Physiology 3 - Gas exchange

Question 1

Anatomical dead space

Answer 1

some inspired air that remains in the airway where is is NOT AVAILABLE for GAS EXCHANGE

Question 2

What is pulmonary ventilation

Answer 2

volume of air breathed in and out per minute

= tidal volume x respiratory rate

Question 3

what is alveolar ventilation

Answer 3

volume of air exchange between atmosphere and alveoli per minute
= (tidal volume - dead space volume) x respiratory rate

Question 4

what is pulmonary ventilation less than alveolar ventilation?

Answer 4

due to the presence of anatomical dead space

Question 5

what 2 things would you need to increase to increase pulmonary ventilation?

Answer 5

1) depth of breathing (tidal volume)

2) rate of breathing (respiratory rate)

Question 6

what is ventilation

Answer 6

RATE at which GAS passes through the lungs

Question 7

what is perfusion

Answer 7

RATE at which BLOOD passes through the lungs

Question 8

is blood flow fastest at top of bottom of lung

Answer 8

blood flow = fastest at BOTTOM

Question 9

is ventilation fastest at top of bottom of lung

Answer 9

ventilation = fastest at TOP of lung

Question 10

what effect does differences in blood flow and ventilation have on average arterial and alveolar partial pressure.

Answer 10

the average arteriole and alveolar partial pressure of O2 is not exactly the same

Question 11

describe alveolar dead space

Answer 11

= ventilated alveoli which are not adequately perfused with blood

when the match between air in the alveoli and blood in pulmonary capillaries is not perfect

Question 12

describer the process that occurs when the perfusion is greater than ventilation

Answer 12

1) accumulation of CO2 in alveoli
2) decreased airway resistance
3) increased airflow

Question 13

describe the process that occurs when the ventilation is greater than perfusion

Answer 13

1) accumulation of O2 concentration
2) causes pulmonary vasodilatation
3) increases blood flow tot match large airflow

Question 14

describer what happens to the; 
- gas levels 
- smooth muscles 
- airflow/bloodflow 
when perfusion is greater than ventilation

Answer 14

• CO2 increases
• O2 decreases
• dilation of local airways
• constriction of local blood vessel
• increased airflow
• decreased blood flow

Question 15

describer what happens to the; 
- gas levels 
- smooth muscles 
- airflow/bloodflow 
when ventilation is greater than perfusion

Answer 15

• O2 increases
• CO2 decreases
• constriction of local airways
• dilation of local blood vessels
• increased blood flow
• decreased airflow

Question 16

4 factors that influence the rate of gas exchange across alveolar membranes

Answer 16

1) partial pressure of O2 & CO2
2) diffusion co-efficient for O2 and CO2
3) surface area of alveolar membrane
4) thickness of alveolar membrane

Question 17

Dalton’s law of partial pressure states that;

Answer 17

the total pressure exerted by a gaseous mixture

= the sum of the partial pressures of each individual components in the gas mixture

Question 18

what determines the pressure gradient for a gas

Answer 18

the partial pressure

Question 19

what is the partial pressure of a gas

Answer 19

the pressure that gas would exert if it occupied the total volume for the mixture in the absence of other components

e.g. if total pressure = 100kPa
partial pressure = 50kPa

Question 20

how would you write the formula for the partial pressure of oxygen in alveolar air

Answer 20

PAO2

BIG ‘A’

Question 21

what is the equation for alveolar gas

Answer 21

PAO2 = PiO2 - [PaCO2/0.8]

Question 22

what does PiO2 stand for

Answer 22

partial pressure of inspired oxygen

Question 23

what does PaCO2 stand for

Answer 23

partial pressure of CO2 in ARTERIAL blood

a = arterial

Question 24

what is 0.8 represent

Answer 24

respiratory exchange rate, amount of CO2 excited fo amount of O2 used

Question 25

how do you calculate the PiO2

Answer 25

• air in respiratory tract is saturated with water
• water vapour contributes 47mmHg to total pressure in the lungs
• therefore, the pressure of inspired air;
  = atmospheric pressure - water vapour pressure
  = 760 - 47
  = 713mmHg
• since O2 is 21% of air;

PiO2 = 713 x 0.21
= 150mmHg

Question 26

why is the partial pressure gradient for CO2 much smaller than that of O2

Answer 26

• because CO2 is far more soluble than O2

Question 27

what is the diffusion co-efficient

Answer 27

the solubility of a gas in membranes

Question 28

what is the diffusion co-efficient of CO2 compared to O2

Answer 28

CO2’s diffusion co-efficient is 20X oft that of O2

Question 29

what if Fick’s Law of diffusion

Answer 29

the amount of gas that moves across a sheet of tissue in unit time is PROPORTIONAL to the AREA OF THE SHEET but INVERSELY PROPORTIONAL to its THICKNESS

Question 30

what role do alveoli have?

Answer 30

• involve in gas exchange
• they are thin walled inflatable sacs in which there walls consists of a single layer of flattened type 1 alveolar cells

Question 31

where are pulmonary capillaries found?

Answer 31

Encircling each alveolus

Question 32

name non-respiratory functions of the respiratory system

Answer 32

1) route for water loss & heat elimination
2) enhances venous returns
3) helps maintain normal acid-base balance
4) enables speech, singing & other vocalisation
5) defends against inhaled foreign matter r
6) removes, modifies, activates or inactivates materials passing though the pulmonary
7) nose serves as organ of smell