Respiratory System, Lecture 4

Question 1

Gas Exchange - Dalton’s Law and Partial Pressure

Answer 1

• looking at individuals pressure gradients for what we need
• air pressure is all the pressures added together
• driven by pressure gradients of individual gases not air
  dalton’s law:
• total pressure exerted by a mixture of gases is sum of pressure exerted independently by each gas in mixture (partial pressure)
• overall pressure is the sum total of all the partial pressures
  partial pressure of a gas: PG = Patm x FG
• PG = gas partial pressure
• Patm = atmospheric pressure
• FG = fraction of gas in mixture (% of gas in air mixture)
• oxygen at sea level: Patm = 760 mmHg / FO2 = 21 %
  
  • PO2 = 760 mmHg x 21 % = 159 mmHg
• Carbon dioxide at sea level: Patm = 760 mmHg / FCO2 = 0.04 %
  
  • PCO2 = 760 mmHg x 0.04 % = 0.3 mmHg
• can do this calculation for any single gas

Question 2

Gas Exchange - external respiration (oxygen and carbon dioxide)

Answer 2

oxygen
-> alveoli - 105mmHg / arterial blood 40mmHg (high in alveoli and low in arterial blood - moving from high to low)
pressure gradient: movement from alveoli to capillaries so oxygen enters capillaries
- blood entered capillaries deoxygenated (40 mmHg) and comes out oxygenated (100 mmHg)
- know the pressures coming in, and gradient will move it to needed side, oxygenating it

carbon dioxide
-> alveoli - 40 mmHg / arterial blood - 46 mmHg (more in blood, less in alveoli -> move into alveoli)
pressure gradient: movement from capillaries to alveoli so C02 enters alveoli (expired with ventilation)
blood entered capillaries (46 mmHg) and comes out (40 mmHg) (lowering capillaries, not changing alveoli (increasing))

• pulmonary circulation takes oxygenated blood (O2 100 mmHg / Co2 40 mmHg) back to heart to be pumped out to systemic circulation
• depends on the gases, how much can move
• deoxygenated coming into capillaries - oxygenated coming out of capillaries

Question 3

Movement across alveolar-capillary membrane regulated by:

Answer 3

• partial pressure gradient of gas
• surface area for diffusion (lots of surface area - does not interfere too much)
• thickness of membrane gas is diffusing through (membrane in lungs is extremely thin, meaning pretty easy for it to move through)
• diffusion coefficient of gas (amount that can cross an area in 1 second) - constant (oxygen has different diffusion coefficient than carbon dioxide, so carbon dioxide can move through easier with higher diffusion coefficient)
• if there are issues then if could lower the determinants hindering movement
• these factors are not much of a barrier if they are functioning normally

Question 4

Ventilation/Perfusion Matching

Answer 4

ventilation: air flow into alveoli
perfusion: blood flow into pulmonary capillaries
how well do they match?
- ventilation-perfusion inequality or mismatch in an area; try to compensate
- sources of inequality/mismatch - damage, blockage (cold, asthma)
- when they match well, the exchange can happen easily
- problem with airflow (decrease) - decreased airflow to some region of the lungs - not going to get good exchange - pulmonary blood gets less oxygen causing vasoconstriction of pulmonary vessels leading to decreased blood flow (less blood flow and less oxygen coming in)
- decrease blood flow to region of lung can decrease CO2 in alveoli causing bronchoconstriction decreasing airflow
- decreased air flow leads to decreased blood flow (vice versa)
- diverting away from problem and sending it to other areas where exchange could be much easier

Question 5

Gas exchange - Internal (oxygen and carbon dioxide)

Answer 5

oxygen
- tissue cells - < 40 mmHg/ arterial blood - 100 mmHg
- pressure gradient: movement capillaries to tissue cells so oxygen enter tissues cells
- blood entered capillaries oxygenated (100 mmHg) and comes out of deoxygenated (40 mmHg)

carbon dioxide
- tissue cells - > 46 mmHg / arterial blood - 40 mmHg
- pressure gradient: movement tissue cells to capillaries so CO2 enters capillaries
- blood entered capillaries (40 mmHg) and comes out (46 mmHg)

• systemic circulation takes deoxygenated blood (O2 40 mmHg / CO2 46 mmHg) back to heart to be pumped out into pulmonary circulation

Question 6

movement across tissue capillary - interstitial fluid - tissue cell membrane regulated by:

Answer 6

• partial pressure gradient of gas
• surface area of diffusion
• thickness of membrane gas is diffusing through
• diffusion coefficient of gas (amount that can cross an area in 1 second)
• same as for external respiration just in a different location

Question 7

Arteriovenous Oxygen Difference in Muscle

Answer 7

arteriovenous oxygen difference (a-v O2 diff)
- difference between oxygen going into capillary bed and oxygen coming out of capillary bed
- difference is amount delivered to tissues

rest: a-v O2 diff 4 – 5 mL oxygen per 100 mL blood
- capillary bed partially open (metarteriole and some precapillary sphincters relaxed)
- some oxygen leaves capillaries to supply resting muscle / large amount still in venous blood (small a-v O2 diff)

exercise: a-v O2 diff 15 mL oxygen per 100 mL blood
- more capillary bed open (more precapillary sphincters relaxed) so more surface area for gas exchange
- more oxygen leaves capillaries to supply now active muscle / less in venous blood (larger a-v O2 diff)

• a-v O2 diff: trainable