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4-18-05
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Blood Gas Continued
Structure of the Brain
Respiratory pigments transport
gases and help buffer the blood
• The low solubility of oxygen in water is a
fundamental problem for animals that rely on the
circulatory systems for oxygen delivery (gill)
– For example, a person exercising consumes almost 2
L of O2 per minute, but at normal body temperature
and air pressure, only 4.5 mL of O2 can dissolve in a
liter of blood plasma (blood without RBCs) in the
lungs.
– If 80% of the dissolved O2 were delivered to the
tissues (an unrealistically high percentage), the heart
would need to pump 500 L of blood per minute - a ton
every 2 minutes (impossible).
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• In fact, most animals transport most of the O2
bound to special proteins called respiratory
pigments instead of dissolved in solution.
– Respiratory pigments, often contained within
specialized cells, circulate with the blood.
– The presence of respiratory pigments increases the
amount of oxygen in the blood to about 200 mL of
O2 per liter of blood (normal output= 5.25liter/min.
– Exercising person output is 5 times normal.
– For our exercising individual, the cardiac output
would need to be a manageable 20-25 L of blood
per minute to meet the oxygen demands of the
systemic system.
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Oxygen Transport Pigments
• Pigments load oxygen in lung or gill and carry it to
the capillaries where it is unloaded for cell
• Hemoglobin--(tetrameric molecule inside cell)
Associated 4 iron molecules bind 4 molecular
oxygens.
• Hemocyanin--large molecule (106 Daltons)
containing many copper atoms colors hemolymph
blue found in crustaceans and molluscs.
• Chlorocruorin--large iron containing molecule found
in polychaete.
Physiologists Study Oxygen
Transport with Oxygen Binding
Curves
• Expose deoxygenated blood to increasing
amounts of air and measure the partial
pressure of oxygen in the blood with an
oxygen electrode. Plot partial pressure of
oxygen in mixtures of air versus partial
pressure of oxygen in the blood.
• Cooperative oxygen binding and release is
evident in the dissociation curve for
hemoglobin.
• Where the dissociation curve has a steep slope,
even a slight change in PO2 causes hemoglobin
to load or unload a substantial amount of O2.
• This steep part
corresponds to the range
of partial pressures
found in body tissues.
• Hemoglobin can
release an O2 reserve
to tissues with high
Fig. 42.28a
metabolism.
• Like all respiratory pigments, hemoglobin must
bind oxygen reversibly, loading oxygen at the
lungs or gills and unloading it in other parts of
the body.
– Loading and unloading depends on cooperation
among the subunits of the hemoglobin molecule.
– The binding of O2 to one subunit induces the
remaining subunits to change their shape slightly
such that their affinity for oxygen increases.
– When one subunit releases O2, the other three
quickly follow suit as a conformational change
lowers their affinity for oxygen.
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• As with all proteins, hemoglobin’s conformation
is sensitive to a variety of factors.
• For example, a drop in pH
lowers the affinity of hemoglobin for O2, an effect
called the Bohr shift.
• Because CO2 reacts with
water to form carbonic acid,
an active tissue will lower
the pH of its surroundings
and induce hemoglobin
to release more oxygen.
Fig. 42.28b
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Figure 42.28 Oxygen dissociation curves for hemoglobin
P50
Partial pressure of oxygen in
Air is 160 mm Hg
P50 is partial pressure at which
blood pigment is 50% saturated
Bohr Effect
• Lower pH shifts oxygen binding curve to
the right. That means that the oxygen is
unloaded more easily at the tissues because
of the lower pH.
• At the lungs the pH rises because the carbon
dioxide is “blown off” and curve shifts to
left making it easier to load oxygen.
Overhead of equilibrium curves
with myoglobin and cytochrome
Oxygen passed from hemoglobin to
myoglobin (in cell) to cytochrome in
mitochrondia
Figure 42.27 Loading and unloading of respiratory gases
Arterial Blood O2 saturation and O2 content
20
100
O2
Content
15
(vol. %)
(= mL O2
10
per 100mL
blood)
5
80
Arterial
blood
60
% O2
saturation 40
20
0
0
30
60
90
PO2 (mm Hg)
Overhead of oxygen content
curve
Correlation between habitat and
amount of oxygen that is carried in
the blood. Can only be observed with
an oxygen content curve.
Figure 42.29 Carbon dioxide transport in the blood
Carbonic anhydrase converts
CO2 + water to bicarbonate
Most CO2 transported
as bicarbonate in plasma
Fig. 42.29, continued
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• In addition to oxygen transport, hemoglobin
also helps transport carbon dioxide and assists
in buffering blood pH.
– About 7% of the CO2 released by respiring cells is
transported in solution.
– Another 23% binds to amino groups of hemoglobin.
– About 70% is transported as bicarbonate ions.
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Deep-diving air-breathers stockpile
oxygen and deplete it slowly
• When an air-breathing animal swims underwater,
it lacks access to the normal respiratory medium.
– Most humans can only hold their breath for 2 to 3
minutes and swim to depths of 20 m or so.
– However, a variety of seals,
sea turtles, and whales can
stay submerged for much
longer times and reach
much greater depths.(Weddell
Fig. 42.30
– 700m)
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Figure 42.30 The Weddell seal, Leptonychotes weddelli, a deep-diving mammal
Unnumbered Figure (page 899) Dissociation curves for two hemoglobins
Fetal hemoglobin
Organophosphates displace
Oxygen from hemoglobin
• One adaptation of these deep-divers, such as the
Weddell seal, is an ability to store large
amounts of O2 in the tissues.
– Compared to a human, a seal can store about twice
as much O2 per kilogram of body weight, mostly in
the blood and muscles.
– About 36% of our total O2 is in our lungs and 51%
in our blood.
– In contrast, the Weddell seal holds only about 5% of
its O2 in its small lungs (small because they exhale
before they dive and their lungs collapse so they can
avoid the bends) and stockpiles 70% in the blood.
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• Several adaptations create these physiological
differences between the seal and other deepdivers in comparison to humans.
– First, the seal has about twice the volume of blood
per kilogram of body weight as a human.
– Second, the seal can store a large quantity of
oxygenated blood in its huge spleen, releasing this
blood after the dive begins.
– Third, diving mammals have a high concentration
of an oxygen-storing protein called myoglobin in
their muscles (meat is reddish black in color).
• This enables a Weddell seal to store about 25% of its O2
in muscle, compared to only 13% in humans.
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• Diving vertebrates not only start a dive with a
relatively large O2 stockpile, but they also have
adaptations that conserve O2.
– They swim with little muscular effort and often use
buoyancy changes to glide passively downward.
– Their heart rate and O2 consumption rate decreases
during the dive (bradycardia) and most blood is
routed to the brain, spinal cord, eyes, adrenal
glands, and placenta (in pregnant seals).
– Blood supply is restricted or even shut off to the
muscles, and the muscles can continue to derive
ATP from fermentation after their internal O2 stores
are depleted (none to the kidneys—our kidneys
would “die”).
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Nervous System
CHAPTER 48
NERVOUS SYSTEMS
An Overview Of Nervous Systems
1. Nervous systems perform the three overlapping functions of sensory input,
integration, and motor output
2. Networks of neurons with intricate connections form nervous systems
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Nervous systems perform the three
overlapping functions of sensory
input, integration, and motor
output
• Peripheral nervous system (PNS).
– Sensory receptors are responsive to external and
internal stimuli.
• Such sensory input is conveyed to integration centers.
– Where the input is interpreted an associated with a response.
Fig. 48.1
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• Motor output is the conduction of signals from
integration centers to effector cells.
– Effector cells carry out the body’s response to a
stimulus.
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• The central nervous system (CNS) is
responsible for integration.
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• The signals of the nervous system are
conducted by nerves.
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Networks of neurons with intricate
connections form nervous systems
• Neuron Structure and Synapses.
– The neuron is the structural and functional unit of the
nervous system.
• Nerve impulses are conducted along a neuron.
– Dentrite  cell body  axon hillock  axon
– Some axons are insulated by a myelin sheath.
Fig. 48.2
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• A Simple Nerve Circuit – the Reflex Arc.
– A reflex is an autonomic response.
Fig. 48.3
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• A ganglion is a cluster of nerve cell bodies
within the PNS.
• A nucleus is a cluster of nerve cell bodies
within the CNS.
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• Schwann cells are found within the PNS.
– Form a myelin sheath by insulating axons.
Fig. 48.5
Degradation of Myelin Sheath=Multiple Sclerosis
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The ability of cells to respond to the
environment has evolved over
billions of years
Nervous systems show diverse
patterns of organization
• Nerve nets.
Fig. 48.15a, b
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• With cephalization come more complex nervous
systems.
Fig. 48.15c-h
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Vertebrate Nervous Systems
1. Vertebrate nervous systems have central and peripheral components
2. The divisions of the peripheral nervous system interact in maintaining
homeostasis
3. Embryonic development of the vertebrate brain reflects its evolution from three
anterior bulges of the neural tube
4. Evolutionarily older structures of the vertebrate brain regulate essential
autonomic and integrative functions
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1. Vertebrate nervous systems have
central and peripheral components
• Central nervous system (CNS).
– Brain and spinal cord.
• Both contain fluid-filled spaces which contain cerebrospinal
fluid (CSF).
– The central canal of the spinal cord is continuous with the ventricles of the
brain.
– White matter is composed of bundles of myelinated
axons
– Gray matter consists of unmyelinated axons, nuclei, and
dendrites.
• Peripheral nervous system.
– Everything outside the CNS.
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The divisions of the peripheral
nervous system interact in
maintaining
homeostasis
• Structural composition of the PNS.
– Paired cranial nerves that originate in the
brain and innervate the head and upper body.
– Paired spinal nerves that originate in the spinal
cord and innervate the entire body.
– Ganglia associated with the cranial and spinal
nerves.
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• Functional composition of the PNS.
Fig. 48.17
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• A closer look
at the (often
antagonistic)
divisions of
the
autonomic
nervous
system
(ANS).
Fig. 48.18
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