Resp Physiology - West

Question 1

How do oxygen/CO2 move between air and blood?

Answer 1

Simple Diffusion

Question 2

Fick’s law of diffusion

Answer 2

Amount of gas that moves across a sheet of tissue = proportional to the area of a sheet, inversely proportional to its thickness

Question 3

Conducting Airways

Answer 3

Trachea –> left, right main bronchi –> lobar bronchi –> segmental bronchi –> segmental bronchioles (smallest airways without alveoli)
As the airways progress distally, proportion of cartilage decreases - smooth muscle increases

Question 4

Anatomic Dead Space

Answer 4

Conducting airways = trachea, main bronchi, lobar/segmental bronchi, segmental bronchioles
Lungs that receive ventilation but no blood flow
Vol = 150mL

Question 5

Respiratory Zone

Answer 5

Respiratory bronchioles - contain occasional alveoli

Alveolar ducts - completely lined with alveoli

Question 6

Acinus

Answer 6

Portion of the lung distal to a terminal bronchiole that forms an anatomical unit

Question 7

During inspiration…

Answer 7

• Vol of the thoracic cavity increases
• Air drawn into the lung
• Increase in vol brought about partly by contraction of the diaphragm –> causes it to descend, partially by action of the intercostal muscles –> raise the ribs and increase cross sectional area of the thx

Question 8

Pressure required to move gas through airways

Answer 8

Normal inspiration: air flow rate of 1L/sec requires a pressure drop of <2cm H20

Question 9

Diameter of capillary segment

Answer 9

7-10um - just large enough for an RBC

Lengths of the segments so short that dense network forms an almost continuous sheet of blood in the alveolar wall

Question 10

Consequences of extreme thinness of blood gas barrier (BGB)

Answer 10

Capillaries = easily damaged –> ex increasing pressure in the capillaries to high levels, inflating the lung to high volumes
Can leak plasma/RBCs into the alveolar spaces

Question 11

Blood-Gas Interface

Answer 11

Extremely thin (0.2-0.3um)
Enormous surface area of 50-100m^2
Large area obtained by having approx 500 million alveoli
So thin that large increases in capillary pressure damage barrier

Question 12

Blood Vessels

Answer 12

Whole output of right heart goes to the lung
Diameter of capillaries = 7-10um
Thickness of much of the capillary walls <0.3um
Blood spends approx 0.75s in the capillaries –> traverses 2-3 alveoli, sufficient for virtually complete equilibration of oxygen and CO2 btw alveolar gas and cap blood

Question 13

Resistance of pulmon circuit

Answer 13

Extremely small

Mean pulmonary arterial pressure of only 20cm H20 (15mm Hg) required for flow of 6L/min

Question 14

Stability of the alveoli

Answer 14

Structure of lung = inherently unstable
Surface tension of liquid lining the alveoli, relatively large forces develop that tend to collapse alveoli
Surfactant –> dramatically lowers

Question 15

Functional residual capacity (FRC)

Answer 15

Vol of gas in lung after normal expiration

Question 16

Boyle’s Law

Answer 16

At constant temperature, pressure x volume = constant

Question 17

How to calculate PO2 given a barometric pressure

Answer 17

PO2 = 0.21 x barometric pressure
If in the airways: PO2 = 0.21 (BP-PH20 vapor)
–> PO2 = 0.21 (BP-47)

Question 18

Minute Ventilation

Answer 18

AKA total ventilation
TV x RR
Total vol of air leaving lung per minute
Vol of air entering the lung very slightly greater bc more oxygen is taken in than CO2 is given out

Question 19

Alveolar Ventilation

Answer 19

Amount of fresh inspired air available for gas exchange
Vol of fresh gas entering respiratory zone per minute: (TV-anatomic dead space vol) x RR
Even though smaller amount of vol enters alveoli with each breath, alveolar vol still expands by full size of the TV as the dead space vol left over at the end of the previous exhalation is drawn into the alveoli with each breath before the fresh gas enters

Question 20

Why is increasing Tv often more effective at increasing alveolar ventilation?

Answer 20

Reduces the fraction of each breath occupied by the dead space ie the dead space fraction