Lecture 18 - Oxygen and carbon dioxide exchange

Question 1

Describe vital capacity

Answer 1

Maximum volume of air that you can shift in and out of your lungs

Question 2

How much blood do we eject from the heart?

Answer 2

CO = SV x HR

Cardiac output = stroke volume (contraction strength) x heart rate (contraction speed)

Question 3

How much air do we breathe in and out?

Answer 3

Ve = Vt x f
Respiratory minute volume (L/min)= tidal volume (breathing strength, L/breath) x respiratory rate (breathing speed, breaths/min)

Question 4

Dead space

Answer 4

Dead space is the volume of air that is inhaled that does not take part in the gas exchange, because it either remains in the conducting airways or reaches alveoli that are not perfused or poorly perfused. In other words, not all the air in each breath is available for the exchange of oxygen and carbon dioxide.

Question 5

How much air that we breath in can get to the alveoli?

Answer 5

VA= (Vt-Vd) x f 
Alveolar ventilation (L/min) = (tidal volume - dead space (L/breath, the air that can’t be used)) x respirator rate

Question 6

Why are tiny rapid breaths not helpful?

Answer 6

Recommended to take controlled deeps breaths when exercising over tiny rapid breaths

Really increase frequency by taking tiny breaths and the problem with this strategy is that because tidal volume is small it is not that much more than the dead space, you are not pulling a lot more fresh air from the outside to the alveoli, you are trapping the small breaths within the dead space - yes you are increasing the frequency but you are multiplying it by a very small number that comes from the tidal volume minus the dead space therefore these breaths are not very useful for getting oxygen into the system, what you are better off doing is increasing your tidal column whilst keeping your respiratory rate relatively constant and then when you do this, the tidal volume is high and the dead space becomes much more negligible so you get a much greater alveolar ventilation and you get more air into the lungs

Question 7

Dalton’s law

Answer 7

The pressure of a mixture of gases is the sum total of the pressures of each individual gas
The air we breath in is not pure oxygen in fact most of it isn’t oxygen

Alveolar air (saturated) has an oxygen content that is lower than inhaled dry air. This is because the purpose of the alveoli is to push as much of the oxygen into the bloodstream to be sent around the body so some of the oxygen content has been lost to this, this has been replaced largely by carbon dioxide

In exhaled air (saturated), oxygen is a bit higher and carbon dioxide is a bit lower …. Different because there is still air trapped in the dead space so when you exhale air from the lungs, this exhaled air mixes with the air that is in the dead space but never made it down into the alveoli and therefore never experienced any gas exchange with the blood therefore still has high oxygen and low carbon dioxide levels

Question 8

Moving gas across the membranes

Answer 8

The goal is to move gas back and forth between the alveoli and the capillaries
Transport inhaled oxygen into the capillaries. Transport carbon dioxide into the alveoli to be exhaled.

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

Question 9

What determines the rate of diffusion?

Answer 9

Surface area of the membrane
Thickness of the membranes
Pressure difference between the two sides

Question 10

Alveolar ventilation is usually a bit ______ than respiratory minute volume

Answer 10

lower

Question 11

What is alveolar ventilation affected by?

Answer 11

The amount of dead space in the respiratory system

Question 12

Alveolar ventilation is measured as a….

Answer 12

A volume of air per unit time

Question 13

Taking deep breaths will increase …

Answer 13

Tidal volume and alveolar ventilation

Question 14

Does the frequency of breaths affect alveolar ventilation?

Answer 14

Yes

Question 15

What characteristics creates lots of surface area for gas exchange?

Answer 15

Bulbous structure (rounded structure with lots of different pockets) of alveoli and the high density of capillaries creases lots of surface area for gas exchange between alveoli and capillaries

Question 16

Emphysema

Answer 16

A disease characterised by dilation (become large and swollen) of the alveolar spaces and destruction of the alveolar walls

Normally lots of little circles with little membranes in between them. In diseased alveoli, spaces and larger and the membranes have broken down and so now there is much less surface area to allow gas exchange across so the capillaries receive less oxygen from the alveoli themselves

Reduction in surface area means less contact between the air and capillaries, so oxygen exchange is greatly reduced and there is therefore low blood oxygen levels

Often associated with smoking

Question 17

The blood air barrier

Answer 17

Alveolar cell layer
Fused basement membranes of alveolar epithelium and capillary endothelium
Capillary endothelium

The blood air barrier is mostly compromised of the alveolar and capillary walls
The distance between the alveolar air and the blood is very small

Question 18

Pulmonary fibrosis

Answer 18

Thickening and scarring of the alveolar membranes - kills a lot of the cells associated with the lungs and replaces them with scar tissue

Can arise from chronic inflammation or exposure to industrial chemicals

Less compliance and scarring causes the blood air barrier to be thickened due to the thickened walls of the lungs, now since they are thicker it is harder to move gas across the membrane

Question 19

3 determinants of how much alveolar oxygen

Answer 19

Atmospheric oxygen
Amount ventilated down into the alveoli themselves
Amount of oxygen in the blood therefore the amount of exchange that is occurring

Question 20

Erythropoiesis

Answer 20

RBC production is controlled by homeostatic mechanism involving erythropoietin (EPO) 

Augmented by testosterone

Reduction in RBCs causes a decrease in oxygen delivery and this is sensed by the kidneys

Question 21

Oxygen pressure in the alveoli at high altitude

Answer 21

At higher altitude there is less available atmospheric oxygen

Decreased atmospheric oxygen means that there is less alveolar oxygen because there is less oxygen arriving at the blood air barrier and this overall means that there is less blood oxygen. To combat this the body makes more red blood cells to carry more oxygen

Question 22

At high activity…

Answer 22

High activity
Increased oxygen consumption
Lower levels of oxygen in venous blood - going to want to pull more oxygen from alveoli

Question 23

At low activity …

Answer 23

Low activity
Reduced oxygen consumption
Higher levels of oxygen in the venous blood

Question 24

Gases diffuse ______their pressure gradient

Answer 24

Down

Question 25

Alveolar oxygen levels depend on

Answer 25

Atmospheric oxygen,, alveolar ventilation, and blood oxygen levels