11 - Gas Exchange

Question 1

What are the molecules of the atmosphere

Answer 1

mostly nitrogen
20% oxygen
0.03% carbon dioxide

Question 2

Why does gas exchange occur

Answer 2

exchanges of gasses between the alveoli, blood and tissues occurs due to differences in partial pressures of gasses

Question 3

how to measure atmospheric pressure

Answer 3

1. pan of mercury with test tube
2. test tube with all the atmosphere taken out of it inverted into the pan of the plate with mercury
3. atmosphere presses down on the surface of the mercury
4. sending it up the tube to sea level (760 mmHg)

Question 4

What is Dalton’s law of partial pressures

Answer 4

our atmosphere is a mixture of gasses (nitrogen, oxygen, water vapour, co2)
- each gas contributes to the total pressure of the system in direct proportion to its percentage in the mixed gas

[pressure] x [gas %] = partial pressure of gas

Question 5

Whats the significance of partial pressure

Answer 5

the direction of diffusion of a gas is determiend by the partial pressure of the gas (from high to low)
- difference of partial pressures drives movement of gasses

Question 6

Describe the partial pressure gradient as atmospheric air enters the alveoli

Answer 6

Po2 decreases
- due to increase in Ph2o (water added when breathed in)
- due to increase in Pco2

Pco2 increases
- due to addition from blood

Question 7

Describe the partial pressure gradient as air moves from the alveoli to the atmosphere

Answer 7

Po2 increases
- due to mixing with dead space air

Pco2 decreases
- due to mixing with dead space air

Question 8

What happens as blood flows past the alveoli in external respiration

Answer 8

CO2 from ‘venous’ blood (pulmonary artery) does into the alveoli
O2 is captured from the alveoli

• ‘arterial’ blood (pulmonary vein) has increased O2 and decreased CO2

Question 9

What would happen to external respiration in a person with edema

Answer 9

surfactant increases in alveoli –> becomes a barrier for gas exchange
- CO2 can still exchange (dissolves easily in water)
- O2 cannot dissolve in water —> cannot equilibrate into the blood (not enough oxygen in blood)

Question 10

What would happen in a high V/Q ratio

Answer 10

alot more ventilation for the amount of blood flow

not enough perfusion of a well-ventilated area
- apex of lung
- pulmonary embolism (blood clot in deep vein that moves up to lung)

Question 11

What would happen in a low V/Q ratio

Answer 11

not enough ventilation to the lung that is getting good blood flow

not enough ventilation of a well perfused area
- base of lung
- asthma (smaller tubes)
- lung cancer (cancer growing into tubes and blocks ventilation)

Question 12

How to correct V/Q mismatch

Answer 12

intrinsic mechanism built into lungs in vasculature the pulmonary arterioles that go up to the capillary beds
- have sensors for o2 and co2 levels

arterioles relax if PaCO2 is low or PaO2 is high
- high V/Q ratio

arterioles constrict if PaCO2 is high or PaO2 is low
- low V/Q ratio

Question 13

What happens to pulmonary arterioles when a person moves to higher elevation

Answer 13

less atmospheric pressure
partial pressure is less

pulmonary arterioles will sense and constrict but no where to shunt blood to better area in lungs (but no better area)
- leads to pulmonary hypertension
(altitude sickness)

Question 14

What happens to pulmonary arteriolar pressure in COPD

Answer 14

gets smaller and permanently smaller over time (constriction) –> pulmonary hypertension

effects ventilation over time

Question 15

How is CO2 transported in blood

Answer 15

CO2 dissolved in plasma (7%)
Incognito as sodium bicarb HCO3- (70%)
CO2 bound to hemoglobin – carbamino-Hg (22%)

Question 16

How is O2 transported by the blood

Answer 16

O2 dissolved in the plasma (1.5%)
O2 bound to hemoglobin (98.5%)

Question 17

Describe the structure of hemoglobin

Answer 17

globin - 4 globular protein chains
- 2 alpha, 2 beta

heme - loose binding site with oxygen (easily reversible)
- binds oxygen in relation to partial pressure (when partial pressure really high, favours O2 binding) (when partial pressrue really low - tissues - favours the oxygen letting go of the hemoglobin)
- higher affinity for carbon monoxide (230x)

Question 18

What are the forms of hemoglobin

Answer 18

A= adult –> different in men and women

F= fetal –> higher affinity for O2 than A form

S= sickle 00> crystallizes within the cell (deoxy)

Question 19

How does hemoglobin change in different saturations of blood O2

Answer 19

low blood O2 (unsaturated, appears bluish) - no O2 bound
- in outer space

when exercising tissuess, partial pressure of O2 can drop 20mmHg
(65% of O2 is released to tissues)

at rest, 75% sat with O2 in tissues
(only ever release 25% O2 in an individual)

high blood O2 (fully saturated, appears bright red) - 4 O2 bound
- almost 100% sat at lungs

a single hemoglobin molecule can be 0%, 25%, 50%, 100% saturated with oxygen
- after hemoglobin binds one oxygen, it becomes easier to bind the next three

Question 20

How is oxygen saturation measured

Answer 20

oxygen sat is a measure of how much hemoglobin (on average) is bound with oxygen

Question 21

What are the benefits of the non-linear shape of the O2-Hb dissociation curve

Answer 21

1. flat top
   - allows lots of O2 pick up even with significant respiratory disease (would make it difficult to ventilate alveoli)
2. steep slope
   - allows tissue to pull off as much O2 as needed

Question 22

What happens when tissues are at a high level of metabolism (intense exercise)

Answer 22

increaseed PCO2
Increased temperature of tissues
decreased pH (increased H+)

affects hemoglobins ability to hold onto oxygen
curve shifts to the right
- allows further oxygen to dissociate from hemoglobin to meet the tissues needs

Question 23

What controls breathing rhythm

Answer 23

respiratory centers of the brainstem (medulla and pons) to determine an appropriate frequency and depth of breathing to support tissue respiration

Dorsal respiratory group (DRG)
- active in quiet breathing
- outputs to internal intercostals and diaphragm
- allow you to take a breath in
- active for inspiration and shuts off to empty into lungs

Ventral respiratory group (VRG)
- deep breathing
- talk to accessory muscles
- contains pacemaker cells

Pontine respiratory group
- in the pons
- receive inputs from body (pH of blood, temperature..) to adjust breathing rate

Question 24

What are the sensory inputs to the pons

Answer 24

inflation reflex
- stretch receptors in lung, sends inhbiotry response

cough reflex
- in trachea when there is something in

proprioceptors
- exercise to increase breathing rate

peripheral chemoreceptors in aortic arch
- fine control of paO2 and paCO2
(changes in blood pressure)

temperature, pain, emotion, stretching the anal sphincter

Question 25

what do central chemoreceptors do

Answer 25

located on ventral surface of medulla

sense CSF H+ levels which are influenced by PaCO2

provide input to respiratory centers to maintain PaCO2

Question 26

What system regulates breathing/stimulates chemoreceptors

Answer 26

negative feedback loop

peripheral chemorecpters stimulated by … to increase ventilation
- increase PaCO2
- decrease arterial pH
- decrease PaO2

ensures that alveolar ventilation is at an appropriate level for tissue respiration occuring at any given time

Question 27

t/f oxygen levels drive breathing

Answer 27

false
co2 levels drive breathing