Intro to Pulmonary Flashcards
Structure of the lungs
Right: 3 lobes
Left: 2 lobes
Both have 10 segments, and middle right lobe has corresponding 4+5 segment on left upper lobe
Pores of Kohn
Fenestrations between alveoli
Channels of Lambert
Connection between small bronchioles and alveoli
Channels of Martin
Between bronchioles
How do alveoli form during development?
Septation
Complete by age 8, then grow
Retinoic acid can induce septation, but not much use in older people with emphysema because septation finished
What is the resistance in the pulmonary blood vessels?
Very low resistance in pulmonary blood vessels (1/6 of aorta) in order to get lower pressure in lungs (the lungs can’t stand the high pressure that the body can!)
Also can lower resistance by recruiting more capillaries and putting them in parallel during exercise
P = RQ
Alveolar-capillary membrane
Air of alveoli –> alveoli epithelium –> basement membranes of alveoli and capillary are FUSED! –> capillary endothelium –> lumen of capillary
(Normally, when you’re not at alveolar-capillary membrane, have two separate basement membranes with space in between)
Type I alveolar epithelial cells
Squamous
Broad, flat, 0.1um thick
93% of alveolar lining membrane
Cannot divide
Type II alveolar epithelial cells
Cuboidal
Have microvilli
Located at septal junctions
Secrete surfactant
Can transform into Type 1 cells (responsible for growth and repair)
Type III alveolar brush cells
Cone shaped cells
Dense microvilli
Rare, found in central part of acinus
Unknown function, maybe chemoreceptor
Alveolar macrophages
Arrive via blood as monocytes
Lie within alveolar lining fluid
Have destructive enzymes to combat infection and scavenge foreign bodies (dust)
Function is impaired by tobacco smoke
Clara cells
Non-ciliated
Reside in bronchioles
Contribute to surfactant production
Contain CYP 450 isoenzymes
Mast cells
Located in sub-pleural area
Secrete heparin, histamine, other mediators
Interstitial cells
Fibroblasts (produce collagen and elastin), myocytes, dendritic cells, neurons (in walls of airways)
Non-respiratory functions of the respiratory system
Filtration of particles
Filtration and dissolution of thrombi (microemboli)
Anti-protease
Hormonal (angiotensin I to angiotensin II)
Lipid metabolism (make surfactant)
Acid/base regulation
Immunological protection
Phonation (talking)
Neurotransmitter removal, paracrine removal, histamine release, antioxidase production
Airway zones and generations
Conduction, transitional, respiratory zones
Trachea
Main (primary) bronchi (R and L)
Lobar (secondary) bronchi
Segmental (tertiary) bronchi
Bronchioles
Terminal bronchioles
Respiratory bronchioles (alveoli bud off)
Alveolar ducts
Alveolar sacs
What happens when you get to generation 16 (end of conducting zone?
Bulk flow drives air until generation 16, then cross-sectional area gets huge and diffusion is now mechanism of ventilation
Function of conducting zone
Humidify, warm, clean, conduct air to respiratory zone
Cilia (until 12th generation) beat to propel mucous viscous layer that captured dust upward –> irritant reflexes in upper airway trigger cough
Which chemoreceptors are used by the lungs?
Peripheral chemoreceptors in carotid body (NOT aortic arch)
Glossopharyngeal nerve (CN IX) is nerve from carotid bodies, and goes to brainstem
At similar level as CN IX comes into brain, have central chemoreceptors
Sense blood draining lungs
What causes negative intrapleural pressure?
Opposing elastic recoil properties of lung and chest wall
Lung wants to collapse and chest wall wants to expand
Note: at 55% VC, chest wall at equilibruim, so past this, chest wall actually wants to collapse too
Functional residual capacity (FRC)
Lung volume at rest/equilibrium when recoil forces of lung and chest wall are equal and opposite
FRC increases if lungs decrease recoil
FRC decreases if lungs increase recoil
Inspiration
1) Respiratory muscle force expands ribcage
2) Pleural space is virtual, so lung expands
3) Lungs increase elastic recoil
4) Pleural pressure becomes more negative
5) Volume increases so alveolar pressure falls
6) Air flows into lung
Expiration
PASSIVE PROCESS
1) Respiratory muscles relax
2) Lung elastic recoil pulls ribcage inward
3) Pleural pressure becomes less negative
4) Volume decreases so alveolar pressure rises
5) Air flows out of lung
Compliance vs. Elastance
Compliance: distensibility; how accommodating; change in voulme per unit distending pressure; V/P
Elastance: stiffness; P/V
Opposites!!
Surfactant
Reduces surface tension in alveoli by breaking up the attractive forces of water lining alveoli
Lipoprotein material (dipalmitoyl phosphatidylcholine; dipalmitol lecithin)
Synthesized in Type II alveolar cells
Advantages of surfactant
1) Reduces surface tension/lung recoil and increases compliance
2) Counters tendency for smaller alveoli to empy into larger ones
3) Prevents trasudation of fluid into alveoli from pulmonary capillaries
Lung compliance
Lungs are not compliant at first because have to get past point where you’ve broken up intermolecular forces and they’re strongest when alveoli are small and molecules are densely packed
Low compliance on the curve is where surface area is increasing faster than surfactant can be added to liquid layer so hard to break up forces.
After enough surfactant added, lung is more compliant the rest of the way up
What does gravity do to regional ventilation?
Top/apex of lung: pleural pressure LESS, -5; alveoli larger so don’t expand as much because don’t have as far to go
Bottom/base of lung: pleural pressure MORE, -1; alveoli smaller expand more (on steep part of compliance curve too)
More ventilation goes to bottom of the lung
