gas exchange- cole and karius Flashcards
Purpose of the cilia
Move mucus and particles towards pharynx
Common airway diseases are characterized by ___ or ___
Excessive mucus
Deficient clearance of particles trapped in mucus
3 cell types that make airway mucus
Goblet cells
Clara cells of terminal bronchiles
Serous cells of submucosal glands
3 main contents of airway mucus
Mucins (MUC5AC, 5B)
Antimicrobial molecules (Ig, lysozyme, etc.)
Immunomodulatory molecules (cytokines, etc.)
Normal mucus is _% solids (non-water)
3%
Which 2 cell types rest on the basal membrane of airways but do NOT reach the lumen?
Which of these can often be cancerous? Name of condition?
Basal cells
Neuroendocrine cells
NE cells - bronchial carcinoid tumors
Describe smoker’s respiratory epithelium
Increased what?
Decreased what?
Change to stratified squamous (less ciliated columnar) for better protection
Increased goblet cells but decreased movement of mucus
Smoker’s melanosis
Benign pigmentations of oral mucosa (black-ish) in mouth
So, typical “respiratory epithelium” consists of what?
Ciliated pseudostratified columnar epithelium w/ goblet cells
How many C-shaped rings of ___ are in the trachea?
Hyaline cartilage
15-20
Where is the trachealis muscle?
Purpose?
In the trachea, between the lumen and the esophagus
Smooth muscle that narrows during cough reflex, thus air velocity increases
What is the fibroelastic ligament?
Near the trachealis muscle
Collagen and elastic fibers that prevent over-distention of lumen
As bronchi divide, what happens to the hyaline cartilage rings?
Become intermittent cartilage plates dispersed behind the mucosa and smooth muscle bundles
What is BALT?
Seen where?
Bronchial-associated lymphoid tissue
Aggregates of lymphoid tissue in the wall of intrapulmonary bronchi
From inside to outside, list these (respiratory wall)?
Mucosa, cilia, adventitia, sub-mucosa
Cilia, mucosa, sub-mucosa, adventitia
Put these in order from inside to outside (respiratory mucosa):
Basement membrane
Elastic fibers
Respiratory epithelium
Epithelium
BM
Elastic fibers
What layer are the cartilage rings/plates in?
Inner part of adventitia (outermost layer)
Primary vs. secondary (lobar) bronchi wall
Primary - cartilage rings
Secondary - cartilage plates (islands)
Respiratory epithelium in terminal bronchioles
No goblet cells, simple ciliated columnar
Goblet cells replaced by clara cells
Asthma - responses to trigger? (2)
Bronchoconstriction of smooth muscle bundles around bronchiolar lumen
Mucus hypersecretion by goblet cells
What is a pulmonary lobule?
Terminal bronchiole and the associated tissue region it supplies
What is a pulmonary acinus?
Respiratory bronchiole and its associated alveoli and alveolar ducts
What is alveolar bronchiolization?
Clara cells proliferate and migrate to replenish alveolar epithelial cells following airway injury
Cystic fibrosis
Abnormally thick mucus by respiratory/GI glands due to defective Cl- transport out and increased Na+ absorption (H2O follows)
Airflow through the conducting airway is affected by ___, which is affected by ___
Resistance
Radius
Equation for resistance of an airway
So how is airflow controlled?
R = 8(visc.)L / r4
Changing radius via smooth muscle contraction, thus changing resistance to FOURTH POWER
Why would we want to change the airway resistance?
Send air to the alveoli that have good blood supply
How to calculate approximate amount of anatomical dead space in any person?
Weight in pounds = dead space in mL’s
150 lbs = 150 mL dead space
2 types of dead space (w/ definitions)
Anatomical - conducting tubes
Alveolar - alveoli w/o gas exchange b/c no blood flow or ventilation
Physiologic dead space
Anatomic + alveolar
Alveolar ventilation definition
If per minute, called what?
Average adult value?
Volume of air reaching the alveoli
VA (dot)
4 L/min
How to calculate alveolar ventilation (per minute)?
Units?
(Tidal volume - dead space) x respiratory rate
mL air / min
Perfusion definition
Average value?
Blood pumped passed alveoli per minute
5 L/min
How to calculate perfusion (Q)?
= cardiac output = SV x HR
Variables that affect diffusion rate (mL/min) of any gas between alveoli and capillaries
Surface area
Diffusion coefficient for the gas
Pressure different across the alveolar membrane
Diffusion distance (alveolar barrier thickness)
Equation for diffusion rate (J) of a given gas
J = (SA x D x (P1 - P2)) / distance
D = coefficient SA = surface area
Normal diffusion rate values (J) for O2 and CO2
O2 - 250 ml/min
CO2 - 200 ml/min
What does it mean that the diffusion rates of O2 and CO2 are different?
They are INDEPENDENT of one another
Which variables for diffusion rate (J) depend on alveolar structure?
SA and distance (barrier thickness)
Typical diameter of an alveolar wall
0.2 mm
Components of the interalveolar septum
2 simple squamous layers w/ an interstitium (capillaries, elastic tissue) in between
2 types of alveolar epithelial cells (w/ percentages of cells vs. surface area)
Location of type 2 cells?
Type 1 - 40% of cells, 90% of surface
Type 2 - 60% of cells, 10% of surface (angles of adjacent alveolar septa)
Function of type 2 alveolar cells
Produce surfactant
Explain acute respiratory distress syndrome steps (6)
- Low/no alveolar surfactant
- Alveolar surface tension increases
- Hypoventilation causes low oxygen, so surfactant production further reduced
- Pulmonary hypoperfusion of gases
- Endothelial cell damage
- Fibrin and other proteins form hyaline membrane, which leads to CO2 retention
Alveolar macrophages
Other name?
Macrophages in alveolar surface that remove debris that escaped the mucus and cilia of conducting system
Dust cells
What are alveolar macrophages called in CHF?
Why?
Heart failure cells
Left ventricle can’t keep up w/ venous return from lungs, so lungs back up, so RBCs pass into alveoli and are phagocytosed
What is surface area in the diffusion rate equation related to?
Number of alveoli in lungs and open pulmonary capillaries
Emphysema
Destruction of elastic tissue in alveoli/respiratory bronchioles leads to enlarged alveoli, decreased fresh gas exchange
How is the elastic tissue destroyed in emphysema?
What normally prevents this?
Elastase (released by neutrophils) breaks it down
Serum alpha-1-antitrypsin neutralizes elastase
What would deficient alpha-1-antitrypsin cause?
Emphysema, since elastase from neutrophils can’t be neutrolized, so elastic tissue of alveoli is destroyed
What is the blood-air barrier?
3 contents?
The shortest diffusion path oxygen can cross to reach the blood
- Cytoplasm of squamous epithelial cells
- Fused basal lamina of type 1 alveolar and capillary epithelial cells
- Cytoplasm of capillary endothelial cells
Which part of the diffusion rate (J) equation is affected by the blood-air barrier?
Distance (denominator)
What happens to that distance in ARDS?
The damage to the alveolar epithelial lining due to hypoperfusion (lack of oxygen causes this) results in increased hydrostatic pressure of capillaries, thus fluid accumulates in the lungs, so the lungs stiffen and hypoxemia can occur
What does the diffusion coefficient for a given gas depend on?
Is that of O2 or CO2 higher? Why?
Solubility of the gas in water (more is better)
Molecular weight of the gas (less is better)
CO2 is 20x higher, because its severely higher solubility in water far outweighs its heavier molecular weight
Which has a larger pressure gradient in the lungs: O2 or CO2?
Oxygen
How long does an RBC spend in a pulmonary capillary?
How long does O2 need to reach equilibrium across the barrier?
How does this change in exercise?
- 75 sec
- 25 sec
During exercise, an RBC spends only 0.25 sec, so there is much less extra time for gas exchange
What is the clinical significance of the time an RBC spends in a pulmonary capillary during exercise compared to rest?
No free time, so person w/ respiratory problems will notice the problem upon exertion
Normal diffusion capacity of the lung for oxygen (DLO2)
21 ml O2/min/mm Hg
mm Hg = average gradient along capillary
Is the diffusion capacity of O2 greater or less than that of CO2?
Value of CO2? Why so?
MUCH less
CO2 = 400 (compared to 21)
Equilibrium is almost immediate (small gradient AND passes much faster through b/c of solubility in H20)
Clinical significance of the difference in diffusion capacity between O2 and CO2
CO2 is much higher, so it would take a MUCH worse lung disease to have problems w/ CO2 retention
Why is alveolar surfactant (type 2 cells) so important?
Alveoli are different sizes, so the pressure in them will be different based on radius
W/o surfactant, air would flow from high to low pressure (small to large alveoli), so small alveoli would get smaller and vice versa, which would reduce surface area
Equation for pressure in an alveolus
Name of it?
P = 2T/r
T = tension r = radius
LaPlace’s Law
Use LaPlace’s Law to describe why alveolar surfactant is important?
Combats the smaller radius of smaller alveoli by decreasing surface tension, so pressure remains the same as that w/in larger alveoli
SO, would you expect to see more surfactant produced in a large or small alveolus? Why?
Small - to reduce surface tension to combat the smaller radius (keep pressure constant to prevent alveolar collapse and thus decreased surface area)
Components of the conducting part of the respiratory system
Nasal cavity Nasopharynx Larynx Trachea Bronchi Bronchioles
The respiratory portion of the nasal cavity is lined by what epithelium?
Pseudostratified columnar ciliated epithelium (Respiratory epithelium)
What else is within the respiratory epithelium? (4)
Goblet cells, lamina propria, seromucous glands, superficial venous plexus
What happens to air in the nasal cavity?
Warmed by blood in venous plexus
Moistened by secretions of seromucous glands/goblet cells
How is all air rubbed up against the epithelium for warming and moistening?
Conchae create turbulence to help move the air around
Paranasal sinuses are lined by what epithelium?
Pseudostratified columnar ciliated, few goblet cells
What is the lamina propria of the respiratory wall made of? (5)
CT, seromucous glands, elastic fibers, bone/cartilage, smooth muscle
Where along the respiratory tract does the epithelial cell population taper off?
Terminal bronchioles
