Transcript Gas Exchange - Crestwood Local Schools

Gas Exchange
By Zoe Kopp-Weber
Coevolution of circulatory
and respiratory systems
 Allowed for vertebrates to develop
larger bodies and locomotion.
 As these abilities grew, the need for
efficient delivery of nutrients and O2
and removal of wastes and CO2 from
the growing mass of tissues grew too.
Coevolution of circulatory
and respiratory systems
(cont.)
 Gills developed in fish and with it the 4-
chamber heart, one of the major
evolutionary innovations in vertebrates.
 Mammals, birds and crocodiles also
have a 4-chamber heart, with 2
separate atria and 2 separate
ventricles.
 Right atrium receives deoxygenated blood
and sends it to right ventricle which pumps
blood to lungs. Left atrium receives
oxygenated blood and delivers it to the left
ventricle to pump the blood to the rest of
the body.
QuickTime™ and a
TIFF (Uncompressed) decompressor
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 For most multicellular animals, gas
exchange requires special
respiratory organs which provide
intimate contact between gases in
the external environment and the
circulatory system.
 Respiration describes the uptake of O2
from the environment and disposal of
CO2 into the environment at a body
system level.
 Cellular respiration = internal
respiration
 Gas exchange = external respiration
 Communication between internal and
external respiration is provided by the
circulatory system.
 Respiration involves processes ranging
from the mechanics of breathing to the
exchange of O2 and CO2 in respiratory
organs.
 Respiratory organs
 Invertebrates: epithelium, trachae and gills
 Fish and larval amphibians: gills
 Other amphibians: skin or epithelia used as
supplemental/primary external respiratory
organ.
 Mammals, birds, reptiles, adult amphibians:
lungs
 Respiration involves the diffusion
of gases across the plasma
membrane
 Which must be surrounded by water
to be stable.
 Thus the external environment is
always aqueous, even in terrestrial
animals.
 Rate of diffusion between 2 sides of the
membrane has a relationship called
Frick’s Law of Diffusion
 R=D x A delta p/d
 R= rate
 D= diffusion constant
 A= area diffusion occurs
 Delta p= difference in concentration btw
interior of organism and external
environment
 d= distance across diffusion occurs
 Evolution has optimized R via increased
surface area, decreased distance and
increased concentration difference.
 Levels of O2 required can’t be obtained
by diffusion alone over distances
greater than 0.5 mm.
 Vertebrates decreased this distance
through the development of respiratory
organs and bringing the external
environment closer to the internal fluid
 Dry air is composed of 78.09% N,
20.95% O2, 0.93% Ar and other inert
gases, and 0.03% CO2.
 This composition remains constant at
altitudes of at least 100 km but the
amount of air decreases as the altitude
goes up.
 Humans don’t survive long over 6000
meters, though the same composition
of O2 is there, the atmospheric
pressure brings it to only half the
amount of 02 than what’s at sea level.
 Though gills are effective in aquatic
environments, there are two reasons
terrestrial animals replaced gills with
other respiratory organs.
 1. Air is less buoyant than water. Gills
collapse out of water while internal air
passages remain open because the body
provides structural support.
 2. Water diffuses into air via evaporation.
Terrestrial animals are constantly
surrounded by air and therefore lose H2O.
Gills would provide a large surface area for
H2O loss.
Terrestrial respiratory
organs
 Trachae – used by insects and is a
network of air-filled tubular passages.
 Lung – moves air through branched
tubular passages. Air is saturated with
H2O before reaching a thin, wet
membrane that allows gas exchange.
 All but birds use a uniform pool of air
 Moves in and out of the same airway passages
 Mammals have higher metabolic rates
so they require a more efficient
respiratory system.
 Lungs are packed with tiny, grape-like
sacs called alveoli. Air is inhaled
through mouth/nose, past the pharynx
to the larynx where it then passes
through the glottis and into the trachea.
 The trachea splits into right and
left bronchi which enter into each
lung and subdivide into bronchioles
that deliver air into the alveoli.
 All gas exchange btw air and blood
occurs across walls of alveoli.
QuickTime™ and a
TIFF (Uncompressed) decompressor
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 Visceral pleural membrane – a thin membrane
that covers the outside of each lung.
 Parietal pleural membrane – lines the inner
wall of the thoracic cavity.
 Pleural cavity – the space between these two
membranes, very small and filled with fluid.
 Fluid allows membranes to adhere to each other,
coupling the lungs to the thoracic cavity.
 Pleural membranes package each lung
separately so if one should collapse, the other
can function.
Mechanics of breathing
 In all terrestrial vertebrates but
amphibians, air is drawn into the lungs
by subatmospheric pressure.
 Boyle’s Law – when the volume of a given
quantity of gas increases, its pressure
decreases.
 When inhaling, volume of thorax is
increased and the lungs expand.
Lowered pressure in lungs allows air to
enter.
 Diaphragm – a muscle that increases
thoracic volume by contracting.
 When it contracts, it assumes a flattened
shape and lowers, expanding the volume of
the thorax and lungs while adding pressure
onto the abdomen.
 External intercostal muscles – also
contributes in increasing thoracic
volume.
 These muscles between the ribs contract,
causing the ribcage to expand.
QuickTime™ and a
TIFF (Uncompressed) decompressor
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 The thorax and lungs have a
degree of elasticity.
 They resists distension and recoil
when distending force subsides.
Breathing measurements
 At rest, each breath moves a tidal
volume of 500 mL of air in and out of
the lungs.
 150 mL in trachea, bronchi and bronchioles
where no gas exchange occurs.
 Anatomical dead space, air here mixes with fresh
air during inhalation.
 Maximum amount of air expired after a
maximum inhalation is called the vital
capacity.
 Averages 4.6 liters in young men and 3.1
liters in young women.
 Hypoventilating - when breathing is
insufficient to maintain normal blood
gas measurements.
 Hyperventilating – when breathing is
excessive for a particular metabolic
rate.
 Increased breathing after exercise isn’t
necessarily hyperventilating because faster
breathing is matched to faster metabolic
rate and blood gas measurements remain
normal.
Mechanism regulating
breathing
 Each breath initiated by a
respiratory controntrol center in
the medulla oblongata.
 Neurons send impulses that stimulate
muscles to contract and expand the
chest cavity.
 Though controlled automatically,
these controls can be overridden by,
for example, holding one’s breath.
 A fall in blood pH stimulates neurons in
aortic and carotid bodies
 These are sensory structures known as
peripheral chemoreceptors in the aorta and
carotid artery.
 Send impulses to the respiratory control
center in the medulla oblongata, which
stimulates increased breathing.
 responsible for immediate stimulation when
the blood partial CO2 pressure rises.
 Central chemoreceptors –
responsible for sustained increase
in ventilation if partial CO2
pressure remains elevated.
Increased respiratory rate acts to
eliminate extra CO2, bringing
blood pH to normal.
Hemoglobin and gas
transport
 When O2 diffuses from alveoli into
blood, the circulatory system then
delivers the O2 to tissues for respiration
and carries away the CO2.
 Amount of O2 dissolved in blood plasma
depends directly on the partial O2 pressure
or the air in the alveoli.
 When lungs function normally, the blood
plasma leaving the lungs have almost
as much DO as possible.
 Whole body carries almost 200 mL/L of O2,
most is bound to molecules of hemoglobin
 Hemoglobin - protein composed of
four polypeptide chains and four
organic compounds (heme
groups).
 Each heme group has an iron atom at
the center, able to bind to a molecule
of O2.
 Allows hemoglobin to carry four
molecules of O2.
 Hemoglobin loaded with O2 forms
oxyhemoglobin.
 Bright red, tomato juice color
 As blood passes capillaries, some
oxyhemoglobin releases oxygen,
becoming deoxyhemoglobin
 Dark red but gives tissues a bluish tinge.
 Red color,
oxygenated
 Blue color,
oxygen-depleted
QuickTime™ and a
TIFF (Uncompressed) decompressor
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 Hemoglobin is used by all
vertebrates, and also by many
invertebrates
 Other invertebrates use
hemocyanin as an oxygen-carrier
 O2 binds to copper rather than iron.
 Not found in blood cells but rather
dissolved in circulating fluid of
invertebrates
Oxygen transport
 As blood travels through the systemic
blood capillaries, O2 leaves the blood
and diffuses into tissues.
 1/5 of O2 is unloaded in tissues, 4/5 in
blood as a reserve.
 The reserve allows the blood to supply
the body O2 during exercise.
 Also ensures enough O2 to maintain life 4-5
minutes if breathing is interrupted or the
heart stops.
 O2 transport affected by
 CO2: produced by metabolizing tissues, it
combines with H2O forming carbonic acid.
This dissociates into bicarbonate and H+,
lowering blood pH.
 Also reduces hemoglobins affinity for O2 and
causes it to release O2 more readily.
 This is all called the Bohr effect.
 Increase in temperature has a similar
effect.
 Skeletal muscles produce CO2 quicker during
exercise, producing heat.
Carbon Dioxide Transport
 Systemic capillaries deliver O2 and
remove CO2 from tissues
 Majority diffuses into red blood cells where
it’s catalyzed with water to form carbonic
acid (H2CO3)
 Disassociates into bicarbonate and H+ and
moves into the plasma, exchanging a
chloride ion for a bicarbonate (chloride
shift).
 Removes large amounts of CO2 from plasma,
facilitating diffusion of additional CO2 into plasma
from surrounding tissues.
 Blood carries CO2 to the lungs in
this form.
 CO2 diffuses out of red blood cells,
into the alveoli and then leaves the
body with exhalation.
Nitric Oxide Transport
 Nitric oxide acts on many cells to
change their shape/functions.
 Causes blood vessels to expand by
relaxing surrounding muscle cells.
 Blood flow/pressure regulated by
nitric oxide in bloodstream.
 One hypothesis proposes hemoglobin
carries super nitric oxide which is able
to bind to cysteine in hemoglobin
 Dumps CO2 and picks up O2 and NO in the
lungs
 To increase blood flow, hemoglobin can
release super NO into blood, making
blood vessels expand
 Can also trap excess NO on vacant iron
atoms, making blood vessels constrict.
 Red blood cells return to lungs,
hemoglobin dumps CO2 and regular
Disease
 Emphysema - usually caused by
cigarette smoking, the vital capacity of
the lungs is reduced and alveoli are
destroyed.
 Bronchitis - a respiratory infection
affecting nose, sinus and throat, then
moves on into the lungs. Cough
produces an excess of mucus.
 Pneumonia - inflammation of the lungs
that can be caused by bacteria, viruses
or fungi. Causes coughing, fever and it
will likely make it harder to breathe.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.