+
Area of Study 2:
EXPECTED LEARNING
To revise homeostasis and immunity
+
Quiz
 What are
two differences between the endocrine
and nervous systems?
 What are
do?
the 5 plant hormones and what do they
 What is
the main difference in the signal
transduction pathway between amine/polypeptide
and steroid hormones?
 Describe the three lines of
defence and the major
parts/cells of the immune system involved in each
 What is
an autoimmune disease? What is an
immunodeficiency disease? (definition and eg)
 What is
involved in an allergic response?
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Homeostasis
The maintenance of a constant internal
environment despite changes in external
environment
NB. Internal environment = The medium in which the body
cells of multicellular organisms are bathed (i.e. extracellular
fluid, interstitial fluid, plasma, lymph)
+
What
needs to be kept within narrow limits?
M.I.T.G.O.W.B + pH + wastes
Metabolites (eg blood glucose concentration)
Ions (eg salts)
Temperature
Gases (eg CO2 and O2)
Osmolarity (ie water balance)
Wastes (e.g. urea)
Blood Pressure
pH
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Detecting signals from external
environment
Mechanoreceptors respond to
mechanicalenergy (e.g. ear drum)
Thermoreceptors respond to heat or cold (e.g.
nerve endings in skin)
Electromagnetic receptors respond to
electromagnetic energy (e.g. ampullae of
Lorenzini in sharks)
Photoreceptors respond to visible light and UV
radiation (e.g. eyes).
Chemoreceptors respond to chemical
stimuli (e.g. olfactory)
+
Stimulus-response model
Stimulus
Receptor
Transmission nerves
Control
centre
Response
Effector
Transmission –
nerves or hormones
+
Stimulus-response model example
Negative Feedback
Increase in
blood CO2
Receptor in
arteries and
veins
Transmission nerves
Respiratory
centre in
brain
Negative feedback –
response counteracts the
stimulus
More CO2
exhaled
Respiratory
muscles in
lungs
Transmission nerves
+
Two Types of Feedback

Positive Feedback

Negative Feedback
Organ or Gland
Organ or Gland
Promotes or
encourages
more of the
original
substance
to be
released
Releases a
substance to act
on a system
Releases a secondary
substance which acts
on the gland or organ
System Acted
Upon
Inhibits
(stops)
further
release of
the
original
substance
Releases a
substance to act
on a system
System Acted
Upon
Releases a secondary
substance which acts
on the gland or organ
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Feedback Loops
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Endocrine System
 Uses
chemical signals for cell to cell
communication
 Coordinates
 Response
the function of cells
to an endocrine signal occurs within
minutes to hours
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Endocrine System
Endocrine glands
Release hormones into the
bloodstream.
Hormones
Chemicals released in one
part of the body that travel
through the bloodstream and
affect the activities of cells in
other parts. body.
+
Hormones

Cell to cell communication molecules
–
Made in gland(s) or cells
–
Transported by blood
–
Distant or local target tissue receptors – can only communicate message to cell
with the corresponding receptor (on cell membrane or within cytosol)
–
Activate physiological response
–
Negative feedback prevents hormone overproduction
+
Types of hormones
+ Long Distance Communication: Endocrine
Hormones
 Made
in endocrine
cells
 Transported
via blood
to act at a site distant
from the secreting
cell or gland
 Receptors
cells
on target
+ Local communication:
Paracrine and Autocrine Hormones
 Act
locally, either on the
secreting cell or a
neighbouring cell
 Diffuse
to target

Autocrine – receptor on same cell

Paracrine – neighbouring cells
 e.g.
cytokines in immune
system
+ Neurocrine Hormones
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Pheromones
 Chemicals released by animals to
communicate with
other members of their own species
 Can be used for:
 Attracting mates

Inducing mating activity

Marking territory

Signalling alarm

Marking food trails
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Plant tropisms
 A plant growth response to an external stimulus
 Light = phototropism
 Gravity = geotropism
 Thigmotropism = touch
http://www.youtube.com/watch?v=1ZuZ_1cQnv4&feature=related
 Growth
towards the stimulus is a positive tropism
 Growth
away from the stimulus is a negative tropism
 Responses rely
upon chemical signals that initiate a
signal transduction pathway in plant cells to produce a
growth response.
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Plant hormones
+ Auxin

Indole acetic acid and related molecules

Photo-and gravitropism

Stimulates cell elongation

Made in the shoot apex

Travels down the stem

Apical dominance

Prevents leaf abscission (ie leaf shedding)

Enhances fruit growth
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Auxin 
Cytokinin
 Cytokinins
delay and even
reverse senescence
 Release
buds from apical
dominance
 Stimulate
cell division
Cytokinins 
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Gibberellins

Essential for stem elongation

Found as the toxin produced by some fungi that caused rice to grow
too tall

Dwarf plant varieties often
lack gibberellins

Gibberellins are involved in bolting of rosette plants

Promote cell division and elongation

Gibberellins are used to improve grapes

Gibberellins are involved in seed germination
–
gibberellins will induce genes to make enzymes that break down starch
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Ethylene gas
 The
smallest hormone
 Important
in seed germination, fruit ripening,
epinasty (i.e. downward bending of leaves), abscission
of leaves
 Sex
expression in cucurbits (i.e. pumpkins, zuccini)
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Abscisic acid (ABA)
 Generally
acts as an inhibitor
 Important
 Causes
in water stress and other stresses
stomatal closure
 Prevents
premature germination of seeds
 Changes
gene expression patterns
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Responding to light
 Plants
possess light-sensitive enzymes –
phytochromes
 Exist in two forms that
interchange according
to the light they are exposed to.


active form (Pfr) at sunrise (i.e. red light)
inactive form (Pr) at sunset (ie far-red light)
 when
exposed to red light the enzyme is able
to catalyse a number of reactions within the
cell, leading to altered transcription of genes
in the nucleus, or activation of proteins
already in the cell
 influences
responses such as seed
germination, stem elongation, and formation
of leaves, flowers, fruits, and seeds
+ Photoperiodism
 Photoperiodism is
a biological response to a change in
relative length of daylight and darkness as it changes
throughout the year.
 Phytochrome, and
other chemicals not yet identified,
probably influence flowering and other growth processes.
 "Long-day
plants" flower in the spring as daylength
becomes longer (e.g. spinach).
 "Short-day
plants" flower in late summer or early autumn
when daylength becomes shorter (e.g. broad beans).
 "Day-neutral
plants" flower when they are mature.
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Signal transduction pathway
A mechanism linking a mechanical or chemical
stimulus to a specific cellular response.
Communicating cells may be
close together or far apart
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Cell communication
1.
Production of extracellular signalling molecule (called a
ligand) by a cell
2.
Detection of this ligand by a receptor protein on or in target
cell
3.
Transduction of ligand through cell
4.
Cellular response
5.
Control or regulation of ligand or response
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2. Detecting the signal
To stimulate a response, hormones bind to specific
receptor on OR in the target cell to form hormonereceptor complex

The cell targeted by a particular signal has a receptor molecule
complementary to the signal molecule, or ligand.

Most amine and polypeptide-based hormones are not able to
move through cell membrane – receptor proteins are on the cell
membrane

Steroid hormones move through membrane and bind with
receptors in cytoplasm
+ Receptor locations
 Cytosolic
–
–
–
Lipophilic ligand enters cell
Often activates gene
Slower response
 Cell
–
–
–
or Nuclear
membrane
Lipophobic ligand can't enter
cell
Outer surface receptor
Fast response
Figure 6-4: Target cell receptors
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3. Transduction

Converts the change in the receptor to a
form that can bring about a cellular
response.

This might involve a series of steps - a signal
transduction pathway - that alters and
amplifies the change.

Small amounts of signalling molecule can
produce a significant response or even
multiple responses due to amplification.
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3. Transduction
 Once
a hormone-receptor complex is formed,
the way the signal is transferred depends on the
type of hormone:

Amine and polypeptide hormones: Second messenger is
produced that stimulates cell response.

Steroid hormones: hormone can enter the cell easily, binding
to receptor and initiating response. Tends to be slower, but
longer lasting than second messenger response.
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Non-steroidal, lipophobic hormones
 Usually
involves the binding of extracellular
signalling molecules, like hormones and
neurotransmitters, to receptors that face outwards
from the membrane and trigger events inside the
cell.
 The
binding of a hormone with a receptor often
stimulates the action of a second protein (e.g. G
protein), or an enzyme, within the cytoplasm.
 This
enzyme can then stimulate the activity of
other enzymes to bring about a response.
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+
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Steroidal, lipophillic hormones

Lipid soluble hormone travels in bloodstream via a
carrier protein( insoluble in water) and passes
through the cell membrane.

Binds to receptor protein found only in target cells.

Hormone-receptor complex then enters the
nucleus.

Binds to specific regulator site for the targeted gene.

Stimulates the gene to produce mRNA.

mRNA is read by ribosomes to produce a specific
protein.
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4. Response
 the
transduction process brings about a cellular
response.

can be one of many different cellular activities, such as:
activation/inhibition of a certain enzyme
 rearrangement of the cytoskeleton
 regulate protein expression through activation of specific
genes.
 Open or close protein channels, etc

 Once
the cellular response is initiated, the ligand is
degraded by cell enzymes
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Summary
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Summary
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The nervous system
 This
communication system
controls and coordinates functions
throughout the body and responds
to internal and external stimuli.
 Maintains
homeostasis by
detecting change and coordinating
action of effector organs
 Responsible
for unidirectional, fast
communication
The Central Nervous System (CNS)
 Consists
of the brain and spinal cord
Cerebrum
brain
Cerebellum
Medulla Oblongata
Spinal Cord
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The peripheral nervous system (PNS)
 Nerves
extending out to the rest
of the body from the CNS
 Includes
all sensory neurons,
motor neurons, and sense
organs
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Nerve cells: Neurons
 The
basic functional unit of the nervous system.
 Send
impulses to and from the CNS and PNS and
the effectors (muscles/glands)
+ Types of Neurons
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The nervous system
 Sensory
receptors monitor changes in the
environment
 Afferent
or sensory nerve cells transfer
messages to the central nervous system (CNS)
 Efferent
or motor nerve cells transfer messages
from the CNS to effector organs
 (See
Jacaranda diagram)
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Nerve impulses
 Information
is transferred in the form of an
electrical impulse
 The

cell membrane of a nerve cell is polarised
i.e. there is a difference in charge between the inside and
outside of the cell
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Neuron at rest: Resting potential
 A condition
where the outside of the membrane is
positively (+) charged compared to the inside which is
negatively (-) charged.
 Neuron is said to be polarized.
+
How is resting potential maintained?
Ion Distribution
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Nerve impulses: Action potential
 As
an impulse moves along an axon, the
permeability of the membrane changes
 Positive
sodium ions move into the neuron
 Potassium ions move out of the neuron
 The inside of the membrane is positively (+) charged
compared to the outside which is negatively (-)
charged.
 This is called an ACTION POTENTIAL
+
Nerve impulses
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter14/a
nimation__the_nerve_impulse.html
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Neuron Communication: Synapses
A
synapse is the junction between two nerve
cells (e.g. axon bulb of one neuron and the
dendrite or cell body of a second neuron).
A
very small gap, called the synaptic cleft, lies
between the two neurons.
 Molecules
called neurotransmitters relay
messages across the synaptic cleft between the
two neurons. The communication between
neurons is chemical in nature.
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Neuron Communication: Synapses
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Neuron Communication: Synapses
 Communication across the synapse involves:

Release of neurotransmitters (e.g. actylcholine) from secretory
vesicles of presynaptic neuron

Exocytosis of neurotransmitter across the presynaptic membrane and
release into the synaptic cleft

Attachment of transmitter to protein receptors on the postsynaptic
membrane, opening protein channels, leading to stimulation of the
neuron or effector cell

Deactivation of neurotransmitter by enzymes and reabsorption into
presynaptic neuron
http://www.youtube.com/watchv=HXx9qlJetSU&feature=related
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Reflex arc
 An involuntary
response that is
processed in the
spinal cord not the
brain.
 Reflexes protect
the body before
the brain knows
what is going on
Definitions
 Immunity

The ability of the body to fight infection
and/or foreign invaders by producing
antibodies or killing infected cells.
 Immune

System
The system in the body responsible for
maintaining homeostasis by recognizing
harmful from non-harmful organisms and
produces an appropriate response.
Foreign Invaders
 Pathogens
 Cellular or
non-cellular
agents that cause
disease/immune response.
 Antigens
 Compounds,
usually
proteins, on the outside of
pathogens that can trigger
the immune system to
respond.
+
Major Parts of the Immune System
1.
Blood - White Blood Cells in particular.
2.
Lymphatic system - vessels carry a type of
fluid named lymph, which bathes the tissue
of the body and also is a ‘transport
network’ for immune cells.
3.
Lymph nodes - the centre of activity where
lymphocytes (a type of white blood cell)
are continually circulating from tissue in
the body, to the lymph nodes and back
again by using the bloodstream and
lymphatic vessels.
4.
Thymus Gland – Produces T Lymphocytes
5.
Bone Marrow – Produces B Lymphocytes
What is self and non-self?
•Self= cells and other substances that are a part of the
organism and carry “self” markers (i.e. MHC markers)
•Non-self = organisms, cells and other substances that are
not part of the organism and carry antigens
Major Histocompatibility Complex
• Simple terms: Major Histocompatibility
complex is a cluster of genes that produce
proteins that form the markers on our cells.
These markers are known as MHC Class 1
molecules.
• Each person’s MHC markers
are different
R.I.P.
Edward
Non-Self
MHC marker
protein recognised
How does the body fight pathogens?
The Body’s THREE lines of Defense
THIRD LINE
SECOND LINE
FIRST LINE
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Pathogen Invades Tissue
Non-Specific Defences
Specific Defences
Barriers to
Entry
Physiological
Mechanisms
Chemical
Mechanisms
Skin
Mucous
Secretions
Natural Flora
Fever
Complement
proteins
Interferons
First line of
defense
Mechanisms
Phagocytes
(granulocytes,
Macrophages),
Natural killer cells
(cytotoxic)
Second line of defense
Inflammation
Mast cells
Release of
Histamine
+
Pathogen Invades Tissue
Non-Specific Defences
Specific Defences
T-cells
B-cells
Plasma cells –
produce
antibodies
Memory cells –
remember
antigen
Helper T-cells
(Th) - stimulate
B cells
Third line of defense
Cytotoxic t-cells
(Tc) kill body cells
infected with a
pathogen
+
Antigens.
ANTIGENS: Any substance foreign to the body that triggers a response from the
immune system, such as producing antibodies in order to neutralise it.
- Usually made up of proteins but can be
polysaccharides
- All have unique shapes
- A way to remember:
antigens = antibody generators
- Antibodies are generated to attack the
pathogen behind the antigen being detected
Antibodies/Immunoglobulins
The third line of defense
involves the production of
antibodies:

Y-shaped protein molecules

Produced by B-cells

Made up of variable (recognizes
antigen) and constant regions.

Function: Recognize antigens,
bind to and deactivate them.
+
ANTIGENS AND ANTIBODIES.
http://www.youtube.com/watch?v=Ys_V6FcYD5I
IgG
IgA
IgM
IgD
IgE
Approx. Concentration in serum (mg/mL)
12
2
1
0.04
0.000.02
Ability to cross placenta
yes
no
no
no
no
Present in saliva and tears
no
yes
no
no
no
Present in milk
yes
yes
no
no
no
Active against viruses
yes
yes
some
no
no
Active against some bacteria
yes
yes
yes
no
no
Involved in allergy reaction
no
no
no
no
yes
+
Immune Response Summary
Displays copy of antigen
on surface of cell
Antigen
Humoral Immunity
Helper T - Cell
Cellular Immunity
Active Cytotoxic T-Cell
Kills Infected Cells
Memory T- Cell
Active B - Cell
Plasma Cell
Antibodies
Deactivates Antigens
Memory B-Cell
+
Clonal selection
+
Acquiring immunity
Short lasting
vaccines
Long lasting vaccines
+
Autoimmune Diseases

Autoimmune diseases cause antibodies in the immune system to act
against the body’s tissues!

There are 80 different types (e.g. MS, Chrohn’s disease etc)

The cause is unknown…
BUT, it is genetic and can pass through your family.

An autoimmune disorder may result in:
-The destruction of body tissue
-Abnormal growth of an organ
-Changes in organ function
+
Immunonodeficiency diseases
 Immunodeficiency
refers to a malfunction or
deficiency in one or more components of the
immune system.
PRIMARY IMMUNODEFICIENCY:
Disorders where part of the immune
system is missing or not functioning
properly. Most are genetic disorders.
SECONDARY IMMUNODEFICIENCY:
Same as Primary Immunodeficiency, but is
caused by a secondary nature, e.g. caused by
another disease, drug treatment or
environmental exposure to toxins (e.g. HIV
leading to AIDS)
+
Allergies

Overreaction of immune system to harmless antigens (e.g. dust,
pollen etc)

Mast cells are immune cells involved in allergic responses.
Circulating basophil cells are also involved in allergic responses, but
to a much lesser extent. Both kinds of cells contain large granules of
histamine.

IgE binds to mast cells and, to some extent, to basophils. IgE
antibodies are made against antigens such as dust, pollen and plant
spores.

If a person contains IgE antibodies for a particular antigen, they are
said to be sensitised to that antigen.

If the person is further exposed to the same antigen, cross links are

formed between the antibody on the mast cells and the antigen.
These antibody–antigen cross links trigger mast cells to release
active agents such as histamine (which causes contraction of smooth
muscle.
+
Quiz
 What are
two differences between the endocrine
and nervous systems?
 What are
do?
the 5 plant hormones and what do they
 What is
the main difference in the signal
transduction pathway between amine/polypeptide
and steroid hormones?
 Describe the three lines of
defence and the major
parts/cells of the immune system involved in each
 What is
an autoimmune disease? What is an
immunodeficiency disease? (definition and eg)
 What is
involved in an allergic response?