Gas Exchange and Gas Transport

Question 1

what is parietal pressure

Answer 1

the pressure exerted by each type of gas in a mixture

Question 2

how is partial pressure calculated

Answer 2

% of volume a particular gas makes up of the gas mixture x10-2 TIMES 760 (atmospheric pressure)

e.g.
oxygen makes up 20.84% of the volume of atmospheric air, so it’s partial pressure 0.2084 x 760 = 158.4mmHg

Question 3

what is Dalton’s Law?

Answer 3

in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases

Question 4

in a mixture of non-reacting gases, what is the total pressure exerted equal to?

Answer 4

the sum of the partial pressures of the individual gases

Question 5

when air comes into contact with water, some of the water turns into gas and evaporates into the air.
The composition of alveolar air is not identical to atmpospheric air: what are 3 reasons for this?

Answer 5

1. air entering the respiratory system during inspiration is humidified
2. oxygen diffuses from alveoli into blood and carbon dioxide diffuses from the pulmonary capillaries into the alveoli
3. air within the alveoli is only partially replaced with atmospheric air during each inspiration

Question 6

what is dead space?
what is anatomic dead space?
what is physiologic dead space?

Answer 6

the part of the respiratory system where gas exchange does not take place is called dead space
anatomic dead space measures 150ml and is formed by the nasal cavity, pharynx, larynx, trachea, bronchi and bronchioles
physiologic dead space is the anatomic space plus the volume of any alveoli in which gas exchange is less than normal

Question 7

what are anatomic and physiologic dead space like in a healthy person, and a person with emphysema?

Answer 7

In a healthy person, anatomic and physiologic dead space are nearly the same, meaning that few non-functional alveoli exist.
In a person with emphysema, alveolar walls degenerate and small alveoli combine to form larger alveoli. the result is fewer alveoli, but alveoli with an increased volume and decreased surface area. although the enlarged alveoli are still ventilated, surface area is inadequate for complete gas exchange, and the physiologic dead space increases.

Question 8

what is the partial pressure of O2 and CO2 in alveolar air?

Answer 8

O2: 104mmHg
CO2: 40mmHg

Question 9

what is the partial pressure of O2 and CO2 in mixed venous blood?

Answer 9

O2: 30-40mmHg
CO2: 40-50mmHg

Question 10

what is the partial pressure of O2 and CO2 in arterial blood?

Answer 10

O2: 75-100mmHg
CO2: 35-45mmHg

Question 11

according to Fick’s law, what affects the rate of diffusion?

Answer 11

gas solubility
surface area
concentration difference
membrane thickness

Question 12

how does gas solubility affect rate of diffusion?

Answer 12

the more soluble a gas is in water, the easier it is for diffusion to occur. O2 and CO2 both dissolve in water so are easily diffused

Question 13

how does surface area affect rate of diffusion?

Answer 13

the larger the surface area available for diffusion, the greater the rate of diffusion will be. large inhalations use more alveoli and so there will be a greater rate of diffusion as a result

Question 14

how does concentration difference affect rate of diffusion?

Answer 14

the greater the difference in gas concentration between the alveoli and the pulmonary circulation, the faster that gas will diffuse. because blood travelling towards the alveoli is deoxygenated there always remains a large difference in concentration of oxygen between the alveoli and pulmonary circulation

Question 15

how does membrane thickness affect rate of diffusion?

Answer 15

the further the distance the gases have to travel, the slower the rate of diffusion will be

Question 16

how are oxygen and carbon dioxide carried in blood

Answer 16

approx 98.5% of oxygen in the blood is transported in combination with haemoglobin the red blood cells, and the remaining 1.5% is dissolved in the water part of the plasma

carbon dioxide is transported in the blood in 3 major ways: approx 7% dissolved in plasma, 23% combined with haemoglobin, and 70% in the form of bicarbonate ions

Question 17

describe how haemoglobin transports oxygen in the blood

Answer 17

haemoglobin is a protein molecule found in RBCs made of 4 sub-units: 2 alpha and 2 beta. each sub unit surrounds a central heme group that contains iron and binds 1 oxygen molecule- this means that one haemoglobin molecule binds with 4 oxygen molecules.

Question 18

describe CO2 and haemoglobin

Answer 18

carbon dioxide can bind to plasma proteins or enter RBCs and bind to haemoglobin. binding of CO2 to haemoglobin is reversible so when CO2 reaches the lungs it can freely dissociate from the Hb and be expelled from the body

Question 19

describe the bicarbonate buffer system

Answer 19

the majority of CO2 in the blood is carried as part of the bicarbonate buffer system. CO2 diffuses into RBCs. carbonic anhydrase within the RBCs quickly converts the CO2 into carbonic acid which then immediately dissociates into bicarbonate ions. this reaction allows for continued uptake of CO2 into blood, down the concentration gradient.