A 24 year old male undergoes surgery due
to a painless swelling in the base of the neck.
During the operation, a superficial 1.0x0.8 cm mass
surrounded by a well-defined fibrous capsule is excised
and sent for histological evaluation which
reveals this tissue to be an ectopic gland tissue.
The slide below depicts one
of the examined specimens.
Which gland does this tissue below belong to?
Answer choice (A) - thyroid gland
Answer choice (B) - parotid gland
Answer choice (C) - sublingual gland
and answer choice (D) - adrenal gland
Now take a moment to come to the answer by
yourself before we go through it together.
Okay, let's jump right in to this question.
First thing we need to determine is
what category of question this is.
And this is a histology question.
They're showing us a histological slide so classically, we
have to be able to interpret the slide to its histology.
Now this is a 2-step question.
The first thing we have to do is be able to interpret
what we're looking at here in our histological slide
and then be able to answer the specific question which
in this case is, 'which gland does this tissue belong to?'
And in this case of course,
the stem is required.
It is a complex question, we have to know what
they're asking according to this histological image.
So let's walk through
this question together.
Step 1 in determining this question is, we need
to determine what type of tissue we are looking at.
Now as we can see in our image,
the histology slide shows secretory cells arranged
in acini and we see the presence of ducts.
So looking at our image, look at the left side where there is
the lighter pink color, we see two circles which are ducts.
And then you see all these secretory acini close to each other,
all these little acini making a circle and if you imagine,
we are taking a sagittal cut through the ducts, which is how
you are seeing it here on end - these nice little circles.
And you can see one on the left
side, at the 12 o' clock position,
also a nice circle of secretory cells
arranged in acini which are ducts.
So here on the left side, we definitely
see the presence of two separate ducts.
Now, really important
high-yield point here.
DO NOT have ducts.
An endocrine gland simply secretes
directly into the bloodstream.
So here, we see two ducts and we can say wow,
if I'm seeing ducts- not an endocrine gland.
That really helps me with my
finding the right answer.
And what this tells me is, the tissue I'm looking at here,
simply by just looking at the left side of the image
right through these two ducts at the
12 o' clock and 9 o' clock positions,
that I'm looking at an exocrine gland because exocrine
glands have ducts where they release their contents,
while endocrine glands do not have ducts and
they secrete directly into the bloodstream.
So that's the first thing I know is,
okay I'm looking at an exocrine gland.
Now step 2- I need to figure out what tissue actually
does originate to produce this histology slide .
Now as we can see, now look at the right side of the image
that there's acini and it shows numerous basophilic granules.
Now this is typical of a
serous secretory cells.
Now if you look at the slide here, we
actually don't have any mucus cells.
So if we look at our answer choices, the
first thing we are going to be looking at
is an exocrine gland with solely serous
cells and that's the parotid gland.
So the answer choice here
is answer choice (B).
Now let's look at our other ones
to figure out why they're wrong.
well the sublingual gland consists of a
mixture of both serous and mucus cells.
well since we don't see any mucus cells and we're
only seeing serous, it cannot be sublingual gland.
and if we look at our other two answer choices
- the thyroid and the adrenal glands,
we know that these are both very traditional endocrine
glands and they secrete directly into the bloodstream
and do not have ducts so
it cannot be those either.
Now a few high yield points regarding both the thyroid and the
adrenal glands if they were to show you a histology slide,
the thyroid will have follicles with a single layer
of either cuboid or low columnar epithelium.
Those are high-yield points to look for.
And then the adrenal gland if they wiere to show
you the cortex - that's the adrenal component,
excuse me that's the actual endocrine
component of the adrenal gland,
we're gonna be looking for three zones - the
glomerulosa, the fasciculata and the reticularis
and separately you
will see the medulla.
Now in conclusion for this
question, let's think about it.
The histology slide is showing us
ectopic tissue, hence the ducts
and we're seeing parotid gland because we
only see the serous and no mucus cells.
So thus the correct answer is answer
choice (B) - the parotid gland.
now let's review some high-yield facts
regarding the histology of the parotid gland.
Now, the parotid glands are largely
salivary glands in humans.
They secrete through the parotid duct into the
mouth which we saw in our histology slide.
And now on histological examination, the parotid gland
shows a capsule made of dense connective tissue,
striated ducts lined in simple columnar epithelium
and intercalated ducts lined with cuboidal epithelium.
Now, the parotid gland also
shows an abundance of fat.
Now you don't see it there in the image so don't panic but
you actually get more fat in the parotid gland with age.
And the parotid gland only contain serous
acini while the other salivary glands,
the sublingual and the submandibular glands
contain both serous and mucinous acini.
This is very high yield to help you determine
what type of gland tissue you're looking at.
Now since the question had mentioned sublingual glands,
let's discuss the histology of the sublingual glands.
Now, sublingual glands are the smallest
major salivary glands in humans.
They are the only salivary glands
that are not encapsulated.
And on histological examination, the sublingual
glands stain much less than do parotid glands
due to the relatively small uptake of
stain by their abundant mucinous acini.