Lung Structure

Question 1

Ventilation

Answer 1

• the flow of air into and out of the lungs
• V(with a dot) = f x TV
• frequency of breathing (breaths/min) = 15 breaths/min
• TV= tidal volume (liter/breath) = 0.5 L/breath
• ventilation usually 7.5 L/min

Question 2

Spirometer measures ventilation

Answer 2

• by collecting expired gas for 1 min or by adding the tidal volumes for 1 min
• typical ventilation is 0.5 L/breath x 15 breaths/min = 7.5 L/min
• during exercise ventilation can rise over 15X to as much as 120 L/min
• as air is inhaled and exhaled into and out of a spirometer, a floating inverted drum moves up and down and an attached pen records the movements on a chart
• from the calibration factor for the apparatus (ml/mm), volumes are measured
• the slope of recording of volume vs. time gives the flow (ml/min)

Question 3

Gas Volume Conventions

Answer 3

• ATPS (ambient temp, pressure, saturation): 25C, 760 mm Hg, 24 mm Hg
• BTPS (body temp, pressure, saturation): 37C, 760 mm Hg, 47 mm Hg
• STPD (standard temp, pressure, dry): 0C, 760 mm Hg, 0 mm Hg)
• convert ATPS to STPD for O2 consumption and CO2 production rates
• convert from ATPS to BTPS for lung volumes

Question 4

Ideal gas law

Answer 4

• PV= nRT (n is moles, R is gas constant 0.083)
• for dry gas its PV/T = nR = constant
• V (BTPS, 37C (lung)) = 1.07V (ATPS, 25C, spirometer)

Question 5

Water vapor pressure

Answer 5

• a function of pressure and is constant at a given temp

- water vapor pressure at body temp of 37C is 47 mm Hg

Question 6

Branches of the lung

Answer 6

• conductive zone: first 16 branches including the trachea, bronchi, bronchioles, and terminal bronchioles
• respiratory zone: last 7 branches includes respiratory bronchioles, alveolar ducts, and alveolar sacs
• 23 branches lead to 300 million alveoli all 250 microns in diameter and is covered with about 1000 pulmonary capillaries

Question 7

Conducting zone

Answer 7

• anatomic dead space (about 150 ml, or 1 ml per lb body weight)
• pseudostratified cilated surface propels mucous secreted by goblet cells
• no exchange of gas with blood in conducting zone
• do not contain pulmonary capillaries
• trachea has cartilaginous rings for structure

Question 8

Respiratory Zone

Answer 8

• Gas (O2 and CO2): exchanges with blood
• type I alveolar epithelial cells: line alveoli
• type II: surfactant, a lipo-protein containing DPPC (dipalmitoylphosphatidylcholine)
• pulmonary macrophages engulf foreign material that was missed by the muco-cilary transport system and leave the lung via the lymphatics or though blood vessels

Question 9

Surfactant

Answer 9

• coats alveoli
• lowers their surface tension making it easier to inhale
• increases mechanical stability of the lung

Question 10

Alveolar cross sectional area

Answer 10

• trachea 2 square cm
• terminal bronchioles area 80
• resp bronchioles 280 cm
• alveolar ducts and sacs 7 x 10^5= 70 square meters
• large increase in surface area so that velocity slows so that diffusion rather than bulk flow carries the gas for the last few microns of distance in the alveoli
• large surface area permits equilibrium of alveolar gas with the blood
• blood gas barrier is extremely thin; average distance is 1.5 micron
• oxygen crosses the surfactant coated alveolar epithelium, the alveolar interstitial space, the capillary endothelium, the plasma, the red blood cell membrane, and finally combines with hemoglobin
• equilibrium when partial pressure O2 is the same in alveolar gas and in pulmonary capillary blood

Question 11

Composition of air

Answer 11

• dry gas fraction F1= ni/nt (number of moles of ith gas/ number moles gas in sample)
• N2= 0.78
• O2= .21
• CO2= 0.0003
• Argon = 0.01

Question 12

Partial Pressure

Answer 12

• dissolved gas does not contrubute to blood pressure
• the sum of all partial pressures of gases in the mixture equals the total gas pressure
• Pi= niRT/V
• dry gas fraction: Fi= ni/nt= Pi/Pt
• partial pressure: Pi= (ni/nt)Pt= FiPt

Question 13

Solubility

Answer 13

• henrys law: [cg]= alpha x Pi
• dissolved gases don’t contribute to blood volume or blood pressure
• partial pressure of a gas in solution equals the partial pressure of the gas with which the solution has equilibrated
• partial pressure of a gas in solution refers only to the dissolved gas

Question 14

Respiratory quotient

Answer 14

-the ratio of tissue metabolic production of Co2 and consumption of O2
-depends on the metabolic substrate being oxidized, ranging for 0.7 for pure fat to 1.0 for carbs
, 0.85 for normal diet