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Physiology > Gas Transport > Flashcards

Gas Transport Flashcards

1
Q

What are the four steps of gas transport?

A
  1. Ventilation of the lungs
  2. Diffusion of oxygen from the alveoli into the capillary blood
  3. perfusion of systemic capillaries with oxygenated blood
  4. diffusion of oxygen from systemic capillaries into the cells
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2
Q

How much O2 diffuses into blood at normal body temp?

How much is actually in the blood?

What causes this difference?

A

0.3 ml O2/100 ml blood

Actually 20.4 mL O2/100 ml blood

This difference is caused by the binding of O2 to hemoglobin

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3
Q

How much O2 can each gram of Hgb bind?

A

1.34 ml O2/g hgb

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4
Q

How is the amt of dissolved O2 calculated?

A

Dissolved O2 = 0.003 x PaO2

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5
Q

What is the makeup of a hemoglobin?

A
  • heme- which is an Iron and porphyrin
  • joined to the protein globin with 4 peptide chains
    • 2 alpha and 2 beta
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6
Q

How does fetal hgb differ from adult hgb?

A

Oxygen has a higher affinity for fetal hgb than adult hgb. This allows the oxygen to leave the mother’s blood and bind to the fetus’ hgb.

Fetal hgb has 2 alpha and 2 gamma peptide chains

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7
Q

What does the oxygen dissociation curve describe?

A

The relationship between oxygen saturation of blood and PO2

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8
Q

What causes the sigmoidal shape of the curve?

A

Oxygen binding cooperatively. When one molecule of O2 binds to the hgb, the other three sites bind O2 more readily, making the middle of the curve steeper.

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9
Q

What factors affect the oxygen dissociation curve?

A
  • PCO2 level
  • pH
  • temperature
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10
Q

_______ in PCO2 causes a right shift in the oxygen dissociation curve.

A

increase

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11
Q

________ in pH causes a shift to the right on the oxygen dissociation curve

A

decrease

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12
Q

What does a shift to the right on the oxygen dissociation curve mean?

A

A right shift results in decreased affinity for the oxygen to the hgb and means the oxygen is more inclined to leave the hgb and go to the tissue

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13
Q

__________ in temperature causes a right shift in the oxygen dissociation curve

A

increase

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14
Q

How does the oxygen dissociation curve of Hgb F differ from a normal curve? Why?

A

It is shifted to the left because fetal hemoglobin has higher affinity for O2 than normal adult Hgb.

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15
Q

How does 2,3 diphosphoglycerate alter the oxygen dissociation curve?

A

Shifts it to the right.

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16
Q

What are the three ways CO2 is transported?

A
  • CO2 is 20x more soluble than O2 so 7% of it is carried dissolved in the blood
  • CO2 + H2O ⇒H2CO3 ⇒H + HCO3, which carries about 70%
  • combined with proteins (carbamino compounds; including hemoglobin)
    • binds to the terminal amino group
17
Q

What happens to O2 binding when a CO2 binds to the hemoglobin?

A

affinity for O2 decreases and the oxygen is released

18
Q

Haldane effect

A

As hgb is deoxygenated in the capillaries, its affinity for CO2 is increased, enabling the hgb to pick up CO2 after it has offloaded its oxygen. When the hgb gets back to the lungs and is oxygenated again, it looses its affinity for the CO2 and it is released and breathed out.

19
Q

What are the essential components that control involuntary respiration?

A
  • brainstem respiratory centers
  • peripheral and central chemoreceptors
  • mechanoreceptors in lungs and joints
20
Q

what are the four respiratory centers in the brain?

A
  • medulla
    • ventral respiratory group
    • dorsal respiratory group
  • pontine areas that send info to medulla
    • pneumotaxic center
    • apneustic center
21
Q

the _________ center inhibits inspiration while the _________ center stimulates inspiration

A

Pneumotaxic center

apneustic center

22
Q

How do central chemoreceptors work?

A

The BBB is not permeable to H+ or bicarb but it is permeable to CO2. When CO2 rises, that will lower the pH of the CSF which will be detected by the chemoreceptors and an increase in RR will result.

NOT sensitive to oxygen!

23
Q

What causes the peripheral chemoreceptors in stimulate ventilation?

A
  • Fall in PaO2 below 60 mmHg
  • Rise in PaCO2
  • Fall in pH
  • **Carotid bodies and Aortic bodies
24
Q

Irritant receptors

A

respond to noxious gases and particulates. These receptors send signals to CNS via vagus nerve and which causes bronchoconstriction and caughing

25
Q

Stretch receptors

A

sense over inflation, stop inspiration

26
Q

Jixtacapillary receptors

A

in the alveolie, stimulated by hyperinflation and various chemical stimuli. Cause rapid, shallow breathing.

off vegas nerve

27
Q

How does your body respond to exercise?

(6)

A
  • Oxygen consumption increases
  • O2 supply is increased by increasing ventilation
  • CO2 production increases
  • mean arterial PaO2 and PaCO2 do not change
  • CO and pulmonary blood flow increase
  • Hb dissociation curve shifts to the right
28
Q

What is hypoxic vasoconstriction?

A

It is caused by low alveolar PO2. Blood is shunted to other, well ventilated portions of the lungs to provide better ventilation and perfusion matching.

**If hypoxia affects all segments of the lungs, the vasoconstriction can lead to PHTN

29
Q

What are the non-respiratory functions of the lung?

(7)

A
  1. Filter small particles
  2. act as reservoir for drugs
  3. metabolized vasoactive substances (produces ACE)
  4. metabolizes bronchoactive substances such as leukotrienes (which cause bronchospasm)
  5. Metabolize drugs
  6. produce immunoglobulins (Iga)
  7. Contain mast cells which produce heparin
30
Q

Sickle cell disease

A
  • HgbS will polymerize when it is deoxygenated, causing the RBCs to become sickle-like shape
  • These wierd shaped cells can then lodge in small capillaries and cause ischemia and infarction
31
Q

What is the problem with CO?

A
  • affinity to bind to hgb is 240x that of oxygen
  • It displaces O2 and forms carboxyhemoglobin instead
  • If it is bound to a hgb with O2, it prevents the O2 from dissociating.
  • False high O2 sats because carboxyhemoglobin is red just like oxyhemoglobin
32
Q

What is the effect of sleep apnea?

A

Person will skip up to a couple of breaths while sleeping, resulting in significant reduction of gas transport.

*Associated with an increased incidence of heart disease and stroke

33
Q

What characterizes COPD?

A

Chronic bronchitis (coughing with sputum) and emphysema (destroyed alveolar walls causing reduced surface area).

Patients become hypoxic and hypercarbic

34
Q

Why do COPD patients develop a hypoxic respiratory drive?

A

They have chronic respiratory acidosis that is metabolically compensated. The CNS always has too much CO2 and the chemoreceptors become unresponsive to CO2.

35
Q

How does altitude sickness cause pulmonary edema?

A

pulmonary vasoconstriction occurs as a response to alveolar hypoxia. The vasoconstriction causes increased permeability which leads to edema.

Physiology (31 decks)

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