G-Protein & G-Protein-Coupled Receptors (GPCR) | Cell Surface Receptor | Physiology | Endocrinology
Summary
TLDRIn this educational video, the host delves into the fascinating world of endocrinology, focusing on cell signal transduction and the pivotal role of G-proteins. The discussion highlights the differences between lipid-soluble and water-soluble hormones, explaining how the latter must interact with cell surface receptors due to their inability to penetrate the lipid cell membrane. The video simplifies complex concepts like G-protein activation, the role of GTP and GDP, and the impact on second messenger systems. It also touches on the physiological significance of these processes, using examples like the sympathetic and parasympathetic nervous systems to illustrate the practical applications of G-protein coupled receptors in medicine.
Takeaways
- 𧬠**Proteins in Cell Signaling**: Almost all active particles in the body are proteins, including channels, pumps, carriers, enzymes, and receptors.
- π **Hormone Classification**: Hormones can be proteins (water-soluble) or fats (lipid-soluble), which affects their mechanism of action and speed.
- πͺ **Lipid-Soluble Hormones**: These hormones are slower in action because they must diffuse through the lipid cell membrane to reach intracellular receptors.
- π **Water-Soluble Hormones**: These hormones bind to cell surface receptors and act quickly, flipping a switch to activate cellular responses.
- π **Role of G Proteins**: G proteins act as middlemen, linking cell surface receptors to intracellular enzymes, especially for water-soluble hormones.
- π **G Protein Activation**: G proteins switch from GDP to GTP binding upon activation, which triggers a series of cellular responses.
- π‘οΈ **G Protein-Coupled Receptors (GPCRs)**: These are the largest family of cell surface receptors and are crucial for signal transduction of water-soluble hormones.
- π **Second Messenger Systems**: Activated by G proteins, these systems amplify signals and initiate various cellular responses, such as changes in ion channel activity.
- π **Termination of Signaling**: GTPase activity converts GTP back to GDP, inactivating G proteins and ending the signal transduction process.
- 𧩠**Integration of Signals**: G proteins integrate signals from cell surface receptors to initiate a cascade of events within the cell, leading to physiological responses.
Q & A
What is the primary reason proteins are involved in most active cellular processes?
-Proteins are involved in most active cellular processes because they are capable of being switched on or off, rotating, or undergoing conformational changes, which are essential for their function. This is due to their complex structures, including primary, secondary, and tertiary structures, and post-translational modifications.
How do lipid-soluble hormones differ from water-soluble hormones in terms of their action speed?
-Lipid-soluble hormones are slower in action compared to water-soluble hormones because they need to diffuse through the lipid cell membrane, which is a slow process. In contrast, water-soluble hormones can quickly bind to cell surface receptors and initiate a response without needing to pass through the membrane.
Why are cell surface receptors for water-soluble hormones located outside the cell?
-Cell surface receptors for water-soluble hormones are located outside the cell because these hormones cannot diffuse through the lipid bilayer membrane. The receptors must be on the outside to bind with the water-soluble hormones directly.
What is the role of the G protein in cell signal transduction?
-The G protein acts as a middleman in cell signal transduction for water-soluble hormones. It links the receptor on the outside of the cell with the enzyme on the inside, facilitating the signal transmission across the cell membrane.
What are the three types of G-protein-coupled receptors mentioned in the script?
-The three types of G-protein-coupled receptors mentioned are: 1) G-protein-coupled receptors, 2) Ligand-gated ion channels, and 3) Enzyme-linked receptors.
How does the G protein switch from an inactive to an active state?
-The G protein switches from an inactive to an active state when a water-soluble hormone binds to the receptor. This binding causes a conformational change in the receptor, which then activates the G protein. The G protein then exchanges GDP for GTP, activating the alpha subunit and leading to the dissociation of the beta and gamma subunits.
What is the function of the GTPase enzyme in the context of G protein activity?
-The GTPase enzyme is responsible for breaking down GTP into GDP, which converts the active G protein back into an inactive state. This hydrolysis reaction terminates the activity of the G protein and stops the signal transduction process.
How does the activation of Gq, Gs, or Gi lead to different cellular responses?
-The activation of Gq typically leads to an increase in intracellular calcium levels and contraction of smooth muscles. Gs activation increases cyclic AMP levels, leading to relaxation of smooth muscles and increased cardiac contractility. Gi activation inhibits adenylate cyclase, resulting in decreased cyclic AMP levels and a variety of inhibitory effects on the cell.
What is the significance of the seven transmembrane helices in G-protein-coupled receptors?
-The seven transmembrane helices in G-protein-coupled receptors provide a complex three-dimensional structure that allows the receptor to span the entire thickness of the cell membrane. This structure is crucial for the receptor's ability to bind the ligand on the outside and interact with the G protein on the inside.
How do different G-protein couplings result in different physiological effects?
-Different G-protein couplings result in different physiological effects because they activate different second messenger systems. For example, Gq activation leads to increased calcium levels and muscle contraction, while Gs activation leads to increased cyclic AMP and muscle relaxation. Gi activation typically inhibits these processes, leading to reduced cellular activity.
Outlines
π¬ Introduction to Cell Signal Transduction and G Proteins
The video begins with an introduction to the topic of cell signal transduction, focusing on cell surface receptors and the role of G proteins. The speaker emphasizes the importance of proteins in biological processes, explaining that almost all active particles in the body are proteins. Hormones, which can be proteins or fats, determine the speed of action based on their solubility. The video sets the stage for a deeper dive into how water-soluble hormones interact with cell surface receptors and G proteins, which are integral membrane proteins that facilitate the signal transmission across the lipid bilayer.
𧬠The Role of G Proteins in Signal Transduction
This section delves into the specifics of G proteins, which are guanine nucleotide-binding proteins that can bind to GTP or GDP. The speaker explains the mechanism by which water-soluble hormones interact with cell surface receptors, leading to the activation of G proteins and subsequent activation of second messenger systems. The video outlines the three types of G-protein-coupled receptors, which are the most significant family of cell surface receptors, and discusses how these receptors, with their seven transmembrane helices, interact with G proteins and effector molecules to initiate cellular responses.
π The Activation and Termination of G Protein Signaling
The paragraph explains the trimeric structure of G proteins, consisting of alpha, beta, and gamma subunits, and how they transition from an inactive GDP-bound state to an active GTP-bound state upon hormone binding. The video describes the activation process where the alpha subunit, once active, dissociates from the beta and gamma subunits, leading to the activation of effector molecules like Gq, Gs, or Gi. It also covers the termination of the G protein activity by GTPase, which hydrolyzes GTP back into GDP, thus returning the G protein to its inactive state.
π¦ The Impact of G Protein Coupling on Cellular Responses
This segment discusses the different outcomes of G protein coupling on cellular responses, depending on whether the G protein is Gq, Gs, or Gi. It explains how Gq activation leads to increases in calcium levels and contraction of smooth muscles, while Gs activation results in the production of cyclic AMP, leading to relaxation of smooth muscles. Gi, on the other hand, inhibits the production of cyclic AMP. The video uses examples from the sympathetic and parasympathetic nervous systems to illustrate these concepts, showing how the same neurotransmitter can have opposite effects on different tissues depending on the receptor and G protein involved.
π Practical Applications and Summary of G Protein Signaling
The final paragraph ties the theoretical concepts back to practical medical applications, discussing how understanding G protein signaling is crucial for comprehending the actions of various hormones and neurotransmitters. It provides examples of how different receptors and G protein couplings are associated with specific physiological responses, such as the vasoconstriction effects of angiotensin II and the dual action of ADH on blood vessels and kidneys. The speaker also promotes their premium courses on endocrine pharmacology and renal physiology, offering a discount code for viewers.
Mindmap
Keywords
π‘Endocrinology
π‘Cell Signal Transduction
π‘G Protein
π‘Water-Soluble Hormones
π‘Ligand-Receptor Complex
π‘Second Messenger Systems
π‘GTPase
π‘G Protein-Coupled Receptors (GPCRs)
π‘Catecholamines
π‘Pituitary Hormones
Highlights
Introduction to the topic of cell signal transduction, focusing on cell surface receptors and the role of G proteins.
Emphasis on the importance of proteins in biological systems, including their role in cell signal transduction.
Explanation of how hormones can be proteins or fats, and their solubility affects their mechanism of action.
Detail on the slow action of lipid-soluble hormones due to their need to diffuse through the lipid cell membrane.
Contrast between the fast action of water-soluble hormones that bind to cell surface receptors.
The necessity for water-soluble hormones to have cell surface receptors due to their inability to pass through the lipid membrane.
Description of G proteins as integral proteins that span the entire cell membrane and their role in signal transduction.
Differentiation between lipid-soluble and water-soluble hormones and their respective receptors.
Explanation of the G protein's function as a middleman linking cell surface receptors to intracellular enzymes.
Enumeration of water-soluble hormones, including pituitary hormones, pancreatic hormones, and catecholamines.
Discussion on the structural components of G proteins and their activation mechanism involving GTP and GDP.
The role of GTPase enzyme in terminating the activity of the G protein by converting GTP back into GDP.
Differentiation between the functions of Gq, Gs, and Gi proteins in cellular responses.
The impact of G protein activation on second messenger systems and the generation of cyclic AMP.
Clinical relevance of understanding G protein-coupled receptors in medicine and pharmacology.
Practical examples of how G protein activation leads to physiological responses, such as smooth muscle contraction and relaxation.
Summary of the video's key points and a call to action for viewers to continue their education on the topic.
Transcripts
what's up lovely people this is
mitochosis perfectionist where medicine
makes perfect sense let's resume our
endocrinology playlist we are in the
topic of cell signal transduction today
we'll focus on a cell surface receptor
and the story of the g protein so let's
get started this is my endocrinology
playlist watch these videos in order
especially the last two if you don't
understand this one here's a very
important fact to keep in your mind
almost all of the active particles in
your body are proteins all channels are
proteins all pumps are proteins all
carriers are proteins all enzymes are
proteins or receptors are proteins
anything that's going to be switched on
switched off rotate have a
conformational change anything of this
sort is going to be a protein for a very
simple reason go back to biochemistry
and molecular biology and remember the
story of dna synthesis transcription and
translation and then you have
post-translational modification remember
the primary structure of protein
secondary structure tertiary structures
proteins are complex indeed however
hormones beg to differ they could be
proteins or fat if they are proteins
they are water soluble if they are fat
of course they are water insoluble but
lipid soluble i don't just mean proteins
i mean proteins peptides polypeptides
amy and the entire family as we have
said gazillion times before there is a
ceo followed by a general manager and
then you have employees and independent
contractors only three glands listen to
the pituitary these three glands who
listen to the pituitary produce
steroidal hormones that are fat soluble
and that's why they are slower in action
contrast that with the independent
contractors they produce peptides
proteins and therefore they are faster
why are lipid soluble hormones slow in
action because you have to leave the
plasma protein and then go until you
reach the cell membrane the cell
membrane is lipid and the hormone is
lipid lipid can diffuse through lipid
but this process is very slow i have to
diffuse throughout the cell membrane and
then go through the cytoplasm and then
reach the receptor maybe in the
cytoplasm or the nucleus this is a very
slow process and wait there is more i
then have to tap on the dna knock on the
door hey dna would you like to like
replicate and transcription translation
make me some brand new proteins oh yeah
sure all of this takes time conversely
if your water soluble hormone you just
cannot pass through the membrane because
the membrane is lipid and you are water
soluble therefore you have to stay
outside and then latch onto a cell
surface receptor and this is like
flipping a switch on and just like your
bedroom when you turn on the lights you
just click on the switch and boom the
light is on it's a very fast process
if the hormone is lipid soluble we put
the receptor inside because you can
diffuse through the membrane but if the
hormone is water soluble we have to put
the receptor outside a soil surface
receptor because the hormone cannot
enter through the lipid bilayer membrane
these receptors especially those coupled
to a g protein are integral proteins
because they take the whole thickness of
the membrane if you wanna remember the
difference between integral proteins and
peripheral proteins go back to my
physiology playlist and check the video
titled the functions of protein in the
cell membrane the distinction between
lipid soluble hormones and water-soluble
hormones was discussed before just
remember today's topic is the g protein
we are talking about water soluble
because the receptor has to be on the
outside who's gonna link the receptor on
the outside with the enzyme on the
inside that's the purpose of the
g-protein what are these water-soluble
hormones there are many including the
pituitary hormones pancreatic hormones
parathyroid hormones and your
catecholamines which include epinephrine
norepinephrine and dopamine if you are a
lipid-soluble hormone which is not
today's topic you just diffuse through
the cell membrane which is made of lipid
until you reach your receptor which is
usually in the cytoplasm or the nucleus
then we have a ligand receptor complex
which will activate hormone response
elements which will activate dna first
replication when you convert dna to dna
or transcription which is dna to rna or
translation from rna to proteins all of
this takes a very long time these are
slow acting examples of these fat
soluble hormones you have all of the
steroidal hormones these include the
hormones secreted by your adrenal cortex
zona glomerulosa zona fasciculata zona
reticularis and then add the testicles
testosterone ovaries estrogens and
progesterone moreover there are the
thyroid hormones t3 and t4 as well as
vitamin d all of these are lipid soluble
that's not today's topic today's topic
is the water soluble hormones can you
diffuse to the membrane that's made of
lipid nope i cannot so therefore you
have to put the receptor on the outside
all right the receptors on the outside
the enzyme the actual action is on the
inside who is the middle man that's
gonna connect the receptor on the
outside with the enzyme on the inside
this is the story of the g protein it's
the middle main why do you call it g
protein why not f as in fme because this
is the guanine nucleotide binding
proteins it can bind to gtp or gdp
that's why we call the g protein so here
is your lovely water soluble hormone
it's going to act on a cell surface
receptor of course all receptors are
proteins when this happens you got the
ligand receptor complex which is active
this will activate the g protein the g
protein will then activate the enzymes
known as second messenger systems who's
the first messenger the water soluble
hormone who's the second messenger you
have many choices that's the action do
you remember this beautiful chart yes we
are done with the intracellular
receptors these are the steroidal
hormones thyroid hormones vitamin d boom
we're done we're talking today about
what g protein coupled receptors which
are the most important cell surface
receptors when the hormone is water
soluble or hydrophilic the receptor has
to be on the cell surface we have three
types g-protein-coupled receptor by far
the largest and the most significant
family ligand-gated ion channels and
enzyme-length receptors now let's talk
about the g-protein-coupled receptor
g-protein-coupled receptors the largest
family of cell surface receptors no
kidding the action of those g protein
coupled receptors depend on three
factors number one the receptor number
two the g protein itself number three
the effector molecules the second
messenger systems the actual freaking
action tell me about this ligand oh
right this ligand is a hydrophilic
hormone something that's water soluble
thank you can you give me example of
these water soluble molecules sure it
could be catecholamine such as
epinephrine norepinephrine dopamine say
thank you to your adrenal medulla could
be acetylcholine oh yeah you see
sympathetic and parasympathetic awesome
glucagon to raise your blood sugar
serotonin to make your brain happy
secretin a hormone that secretes and
pituitary hormones such as tsh acth fsh
and lh tsh is stimulating the thyroid
gland acta stimulating the adrenal
cortex fsh and lh are submitting the
gonads thyroid gland adrenal cortex
gonads these are the three employees the
three glands that obey the pituitary but
homo medicosis haven't you said that the
three glands that obey the pituitary
secrete lipid-soluble hormones that's
true the glands themselves secrete
lipid-soluble hormones but these glands
get stimulated by pituitary hormones
that are water-soluble big difference so
tsh acth fs8 and lh are water soluble
however thyroid hormone t3 and t4
cortisol aldosterone testosterone
estrogens and progesterone these are
lipid soluble we're done with the ligand
tell me about the receptor this receptor
has seven trans membrane helices you
know a helix yeah you have seven of
these making the receptor a very complex
three-dimensional structure but just
let's keep it simple and we'll do seven
healthy right there look at this one
two three four five six seven talk to me
about the outer surface of the or the
outer region of the receptor well the
outer part is extra extracellular no
kidding and it's the binding site of the
ligand which is a water-soluble molecule
thank you tell me about the inner
surface the inner surface of the
receptor is intracellular of course is
the binding site of the g-protein
thank you and after the g protein what
do we got here the effector molecules
which are three gq gs or gi so we have
seven transmembrane helices and three
intracellular effector molecules they
are intracellular but they are still
bound to the inner surface of the cell
membrane okay mitochosis now i know
about the ligand now i know about the
receptor tell me about the g protein
your wish is my command the g protein g4
guanine nucleotide binding protein what
do you mean by guanine nucleotide i mean
either gtp or gdb this g protein will
bind gdb when the g protein is inactive
but when the g protein gets activated
it's gonna bind to the gtp because it
has an extra phosphate group how can the
gdp become gtp just acquire a phosphate
group but how will the gtp become gdp
destroy a phosphate group break down a
phosphate from it how do i break it down
hydrolysis what's the name of the enzyme
gt phase which broke down the gtp when
you convert gtp into gdp this is
converting the active g protein into an
inactive g protein and that's why gt
pays terminates the activity of the g
protein all right let me tell you about
this g protein has a trimeric protein
structure three subunits alpha subunit
which is the story beta subunit and
gamma subunit and the story of the g
protein looks like this the g protein
was inactive which means bound to gdp
suddenly it decided to become active how
did it decide well a soluble particle
came and bound to the receptor now the g
protein is active when it's active it's
gonna ditch that gdp and it's gonna bind
gtp gtp will activate the alpha subunit
when the alpha subunit gets active it
will kick the beta and the gamma subunit
away from it and the alpha will remain
alone alone in an active form who will
end the alpha subunit's entire career gt
pays because it breaks down the gtp into
gdp what's the function of the beta
subunit it just forms a complex with the
gamma subunit what's the function of the
gamma subunit it forms a complex with
the beta subunit this structure is
anchored to the cell membrane via a
lipid anchor because the cell membrane
is made of lipid activation of the g
protein first this water soluble
hydrophilic extracellular ligand is
going to bind to the receptor thank you
the receptor will undergo a
conformational change its
three-dimensional structure is gonna
change in shape this activated receptor
is gonna bind to the g protein which is
an intracellular structure when g
proteins becomes active it's gonna bind
gtp instead of gdp when you're buying
gtp when you are active alpha subunit is
gonna kick the beta and gamma complex in
the teeth get away from me i am active
eagles fly alone and when the alpha
subunit is active it's going to activate
the effector molecules gq gs or gi
that's the story of activation who will
end this activation process who will end
the alpha subunit's career this is the
gt phase because it breaks down gtp into
gdp and phosphate i hope that you know
that atp can be converted to click amp
via adelaide cyclase enzyme you can take
the cyclic emp to the cleaners by
phosphodiesterase enzyme which converts
cyclic mp into inactive metabolites or
degradation products or basically pieces
of trash absolute rubbish who stimulates
adenolate cyclase gs coupled receptor
who inhibits adelaide cyclase gi coupled
receptor s stands for stimulation i
stands for inhibition no duh how can we
inhibit the phosphodies trace enzyme by
a phosphodiesterase inhibitor in other
words there are two mechanisms by which
you can increase the level of cyclic mp
the first method is to boost the
activity of adelaide cyclase by gs
coupled receptor the second way to
increase cyclic emp is to destroy the
phosphodius trace so that no one will
take me to the cleaners so that the
level of cyclic mp will rise so if you
leave it to gs coupled receptors you
will have more cyclic amp if you leave
it to gi you will have less cyclic mp if
you give a phosphodiesterase inhibitor
you'll have more cyclic emp when you
write cyclic amp make sure the c is
lowercase because this has a completely
different meaning you know the saying
health books are the only books that can
kill you because of a typo you should
also grasp the fact that when an enzyme
is called kinase it's usually gonna add
a phosphate but when the enzyme is
called phosphatase it's gonna remove a
phosphate let's do it again the water
soluble hormone is now bound to the
receptor protein and then when this is
active i can activate the g protein
alpha will fly alone beta and gamma will
make a complex and get out of here alpha
is active to do what to activate gs gq
or gi when the g protein was inactive it
was like this bound to gdp and these
three were together but look at here
look when it's active when it's active
different things will happen but first
of all who activated the g-protein the
binding of the water-soluble hormone to
the receptor a conformational change
will happen to this receptor now the
g-protein is active and it's going to
bind gtp
instead of gdp the alpha subunit is now
active and it's going to kick the beta
gamma complex in the teeth get out of
here alpha subunit is active to do what
to activate gq gs or gi depending on the
situation gq will do what when you
activate gq you'll activate
phospholipase c which will increase
calcium gq
calcium also think of gq magazine very
muscular dudes when you activate gs it
will activate at a late cyclase more
cyclic emp when you activate gi it's
going to inhibit adelaide cyclase less
cyclic amp when i am inactive i am bound
to gdp who did this the jt pays gt pays
destroyed the gtp and now you have gdp
when you're buying gdp you are inactive
and you are inactive because the water
soluble hormone is detached but when you
are active the water soluble hormone is
attached and the gdp is becoming gtp by
acquiring an extra phosphate group pause
and review if you have watched the last
video what did we say we said that alpha
1 m1 m3 m5 h1 v1 and others are gq
coupled gq meaning phospholipase c and
therefore calcium contraction of smooth
muscles vasoconstriction
bronchoconstriction uterine contractions
all kinds of smooth muscle contraction
that's why oxytocin is gq coupled
because it increases uterine wall
contraction and the uterus has smooth
muscles that's why angiotensin ii is gq
coupled because it causes
vasoconstriction of blood vessels again
contraction of smooth muscles that's why
the v1 receptor of adh is gq coupled
because it causes vasoconstriction how
about the gs coupled receptors remember
your sympathetic stuff especially the
betas beta 1 beta 2 beta 3 because the
alpha is here alpha 1 is gq coupled
alpha 2 is gi because it's inhibitory
alpha 2 is an sob alpha 2 is
anti-sympathetic but the betas all of
them are gs coupled therefore activate
adelaide cyclase converts atp into
cyclic mp activates protein kinase a
everything here is a adelaide cyclase
atp cyclic amp protein kinase a to do
what increase the contraction of the
heart increase cardiac contractility
and vasodilation so i relax smooth
muscles unlike the calcium story
phospholipase
contracts smooth muscles but protein
kinase a
relaxes smooth muscles bronchodilation
vasodilation what's the opposite of
uterine contractions it's called
tocolysis which is relaxation of uterine
smooth muscles moreover beta 1 will
increase renal secretion also increase
aqueous humor secretion in the eye let's
do the g protein story one more time a
water soluble hormone is now bound to
the receptor let's talk about gs make
this about gs okay
this is active right g protein when it's
active is going to bind gtp alpha
subunit is going to dissociate from the
beta gamma complex alpha alone will
activate adelaide cyclase enzyme which
converts atp into cyclic amp cyclic amp
activates protein kinase a when i'm
called a kinase what's the function i
will add a phosphate this is the enzyme
before the kinase this is the enzyme
after the kinase it has acquired a
phosphate and therefore became active
most of the time here's the transporter
before the protein kinase a but here's
the transporter after protein kinase a
protein kinase a adds a phosphate
therefore the transporter is active most
of the time receptor becomes receptor
phosphate transcription factor becomes
transcription factor phosphate ion
channel becomes ion channel phosphate
structure protein structure protein
phosphate i converted everything from
inactive to active i am the protein
kinase a but hey where did you get the
phosphate group from easy i got it from
the gtp that's why the active form of g
protein always binds gtp and not gdp
because i need this extra phosphate to
activate all kinds of stuff all right
how can we go from the active state back
to the inactive state easy the cyclic mp
is gonna be taken to the cleaners thanks
to phosphodiesterase enzyme and the
protein kinase a will not be active
instead you will activate a phosphatase
what does a phosphatase do remove the
phosphate the enzyme phosphate will go
back to become an enzyme transporter
phosphate will become a transporter and
so and so forth basically converting the
active form into the inactive form this
was the story of the g protein it's a
very simple concept it's just your work
professor cannot teach do you remember
the sympathetic nervous system yeah we
had many sympathetic receptors including
alpha-1 which is gq you know why because
it needs to constrict blood vessels
calcium contraction of smooth muscles
how about alpha 2 alpha 2 is
anti-sympathetic because when you
stimulate the alpha 2 it decreases
norepinephrine it's anti-sympathetic
when something inhibits its gi because i
is inhibitory how about the betas the
betas are gs because i need to relax the
vessels relax the uterus but increase
cardiac contractility i also need to
secrete more renin and more icus humor
let's talk about the muscarinic
receptors of parasympathetic easy m1 m3
and m5 the odd numbers want to contract
stuff contract smooth muscles and
contract the asanas of the gland to
secrete stuff because this is secreto
motor parasympathetic therefore when you
want to contract smooth muscles you
better be gq to increase the calcium but
how about m2 and m4 i want to inhibit
everything gi the odd numbers are gq the
even numbers are gi the functions make
perfect sense pause and review but hey
medical says why is this so important
take it easy my friend take it look at
this sympathetic nervous system secretes
norepinephrine right yeah i know this
norepinephrine on the bladder what did
it do it relaxes the wall and constricts
this fainter because i was running from
a tiger relaxation and contraction are
two different functions how come one
ligand produces two opposite functions
because the receptor is different and
the g protein coupled receptor is
different if you want to relax the wall
of a smooth muscle you better be gs if
you want to contract a smooth muscle you
better be gq to increase the calcium it
makes sense how about the
parasympathetic nervous system is
acetylcholine wants to calm the heart
down how do i calm someone down gi is
inhibitory that's why it's m2 it has to
be an even number i want to contract the
walls of this bladder to get the urine
out m3 gq coupled gq calcium contraction
of smooth muscles i want to squeeze
those gastric glands because i am
secreto motor m3 is gq coupled gq
calcium constriction what does your
posterior pituitary gland release adh
and oxytocin who synthesized these two
hormones the prescription heck no it was
the hypothalamus and we talked about why
in previous videos in this endocrinology
playlist what's the only function of adh
to maintain your blood pressure to
prevent your blood pressure from
dropping so let's say that you were
walking down the street distracted with
your phone and then you got hit by a car
and lust lots of blood
if we leave you alone you will die from
hypotension but thankfully there is adh
coming to try to save the day adh has
one function in life to prevent your
blood pressure from dropping to maintain
a robust blood pressure let's go adh is
gonna do this by two receptors v1 and v2
why v because it's a vasopressin
vasopressin what do you think will do to
the vessels of vasoconstriction press
them constrict them how do i do this v1
receptor will do this for you how about
v2 v2 goes to the kidney and gets the
water out reabsorbs the water so that
the water goes back to the blood when we
increase the amount of volume in your
blood will increase the venous return
and therefore increase the preload and
increase the cardiac output and will
increase the blood pressure preventing
hypotension now take a wild guess if v1
wants to constrict vessels does it need
gq gs or gi oh that's easy of course gq
because gq calcium contraction of smooth
muscles how about dilating those
beautiful collecting tubules and get the
water out oh dilation relaxation of
smooth muscles cyclic mp therefore gs
coupled it's so easy tell me about
dopamine there is d1 receptor and d2 d1
activates the direct pathway d1 dilates
renal vessels mesenteric vessels as well
d2 inhibits so when d1 activates do you
think it's gs gq or gi and when g2
inhibits what kind of g-protein does it
need well it has to be s for stimulation
and i for inhibition also gs increases
cyclic mp which dilates and relaxes
smooth muscles see medicine makes so
much sense once you understand what the
flip you're talking about it's so simple
and easy there is no need to invent some
woke mnemonics to remember these just
think about it the best mnemonic is
understanding histamine h1 wants to
bronch a constrict h2 wants to increase
gastric acid secretion and of course you
cannot secrete without vasodilation
because you get those secretions from
the blood vessels and therefore h1 is gq
coupled h2 is gs coupled
to be continued in the next video don't
forget i have a premium endocrine
pharmacology course on my website
medicosisperfectionaries.com
my website also has a renal physiology
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