1. Gas Exchange
Chapter 22

2. The Air Up There Air is a fixed ratio of partial pressures (Px)
Air thins with increasing altitude
Gas in same ratio, but less of
3000 m 1/3 less O2
Sherpas, athletic training, and blood doping
Mountain sickness

3. Revisiting Respiration
Gas Exchange
Breathing
Organismal level
O2 in CO2 out via diffusion
Cellular level
Use O2 to produce CO2 and ATP
Cellular Respiration
Exchange
Application

4. Respiratory Surfaces Thin Diffusion distance Speed Moist
Gases dissolved in solution
Large
SA to volume ratio
Energy demands

5. Respiratory Mediums Water Air Pro Con Pro Con
Direct contact of respiratory surface to medium
Con
Less O2
warm and salty even less
O2 diffusion slower
More energy to ventilate
Larger structures
Water supports weight
Pro
High concentration of O2
Less dense
O2 diffusion faster
Con
Desiccation of respiratory surface
Small openings externally
Indirect contact of respiratory surface to medium

6. Gill Systems Aquatic organisms
Convoluted extensions of body surface (pink)
Ventilation varies between organisms
Move respiratory medium across respiratory surfaces
Inefficient on land
Desiccation
Tissue Mass
Mollusks, annelids, arthropods, echinoderms, fish, and amphibians

7. Countercurrent Exchange
Exchange between 2 oppositely flowing currents
Maximizes O2 diffusion out of H2O
Concentration gradient maintained entire length
Compare to concurrent

8. ‘Skin Breathers’ Earthworms and some amphibians
Skin is respiratory surface
Circulatory system to distribute (hemoglobin assists)
Lower invertebrates without
Moist environments

9. Tracheal System Insects Internal branched tube system Direct exchange
Connect all cells to environment
Prevents desiccation
Direct exchange
Open circulatory system
Hemolymph = nutrients only
Body movements assist

10. Lungs Branched internal sacs Pigmented, closed circulatory system
Moist epithelium
Pigmented, closed circulatory system
Nutrient and gas transport
Most terrestrial vertebrates
Elaboration with movement to land
Variations between classes
Amphibians: positive, others negative

11. Lung Adaptation Amphibians Birds Mammals
O2 via positive pressure into small sacs
Skin also for exchange
Birds
1 way flow increases efficiency
2 cycles to complete
Mammals
Negative pressure
Incomplete removal
Myoglobin content varies

12. Mammalian Respiratory System
Upper respiratory system
Nasal cavity
Warms air
Smells
Pharynx
Larynx
Vocal cords tensed to create sound
Lower respiratory system
Trachea
Cartilage rings
Bronchi (2)
Bronchioles
Alveoli
Diffusion with capillaries through interstial fluid

13. Respiratory Cycle Inhale Exhale
Rib muscles (up) and diaphragm (down) contract
Chest cavity increases
Lowers air pressure in alveoli
Rib muscles (down) and diaphragm (up) relax
Chest cavity decreases
Increases air pressure in alveoli

14. Respiratory Disruptions
Smoking
Inhibit cilia movement causes ‘smoker’s cough’
Thicken bronchioles and reduce elasticity
Alveoli rupture
Stopping allows cilia and alveoli damage to reverse
Premature birth (37 weeks or less)
Surfactant production incomplete
Keeps alveoli from collapsing
Each breath requires large effort
Emphysema
Bronchi swell, tearing alveoli
Reduced SA for gas exchange
Pneumonia
Fluid in alveoli
Bronchitis inflames of bronchioles

15. Respiratory Gas Transport
Blood circulates to all cells
Hemoglobin binds/carries
Protein bound to a metal
Carry 4 O2 molecules, some CO2 too
PO2 and PCO2 vary within the circulatory system
Blue and red vessels
Lungs: high O2, low CO2
Body tissues: low O2, high CO2
Pressure gradient facilitates gas exchange in tissue capillaries (purple)

16. Control of Human Breathing
Most is involuntary
Control centers in brain
Medulla: inhalation signaling
Pons: smoothes out rhythm and depth
Driven by [CO2] in blood
Reactions
CO2 + H2O H2CO3 (carbonic acid)
H2CO H+ + HCO3
CO2 levels increase
pH in blood/CSF lowered
Respiratory centers signaled
Carotid arteries and aorta monitor O2 also
Severe deficit, i.e high altitude
Increase rate and depth

17. Human Fetus Amniotic sac in uterus Placental role
Lungs are fluid filled
Placental role
Blood exchange with mother
Fetal hemoglobin
Birth stops gas exchange
pH drop, why?
First breath