immune system
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Types of White Blood Cells
White blood cells (leukocytes) are immune
cells. They are produced in the bone marrow
and thymus and are transported to other
tissues via the bloodstream. There are
three main types of leukocytes in the blood:
granulocytes, monocytes, and lymphocytes.
Granulocytes (neutrophils, eosinophils,
3.
basophils, and mast cells) are inflammatory
cells that are involved in killing microbes
2
and in allergic reactions. They have large
numbers of intracellular vesicles called
granules, which contain degradative
4.
enzymes, antìmicrobial peptides, and
inflammatory mediators that can
be released by degranulation to kill
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extracellular pathogens and mobilise other
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immune cells.
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Monocytes enter tissues, where they
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become macrophages. They engulf
microbes and clear tissue debris by
phagocytosis. Lymphocytes include B cells
and T cells. B cells produce antibodies,
while T cells can activate other immune
cells or kill infected cells.
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Granulocytes and monocytes are
innate immune cells. They are particularly
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important in the early stages of immune
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responses against invading microbes. Other
granules
innate immune cells include dendritic cells
(which activate T cells) and natural killer
cells (which release their granules to kill
infected cells). Lymphocytes are adaptive
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slowly but are responsible for the
long-lasting immune memory that
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confers protection against re-infection.
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182
immune system
Function of Macrophages and Granulocytes
Macrophages patrol tissues, where they clear debris and monitor for invading microbes. They employ phagocytosis to engulf
and internalise dead cells and small microbes such as bacteria. Macrophages kill and degrade internalised microbes in acidic
intracellular compartments using enzymes and reactive oxygen and nitrogen compounds. When they detect invading microbes,
macrophages also produce inflammatory mediators to attract other immune cells.
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Neutrophils are usually the first immune cells recruited to infected tissues. Like macrophages, they undergo phagocytosis to
c¿pturc ¿nd killstr¿ll rlicroLres, bul. Lhey c¿n ¿lso kill rnicrobes that are tclo big tcl be internalised. Neutrophils undergo degranulation
to release the contents of their intracellular granules (including enzymes and antimicrobial peptides) onto extracellular targets.
They can also catch extracellular microbes in a web of extruded DNA known as a neutrophil extracellular trap (NET).
The other granulocytes - eosinophils, basophils, and mast cells - also release the contents of their granules. They are
particularly important for killing parasitic worms. ln addition, they release histamine, which increases the permeability of blood
vessels to allow more leukocytes to enter the tissues to kill invading microbes. Histamine release by these cells also triggers many
of the symptoms associated with allergies and asthma.
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irnmune system
Humoral Defence: B Lymphocytes
and Antibody Production
B cells are
lymphocytes that use
5.
immunoglobulins to detect molecular
structures known as antigens (e.9.
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components of bacteria or viruses).
lmmunoglobulins (lgA, lgD, lgE, lgG, lgM)
exist both as B cell receptors on the cell
surface and as secreted molecules known
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B
cell activation
B Cell
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as antibodies.
B cells are
activated when their B cell
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receptors detect specific antigens. Activated
B cells (known as plasma cells) produce
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antibodies, which recognise the same
antigens as the B cells that produced them.
Antibodies therefore coordinate immune
responses against specific targets.
lgA
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is secreted
in mucosal tissues (e.9.
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nd u rogenita I tracts).
lgG plays several important roles in
protection from infection. For example, it
6.
can neutralise viruses to limit their spread,
attach to bacteria to promote their uptake
by macrophages and neutrophils, or identify
cells infected with viruses to promote their
destruction by cytotoxic T cells
and natural killer cells. lgG
can
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also cross the placenta to
protect the unborn child.
lgE
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marks extracellular targets such
as parasitic worms
for destruction by
for
eosinophils and is also responsible
triggering allergic reactions.
Some activated
B cells
9.
become memory
cells, which can be reactivated months or
even years later if a specific threat is
detected again.
lmmunoglobulin
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184
immune system
Cellular Defence: T Lymphocytes
and Cell-Med¡ated lmmunity
T Cell Activation
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T cells are lymphocytes involved in adaptive immune responses. They are actlvated when their T cell
receptors detect specific antigens, but the antigens must be presented to T cells by antigen-presenting
cells such as dendritic cells. T cells mature in the thymus and are stored in lymphoid tissues (spleen
and lymph nodes). They can be effector cells, memory cells, or regulatory cells. Effector T cells can be
helper cells or cytotoxic cells. Helper T cells orchestrate cell-mediated immune responses by releasing inflammatory mediators
such as chemokines and cytokines, which attract and activate other immune cells, including macrophages and neutrophils. ln
addition, helper T cells assist in the activation of cytotoxic T cells and B cells.
Cytotoxic T cells undergo degranulation to release their granule contents to kill targets such as tumour cells or cells infected
with viruses. Some activated T cells become memory T cells, which can be reactivated upon subsequent detection of the same
threat. Along with memory B cells, they are responsible for the long-lasting immunoprotective effects of vaccines. T cells that
recognise self-antigens rather than foreign antigens are deleted in the thymus to avoid autoimmunity. Regulatory T cells also
prevent autoimmunity by suppressing immune responses.
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Degranulation of
Cytotoxic T Cell
Answers
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integration of function
Response
to
185
Exerc¡se: Metabolism
The regulation of metabolism during exercise is complex and is influenced by a number of factors, including the duration and
intensity of exercise (o/oVOrmax). ln general, low-intensity exercìse is primarily reliant on lipìd (fat)as a fuelsource, and as
exercise intensrty increases, carbohydrates (glucose) become the primary fuel source. ln contrast, proteins play a small role as a
fuel source during exercise and must first be degraded into amino acids. Proteases may be activated during extended exercise
periods (two hours or more), and amino acids may contribute as a fuel source during such times.
Accordingly, during low-intensity exercise, plasma free fatty acids (FFAs) are the primary source of fuel. As exercise intensity
increases from low to moderate, the contributron of plasma FFAs declines and there is an increased reliance upon muscle
triglycerides. At higher exercise intensities, the contribution of plasma FFAs and muscle triglycerides are equaland much smaller
in comparison to that of muscle glycogen.
100
muscle triglycerides
muscle glycogen
plasma free fatty acids
plasma glucose
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Fill in the colours that represent
the contribution of that substrate
during a given exercise intensity.
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lntegrative Response to
Exercise: Metabolism
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65
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exercise intensity (% VO, max)
Glucose is stored in the liver and skeletal muscle as glycogen. Muscle glycogen stores are affected by training status such
that aerobically trained indivrduals are able to store a greater amount of muscle glycogen to serve as a muscle fuel source.
Liver glycogen stores primarily serve to maintain blood glucose levels at rest and during low-intensity exercise, and this plasma
glucose can serve as a fuel source for muscle. As exercise intensity increases, there is a large increase in the reliance upon
muscle glycogen stores as a fuel source. The contribution of skeletal muscle glycogen as a fuel source for exercising muscle ìs
an intensity-dependent relationship.
Answers
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Response
integration of function
to Exerc¡se: Cardiovascu lar
During acute exercise, there is an elevated demand for oxygen from the working muscles. As a means to meet this elevated oxygen
demand, blood flow and oxygen delivery increase to the working tissues, in part by elevating cardiac output and redistributing
blood flow away from non-working muscles and the viscera, and towards exercising muscles via local vasodilation. ln addition to
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redistribution of blood in the periphery. there appears to be significant increase in brain blood flow associated with exercise.
Ventilation increases with exercise intensity as a means of oxygenating the blood. Further, a greater surface area of the lung is both
ventilated and perfused with blood to maximise loading of oxygen and unloading of carbon dioxide; this is reporled as improved
matching of ventilation and perfusion within the lung. lncreased cardiac output facilitates the increased delivery of oxygenated blood
to the periphery, mainly through an elevated heart rate. This increased work of the heart leads to an elevated metabolic demand on
the cardiac tissue and a subsequent increase in oxygen demand. Accordingly, blood flow within the heart muscle is also elevated to
facilitate the matching of oxygen delivery to demand. Skeletal muscle blood flow can increase 1O0{old during high-intensity exercise,
due to elevations in cardiac output and blood flow redistribution. Another adaption that occurs during exercise is a reduction in
plasma volume through a loss of water to the
contracting skeletal muscle. This leads to
haemoconcentration of red blood cells, which
facilitates extraction of oxygen by the tissue
(contracting muscle).
Cardiovascular
System Response
to Acute Exercise
brain
neural activity
_
6.
ventilation and gas exchange
7.
_
_
9. _
10. _
cardiac output
8.
coronary blood flow
_
12. _
3. _
haemoconcentration
5.
skin
blood flow
25.
._
2. _
3. _
4. _
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blood flow
blood distribution
metabolism
blood flow
lungs
24.
_
blood flow (possibly)
oxygen consumption
blood f low distribution?
heart
digestive system
1
1.
1
oxygen content
levels of energy substrates
blood
_
15. _
14.
23.
blood flow
22.
mechanical strain
21.
release of stem cells
skeleton
circulatory system
muscles
_
17. _
16.
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8.
19.
Indicate the direction of change for each element using t, !, or -. Some
answers should have two or three arrows to indicate heightened response.
_
_
20.
arterial dilation
capillary pressure and
energy substrate exchange
blood distribution
ven oco
nstriction
metabolism and blood f low
oxygen extraction and
consumption
mechanical strains
Answers
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integration of function
Response
to
Exercise: Endocrine
As exercise ensues there is withdrawal of the
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parasympathetic nervous system and activation
of the sympathetic nervous system (SNS), and the
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increase in this branch of the nervous system is
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graded with exercise intensity. At approximately
60 per cent of VO, max, there is a marked
increase in SNS activity, resulting in elevated
catecholamines concentration (noradrenaline
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and adrenaline). These catecholamines increase
heart rate and help redistribute blood flow
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to the working muscles by evoking peripheral
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(-)
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vasoconstriction. Additionally, the catecholamines
work to help mobilise fuel sources by stimulating
(- -)
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glycogenolysis and lipolysis. Another hormone
that aids in mobilising fuels for exercise is cortisol.
Released from the adrenal cortex. cortisol
100
increases gluconeogenesis and lipolysis.
Additionally, the SNS suppresses insulin secretion
during exercise in an effort to maintain blood
glucose levels. During exercise, skeletal muscle
50
20
40
60
80
40
60
80
100
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glucose uptake occurs in an insulin-independent
manner and the rate of glucose uptake during
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exercise far exceeds that observed during rest. lt
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that increases in intracellular calcium
associated with skeletal muscle contractions drive
is believed
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the insulin-independent uptake of glucose
observed with exercise. Additionally, the kidney is
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innervated by the SNS and upon activation, blood
flow to the organ will decrease in an effort to
20
100
400
redistribute blood to working muscles.
Additionally, SNS stimulation increases the
secretion of renin from the kidney which, along
300
with aldosterone and angíotensin ll, work to
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maintain blood pressure over the long term by
affecting fluid and electrolyte balance.
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Label the hormones in each graph
200
100
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Endocrine System
Response During
Acute Exercise
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6.
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Answers
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