HUBS192 Lecture 18 - Oxygen and Carbon Dioxide Exchange

Question 1

what is the equation for how much air we breathe in and out?

Answer 1

• Vf = Vt x f
• respiratory minute volume = tidal volume (breathing strength) x respiratory rate (breathing speed)
• (L/min) = (L/breath) x (breaths/min)

Question 2

what is respiratory minute volume?

Answer 2

volume of air respired (breathed in and out) per minute in L/min

Question 3

what is the dead space (Vd)?

Answer 3

air in conducting portion of the respiratory system (anatomic dead space)
-volume of air trapped in the bronchial tree that does not interact with the alveoli

Question 4

what is alveolar ventilation?

Answer 4

the amount of air that is getting in the alveoli that can be used in gas exchange per time

Question 5

what is the equation for alveolar ventilation?

Answer 5

• Va = (Vt - Vd) x f
• Alveolar ventilation = (tidal volume (breathing strength) - dead space (the air that can’t be used) x respiratory rate (breathing speed)
• (L/min) = ((L/breath) - L/breath)) x (breaths/min)

Question 6

what is not helpful to increasing alveolar ventilation?

Answer 6

tiny rapid breaths are not helpful

Question 7

why are tiny rapid breaths not helpful in increasing alveolar ventilation?

Answer 7

because tidal volume is small its not much more than the dead space therefore trapping the fresh air within the dead space and not coming in contact with the alveoli
-respiratory rate is increased

Question 8

how do you increase alveolar ventilation?

Answer 8

• increase tidal volume
• keep respiratory rate highly constant
• results in a negligable dead space

Question 9

what is daltons law?

Answer 9

the pressure of a mixture of gases is the sum total of the pressures of each individual gas

Question 10

what is the largest component of air?

Answer 10

nitrogen

Question 11

what is the ratio of gases when inhaling air?

Answer 11

• mostly nitrogen (nitrogen content in the alveoli is relatively the same)
• quite a lot of oxygen (oxygen content in the alveoli is very low)
• almost no carbon dioxide or water vapour

Question 12

what is the ratio of gases when exhaling air?

Answer 12

• mostly nitrogen
• oxygen is decreased
• carbon dioxide is increased

Question 13

what is the goal of moving gas across the membranes?

Answer 13

the goal is to move gas back and forth between the alveoli and the capillaries (CO2 and O2)

Question 14

where is inhaled oxygen transported?

Answer 14

transports inhaled oxygen into the capillaries

Question 15

where is carbon dioxide (CO2) transported?

Answer 15

transports carbon dioxide into the alveoli to be exhaled

Question 16

how do gases move across the membranes?

Answer 16

gases move across the membranes between the alveoli and the capillaries by diffusion

Question 17

what 3 things determine the rate of diffusion of gases?

Answer 17

1) surface area of the membranes
2) thickness of the membranes
3) pressure difference between the two sides

Question 18

what creates the high surface area for gas exchange?

Answer 18

bulbous structure of alveoli and the high density of capillaries

• creates lots of air pockets
• surface area as large as a tennis court

Question 19

what is emphysema?

Answer 19

disease characterised by diction of the alveolar spaces and destruction of the alveolar walls

Question 20

what is the result of emphysema?

Answer 20

reduction in surface area means less contact between the air and capillaries, oxygen exchange is greatly reduced

Question 21

what is the blood air barrier mostly composed of?

Answer 21

mostly composed of the alveolar and capillary walls

Question 22

what is the relationship between the distance between of the alveolar air and the blood?

Answer 22

small distance between the alveolar air and the blood

-affects diffusion

Question 23

what are the 3 key determinants of how much alveolar oxygen we have at any given moment?

Answer 23

1) atmospheric oxygen
2) alveolar ventilation
3) blood oxygen (amount of exchange that Is occurring)

Question 24

what is the relationship between exercise and blood oxygen?

Answer 24

exercise depletes blood oxygen

Question 25

what is happening in the body at low activity in terms of oxygen consumption and oxygen in venous blood?

Answer 25

• reduced oxygen consumption

- higher levels of oxygen in the venous blood

Question 26

what is happening in the body at high activity in terms of oxygen consumption and oxygen in venous blood?

Answer 26

• increased oxygen consumption

- lower levels of oxygen in the venous blood

Question 27

what are the things that 3 determine how much alveolar carbon dioxide we have at any given moment?

Answer 27

1) atmospheric CO2
2) alveolar ventilation
3) blood CO2

Question 28

how do gases diffuse in terms of their pressure gradient?

Answer 28

gases diffuse down their pressure gradient