a hair
follicle which is depicted here in the schematic.
This is basically a hair follicle from womb
to tomb, starting with the Anagen phase.
Seen here in this little block of scalp
is a hair bulb, the hair follicle itslef
and then a derma papillae which it's attached to,
which is the growing zone for hair follicle.
So the anagen phase is a period
of growth for hair follicle
and it essentially dictates how long a
hair on a particular area is going to be.
On the scalp, this phase coul be in the
order of many years or even decades.
Whereas this phase is fairly
short on the eyebrows,
which is why we don't have
to comb our eyebrows.
The anagen phase then transitions to a
Catagen phase, which is a fairly brief phase.
It ultimately leads to the Telogen phase.
And all we can see is that the hair follicle is slowly
separating from the dermal pappillae and ceasing its growth.
The telogen phase is a potentially prolonged
phase of rest for the hair follicle.
The hairs may not grow for long periods of time but ultimately
will be shed in a phase called exogen - not shown here.
So everyday about 50-100 telogen
phase hair shafts are gonna be shed
and replaced by 50-100 brand
new anagen phase hair shafts.
A simple test to try and determine whether or not there's
a pathologic amount of hair cells in the telogen phase
is called the Hair Pull test.
As you might imagine, since those hair follicles are fairly
uprooted and no longer connected to the dermal papillae,
If you tug on certain hair cells, if a large
proportion of them are in the telogen phase,
you're gonna tug a lot of
hairs out all at once.
Whereas for normal hairs, normal scalp tissue, when you
pull on the hairs, only a few - probably less than 3
would come out by pulling on a
small grouping of hair follicles.