Title: Ever wonder why you shiver, or why you sweat? Why do you pee or poop? Or, breath out CO2? Why??
1Ever wonder why you shiver, or why you
sweat? Why do you pee or poop? Or, breath out
CO2?Why??
Homeostasis
2Why do you shiver?
3Why do you sweat?
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6To Regulate??
- Shiver and sweat To regulate/maintain
Temperature of your body - Pee To regulate/maintain stable Water/salt/urea
level of your body - Poop To regulate waste or undigested food level
- Why EAT? Why breath?
- To maintain energy level to run the cells
7Kidneys???Too much waterOUT!!(pee)
8Regulation
- rule, requirement
- managing, organizing
- RULES???
9WHY Regulation?????
- So all systems can work together to maintain the
STABLE conditions in your body. - I mean to maintain HOMEOSTASIS! (maintaining a
stable or constant internal environment) - How ???
10By Control and coordination of all the body
systems
- Coordination?
- Working together in harmony
11IT'S ALL ABOUT HOMEOSTASIS
- Homeostasis is achieved by making sure the
temperature, pH (acidity/alkalinity), and oxygen
levels (and many other factors) are set just
right for your cells to survive. Homeostasis
levels are different for each species. - Who does Homeostasis?
- Well, if you are living, you got to do
HOMOEOSTASIS!!!! NO EXCEPTIONS!!!!!!
12What happens if an organism fail to do
HOMEOSTASIS?
13WHO in my body helps maintain homeostasis?
- Who tells me to shiver, sweat, pee, poop, eat,
breath, drink.blah blah blah - Brain?
- Yeah for the most part, but it has help!
14Parts that work with brain
- Well, there is spinal cord.
- And then, there are nerves going everywhere,
- there are chemicals (like hormones,
neurotransmitters) acting as messengers to inform
brain, spinal cord, cells.
15Lets talk about the nervous system...
16Which parts constitute(make) the nervous system?
- BRAIN
- SPINAL CORD
- NERVES
- Nervous system is the control center for your
entire body. Your brain uses information it
receives from your nerves to coordinate all of
your actions and reactions. - Yes copy!
17Nervous system is divided into 2 main parts
Central and Peripheral.
18Human Nervous System has 2 parts copy yes
- Central Nervous System
- 2) Peripheral Nervous System
Brain
Spinal Cord
NERVES
19Lingo of Nervous system
20Stimulus
- Something causing a response.
- An agent, action, or condition that elicits or
accelerates a physiological or psychological
activity or response. - Something that incites or rouses an action an
incentive
21Response
- The act of responding.
- A reply or an answer.
- A reaction, as that of an organism or a
mechanism, to a specific stimulus.
22Impulse
- MESSAGES conducted through the cells of nervous
system
23What is nervous system made up of?
- Cells, of course
- called nerve cells or neurons.
- are specialized to carry "messages" through an
electrochemical process. - The human brain has approximately 100 billion
neurons.
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25A Neuron
26A Neuron
27Neuron Anatomy
28Lets first talk about brain
- Parts of Brain
- cerebrum
- cerebellum
- brain stem (Medulla)
- hypothalamus
- pituitary gland
29The Biggest Part the Cerebrum
- The biggest part of the brain is the cerebrum.
The cerebrum makes up 85 of the brain's weight,
and it's easy to see why. The cerebrum is the
thinking part of the brain and it controls your
voluntary muscles the ones that move when you
want them to. So you can't dance or kick a
soccer ball without your cerebrum.
30And many other jobs
- When you're thinking hard, you're using your
cerebrum. You need it to solve math problems,
figure out a video game, and draw a picture. Your
memory lives in the cerebrum both short-term
memory (what you ate for dinner last night) and
long-term memory (the name of that roller-coaster
you rode on two summers ago). The cerebrum also
helps you reason, like when you figure out that
you'd better do your homework now because your
mom is taking you to a movie later.
31Cerebrum has 2 halves
- One on either side of the head. Some scientists
think that the right half helps you think about
abstract things like music, colors, and shapes.
The left half is said to be more analytical,
helping you with math, logic, and speech.
Scientists do know for sure that the right half
of the cerebrum controls the left side of your
body, and the left half controls the right side.
32Your Brain on Shopping
- Ladies! Have you ever felt jealous of your boy
friend/fiancé/brother? I have! - The shopping process just seems so easy for men.
They decide what they want, do a little research,
bada-bing, bada-boomand he buys what he wants. - We, however, turn it into a prime time soap
opera. - I attribute it to wiring in the brain, and I
think it applies to many men and women out there. - As a refresher, remember that the left brain is
the logical, analytical side of the brain - it is
the worker bee, focusing and analyzing one thing
at a time. The right brain is free to play -
its the home of imagination, emotional memory
and bonding with others.
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34 The Balancing Act
Cerebellum
- Next up is the cerebellum. The cerebellum is at
the back of the brain, below the cerebrum. It
controls balance, movement, and coordination (how
your muscles work together).
35Brain Stem Keeps You Breathing and More
- Another brain part that's small but mighty is the
brain stem. The brain stem sits beneath the
cerebrum and in front of the cerebellum. - It connects the rest of the brain to the spinal
cord, which runs down your neck and back. The
brain stem is in charge of all the functions your
body needs to stay alive, like breathing air,
digesting food, and circulating blood.
36- Part of the brain stem's job is to control your
involuntary muscles the ones that work
automatically, without you even thinking about
it. There are involuntary muscles in the heart
and stomach, and it's the brain stem that tells
your heart to pump more blood when you're biking
or your stomach to start digesting your lunch.
Whew! It's a big job being the brain's stem!
37Hypothalamus Controls Temperature
- The hypothalamus is like your brain's inner
thermostat (that little box on the wall that
controls the heat in your house). The
hypothalamus knows what temperature your body
should be (about 98.6 Fahrenheit or 37
Celsius). If your body is too hot, the
hypothalamus tells it to sweat. If you're too
cold, the hypothalamus gets you shivering. Both
shivering and sweating are attempts to get your
body's temperature back where it needs to be.
38Voluntary and involuntary
- Voluntary
- At willjob of cerebrum
- Involuntary
- Automaticnot under your control
- Medulla
- Spinal cord
39Pituitary gland!
- Hey! Its TINYbut dont let the size fool you!!!
Its the MASTER GLAND for crying out loud - only about the size of a pea!
40Pituitary Gland Controls Growth
- Has a big JOBgtgtgtto produce and release HORMONES
into your body (I mean in ______). If your
clothes from last year are too small, it's
because your pituitary gland released special
hormones that made you grow. - This gland is a big player in puberty too. This
is the time when boys' and girls' bodies go
through major changes as they slowly become men
and women, all thanks to hormones released by the
pituitary gland - Will talk about other hormones later.
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45Nervous System Cells Why do they have long
tail-like AXON?
- Neurons have long axons that enable them to
transmit signals
46So what are nerves??
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49How many types of neurons do you think are
there? A General Sense
50Neurons Are they all the same?
- No, Neurons can be classified by the direction
that they send information. - They are of 3 types
51- 1) Sensory (or afferent) neurons send
information from sensory receptors (e.g., in
skin, eyes, nose, tongue, ears) TOWARD the
central nervous system. - 2) Motor (or efferent) neurons send information
AWAY from the central nervous system to muscles
or glands. - 3) Interneurons Make brain and spinal cord
(central nervous system). They send information
between sensory neurons and motor neurons. - Copy yes
52whos the receptor and whos the effector
53Anatomy of a Neuron
- Cell body main part
- Dendrite receives action potential
(stimulation) - Axon branches from cell body, where the action
potential/signal travels - Axon terminal/End brushes end of an axon
54___________ Nervous System
- Sensory neurons carry messages _________ the CNS
from _________ __________ all over body. - Sensory receptors convert the signal into an
__________ onealso called the action potential
of a nerve. - Sensory receptors are in sense organs, such as
eyes, ears, mouth, nose, skin and different
regions of the brain respond to different
signals. - Interneuronsare there in the brain and spinal
cord to make sense of the stimulus. - Motor neuronstake the signal back to the
muscles/sensory organs
55- 4 Which process is most directly responsible for
- maintaining internal stability in an organism
- when its environment is constantly changing?
- (1) digestion (3) reproduction
- (2) feedback (4) evolution
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57- 52 Describe what would happen if a drug molecule
shaped like were introduced into - this nerve pathway. 1
- __________________________________________________
_____________________ - __________________________________________________
_____________________ - 53 Identify one substance, other than the
secretions from nerve cells, used in cell - communication. 1
- __________________________________________________
_____________________
58How do dendrites
59How do dendrites receive the message?
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61Cell Membrane
- How do cells receive messages and talk to each
other - I mean communicate with each other
- Through receptor proteins present on the cell
membrane
62Cell membrane is made up of a phospholipid
bilayer its the fluid mosaic model
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66- Cell Membrane
- We have to start somewhere. Let's start on the
outside. Around every cell is a CELL MEMBRANE.
The membrane is like a big plastic bag with tiny
holes in it. Scientists also call the cell
membrane a PLASMA MEMBRANE.
67- WHAT'S IT FOR? The purpose of the cell membrane
is to hold the cell together. It keeps all of the
pieces, like the organelles and the CYTOPLASM,
inside. The membrane also controls what goes in
and out of the cell. It acts like a crossing
guard and says "You better stop right there
buddy. You aren't getting in here." CELL
MEMBRANE STRUCTURE Scientists have a theory
about the way a cell membrane works. The theory
is called the FLUID MOSAIC MODEL. The idea says
that there are two layers of MOLECULES, a
BILAYER. These two layers are made up of
molecules called phospholipids. Take a look, it's
like a sandwich with two pieces of bread and some
alfalfa on the inside. Each phospholipid has an
HYDROPHOBIC and HYDROPHILIC end. They are big
words, but they mean very simple things. HYDRO
means water. PHOBIC means afraid. PHILIC means
loving. So one end of the molecule is afraid of
the water, and one end loves being in the water.
Millions of these molecules line up together to
form a cell membrane.
68- CELL MEMBRANE PROTEINS Throughout the membrane
are proteins stuck inside the membrane. These
proteins cross the bilayer and make the holes
that let ions and molecules in and out of the
cell. (That crossing guard thing again.) When
ions move through the cell membrane, it is called
FACILITATED DIFFUSION. Facilitated means helped.
Diffusion means moving from one area to another.
So facilitated diffusion is a procedure where an
ion is helped across the membrane. (Like helping
an old lady across the street.)
69Direction of impulse
- How do dendrites receive the message?
- Receptor proteins on their cell membranes!
- copy
70Receptor
- In biochemistry, a receptor is a protein on the
cell membrane that binds to a specific molecule
(a ligand), such as a neurotransmitter, hormone,
or other substance, and initiates the cellular
response to the ligand.
71Aim How do neurons conduct impulses?
- Do Now What will happen if your homeostasis is
disturbed/breaks down?
72Impulse travelingits a relay race
73Transmission of neural signals How it Works
- Signaling activity of the nervous system is
composed of - electrical activity within neurons and
- chemical flow between neurons.
74- Dendritesreceive signal
- Impulse passes through axon as electric (or
action) potential - When it reaches the terminal end of axon,the end
brushes secret neurotransmitters - Receptors on dendrites of the next neuron bind to
the neurotransmitters - And the impulse travels through the next neurons
body as ___________
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76How do neurons conduct (carry!) the messages (or
impulses)?
- In general, the signaling activity of the nervous
system is composed of electrical activity within
neurons and chemical flow between neurons. Quite
a complex network! - 200 years ago found out that a recently dead
animal will still contract muscles if an
electrical stimulation is sent through. - copy
77- DO YOU THINK BRAIN KNOWS/CONTROLS EVERY SINGLE
MOVEMENT IN YOUR BODY? - NOOOSometimes spinal cord comes in handyfor
emergency responses
78The Patellar Reflex
79Reflex action
- Being an involuntary action or response, such as
a sneeze, blink, or hiccup. - Produced as an automatic response or reaction
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83Peripheral Nervous System(2 Types)
- Somatic nervous system
- is for voluntary muscle control. These neurons
control the skeletal muscles. - Also some spinal reflexes. EX patellar reflex
- Autonomic nervous system
- is automatic. Control of heart rate,
respiration, blood pressure, smooth muscle, etc.
- This has 2 separate divisions sympathetic and
parasympathetic - Copy yes
84An Overview of the (copy) Nervous
System
Peripheral Nervous System
Central Nervous System -Brain -Spinal
Cord
Motor Neurons -carry signals
away from CNS
Sensory Neurons -carry messages towards spinal
cord from sensory receptors
Somatic System Voluntary Nerves --neurons
control skeletal muscles
Autonomic System Visceral, Involuntary --heart,
blood vessels, digestive organs, smooth muscle
Sympathetic Division --fight or
flight --activated by stress
Parasympathetic Division --Routine
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86- Acetylcholine in skeletal muscles
- Norepinephrine and Epinephrine respond to stress
- Dopamine Serotonin in the brain
- Enzymes break down neurotransmitters so neurons
are not over stimulated. - Ex. cholinesterase (breaks down
acetylcholine).
87Human Nervous System
88A General Sense
89An Overview of the Nervous System
Peripheral Nervous System
Central Nervous System -Brain -Spinal
Cord
Motor Neurons -carry signals
away from CNS
Sensory Neurons -carry messages towards spinal
cord from sensory receptors
Somatic System Voluntary Nerves --neurons
control skeletal muscles
Autonomic System Visceral, Involuntary --heart,
blood vessels, digestive organs, smooth muscle
Sympathetic Division --fight or
flight --activated by stress
Parasympathetic Division --Routine
90Nervous System Cells
- Called neurons
- Neurons have long axons that enable them to
transmit signals. Many neurons together are
called a nerve. - Each nerve has a dorsal root (info into the CNS)
and a ventral root (info out from CNS to body).
91Neuron Anatomy
92Anatomy of a Neuron
- Cell body main part
- Dendrite receives action potential
(stimulation) from other neurons - Axon branches from cell body, where the action
potential occurs - Axon terminal end of an axon
- Myelin sheath lipid layer for protection over
neurons that allows for increase in speed of
signal transmission made by Schwann cells - Nodes of Ranvier gaps in myelin sheath along
the axon, where most Na pumps are located - Synaptic Cleft gap between neurons between the
axon terminal of 1 neuron and the dendrite of a
2nd neuron
93Anatomy of a Neuron-Draw this!
94Central Nervous System (CNS)
- BRAIN
- About 1.4 kg, 2 of body weight
- About 100 billion neurons
- 12 pairs of cranial nerves are connected to the
human brain - Example Pupil reflex in response to bright
light, to avoid damage to retina. Nerves that
control this reflex are connected to the brain. - Others blinking, Hering-Breuer reflex
95Spinal Cord
- Starts at the medulla oblongata (in the brain)
- Outer area is made up of the axons of motor and
sensory neurons white matter - Inner, rigid core made up of motor neuron cell
bodies gray matter - 31 pairs of spinal nerves branch out to the body
- Spinal Reflexes these dont go to the brain,
instead they go to the spinal cord--patellar
reflex
96The Patellar Reflex
97Peripheral Nervous System(Motor and
Sensory)Motor Division signals away from CNS
- Somatic nervous system is for voluntary muscle
control. These neurons control the skeletal
muscles. Also some spinal reflexes. EX
patellar reflex - Autonomic nervous system is automatic. Control
of heart rate, respiration, blood pressure,
smooth muscle, etc. - This has 2 separate divisions sympathetic and
parasympathetic
98Autonomic Sympathetic Division Parasympathetic
Division
- Sympathetic Shunting of blood from one part of
body (ex stomach to heart) to another.
Activated by physical or emotional stress. Fight
or Flight response. - Parasympathetic Routine life, conserves energy,
heart rate lowers, digestive organs back to
normal. Rest and Ruminate response.
99Autonomic NS Parasympathetic and Sympathetic
Controls
100Peripheral Nervous SystemSensory Division
- Sensory neurons carry messages toward the CNS
from sensory receptors all over body. - Sensory receptors act as energy transducers. A
transducer is a device for converting a
non-electrical signal into an electrical one. In
this case, the electrical signal produced is the
action potential of a nerve. - Sensory receptors are in sense organs, such as
eyes, ears, mouth, nose, skin and different
regions of the brain respond to different
signals.
101Warm Up
- Thursday 1/4/07
- What are the two types of neurons of the
Peripheral Nervous System and what do they do?
102Types of Sensory Receptors
Stimulus Type of Sensory Receptor Location
Light Photoreceptors Retina
Mechanical Mechanoreceptors Under the skin, inner ear
Heat Thermoreceptors Hypothalamus, under the skin
Pressure Baroreceptors Walls of some arteries
Chemicals Chemoreceptor Mouth, nose
103Transmission of neural signals How it Works
- In general, the signaling activity of the nervous
system is composed of electrical activity within
neurons and chemical flow between neurons. Quite
a complex network! - 200 years ago found out that a recently dead
animal will still contract muscles if an
electrical stimulation is sent through.
104Within one neuron
- The resting potential of a neuron is -70
millivolts. The inside of the cell is relatively
more negative than the outside, due to an
imbalance of ions and some negatively charged
proteins inside. - When a dendrite/cell body is stimulated
(pressure, light, air vibrations, etc.),
membranes become temporarily permeable to Na ion
at the site of stimulation (triggers these gates
to open). - Na ions rush into the cell, through gated
protein channels, and the inside becomes more
positive. This reverse of polarity begins an
action potential. The action potential starts
where the cell body meets the axon. Threshold
potential is about -50 millivolts, action
potential is about 30 millivolts. - Gated channels keep opening along the axon, and
Na continues to enter. Much like fire burns
down a rope. Action potential continues from
start of axon to terminal, always in one
direction.
105And even more AH!
- Shortly after Na channels open, they close, and
the K channels open, allowing K ions to leave
the cell, and the resting potential returns. - The neuron cannot generate another action
potential during this time. Na gates close, K
flow out returns the neuron to resting potential.
This period is called the refractory period. - The Na/K pump (that we learned about in active
transport) pumps away to keep the proper
concentrations of ions across the membrane. This
requires lots of energy ATP!
106Diagram of action potential through an axon
107Transmitting to another neuron
- When the Action Potential reaches the terminal,
Ca2 gates open, Ca2 comes into the cell. - Increase in Ca2 concentration causes vesicles to
fuse with the pre-synaptic membrane and release
neurotransmitters into the synapse. - Neurotransmitters bind to receptor proteins on
the post-synaptic membrane of the next neuron,
which signals Na gates to open and the action
potential starts all over again.
108Examples of Neurotransmitters
- Acetylcholine in skeletal muscles
- Norepinephrine and Epinephrine respond to stress
- Dopamine Serotonin in the brain
- Enzymes break down neurotransmitters so neurons
are not over stimulated. - Ex. cholinesterase (breaks down
acetylcholine).
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113A Little Quiz
- 1. What is the potential for the resting neuron?
- 2. What is the potential for a neuron that is
sending an action potential? - 3. When a neuron goes from its resting potential
to its action potential which ion moves? Where
does the ion move? How does it move? Active or
Passive? - 4. When a neuron goes from its action potential
to its resting potential which ions move? Where
do they move? How does it move? Active or
Passive?
114A Few More
- 5. Where in the neuron is the presynaptic
membrane? (axon, cell body, or dendrite) - 6. What happens when the action potential reaches
the presynaptic membrane? - 7. What happens when the neurotransmitter binds
to the receptors on the postsynaptic membrane?
115Warm Up
- Thursday 1/4/07
- What are the two types of neurons of the
Peripheral Nervous System and what do they do?
116Neurons are special cells!
- Neurons have specialized extensions called
dendrites and axons. Dendrites bring information
to the cell body and axons take information away
from the cell body. - Neurons communicate with each other through an
electrochemical process. - Neurons contain some specialized structures (for
example, synapses) and chemicals (for example,
neurotransmitters).
117- Neurons come in many different shapes and sizes.
(Remember that 1 micron is equal to one
thousandth of a millimeter!).
118- In the peripheral nervous system, neurons can be
functionally divided in three ways - Sensory (afferent) - carry information INTO the
central nervous system from sense organs or motor
(efferent) - carry information away from the
central nervous system (for muscle control). - Cranial - connects the brain with the periphery
or spinal - connects the spinal cord with the
periphery. - Somatic - connects the skin or muscle with the
central nervous system or visceral - connects the
internal organs with the central nervous system.
119- Unlike cold-blooded animals like lizards and
snakes, humans keep the same body temperature at
all times - discover how a part of your brain called the
hypothalamus acts as a kind of thermostat,
keeping you as close to normal temperature as
possible!
120- discover how a part of your brain called the
hypothalamus acts as a kind of thermostat,
keeping you as close to normal temperature as
possible! - Youll also learn about different forms of
homeostasis, like how your immune system defends
you from invading viruses, how your respiratory
system regulates the amount of oxygen in your
blood, and more. If youve ever wondered how your
body regulates itself, this is the movie for you!
121What is homeostatic regulation?
- Answer
- Homeostatic regulation is controlled in the body
by the autonomic nervous system and seeks to
maintain relatively stable conditions in the
internal environment. The main gland of
homeostasis is the hypothalamus and the major
organ of homeostasis are the kidneys. -
122- NEGATIVE FEEDBACK
- Negative feedback is a process that happens when
your systems need to slow down or completely stop
a process that is happening. When you eat, food
travels into your stomach, and digestion begins.
You don't need your stomach working if you aren't
eating. The digestive system works with a series
of hormones and nervous impulses to stop and
start the secretion of acids in your stomach.
Another example of negative feedback occurs when
your body's temperature begins to rise and a
negative feedback response works to counteract
and stop the rise in temperature. Sweating is a
good example of negative feedback
123- POSITIVE FEEDBACK
- Positive feedback is the opposite of negative
feedback in that encourages a physiological
process or amplifies the action of a system.
Positive feedback is a cyclic process that can
continue to amplify your body's response to a
stimulus until a negative feedback response takes
over. An example of positive feedback also can
happen in your stomach. Your stomach normally
secretes a compound called pepsinogen that is an
inactive enzyme. As your body converts pepsinogen
to the enzyme pepsin, it triggers a process that
helps convert other pepsinogen molecules to
pepsin. This cascade effect occurs and soon your
stomach has enough pepsin molecules to digest
proteins.
124- BODY TEMPERATURE EXAMPLE
- A good example of system regulation of your body
can be found in the regulation of body
temperatures. You are a homoeothermic organism,
which means you regulate your own body
temperature. Other species like reptiles are not
homoeothermic. Anyway, if your body gets too
cold, a series of actions are taken to warm your
body. Sensors throughout your nervous system can
recognize when the temperature drops and might
trigger your muscular system to start shivering.
The constant contractions of your muscles allow
heat to be generated. Your nervous and endocrine
systems may also contract the blood vessels of
your circulatory system to keep blood in the core
of your body and not the extremities (like
fingers).
125- Shivering is one of the methods that the human
body uses to warm itself. It is a neurological
reaction, that the body executes when it gets too
cold. Joggers are familiar with the concept of
moving to stay warm they run in the coldest of
weather and manage to stay warm. Basic physics
dictate that energy taken from a storage source
(like our fat) and changed to another form of
energy (your body movements), results in yet
another form of energy - heat. So when your
muscles start moving back and fourth rapidly,
they make heat, which helps warm the body in the
cold.
126Panting?
- We know from our own experience that humans sweat
to increase cooling by evaporation. Dogs, in
contrast, have few sweat glands, and they cool
primarily by panting - a very rapid, shallow
breathing that increases evaporation from the
upper respiratory tract. Some animals use a third
method for increasing evaporation They spread
saliva over their fur and lick their limbs, thus
achieving cooling by evaporation....
127- Most homeostatic regulation is controlled by the
release of hormones into the bloodstream. However
other regulatory processes rely on simple
diffusion to maintain a balance. - Homeostatic regulation extends far beyond the
control of temperature. All animals also regulate
their blood glucose, as well as the concentration
of their blood. Mammals regulate their blood
glucose with insulin and glucagon. These hormones
are released by the pancreas. If the pancreas is
for any reason unable to produce enough of these
two hormones diabetes results. The kidneys are
used to remove excess water and ions from the
blood. These are then expelled as urine. The
kidneys perform a vital role in homeostatic
regulation in mammals removing excess water, salt
and urea from the blood. These are the body's
main waste products. - Sleep timing depends upon a balance between
homeostatic sleep propensity, the need for sleep
as a function of the amount of time elapsed since
the last adequate sleep episode, and circadian
rhythms which determine the ideal timing of a
correctly structured and restorative sleep
episode.1
128- Control Mechanisms
- All homeostatic control mechanisms have at least
three interdependent components for the variable
being regulated The receptor is the sensing
component that monitors and responds to changes
in the environment. When the receptor senses a
stimulus, it sends information to a control
center, the component that sets the range at
which a variable is maintained. The control
center determines an appropriate response to the
stimulus. The result of that response feeds to
the effector, either enhancing it with positive
feedback or depressing it with negative feedback
2
129Negative Feedback Mechanisms
- Negative feedback mechanisms reduce or suppress
the original stimulus, given the effectors
output. Most homeostatic control mechanisms
require a negative feedback loop to keep
conditions from exceeding tolerable limits. The
purpose is to prevent sudden severe changes
within a complex organism. There are hundreds of
negative feedback mechanisms in the human body.
Among the most important regulatory functions are
thermoregulation, osmoregulation, and
glucoregulation. The kidneys contribute to
homeostasis in five important ways regulation of
blood water levels, re-absorption of substances
into the blood, maintenance of salt and ion
levels in the blood, regulation of blood pH, and
excretion of urea and other wastes. - . 2
130- A negative feedback mechanism example is the
typical home heating system. Its thermostat
houses a thermometer, the receptor that senses
when the temperature is too low. The control
center, also housed in the thermostat, senses and
responds to the thermometer when the temperature
drops below a specified set point. Below that
target level, the thermostat sends a message to
the effector, the furnace. The furnace then
produces heat, which warms the house. Once the
thermostat senses a target level of heat has been
reached, it will signal the furnace to turn off,
thus maintaining a comfortable temperature - not
too hot nor cold
131- Examples of the use of negative feedback to
control its system are thermostat control,
phase-locked loop, hormonal regulation, and
temperature regulation in animals. - A simple and practical example is a thermostat.
When the temperature in a heated room reaches a
certain upper limit the room heating is switched
off so that the temperature begins to fall. When
the temperature drops to a lower limit, the
heating is switched on again. Provided the limits
are close to each other, a steady room
temperature is maintained. The same applies to a
cooling system, such as an air conditioner, a
refrigerator, or a freezer.
132Positive Feedback Mechanisms
- Positive feedback mechanisms are designed to
accelerate or enhance the output created by a
stimulus that has already been activated. - Unlike negative feedback mechanisms that initiate
to maintain or regulate physiological functions
within a set and narrow range, the positive
feedback mechanisms are designed to push levels
out of normal ranges. To achieve this purpose, a
series of events initiates a cascading process
that builds to increase the effect of the
stimulus. This process can be beneficial but is
rarely used by the body due to risks of the
acceleration becoming uncontrollable.
133- One positive feedback example event in the body
is blood platelet accumulation, which, in turn,
causes blood clotting in response to a break or
tear in the lining of blood vessels. Another
example is the release of oxytocin to intensify
the contractions that take place during
childbirth.2 - Positive feedback can also be harmful. One
particular example is when a fever causes a
positive feedback within homeostasis that pushes
the temperature continually higher. Body
temperature can reach extremes of 45C (113F),
at which cellular proteins denature, causing the
active site in proteins to change, thus causing
metabolism to stop, resulting in death.
134What is a "Feedback Loop"?Scientists 'Feedback
Loops' Are the Single-Biggest Threat to
Civilization From Global Warming
135Today it is another beautiful, sunny day in NY
and on the Arctic tundra
- It may sound nicer that way -- but it's a big
problem for the Earth. - Scientists say the warm weather adds to global
warming because of "feedback loops." - In a feedback loop, the rising temperature on the
Earth changes the environment in ways that then
create even more heat. Scientists consider
feedback loops the single-biggest threat to
civilization from global warming
136Homeostatic Imbalance
- Much disease results from disturbance of
homeostasis, a condition known as homeostatic
imbalance. As it ages, every organism will lose
efficiency in its control systems. The
inefficiencies gradually result in an unstable
internal environment that increases the risk for
illness. In addition, homeostatic imbalance is
also responsible for the physical changes
associated with aging. Even more serious than
illness and other characteristics of aging, is
death. Heart failure has been seen where nominal
negative feedback mechanisms become overwhelmed,
and destructive positive feedback mechanisms then
take over.2 - Diseases that result from a homeostatic imbalance
include diabetes, dehydration, hypoglycemia,
hyperglycemia, gout, and any disease caused by a
toxin present in the bloodstream. All of these
conditions result from the presence of an
increased amount of a particular substance. In
ideal circumstances, homeostatic control
mechanisms should prevent this imbalance from
occurring, but, in some people, the mechanisms do
not work efficiently enough or the quantity of
the substance exceeds the levels at which it can
be managed. In these cases, medical intervention
is necessary to restore the imbalance, or
permanent damage to the organs may result
137- Some biological systems exhibit negative feedback
such as the baroreflex in blood pressure
regulation and erythropoiesis. Many biological
process (e.g., in the human anatomy) use negative
feedback. Examples of this are numerous, from the
regulating of body temperature, to the regulating
of blood glucose levels. The disruption of
negative feedback can lead to undesirable
results in the case of blood glucose levels, if
negative feedback fails, the glucose levels in
the blood may begin to rise dramatically, thus
resulting in diabetes.
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