- Hey, y'all.
My name is Prashanth Kumar or PK.
I'm MCAT tutor at Shemmassian Academic Consulting.
Today, we're gonna be doing an MCAT bio passage walkthrough.
So you can see exactly what's going on in my head
as I take on this section.
You should be taken roughly six and a half minutes
on each of these passages,
but we're be going more in depth today,
so you can see exactly what tips, what strategies
and what's going on as I take on this section.
Let's get it.
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All right.
So I've gone ahead and put the passage on the left
and the questions on the right.
So feel free to take a moment and pause the video
and come back to us.
If not, let's get right into it.
First, let's talk strategy.
We need to have a game plan going into any passage.
Regardless of whether it's easy or hard,
this should be something we come to
at the beginning of any passage as we started.
For me, that's reading the paragraph,
writing three to five word summary,
asking myself what's going on,
and then going onto the next paragraph.
Doing this gives me a quick check-in at each paragraph end
and make sure I'm reading for content, not just words.
Often find myself reading all the way
'til the end of the passage,
and then having to stop
and come back to read all over again.
This is a huge time drain on the MCAT.
So let's get right into and start practicing this.
So the first thing is the pituitary gland worked closely
with the hypothalamus to regulate homeostasis, metabolism,
reproduction and growth in multiple target organs.
The pituitary gland is separated into adenohypophysis
and neurohypophysis
known as the anterior and posterior lobes, respectively.
The anterior pituitary secretes five distinct types
of hormones.
Somatotrophs HGH, lactotrophs PRL or prolactin,
thyrotrophs TSH, corticotrophs ACTH,
and gonadotropes FSH and LH.
So the question I continuously ask myself
is what's happening.
For me, that's just anterior pituitary
releases five hormones.
So quick three to five word summary, nothing too in depth.
We just wanna have this as like a roadmap,
making sure we understand.
We're not worried about details here.
Let's go on to the next paragraph.
Pituitary organogenesis and hormone synthesis
is a complex process does not completely understood.
Many different transcription factors
are temporally and spatially regulated.
Pit-1, for example,
is required for pituitary cell differentiation
and the Pit-1 gene has been implicated in growth hormone,
TSH and prolactin deficiency.
So here we're asking same question.
What's happening?
Oftentimes, we struggle with this because it's complicated.
There's a lot of details.
So I like to use first sentence
as a sort of a topic sentence or a guiding sentence.
So it's just saying pituitary genesis equals complex, right?
That's all it's saying.
It gives us this detail about Pit-1 required
for cell differentiation and what hormones is involved in.
But here, I'm just gonna say, this is a roadmap.
So we're not focusing on the details.
Next in a recent study,
scientists have discovered a transcription factor, ZBTB20,
that could play a key role in anterior pituitary development
and lactotrope specification in mice.
ZBTB20 is a zinc finger protein
that contains BTB/POZ domains
and C2H2 Kruppel type zinc fingers.
So a lot of details right there.
We're not worried about it.
What is the main idea?
It's this.
I'll just write Z20 equals anterior pituitary development.
Okay.
So this is really how I write it, right?
It doesn't matter if anyone else understands it.
It doesn't have to be the most detailed thing.
I like to use simple words, abbreviations, symbols,
really makes me save time.
At the end of the day, if you understand it,
it doesn't really matter who else understands it.
All right, let's go on to the next one.
To further characterize the role of ZBTB20
in anterior pituitary development,
scientists performed a knockout experiment in mice.
ZBTB20 global knockout mice were bred
and their phenotypes characterized.
Hypopituitarism was found to be a result
of the ZBTB20 knockout.
For the results of this study are presented in figure one.
So here we have a study.
So what type of study is it?
It's a knockout experiment.
This results in what?
Hypopituitarism.
I'll just write hypopit.
But I'm just saying, when we knock this out,
we result in this deficiency.
All right, so next we have a figure.
I don't like to spend too much time on figures.
Maybe just focusing on the x-axis, the y-axis,
because that gives us an independent and dependent variable.
We see age and weeks and body weight.
So I'm not even gonna spend too much time on that
because we don't know what questions will be asked
if any about this.
So it doesn't make sense to spend too much time
on something we don't really know.
So let's go on to the next paragraph.
Research has followed the mice throughout their lifespan.
At postnatal day 21 or P21,
scientists performed ELISA experiments
to analyze anterior pituitary hormonal contents
in both wild type and knockout mice.
The results are presented in figure two.
Okay, so this is just experiment two
equals a P hormone contents.
Okay, so that's all I really worry about.
I'm not even gonna worry about the details again.
We see these graphs, this is an ELISA experiment,
so we should have something going on in our head,
but we're not gonna worry about it
until we get to the questions themselves.
All right, great.
So now we're ready to go right into questions.
So I'll start with question number one.
I'll put it right here.
Suppose a patient presents unregulated over-secretion
of thyrotropes from the anterior pituitary,
which of the following symptoms is this patient most likely
to experience?
All right, so right away,
I like to think about what exactly is the main like thing.
Over-secretion of thyrotropes, pretty important.
And then we're looking at like symptoms,
like what's exactly gonna happen?
So first, that requires us to understand
what thyrotropes are.
This was mentioned early in the first paragraph, right?
We see thyrotropes mentioned with TSH.
What is TSH?
Well, this should be something covered
in our content review.
Thyroid stimulating hormone.
So I'll write TSH equals thyroid stimulating hormone.
What does this do?
Well, this directly results in T3 and T4.
So these are very important hormones.
So we have to ask ourselves,
what does T3 and what does T4 do?
This is a question of understanding of a prior thing.
So what does it do?
Well, T3 and T4 are metabolism hormones.
If we have increased T3 and T4,
we expect to have higher levels of our basal metabolic rate.
So we're gonna write this results in increased metabolism.
Okay.
So now we have to look at our answer choices
and think, what does increase metabolism lead to?
Does it lead to weight loss?
That looks like a great answer.
So I'm gonna leave that for now, right?
Increased weight loss is a result of we're working out,
we're doing all this, right.
We'd expect weight loss if we have an increased metabolism.
Vasodilation of heart and lungs.
That doesn't really make sense
just from thyroid stimulating hormone
in an increased vasol rate.
Increase sex hormone levels.
That's not really you're associated with that.
That's more associated with sort of gonadotrope
and the gonadotrope.
So that's we're cross-out.
Gigantism.
Not really associated with this.
Probably, more growth hormone associated.
So we're gonna cross that out as well.
We're gonna stick with A, weight loss,
and already we're one for one.
Great work.
All right, so let's go onto question two.
Abnormal levels of which hormone most likely explains
the results shown in figure one?
A, ACTH.
B, prolactin.
C, TSH.
And D, HGH.
All right, so this is a question where it really tells us
where we have to go back to.
We have to go back to that figure, figure one, right?
So it says it right here.
So we're gonna go right here.
So we're looking for what's significantly different
between sort of this knockout mouse group
and this normal group.
So if we look at the passage itself,
it says hypopituitarism was found to be a result
of the ZBTB20 knockout.
So that's less hormones.
Hypo means less.
Less hormone secreted from the pituitary.
So we are seeing what?
Well, we have age and we have body weight.
Independent variable is age, dependent is body weight.
So we're seeing a significant change in weight
between the knockout group and the normal group.
The normal group sort of increases at this steady pace.
It follows this like upward path.
Whereas this knockout group sort of goes,
it increases a little bit and then flatlines, it plateaus.
So right away, we noticed that a very different pattern,
and this is supported by these stars.
What are these star show?
Statistical significance.
So right away, we realize, okay,
we are looking at statistically significant amounts
of weight difference between this knockout group
and this normal group.
So we're looking for hormones
that would be attribute to that.
Okay, and remember, this is hypopituitarism.
So we're gonna have a decrease in the amount
of hormone released, resulting in increased
oh, sorry, in decreased weight for knockout group.
Okay.
So decrease amount of this hormone from hypopituitarism
results in decreased weight.
So right away, let's start eliminating,
because that's always so super helpful too.
Prolactin is not associated with weight,
it's associated with milk production.
So we're gonna cross that out first.
Well, what is ACTH?
Adrenal corticotropin hormone is more related
to stress and cortisol levels.
So we're gonna cross that out as well.
So now we have HGH and TSH.
So we just talked about TSH,
but we're saying a decrease in amount of TSH
would result in what?
A decreased amount of TSH would result
in decreased T3 and T4,
which result in less basal metabolic rate,
which would be an increase in body weight, not a decrease.
So right away, we see decrease would result
in an increase in body weight.
So we can cross this out.
Whereas HGH, if we had a decrease
in the amount of human growth hormone available,
then we'd expect a decrease in body weight.
That's why D is our answer.
Really eliminating these first answer choices helps us get
to this one.
We might've been confused between TSH and HGH,
but using this and getting down to those answer choices
and then using the passage to help us guide us
really helps eliminate TSH, prolactin, and ACTH,
and leaves us with D.
Great.
We're two for two.
All right, let's go on to question three.
Which of the following hormones are secreted
by the neurohypophysis?
A, epinephrin.
B, oxytocin.
C, progesterone.
And D, aldosterone.
Alright, so this can be a scary word, neurohypophysis,
but we remember reading that somewhere
in the passage before.
So we're gonna go back just because we might not know
what that means on first.
So where is that?
Well, that's right in the first paragraph.
We have neurohypophysis known as the posterior lobe.
And then we have adenohypophysis, put it in green,
is known as the anterior,
but we don't really need that here.
So we're looking for hormones secreted by the posterior lobe
of the pituitary gland.
So posterior lobe.
So this is a super helpful time to focus on these hormones
because these two are very, very important.
The pituitary gland is one of the most important secretors
of hormones, and it's important to have an understanding
of what does what.
So posterior, we have to use oxytocin and vasopressin.
Those are the ones released.
Vasopressin is also called ADH.
So you might see that.
Anterior lobe, there's a very helpful mnemonic
called FLATPEG.
I won't go into it now,
but feel free to look up this mnemonic
in anterior pituitary gland on the Shemmassian website
and it'll come up.
But this is a very helpful mnemonic
to go through all of the anterior lobe hormones.
All right, so right away with this piece of information,
we don't even need to look back into the passage anymore.
We see oxytocin.
That is our hormone.
That's released from the posterior lobe of the pituitary.
But let's go through the other ones.
Where is epinephrin released from?
This is released from the adrenal gland,
specifically the adrenal medulla.
What about progesterone?
Well, progesterone is one secreted by the gonads.
Finally, whereas aldosterone,
well, aldosterone is also from the adrenal gland,
but it's from the cortex, not the medulla.
So right away, having this piece of information
are very important for the MCAT,
especially when you're dealing with what do hormones do,
where are they coming from.
Now, having this understanding, perfect.
So we are three for three.
Right onto question four, our final question.
Which of the following conclusions can be drawn
from figure two?
A, ZBTB20 knockout leads to decreased production
in all hormones from the anterior pituitary.
B, ZBTB20 knockout has little to no effect on mice.
C, ZBTB20 knockout, these is severe defect of lactotrophs.
D, ZBTB20 is necessary for anterior pituitary organogenesis.
All right.
So we have to look at figure two.
This is something directly stated by the question.
So we're going right back and we see five graphs.
This can be overwhelming at first,
but we really are trying to focus on what is happening
in the bigger picture
and use that to eliminate answer choices.
So let's just take a look.
On the x-axis, we have sort of this normal group
and this knockout group again.
I'm gonna put normal and knockout.
Plus, plus versus minus, minus.
We're looking on the y-axis and we have growth hormone.
PRL, TSH, ACTH, LH.
We have these hormones
and this amount released by the pituitary.
So this is what we're looking at.
We're looking at two different types of mice
and the hormones they release.
So having this big picture understanding allows us
to understand what is going on.
What is the difference between these two mice?
Is there a difference?
So usually, I love to just look for stars.
That's the first thing I like to do.
Stargazing, basically.
We're looking for that statistical significance.
That automatically can show that there is differences
happening between this knockout and normal groups.
So right away, we can eliminate B, right?
Little to no effect on mice.
There are significant differences
between this normal, knockout group.
So we leave that.
But is there significance in these three choices?
No, we don't see stars.
We can only say something's happening
if there's statistical significant evidence for that.
So we can eliminate answer choice A,
because answer choice A says,
oh, it's decreased production for all hormones.
That's not true.
TSH, LH, and ACTH all show that there's no increase.
So now we're left with this ZBTB20 knockout
ELISA severe defect of lactotrophs.
ZBTB20 is necessary for anterior pituitary organogenesis.
So again, we're using these words like lactotrophs.
Lactotrophs, when did it say up here, right?
It is PRL or prolactin.
So we're specifically looking at the prolactin column.
Okay, great.
So we are looking for prolactin and that's right here.
We see there is a significant decrease
in the amount of PRL compared to our normal
or control group.
So C has support for its answer.
So we're gonna circle that.
Let's just check D too.
ZBTB20 is necessary for anterior pituitary organogenesis.
Is this true?
Well, this isn't exactly true.
As the hormones are still produced in equal quantities
for nearly for three of the five hormones
while it won't be exactly is not necessary.
So necessary is an extreme word
and we see that it's not necessary
for three of the five hormones.
So we gotta be careful with that.
We generally wanna stay away from extreme answer choices.
So C is the best supported answer.
There we have it.
We're four for four.
All right, great work team.
We knocked out a lovely bio passage dealing with hormones,
the anterior and posterior pituitary gland
and some experimental design.
Great work.
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