Pulm Flashcards
Collapsing pressure
Collapsing pressure = 2 * surface tension / radius
Alveoli have increased tendency to collapse on expiration as radius decreases (Law of Laplace)
Surfactant
Secreted by type II pneumocytes
Complex mix of lecithins, lecithin to spinhingomyelin ratio greater than 2 indicates fetal lung maturity
Club (clara) cells
Nonciliated, low-columnar/cuboidal with secretory granules
Secretes component of surfactant, degrade toxins, and act as reserve cells
Respiratory tree
Large airway warms, humidifies, and filters air, ends at bronchi
Cartilage and goblet cells extend to end of bronchi
Pseudostratified ciliated columnar cells extend to beginning of bronchioles, then transition to cuboidal cells
Airway smooth muscles extend to end of terminal bronchioles
Simple squamous cells from end of terminal bronchioles all the way to alveoli
Methemoglobin
Oxidized form of Hb (Fe3+) that does not bind O2 as readily, but has increased affinity for cyanide
Nitrates cause poisoning by oxidizing Fe
Methemoglobinemia may present w/ cyanosis and chocolate-colored blood
Methemoglobinemia can be treated w/ methylene blue
- To treat cyanide poisoning:
1. Use nitrate to created methemoglobin, which binds nitrate
2. Add thiosulfate to bind cyanide and excrete cyanide renally
Carboxyhemoglobin
Form of Hb bound to CO in place of O2
CO has 200x greater affinity than O2 for Hb
Cause decrease in oxygen binding capacity leading to decreased O2 delivery and unloading in tissue
Oxygen-hemoglobin dissociation curve
Sigmoidal shape due to positive cooperativity of Hb (increased O2 binding leads to greater affinity for O2)
Myoglobin is monomeric and thus does not show cooperativity
When curve shifts to right (H+, CO2, altitude, temperature), decreased O2 binding affinity leading to greater O2 unloading into tissue
Fetal Hb has higher binding affinity for O2 and thus curve shift to left
V/Q mismatch
Apex of lung: V/Q = 3 (wasted ventilation)
Base of lung: V/Q = 0.6 (wasted perfusion)
Ventilation and perfusion are both greater at the base of the lung, but increase in perfusion is much greater than increase in ventilation at bottom of lung
With exercise, vasodilation of apical capillaries, resulting in V/Q that approaches 1
V/Q = 0, airway obstruction (shunt), does not improve w/ 100% O2 V/Q = infinity, blood flow obstruction (physiologic dead space), improves w/ 100% O2 as additional capillaries/alveoli can open up to compensate for obstructed blood flow assuming dead space < 100%
Haldane effect
In lung, oxygenation of Hb promotes dissociated of H+ from Hb, shifting equilibrium toward CO2 production and release by combining w/ existing HCO3
(H+ + HCO3 –> H2CO3 –> H20 + CO2)
Increased oxygenation also shifts dissociation curve to the left, leading to release of CO2 from RBC
Haladane (hoard oxygen)
Bohr effect
In peripheral tissue, increased CO2 from tissue metabolism shifts equilibrium to production of HCO3 and H+ (CO2+H2O –> H2CO3 –> H+ + HCO3
H+ binds to Hb, leading to a rightward shift of dissociation curve, and increased O2 release into tissue
CO2 transport
3 forms:
HCO3: 90%
Carbaminohemoglobin: 5% HbCO2
Dissolved in plasma: 5%
Response to high altitude
Decreased atm O2 leading to decreased PaO2 –> increased ventilation –> decreased PaCO2
Decreased PaO2 –> increased erythropoietin –> increased hematocrit and Hb
Decreased PaO2 –> increased 2,3BPG –> increased O2 release in tissue
Decreased PaO2 –> increased renal excretion of HCO3 to compensate for decreased PaCO2 (respiratory alkalosis)
Response to exercise
No change in PaO2 and PaCO2
Increased CO2 production and O2 consumption
Increased ventilation to meet O2 demand, apex/bottom V/Q becomes more uniform
Increased pulmonary blood flow due to increased cardiac output
Increase in venous CO2 content and decrease in venous O2 content
Asbestosis
Associated w/ shipbuilding, roofing, and plumbing
“Ivory white” calcified pleural plaques
Affects lower lobes
Increased incidence of bronchogenic carcinoma and mesothelioma
Silicosis
Associated w/ foundries, sandblasting, and mines
Macrophages respond to silica and release fibrogenic factors, leading to fibrosis
Affect upper lobes
Silica may disrupt phagolysosomes and impair macrophages, increasing susceptibility to TB
Increased incidence of bronchogenic carcinoma
