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26-1
Chapter 26
Lecture Outline
See PowerPoint Image Slides
for all figures and tables pre-inserted into
PowerPoint without notes.
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Coordination in Multicellular Animals
Maintaining a constant internal environment is crucial for large multicellular organisms.
– Accomplished by monitoring and modifying the functioning of various systems
– Called homeostasis
Homeostasis maintains oxygen levels, blood pressure, heart rate, body temperature, fluid levels, pH, etc.
Homeostasis is maintained by the nervous, endocrine and immune systems.
Example: Running up a hill
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Negative Feedback Control
A common homeostatic mechanism
Occurs when an increase in the stimulus results in a decrease in response
Functions to maintain a set point
Example: Thermostat
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Positive Feedback Regulation
When an increase in stimulus results in an increase in response
Does not result in homeostasis, but plays an important role in homeostasis
– Childbirth
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Nervous System Function
Important in making adjustments over a short time period
Transmission of information is very fast in the nervous system.
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The Structure of the Nervous System
Consists of a network of cells that carry information from one part of the body to another
Made up of specialized cells called neurons– Cell body or somacontains the nucleus– Dendritesreceive information and carry it to the
cell body– Axonscarry information away from the cell body
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The Anatomy of a Neuron
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Central Nervous System
Brain and spinal cord Protected by skull and vertebrae Receives input from sensory organs Interprets and integrates information Generates responses
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Peripheral Nervous System
Located outside the skull and vertebral column
Consists of bundles of axons and dendrites called nerves– Somatic nervous system
Nerves that control the skeletal muscles
– Autonomic nervous system Nerves that control the involuntary muscles, the heart
and glands
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Types of Neurons
Motor neurons– Carry messages from the central nervous system
to muscles and glands– Usually have one long axon that runs from the
spinal cord to the muscle or gland Sensory neurons
– Carry input from sense organs to the central nervous system
– Have long dendrites that carry input from the sense organ to the brain or spinal cord
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Organization of the Nervous System
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The Nature of Nerve Impulses
Information is transmitted through neurons in the form of nerve impulses.– Also known as action potentials– Involve a sequence of chemical events at the cell
membrane of the neuron
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Neurons have an Unequal Distribution of Ions Inside and Outside of the Cell
Active transport pumps sodium out and potassium in– More sodium is pumped out than potassium
pumped in– As a result
Sodium is concentrated outside the cell. Potassium is concentrated inside the cell.
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Neurons have an Unequal Distribution of Ions Inside and Outside of the Cell
This unequal distribution of charge generates a voltage across the neuronal cell membrane.
– Voltage is a measure of the electrical charge difference that exists between two points.
– The inside of the cell is more negative than the outside.– At rest, the membrane voltage of a neuron is about -70mV.
The voltage across the membrane makes it polarized.
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The Polarization of Cell Membranes
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Generation of a Nerve Impulse
When a neuron is stimulated by an input …– The cell membrane becomes more permeable to
sodium.– Sodium ions enter the cell down their
concentration gradient.– The inside of the cell becomes more positive.– The cell is depolarized.
The depolarization spreads down the axon.
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Generation of a Nerve Impulse
Depolarization of any one segment of membrane is brief.– Membrane becomes repolarized when potassium
flows out of the cell
Repolarization is followed by the pumping of sodium out of and potassium into the cell.– This re-establishes the original concentration
gradients.– This brings the cell back to its resting membrane
potential.
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The Nerve Impulse
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Activities at the Synapse
The synapse is the small space between the axon of one neuron and the dendrite of another neuron.
Neurons communicate with one another through the activities at the synapse.
When the nerve impulse in one neuron reaches the synapse, chemicals are released from the end of the axon.
– Called neurotransmitters– Diffuse across the synapse and bind to receptor sites on the
dendrite of the other neuron– This can cause depolarization and generate a nerve
impulse in the second neuron.
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Events at the Synapse
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Neurotransmitters
Made in the cell body and transported to the end of the axon to be stored until released.
– Acetylcholine was the first neurotransmitter identified.
Bind to receptors and stimulate them as long as they are bound
Enzymes in the synapse destroy neurotransmitters, allowing the second cell to return to resting state.
– Acetylcholinesterase is the enzyme that breaks down acetylcholine.
Many drugs interfere with neurotransmission at the synapse.
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Direction of Information Flow
Information in the nervous system only travels in one direction…– From the axon of one cell to the dendrite of
another in a synapse– From the dendrites to the cell body of one neuron– From the cell body through the axon to the
synapse
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The Organization of the Central Nervous System
The brain consists of several different regions that have specific functions.
The functions of the brain can be divided into three major levels.– Automatic activities– Basic decision making and emotions– Thinking and reasoning
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The Organization of the Central Nervous System
Spinal cord– Collection of neurons and nerve fibers surrounded by the
vertebrae– Conveys information to and from the brain
Medulla oblongata– The base of the brain where the spinal cord enters the brain– Controls fundamental life support activities such as
Blood pressure Breathing Heart rate
– Fibers from the spinal cord cross sides in the medulla Right side of body is controlled by left side of brain and vice
versa
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The Organization of the Central Nervous System
Cerebellum– Large bulge at the base of the brain– Connected to the medulla oblongata– Receives information from sensory organs that
involve balance Inner ear, eyes, pressure sensors in muscles and
tendons
– Regulates muscle activity to establish balance and coordination
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The Organization of the Central Nervous System
Pons– The region of the brain that is anterior to the medulla
oblongata– Controls many sensory and motor functions of the head and
face Thalamus
– Located between the pons and the cerebrum– Relays information between the cerebrum and the lower
centers of the brain Spinal cord, medulla, pons
– Important in awareness– Involved in sleep and arousal
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The Organization of the Central Nervous System
Hypothalamus– Involved in sleep and arousal– Important in emotions
Fear, anger, pleasure, hunger, sexual responses, pain
– Regulates body temperature, blood pressure and blood volume
– Connected to and controls the pituitary gland Controls the release of hormones
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The Functions of More Primitive Brain Regions
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The Organization of the Central Nervous System
Cerebrum– The thinking part of the brain.– Comprised of two hemispheres– Controls memory, language, movement– Responsible for the integration of sensory input– The major site of association and cognition.
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Specialized Areas of the Cerebrum
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Endocrine System
The Endocrine system– A collection of glands that communicate with one another and with
body tissues through the release of hormones. Hormones
– Chemical signals released by one organ that are transported to another organ where it triggers a change in activity
Glands– Organs that make and release specific chemicals– Endocrine glands
Lack ducts Secrete hormones in to the circulatory system
– Exocrine glands Have ducts Release their products into the digestive tract or onto the skin Digestive glands, sweat glands
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Endocrine Glands
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Endocrine System Function
Hormones released by endocrine glands travel throughout the entire body.– However, they only bind to and affect target cells
that have receptors. Target cells respond by
– Releasing products that have been previously made
– Making new molecules or increasing metabolic activity
– Dividing and growing
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Some Examples of Hormone Action
Epinephrine and norepinephrine– Released by the adrenal medulla during emergency
situations– Acts quickly
Increases heart rate, blood pressure and breathing rate Shunts blood to muscles
Antidiuretic hormone– Released from posterior pituitary in response to dehydration– Acts more slowly
Targets kidney cells Increases the re-absorption of water
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Some Examples of Hormone Action
Insulin– Works rapidly– Produced and released from the pancreas– Stimulates cells to take in glucose – Is released in response to high glucose levels in the blood
Would occur after a high carbohydrate meal– Diabetes is a lack of insulin
Cells don’t take in glucose
Growth-stimulating hormone– Works over a period of several years during childhood– Produced by the anterior pituitary– Stimulates growth
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Integration of Nervous System and Endocrine System Function
The pituitary gland links the endocrine system to the nervous system.
– Located at the base of the brain– Divided into two parts
Anterior pituitary– An endocrine gland– Produces hormones that trigger other glands to release their
hormones– Receives commands from the chemicals released from the
hypothalamus Posterior pituitary
– Part of the brain– Holds the axons from cells in the hypothalamus– Releases specific hormones into the bloodstream
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Hormones of the Pituitary
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Integration of Nervous System and Endocrine System Function
Example: In songbirds, the length of day causes hormonal changes that prepare the animals for reproduction.
– Length of day is sensed by the pineal body in the brain.– The pineal gland controls the release of chemicals from the
hypothalamus.– The chemicals released by the hypothalamus trigger the
pituitary to release hormones into the bloodstream.– These pituitary hormones stimulate the reproductive organs
to secrete reproductive hormones.– These reproductive hormones trigger courtship and mating
rituals in birds.
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Interaction Between the Endocrine and Nervous Systems
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Sensory Input
The nervous and endocrine systems respond to sensory input.– This input comes from sense organs.– Some sense organs detect external stimuli.
Vision, hearing, touch
– Other sense organs detect internal stimuli. Pain and pressure
The sense organs detect changes; the brain is responsible for perception.
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Chemical Detection
All neurons have chemical receptors on their surface.– When chemicals bind to these receptors, the
activity of the cell changes.– Usually results in depolarization and the
generation of a nerve impulse. Other types of cells have chemical receptors
as well.– The aorta can sense and respond to changes in
hydrogen ions, carbon dioxide and oxygen in the blood.
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Taste
Taste buds are sensory cells located on the tongue.
They have chemical receptors that respond to classes of molecules.
These classes correspond with the five kinds of taste we experience.– Sweet, sour, salt, bitter and umami (meaty)
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Taste
Sour and salty sensation results from ions entering taste buds and causing a depolarization.
– Sour sensing taste buds respond to hydrogen ions.– Salty sensing taste buds respond to sodium chloride.
Sweet, bitter and umami sensations result from molecules binding to receptors on taste buds.
– Sweet receptors are stimulated by sugars, artificial sweeteners, etc.
– Umami receptors are stimulated by glutamate.
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Smell
The sensory receptors in the nose are more versatile than taste buds.– They can sense thousands of different molecules
at low concentrations.– Found in the olfactory epithelium– Very sensitive– Fatigue quickly
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Vision
The sensory cells in the eyes respond to changes in the flow of light energy.
Light-sensing cells are found in the retina.– At the back of the eye– The other parts of the eye are designed to focus light
onto the retina Light-sensing cells are called rods and cones.
– Rods are very sensitive and can detect dim light but not color.
– Cones are less sensitive, but can detect different wavelengths of light (color).
– This is why we cannot see color at night.
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The Structure of the Eye
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Vision
The fovea centralis is a region in the retina with many cones and no rods.
– This area gives us the most focused and detailed vision. Rods and cones sense light because they contain
pigment molecules.– Rhodopsin is the pigment in rods.– When light hits rhodopsin, it changes shape and causes the
rod to depolarize.– This generates a nerve impulse that is sent to the brain.– Different types of cones have different pigments that
respond to specific wavelengths of light.
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Light Reception by Cones
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Hearing and Balance
One set of sensory cells in the ear responds to changes in sound waves.
– These sensory cells are found in the cochlea.– Sound is produced by the vibration of molecules.
Volume is a measure of the intensity of the vibration. Pitch is determined by the frequency of the vibration.
The other set of sensory cells in the ear responds to movements of the head.
– These cells are found in the fluid-filled semi-circular canals.– They sense the position of the head with respect to the
force of gravity. Helps maintain balance
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The Anatomy of the Ear
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Hearing
The ear is designed to funnel sound and transmit the vibrations to the sensory cells.
– External ear funnels sound to the eardrum.– The eardrum (tympanic membrane) vibrates in response to
sound.– The vibration is passed to small bones (malleus, incus and
stapes) in the middle ear.– The bones, in turn, vibrate another membrane covering the
oval window.– The oval window is an opening into the cochlea.
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Hearing
The cochlea is a tube filled with fluid under pressure. When the oval window vibrates, the fluid in the
cochlea vibrates. This vibration causes the basilar membrane to
vibrate. Sensory cells on the basilar membrane are
depolarized when it vibrates. The depolarization generates a nerve impulse that is
transmitted to the brain.
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Touch
Sensory receptors in the skin and internal organs respond to changes in pressure and temperature.
– Found all over the body, but more concentrated in certain areas
Tips of fingers, genitalia, lips, etc. That is why these areas are the most sensitive to touch.
Pain receptors in the skin and internal organs respond to cell damage and extreme pressure and temperature.
– Allows our brain to monitor our internal activities
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Output Coordination
After sensing changes in the external or internal environments,– The nervous and endocrine systems work
together to cause a change in response.
Responses may involve– Muscle contraction– Hormone secretion by glands
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Muscles
Muscle contraction facilitates movement. Muscles pull by contracting.
– But, they do not push by lengthening.– Relaxation is merely passive.
Muscles exist in antagonistic sets.– The biceps cause the arm to bend.– The triceps cause the arm to extend.– Biceps and triceps are antagonistic muscles.
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Antagonistic Muscles
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Muscular Contraction
A muscle is made up of many muscle cells. Muscle cells are made up of many myofibrils. Myofibrils are bundles of fibers made up of
myofilaments.– When these fibers move past one another, the
muscle contracts.– This movement requires the energy from ATP.
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Myofilaments and Contraction
Myofilaments are either thick or thin.– Thick filaments are made of myosin.
Shaped like a golf club The head of the ‘golf club’ is positioned to bind to the
thin filaments.– Thin filaments are made of actin, tropomyosin and
troponin. Actin filaments are shaped like two pearl necklaces
intertwined. Tropomyosin and troponin are shaped like a gold thread
that is laid on the pearl necklace.– These molecules block actin and prevent the interaction
between actin and myosin.
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The Events of Muscle Contraction
The nerve impulse arrives at the muscle cell. The muscle cell depolarizes. Calcium ions are released onto the myofibrils. The calcium ions bind to troponin, causing the
troponin-tropomyosin complex to move. This exposes actin, allowing myosin and actin to
interact. Myosin heads bind to actin, the heads flex, pulling
actin. This causes the muscle cell to shorten (contract).
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Interaction Between Actin and Myosin
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Types of Muscles
There are three types of muscles:– Skeletal
Mediate voluntary movement Arms, legs, neck, back, abdomen, lungs
– Smooth Mediate involuntary movement Digestive tract, reproductive tract
– Cardiac Heart muscle
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Skeletal Muscles
Voluntary muscle Controlled by the brain
– Brain sends the command to the spinal cord– Spinal cord sends the command to the muscles
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Skeletal Muscles
Many neurons from the spinal cord end in each muscle.– Each neuron stimulates a specific set of muscle
cells called a motor unit. A motor unit is one neuron and all of the muscle cells it
stimulates to contract.
– Each muscle has many motor units.– This allows for different intensities of contraction
in one muscle.– The intensity of contraction is dependent on how
many motor units are stimulated at once.
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Skeletal Muscles
Skeletal muscle cells contract quickly, but fatigue quickly.– Different motor units must be recruited to keep a
muscle contracted for a long time.
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Motor Units
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Smooth Muscles
Found in the muscular walls surrounding internal organs
Contract in response to being stretched– Digestive system
Is constantly stretched as food passes through The responsive contractions result in rhythmic movements that
move food through
Involuntary– Do not need direct messages from nervous system– Some respond to hormones
Uterine contractions in response to oxytocin
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Cardiac Muscle
Makes up the heart Can contract rapidly without direct nervous
system stimulation The rate of contraction can be controlled by
– The nervous system– Hormones (epinephrine and norepinephrine)
Cannot stay contracted for a long time– Must relax between contractions
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Characteristics of Different Kinds of Muscles
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Activities of Glands
There are two types of glands.– Endocrine glands
Secrete hormones into the bloodstream Pituitary, thyroid, ovary, testes, etc.
– Exocrine glands Secrete substances to the surface of the body or into the
tubular organs (gut, reproductive tract) Salivary glands, intestinal mucus glands, sweat glands, etc. Some are controlled by the nervous system (salivary). Some are controlled by hormones (digestive).
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Growth Responses
Hormones regulate growth.– Growth-stimulating hormone is produced throughout
childhood to increase the size of the body.– Testosterone released during puberty in males stimulates
Bone and muscle growth– This is why men are generally taller and more muscular than
women. Growth of the penis, larynx and hair on face and body
– Estrogen released during puberty in females stimulates Growth of reproductive organs Development of breast tissue Start of the menstrual cycle
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The Body’s Defense Mechanisms
Immunity is the ability to maintain homeostasis by resisting or defending against potentially harmful agents.
– Microbes, toxins, tumor cells, etc.
The immune system is made up of specialized cells and molecules that fight infection and disease.
– Generates nonspecific and specific defenses– Nonspecific defenses protect the body from a lot of things.– Specific defenses recognize specific threats and attack
them in specialized ways.
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Nonspecific Defenses
General ways that the body prevents disease and infection
No previous contact with the danger is required.
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Nonspecific Defenses
Defensive barriers – Skin and mucous membranes – Block the entry of pathogens– Lysozyme, found in skin, destroys bacterial cells.– Mucus traps pathogens so that they can be eliminated.
Chemicals – Complement proteins circulate in the blood and help
immune cells attack and kill pathogens.– Interferons are proteins that prevent viruses from attaching
to and entering cells. Certain types of cells
– Cells and chemicals interact to mediate inflammation. A series of events that clears a damaged area of harmful
agents and damaged tissue
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Inflammation
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Specific Defenses
These mechanisms must be turned on by a primary exposure to the harmful agent.
– Therefore, it is called “acquired immunity”. The harmful agent that causes a response is called an
antigen.– Usually a large protein– Stimulates the production of a specific defense mechanism– Becomes neutralized or destroyed by that mechanism– Can be toxins or parts of viruses or bacterial cells
T-lymphocytes and B-lymphocytes respond to antigens.– Each type of lymphocyte works a little bit differently.– Each are needed for specific immunity to work correctly.
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B-cell and Antibody Mediated Immunity
B-lymphocytes (B-cells) are made in bone marrow.– Found mostly in lymph nodes and spleen
When a B-cell contacts an antigen– Information is sent to the nucleus and genes are activated.– This results in an antibody being made that is specific to
that antigen.– The antibody will be released by the B-cell and will bind to
the antigen, making it a target for destruction.
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Classes of Antibodies
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B-cell and Antibody Mediated Immunity
After antigen binding, that B-cell will only make that specific antibody. – It has been activated.– All of their descendants will only produce that antibody.– Some descendants will be plasma cells that make and
release antibodies.– Some descendants will be memory cells.
During the infection/danger, plasma cells outnumber memory cells.
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B-cell and Antibody Mediated Immunity
After the infection/danger, plasma cell number drops; but memory cells remain.
When the same antigen appears again– The memory B-cells produce more plasma cells
very rapidly.– The plasma cells make and release antibody that
leads to the elimination of the threat.
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Immunization
A technique to induce an acquired immune response
Utilizes vaccines to expose the body to an antigen without causing an infection– Usually contains pieces of the bacteria or virus– Some are synthetic, with molecules that mimic the
real antigen.
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Immunization
When the vaccine is given, the B-cells react as described.– This is called a primary immune response.– Generates memory B cells
When the real antigen is encountered again (during infection)– The memory B cells generate a swift, massive
response.– Eliminates the infection before illness sets in
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Active Immunity due to Immunization
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T-cell and Cell-mediated Immunity
T-lymphocytes (T-cells) are made in bone marrow.– Mature in thymus– Found in blood, lymph and lymph tissue– Regulate B-cell activity– Rupture pathogens, virus-infected cells and
cancer cells
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Becoming a Specialized T cell
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Activating T-cells
T-cells only become active if the pathogen is “presented” to it by other cells.– Called antigen presenting cells (APCs)– These are macrophages that have ingested the
pathogen.– They break the pathogen into pieces and send
the pieces to their cell surface.– The APCs then present the antigen to the T-cells.
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Activating T-cells
When the T-cell detects the antigen, a signal is sent to the nucleus, DNA is altered and the cell becomes differentiated into one of three forms.– T-regulator cells– Cytotoxic T-cells– T-memory cells
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Types of T-cells
T-regulator cells– Communicate with B-cells and help them control
the amount of antibody produced– Two types of T-regulator cells
T-helper cells encourage B-cells to make antibodies. T-suppressor cells inhibit B-cells from making
antibodies.
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Types of T-cells
Cytotoxic T-cells– Move toward the pathogen and make holes in it– Target bacteria, cancer cells, transplanted cells,
parasites– Release cytokines, chemicals that attract WBCs
to the site of infection T-memory cells
– Remember specific antigens so that a faster response can be initiated upon repeated exposure
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Allergic Reactions
An allergy is an abnormal immune reaction to an antigen.– If the antigen comes from outside the body, it is
called an allergen. Food, pollen, drugs
– Involves an interaction between the antigen and a B-cell antibody
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Allergic Reactions
Type I hypersensitivity– Associated with an antibody called IgE– Upon first exposure, the allergen stimulates a
B-cell to make IgE.– Upon second exposure to the allergen, the B-cells
make a lot of IgE. IgE stimulates the release of histamine, leukotrienes
and prostaglandins. These chemicals cause skin rashes, hives, asthma,
eczema, headaches, etc.
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Allergic Reactions
Anaphylactic shock– The most severe allergic reaction– Starts with reddening of the skin and progresses
through a severe drop in blood pressure and can lead to death.
– Epinephrine will block the progression of anaphylactic shock.
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How an IgE Allergy Works
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Autoimmune and Immunodeficiency Diseases
Autoimmune diseases result from the immune system turning against normal cells or molecules in one’s body.
– The immune system attacks and kills normal, healthy cells.– Rheumatoid arthritis - normal cartilage is attacked.– Type I diabetes - cells that make insulin are attacked.
Immunodeficiency disease results when one or more components of the immune system do not work properly.
– Makes people more susceptible to infections and cancers.– SCIDS - a genetic immunodeficiency disease– AIDS - a viral-induced immunodeficiency disease