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Physiology > Gas Transport by the Blood > Flashcards

Gas Transport by the Blood Flashcards

1
Q

Three ways CO2 is transported in the blood

A
  • Free CO2 dissolved in blood
  • Carbamino compounds associated with hemoglobin
  • Bicarbonate ions(mostly): HCO3- formed when CO2 combines with water
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2
Q

Haldane effect

A

Deoxyhemoglobin buffers H+

Hemoglobin’s affinity for CO2 as carbamino compounds is greater when hemoglobin is in the deoxygenated state

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3
Q

Explain and quantify (in numeric terms) the two ways oxygen is transported in the blood

A

Everything on the left of the plus sign is oxygen carried by hemoglobin.

Everything on the right is oxygen physically dissolved in blood.

Nromally, most oxygen is carried by hemoglobin

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4
Q

For each mmHg of air pressure, there is how much oxygen in the blood?

A

.003mL O2 / 100mL blood.

So if PO2 is 100, then there’s 0.3mL of dissolved O2 per 100mL of blood. This alone is not enough for tissues, which is why we also have hemoglobin.

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5
Q

What are 4 characteristics of tissues cause hemoglobin to release its oxygen?

A
  • Indicates metabolically active:
    • Low pH (acidity)
    • Increased temperature
    • Increased CO2
  • At high altitudes where oxygen is low: 2,3-BPG

Shifts the curve to the right (release)

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6
Q

A 38 yo woman moves to colorado. What will happen to the hemoglobin-O2 dissociation curve?

A

Shift to the right

Increase in 2,3BPG in red blood cells will decrease the affinity of hemoglobin for oxygen

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7
Q

Is the fetal hemoglobin curve on the left or right of the adult hemoglobin curve?

A

Fetal hemoglobin has a greater affinity for oxygen (does not want to release) in order to take oxygen from maternal blood, so it’s shifted left.

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8
Q

Oxygen saturation

A

The % of available Hb binding sites that have O2 attached.

At PO2 of 100mmHg (arterial blood), it’s 97.5%

At PO2 of 40mmHg (mixed venous blood), it’s 75%

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9
Q

What causes cyanosis?

A

A significant proportion of hemoglobin is desaturated (deoxyhemoglobin), causing de-oxygenated blood to appear bluish

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10
Q

Whats the difference between cyanosis in a patient with anemia vis polycythemia?

A

Polycythemia ( a very high [hemoglobin]) may have cyanosis, but adequate oxygen delivery to the body tissues

Anemia may not have cyanosis ( all hemoglobin is saturated), but still have inadequate oxygen delivery due to the lack of hemoglobin int he blood

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11
Q

How will a person at point A appear? What about at point B?

A

Point A: cyanotic, but 16 mL/dL of oxygen may be adequate to meet oxygen demands of the body

Point B: normal, but 12mL/dL is not enough to meet th ebody’s needs.

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12
Q

The formation of carbonic acid is facilitated by _

It dissociates into

A

Carbonic anhydrase within the red blood cells

Dissociates into protons and bicarbonate(makes it acidic)

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13
Q

Why does adding CO2 to water in teh presence of carbonic anhydrase cause acidosis?

A

carbonic anhdrase will turn CO2 into H+ and HCO3-

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14
Q

What is the clinical relevance of Haldane effect?

A

When you give a patient excessive oxygen.

The rapid increase in oxygen increases the amt of oxyhemoglobin

–> rapidly releases the carbamino form of CO2 from RBCs

–> pCO2 in the blood increases and the blood pH decreases

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15
Q

In regards to forming carbamino compounds, carbon dioxide binds to hemoglobin.

The affinity of hemoglobin for CO2 is greater when hemoglobin is in the ___ state

A

Deoxygenated state

Becuase deoxyhemoglobin is a better proton aceptor (more basic) than oxygenated hemoglobin

Haldane effect

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16
Q

Compare and contrast the the carbon dioxide dissociation curve (whole blood CO2 content vs PCO2) w the oxygen dissociation curve

A
  • Plateau at the top of oxyhemoglobin curve because saturated Hb can’t be further loaded w oxygen
    • Important bc changes in PO2 above 55 mmHg will not cause significant release of O2 from hemoglobin, keeping oxygen bound throughout all portions of the lung w varying oxygen tension
  • CO2 is mostly transported as bicarbonate and tehre’s no carrier molecule to saturate –> linear and steeper
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17
Q

How care changes in hemoglobin saturation detected by the pulse oximeter?

A

Changes in saturation confer change in the way hemoglobin absorb light

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18
Q

Why is the shape o fhte oxygen dissociation curve sigmoidal? AKA why does the rate of desaturation per change get much faster as you move from right to left and the curve is so steep?

A

Cooperativity

Once the first oxygen is relased, it takes less change in pressure to release the second molecule and even less for the 3rd and 4th. Makes sense because we want to deliver oxygen quickly when its needed (55mHg and below)

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19
Q

In contrast to oxygen, which is very steep at lower oxygen tensions an dplateaus at higher oxygen tensions after hemoglobin is saturated, CO2…

A

Does not have a limit on saturation since it is predominantly transported in the blood as bicarbonate

20
Q

The difference between arterial and mixed venous blood is __ with oxygen and ___ w carbon dioxid

A

Large for oxygen (90 to 40 mmHg)

Small with CO2 (40 to 45 mmHg)

21
Q

What is the bicarbonate equation?

A

The pH status of the blood is maintained in the normal rnage (7.35-7.45) based upont he pulmonary excretion of carbonic acid in the form of CO2

22
Q

___ control CO2 excretion on the left side and ___ control bicarbonate excretion on the right side

A

lungs control CO2 excretion

kidneys control bicarbonate excretion

23
Q

According to the Henderson Hasselbach equation, if the ratio between the ___ and ___ stay the same, the ___ will remain the same

A

If the relationship between bicarbonate and pCO2 remains the same, the pH will remain the same

24
Q

Alveolar ventilation determines the pCO2 of the blood, which will affect pH.

Hyperventilation causes ___

Hypoventilation causes ___

A

Hyper -> respiratory alkalosis

Hypo –> respiratory acidosis

25
Q

Consuming aspirin

A diabetic not taking insulin

Inadequate oxygen delivery

Diarrhea

A

Metabolic acidosis

  • Aspirin is an acid
  • Diabetics without insulin will form keto-acids
  • Inadequate oxygen delivery to the tissues will form lactic acid
  • Diarrhea will cause a loss of bicarbonate
26
Q

Decreased serum bicarbonate concentration when respiratory rate and tidal volume are held constant indicates

A

metabolic acidosis

27
Q

Given that the body doesn’t naturally hold respiratory rate or renal functino perfectly constant, how do you determine the cause of the primary acid base disturbance?

A
  1. Is the pH low (acidemia) or high(alkalemia)?
  2. Is pCO2 high or low?
  3. Is HCO3- high or low?
28
Q

A primary respiratory acidosis (increased pCO2) will be compensated by

A primary respiratory alkalosis (decreased pCO2) will be compensated by

A

Respiratory acidosis (high pCO2)-> metabolic alkalosis (high HCO3)

Respiratory alkalosis (low pCO2) -> metabolic acidosis (low HCO3-)

29
Q

A primary metabolic acidosis (decreased HCO3 −) will be compensated by _

A primary metabolic alkalosis (increased HCO3 −) will be variably compensated by_

A

a respiratory alkalosis (decreased pCO2)

a mild respiratory acidosis (normal to increased pCO2).

30
Q

In general, compensation is the body just trying to maintain pH by keeping the ratio of CO2 and bicarbonate ___

A

the same

e.g. if one goes up, the other will go up.

31
Q

Hypoxic hypoxia

Anemic hypoxia

Circulatory hypoxia

Histotoxic hypoxia

A

Hypoxic hypoxia:low blood O2 from pulmonary disease

Anemic hypoxia: reduced ability to carry oxygen from anemia

Circulatory hypoxia: reduced tissue blood flow from shock or obstructed blood flow

Histotoxic hypoxia: inability to use oxygen from cyanide poisoning

32
Q

What happens to PAO2 and PaO2 in hypoventilation and why?

A

Both are decreased becuase of elevated CO2 in the blood and alveolar gas

33
Q

Both diffusion impairment and shunt cause hypoxemia because ___

Is O2 administration helpful in shunt?

A

Both cause hypoxemia due to blood-gas interface; the gases are normal

The only benefit of additional O2 in shunt is to increase dissolved oxygen (pO2) since hemoglobin can’t carry more O2 once it is saturated.

34
Q

Anemia and CO poisoning

A

decrease the oxygen-carrying capacity of blood because of an actual or effective hemoglobin deficiency

35
Q

How does cyanide cuase tissue hypoxia?

A

Blocks electron transport chain -> can’t use oxygen -> inadequate tissue oxygenation

  • organ dysfunction
  • headache
  • vomiting
  • shortness of breath
  • lactic acidosis
  • Arterial oxygen will be normal, Venous oxygen will be elevated
36
Q

What direction does HbCO shift the oxygen dissociation curve?

A

To the left (doesn’t want to release)

37
Q

Water & CO2 ___ cells in systemic capillaries

Water & CO2 ___ cells in pulmonary capillaries

A

Water & CO2 enter the cells of systemic capillaries–> swell a lil

Water & CO2 leave the cells of pulmonary capillaries –> shrink a lil

38
Q

The pH of venous blood is only slightly more acidic than teh pH of arterial blood because

A

The H+ generated from CO2 and H2O is buffered by deoxyhemoglobin in venous blood because deoxyhemoglobin has increased ability to carry CO2

39
Q

If you give too much oxygen, carbon dioxide can go up. Why?

A
  • Reversal of V/Q mismatch
  • Haldane Effect**: less deoxyhemoglobin available carry CO2
  • Decreased hypoxic drive to breathe (later)
40
Q

Why would bicarbonate go up when you increase CO2 blood gas?

A

By le chatelier’s, increased CO2 will push the equation toward the right.

However, it doesn’t go up enough to normalize the pH until the kidney actually starts retaining a bunch of bicarb to normalize the pH.

41
Q

Example ABG:

pH=7.24

pCO2 = 60

pO2 = 50

HCO3- = 26

What’s the problem?

A

Acute respiratory acidosis (e.g. drug overdose)

Acute because the bicarb is mostly normal (~24+/-2), so the kidneys haven’t time to compensate

Respiratory becuase pCO2 is high (normal: 40)

Acidosis because pH is low (normal: 7.4)

42
Q

Example ABG:

pH=7.35

pCO2 = 60

pO2 = 50

HCO3- = 32

What’s the problem?

A

Chronic respiratory acidosis (e.g. lung disease)

Chronic because HCO3- is very high (32 vs 24), which indicates that the kidneys are working right and just trying to compensate

Respiratory because pCO2 is high (60 vs 40)

Acidosis because pH is low (7.35 vs 7.4)

43
Q

Example ABG:

pH=7.6

pCO2 = 20

pO2 = 60

HCO3- = 22

What’s the problem?

A

Respiratory alkalosis (e.g. high altitude sickness)

Alkalosis because pH is high (7.6 vs 7.4)

Respiratory because pCO2 is way too low (20 vs 40)

44
Q

Example ABG:

pH=7.1

pCO2 = 40

pO2 = 90

HCO3- = 12

What is this?

A

Acute Metabolic acidosis (e.g. acute kidney disease)

Acidosis because pH is low (7.1 vs 7.4)

Metabolic because HCO3- is very low (12)

Acute becuase PCO2 is still normal, so it hasn’t had the time to compensate

45
Q

Example ABG:

pH=7.20

pCO2 = 20

pO2 = 90

HCO3- = 8

What’s the problem?

A

Metabolic acidosis w respiratory compensation (e.g. chornic kidney disease)

  • pCO2 is really low in an effort to compensate fo rmetabolic acidosis
46
Q

There is a ___ in PA between adjacent open capillaries perfusing tissue

A

A fall

Physiology (42 decks)

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