CHAPTER 39--- Diffusion of O2 and CO2 Through the Respiratory Membrane

Question 1

______ __________—- represents the gas exchange between the alveoli and the pulmonary capillaries.

Answer 1

Pulmonary diffusion

Question 2

CO2 in the capillary blood coming from the _____ ventricle (via the right and left pulmonary arteries) diffuses from the blood into the alveoli so that it can be expired.

Answer 2

right

Question 3

O2 enters the alveoli during inspiration, diffuses from the _______ _______ into the blood, and is carried by hemoglobin contained in the RBCs—remember, there are 250 million Hb molecules per RBC and each Hb has 4 binding sites so each RBC has the capacity for carrying 1 billion O2molecules (250 M X 4 = 1B/RBC).

Answer 3

alveolar sacs

Question 4

“Partial Pressures” of Individual Gases in a Mixture of Gases–1

The RATE of DIFFUSION of each gas is DIRECTLY proportional to the PRESSURE caused by that gas alone—this is referred to as the _______ _______ of each gas.

Answer 4

partial pressure

Question 5

“Partial Pressures” of Individual Gases in a Mixture of Gases–2

The partial pressure of each gas is directly proportional to the ________ of each type of gas molecule in the
mixture.

The total pressure of mixed air at sea level averages ____ mmHg. ***SEE SLIDE 4

Answer 5

concentration

760

Question 6

Pressure Difference Causes Net Diffusion—–1

When the partial pressure of one gas is greater in one area than in another area, there will be net diffusion from the area of ______pressure to the area of _______ pressure.

Answer 6

higher

lower

Question 7

Pressure Difference Causes Net Diffusion—–2

Diffusion occurs because gas molecules have ______energy and are constantly moving in a random fashion. When there are more of a specific type of molecule in one end of a vessel, they will move toward the end where there are fewer molecules.

Answer 7

kinetic

Question 8

Pressure Difference Causes Net Diffusion—–3

There are more oxygen molecules on End A of the vessel as compared to End B. The molecules on both ends will move toward the opposite end, but because there are more molecules on End A, there is more pressure therefore, the oxygen molecules on End A will move at a faster rate toward End B. The differences in
the lengths of the arrows represents ____ _________.

Answer 8

net diffusion

Question 9

Humidified Air in the Respiratory Passages–1

As soon as _________ ________enters the respiratory passages, if becomes humidified so even BEFORE it enters the alveoli, it is essentially 100% humidified.

Answer 9

atmospheric air

Question 10

Humidified Air in the Respiratory Passages–2

The partial pressure of water vapor (PH2O) at normal body temperature (37o C) is _______mmHg which becomes the PH2O in alveolar air.

Answer 10

47

Question 11

Humidified Air in the Respiratory Passages—3

Because total alveolar pressure CANNOT exceed atmospheric pressure of 760 mmHg, this water vapor ________ the partial pressures of the other gases (see table below)

Answer 11

dilutes

Question 12

Why Atmospheric Air and Alveolar Air Are Different

• ** Alveolar air has a lower PO2 and a higher PCO2 than atmospheric air. Why?
  1. Alveolar air is only partially replaced with atmospheric air with each breath.
  2. O2 is constantly diffusing ____ of the alveoli into the blood of the pulmonary capillaries.
  3. CO2 is constantly diffusing _____ the alveoli from the blood in the pulmonary capillaries

Answer 12

out

into

Question 13

Rate of Alveolar Air Renewed by Atmospheric Air—1

1– alveolar air is only _______ replaced with new atmospheric air \with each breath.

2–The volume of alveolar air replaced with each breath is 1/7 of ______ _______ air, so it requires multiple breaths to replace the majority of alveolar air.

Answer 13

partially

total atmospheric

Question 14

Rate of Alveolar Air Renewed by Atmospheric Air—2

This _____replacement of alveolar air helps prevent:
(a) sudden changes in gas concentrations in the blood
(b) sudden changes in blood pH when respiration is
temporarily interrupted.

Answer 14

slow

Question 15

O2 Concentration and PO2 in Alveoli–1

1–O2 is continually diffusing from the alveoli into the _______ capillaries. Also, NEW O2 is being taken into the alveoli from the atmosphere.

Answer 15

pulmonary

Question 16

O2 Concentration and PO2 in Alveoli–2

2–The more rapidly O2 diffuses into the blood, the
_______ the concentration in the alveoli. Conversely, the more rapidly O2 is breathed into the alveoli, the higher the concentration in the alveoli.

Answer 16

lower

Question 17

O2 Concentration and PO2 in Alveoli–3

Therefore, O2 concentration in the alveoli, and thus the PO2 is controlled by –

(1) the rate of diffusion of O2 into the blood
(2) the rate of ______of new O2 into the lungs through ventilation

Answer 17

entry

Question 18

CO2 Concentration and PcO2 in Alveoli—-1

1–CO2 is continually being made in the body, transported to the lungs, and excreted via __________(expiration)

Answer 18

ventilation

Question 19

CO2 Concentration and PcO2 in Alveoli—-2

During RESTING conditions (200 ml), the normal PCO2 is 40 mmHg. During moderate exercise, when CO2
production is increased, to maintain the PCO2 at 40 mmHg, alveolar ventilation must INCREASE more than ____-fold (from 5L to 15 L/min)

Answer 19

three

Question 20

Location of Gas Diffusion—-1

1–__________ ________(also called respiratory
lobule) is composed of respiratory bronchioles,
alveolar ducts, and alveolar sacs.

2—There are about _______ million alveoli in the two
lungs.

Answer 20

Respiratory Unit

300

Question 21

Location of Gas Diffusion—–2

3—The alveolar walls are extremely thin and ______ the alveoli is a solid network of interconnecting capillaries.

4–The extensiveness of this capillary plexus is described as a “_________” of flowing blood.

Answer 21

between

sheet

Question 22

Location of Gas Diffusion—-3

5–Therefore, the gases are in close proximity to both the blood and the alveoli which facilitates rapid diffusion across the_____________

6— All these membranes are referred to as the
_____________ membranes or _________
membranes.

Answer 22

membranes.

respiratory

pulmonary

Question 23

Rate of Gas Diffusion Through the Respiratory Membrane–1

Despite the layers between the inside of the alveoli and the RBC, the overall ______ of the respiratory membrane in some areas is as little as 0.2 micrometers and averages about 0.6 micrometers.

Answer 23

thickness

Question 24

Rate of Gas Diffusion Through the Respiratory Membrane-2

The average thickness of a RBC is __ micrometers, so the RBCs must squeeze through the small diameter capillaries. As a result, the RBC membrane touches the capillary wall making it easy for O2 and CO2 to diffuse across these membranes.
***This INCREASES the rate of diffusion of the
gases.

Answer 24

5

Question 25

Rate of Gas Diffusion Through the Respiratory Membrane-3

The surface area of the respiratory membrane is large and contains a small amount of blood and this also contributes to
an increased rate of ______ ______.

Answer 25

gas exchange

Question 26

4 Factors that Affect Rate of Gas Diffusion–1

1. ________ of the respiratory membrane. If thickness increases, rate of diffusion decreases. Anything that causes an increase in thickness to 2 to 3 times normal can significantly interfere with respiratory gas exchange (ex. pulmonary edema and fibrosis factors).

Answer 26

Thickness

Question 27

4 Factors that Affect Rate of Gas Diffusion–2

2. ________ ________of the respiratory membrane. Anything that causes a decrease in surface area is detrimental to gas exchange even under resting conditions (ex. removal of one lung cuts surface area in half and emphysema significantly reduce surface area of the lungs by ¼ ).

Answer 27

Surface area

Question 28

4 Factors that Affect Rate of Gas Diffusion–3

3. Diffusion coeffiecient. This is dependent on the gas’s solubility or the gas’s molecular weight (MW). In terms of solubility, CO2 is ___ times more soluble than O2. Therefore, CO2 diffuses ___ times more quickly than O2. Conversely, diffusion rate is ________ proportional to MW—the higher the MW, the slower the rate of diffusion.

Answer 28

20

20

inversely

Question 29

4 Factors that Affect Rate of Gas Diffusion–4

4. Pressure __________. The partial pressure differences of the gases between the alveoli and the capillary blood. PO2 is higher in the alveoli so O2 diffuses into the blood. PCO2 is higher in the blood returning to the lungs so CO2 diffuses from the blood into the alveoli

Answer 29

difference