chapt 48 respiratory lecture
TRANSCRIPT
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Copyright (c) The McGraw-Hill
Companies, Inc. Permission requiredfor reproduction or display. 1
CHAPTER 48
RESPIRATORYSYSTEMS
Prepared by
Brenda Leady, University of Toledo
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Gas exchange moves carbon dioxide and
oxygen between the air and blood and betweenblood and cells
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Gases Air is
21% oxygen
78% nitrogen
Less than 1% carbon dioxide and other gases
Nitrogen gas usually ignored because it is
not part of the respiratory process
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Gas pressure Atmospheric pressure pressure exerted
by the atmosphere on the body surfaces of
animals
Measure in mmHg or kPa
1kPa = 7.5 mmHg
Sea level = 760 mmHg
Atmospheric pressure decreases at higher
elevations
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Atmospheric pressure is the sum of the partialpressure (pressures exerted by each gas in air)
in proportion to their amounts
PO2 = 0.21 x 760 mmHg = 160 mmHg
Percentage of gases remain the same
regardless of altitude, but lower atmospheric
pressure results in lower partial pressures
Diffusion is driven by partial pressure gradients Rate of oxygen diffusion into blood is lower at
higher elevations
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Solubility of gases Gases dissolve in solution fresh water,
sea water or body fluids
Most gases dissolve poorly in water
Factors influencing solubility in water
Higher pressures will result in more gas in
solution up to a limit for each gas Cold water holds more gas than warm water
Other solutes decrease the amount of gasthat dissolves into solution
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Types of respiratory organs Few mechanisms for gas-exchange
Across the body surface
Across specialized organs like gills,
tracheae, or lungs
Ventilation is the process of bringing
oxygenated water or air into contact with a
gas-exchange surface
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Adaptations for gas exchange
All respiratory organs share certaincommon features
Moist surfaces in which gases dissolveand diffuse
Increased surface area for gas exchange
Extensive blood flow Thin, delicate structure
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Terrestrial vs. aquatic Different challenges to gas exchange
Aquatic animals have less available oxygen
When temperatures change in water, oxygenavailability also fluctuates
Terrestrial animals have to deal withdesiccation of respiratory membranes
Moving water of respiratory membranes takesmore effort Water is denser than air, removes heat from gill
surface and can create osmotic movement
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Body surfaces for gas exchange
Invertebrates with one or a few cell layerscan use diffusion for gas exchange
Some do not even need specializedtransport mechanisms
Some large, complex animal body
surfaces may be permeable to gases Amphibians are the only vertebrates to rely on
their skin for gas exchange under water
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External gills Vary widely in appearance but all have a
large surface area (extensive projections)
May exist in one body area or be scatteredover a large area
Limitations
Unprotected and subject to damage Energy required to wave gills back and forth
Appearance and motion may attract predators
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Internal gills Fish gills are confined and protected within
opercular cavity covered by the operculum
Gill arches main support structure Filaments branch off of gill arches
Lamellae branch off of filaments
Blood vessels run the length of the filaments Oxygen-poor blood travels through afferent vessel
Oxygen-rich blood travels through efferent vessel
Countercurrent exchange arrangement of waterand blood flow maximizes oxygen diffusion intoblood
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2 mechanisms to ventilate gills Buccal pumping hydrostatic pressure
gradient created by lowering jaw to suckwater in and opening operculum to drawwater through Flap of tissue prevents fish from swallowing
water they inhale
Ram ventilation swimming with mouth
open is more efficient Many fish use both methods
Both are flow-through systems watermoves unidirectionally
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Insect tracheae Spiracles on the body surface lead to tracheae
that branch into tracheoles terminating nearevery body cell
Small amount of fluid for gas to diffuse into Muscular movements of body draw air into and
out of tracheae
Open circulatory system of insect not used in
gas exchange Oxygen diffuses directly from air to tracheae to
tracheoles to body cells
Very efficient supports insect flight muscleswith highest metabolic rate known
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A
ir-breathing lungs With few exceptions, all air-breathing
terrestrial vertebrates use lungs
Scorpions and some spiders have book
lungs that resemble gills more
Lungs may be filled using positive or
negative pressure
Lungs can be ventilated using tidal or flow-
through systems
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Most amphibians have lungs that are simplesacs
Low surface area
Ventilate lungs similar to buccal pumping of fish
Boyles law relates gas volume and gas
pressure Decreased volume creates increased pressure
Lowers bottom jaw to create pressure gradientto suck air in
Closes mouth to raise pressure and force air intolungs positive pressure filling
A few species of reptiles also use positivepressure filling
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Mammalian respiratory systems Nose and mouth air is warmed and
humidified
Mucus in the nose cleans the air of dust Pharynx
Larynx vocal cords
Trachea glottis (opening to trachea)protected by epiglottis, rings of cartilage,cilia and mucus trap particles
Lungs
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Trachea branches into 2 bronchi
Bronchioles surrounded by circular
muscle to dilate or constrict passage Alveoli site of gas exchange
One cell thick
Coated with extracellular fluid for gases todissolve
Surfactant prevents alveoli from collapsing
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Pleural sac encases each lung
2 layers
Fluid between layers acts as lubricant andmakes layers adhere to each other
Movements of chest wall will result in lungalso moving
Lungs will be inflated by expansion of thechest wall
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Negative pressure ventilation Reptiles, birds, and mammals
Volume of lung expands, creating negative
pressure, and air drawn into lungs Mammals tidal ventilation
Inhalation intercostals contract to movechest wall up and out, diaphragm contracts
and drops down thoracic cavity enlarges,pressure drops, air sucked in
Exhalation intercostals and diaphragm relax thoracic cavity compressed, pressureincreases, air pushed out
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Tidal volume volume of air normally
breathed in and out at rest (~0.5L)
Lungs can be deflated or inflated further
Lungs never completely deflate
Held open by adherence to chest wall
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Avian lung
Flow-through system
Air sacs expand and shrink not lungs
Air sacs do not participate in gasexchange
Air enters trachea, 2 bronchi
Then parabronchi lungs
Regions of gas exchange
Blood flows crosscurrent with respect tooxygen movement (not as good as fish butbetter than mammals)
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Schmidt-Nielsen Mapped Airflow
in the Avian Respiratory System Determined pattern of air movement using
ostriches
Air flows through trachea, down bronchi, and intoposterior air sacs during inhalation
As bird exhales, air exits posterior air sacs andflows into parabronchi from back to front in the
lungs gas exchange occurs During next inhalation, air at anterior end of lungs
flows into anterior air sac
During second exhalation, air in anterior air sac
exits body
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Control of ventilation in mammals
Respiratory centers in several regions of thebrainstem
Signals travel from brain through Intercostal nerves to intercostal muscles
Phrenic nerves to diaphragm
Stretch receptors send signals to brain that
lungs are inflated this inhibits stimulus tocontract until exhalation
Can be overridden to increase or decrease rate
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Chemoreceptors in aorta, carotid arteries
and brainstem monitor Hydrogen ions (pH)
Partial pressures of oxygen and carbon
dioxide
Increase breathing rate if
Oxygen levels fall
pH drops due to increased acid production
from anaerobic metabolism or carbon dioxidefrom aerobic metabolism
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Carbon dioxide produced as wasteproduct of metabolism
Carried in blood 66% as bicarbonate ions made reversibly by
carbonic anhydrase in red blood cells
25% bound to hemoglobin
7-10% dissolved in solution in plasma and redblood cells
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Small animals have higher metabolic rates
Higher breathing rates to exchangeenough gas
Respiratory centers set at a higher frequency Similar to differences in cardiac output
Small animals have heart and lungs
proportional to body size that must beatfaster/breathe at a higher frequency tosupply higher metabolic rate
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Oxygen transport
Not enough oxygen dissolves into blood to
support metabolic needs
Respiratory pigments increase the amount
of gas carried in solution
May be contained within red blood cells or in
plasma Proteins with one or more metal ions
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Respiratory pigments
Hemoglobin iron Fe2+
4 protein subunits
Each has a heme unit contains iron
Single hemoglobin molecule binds up to 4 oxygen
molecules
Hemocyanin copper Cu2+
All have a high affinity for oxygen
Binding of oxygen is noncovalent and reversible
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Oxygen-hemoglobin dissociation curve
When PO2 is high, more O2 binds to
hemoglobin
When PO2 is low, less O2 binds to
hemoglobin
Sigmoidal curve due to cooperation
shape of hemoglobin changes as oxygenloads and unloads
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Curve can shift in
response tometabolic waste
products
Increasing amountsof CO2, H+ and
temperature make
oxygen load and
unload easier
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Curve can shift
between specieswith different
metabolic rates
Smaller animalsunload hemoglobin
more readily at any
given temperature
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Hemoglobin Evolved over 500 Million
Years Ago Oxygen-carrying molecules appear to have begun
as single-subunit proteins like myoglobin
Gene duplication resulted in hemoglobin and in
subunits of hemoglobin Mutations affect the affinity of hemoglobin for
oxygen
Sickle-cell anemia single amino acid substitutionforms long strands that deform red blood cell underlow oxygen conditions leads to anemia
Relationship between malaria and sickle-cellanemia in Africa
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Malaria caused by
Plasmodiumfalciparum growingand multiplying insidered blood cells
Sickle-cell traitprotects individualfrom developing fullblown malaria
Heterozygoteadvantage nopronounced anemia orsevere malaria
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Extreme conditions
High altitudes hemoglobin with higheraffinity for oxygen, larger hearts and lungs
than predicted for body size, highernumber of red blood cells per volume
Extended diving high numbers of redblood cells, larger blood volumes, large
amounts of myoglobin (spare oxygen forcritical structures lacking myoglobin)
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Impact on public health
Asthma Muscles around bronchioles are hyperexcitable
May have genetic basis Smoking
One of leading global causes of death
Up to 85% of all new cases of lung cancer each
year attributed to smoking In addition to its effects on cancer,
cardiovascular disease, and lung function, long-term smoking is the major cause ofemphysema
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Emphysema
Involves extensivelung damage
Reduces elasticquality of lungsand total surfacearea of alveoli
Reduced bloodoxygen and poorlung function
Several causes
Over 85% ofcases due tosmoking
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Pneumonia Infectious disease
most often caused byviruses, bacteria orother microorganismsthat enter lungs andmultiply
Fluid buildup interfereswith gas exchange
Bacterial form vaccine, antibiotics
Viral form run itscourse
Usually not serious inhealthy people