1. The Plan Introduction – general concepts Anatomy
Mechanics – moving air into the lungs
Structures, pressure changes
Gas Exchange – moving air from the lungs to blood and tissues
Moving O2 in and CO2 out of tissues
Control mechanisms
Local
CNS

2. Readings - Respiratory
McKinley, O’Loughlin, and Bidle, Anatomy and Physiology An integrative Approach, p
Gas exchange

3. Objectives
Describe the difference between external and internal respiration.
Discuss the roles of Boyle’s, Dalton’s and Henry’s laws with respect to gas exchange in the lungs.
Describe the role of partial pressure and diffusion during gas exchange.
Discuss the influence of temperature and pH influence gas exchange.
Discuss how CO2 and O2 are transported in blood.

4. Introduction to Gas Exchange
How do you get oxygen (O2) from the air into your cells?
Principle of diffusion
Air is composed of many gases
Gases dissolve into liquids
Respiratory - Cardiovascular systems interact
RBCs (in blood vessels) carry O2 and CO2

5. Introduction to Gas Exchange
Respiration refers to two integrated processes
External respiration
Includes all processes involved in exchanging O2 and CO2 from the environment
Internal respiration
Involves the uptake of O2 and production of CO2 associated with individual cells
CELLULAR RESPIRATION – use of O2 in the cell’s mitochondria in the electron transport system during metabolism
Movement of O2 from air to alveoli to blood (in lungs then system) to interstitium
Movement of O2 from interstitium into cells

6. Blood supply to the Lungs
Review
Remember: bronchial arteries and veins
Air
Trachea
Pulmonary artery (deoxygenated; from right ventricle; follows bronchial tree)
Pulmonary
capillaries
Pulmonary circulation
Pulmonary veins (oxygenated; to left atrium)
Artery: deoxygenated blood
Systemic circulation
Systemic
capillaries
Target cells like muscle, bone, etc.
(a)

7. Gas Exchange Gas Exchange Occurs between alveolar air and blood
across membranes: the blood-air barrier
into a liquid – plasma and then
into hemoglobin in the RBC
Depends on
Partial pressures of the gases
Diffusion of molecules between gas and liquid
Air (nitrogen, oxygen, carbon dioxide, etc enters alveolus and via diffusion moves across the blood-air barrier into a fluid phase – plasma and then into the RBC to attach to hemoglobin. Examine each step …
air space

8. Gas Exchange The Gas Laws
Diffusion occurs in response to concentration gradients
Rate of diffusion depends on physical principles or gas laws
For example, Boyle’s law (Pressure = 1/V)
For example, Dalton’s law
For example, Henry’s law
Movement is: high to low concentration i

9. Gas Exchange Composition of Air Air in a container – has a pressure
Nitrogen (N2) is about 78.6%
Oxygen (O2) is about 20.9%
Water vapor (H2O) is about 0.5%
Carbon dioxide (CO2) is about 0.04%
Air in a container – has a pressure
All molecules in air contribute to the total pressure
each gas has a Partial pressure
All partial pressures together add up to 760mm Hg

10. Gas Exchange Patm = 760 mm Hg = PN2 + PO2 + PH20 + PCO2
Dalton’s Law and Partial Pressures (abbreviated Px)
Atmospheric pressure (Patm = 760 mm Hg)
Produced by air (gas) molecules bumping into the container wall
Each gas contributes to the total pressure
In proportion to its number of molecules (Dalton’s law) … (Air: N2 > O2 > CO2)
In 760 mm Hg of air … 78.6% = N2; 20.9% = O2; 0.04% = CO2
Patm = 760 mm Hg = PN2 + PO2 + PH20 + PCO2
More bumping = more pressure
Dalton:

11. Gas Exchange Henry’s Law (1803)
When gas (O2, CO2 …) under pressure comes in contact with liquid (plasma)
Gas dissolves in liquid until equilibrium is reached
At a constant temperature
Amount of a gas that dissolves in a given type and volume of liquid is directly proportional to partial pressure of that gas in equilibrium with that liquid
Gas into liquid
More partial pressure more able to dissolve into liquid

12. Gas Exchange – gas into a liquid
Henry’s Law and the Relationship between Solubility and Pressure.
Increased pressure by decreasing vol.
Decreased pressure by increasing vol.
Copyright 2009 Pearson Education Inc. publishing as Pearson Benjamin Cummings

13. Gas Exchange Gas Content PCO2 = 40mm Hg PO2 = 104mm Hg PN2 = 573mm Hg
The actual amount of a gas in solution (at given partial pressure and temperature) depends on the solubility of that gas in that particular liquid
Normal Partial Pressures (Px) -pulmonary vein (oxygenated)
PCO2 = 40mm Hg
PO2 = 104mm Hg
PN2 = 573mm Hg
Solubility in Body Fluids (plasma)
CO2 is very soluble
O2 is less soluble
N2 has very low solubility

14. Blood flow in pulmonary capillary
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Summary diagram
Air Space
Po2 = 104 mm Hg
Air
Respiratory
membrane
Trachea
Pco2 = 40 mm Hg
Alveolus
Pulmonary
capillaries
CO2
Po2 = 40 mm Hg
Pco2 = 45 mm Hg O2
Pulmonary circulation
Blood flow in pulmonary capillary
Po2 = 104 mm Hg
Pco2 = 40 mm Hg
Alveolar endothelium
Fused basement membranes
of the alveolar epithelium and
the capillary endothelium
Respiratory
membrane
Capillary endothelium
(b) Alveolar gas exchange
Systemic
capillaries
Systemic circulation
104 mm Hg pressure drops to 95mm Hg when blood mixes from pulmonary artery to bronchial artery
Blood flow in systemic capillary
Po2 = 95 mm Hg
CO2
Pco2 = 40 mm Hg
Po2 = 40 mm Hg
Pco2 = 45 mm Hg
Target = muscle cells, etc.
(a)
Po2 = 40 mm Hg O2
Tissue cells
Pco2 = 45 mm Hg
Plasma membrane
Interstitial fluid
Capillary endothelium
(c) Systemic gas exchange

15. Gas Exchange - gas into a liquid (plasma)
Diffusion and the Blood-Air Barrier
Direction and rate of diffusion of gases across the respiratory membrane is determined by differences in partial pressures and solubilities
Alveolus
Blood-Air Barrier O2
CO2
Alveolar
capillary

16. Necessities for Gas Exchange
Efficiency of Gas Exchange Due to:
Substantial differences in partial pressure across the respiratory membrane
diffusion gradients required
Distances involved in gas exchange are short
O2 and CO2 are lipid soluble
Total surface area is large
more chances for diffusion
need more walls – hence more surface area
Blood flow and airflow are coordinated
blood takes O2 away from alveoli
liquid
(plasma)
gas
Copyright 2009 Pearson Education Inc. publishing as Pearson Benjamin Cummings

17. Problems for Gas Exchange
Insufficiencies in Gas Exchange may occur:
Substantial differences in partial pressure across the respiratory membrane
Skiing in Colorado (lower oxygen levels in mountains)
Receiving O2 in the hospital (higher oxygen levels received)
Distances involved in gas exchange are short
Fibrosis (increased CT = increased wall thickness)
O2 and CO2 are lipid soluble
always true …
Total surface area is large
Emphysema – surface area decreased
Blood flow and airflow are coordinated
Congestive heart failure – slows blood flow
Less partial pressure, less oxygen into system (Colorado pressure)
Emphysema: lose walls of epithelium

18. Gas Exchange: alveoli vs blood
O2 and CO2
Blood arriving in (to lungs) pulmonary arteries has
Low PO2
High PCO2
The concentration gradient causes
O2 to enter blood
CO2 to leave blood
Gas exchange follows the gradients and requires coordination between blood and air flow
= deoxygenated blood from the system; right side of heart
PO2 is high in alveolar air space PCO2 is low “ “ “ “

19. Gas exchange: alveoli to blood
Blood from pulmonary artery
Air Space
Type 1 pneumocytes
Type 2 secrete surfactant

20. Gas Exchange: blood to ‘target’ cells
Interstitial Fluid blood in systemic capillaries
PO2 40 mm Hg = PO2 = 95 mm Hg
PCO2 45 mm Hg = PCO2 = 40 mm Hg
Concentration gradient in systemic capillaries is opposite of lungs
O2 diffuses out of blood – donated to interstitium/cells
CO2 diffuses into blood from interstitium/cells

21. Gas exchange: blood to systemic cells
Air Space
NOTE: change in PO2 from lung capillaries (104mm) to systemic capillaries (95mm)
Blood from lung capillaries
**should know this slide
Target cells = muscle cells, etc.

22. Gas Exchange: a problem
Gas Pickup and Delivery
O2 solubility coefficient is very low in blood plasma.
In fact only approximately 2% of the O2 is transported in plasma – thus plasma alone cannot transport enough to meet physiological needs

23. Gas Transport: Red blood cells
Red Blood Cells (RBCs) with hemoglobin
O2 and CO2 saturate plasma - this allows gases to diffuse into red blood cells
Transport O2 to … and CO2 from … peripheral tissues
Blood (cells and plasma) carries O2
1. only 2% dissolved in plasma
2. 98% all O attached to heme groups in RBCs
Hb + O Hb O2 = oxyhemoglobin

24. Gas Transport: RBCs Oxygen Transport Hemoglobin Saturation
O2 binds to iron ions in hemoglobin (Hb) molecules
In a reversible reaction
Each RBC has about 280 million Hb molecules
Each binds four oxygen molecules
Hemoglobin Saturation
The percentage of heme
units in a hemoglobin molecule that contain bound oxygen
If it is not attached to hemoglobin, it is free.
If hemoglobin is saturated, oxygen is not free

25. Oxygen–Hemoglobin Saturation Curve
Is a graph relating the saturation of hemoglobin to partial pressure of oxygen
Higher PO2 results in greater Hb saturation
It’s a curve rather than a straight line
Because Hb changes shape each time a molecule of O2 is bound
Each O2 bound changes Hb configuration and makes next O2 binding easier
This allows Hb to bind O2 when O2 levels are low
Steep curve: allows hemoglobin to bind oxygen even when oxygen is low

26. Oxygen–Hemoglobin Saturation Curve: How to read it
*know this slide
Lower partial pressure, more free oxygen, less saturated hemoglobin
How much O2 is saturated or how much is free?

27. Gas Transport Oxygen Reserves O2 diffuses
from systemic capillaries (high PO2)
into interstitial fluid (low PO2) and then eventually to the target cells, eg. muscle cells
Amount of O2 released depends on interstitial PO2
Up to 3/4 (75%) may be reserved by RBCs
Interstitial fluid: around cells
Carbon monoxide takes same sites as oxygen: dangerous

28. Factors altering Gas Transport
Carbon Monoxide
CO from burning fuels
Binds strongly to hemoglobin on the heme sites
May displace O2 and is difficult to dissociate
Can result in carbon monoxide poisoning

29. Factors altering Gas Transport
Environmental Factors Affecting Hemoglobin
PO2 of blood
the higher PO2 = higher saturation
Temperature
Blood pH
Metabolic activity within RBCs

30. Effects of pH and temp. on Gas Transport
The Oxygen–Hemoglobin Saturation Curve
Is standardized for normal blood (pH 7.4, 37°C)
When pH drops or temperature rises
More oxygen is released, less saturation
Curve shifts to right
When pH rises or temperature drops
Less oxygen is released
Curve shifts to left

31. Gas Transport: temp. & pH
normal temp.
The Effects of pH and Temperature on Hemoglobin Saturation.
Increase temperature, more free oxygen (“burns oxygen off”)
Decrease pH, more free oxygen
Copyright 2009 Pearson Education Inc. publishing as Pearson Benjamin Cummings

32. Bohr Effect: CO2/pH and O2
Think of muscles undertaking metabolism. They give off CO2. CO2 leaves muscle and enters the systemic capillaries, into the RBCs and enters into the following reaction:
CO2 + H2O H2CO H+ + HCO3-
An increase in CO2 drives the reactions to the right and the pH drops. The pH drops because more H+ is formed.
When the ([H+] increases it binds to hemoglobin, alters the configuration of Hb and forces more O2 off of the hemoglobin molecules.
The release of O2 from hemoglobin is good because the muscles can use it to undertake more metabolism
Bohr Effect = the H+ -induced decrease in affinity of O2 for Hb
carbonic anhydrase (enzyme)
carbonic acid
bicarbonate ion
A lot of CO2 drives reaction to right (H ions & bicarbonate)
Hydrogen binds to hemoglobin, releases oxygen
Low pH (more CO2), oxygen releases so you can use it

33. Decrease in O2 saturation of Hb means more O2 is released
Temperature increase = Hb saturation decrease
pH decrease = Hb saturation decrease
Glucose metabolism increase = Hb saturation decrease
CO2 binding to Hb = oxygen release

34. Gas Transport: Fetal hemoglobin
Fetal and Adult Hemoglobin
The structure of fetal hemoglobin
Differs from that of adult Hb
At the same PO2
Fetal Hb binds more O2 than adult Hb
Which allows fetus to take O2 from maternal blood
Lower partial pressure will travel more oxygen to hemoglobin

35. Gas Transport
A Functional Comparison of Fetal and Adult Hemoglobin.

36. How is Gas Transported? Carbon Dioxide Transport (CO2)
Is generated as a by-product of aerobic metabolism (cellular respiration)
CO2 in the bloodstream
converted to carbonic acid
bound to protein portion of hemoglobin (not heme groups)
dissolved in plasma
Oxygen Transport (O2)
Plasma & hemoglobin

37. CO2 Transport CO2 in the Bloodstream
70% is transported as carbonic acid (H2CO3) – really HCO3-
Which dissociates into H+ and bicarbonate (HCO3-)
23% is bound to amino groups of globular proteins in Hb molecule
Forming carbaminohemoglobin
7% is transported as CO2 dissolved in plasma
CO2 has a higher solubility coefficient than O2
Copyright 2009 Pearson Education Inc. publishing as Pearson Benjamin Cummings

38. CO2 – from tissues to alveoli
Figure 23.27
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Systemic capillary
This process occurs as blood moves through systemic
capillaries and carbon dioxide (CO2) moves into the blood
plasma.
Basement membrane
Erythrocyte
Endothelium 1
CO2 diffuses into an erythrocyte. #3 2
Once inside the RBC, CO2 is joined to H2O to form
H2CO3 by carbonic anhydrase. Carbonic acid (H2CO3) splits into bicarbonate (HCO3–) and hydrogen ion (H+).
CO2 + H2O H2CO HCO3– + H+ Hb H+ 2 3
HCO3–, which is negatively charged, exits from the
erythrocyte. Simultaneously chloride ion (Cl–) goes into
the erythrocyte to equalize the charges (to prevent
development of a negative charge on the outside of the
erythrocyte). The movement of HCO3– out of the
erythrocyte as Cl– moves into the erythrocyte is called
the chloride shift. [Note: H+ attaches (and is buffered)
by hemoglobin within erythrocyte.]
CO2 + H2O
H2CO2
Cl–
Carbonic
anhydrase
HCO3– 1 #2 3
Cl–
HCO3–
CO2 #1
Plasma
Tissue cells
(a) Systemic capillaries
Pulmonary capillary
Erythrocyte
Fused basement
membranes Hb 2 H+
This process is reversed as blood moves through
pulmonary capillaries. 3
CO2 + H2O
H2CO3
CO2
Carbonic
anhydrase
HCO3– moves into the erythrocyte as Cl– moves
out.
HCO3– 1 1
CI– 2
HCO3– recombines with H+ to form H2CO3,
which dissociates into CO2 and H2O.
HCO3– 3
CO2 diffuses out of the erythrocyte into the plasma.
CO2 then diffuses into an alveolus.
Alveolus
CI–
(b) Pulmonary capillaries

39. Gas Transport: O2
A Summary of the Primary Gas Transport Mechanisms: Oxygen Transport.
2% O associated with plasma
98% O associated with hg
Copyright 2009 Pearson Education Inc. publishing as Pearson Benjamin Cummings

40. Transport mechanisms: O2 enters and CO2 leaves
Red blood cells
Cells in
peripheral
tissues
Plasma
Alveolar
capillary Hb Hb O2 Hb O2 O2 O2 O2 O2 Hb O2
Alveolar
air space O2
Systemic
capillary
O2 pickup
O2 delivery
Cl
HCO3
Alveolar
capillary
Chloride
shift
HCO3
Alveolar
air space Hb
H+ + HCO3
Cl
H+ + HCO3 Hb Hb H+
H2CO3
H2CO3 Hb H+
CO2
CO2
H2O
CO2
H2O
CO2 Hb Hb
CO2
Systemic
capillary Hb
CO2 Hb
CO2
CO2 delivery – to air space in lungs
CO2 pickup - from tissues

41. For those who want more:
Remember that high concentration of nitrogen (78.6%) in air? Your probably familiar with ‘the bends’ a problem encountered during deep sea diving.
You’re diving and as you go deeper and deeper the pressure increases. According to Boyle’s law, the more pressure causes more gas to be dissolved – in this case N2 in the air - is dissolved into plasma.
As you come back up to the surface, the pressure decreases and N2 begins to leave the plasma and form bubbles. Since the bubbles can go anywhere, the symptoms may vary – from skin itching, pain in the joints, muscle pain, neurologic problems like disorientation, etc.
To minimize this problem, divers have to ascend at a rate – using diving tables - that is slow enough to allow N2 to escape from the blood. This rate allows it to be eliminated from the respiratory system via normal breathing. Alternatively, a diver has to go into a hyperbaric chamber until the N2 is eliminated. A hyperbaric chamber holds the diver in a chamber that has a pressure higher than atmospheric pressure and also has a high O2 concentration. Again the principle is to allow N2 to escape at a slow rate and be eliminated by normal methods. The chamber that has a high oxygen concentration to facilitate the supply of enough oxygen for normal metabolic functions.
For more information see the WIKI site below.