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medical physiology > quotes from rosens notes... chapter 8 > Flashcards

quotes from rosens notes... chapter 8 Flashcards

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USMLE® Step 1 flashcards
1
Q

partial pressure defines

A
  • it defines the diffusion of gas

- it allows comparisons of gas activities in both LIQUID and GASEOUS states

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2
Q

henry’s law is?

describes ?

A
  • relationship between partial pressure and the amout of gas in solution
  • Concentration = solubility * partial pressure
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3
Q

daltons law describes?

A

how the partial presures of multiple gasses collide with a container and make a final total pressure

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4
Q

daltons law equation is?

A

{partial pressure of gas x} = {total pressure} * {% of gas in air}

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5
Q

what is the not so obvious thing about daltons law?

A
  • in lungs, you have to take into account the partial pressure of water.
  • it contributes to the total gas pressure and (in the lungs) is 47 mmHg
  • so, if total pressure is 760, water makes up 47 of that… the other 713 is the other gasses)
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6
Q

diffusion rate of gasses is proportional to

A

*** trick… its INVERSELY proportional to the square root of MW
==> overweight gasses take longer to move

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7
Q

diffusion rate of gasses in SOLUTION is proportional to

A
  • again INVERSELY proportional to the square root of MW

- then multiply by the solubility

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8
Q

compare and contrast diffusion rate of CO2 and O2 in solution

A

in solution, CO2 is 20 times faster than O2 because it is WAAAY more soluble (even though CO2 is heavier)

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9
Q

Fick’s law

A

Kylie and I call this Dicks law
stress = (penis * radius) / (condom wall thickness)
he gives it different names, but it describes how much something presses on a membrane wall

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10
Q

disease of fick’s law

A

hyaline membrane disease…. premature babies. remember positive pressure ventilator?

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11
Q

how do gases move across membranes

A

capillary exchange ( has two parts, each with its own resisitance)
1- membrane resistance
2- chemical reaction resistance

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12
Q

relationship between diffusion, conductance, and resistance

A
  • diffusion is considered analogous to conductance

- conductance is the inverse of resistance

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13
Q

what affects membrane resistance

A
  • 1 / (membrane diffusion rate)

- affected by anything that changes the alveolar capillary interface or the erythrocyte membrane

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14
Q

what affects chemical reaction resistance

A
  • 1 / [(oxygen’s binding rate) * (capillary blood volume)]

- anything that change the affinity of O2 for Hb

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15
Q

total diffussive resistance =

A

membrane resistance + chemical reaction resistance

** look at the equation… it looks hard but it isn’t

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16
Q

what value duration of depends on % saturation of Hb? result?

A
  • theta
  • when Hb is saturated, theta (oxygen affinity) gets small and chemical resistance is the major contributor to overall resistance
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17
Q

Compare gas exchange of CO2 and O2 in lungs

A
  • diffusion may be 20 times faster for CO2, but the reaction rate for CO2 release is much slower
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18
Q

how long does it take to exhcnge gas?

A
  • in a normal lung exchanging CO2 for O2 takes about 250 ms

- a RBC is in the pulmonary capillary about 750 ms

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19
Q

when you exercise, what does your lung do?

A

it shortens the transit time of a RBC in the capillary, but thats ok in a normal person because it does not reduce the final PO2

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20
Q

what type of lung would have a hard time with exercise?

A
  • one with an abmormal thickening of the blood-gas barrier (increase in membrane resistance)
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21
Q

what woudl altitude do to PO2

A
  • depends… if you are at rest, its ok

- if you are exercising, you will have a reduced PO2

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22
Q

Lung diffusion capcity equation

A

D(L) = rate of diffusion / ((alvolar press. - capillary press.)

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23
Q

what affects the lung diffusion capacity?

A

body size (small person, small #)
exercise (demand = big #)
thickened alvolar/capillary membrane (lower #)
decreased alveolar surface area (lower #)

24
Q

if you want to decrease the lung’s surface area?

A

collapse a lung!!

25
Q

normal pH?
normal PO2?
normal CO2?
normal bicarb?

A

7.35-7.45
80-100
35-45
22-26

26
Q

pressure gradients exist to move O2 from?

A

inspired air ==> alveoli ==> systemic arterial blood ==> tissues

27
Q

anatomical shunting =

A

some of the blood bypasses pulmonary capillaries and does not contribute to gas exchange (thebesian circulation)

28
Q

what is the effect of anatomical shunting?

A

anatomical abnormalities will increase shunting, and in the end, it lowers PO2 in sysstemic arteries relative to the PO2 in the alveoli

29
Q

V/Q ratio

A

ratio of alveolar air flow to alvolar blood flow

30
Q

normal V/Q ratio

A

0.8

31
Q

what can change V/Q ratio

A

either an air or a blood obstruction
blood obstruction increases the V/Q
air obstruction decreases the V/Q
This is useful in diagnosing pulmonary emboli

32
Q

base of lung gets ____ blood, ___ air

A

tooons of blood,and the greatest amount of air

33
Q

V/Q at base of lung compared to the apex of lumg?

A

when you are standing, the V/Q is lower at the base of the lung

34
Q

why is there a difference in ventilation of the lung?

A

“primarily due to the gradient of intrapleural pressure from apex to base of lungs”

  • at the base of the lung, alveoli are less expanded due tothe gravitational force, but have the best compliance because gravity pulls the surfactant down to the bottom of the lung
35
Q

perfusion is the greatest at the base of the lung because

A
  • hydrostatic pressure decreases above the heart and icnreases below it
  • this distends the very flexible pulmonary vessels, decreasing their resistance and further increasing flow
36
Q

how does your body accomodate when V/Q is too high

A
  • remember this means a blood obstruction
  • constrict broncioles to reduce V
  • vasodilate to increase Q
37
Q

how does your body accomodate when V/Q is too low

A
  • remember this is an air obstruction
  • bronchiole dilation
  • vascular constrictuion
38
Q

partial pressure of CO2 and O2 determine

A
  • amount of dissolved gas in solution

- rate of diffusion

39
Q

which gas is better at dissolving in plasma?

A

CO2 is still the better dissolver

40
Q

how much O2 can a hemoglobin hold?

A

one oxygen per heme subunit (4 of them)

41
Q

heme sandwich?

A

one role of Hb is to prevent the heme sandwich (when two hemes sandwich an oxygen between them)

42
Q

how is Hb different from Mb?

A

myoglobin is not cooperatve like hemoglobin

43
Q

how does pH affect oxygen binding

A

when the pH goes down (like with exercise) oxygen likes to jump off Hb
this is the bohr effect

44
Q

what happens to oxygen binding when temperature rises

A

when the pH goes down (like with exercise) oxygen likes to jump off Hb

45
Q

BPG effect?

A
  • present in fetal erythrocytes
  • increases the O2 affinity to a value greater than maternal Hb
  • i thought that fetal Hb expressed a different type of heme protein… but whatever
46
Q

Consequence of Hb chemistry for O2 transport

A

sigmoidal O2 dissociation curve

O2 delivered is unaffected by a moderate drop in alveolar PO2 unless you are anemic

47
Q

what things shift the O2 dissociation curve to the right

A
  • increased H (decreased pH)
  • increased PCO2
  • increased temp
  • increased 2,3 BPG
48
Q

How is CO2 transported?

A

carbamino compounds ==> produced by combination with plasma proteins, but really low transport
bicarb ==> need RBC enzyme to turn into H2CO3

49
Q

RBC CO2 enzyme? how does RBC maintain electroneutrality?

A

carbonic anhydrase; each bicarb anion is exchanged for Cl- so there is also a net movement of water

50
Q

how is pulmonary circulation different from systemic? why?

A
  • low pressure, lowe resistance, high compliance
  • wall thickness is about 1/3 of systemic
  • arterioles have little smooth muscle
51
Q

what is the same in pulmonary and systemic circulations

A

blood flow. duh

52
Q

increase in pulmonary artery pressure is associated with

A
  • exercise
  • decrease in pulmonary vascular risistance because of distension and recruitment of unused or poorly perfused capillaries
53
Q

most of the total compliance is a result of ?

A

small vessels (smaller than 100 microns)

54
Q

how do vessels respond to alveolar inflation

A

less than 50 microns ==> decrease in diameter

small arteries and veins ==> increase in diameter because they are tethered to alveoli by CT

55
Q

why do people with COPD purse their lips?

A

they use Ficks law to increase the pressure in their lungs; it helps the O2 get across the membranes

56
Q

possible cause of pulmonary edema?

A

congestive heart failure; treat with IV diuretics

medical physiology (9 decks)

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