chapter 42: gas exchange 1.why is gas exchange important? -aerobic organisms need o 2 for oxidative...
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Chapter 42: Gas Exchange
1. Why is gas exchange important?- Aerobic organisms need O2 for oxidative phosphorylation (making ATP)- CO2 from citric acid cycle must be removed
Figure 42.19 The role of gas exchange in bioenergetics
Organismal level
Cellular level
Circulatory system
Cellular respiration ATPEnergy-richmoleculesfrom food
Respiratorysurface
Respiratorymedium(air or water)
O2CO2
Chapter 42: Gas Exchange
1. Why is gas exchange important?- Aerobic organisms need O2 for oxidative phosphorylation (making ATP)- CO2 from citric acid cycle must be removed
2. How have gas exchange systems changed as animals evolved? - Small, thin organisms – diffusion directly across skin- Larger organisms need a larger surface area (gills, trachea or lungs)
Figure 42.20 Diversity in the structure of gills, external body surfaces functioning in gas exchange
(a) Sea star. The gills of a sea star are simple tubular projections of the skin. The hollow core of each gillis an extension of the coelom(body cavity). Gas exchangeoccurs by diffusion across thegill surfaces, and fluid in thecoelom circulates in and out ofthe gills, aiding gas transport. The surfaces of a sea star’s tube feet also function in gas exchange.
(b) Marine worm. Many polychaetes (marine worms of the phylum Annelida) have a pair of flattened appendages called parapodia on each body segment. The parapodia serve as gillsand also function incrawling and swimming.
(d) Crayfish. Crayfish and other crustaceanshave long, feathery gills covered by the exoskeleton. Specialized body appendagesdrive water over the gill surfaces.
(c) Scallop. The gills of a scallop are long, flattened plates that project from themain body mass inside the hard shell.Cilia on the gills circulate water around the gill surfaces.
GillsGills
Gill
Parapodia
Gills
Tube foot
Coelom
Chapter 42: Gas Exchange
1. Why is gas exchange important?- Aerobic organisms need O2 for oxidative phosphorylation (making ATP)- CO2 from citric acid cycle must be removed
2. How have gas exchange systems changed as animals evolved? - Small, thin organisms – diffusion directly across skin- Larger organisms need a larger surface area (gills, trachea or lungs)
3. How have fish gills evolved for maximal gas exchange?
Figure 42.21 The structure and function of fish gills
Gill arch
Water flow Operculum
Gill arch
Blood vessel
Gillfilaments
Oxygen-poorblood
Oxygen-richblood
Water flowover lamellaeshowing % O2
Blood flowthrough capillariesin lamellaeshowing % O2
Lamella
Countercurrent exchange
100%
40%
70%
15%
90%
60%
30% 5%
At best, concurrent exchange would give blood O2 of 50%.Fish expend lots of energy ventilating – forcing water across gills to get O2.
Chapter 42: Gas Exchange
1. Why is gas exchange important?- Aerobic organisms need O2 for oxidative phosphorylation (making ATP)- CO2 from citric acid cycle must be removed
2. How have gas exchange systems changed as animals evolved? - Small, thin organisms – diffusion directly across skin- Larger organisms need a larger surface area (gills, trachea or lungs)
3. How have fish gills evolved for maximal gas exchange?4. Why don’t gills work on land?
- Too dry for gills large surface area- External gas exchange will not occur
5. What adaptations do land animals have?- Internal exchange- Tracheal systems with many openings (spiracles)
Figure 42.22 Tracheal systems
Spiracle
Tracheae
Air sacsAirsac
Body cell
Air
Trachea
Tracheole
Tracheoles Mitochondria
MyofibrilsBody wall
2.5 µm
(a) The respiratory system of an insect consists of branched internaltubes that deliver air directly to body cells. Rings of chitin reinforcethe largest tubes, called tracheae, keeping them from collapsing. Enlarged portions of tracheae form air sacs near organs that require a large supply of oxygen. Air enters the tracheae through openings called spiracles on the insect’s body surface and passes into smaller tubes called tracheoles. The tracheoles are closed and contain fluid(blue-gray). When the animal is active and is using more O2, most ofthe fluid is withdrawn into the body. This increases the surface area of air in contact with cells.
(b) This micrograph shows crosssections of tracheoles in a tinypiece of insect flight muscle (TEM).Each of the numerous mitochondriain the muscle cells lies within about5 µm of a tracheole.
Chapter 42: Gas Exchange
1. Why is gas exchange important?2. How have gas exchange systems changed as animals evolved? 3. How have fish gills evolved for maximal gas exchange?4. Why don’t gills work on land?5. What adaptations do land animals have?
- Internal exchange- Tracheal systems with many openings (spiracles)- Lungs in spiders, terrestrial snails & vertebrates
- 1 location for opening- Dense net of capillaries
6. What is the flow of air in our respiratory system?Nostrils nasal cavity pharynx larynx tracheaBronchi bronchioles alveoli
Branch from the pulmonary vein (oxygen-rich blood)
Terminal bronchiole
Branch from thepulmonaryartery(oxygen-poor blood)
Alveoli
Colorized SEMSEM
50 µ
m
50 µ
m
Heart
Left lung
Nasalcavity
Pharynx
Larynx
Diaphragm
Bronchiole
Bronchus
Right lung
Trachea
Esophagus
Figure 42.23 The mammalian respiratory system
- Mostly lined with cilia & thin layer of mucus
Chapter 42: Gas Exchange
1. Why is gas exchange important?2. How have gas exchange systems changed as animals evolved? 3. How have fish gills evolved for maximal gas exchange?4. Why don’t gills work on land?5. What adaptations do land animals have?6. What is the flow of air in our respiratory system?7. What is the difference between positive & negative breathing?
- Positive – tongue pushes air down into lungs – frogs- Negative – air pulled down into lungs - us
Figure 42.24 Negative pressure breathing
Rib cage expands asrib muscles contract
Rib cage gets smaller asrib muscles relax
Air inhaled Air exhaled
INHALATIONDiaphragm contracts
(moves down)
EXHALATIONDiaphragm relaxes
(moves up)
Diaphragm
Lung
Thoracic cavity expands & air is forced into nose.
Muscles relax & thoracic cavity gets smallerand air is forced out of nose.
Chapter 42: Gas Exchange
1. Why is gas exchange important?2. How have gas exchange systems changed as animals evolved? 3. How have fish gills evolved for maximal gas exchange?4. Why don’t gills work on land?5. What adaptations do land animals have?6. What is the flow of air in our respiratory system?7. What is the difference between positive & negative breathing?8. How is breathing controlled? (oxygen homeostasis)
- Medulla oblongata & pons- O2 sensors in aorta & carotids & CO2 sensors in carotids
PonsBreathing control centers Medulla
oblongata
Diaphragm
Carotidarteries
Aorta
Cerebrospinalfluid
Rib muscles
The control center in themedulla sets the basic
rhythm, and a control centerin the pons moderates it,
smoothing out thetransitions between
inhalations and exhalations.
Nerve impulses trigger muscle contraction. Nerves
from a breathing control centerin the medulla oblongata of the
brain send impulses to thediaphragm and rib muscles, stimulating them to contract
and causing inhalation.
In a person at rest, these nerve impulses result in
about 10 to 14 inhalationsper minute. Between
inhalations, the musclesrelax and the person exhales.
The medulla’s control center alsohelps regulate blood CO2 level. Sensorsin the medulla detect changes in the pH (reflecting CO2 concentration) of the blood and cerebrospinal fluid bathing the surface of the brain.
Nerve impulses relay changes in CO2 and O2 concentrations. Other sensors in the walls of the aortaand carotid arteries in the neck detect changes in blood pH andsend nerve impulses to the medulla. In response, the medulla’s breathingcontrol center alters the rate anddepth of breathing, increasing bothto dispose of excess CO2 or decreasingboth if CO2 levels are depressed.
The sensors in the aorta andcarotid arteries also detect changesin O2 levels in the blood and signal the medulla to increase the breathing rate when levels become very low.
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Figure 42.26 Automatic control of breathing
Chapter 42: Gas Exchange
1. Why is gas exchange important?2. How have gas exchange systems changed as animals evolved? 3. How have fish gills evolved for maximal gas exchange?4. Why don’t gills work on land?5. What adaptations do land animals have?6. What is the flow of air in our respiratory system?7. What is the difference between positive & negative breathing?8. How is breathing controlled? (oxygen homeostasis)9. How are gases exchanged across selectively permeable membranes?
- Simple diffusion
Inhaled air Exhaled air
160 0.2O2 CO2
O2 CO2
O2 CO2
O2 CO2 O2 CO2
O2 CO2 O2 CO2
O2 CO2
40 45
40 45
100 40
104 40
104 40
120 27
CO2O2
Alveolarepithelialcells
Pulmonaryarteries
Blood enteringalveolar
capillaries
Blood leavingtissue
capillaries
Blood enteringtissue
capillaries
Blood leaving
alveolar capillaries
CO2O2
Tissue capillaries
Heart
Alveolar capillaries
of lung
<40 >45
Tissue cells
Pulmonaryveins
Systemic arteriesSystemic
veinsO2
CO2
O2
CO 2
Alveolar spaces
12
43
Figure 42.27 Loading and unloading of respiratory gases
Chapter 42: Gas Exchange
1. Why is gas exchange important?2. How have gas exchange systems changed as animals evolved? 3. How have fish gills evolved for maximal gas exchange?4. Why don’t gills work on land?5. What adaptations do land animals have?6. What is the flow of air in our respiratory system?7. What is the difference between positive & negative breathing?8. How is breathing controlled? (oxygen homeostasis)9. How are gases exchanged?10. How is the O2 carried in the blood?
- By hemoglobin in RBCs
Figure 42.28 Hemoglobin loading and unloading O2
Heme group Iron atom
O2 loadedin lungs
O2 unloadedIn tissues
Polypeptide chain
O2
O2
1 RBC has 250 million Hb molecules X 4 O2 molecules =
1 billion O2 per RBC X 25 trillion RBC per person =
1 billion O2 per RBC
2.5 x 1022 O2 total
Cooperativity works in loading & unloading of O2.RBC do not have a nucleus so more room for Hb.
Chapter 42: Gas Exchange
1. Why is gas exchange important?2. How have gas exchange systems changed as animals evolved? 3. How have fish gills evolved for maximal gas exchange?4. Why don’t gills work on land?5. What adaptations do land animals have?6. What is the flow of air in our respiratory system?7. What is the difference between positive & negative breathing?8. How is breathing controlled? (oxygen homeostasis)9. How are gases exchanged?10. How is the O2 carried in the blood?11. How is O2 dumped from hemoglobin?
Figure 42.29 Dissociation curves for hemoglobin
O2 unloaded fromhemoglobinduring normalmetabolism
O2 reserve that canbe unloaded fromhemoglobin totissues with highmetabolism
Tissues duringexercise
Tissuesat rest
100
80
60
40
20
0
100
80
60
40
20
0
100806040200
100806040200
Lungs
PO2 (mm Hg)
PO2 (mm Hg)
O2 s
atur
atio
n of
hem
oglo
bin
(%)
O2 s
atur
atio
n of
hem
oglo
bin
(%)
Bohr shift:Additional O2
released from hemoglobin at lower pH(higher CO2
concentration)
pH 7.4
pH 7.2
(a) PO2 and Hemoglobin Dissociation at 37°C and ph 7.4
(b) pH and Hemoglobin Dissociation
Chapter 42: Gas Exchange
1. Why is gas exchange important?2. How have gas exchange systems changed as animals evolved? 3. How have fish gills evolved for maximal gas exchange?4. Why don’t gills work on land?5. What adaptations do land animals have?6. What is the flow of air in our respiratory system?7. What is the difference between positive & negative breathing?8. How is breathing controlled? (oxygen homeostasis)9. How are gases exchanged?10. How is the O2 carried in the blood?11. How is O2 dumped from hemoglobin?12. How does CO2 travel from tissues to lungs?
- Most dissolved in plasma as bicarbonate ion
Figure 42.30 Carbon dioxide transport in the blood
Tissue cell
CO2Interstitialfluid
CO2 producedCO2 transportfrom tissues
CO2
CO2
Blood plasmawithin capillary Capillary
wall
H2O
Redbloodcell
HbCarbonic acidH2CO3
HCO3–
H++Bicarbonate
HCO3–
Hemoglobinpicks up
CO2 and H+
HCO3–
HCO3– H++
H2CO3Hb
Hemoglobinreleases
CO2 and H+
CO2 transportto lungs
H2O
CO2
CO2
CO2
CO2
Alveolar space in lung
2
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5 6
7
8
9
10
11
To lungs
Carbon dioxide produced bybody tissues diffuses into the interstitial fluid and the plasma.
Over 90% of the CO2 diffuses into red blood cells, leaving only 7%in the plasma as dissolved CO2.
Some CO2 is picked up and transported by hemoglobin.
However, most CO2 reacts with water in red blood cells, forming carbonic acid (H2CO3), a reaction catalyzed bycarbonic anhydrase contained. Withinred blood cells.
Carbonic acid dissociates into a biocarbonate ion (HCO3
–) and a hydrogen ion (H+).
Hemoglobin binds most of the H+ from H2CO3 preventing the H+ from acidifying the blood and thuspreventing the Bohr shift.
CO2 diffuses into the alveolarspace, from which it is expelledduring exhalation. The reductionof CO2 concentration in the plasmadrives the breakdown of H2CO3 Into CO2 and water in the red bloodcells (see step 9), a reversal of the reaction that occurs in the tissues (see step 4).
Most of the HCO3– diffuse
into the plasma where it is carried in the bloodstream to the lungs.
In the HCO3– diffuse
from the plasma red blood cells, combining with H+ released from hemoglobin and forming H2CO3.
Carbonic acid is converted back into CO2 and water.
CO2 formed from H2CO3 is unloadedfrom hemoglobin and diffuses into the interstitial fluid.
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