1. Respiratory System
Gas Exchange

2. Why do we need a respiratory system?
respiration for respiration
Why do we need a respiratory system?
Need O2 in
For aerobic respiration
Make ATP
Need CO2 out
Waste product from Krebs cycle
food
ATP O2
CO2

3. Some vocabulary Ventilation Gas exchange Cell respiration
The exchange of air between the lungs and the atmosphere; it is achieved by the physical act of breathing
Gas exchange
The exchange of O2 & CO2 in the alveoli and the blood stream; it occurs passively via diffusion
Cell respiration
The release of ATP from organic molecules; it is greatly enhanced by the presence of oxygen (aerobic respiration)

4. Gas exchange O2 & CO2 exchange between environment & cells
Need moist membrane
Need high surface area

5. Optimizing gas exchange
Why high surface area?
Maximizing rate of gas exchange
CO2 & O2 move across cell membrane by diffusion
Rate of diffusion proportional to surface area
Why moist membranes?
Moisture maintains cell membrane structure
Gases diffuse only dissolved in water
High surface area? High surface area! Where have we heard that before?

6. Gas exchange in many forms …
one-celled
amphibians
echinoderms
cilia
insects
fish
mammals
size •
water vs. land •
endotherm vs. ectotherm

7. Why is this exchange with the environment RISKY?
Exchange tissue: spongy texture, honeycombed with moist epithelium
Lungs
Why is this exchange with the environment RISKY?

8. Alveoli Gas exchange across thin epithelium of millions of alveoli
Total surface area in humans ~100 m2

9. Alveoli T: thin wall R: rich capillary network
I: increases SA/Vol ratio
M: moist
Adaptation
Advantage
Spherical shape
Provides large surface area for diffusion of gases
Single, cell thickness
Increases rate of diffusion (decreases distance)
Moist inner lining
Allows for efficient diffusion
Capillary bed nearby

10. Negative pressure breathing
Breathing due to changing pressures in lungs
Air flows from higher pressure to lower pressure
Pulling air instead of pushing it

11. Partial pressure
Partial pressure is the pressure exerted by a single type of gas when it is found within a mixture of gases
The partial pressure of a given gas will depend on:
The concentration of the gas in the mixture
i.e. O2 levels may differ in certain environments
The total pressure of the mixture
Air pressure decreases at higher altitudes

12. Mechanics of breathing
Air enters nostrils
Filtered by hairs, warmed & humid
Sampled for odors
Pharynx  glottis  larynx (vocal cords)  trachea (windpipe)  bronchi  bronchioles  air sacs (alveoli)
Epithelial lining covered by cilia & thin film of mucus
Mucus traps dust, pollen & particulates
Beating cilia move mucus upward to pharynx, where it is swallowed

13. Mechanics of breathing

14. Autonomic breathing control
don’t want to have to think to breathe!
Autonomic breathing control
Medulla sets rhythm & pons moderates it
Coordinate respiratory, cardiovascular systems & metabolic demands
Nerve sensors in walls of aorta & carotid arteries in neck detect O2 & CO2 in blood

15. Medulla monitors blood
Monitors CO2 level of blood
Measures pH of blood & cerebrospinal fluid bathing brain
CO2 + H2O  H2CO3 (carbonic acid)
If pH decreases, then increase depth & rate of breathing & excess CO2 is eliminated in exhaled air

16. Transporting CO2 in blood
Dissolved in blood plasma as carbonate ion
Tissue cells
Plasma
CO2 dissolves
in plasma
CO2 combines
with Hb
CO2 + H2O
H2CO3
H+ + HCO3–
HCO3–
CO2
Carbonic
anhydrase
Cl–
carbonic acid
CO2 + H2O  H2CO3
hyrdogen carbonate
H2CO3  H+ + HCO3–
carbonic anhydrase
~75%
~25%
Called carbaminohemaglobin
the lungs

17. Transporting CO2 in blood
Dissolved in blood plasma as carbonate ion
HCO3- diffuses out through a carrier protein
HCO3- diffuses out
Cl- diffuses in
“chloride shift”
H+ attaches to Hb-
Helps maintain pH
Known as buffering
hydrogen carbonate
H2CO3  H+ + HCO3–
Tissue cells
Plasma
CO2 dissolves
in plasma
CO2 combines
with Hb
CO2 + H2O
H2CO3
H+ + HCO3–
HCO3–
CO2
Carbonic
anhydrase
Cl–

19. Releasing CO2 from blood at lungs
Lower CO2 pressure at lungs allows CO2 to diffuse out of blood into lungs
Plasma
Lungs: Alveoli
CO2 dissolved
in plasma
HCO3–Cl–
CO2
H2CO3
Hemoglobin + CO2
CO2 + H2O
HCO3 – + H+

20. Breathing & homeostasis
ATP
Homeostasis
Keeping the internal environment of the body balanced
Need to balance O2 in and CO2 out
Need to balance energy (ATP) production
Exercise
Breathe faster
Need more ATP
Bring in more O2 & remove more CO2
Disease
Poor lung or heart function = breathe faster
Need to work harder to bring in O2 & remove CO2
CO2 O2

21. Diffusion of gases
Concentration gradient & pressure drives movement of gases into & out of blood at both lungs & body tissue
capillaries in lungs
capillaries in muscle O2 O2 O2 O2
CO2
CO2
CO2
CO2
blood
lungs
blood
body

22. Hemoglobin Why use a carrier molecule? Reversibly binds O2
O2 not soluble enough in H2O for animal needs
Blood alone could not provide enough O2 to animal cells
Hemocyanin in insects = copper (bluish/greenish)
Hemoglobin in vertebrates = iron (reddish)
Reversibly binds O2
Loading O2 at lungs/gills & unloading at cells
heme group
cooperativity

23. Cooperativity in hemoglobin
Binding O2
Binding of O2 to 1st subunit causes shape change in other subunits
Conformational change
Increases attraction for additional O2
Releasing O2
When 1st subunit releases O2, causes shape change to other subunits
Lowers attraction for additional O2

24. Cooperativity in hemoglobin
As each oxygen molecule binds, it alters the conformation of hemoglobin, making it easier for others to be loaded (cooperative binding)
Conversely, as each oxygen molecule is released, the change in hemoglobin makes it easier for other molecules to be unloaded

26. O2 dissociation curve for hemoglobin
Bohr shift
Drop in pH lowers affinity of Hb for O2
Active tissue (producing CO2) lowers pH & induces Hb to release more O2
Effect of pH (CO2 concentration)
PO2 (mm Hg) 10 20 30 40 50 60 70 80 90
100
120
140
More O2 delivered to tissues
pH 7.60
pH 7.20
pH 7.40
% oxyhemoglobin saturation

27. O2 dissociation curve for hemoglobin
Bohr shift
Increase in temperature lowers affinity of Hb for O2
Active muscle produces heat
Effect of Temperature
PO2 (mm Hg) 10 20 30 40 50 60 70 80 90
100
120
140
More O2 delivered to tissues
20°C
43°C
37°C
% oxyhemoglobin saturation

28. Adaptations for pregnancy
Mother & fetus exchange O2 & CO2 across placental tissue
Why would mother’s Hb give up its O2 to baby’s Hb?

29. Fetal hemoglobin (HbF)
HbF has greater attraction to O2 than Hb
Low % O2 by time blood reaches placenta
Fetal Hb must be able to bind O2 with greater attraction than maternal Hb
What is the adaptive advantage?
2 alpha & 2 gamma units

30. What is the adaptive advantage?
Myoglobin
Myoglobin has only 1 heme group
Cannot undergo cooperative binding
Has a greater affinity for O2 and can become saturated at lower concentrations
Found in muscle cells
Stores O2 until levels are low
Delays anaerobic respiration during exercise
What is the adaptive advantage?

31. Gas exchange at high altitudes
High altitude = lower air pressure = lower partial pressure of O2
Makes oxygen uptake difficult
Results in fatigue, breathlessness, rapid pulse, nausea, and headaches
Over time, the body acclimates
Increase production of red blood cells
Increase hemoglobin concentration in rbc
Increase ventilation rate
Muscles produce more myoglobin & have increased vascularization
Increase diffusion of O2 into muscles
Long-term exposure = greater lung surface area, more dense alveoli, & larger chest size

32. Take a deep breath.
Any questions?