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14 Cards in this Set

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Explain Fick's Law of Diffusion.
F=P/A - Amount of gas that flows across a sheet of tissue is proportional to the area of the sheet, and inversely proportional to its thickness. So
A/T x D
D=solubility of gas/square root of MW
(ie for asthmatics u can add helium to decrease the density which decreases the turbulence, making it more laminar flow, which in turn increases velocity.
Also, any disease that increases the thickness (pulm edema, interstitial fibrosis) because hypoxia b/c fick's principle gas exhange cannot happen!
So you want a large surface area that's very thin. Capillaries are wrapped around alveoli.There are 300 million alveoli with a surface area of 85 square meters!
AIRFLOW - air is sucked in by the negative area created by the muscles of the chest wall. (-P = 2 cms H2O to generate a flow rate of 1 L/sec)
Inspiration - diaphram contracts and descends, intercostal muscles raise the ribs and spread them apart. This creates the - P.
When the air hits the alveoulus the cross sectional area increases dramatically, and since flow is inversely related to area... the flow drops to the point that the air is virtually at a standstill in the alveolus.
What is the conducting zone and the respiratory zone?
As we go down the bronchi the A increases, while the F decreases, and the P stays the same.
-Conducting Zone: smallest a/w's w/o alveoli. They constitute the anatomical dead space, with a volume of about 150 mls.
Trachea - 0
Bronchi - 1-4
Bronchioles - 5-16 (7th G = area of maximum resistance)
Terminal Bronchioles - @ 16
-Respiratory Zone: resp bronchioles have occasional alveoi budding from the walls, and alveolar ducts which are completely lined w/ alveoli.
Resp Bronchioles - 17-19
Alveolar Ducts - 20-22
Alveolar Sacs - 23
How does pulmonary circulation work?
The pulmonary circulation is a low resistance circuit, b/c the walls of pulm artery and its branches are extremely thin, and contain relatively little smooth muscle. P=FxR b/c R is low a MPAP of only 20 cm H2O (15 mmHg) is needed for a flow of 6 L/min, which is the CO for RV.
***R is low in the pulm capill and F of air is slow.
Thus each RBC only spends 3/4 sec in capillary network, traversing only 2 or 3 alveoli, but it's enough!
Bronchial Circulation supplies the conducting system, but this blood cannot get oxygenated. This accounts for the pumonary venous O2 saturation being less then 100%.
What are the factors affecting the caliber of pulmonary vessels?
1. Pressures around them: As lungs expand, ^V so decreased P, larger vessels are pulled open by the traction of expanding lung parenchyma
2. At higher lung volumes the alveolar pressure compresses the capillaries.
3. Recruitment - pulm vascular R may decrease by an increase in BF. Opening capillaries that are normally closed.
4. The Critical Opening Pressure - if the lung is collapsed... pulm a. P must be raised to several cms above downstream P to cause F.
5. Pulm Vascular R increases w/ alveolar hypoxia, due to cx of small pulm a.'s.
6. Nitric Oxide - potent selective pulmonary vasodilator. (Used in newborns with persistant pulm HTN)
What happens at different lung volumes?
Low Lung Volumes - Alveolar vessels are larger, making R lower at LLVs. But since extra-alveolar vessels are smaller, R is greater b/c there's nothing to pull them open.
High Lung Volumes - has the opposite effect. The high alveolar air P causes alveolar vessels to get squashed. But due to traction the small extra-alveolar vessels are pulled open creating a decreased R.
What is the function of surfactant?
The lung is a collection of 300 million bubbles whose surface tension tends to reduce their surface area - making them predisposed to collapse. This inherent instability is countered by surfactant, a phospholipid produced by type 2 pneumocytes, which lines the alveoli. Neonates can be administered surfactant (surfactant is not produced by the body until 4-7 months)
What are some of the ways the lungs are protected from direct exposure to the outside environment?
1. The nose has cilia which filter large particles, causing a sneeze.
2. The cough and gag reflex prevent us from inhaling or aspirating secretions or foreign substances.
3. The ciliated columnar epithelium of the bronchial tree has mucous glands and goblet cells that secrete mucous. The cilia beat to propel this mucous towards the oral cavity, like an escalator, carrying debris from the lower a/w's to the trachea to be coughed up or swallowed.
What are some other functions of the lungs besides for CO2 and O2 gas exchange?
1. Acts as a filter: filters small clots before they get reach the brain or heart.
2. Metabolism of vasoactive substances - Peptides such as Angio I are converted to Angio II by ACE which is located in small pits on the capillary endothelial cells.
3. ACE also inactivates bradykinin
4. Metabolism of bronchoactive substances - such as leukotrienes, which are breakdown products of archidonic acid and play a role in asthma.
5. The lung produces immunoglobulins, particularly IgA in bronchial mucous which helps fight infection.
6. The lung contains mast cells that produce heparin.
**How does the compliance curve work?**
V on the y-axis, P on the x-axis. Normally it looks like a stretch out S. But if there is lung thickening (^pulm venous P, pulm fibrosis, alveolar edema) then the S is lower and to the Right. So it takes more P to get V. But if there is a thin lung (aging, emphysema) the S curve shifts to the Left. Meaningt takes less P to gain V!
In the case of diving there is an increase in pressure to work against (reynold's # goes up) so you mix lower density gases to get less turbulence.
It's also important to remember that lung vessels constrict with hypoxia!
What is Boyle's Law? What are the muscles used in inspiration? (related topics)
Inspiration is an active, involuntary process during quiet breathing.
Boyles Law - states that V is inversely proportional to P at a constant temp. So since V increases around decreased P, Bulk Flow occurs from high P to low P.
The 2 muscles effecting inspiration together cause a decrease in pressure in the thoracic cage, causing air to rush into the lung by bulk flow.
1. The diaphragm - which moves into the abd cavity, ^ dimen of chest cavity.
2. The external intercostal muscles - pulling the ribs forward and up and swinging the ribs outward and increasing lateral diameter.
(as a side note: *narrow a/w's cause a decrease in flow*)
What occurs during expiration?
Expiration is passive during quiet breathing. The lungs and chest wall are elastic and tend to return to equilibrium after actively expanded during inspiration.
Expiration can be active during exercise, while blowing up a balloon or trombone, or Hyperventilating due to anxiety.
Active expiration use 2 muscle groups:
1. Muscles of the abd wall - such as rectus abdominis, internal/external obliques, and transverse abdominis: together they push the diaphragm up, decreasing thoracic volume.
2. The internal intercoastal muscles - tightens the chest by pulling the ribs downward and in. Limiting volume will increase pressure, forcing air out of the lungs (Boyle's Law).
What is Poiseuille's Law?
Poiseuille's Law - R=Driving P / Flow
or R = P diff btwn mouth and alveolus / Flow
Poiseuille's Law applies to pressure-flow characteristics for laminar flow, where stream lines are parallel to the sides of the tube. THP: Poiseuille's Law tells us that radius impacts resistance significantly. For example, if radius is halved, resistance increases 16 fold. Seen w/ kids who get inflammation/edema. There a/w is small to begin with... add inflammation and decrease in radius becomes very significant.
What is the significance of Turbulent Flow?
Turbulent Flow: occurs at branch points along the resp tree, and any areas of pathological obstruction or increased resistance to airflow, such as bronchospasm and edema.
TF does not have the high axial velocity of laminar flow and the P gradient needed is proportional to the square of the FR. Density of a gas in TF is important b/c the higher the D, the higher the P drop for a given flow. (High D=Low Flow) Using heliox reduces the P gradient needed to sustain flow, and thus reduces WOB in conditions where flow is turbulent.
What is Reynold's #, and what is it application?
The calculation of Reynold's Number helps determine whether flow is laminar or turbulent. Turbulence occurs when Reynold's # exceeds 2000. In most areas of the Resp tract flow is transitional.
Reynold's # includes in it's equation: radius, velocity, density, and viscosity. The site of max a/w resistance... 7th generation bronchioles.