Week 8- Gas Exchange and Transport

Question 1

Gas Exchange in the Lungs

Answer 1

• Takes place between alveolar sir and blood flowing through the lung capillaries
• Physiologically, air in the lungs is not part of the body’s internal environment
• Before O2 can enter and CO2 can leave the internal environment they must cross a barrier

Question 2

Respiratory Membrane Thickness

Answer 2

• Increased thickness= decreased diffusion
• Result of pulmonary edema
• Gas exchange is decreased

Question 3

O2 & CO2 Diffusion

Answer 3

• Gases move in both direction through the respiratory membrane
• oxygen enters the blood from the alveolar air because the PO2 of the incoming blood (remember things move from high to low conc)
• Simultaneously, CO2 molecules exit the blood by diffusing down the pressure gradient into the alveolar air
• PCO2 of venous blood is much higher than the PCO2 of alveolar air
• This 2 way exchange of gases converts deoxygenated blood to oxygenated blood

Question 4

The amount of O2 diffused into the blood each minute depends on several factors:

Answer 4

1. The alveolar pressure gradient
2. The total functional of the respiratory membrane
3. The respiratory minute volume (RR/ min x the volume of air inspired per respiration)- how much we breathe to bring in that oxygen
4. Alveolar ventilation

General rule: anything that decreases the alveolar PO2 tends to decrease the alveolar- blood oxygen pressure gradient, reducing the amount of O2 entering the blood

Question 5

Application 1- O2 Pressure Gradient

Answer 5

• Alveolar PO2 decreases as altitude increases, thus less O2 enters the blood at high altitudes
• Eventually, the PO2 in the alveolar air equals the PO2 of blood

Question 6

Application 2- Functional Surface Area

Answer 6

• Anything that decreases the functional surface area of the respiratory membrane tends to decrease oxygen diffusion into the blood
• Eg. Emphysema pt- the total functional area decreases and is one of the factors responsible for poor oxygenation

Question 7

Application 3- Resp. Minute volume

Answer 7

• Anything that decreases RR tends to decrease blood oxygenation
• Eg. Morphine slows respirations and therefore decreases the respiratory minute volume and tends to lessen the amount of O2 entering the blood

Question 8

How blood transports gases

Answer 8

• Blood transports O2 and CO2 either solutes or combined with other chemicals
• Immediately upon entering the blood, both O2 and CO2 dissolve in the plasma
• B/c fluids can only hold small amounts of gas most of the O2 and CO2 rapidly form a chemical union with other molecules such as hemoglobin, plasma, proteins or water
• Once they are bound to a molecule, their plasma concentration decreases and more gas can diffuse into the plasma- allowing large amounts of gases to be transported

Question 9

Hemoglobin

Answer 9

• Reddish protein pigment found in the RBCs
• Contains iron, alpha, and beta chains
• Contains iron- O2 affinity for iron atoms, allowing the iron to act as oxygen sponge that chemically absorbs O2 molecules from the surrounding solution
• CO2 has an affinity for the alpha and beta amino acid chains, allowing HB to “sponge” the CO2 and carry it as well

Question 10

Transport of O2

Answer 10

• HB combines with O2- forms oxyhemoglobin
• Each gram of HB can untie with 1.34ml of O2
• As a result, the exact amount of O2 in the blood depends largely on the amount of HB present
• Think in percent- normal arterial blood contains 20% O2. This means 20 mls of O2 in 100 mls of blood.
• The higher the HB percentage, naturally the higher the O2 carrying capacity of the blood is and vice versa
• At rest, fully saturated HB molecule unloads only 25% of O2, during stress/ exercise- up to 70%

Question 11

Oxygen Hemoglobin Dissociation Curve

Answer 11

• To combine with HB, O2 must diffuse from the plasma into the RBC (millions of HB molecules are in the RBC)
• The higher the PO2 in the blood- acceleration of O2 being bound to HB
• The lower the PO2 in the blood- lowers the rate O2 is being bound to HB

Question 12

O2 Dissociation Curve

Answer 12

• Describes the relationship between the PO2 (x axis) and the O2 saturation (y axis)

Question 13

HB O2 affinity increases as more O2 binds

Answer 13

• This continues to move up until a max amounts is reached
• As this limit is reached, little to no more binding occurs, you will see the curve level out as all HB are saturated with O2
• This typically happens at pressures of PO2 >60 mmHg (this means that no matter how much you increase the PO2, the SPO2 will not arise any more past this level)

Question 14

Factors that affect the curve

Answer 14

• The strength at which O2 binds to HB is affected by several factors
• This will alter or shift the shape of the curve

Question 15

Rightward Shift

Answer 15

• Indicated the HB has a decreased affinity for O2 (doesn’t want it anymore)
• Means a higher PO2 would be required to reach the same O2 saturation of a healthy person
• Also means it is easier for the HB to release the O2 molecules
• When it needs oxygen
• Higher CO2, Lower pH, Higher temp

Question 16

Why the right shift?

Answer 16

• Typically shifts this way during times O2is needed most- exercise, stress, shock
• C- CO2
• A- Acid
• D- DPG (factor that controls how easily/ difficult O2 is bound)
• E- Exercise
• T- Temp

Question 17

Right- Bohr Effect

Answer 17

This curve shifts down (off) to the right when:
- high CO2
- low pH
- high temp
- high DPG (enzyme that helps to release O2) gets rid of oxygen (decreasing the affinity) releasing this enzyme

• Therefore more O2 is released to the tissues

Question 18

Leftward shift

Answer 18

• HB has an increased affinity for O2
• Binds more easily, unloads more reluctantly

Question 19

Left- Bohr Effect

Answer 19

The curve shifts up (over) to the left when:
- low CO2
- high pH
- low temp
- low DPG

• Therefore more O2 will be bound to HB

Question 20

Why the left shift?

Answer 20

Patient presentations of a left shift could be:
- Carbon monoxide poisoning
- Hypothermia
- Cancers of the head and neck- due to smoking and alcohol

Question 21

Temperture

Answer 21

High temp: right shift

Low temp: left shift

Question 22

2,3-BPG

Answer 22

High 2,3-BPG: right shift

Low 2,3-BPG: left shift

Question 23

PCO2

Answer 23

High PCO2: right shift

Low PCO2: left shift

Question 24

Acidity [H+]

Answer 24

High acidity: right shift

Low acidity: left shift

Question 25

Transport of CO2- Dissolved CO2

Answer 25

• small amount of CO2 dissolves in plasma and is transported as a solute (10% of the total volume is carried this way)
• this dissolved CO2 produces the PCO2 of blood plasma

Question 26

Transport of CO2- Carbamino compounds

Answer 26

• 1/5 to 1/4 of CO2 in blood unites with NH2 amino acid chains
• When CO2 combines with these chains, it forms carbamino compounds
• CO2 combines with HB and creates carbaminohemoglobin
• The higher the PCO2 levels- accelerates this binding process
• The lower the PCO2 levels- slows this process

Question 27

Biocarbonate

Answer 27

• More the 2/3 of the blood CO2 is carried in the form of bicarbonate ions (HCO3-)

Question 28

How does the bicarbonate process work?

Answer 28

• CO2 dissolves in the plasma (water present), some molecules bind with the H2O to form carbonic acid (H2CO3)
• Some then dissociate to form H+ and Bicarbonate (HCO3-) ions
• The more CO2 that is present= higher levels of carbonic acid
• The higher levels of carbonic acid= pulls the system towards the bicarbonate ions, increasing the rate of bicarbonate formation
• This allows for more CO2 to dissolve in the plasma, increasing the CO2 carrying capacity of the blood

Question 29

Bohr Effect/ Haldane Effect

Answer 29

• Reciprocal interrelationship between O2 and CO2 transport

Question 30

Bohr Effect

Answer 30

• Increased PCO2 decreases the affinity between HB and O2- called a “right shift’ on the O2 HB dissociation curve