Chp. 1: Structure & Function Flashcards
Fick’s Law of Diffusion
Amount of gas that moves across a sheet of tissue is proportional to the area of the sheet but inversely proportional to its thickness
Area of blood-gas barrier
50-100m^2
Conducting airways
Trachea
Right and left main bronchi
Lobar bronchi
Segmental bronchi
Terminal bronchioles
Function of conducting airways
Lead inspired air to gas-exchanging regions of the lung
Airway lining, structure
Larger, proximal airways: Ciliated, columnar epithelium with lots of cartilage in walls
Distally, cartilage decreases and smooth muscle increases
What constitutes the “anatomic dead space”?
The conducting airways
Volume of anatomic dead space
~150mL
Respiratory zone
Respiratory bronchioles
Alveolar ducts
Alveolar sacs
Acinus
Portion of lung distal to a terminal bronchiole
What zone makes up most of the lung?
Respiratory (2.5-3L)
How does air move through the respiratory system?
Flows by bulk flow to terminal bronchioles (down pressure gradient in conducting zone)
Beyond there, combined cross-sectional area of airways is so enormous because of the large number of branches that forward velocity of gas becomes small. Diffusion then takes over.
Why does inhaled dust settle in the terminal bronchioles?
Because velocity of gas falls rapidly in this region
Bronchovascular bundle
Arteries and bronchi trace together down the centers of the lobules
Diameter of pulmonary capillary segment
7-10um
How thin is the blood-gas interface?
Extremely–0.2-0.3um over much of its area
Surface area of blood-gas interface
50-100m^2
How is the large area of the blood-gas interface obtained?
500 million alveoli
Risk of think blood-gas barrier
So thin that large increases in capillary pressure can damage the barrier
How long does the RBC spend in the capillary network of the lung?
0.75s
What circulation provides blood to the conducting airways?
Bronchial circulation
What is the purpose of surfactant?
Dramatically lowers surface tension
How are particles removed from the alveoli?
No cilia, so particles deposited there are engulfed by large wandering cells (macrophages)
Role of lungs in removal of blood material
The branching network of small blood vessels traps small pieces of infected material or blood clots that form in or enter the venous circulation
KEY CONCEPTS of lung structure and function
1) Blood-gas barrier extremely thin with large area, making it ideal for gas exchange by passive diffusion
2) Conducting airways extend to terminal bronchioles with volume of 150mL. Gas exchange occurs in respiratory zone with volume of 2.5-3L
3) Convective flow take inspired gas to terminal bronchioles; beyond, gas moves increasingly by diffusion in the alveolar region
4) Pulmonary capillaries occupy huge area of alveolar wall and RBC spends 0.75s in the capillary
5) Surfactant maintains stability of alveoli. Cilia eliminate foreign material from airways. Smallest pulmonary IVs trap foreign material in blood.
