Organismal Respiration

Organismal Respiration
Chapter 23

Fig 23.1 Generalized features of animal gas exchange
Movement of gas molecules from external to internal compartments Ventilation facilitates diffusion by convection 1) Convection (ventilation or diffusion), 2) Diffusion across epithelium, 3) Internal Transport, 4) Diffusion into tissues anphys-fig jpg

Why we need gas exchange systems
As organisms grow larger, surface area to volume ratio decreases This limits the relative area available for diffusion and increases the diffusion distance Surface [O2 ] would be depleted if r > 1mm. SA  V2/3

Animals typically have respiratory organs
The ratio of ‘respiratory surface area’ to ‘body surface area’ needs to increase as body size increases. In humans, the lung surface area is m2, and the remaining body surface area ~ 2 m2 Thin cell layers

Fig 23.2 Types of specialized breathing structures
Gills – body surface turned out; rarely used in air. May be secondarily enclosed in a cavity Lungs – body surface turned in; ventilated or diffusion

More types of specialized breathing structures
Cutaneous – amphibians Tracheae – insects combine “circulation” and gas exchange into a single structure

Passive ventilation relies on water currents
Ventilation of respiratory surfaces reduces the formation of static boundary layers Passive ventilation relies on water currents Nondirectional - medium flows past the respiratory surface in an unpredictable pattern Directional: current flow (e.g, stream, tide) Respiratory surfaces increase surface area for diffusion of CO2 and O2. life.uiuc.edu/ib/150/lectures/Lecture19.ppt Are there physiological tradeoffs in the type of respiratory surface that may have ecological implications?

Requires energy expenditure by muscles and/or cilia can be regulated.
Active ventilation Requires energy expenditure by muscles and/or cilia can be regulated. Respiratory surfaces increase surface area for diffusion of CO2 and O2. life.uiuc.edu/ib/150/lectures/Lecture19.ppt Are there physiological tradeoffs in the type of respiratory surface that may have ecological implications?

Tidal gas exchange Fig 23.3 O2 transfer from the environmental medium to the blood in a tidally ventilated lung Medium moves in and out Differences in partial pressures drive movement of respiratory fluid (air) anphys2e-fig jpg

Unidirectional flow: O2 transfer from the environmental medium to the blood when ventilation is unidirectional medium enters the chamber at one point and exits at another Cocurrent, countercurrent, and crosscurrent

Cocurrent exchange: Follow the differences in partial pressures
anphys2e-fig jpg Figure 23.4a

Countercurrent gas exchange:
anphys2e-fig jpg Figure 23.4b

Figure 23.5 Cross-current gas exchange:
anphys2e-fig jpg Figure 23.5

Exponential relationship What is the slope for mammals?
Area of gas-exchange membrane (gills or lungs) of vertebrates as function of body size. What kind of graph? Exponential relationship What is the slope for mammals? anphys2e-fig r.jpg Fig 23.7

1 4 Run = X2 –X1 10,000 - 10 4 -1 Rise = >50,000 - 400 mammals?
anphys2e-fig r.jpg 1 4

1 4 When log X = 4, log Y = ? Slope = = .8 (5-2.6) / (4-1)
anphys2e-fig r.jpg 1 4

Slope = (5 - 2.6) / (4 - 1) = .8 Positive allometry? Isometry?
Negative allometry?

Animal Locomotion By Andrew A. Biewener
The slope is 0.92 when plotted on logarithmic axes. This indicates that the lungs of larger mammals are much more finely partitioned than would be expected if they were geometrically similar to the lungs of small mammals. The observed scaling of lung surface area also suggests a greater aerobic locomotor capacity than if the lungs of larger animals remained isometric in design. This provides an example in which the scaling of a key structural feature of the lungs which is important to diffusive gas exchange can be related to the metabolic demand for gas exchange. If, on the other hand, different- sized animals retain similar shape (i.e. scale close to geometric similarity), alternative mechanisms must often be evolved to compensate for functional constraints of size. We shall see how size affects locomotor mechanisms. Indeed, much of the locomotor diversity of animals reflects this fundamental aspect of their biology.

What else can you learn from the information on this graph?
e.g., reptiles vs birds, etc.? (next slide)

Area of the gas-exchange membrane as function of body size
Fish, amphibians, and reptiles have smaller surface areas. Birds and mammals have high surface areas, Increased Surface Area from folding and increased size of lung required for endothermy and 5-10 fold increase in metabolic rates Note the Yellow Fin tuna!!! anphys2e-fig r.jpg Figure 23.7

Scaling of alveolar epithelial surface area against body mass (M; ♦) and respiratory rate (f; ◊).
Scaling of alveolar epithelial surface area against body mass (M; ♦) and respiratory rate (f; ◊). Regression formulas, as well as the regression coefficient (R2), are given for M and f. Wirkes A et al. J Appl Physiol 2010;109:

Thinnest in mammals and birds
Figure 23.7b Total area and thickness of the gas-exchange membrane in the gills or lungs of vertebrates as functions of body size (Part 2) Thinnest in mammals and birds anphys2e-fig r.jpg

Percentage of O2 and CO2 exchange that occurs across the skin
Skin is important in gas exchange for some vertebrates. Aquatic and semiaquatic tetrapods have higher rates of cutaneous respiration than purely terrestrial. Reptiles and mammals have skins designed to prevent desiccation and so greatly reduced gas exchange. anphys-fig jpg Figure 23.8

Gas exchange surfaces

Ventilation and Gas Exchange
Because of the different physical properties of air and water, animals use different strategies depending on the medium in which they live Air breathers can use tidal (reciprocal) ventilation, while water breathers use one way flow.

Challenges in Breathing Water
Water is 1,000 times as dense as air Water has 1,000 times greater viscosity The solubility of O2 is 30 times lower in water Water breathers need 30 times the volume of medium to acquire the same amount of O2

anphys2e-table jpg

Comparison of air and water as respiratory medium

Work of respiration water viscosity > air viscosity pressure gradient is increased in proportion to viscosity work increases therefore increases At 20 °C water = 1 cP (centipoise) air = 0.02 cP thus water 50x greater than air and requires 50x energy for movement

Advantages in Breathing Water
It is easier to get rid of CO2 Air breathing causes dehydration

Ventilation of Gills Renewal of water across the surface is needed to replenish oxygen delivery move the gill through the water move water over the gill Moving the gill through the water limited to smaller organisms (aquatic insect larvae) Moving water over the gill ciliary action (e.g., mussels and clams) mechanical pump (more common)

In the countercurrent exchange system of fish gills,
blood and water flow in the same direction. water flow over the gills reverses direction with every inhalation. blood flow in the gills reverses direction with every heartbeat. blood and water flow in opposite directions. blood and water are separated by a thick polysaccharide barrier. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

In tuna, the counter-current arrangement of blood flow through the gill and water flow over the gill
Enables the retention of heat in the swimming muscles of the fish. Enables the partial pressure gradient for CO2 diffusion to be maximized because blood with the highest partial pressure of CO2 (PCO2) meets water with the lowest PCO2. Enables the maintenance of a constant partial pressure gradient for gas diffusion across the entire gas exchange surface. Enables all the O2 to be extracted from the water. None of the above is true of the counter-current blood and water flow at the tuna gill 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

In tuna, the counter-current arrangement of blood flow through the gill and water flow over the gill
Enables the retention of heat in the swimming muscles of the fish. FALSE, it is countercurrent in the muscles, not the gills Enables the partial pressure gradient for CO2 diffusion to be maximized because blood with the highest partial pressure of CO2 (PCO2) meets water with the lowest PCO2. FALSE, the PCO2 of water is highest at this point Enables the maintenance of a constant partial pressure gradient for gas diffusion across the entire gas exchange surface. TRUE Enables all the O2 to be extracted from the water. FALSE None of the above is true of the counter-current blood and water flow at the tuna gill

Gill Ventilation in Bony Fish
Figure The branchial breathing system in teleost fish

Figure 23.10 The branchial breathing system in teleost (advanced bony) fish
Gas exchange occurs in the secondary lamellae (highly vascular, flat folds of the gill filaments) anphys2e-fig jpg

Countercurrent Flow in Fish Gills
Countercurrent blood flow relative to direction of water flow through buccal cavity Figure 10.14

The branchial breathing system in teleost fish
Figure 23.10 AnPhys3e-Fig R.jpg

Figure 23.11 The breathing cycle in teleost fish
Water pumping Buccal (oral) Pump Opercular pump Higher pressure in the oral versus opercular cavity allows for continuous one-way flow of water over the gill lamella. anphys2e-fig jpg

Ram Ventilation Continuous swimming, with mouth open Water flows backward relative to body movement Water flows over gills Gills ventilated Common in large, fast-swimming pelagic fish, e.g., sharks, tuna

The rate of O2 uptake by a fish would be negatively impacted by
Increasing the thickness of the gill epithelium. Increasing ventilation (i.e. the rate at which water next to the gill is refreshed). Increasing the surface area of the gills. Increasing the partial pressure of O2 in the blood of the fish. Both 1 and 4 would negatively impact the rate of O2 uptake by a fish. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Several hundred species of bony fish are able to breath air.
Live in oxygen poor environments Use various vascularized tissues Vertebrate lungs are outpocketings of the esophogus

Water to Land More O2 in air than in water Water = 0.5 – 1% Land = ~ 21% A few members of aquatic groups (mollusks, arthropods and fish) came on land. Two problems to overcome Gills collapsed….no support Water evaporation of gills

Figure 23.13 Breathing organs of amphibians
Types of respiratory structures Cutaneous respiration External gills Simple bilobed lungs; more complex in terrestrial frogs and toads anphys2e-fig jpg

Ventilation is tidal using a buccal force pump (Positive pressure)
Figure The three major steps in the ventilatory cycle of an adult bullfrog (Lithobates catesbeianus) Ventilation is tidal using a buccal force pump (Positive pressure) frog takes air into mouth closes mouth and nostrils forces air into lungs by elevating floor of mouth anphys2e-fig jpg

Cutaneous Respiration
skin respiration normal and important for amphibians moist well-vascularized skin for diffusion

Complex developmental changes
Figure The development of external respiration in the bullfrog (Lithobates catesbeianus) Complex developmental changes Gills/skin as tadpoles Lungs/skin as adults Carbon dioxide excretion versus oxygen absorption anphys2e-fig jpg

Figure Reptile lungs Most have two lungs; in snakes one lung is reduced or absent Can be simple sacs with honeycombed walls or highly divided chambers in more active species More divisions result in more surface area

Results in the separation of feeding and respiratory muscles
Reptile Ventilation Tidal Rely on suction pumps Results in the separation of feeding and respiratory muscles Two phases: inspiration and expiration Use one of several mechanisms to change the volume of the chest cavity

“Unidirectional Airflow in the Lungs of Alligators” by C. G
“Unidirectional Airflow in the Lungs of Alligators” by C. G. Farmer and Kent Sanders in Science, 15 January 2010, Vol 327.

Mammal Respiratory Tracts
Two main parts Upper respiratory tract: mouth, nasal cavity, pharynx, trachea Lower respiratory tract: bronchi and lungs The airways of the lungs are the bronchioles alveoli The alveoli are the sites of gas exchange Figure 10.24

Figure 23.17 The airways in human lungs
Lungs require tidal ventilation and are highly vascularized (red). Lungs have high surface area and low diffusion distances anphys2e-fig jpg Red = blood vessels White = air passages

Fig. 23.18 Respiratory airways of the mammalian lung
Alveoli in mammal provide more finally divided structure frog 1 cm3 = 20 cm2 surface area mouse 1 cm3 = 800 cm2 surface area thickness (diffusion barrier) alveolar membrane 0.2 microns (paper 50 microns) anphys2e-fig jpg

0.2 mm Hg 160 mm Hg 20 mm Hg 76 mm Hg 508 mm Hg
At sea level, atmospheric pressure is 760 mm Hg. Oxygen gas is approximately 21% of the total gases in the atmosphere. What is the approximate partial pressure of oxygen? 0.2 mm Hg 160 mm Hg 20 mm Hg 76 mm Hg 508 mm Hg 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

0.001 ml O2/ml H2O 0.003 ml O2/ml H2O 0.004 ml O2/ml H2O
Henry's Law: The volume of a gas (Vx) dissolved in a liter of water is Vx = (pX)*(SC) where pX is the partial pressure in atmospheres and SC is the solubility coefficient. At one atmosphere and 37 degrees Celsius, the solubility coefficient for oxygen is ml O2/ml H2O. How much oxygen can dissolve in a liter of water at 37 degrees Celsius if the partial pressure of oxygen is 95 mm Hg? 0.001 ml O2/ml H2O 0.003 ml O2/ml H2O 0.004 ml O2/ml H2O 0.008 ml O2/ml H2O 0.012 ml O2/ml H2O 0.024 ml O2/ml H2O 0.036 ml O2/ml H2O 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

The viscera are used to fill and empty the lungs in
frogs crocodilians snakes amphisbaenians turtles 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Fig. 23.19 Dynamic lung volumes in healthy young adult men
Tidal volume (VT) volume of air inhaled or exhaled per breath (resting VT = 500 mL) Inspiratory reserve volume amount forcibly breathed in above tidal volume Expiratory reserve volume amount forcibly exhaled after tidal volume exhaled Vital capacity. maximum possible tidal volume Residual volume amount remaining in lung after forcible exhalation anphys-fig jpg

Dead Space Dead Space Volume of air held in parts of lung with no exchange surfaces (150 mL of air in male humans) Two components Anatomical dead space – volume of the trachea and bronchi Alveolar dead space – volume of any alveoli that is not being perfused with blood

Lung Volumes and Capacities
Figure 10.28

Bulk flow down to the bronchioles
Figure Mechanisms of gas transport in the final branches of mammalian lungs during inhalation Bulk flow down to the bronchioles Gases in the alveoli are motionless anphys2e-fig jpg

INHALATION AND EXHALATION
For tidal volume of 500 ml Dead space air (150 ml) is first air to enter alveoli Only about 350 ml of fresh air reaches the alveoli During exercise tidal volume increases while dead space remains constant, thus a greater % of fresh air reaches the alveoli However, there is mixing with air already present alveolar air composition remains constant at 15% O2 and 5 % CO2.

RESPIRATORY MECHANICS
Lungs exist within sealed Pleural Cavity Inhalation Slight negative pressure in the pleural cavity stretches lungs open Costal muscles and rib cage expansion muscular diaphragm in mammals Exhalation passive due to elastic recoil of lungs or can be aided by muscle contraction

Air rushes into the lungs of humans during inhalation because
pressure in the alveoli increases. the rib muscles and diaphragm contract, increasing the lung volume. gas flows from a region of lower pressure to a region of higher pressure. a positive respiratory pressure is created when the diaphragm relaxes. pulmonary muscles contract and pull on the outer surface of the lungs. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

UNUSUAL OBSERVATIONS ON BIRD BREATHING
Bird lungs are smaller and less compliant than lungs of a similar sized mammal. When birds inhale, their lungs contract, and when birds exhale, their lungs expand. Avian airways, lungs, and air sacs are interconnected. Birds can sustain very high metabolic rates at high altitudes.

Lung is stiff and changes little in volume
Birds Lung is stiff and changes little in volume Rely on a series of flexible air sacs Gas exchange occurs at parabronchi Fig

Figure 23.23 Parabronchi and air capillaries: The gas-exchange sites in avian lungs
anphys2e-fig jpg

Respiration in birds Requires two cycles of inhalation and exhalation Air flow across the respiratory surfaces is unidirectional

Fig. 23.22 Air flow in the lungs and air sacs of birds
Posterior air sacs 1 Trachea 2 Parabronchi anphys2e-fig jpg Anterior air sacs 3 4 Trachea

Figure 23.22 Airflow in the lungs and air sacs of birds
Air flows through the parabronchi from posterior to anterior. (b) Inhalation The anterior air sacs expand and fill with gas that has passed across the respiratory exchange surfaces. The posterior air sacs expand and fill with fresh air coming directly from the environment. (c) Exhalation As during inhalation, air flows through the parabronchi from posterior to anterior. The anterior air sacs are compressed, discharging stale gas stored in them. The posterior air sacs are compressed. The fresh air in them is directed primarily into the posterior secondary bronchi. The gas that is exhaled has passed across the respiratory exchange surfaces even if temporarily held in the anterior air sacs. Outflow to the environment along the length of the mesobronchus is minimal, according to available evidence. Fresh air Stale gas (i.e., depleted in O2, enriched in CO2) air

RESPIRATORY DEMANDS ON BIRDS ARE EXTREME
Energy demands of flight x Basal M.R., for extended periods of time. Best trained human athletes can approach this for only a few moments before incurring O2 debt. Extended flights frequently at high altitude where concentration of O2 is low. Atmosphere 20.9% O2 at all altitudes means 20.9% of total air pressure. at sea level 20.9% of 760 mm Hg = ~160 mmHg on Everest B.P. = 250 mmHg, so pO2 = 52 mmHg

Why is the respiratory system of a bird more efficient than the human respiratory system?
The human respiratory system ends in small parabronchi, which reduce the amount of surface area available for gas exchange. The bird respiratory system does not mix exhaled air with inhaled air. A bird lung contains multiple alveoli, which increases the amount of surface area available for gas exchange. Both A and C are correct. Both B and C are correct. A, B, and C are correct. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Insects and arachnids Gas exchange does not rely on a their circulatory system Extensive tracheal system - series of air-filled tubes Tracheoles – terminating ends of tubes that are filled with hemolymph Open to outside via spiracles Gases diffuse in and out

Figure Insects breathe using a tracheal system of gas-filled tubes that, branching and rebranching, reaches all tissues from the body surface anphys2e-fig jpg

Regulation of Respiratory Systems
Vertebrate respiratory and circulatory systems work together to regulate gas delivery by Regulating ventilation Altering oxygen carrying capacity and affinity Altering perfusion (movement of fluid through a tissue, e.g. capillary exchange)

medulla and pons contain respiratory centers
medulla and pons contain respiratory centers chemosensitive areas to H+ from the reaction of CO2 + H2O <-> H2CO3 <-> H+ + HCO3 <-> 2H+ + CO32- oxygen sensitivity is located in the peripheral chemoreceptors in the arch of the aorta and carotid bodies

Regulation of Respiration
Mediated by chemoreceptors and effect of CO2 Two major pathways: Cerebral cortex voluntary Medulla oblongata Involuntary controls diaphragm and intercostals Influenced by neurons in the pons

Regulation of Ventilation
Rhythmic firing of central pattern generators within the medulla initiate ventilatory movements Figure 10.38

Regulation of Ventilation, Cont.
Chemosensory input helps modulate the output of the central pattern generators Chemoreceptors detect changes in CO2, H+, and O2 Figure 10.39

Balance between oxygen consumption & delivery An increase in consumption is met by an increase in ventilation Oxygen is the primary regulator in water-breathers while CO2 is the primary regulator in air-breathers

For aquatic animals the primary stimulus for respiration is a lack of O2 CO2 is easily dumped to the water , so never build a high tension in the circulatory fluids (blood) CO2 is also not a good indicator of O2 content of the water

In homeothermic vertebrates (mammals and birds) ventilation is precisely adjusted to O2 consumption primary regulator is CO2

RESPIRATION MORE SENSITIVE TO ARTERIAL CO2 THAN O2
If CO2 increases from .03% to 2.5 % almost doubles ventilation. Lungs contain about 5% CO2 If O2 is decreased by 2.5% there is no effect on ventilation rate

Environmental Hypoxia
Hypoxia – lower than normal levels of oxygen Can be caused by environmental hypoxia, inadequate ventilation, reduced blood hemoglobin content Hyper-, hypocapnia – higher or lower than normal levels of CO2

High-Altitude Hypoxia
Figure 10.40

Hyperventilation Increased rate of breathing Results in increase intake of O2 Also increase expiration of CO2 (decrease CO2 in blood) Depletes body’s supply of CO2 (decreased H+) Condition called alkalosis

Hyperventilation Hyperventilation decreases the urge to breathe as a result of venting carbon dioxide Unconsciousness results when the brain is starved for O2. Dangerous , may cause loss of consciousness in free diver Breathing into a paper bag retains carbon dioxide.

Hypoventilation Decrease in rate or depth of breathing Less CO2 exhaled, builds up in the blood Results in acidic blood Condition known as acidosis

Blood Transport of Respiratory Gases
Mammals at high altitude have different hemoglobin binding curves Hemoglobin becomes saturated with O2 at lower PO2 values than that of other animals e.g. llamas

Brain stem generates breathing rhythm via autonomic nervous system
Figure Breathing Is Generated in the Brain Stem Brain stem generates breathing rhythm via autonomic nervous system Neurons within medulla increase firing rate just prior to inhalation  diaphragm contracts and inhalation occurs Firing stops  diaphragm relaxes  exhalation Exhalation is passive elastic recoil of lung tissue

If brain stem is cut just below pons  breathing continues irratically
Figure Breathing Is Generated in the Brain Stem If brain stem is cut just below pons  breathing continues irratically If spinal cord is cut below medulla  breathing stops

48.5 How Is Breathing Regulated?
In humans and mammals, breathing rate is more sensitive to changes in PCO2 than to PO2 PCO2 of blood is primary metabolic feedback for breathing CO2 O2

Figure 48.16 Carbon Dioxide Affects Breathing Rate
Small amount of CO2 in inhaled air stimulates large increase in breathing rate. But large drop in %O2 in inhaled air has little effect. CO2 O2

Figure 48.17 The Sensitivity of the Respiratory Control System Changes with Exercise (Part 1)

48.5 How Is Breathing Regulated?
The major site of sensitivity to PCO2 is on medulla’s ventral surface Sensitivity to PO2 is monitored by carotid and aortic bodies in blood vessels leaving heart If PO2 falls, chemoreceptors in these bodies send nerve impulses to brain stem to stimulate breathing CO2 sensors O2 sensors

Figure 48.18 Feedback Information Controls Breathing

Organismal Respiration

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