all right all this is dr. Alsup and we are going to discuss our first two glands of this course
which are going to be the thyroid and parathyroid glands I'm super excited so let's get started so
our major learning objectives for this lecture video will be to understand where the thyroid
and parathyroid glands are located whew I made a fancy design there parathyroid glands are located
also we're going to understand the functions of these glands so these are endocrine glands
we'll understand what that means and like most endocrine glands the thyroid and parathyroid
glands have a very robust vascular supply so we will talk about which arteries will be the supply
and what veins will drain all right so when one reflects the sternothyroid muscle you will see the
very large thyroid gland just deep to this muscle it is located approximately between the c5 and T1
vertebral levels and the thyroid gland is often described as butterfly shape so you'll have these
two lobes right here and here and one is gonna be underneath this muscle the sternothyroid and
these will be connected by a central isthmus the thyroid gland is the largest endocrine gland so
what even is an endocrine gland well it's not an exocrine gland and we will talk about some
of those in more detail when we're discussing the salivary glands endocrine glands are ductless all
right so ductless no ducts associated with these and also importantly they will secrete hormones
they're gonna secrete hormones towards the blood and we'll talk we'll talk a little bit more about
that in a moment the hormones released by the thyroid gland will affect most areas of the body
these hormones are the thyroid hormone which will play a role in terms of controlling the rate of
metabolism and calcitonin which controls calcium levels and calcium is very important in terms of
strength of bone but it's also really important in terms of muscle contraction and so the calcitonin
will reduce blood calcium levels if they are too high so it will reduce blood calcium levels all
right let's talk about the vascular supply the thyroid gland is highly vascularized by two main
arteries the first will be the superior thyroid artery which is typically that first branch of
the external carotid artery the inferior thyroid artery supplies the more inferior portions of the
gland as its name would suggest and is a branch of the thyrocervical trunk which is off of the first
part of the subclavian artery and we'll talk more about those divisions of the subclavian artery
in the next session the inferior thyroid artery has a very close relationship with the recurrent
laryngeal nerve and this relationship brings up a really good question why do we keep asking you to
learn these anatomical relationships why does this matter let's use this relationship as an example
note how close here as you can see in this kind of close-up of this region how close the inferior
thyroid artery is to the recurrent laryngeal nerve so if you're performing a thyroidectomy or a
removal of a portion of the thyroid gland one has to really watch where the inferior thyroid artery
is ligated or tied off or closed off for surgery because it's a recurrent laryngeal nerve which
is really close it's also is injured during this process this has tremendous implications in the
function of the larynx because recurrent laryngeal nerve innervates all intrinsic laryngeal muscles
except the cricothyroid it also provides afferent supply inferior to the vocal bones
so anatomic relationships often have important clinical implications and this one is just many
one of the many reasons we have you focus on these relationships much all right unlike how there are
two main arteries that supply the thyroid gland there are three sets of veins that drain the
thyroid the superior thyroid vein which is going to usually accompany fairly close with a superior
thyroid artery will drain the more superior areas and it will drain blood directly to the internal
jugular vein typically the middle thyroid vein it's also going to drain into the internal jugular
vein and it has a generally close relationship to the inferior thyroid artery even though it's not
quite as close as what we have with the superior's here the inferior thyroid vein which you can see
kind of heading up in this region with numerous tributaries it's kind of a loner it doesn't have
a close relationship with either the superior or inferior thyroid artery this vein is usually
the largest and will typically drain into the left brachiocephalic vein although it could also
drain into the right brachiocephalic vein so it's not uncommon for it to drain to the right but the
more typical pattern is to drain into the left so it's kind of right in this middle portion right
here I kind of heading towards the isthmus region but you can have tributaries all over this region
when performing a thyroidectomy the posterior part of the thyroid gland is preserved and
possible this will help of course in protecting the important area of vasculature but also it
will preserve and protect the parathyroid glands that are typically located just in the posterior
portion of the thyroid gland it often looks like these are actually embedded within the thyroid
gland but these are very separate glands with separate functions so you can kind of see those
here in this image the parathyroid glands are also endocrine glands these produce or secrete
parathyroid hormones which you often hear referred to as PTH and this is also important in terms of
calcium homeostasis along with other ions like phosphates so calcium is big here as well and it
will actually increase blood calcium levels which is the opposite function of calcitonin if you
recall it's most typical to have four parathyroid glands like you see here a superior pair in an
inferior pair there can certainly be more or less but the superior pair is typically the most
constant in position the parathyroid glands may be supplied by either thyroid artery as determined
by location but typically the inferior thyroid artery is the dominant supply for the parathyroids
now in about 10% of people there is a small unpaired artery that runs kind of write down
this midline region associated with the trachea here and it's branching from the
brachiocephalic trunk the possible presence of this artery must be considered when performing
procedures in that midline region of the neck so a thyroidectomy is a certain case that where
you need to be aware if you're working around this region or a tracheostomy because you can
see the trachea right here occasionally there can be at normal abnormal growth of the thyroid
gland which is referred to as a goiter quarters result most typically from a lack of iodine or
less frequently due to an autoimmune disease some of these are named here don't get you don't have
to memorize these specific ones just there here for example or to kind of clarify that
just looking at this image you can really see how a goiter can potentially compress deeper
structures or structures that are more lateral than where the thyroid gland typically extends
to so that could obstruct blood flow or cause other issues all right so let's think through a
question together okay so that thyroid ima artery that we just spoke about that's present in about
ten percent of people so if there's a thyroid ima artery yeah it is likely to have a close
relationship to which vein is it the inferior thyroid vein the middle thyroid vein or this C.
superior thyroid vein this one is a little in the trickier side we didn't talk through this
relationship but you really have to kind of rely and think about the location of where the
thyroid ima is and where these veins would be so which ones are in a relatively similar area
okay so the correct answer is A. the inferior thyroid vein which is that independent one that
typically drains into the left brachiocephalic vein or sometimes the right brachiocephalic
vein but it's kind of right in that midline region which is where the thyroid ima would be located as
well if present the middle thyroid vein is more closely related to the inferior thyroid artery
not the vein while the superior thyroid vein is near the similarly named superior thyroid artery
alright so those are the thyroid and parathyroid glands make sure you understand the vascular
supplies and the venous drainage as they are closely related to other structures of the neck
thank you for all your time and attention during these videos and I hope you have an amazing day