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Organismal
Systems
A Summary of Biological
Systems
Chemical Defense Systems
Animal
and plants have chemical
defenses to fight against foreign invaders.
The vertebrate immune system is one of
the best studied of these systems.
Vertebrate Immune System
The
immune system
recognizes foreign
invaders such as
viruses, bacteria, fungi,
parasites and other
pathogens.
Two major modes of
attack have evolved:
Innate Immunity
(Nonspecific,
Generalized Attack)
Acquired Immunity
(Specific, Specialized
Attack)
“Generalized Attack”:
these cells wage an
instant campaign of
destruction against any
pathogen while
signaling other cells of
the presence of intruders
“Specialized Attack”:
these cells wage a more
specific and enduring
attack and are capable
of producing lasting
immunity against
specific invaders.
Lines of Defense
The
immune system has
3 main lines of defense:
1st line: Physical barriers,
chemical barriers, and
mechanical barriers.
2nd line: Phagocytes,
complement,
inflammation, fever
3rd line: Cell-mediated
and humoral
Innate and Nonspecific
Acquired and Specific
Innate vs. Acquired Immunity
Innate
Immunity: is present at birth
(before exposure to pathogens), is
nonspecific and consists of external
barriers plus internal cellular and
chemical defenses
Acquired Immunity: develops after
exposure to foreign invaders and
involves a very specific response to
pathogens.
Fig. 43-2
Pathogens
(microorganisms
and viruses)
INNATE IMMUNITY
• Recognition of traits
shared by broad ranges
of pathogens, using a
small set of receptors
• Rapid response
ACQUIRED IMMUNITY
• Recognition of traits
specific to particular
pathogens, using a vast
array of receptors
• Slower response
Barrier defenses:
Skin
Mucous membranes
Secretions
Internal defenses:
Phagocytic cells
Antimicrobial proteins
Inflammatory response
Natural killer cells
Humoral response:
Antibodies defend against
infection in body fluids.
Cell-mediated response:
Cytotoxic lymphocytes defend
against infection in body cells.
A Microbe Invading the Body will
Encounter the Following Defenses:
1st Line of Defense:
Barrier defenses:
Skin: physical barrier prevents
entry into body: low pH prevents
microbial growth
Mucous membranes of
respiratory, urinary, and
reproductive tracts: traps
microbes, low pH of body fluids is
hostile to microbes
Once past the 1st line:
2nd
Line of Defense:
White blood cells are the
key players in a series of
increasingly specific
attacks against invading
microbes.
White
blood cells
(leukocytes): engulf a
pathogen in the body and
trap it within a vacuole. The
vacuole then fuses with a
lysosome to destroy the
microbe (phagocytosis).
Many cells are involved in
this “Generalized Attack”
The Generalized Attack
“On-the-ready”
cells of the generalized attack:
Neutrophils: “eat” pathogens and send out distress
signals.
Macrophages: arise from monocytes. They are the
“big eaters”. They circulate through the lymph
system looking for any foreign invader. Some reside
permanently in the spleen and lymph nodes, lying in
wait for microbes.
Eosinophils: release destructive enzymes to attack
large invaders like parasitic worms. Also involved in
the inflammatory response.
Basophils: contain histamines that are released
during the inflammatory response.
Dendritic cells: arise from monocytes. They stimulate
the development of acquired immunity.
Notice that all of
the immune cells
are derived from
a multi-potent
cell in the bone
marrow known as
a Hematopoietic
stem cell.
(Dendritic cells not shown)
Proteins, Complement and Inflammation
The
remaining components of the 2nd line
of defense do not involve white blood
cells.
Peptides
and proteins attack microbes
directly or impede their reproduction.
Example:
Interferon proteins provide innate
defense against viruses and help to activate
macrophages.
Interferon produced by one infected cell can induce
nearby cells to produce substances that interfere with viral
reproduction. This limits the cell-to-cell spread of viruses
About
30 proteins
make up the
complement
system, which
causes lysis of
invading cells and
helps trigger
inflammation
Inflammatory Responses
Following
an injury, mast cells release
histamine, which promotes changes in
blood vessels; this is part of the
inflammatory response
These changes increase local blood
supply and allow more phagocytes and
antimicrobial proteins to enter tissues.
Pus (a fluid rich in white blood cells, dead
microbes, and cell debris) accumulates at
the site of inflammation.
Fig. 43-8-1
Pathogen
Splinter
Chemical Macrophage
signals
Mast cell
Capillary
Red blood cells Phagocytic cell
Fig. 43-8-2
Pathogen
Splinter
Chemical Macrophage
signals
Mast cell
Capillary
Red blood cells Phagocytic cell
Fluid
Fig. 43-8-3
Pathogen
Splinter
Chemical Macrophage
signals
Mast cell
Capillary
Red blood cells Phagocytic cell
Fluid
Phagocytosis
Symptoms
of inflammation include
redness, warmth, pain, and swelling.
Inflammation can be either local or
systemic (throughout the body)
Fever is a systemic inflammatory
response triggered by pyrogens released
by macrophages, and toxins from
pathogens.
Septic shock is a life-threatening
condition caused by an overwhelming
inflammatory response.
Natural Killer Cells
The
last component of the innate immune
system are the natural killer cells.
All cells in the body (except red blood
cells) have a class 1 MHC protein on their
surface. (major histocompatibility
complex)
Cancerous or infected cells no longer
express this protein
Natural killer (NK) cells attack these
damaged cells, inhibiting further spread
of the virus or cancer.
Evading the Innate Immune System
Some
pathogens evade the innate
immune attack by modifying their surface
to prevent recognition or by resisting
breakdown following phagocytosis.
Example: Tuberculosis (TB)—these
bacterium are resistant to the enzymes
inside the lysosomes. Thus, they can hide
inside white blood cells without being
digested. This disease kills more than a
million people per year.
Acquired Immunity
The
3rd Line of Defense:
White blood cells called
lymphocytes recognize
and respond to antigens
(foreign molecules).
Lymphocytes that mature
in the thymus above the
heart are called T cells,
and those that mature in
bone marrow are called
B cells.
These are the cells
involved in the
“Specialized Attack”
Lymphocytes
contribute to
immunological memory, an enhanced
response to a foreign molecule
encountered previously. This is what
allows us to develop lifetime immunity
to diseases like chickenpox.
The specialized attack usually occurs
after being signaled by cells already
involved in the generalized attack.
Cytokines are secreted by
macrophages and dendritic cells to
recruit and activate lymphocytes.
The Specialized Attack
The
three stars of this more specialized
attack are the B cells, Helper T cells,
and Killer T cells (cytotoxic T cells).
B cells mature into plasma cells that
generate highly specific antibodies
capable of lasting immunity.
Helper T cells play a central role in
coordinating the attack
Killer T cells, once activated, destroy
virus-infected cells.
B
cells and T cells have
receptor proteins that can bind
to foreign molecules.
Each individual lymphocyte is
specialized to recognize a
specific type of molecule.
Antigen Recognition by Lymphocytes
An
antigen is any foreign
molecule to which a
lymphocyte responds
A single B cell or T cell has
about 100,000 identical antigen
receptors.
A typical immune response to a
virus is seen in the following
diagram.
From
the diagram, we can see
that there are two types of
specific responses: humoral
response (involving B-cells)
and cell mediated response
(involving cytotoxic T-cells)
The helper T cells can initiate both
responses.
Antigen Recognition
Recognition
of the antigen begins when
a macrophage (as seen in the diagram),
a B-cell, or a dendritic cell presents the
foreign antigen by engulfing the invader,
digesting the particle, and then
presenting the antigen on the cell’s
surface.
MHC
molecules (major histocompatibility
complex) are used to present the antigens
Fig. 43-12
Infected cell
Microbe
Antigenpresenting
cell
1 Antigen
associates
with MHC
molecule
Antigen
fragment
Antigen
fragment
1
Class I MHC
molecule
1
T cell
receptor
(a)
2
2
T cell
receptor
2 T cell
recognizes
combination
Cytotoxic T cell
Class I are found on body cells.
Display antigens to cytotoxic T cells
Class II MHC
molecule
(b)
Helper T cell
Class II are on macrophages,
dendritic cells or B cells. Display
to cytotoxic T cells and Helper T cells
Helper
T cells then bind to the
presented antigen and signal the
production of more T and B cells by
releasing cytokines.
This initiates both the humoral and
the cell-mediated response.
The Humoral Response
In
the humoral response, activated
B cells give rise to plasma cells,
which secrete antibodies or
immunoglobulins (Ig) specific to the
antigen presented.
Memory B cells also form during the
humoral response and persist long
after the initial infection ends.
Fig. 43-14
Antigen molecules
B cells that
differ in
antigen
specificity
Antigen
receptor
Antibody
molecules
Clone of memory cells
Clone of plasma cells
The Role of Antibodies
By
binding to a pathogen, antibodies can
neutralize the pathogen so that it can no
longer infect a host cell.
By binding to a pathogen, antibodies can
flag them so that they are more easily
and quickly identified and destroyed by
phagocytic cells.
Antibodies, together with proteins of the
complement system generate a
membrane attack complex and cell lysis.
Fig. 43-21
Viral neutralization
Opsonization
Activation of complement system and pore formation
Bacterium
Complement proteins
Virus
Formation of
membrane
attack complex
Flow of water
and ions
Macrophage
Pore
Foreign
cell
The Cell-Mediated Response
In
the cell-mediated response,
cytotoxic T- cells target intracellular
pathogens which B-cells cannot
recognize.
Antibodies are not used.
Cytotoxic T-cells and Natural Killer
cells detect and destroy altered or
infected body cells.
Memory T-cells are also generated.
Fig. 43-16
Humoral (antibody-mediated) immune response
Cell-mediated immune response
Key
Antigen (1st exposure)
+
Engulfed by
Gives rise to
Antigenpresenting cell
+
Stimulates
+
+
B cell
Helper T cell
+
Cytotoxic T cell
+
Memory
Helper T cells
+
+
+
Antigen (2nd exposure)
Plasma cells
Memory B cells
+
Memory
Cytotoxic T cells
Active
Cytotoxic T cells
Secreted
antibodies
Defend against extracellular pathogens by binding to antigens,
thereby neutralizing pathogens or making them better targets
for phagocytes and complement proteins.
Defend against intracellular pathogens
and cancer by binding to and lysing the
infected cells or cancer cells.
Primary and Secondary Responses
The
first exposure to a specific
antigen represents the primary
immune response.
During this time, plasma cells are
generated, T cells are activated,
antibodies and memory B and T
cells are produced.
In the secondary immune response,
memory cells facilitate a faster,
more efficient response.
Fig. 43-15
Antibody concentration
(arbitrary units)
Primary immune response
to antigen A produces
antibodies to A.
Secondary immune response to
antigen A produces antibodies to A;
primary immune response to antigen
B produces antibodies to B.
104
103
Antibodies
to A
102
Antibodies
to B
101
100
0
7
Exposure
to antigen A
14
21
28
35
42
Exposure to
antigens A and B
Time (days)
49
56
Lymphocyte Development
The acquired immune system has three
important properties
Receptor diversity—our cells have an amazing
ability to rearrange genes to generate over 1
million different B cells and 10 million different T
cells.
A lack of reactivity against host cells—as
lymphocytes mature, any that exhibit receptors
specific for the body’s own molecules are
destroyed by apoptosis.
Immunological memory—there is an increase in
cell number and behavior triggered by the
binding of antigen that allows the immune
system to “remember attackers”
Active and Passive Immunity
Active
immunity develops naturally in
response to an infection.
It can also develop following immunization,
also called vaccination.
Passive
immunity provides immediate,
short-term protection
It is conferred naturally when antibodies
cross the placenta from mother to fetus or
from mother to infant in breast milk.
It can be conferred artificially by injecting
antibodies into a non-immune person
Immune Rejection
Cells
transferred from one person to
another can be attacked by immune
defenses
This complicates blood transfusions and
organ transplants.
MHC molecules are different from person
to person and this difference stimulates
most organ rejections.
Successful transplants try to match MHC
tissue types and utilize immunosuppressive
drugs.
Blood Groups
Antigens on red blood cells
determine whether a person
has blood type A (A antigen),
B (B antigen), AB (both A and
B antigens), or O (neither
antigen)
Antibodies to nonself blood
types exist in the body
Transfusion with incompatible
blood leads to destruction of
the transfused cells
Recipient-donor
combinations can be fatal or
safe
Disruptions of
Immune System
Function
Allergies:
exaggerated
responses to certain
antigens called
allergens
Anaphylactic shock:
an acute, allergic, lifethreatening reaction
that can occur within
seconds of allergen
exposure
Autoimmune
Diseases: the immune
system loses
tolerance for self and
turns against certain
molecules of the
body.
Examples: Lupus,
rheumatoid arthritis,
and multiple sclerosis.
Acquired Immunodeficiency
Syndrome (AIDS):
Caused by human
immunodeficiency virus (HIV)
Infects Helper T-cells
Impairs both the humoral and the
cell-mediated immune responses.
HIV eludes the immune system
because of antigenic variation and
an ability to remain latent while
integrated into host DNA.
People with AIDS are highly
susceptible to opportunistic infections
and cancers that take advantage of
an immune system in collapse.
Cancer:
The frequency of certain
cancers increases when the immune
response is impaired.
Two suggested explanations are:
Immune system normally suppresses
cancerous cells
Increased inflammation increases the risk of
cancer.
Eliminating Wastes and
Obtaining Nutrients
Organisms
have a variety of mechanisms
for obtaining nutrients and eliminating
wastes.
These mechanisms all contribute to
maintaining homeostasis in living things.
Removal of Nitrogen Waste
All
animals must regulate the amount of, and
composition of, their body fluids.
Examples:
Sponges: have no excretory organs,: nitrogen
waste diffuses out across the body wall.
Flatworms: have a tubular excretory organ that
delivers nitrogen waste in the form of ammonia to
a special pore in the body surface.
Insects: convert ammonia to uric acid to reduce
water loss.
Vertebrates: have a urinary system with two
kidneys that filters the blood and adjusts its solute
concentration.
Circulation and Gas Exchange
In
most organisms, circulation and gas
exchange play a critical role in carrying
nutrients and oxygen to cells and assisting
in the removal of wastes.
Circulation and Gas Exchange
In
most animals, the circulatory and
respiratory systems are closely linked.
In small and/or thin animals, cells can
exchange materials directly with the
surrounding medium
In other animals, transport systems
connect the organs of exchange with
the body cells.
Most complex animals have internal
transport systems that circulate fluid.
Gastrovascular Cavities
Simple
animals, such as cnidarians
and flatworms, have a body wall
that is only two cells thick and
encloses a gastrovascular cavity.
This cavity functions in both
digestion and distribution of
substances throughout the body.
Fig. 42-2
Circular
canal
Mouth
Pharynx
Mouth
Radial canal
(a) The moon jelly Aurelia, a cnidarian
5 cm
2 mm
(b) The planarian Dugesia, a
flatworm
Open and Closed Circulatory
Systems
More
complex animals have either
open or closed circulatory systems.
Both systems have three basic
components:
A circulatory fluid (blood or
hemolymph)
A set of tubes (blood vessels)
A muscular pump (the heart)
In
insects, other arthropods, and most
molluscs, blood bathes the organs
directly in an open circulatory system
There is no distinction between blood
and interstitial fluid, and this general
body fluid is more correctly called
hemolymph.
Vertebrate animals have a closed
circulatory system in which blood is
confined to vessels and is distinct from
the interstitial fluid.
Closed systems are more efficient.
Fig. 42-3
Heart
Hemolymph in sinuses
surrounding organs
Pores
Heart
Blood
Interstitial
fluid
Small branch vessels
In each organ
Dorsal vessel
(main heart)
Tubular heart
(a) An open circulatory system
Auxiliary hearts
Ventral vessels
(b) A closed circulatory system
Organization of Vertebrate
Circulatory Systems
The
circulatory system is an example of a
homeostatic mechanism that supports the
idea of common ancestry.
It carries nutrients and oxygen to cells and
assists in the removal of wastes from cells.
All vertebrate circulatory systems are closed
(common ancestry)
However, there are variations between fish,
amphibians, and mammals that have evolved
over millions of years (diversity)
Fish: heart has two chambers (one atrium and one
ventricle) and blood flows through one circuit. It
picks up oxygen in the capillary beds of the gills and
delivers it to capillary beds in all body tissue.
Amphibians: heart has three chambers (two atria
and one ventricle) and blood flows along two
partially separated circuits. Oxygenated blood and
oxygen-poor blood mix a bit in the ventricle.
Mammals and Birds: heart has four chambers (two
atria and two ventricles) and blood flows through
two fully separated circuits. One goes to the lungs
and back and the second goes from the heart to all
body tissues and back. This keeps oxygen rich
blood completely separate from the oxygen poor
blood.
Fig. 42-4
Gill capillaries
Artery
Gill
circulation
Ventricle
Heart
Atrium
Vein
Systemic
circulation
Systemic capillaries
Fig. 42-5
Amphibians
Reptiles (Except Birds)
Mammals and Birds
Lung and skin capillaries
Lung capillaries
Lung capillaries
Pulmocutaneous
circuit
Atrium (A)
Right
systemic
aorta
Atrium (A)
Ventricle (V)
Left
Right
Systemic
circuit
Systemic capillaries
Pulmonary
circuit
A
V
Right
Pulmonary
circuit
A
A
V
Left
Systemic capillaries
Left
systemic
aorta
A
V
V
Right
Left
Systemic
circuit
Systemic capillaries
Mammalian Circulation
Mammals
provide an excellent example
of double circulation.
Blood begins its flow with the right
ventricle pumping blood to the lungs
In the lungs, the blood loads O2 and
unloads CO2
Oxygen-rich blood from the lungs enters
the heart at the left atrium and is pumped
through the aorta to the body tissues by
the left ventricle
The aorta provides blood to the heart
through the coronary arteries
Blood
returns to the heart through
the superior vena cava (blood from
head, neck, and forelimbs) and
inferior vena cava (blood from trunk
and hind limbs)
The superior vena cava and inferior
vena cava flow into the right atrium
Four valves prevent backflow of
blood in the heart.
Two
atrioventricular (AV) valves
separate each atrium and ventricle.
The semilunar valves control blood
flow to the aorta and the pulmonary
artery.
Fig. 42-6
Superior
vena cava
Capillaries of
head and
forelimbs
7
Pulmonary
artery
Pulmonary
artery
Capillaries
of right lung
Aorta
9
3
Capillaries
of left lung
3
2
4
11
Pulmonary
vein
Right atrium
1
Pulmonary
vein
5
Left atrium
10
Right ventricle
Left ventricle
Inferior
vena cava
Aorta
8
Capillaries of
abdominal organs
and hind limbs
Fig. 42-7
Pulmonary artery
Aorta
Pulmonary
artery
Right
atrium
Left
atrium
Semilunar
valve
Semilunar
valve
Atrioventricular
valve
Atrioventricular
valve
Right
ventricle
Left
ventricle
The Mammalian Heart
A
closer look at the mammalian heart
provides a better understanding of
double circulation.
The contraction, or pumping, phase is
called systole.
The relaxation, or filling, phase is called
diastole.
Fig. 42-8-1
Semilunar
valves
closed
AV
valves
open
1 Atrial and
ventricular
diastole
0.4 sec
Fig. 42-8-2
2 Atrial systole;
ventricular
diastole
Semilunar
valves
closed
0.1 sec
AV
valves
open
1 Atrial and
ventricular
diastole
0.4 sec
Fig. 42-8
2 Atrial systole;
ventricular
diastole
Semilunar
valves
closed
0.1 sec
AV
valves
open
1 Atrial and
ventricular
diastole
0.4 sec
Semilunar
valves
open
0.3 sec
AV valves
closed
3 Ventricular systole;
atrial diastole
Vessels of the Circulatory System
Three
main blood vessels are: arteries, veins
and capillaries
Arteries: carry oxygenated blood away from
heart; branch into arterioles and then to
capillaries
Capillaries: form a network known as
capillary beds; provide the site for chemical
exchange between the blood and interstitial
fluid.
Veins: carry deoxygenated blood back to
heart; capillaries converge into venules and
then into veins
The
critical exchange of substances
between the blood and interstitial fluid
takes place across the thin endothelial
walls of the capillaries
The difference between blood pressure
and osmotic pressure drives fluids out of
capillaries at the arteriole end and into
capillaries at the venule end
Fig. 42-16
Body tissue
INTERSTITIAL FLUID
Capillary
Net fluid
movement out
Net fluid
movement in
Direction of
blood flow
Pressure
Blood pressure
Inward flow
Outward flow
Osmotic pressure
Arterial end of capillary
Venous end
The
lymphatic system returns fluid that
leaks out in the capillary beds
This system aids in body defense
Fluid, called lymph, reenters the
circulation directly at the venous end
of the capillary bed and indirectly
through the lymphatic system
The lymphatic system drains into veins
in the neck
Lymph
nodes are organs that filter
lymph and play an important role in
the body’s defense
Edema is swelling caused by
disruptions in the flow of lymph
Gas Exchange
Gas
exchange supplies oxygen for
cellular respiration and disposes of
carbon dioxide.
Gases like O2 and CO2, diffuse down
pressure gradients in the lungs and
other organs from where their
partial pressures are higher to
where they are lower.
Respiratory Media
Animals
can use air or water as a source
of oxygen.
Obtaining oxygen from water actually
requires greater efficiency than air
breathing since there is less oxygen
available in water than in air.
Gas exchange takes place by diffusion
across either the skin, gills, tracheae, or
lungs.
All respiratory organs increase surface
area for gas exchange.
Gills
Gills
are out foldings of the body
Fish move water over their gills and
use a countercurrent exchange
system, where blood flows in the
opposite direction to water passing
over the gills; blood is always less
saturated with O2 than the water it
meets.
Fig. 42-22
Fluid flow
through
gill filament
Oxygen-poor blood
Anatomy of gills
Oxygen-rich blood
Gill
arch
Lamella
Gill
arch
Gill filament
organization
Blood
vessels
Water
flow
Operculum
Water flow
between
lamellae
Blood flow through
capillaries in lamella
Countercurrent exchange
PO2 (mm Hg) in water
150 120 90 60 30
Gill filaments
Net diffusion of O2
from water
to blood
140 110 80 50 20
PO2 (mm Hg) in blood
Tracheal Systems
The
tracheal system of insects consists of
tiny branching tubes that penetrate the
body.
These tubes supply O2 directly to body
cells.
The respiratory and circulatory systems
are separate.
Larger insects must ventilate their tracheal
system to meet O2 demands.
Fig. 42-23
Air sacs
Tracheae
External
opening
Tracheoles
Mitochondria
Muscle fiber
Body
cell
Air
sac
Tracheole
Trachea
Air
Body wall
2.5 µm
Lungs
Lungs
are in-foldings of the body surface.
The circulatory system (open or closed)
transports gases between the lungs and
the rest of the body.
Air inhaled through the nostrils passes
through the pharynx to the larynx,
trachea, bronchi, bronchioles, and
alveoli.
Fig. 42-24
Branch of
pulmonary
vein
(oxygen-rich
blood)
Branch of
pulmonary
artery
(oxygen-poor
blood)
Terminal
bronchiole
Nasal
cavity
Pharynx
Larynx
Alveoli
(Esophagus)
Left
lung
Trachea
Right lung
Bronchus
Bronchiole
Diaphragm
Heart
SEM
50 µm
Colorized
SEM
50 µm
How animals breath
An
amphibian ventilates its lungs by
positive pressure breathing, which
forces air down the trachea.
Mammals ventilate their lungs by
negative pressure breathing, which pulls
air into the lungs.
In either case, the gas exchange must
be coordinated with circulation.
Coordination of Circulation and
Gas Exchange
Blood
arriving in the lungs has a low partial
pressure of O2 and a high partial pressure of CO2
relative to air in the alveoli
In the alveoli, O2 diffuses into the blood and CO2
diffuses into the air
In tissue capillaries, partial pressure gradients
favor diffusion of O2 into the interstitial fluids and
CO2 into the blood
Respiratory Pigments
Respiratory
pigments, proteins that
transport oxygen, greatly increase the
amount of oxygen that blood can
carry
Arthropods (other than insects) and
many molluscs have hemocyanin with
copper as the oxygen-binding
component
Most vertebrates and some
invertebrates use hemoglobin
contained within erythrocytes
Carbon Dioxide Transport
Hemoglobin
also helps transport CO2
and assists in buffering
CO2 from respiring cells diffuses into
the blood and is transported either in
blood plasma, bound to hemoglobin,
or as bicarbonate ions (HCO3–)
Developmental Regulation
Many
mechanisms control the
development of an organism.
All cells in a multicellullular organism are
derived from the same fertilized egg and
contain the same genes.
Differentiation is the process in which cells
become specialized to express certain
genes.
Example:
all cells
express genes that code
for the enzymes of
glycolysis: but only red
blood cells express the
genes that code for
hemoglobin.
Most cells use less than
10% of their genes
Cells contain
transcription factors
(regulatory proteins) that
turn on certain genes
Master Genes
Master
genes control other genes.
Example: Homeotic genes (a type of master
gene)code for the transcription factors needed
to express certain other genes. The products of
these homeotic genes cause cells to differentiate
into tissues that form specific structures like the
head.
The products of these genes create gradients
which affect other genes.
Thus, development of an embryo is controlled
layer after layer by master genes.
Defect in a Master Gene (Antennapedia gene) in
fruit flies causes legs to grow on the head.
Apoptosis
Apoptosis
(programmed cell
death) also plays a role
in normal development.
Many cells must self
destruct at a specific
time in order to ensure
proper development.
Example: Formation of
human hand
Nervous System
Many
animals have a complex
nervous system that consists of:
A central nervous system (CNS):
where integration takes place.
Consists of brain and spinal cord.
A peripheral nervous system
(PNS): brings information into and
out of the CNS.
Introduction to Information
Processing
Nervous
systems process information in
three stages: sensory input, integration,
and motor output
Sensory
receptors collect information from both
outside and inside the body. Ex: rods and
cones of the eyes; pressure receptors in the skin.
They send this information along sensory
neurons to the brain or ganglia.
Here interneurons connect sensory and motor
neurons or make local connections in the brain
and spinal cord.
Motor output leaves the brain or ganglia via
motor neurons, which transmit signals to
effectors, such as muscle cells and glands, to
trigger a response.
Fig. 48-3
Sensory input
Integration
Sensor
Motor output
Effector
Peripheral nervous
system (PNS)
Central nervous
system (CNS)
Neurons
Neurons
= nerve cells
Use two types of signals: electrical signals (long
distance) and chemical signals (short distance)
3 parts:
Cell
body—contains the nucleus and organelles
Dendrites—short extensions: receive incoming
messages from other cells
Axons—long extensions: transmit messages to other
cells.
A Synapse is a junction between an axon and
another cell.
The
synaptic terminal of one axon passes
information across the synapse in the form
of chemical messengers called
neurotransmitters
Examples of neurotransmitters include
acetylcholine, dopamine, and serotonin.
Information is transmitted from a
presynaptic cell (a neuron) to a
postsynaptic cell (a neuron, muscle, or
gland cell)
Most neurons are nourished or insulated
by cells called glia
Fig. 48-4
Dendrites
Stimulus
Nucleus
Cell
body
Axon
hillock
Presynaptic
cell
Axon
Synapse
Synaptic terminals
Postsynaptic cell
Neurotransmitter
Ion pumps and ion channels
Membrane
potential (Voltage) is
the difference in electrical charge
across the plasma membrane of a
cell.
Messages are transmitted as
changes in membrane potential
The resting potential is the
membrane potential of a neuron
at rest.
Formation of the Resting Potential
In
a mammalian neuron at resting
potential, the concentration of K+ is
greater inside the cell, while the
concentration of Na+ is greater
outside the cell
Sodium-potassium pumps use the
energy of ATP to maintain these K+
and Na+ gradients across the plasma
membrane
These concentration gradients
represent chemical potential energy
Fig. 7-16-7
EXTRACELLULAR
FLUID
[Na+] high
[K+] low
Na
Na
+
+
Na
+
Na
Na
+
+
Na
Na
+
+
Na
+
CYTOPLASM
1
Na
+
[Na+]
low
[K+] high
2
P
ADP
ATP
P
3
P
6
5
4
P
The
opening of ion channels in the
plasma membrane converts chemical
potential to electrical potential
A neuron at resting potential contains
many open K+ channels and fewer
open Na+ channels; K+ diffuses out of
the cell
Anions trapped inside the cell
contribute to the negative charge
within the neuron
Fig. 48-6a
OUTSIDE [K+]
CELL
5 mM
INSIDE [K+]
CELL 140 mM
(a)
[Na+]
[Cl–]
150 mM 120 mM
[Na+]
15 mM
[Cl–]
10 mM
[A–]
100 mM
Fig. 48-6b
Key
Na+
K+
OUTSIDE
CELL
INSIDE
CELL
(b)
Sodiumpotassium
pump
Potassium
channel
Sodium
channel
The Generation of Action Potentials
The
signals carried by axons are
called Action Potentials.
An Action potential begins when
gated ion channels opens or
closes in response to stimuli which
changes the membrane potential
of the cell.
The potassium and sodium gates
are the most important for
stimulating action potentials.
When
gated K+ channels open, K+
diffuses out, making the inside of the
cell more negative
This is hyperpolarization
If gated Na+ channels open and Na+
diffuses into the cell, then the inside
of the cell is more positive
This is depolarization.
Graded potentials are changes in
polarization where the magnitude of
the change varies with the strength
of the stimulus
Fig. 48-9a
Stimuli
Hyperpolarization
Membrane potential (mV)
+50
0
–50 Threshold
Resting
potential
–100
Hyperpolarizations
0 1 2 3 4 5
Time (msec)
(a) Graded hyperpolarizations
Fig. 48-9b
Stimuli
Depolarization
Membrane potential (mV)
+50
0
–50 Threshold
Resting
potential
–100
Depolarizations
0 1 2 3 4 5
Time (msec)
(b) Graded depolarizations
An
action potential is a brief all-or-none
depolarization of a neuron’s plasma
membrane
It occurs if a stimulus causes the
membrane voltage to cross a particular
threshold
A neuron can produce hundreds of
action potentials per second
The frequency of action potentials can
reflect the strength of a stimulus
At resting potential
1.
Most voltage-gated Na+ and K+ channels are
closed, but some K+ channels (not voltagegated) are open
Fig. 48-10-1
Key
Na+
K+
Membrane potential
(mV)
+50
Action
potential
–50
Plasma
membrane
Cytosol
Inactivation loop
1
Resting state
2
–100
Sodium
channel
4
Threshold
1
Resting potential
Depolarization
Extracellular fluid
3
0
Time
Potassium
channel
5
1
When
an action potential is
generated
2.
3.
4.
Voltage-gated Na+ channels open first and
Na+ flows into the cell
During the rising phase, the threshold is
crossed, and the membrane potential
increases
During the falling phase, voltage-gated Na+
channels become inactivated; voltage-gated
K+ channels open, and K+ flows out of the cell
Fig. 48-10-2
Key
Na+
K+
Membrane potential
(mV)
+50
Action
potential
–50
2
Plasma
membrane
Cytosol
Inactivation loop
1
Resting state
2
–100
Sodium
channel
4
Threshold
1
Resting potential
Depolarization
Extracellular fluid
3
0
Time
Potassium
channel
5
1
Fig. 48-10-3
Key
Na+
K+
3
Rising phase of the action potential
Membrane potential
(mV)
+50
Action
potential
–50
2
Plasma
membrane
Cytosol
Inactivation loop
1
Resting state
2
–100
Sodium
channel
4
Threshold
1
Resting potential
Depolarization
Extracellular fluid
3
0
Time
Potassium
channel
5
1
Fig. 48-10-4
Key
Na+
K+
3
4
Rising phase of the action potential
Membrane potential
(mV)
+50
Action
potential
–50
2
Plasma
membrane
Cytosol
Inactivation loop
1
Resting state
2
–100
Sodium
channel
4
Threshold
1
Resting potential
Depolarization
Extracellular fluid
3
0
Time
Potassium
channel
5
1
Falling phase of the action potential
5.
During the undershoot, membrane permeability to
K+ is at first higher than at rest, then voltage-gated K+
channels close; resting potential is restored
Fig. 48-10-5
Key
Na+
K+
3
4
Rising phase of the action potential
Falling phase of the action potential
Membrane potential
(mV)
+50
Action
potential
–50
2
2
4
Threshold
1
1
5
Resting potential
Depolarization
Extracellular fluid
3
0
–100
Sodium
channel
Time
Potassium
channel
Plasma
membrane
Cytosol
Inactivation loop
5
1
Resting state
Undershoot
Saltatory Conduction
Action
potentials travel in one direction
only.
Their speed is influenced by the myelin
sheath (insulating layer of glia cells)
Action potential form only at the Nodes of
Ranvier (gaps in the myelin sheath)
They jump from node to node in a
movement called, saltatory conduction,
which greatly increases their speed.
Fig. 48-13
Schwann cell
Depolarized region
(node of Ranvier)
Cell body
Myelin
sheath
Axon
Synapses
Nerve
cells communicate with each other
at gaps known as synapses
Most synapses are chemical synapses
and involve neurotransmitters.
Action potentials cause the release of
neurotransmitters.
They travel across the synaptic cleft and
affect the post synaptic cell.
Neurotransmitters can be excitatory or
inhibitory.
Fig. 48-15
5
Synaptic vesicles
containing
neurotransmitter
Voltage-gated
Ca2+ channel
1 Ca2+
Synaptic
cleft
Presynaptic
membrane
Postsynaptic
membrane
4
2
3
Ligand-gated
ion channels
6
K+
Na+
Five Major Types of Neurotransmitters