UT Bio365S Human System Physiology Online Lecture – Cell Communication and Homeostasis03.
– Let's look at the homeostasis loop.
You have the input signal,
could be your body temperature,
so you have body temperature.
You will send it to the control center.
Control center is in your hypothalamus.
If your body temperature is too high,
it will go to the output.
Output is your sweat gland,
and sweat glands produce sweat.
When the sweat goes to the surface
of your skin, it evaporate,
it bring the heat away,
so it lowers your body temperature.
This is the homeostasis control system.
In your body, you have a lot of this
system to control your body temperature.
You have the stimulus,
you have a receptor.
Receptor picks up the signal,
could be the receptor on your skin,
pick up the stretch,
the temperature, or it could be
the receptor inside your body.
You're going to send information
to the control center.
Control center is going to send the signal
out and the one response
is called the effect,
or like the previous example,
I said your body temperature
increase and you sweat,
the effect will be your sweat gland.
Eventually, your body temperature
lower, and there's homeostasis.
This kind of control loop,
your body have a lot.
It can control your body temperature,
it can control your blood sugar level,
it can control your osmolarity in your body.
We'll talk about this component.
Say your body temperature increase,
you have a sensor,
and they send a signal into
the integrating center,
then it goes to the effected,
there's your sweat glands,
and the response, sweat.
Eventually, your body temperature drop,
and the output can work as a
feedback because the input.
So it goes through the negative feedback.
So your body temperature drop, drop, drop,
and it won't keep dropping until your
body temperature goes to 70 Fahrenheit,
and you freeze to death.
The reason is, the body temperature drop,
it can work as the input.
When the temperature drop to normal,
then that's good enough,
you won't sweat anymore.
We call this loop, negative feedback loop.
So you are able to
maintain something because
your body have a lot of
negative feedback loop.
You have a set point for your temperature,
for your blood sugar level,
or like last time, we talk about osmolarity,
and about 300 meters there
and that's your set point.
Here are two examples of homeostasis.
So if a body temperature is too high,
well, we’ll talk about this, you sweat.
If your body temperature is too low,
still your hypothalamus,
this is your control center,
and this time it is not your sweat gland.
When your body temperature
is low, you're shivering.
It will send a signal to
your skeletal muscle.
When your skeletal muscle contracts,
it creates a movement,
that's the main purpose,
but this time its bi-product is heat,
and this time we want the bi-product.
So the heat is going to warm you up.
This is the purpose you are shivering.
Your body just have a lot
of this kind of loop.
Homeostatic response can
be local, can be systemic.
We'll talk about maintaining
your body temperature.
These are systemic, because you
require long distance communication.
Could be local, could be those paracrine
signal in your digestive system,
and these are local signals.
Or when we talk about the less
unit in the renal system.
Your renal control your granular
filtration rate, your GFR.
Your filtration rate need to be constant.
This feedback, these control are
mainly local, so they are paracrine.
If is systemic control,
long distance control,
your body have two long
distance control system
and the nervous system
and the endocrine system.
The nervous system, let's talk about
what like a simple neural reflex.
You touch something hot,
you quickly move your hand back.
This is simple neural reflex.
So the signal, that's the heat go to
your skin and your skin is the receptor.
It’s going to send the signals
through your sensory neuron,
it will go through the dorsal part,
the dorsal part is the sensory input.
We'll talk more about this
in the nervous system.
It will go to the integrating center.
Integrating center is your
spinal cord or your brain.
This time is your spinal cord.
You will go to the output,
so your motor neuron as your
skeletal muscle to contract.
So your response, you move your hand back.
The purpose of this is
decrease the damage because
the sooner you move your hand back
and the less damage you can create.
When you do your annual health check,
they can do this check.
They won't ask you to touch something hot,
you can sue them, but they
can take a small hammer.
They hit your knee.
When they hit your knee, it’s
actually the receptor is in your,
called the muscle spindle is
buried inside those quadricep
muscle, those big muscle.
When they hit the knee,
they're going to stretch
the quadricep muscle when
they're being stretched.
So the sensory neuron gets any
information in and so the motor neuron
that go to counteract those quadracep
muscles relax the hamstring muscle,
so end up if you kick,
so this how they test this response.
This circuitry neuronal sexual is still
working and this is simple neuronal reflex.
It can be the endocrine,
so let's look at a simple endocrine reflex.
After you eat a big meal,
your blood sugar level is high,
go out of the higher than
the set point and your body,
your pancreas can then release insulin.
Insulin's function is too
lower your blood sugars,
so you will go through the blood,
carry those endocrine signal.
You will reach the target cell,
the target cell is skeletal muscle,
this is the main target
cell and also your adipose,
your fat cells and both of them
will sue the upregulation.
We'll just talk about upregulation and put
more insulin receptor and put more
glucose carrier on the cell membrane,
and when you have more glucose carrier,
you're going to carry more
glucose into the cell so
blood sugar level drop
and maintain homeostasis.
For normal people, healthy people,
you won't have high blood
sugar level problem,
you have to eat big meal because
your blood have insulin.
If your blood sugar level is too low,
this' not good because you can be dizzy,
you can fall into coma.
So your blood sugar level goes too low,
your pancreas still your pancreas,
alpha cells, alpha cells are
going to raise glucagon.
Glucagon's function is to
increase your blood sugar,
It will go to your liver.
So in your liver you have bladder glycogen,
there's the polysaccharide
is a lot of sugar together.
You're going to cut those
glycogen become monosaccharides,
this is the simple sugar, it's the glucose,
so you're blood sugar
level starts to increase.
You may have the experience,
you feel very hungry,
but after 20-30 minutes,
you're still hungry, but it's bearable.
The reason is this circulatory response.
When your blood sugar level drops,
this why you feel hungry and when you
reach the certain level
you're going to start this,
and glucagon release and
increase your blood sugar,
so you bless your blood sugar level is
maintained the label is maintained.
We talked about diabetes,
diabetes is this one,
either your body don't have insulin,
this is diabetes 1, or their body
becomes insensitive to insulin,
this is diabetes 2.
They won't be able to go through
the signal transduction pathway to put
more glucose carrier on the cell membrane,
and the blood sugar level remain high.
This high blood sugar can damage
the filter which is the kidney,
it can also damage the small
blood vessel and your eye.
Your eye thus the area retina,
have a lot of small blood vessel,
they're all called small
blood vessels capillary.
When they got damage the retina, the rods,
and cones for the receptor dies
and turn out they become blind.
Diabetes is number 1 reason to cause
blindness in the United
States in the 21st century,
because we have 20 people with
high blood sugar problem.
This symbol endocrine reflex should
maintain your blood blood sugar level.
A lot of things in your body temperature,
blood sugar, blood pressure,
and they they just need to
stay in the normal range.
Next time we'll talk about osmolarity,
they stay in the normal range,
and the mechanism, negative feedback.
We talked about a negative feedback,
the output can work like a input
and control your body temperatures.
So when your body temperature
go back to normal,
your body now stop this process
and this' negative feedback.
We also have a positive feedback.
Positive feedback is the output and it's
going to work to amplify the signal.
You may have the experience,
you've found some people using a microphone
and they found the speakers
too close to the microphones.
The signal goes through the
speaker, being amplified,
being picked up by the microphone, again,
amplified again and quickly
they go out of control.
So you hear a loud,
sharpened more noise and
this' positive feedback.
Positive feedback is not stable,
that's why your body don't have
too many positive feedback.
Most of the feedbacks are negative feedback,
like the one that control,
maintain your blood sugar,
maintain your body temperature,
they are all negative feedback.
Your body has three positive feedback,
they don't contribute to homeostasis,
which is the stable environment.
They don't. But your body have
those three positive feedback,
they're feedback loops, positive feedback.
The first one, milk let-down reflex.
Milk let-down reflex. You have it in female.
When the baby suck the nipple,
this is the stimulus.
The sensory stimulus going
to the control center
is the hypothalamus and the trigger
of hormone release called oxytocin.
Oxytocin is a hormone released from
the posterior pituitary gland.
We will learn later.
It will go to the breast and it will
ask the milk gland to release milk.
It's a positive feedback
so quickly the baby learn,
"The harder I work, more food come out."
It needs to be positive feedback.
Because if it's negative feedback and
the baby tried to eat and it stopped,
then the baby won't get food.
This is a positive feedback example.
The other two positive feedback,
the second one, blood clotting.
This happens in both male and female.
Blood clotting is the blood when
they come out of the blood vessel.
In the blood you have platelet;
it would trigger response.
They will start from a chemical response.
They will recruit a blood clotting factor.
It will start to form the clot,
and at first, a small clot and this
clot will become bigger and bigger.
They start to recruit red blood cell
because you have so many red blood cell.
This is where you see the dried blood.
The clotting will become bigger and bigger.
It is a positive feedback and you need
positive feedback because eventually
you need to stop bleeding.
It is a negative feedback if the clot
disappear and eventually this
person going to bleed to deaths.
This is a positive feedback
happening to both gender.
The third one is giving
birth, uterine contraction.
During the labor it start from
the small contraction in female.
You found those three positive feedback;
two in female, only one in both gender.
Start from the uterus contraction,
and this contraction is small and short
frequencies or every 30 minutes
and the pregnant woman found,
"I have a contraction."
If you're a little bit uncomfortable
and is a positive feedback.
This contraction start from every
30 minutes per contraction,
go to every 20 minutes,
go to every ten minutes.
The contraction intensity start to increase.
First, they feel uncomfortable.
This is the time they tell their husband,
"Hey honey, there is time
to go to the hospital."
Now it become more painful
and it will keep contracting.
The cervix, the opening of
the uterus, start to open.
You start from one to two,
means two centimeter.
It will keep going is a positive feedback.
It will go to four, five.
This is the time the wife grab the husband,
say "It's all your fault.
It's very painful."
You will keep going this positive feedback,
so it will keep going until it go to 10.
Ten is 10 centimeter and until
the baby's head come out and
finish this labor process.
Is a positive feedback because if it is
a negative feedback start from uterine
contraction and the brain shut it down,
then the baby would never come out.
You only have three positive feedbacks.
Milk let-down reflex, uterine contraction,
both of them in female only.
The third one, blood clotting
happen in both gender.
In the anatomy and
physiological point of view,
yes, the female's body is
more complicated than male.
Males' bodies is simpler.
The reason is the baby need to grow inside.
Female's body is more advanced than
the male in the anatomical
term point of view.
We talked about those neuronal
reflex, simple reflex.
We talked about the single neuronal
reflex like take a hammer,
hit your knee, you're going to kick.
This belong to this one.
We also talked about the simple
endocrine reflex. There's this one.
That's the insulin control the blood sugar.
We also talked about the neurohormone
reflex, the milk let-down reflex.
The start from the stimulus in
the nipple and eventually going
to release the neurohormone,
trigger the milk gland to
release the breast milk.
The next topic when we go to
the neuroendocrine reflex,
the circuitry become more
and more complicated.
That's it for today.

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