• video on amoeba

• paramecium+moving

Ever wonder why you shiver, or why you sweat? Why do you pee or poop?

Or, breath out CO2?Why??

Why do you shiver?

Why do you sweat?

To 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

Kidneys???Too much water…OUT!!(pee)

WHY 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 ???

By Control and coordination of all the body systems

Coordination?

Working together in harmony

IT'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!!!!!!

What happens if an organism fail to do HOMEOSTASIS?

•Sickness

•Disease

WHO in my body helps maintain homeostasis?

• Who tells me to shiver, sweat, pee, poop, eat, breath, drink….blah blah blah

• Brain• Spinal cord• Nerves…• Together makes the nervous system• NEEDS HELP…• ENDOCRINE SYSTEM is the assistant

system• Makes hormones…

Regulation

• rule, requirement

• managing, organizing

• RULES???

Endocrine system

• Made up of glands

• Glands make hormones

Endocrine system

• Made up of glands

• Glands make hormones

• Digestive system

What does pancreas do?• The pancreas produces chemicals that are

crucial to proper • digestion and• blood sugar regulation. • Important hormones secreted by the pancreas

include

• insulin and

• glucagons, • which maintain the appropriate levels of

sugar throughout our body. • The parts of the pancreas responsible for the

production of hormones are called the Islets of Langerhans, which are small clusters of cells

• liver stores glucose as GLYCOGEN. Glucagon breaks down the glycogen variety of sugar and releases its components into the blood. INSULIN then appears at the site of cells to help them easily absorb the sugar. This is the process that maintains a non-diabetic's blood sugar at healthy levels.

• Explain how your body regulates blood sugar levels.

• ____________________________________________________________________________________________________________________________________________________________________________

What does an air conditioner have to do with a negative feedback loop you ask?

• What does an air conditioner have to do with a negative feedback loop you ask? Actually, more than you would think! Generally, an air conditioner has a thermostat that you set to a specific temperature.Throughout the day and especially during the summer, your home heats up to the point where it gets warmer than the temperature set on your air conditioner thermostat. As the temperature gets to hot, the air conditioner kicks on and cools the house to the set temperature. When it reaches that set temperature, the air conditioner turns off and the process continues again. This system ensures that your home is never too hot or too cold!

Parts 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….

Which 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!

Nervous system is divided into 2 main parts: Central and

Peripheral.

Human Nervous System has 2 parts

copy yes1) Central Nervous

System

2) Peripheral Nervous System

Brain Spinal Cord

NERVES

Lingo of Nervous system

•Stimulus

Stimulus• 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:

Response•The act of responding. •A reply or an answer. •A reaction, as that of an organism or a mechanism, to a specific stimulus.

Impulse• MESSAGES conducted through the cells

of nervous system

What 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.

A Neuron

A Neuron

• (Copy)

Neuron Anatomy

Lets first talk about brain…Parts of Brain: • cerebrum • cerebellum • brain stem (Medulla)• hypothalamus • pituitary gland

The 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.

And 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.

Cerebrum 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.

Your 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-boom…and 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 - it’s the home of imagination, emotional memory and bonding with others. 

The Balancing Act

• 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).

Brain 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.

• 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!

Hypothalamus 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.

Voluntary and involuntary

•Voluntary: •At will…job of cerebrum• Involuntary:•Automatic…not under your

control•Medulla…•Spinal cord

Pituitary gland! • Hey! Its TINY…but

don’t let the size fool you!!! It’s the MASTER GLAND for crying out loud…

•only about the size of a pea!

Pituitary Gland Controls Growth• Has a big JOB>>>to

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….

Nervous System Cells: Why do they have long tail-like

AXON?• Neurons have long

axons that enable them to transmit signals…

So what are nerves??

• A bundle of neurons

How many types of neurons do you think are there?

A General Sense…

Neurons: Are they all the same?

• No, Neurons can be classified by the direction that they send information.

•They are of 3 types…

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

who’s the receptor and who’s the effector…

Anatomy 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

___________ Nervous System• Sensory neurons carry

messages _________ the CNS from _________ __________ all over body.

Sensory receptors convert the signal into an __________ one…also 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.

Interneurons…are there in the brain and spinal cord to make sense of the stimulus.

Motor neurons…take the signal back to the muscles/sensory organs…

• 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

• 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]

• _______________________________________________________________________

How do dendrites

How do dendrites receive the message?

Cell 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

Cell membrane is made up of a phospholipid bilayer: it’s the

fluid mosaic model

• 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.

• 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.

• 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.)

Direction of impulse• How do

dendrites receive the message?

•Receptor proteins on their cell membranes!

• copy

Receptor

• 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.

Aim: How do neurons conduct impulses?

• Do Now: What will happen if your homeostasis is disturbed/breaks down?

Impulse traveling…it’s a relay race…

Transmission of neural signals: How it Works…

• Signaling activity of the nervous system is composed of

• electrical activity within neurons and

• chemical flow between neurons.

• Dendrites…receive 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 neuron’s body as ___________

How 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

•DO YOU THINK BRAIN KNOWS/CONTROLS EVERY SINGLE MOVEMENT IN YOUR BODY?

•NOOO…Sometimes spinal cord comes in handy…for emergency responses

The Patellar Reflex

Reflex action

• Being an involuntary action or response, such as a sneeze, blink, or hiccup.

• Produced as an automatic response or reaction

• The reflex action

Peripheral 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

parasympatheticCopy yes

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

An Overview of the (copy) Nervous System:

• 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).

Human Nervous System

Central and Peripheral

A General Sense…

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

An Overview of the Nervous System:

Nervous 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).

Neuron Anatomy

Anatomy 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

Anatomy of a Neuron-Draw this!

Central 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

Spinal 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 don’t go to the brain, instead they go to the spinal cord--patellar reflex

The Patellar Reflex

Peripheral 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

Autonomic: 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.

Autonomic NS: Parasympathetic and Sympathetic Controls

Peripheral 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.

Warm Up

• Thursday 1/4/07

What are the two types of neurons of the Peripheral Nervous System and what do they do?

• Answer:

Types 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

Transmission 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.

Within 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.

And 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!

Diagram of action potential through an axon…

Transmitting to another neuron…

• When the Action Potential reaches the terminal, Ca+2 gates open, Ca+2 comes into the cell.

• Increase in Ca+2 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.

Examples 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).

A 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?

A 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?

Warm Up

• Thursday 1/4/07

What are the two types of neurons of the Peripheral Nervous System and what do they do?

• Answer:

Neurons 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).

• Neurons come in many different shapes and sizes. (Remember that 1 micron is equal to one thousandth of a millimeter!).

• 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.

• 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!

• 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!

• You’ll 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 you’ve ever wondered how your body regulates itself, this is the movie for you!

What 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.  

•

• 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

• 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.

• 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).

• 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.  

Panting?

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....

• 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]

• 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]

Negative Feedback Mechanisms• Negative feedback mechanisms reduce or suppress the

original stimulus, given the effector’s 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]

• 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

• 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.

Positive 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.

• 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 45°C (113°F), at which cellular proteins denature, causing the active site in proteins to change, thus causing metabolism to stop, resulting in death.

What is a "Feedback Loop"?Scientists: 'Feedback Loops' Are

the Single-Biggest Threat to Civilization From Global Warming

Today 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

Homeostatic 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

• 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.