1. Gas Exchange
Chapter 44

2. Learning Objectives
Define Physiological Respiration, Ventilation and Perfusion
Diagram the human respiratory tract and explain functions of the organs
Define Tidal Volume, Vital Capacity and Residual Volume
Compare and contrast negative and positive pressure breathing
Describe how breathing is both a conscious and subconscious effort
Describe the physiological gradient that allows for CO2 and O2 diffusion within the body
Define COPD and health impact

3. Physiological Respiration
Process by which animals exchange O2 and CO2 with the environment

4. Physiological respiration
Cellular respiration
Physiological respiration
Respiratory surface (body surface, gills, or lungs)
Mitochondrion
Circulatory system
Figure 44.1
The relationship between cellular respiration and physiological respiration.
Respiratory medium
(air or water)
Fig. 44.1, p. 998

5. Breathing (Gas Exchange)
Two primary operating features of gas exchange
The respiratory medium, either air or water
The respiratory surface, a wetted epithelium over which gas exchange takes place

6. Respiratory Surfaces
In some invertebrates, the skin is the respiratory surface
In other invertebrates and all vertebrates, gills or lungs are the primary respiratory surfaces

7. Gas Exchange
Simple diffusion of molecules drives exchange of gases across the respiratory surface
From regions of higher concentration to regions of lower concentration
Area of respiratory surface determines total quantity of gases exchanged by diffusion

8. Maximizing Gas Exchange
Concentration gradients of O2 and CO2 across respiratory surfaces are kept at optimal levels by ventilation and perfusion
Ventilation: Movement of respiratory media over the external respiratory surface
Perfusion: Movement of circulatory fluid over the internal respiratory surface

9. Air Breathers Air is high in O2 content
Allows air-breathers to maintain higher metabolic levels than water breathers
Air has lower density and viscosity than water
Allows air breathers to ventilate respiratory surfaces with relatively little energy

10. Insects: Tracheal System
Insects breathe by a tracheal system
Air-conducting tubes (trachea) lead from the body surface (through spiracles) and branch to all body cells
Gas exchange takes place in fluid-filled tips at ends of branches

11. Lungs (Air Breathers) Invaginations of the body surface
Allow air to become saturated with water before it reaches the respiratory surface
Reduce water loss by evaporation

12. Lung Ventilation Positive pressure breathing (Frogs do this)
Air is forced into lungs by muscle contractions
(Frogs do this)
Negative pressure breathing
Muscle contractions expand lungs, lowering air pressure inside
Allows air to be pulled into the lungs

13. Mammalian Respiratory System
Air enters the respiratory system through the nose and mouth and passes through the pharynx, larynx, and trachea
Trachea divides into two bronchi leading to lungs
Within lungs, bronchi branch into bronchioles, leading into alveoli surrounded by networks of blood capillaries

14. Closes off larynx during swallowing Pleura
Nasal passages
Chamber in which air is moistened, warmed, and filtered and in which sounds resonate
Mouth
Supplemental airway
Pharynx (throat)
Airway connecting nasal passages and mouth with larynx; enhances sounds; also connects with esophagus
Epiglottis
Closes off larynx during swallowing
Pleura
Double-layered membrane that separates lungs from the wall of the thoracic cavity; fluid between its two layers lubricates breathing movements
Larynx (voice box)
Airway where sound is produced; closed off during swallowing
Trachea (windpipe)
Airway connecting larynx with two bronchi that lead into the lungs
Intercostal muscles
Skeletal muscles between ribs that contract to fill and empty lungs
Lung
Lobed, elastic organ of breathing exchanges gases between internal environment and
outside air
Diaphragm
Muscle sheet between the chest cavity and abdominal cavity that contracts to fill lungs
Bronchi
Increasingly branched airways leading to alveoli of lung tissue
Figure 44.8
The human respiratory system, which is typical for a terrestrial mammal.
Alveoli (sectioned)
Bronchiole
Alveoli
Alveoli
Pulmonary capillaries
Fig. 44.8, p. 1004

15. Ventilation: Mammals Negative pressure mechanism
Air is exhaled passively
Relaxation of diaphragm and external intercostal muscles between ribs
Elastic recoil of lungs (pleural membranes)
Deep and rapid breathing
Forceful expulsion of air driven by contraction of internal intercostal muscles

16. Outward bulk flow of air Internal intercostal muscles
Inward bulk flow of air
Outward bulk flow of air
Internal intercostal muscles
External intercostal muscles
Diaphragm
Figure 44.9: The respiratory movements of humans during breathing at rest.
The movements of the rib cage and diaphragm fill and empty the lungs. Inhalation is powered by contractions of the external intercostal muscles and diaphragm, and exhalation is passive. During exercise or other activities characterized by deeper and more rapid breathing, contractions of the internal intercostal muscles and the abdominal muscles add force to exhalation. The X-ray images show how the volume of the lungs increases and decreases during inhalation and exhalation.
Inhalation.
Diaphragm contracts and moves down. The external intercostal muscles contract and lift rib cage upward and outward. The
lung volume expands.
Exhalation during breathing or rest. Diaphragm and external intercostal muscles return to the resting positions. Rib cage moves down. Lungs recoil passively.
Fig. 44.9, p. 1005

17. Measuring Lung Ventilation
Tidal volume
Amount of air moved in and out of lungs during an inhalation and exhalation
Vital capacity
Total volume of air a person can inhale and exhale by breathing as deeply as possible
Residual volume
Air remaining in the lungs after as much air as possible is exhaled

18. Control of Breathing Control mechanisms Control functions
Local chemical controls
Regulation centers in the brain stem
Control functions
Match rate of air and blood flow in lungs
Link rate and depth of breathing to body’s requirements for O2 uptake and CO2 release

19. Interneurons Regulate Breathing
Basic rhythm of breathing
Produced by interneurons in the medulla
When more rapid breathing is required
Other interneurons in the medulla reinforce inhalation, produce forceful exhalation
Fine-tuned breathing
Two interneuron groups in the pons stimulate or inhibit the inhalation center in the medulla

20. Blood Gas Control
Sensory receptors in medulla detect changes in levels of O2 and CO2 in blood and body fluids (aortic and carotid, too)
Control centers in medulla and pons adjust rate and depth of breathing to compensate for changes in blood gases

21. O2 Transport O2 diffuses from alveolar air into blood
Partial pressure of O2 is higher in alveolar air than in blood in capillary networks surrounding alveoli
Most O2 entering the blood combines with hemoglobin inside erythrocytes

22. Capillaries entering lungs
Dry inhaled air
Moist exhaled air
100 40
Alveolar sacs
160
0.04
120 27
Capillaries entering lungs
40 O2
46 CO2
Alveolar sacs O2
Pulmonary veins
100 40
Pulmonary arteries
CO2
100 40 40 46 O2
CO2
Start of veins in body tissues
Figure 44.11
The partial pressures of O2 (pink) and CO2 (blue) in various locations in the body.
Start of capillaries in body tissues 40 46
Cell
100 40
Capillaries entering tissues
Cells of body tissues
Less than 40
More than 46
100 O2
40 CO2
Fig , p. 1008

23. Hemoglobin and Oxygen
One hemoglobin molecule can combine with four O2 molecules
Large quantities of O2 combined with hemoglobin maintain a large partial pressure gradient between O2 in alveolar air and in blood

24. a. Hemoglobin saturation level in lungs
Oxygen saturation (%)
Figure 44.12
Hemoglobin–O2 dissociation curves, which show the degree to which hemoglobin is saturated with O2 at increasing PO2.
Body tissues
PO2
(mm Hg)
Alveoli
In the alveoli, in which the PO2 is about 100 mm Hg and the pH is 7.4, most hemoglobin molecules are 100% saturated, meaning that almost all have bound four O2 molecules.
Fig a, p. 1009

25. O2 Diffuses into Body Cells
O2 concentration in interstitial fluid and body cells is lower than in blood plasma
O2 diffuses from blood into interstitial fluid, and from interstitial fluid into body cells

26. CO2 Transfer: Body Tissues
Partial pressure of CO2 is higher in tissues than in blood
About 10% of CO2 dissolves in blood plasma
70% is converted into H+ and HCO3- (bicarbonate) ions
20% combines with hemoglobin

27. a. Body tissues Body cells CO2 Slow HCO3– + H+ CO2 + H2O
In body tissues, some of the CO2 released into the blood combines with water in the blood plasma to form HCO3– and H+. However, most
of the CO2 diffuses into erythrocytes, where some combines directly with hemoglobin and some combines with water to
form HCO3– and H+. The H+ formed by this reaction combines with hemoglobin; the HCO3– is transported out of erythrocytes to add to the HCO3– in the blood plasma.
HCO3– + H+
CO2 + H2O
Capillary wall
Erythrocyte
CO2 + H2O
CO2
Fast
Figure 44.13
The reactions occurring during the transfer of CO2 from body tissues to alveolar air.
Hemoglobin
HCO3– + H+
Capillary
Fig a, p. 1009

28. b. Lungs Slow HCO3– + H+ CO2 + H2O HCO3– + H+ Hemoglobin Fast
In the lungs, the reactions are reversed. Some of the HCO3– in the blood plasma combines with H+ to form CO2 and water. However, most of the HCO3– is transported into erythrocytes, where it combines with H+ released from hemoglobin to form CO2 and water. CO2 is released from hemoglobin. The CO2 diffuses from the erythrocytes and, with the CO2 in the blood plasma, diffuses from the blood into the alveolar air.
HCO3– + H+
Hemoglobin
Fast
CO2 + H2O
CO2
Figure 44.13
The reactions occurring during the transfer of CO2 from body tissues to alveolar air.
Capillary wall
CO2
Alveolar air
Alveolar wall
CO2
Fig b, p. 1009

29. 44.5 Respiration at High Altitudes and in Ocean Depths
High altitudes reduce the PO2 of air entering the lungs
Diving mammals are adapted to survive the high partial pressures of gases at extreme depths

30. High Altitudes: PO2 Decreases
When mammals move to high altitudes, the number of red cells and amount of hemoglobin per cell increase
These changes are reversed if the animals return to lower altitudes

31. Adaptations to High Altitudes
Humans living at higher altitudes from birth develop more alveoli and capillary networks in the lungs
Some mammals and birds adapted to high altitudes have forms of hemoglobin with greater O2 affinity
Allows saturation at lower PO2

32. Deep-Diving Marine Mammals
Blood (compared to other mammals)
Contains more red blood cells
Has higher hemoglobin content
Greater blood volume per unit of body weight
Muscles contain more myoglobin
Allows more O2 to be stored in muscle tissues

33. Adaptations for Deep-Diving
During a dive
Heartbeat slows
Circulation is reduced to all parts of the body except the brain

34. COPD Chronic Obstructive Pulmonary Disorder
Number 4 leading cause of Death in US
24 million adults affected
Causes include tobacco use and asthma
Asthma- Percent of noninstitutionalized adults who currently have asthma: 7.3%
Percent of children who currently have asthma: 9.4%