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intro bio ii exam 2 > Gas Exchange and Transport > Flashcards

Gas Exchange and Transport Flashcards

1
Q

PO2 and PCO2 in alveoli and arterial blood just after gas exchange

A

Same partial pressures

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2
Q

Venous blood arriving at the alveoli has around what PO2 & PCO2?

A

Low PO2 (~ 40 mm Hg) and higher PCO2 (~ 46 mm Hg)

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3
Q

Factors that influence alveolar gas exchange

A
  1. The amount of oxygen that reaches the alveoli
  2. The ability for gas to diffuse between the alveoli and blood
  3. Adequate perfusion of the alveoli (are there enough functional capillaries around the alveoli)
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4
Q

Factors that that influence the amount oxygen that reaches the alveoli

A
  • Composition of inspired air

- alveolar ventilation (rate and depth of breathing, airway resistance, lung stretchiness)

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5
Q

Factors that influence the ability for gas to diffuse between alveoli and blood

A
  • surface area

- diffusion distance (affected by barrier thickness, amount of fluid through which gasses must diffuse)

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6
Q

Emphysema

A

Destruction of alveoli —> less SA for gas exchange

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7
Q

Fibrotic lung disease

A

Thickened alveoli membrane —> slower gas exchange

Lung becomes less stretchy —> decreased ventilation

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8
Q

Pulmonary edema

A

Increase in fluid between alveoli and epithelial cells of capillary which increases distance for gas diffusion

Leads to increased arterial PCO2 b/c CO2 is more soluble in water than O2

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9
Q

Asthma

A

Increased airway resistance due to bronchoconstriction decreases amount of oxygen that arrives at the alveoli

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10
Q

Hypoxic hypoxia

A

Low arterial partial pressure of oxygen

Causes:
High altitude, hypoventilation, abnormal alveolar perfusion

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11
Q

Anemic hypoxia

A

Decreased total amount of oxygen bound to hemoglobin

Causes:
Blood loss, anemia, carbon monoxide poisoning

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12
Q

Ischemic hypoxia

A

Reduced blood flow

Causes:
Heart failure, shock, thrombosis

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13
Q

Histotoxic hypoxia

A

Failure of cells to use oxygen because cells have been poisoned

Causes:
Cyanide and other metabolic poisons (flea dip!)

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14
Q

How does oxygen get loaded onto Hb?

A

Diffuses across alveolar membrane into plasma where it briefly dissolves. Diffuses across RBC membrane where it is loaded onto Hb.

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15
Q

Oxygen carrying capacity

A

The amount of oxygen bound to Hb

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16
Q

What influences oxygen carrying capacity?

A
  • amount of oxygen dissolved in plasma (determines % saturation of Hb)
  • amount of hemoglobin (which determines the number of Hb binding sites)
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17
Q

Total number of Hb binding sites is calculated from…?

A

Hb content per RBC x # of RBCs

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18
Q

How many heme groups are on each Hb?

A

An Hb has four subunits and each subunit has one heme group so thats four binding sites per Hb

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19
Q

How many coordination sites does iron have?

A

6

4 nitrogen
1 histidine side chain
1 for molecular oxygen

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20
Q

How would removal of histidine side chains affect oxygen heme binding?

A

Inhibit

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21
Q

How does Hb increase the oxygen carrying capacity of the blood?

A

PO2 in alveoli and plasma will equilibrate so when Hb binds oxygen in the RBC, equilibrium will shift to replenish the oxygen in the plasma increasing the overall oxygen carrying capacity

22
Q

How does Hb change when binding oxygen?

A

Conformational change which increases the affinity for the next oxygen

23
Q

Hb binding curve

A

S-shaped/sigmoidal curve characteristic of cooperative binding

Shows that each consecutive oxygen binding increases the affinity for oxygen of the next binding site when picking up oxygen and vice versa when dropping off oxygen

24
Q

Partial pressure of oxygen leaving the lungs

A

100 mm Hg

25
Q

Partial pressure of oxygen returning to the lungs

A

40 mm Hg

26
Q

Normal percent oxygen reserve

A

75% of Hb binding sites are occupied by oxygen normally so that this oxygen reserve can be released to tissues with low oxygen (PO2 < 40 mm Hg) such as during exercise

27
Q

What percentage of binding sites exchange oxygen in the lungs?

A

25% or 1 binding site per Hb

28
Q

What does the Hb binding site affinity change with each subsequent O2 picked up/dropped off?

A

Stepwise conformational changes of Hb structure

29
Q

Hb left shift

A

Higher of affinity of Hb for O2

Good for pick up in lungs (up to max), bad for drop-off at tissues

30
Q

Hb right shift

A

Lower affinity of Hb for oxygen

Good for drop-off at tissues, bad for pick-up in lungs

31
Q

How does fetal Hb differ from maternal/adult Hb?

A

Has two gamma units in place of two beta units which have a lower affinity for BPG

Fetal Hb binding curve is shifted left compared to maternal Hb binding curve

Fetal blood supply receives oxygen from maternal blood supply

32
Q

Factors that shift Hb binding curve right

A

Decreasing pH (more acidic, such as during exercise/formation of lactic acid), increasing temperature, increasing partial pressure of CO2, increasing BPG

33
Q

2, 3 BPG

A

Binds in place of oxygen which facilitates the drop off of oxygen to the tissues

High altitude & exercise induced adaptation

34
Q

What factors influence the percent saturation of Hb?

A

PCO2, pH, Temperature, and BPG

35
Q

How might you change the total number of Hb binding sites?

A

Increase the Hb content per RBC

Increase the number of RBCs via hormone EPO (increase hematocrit)

36
Q

Myoglobin

A

Monomeric heme protein in the sarcoplasm of muscle cells

Has a higher affinity for oxygen than hemoglobin

Since myoglobin only has one binding site, oxygen bonding is not cooperative

There is a certain PO2 threshold at which myoglobin drops off oxygen (~20 mm Hg)

37
Q

Animals living at high altitudes tend to have ____ shifted Hb binding curves.

A

Left

38
Q

Short and long term human adaptations to high altitude

A

Short - increase in breathing rate, hyperventilation

Long - increased EPO leading to increased RBC production/hematocrit, increased angiogenesis

39
Q

Ways in which CO2 is carried in the blood

A
  • as bicarbonate (HCO3-) - 70-90%
  • dissolved in blood plasma - 5-10%
  • bound to amino groups in hemoglobin (carbaminohemoglobin) - 5-15%

H+ binding reduces the affinity of Hb for oxygen

40
Q

How is carbon dioxide converted to bicarbonate?

A

In the RBC, carbon dioxide reacts with water to become carbonic acid. Carbonic acid is then converted into bicarbonate and hydrogen ions. (H2CO3 —> HCO3- + H+). Both reactions are catalyze by carbonic anhydrase.

41
Q

How is plasma neutrality maintained when bicarbonate ions move into the plasma?

A

Negatively charged chloride moves into the RBC from the plasma making the net charge change = 0

42
Q

Why does carbon dioxide unbind from Hb and diffuse out of the RBC?

A

Law of mass action due to carbon dioxide diffusing out of the plasma, into the alveoli, and being exhaled

43
Q

How does Hb buffer H+ ions?

A

Histidine on Hb can pick up protons to prevent acidification thus acting as a buffer

44
Q

Respiratory acidosis

A

Breathing rate is insufficient to clear carbon dioxide at the rate that it is being made

Hypoventilation

45
Q

Metabolic acidosis

A

Caused by the build up of ketones, ingestion of acid, kidney failure, excessive lactic acid fermentation

46
Q

Why does carbon dioxide diffuse out of the plasma, into the alveoli, and then into the air to be exhaled?

A

The partial pressure of carbon dioxide in the air is always lower than in the alveoli so carbon dioxide moves down its pressure gradient when moving into the air

47
Q

Oxygen dissolves better in what temperature water?

A

Cold

48
Q

How do chemosensors in the carotid body signal to medullary centers to increase ventilation?

A

(Very very) Low partial pressure of oxygen in the blood signals to the K+ channels in the carotid body to close causing the cell to depolarize. Depolarization of the membrane opens voltage-gated calcium channels. Calcium aids in the exocytosis of neurotransmitters which trigger an action potential on a sensory neuron that signals to the medullary centers to increase ventilation.

Aortic chemoreceptors also monitor partial pressure of oxygen. Both also monitor CO2(respiratory acidosis) and pH (metabolic acidosis).

49
Q

Central chemoreceptors monitor the partial pressure of which gas in the cerebrospinal fluid?

A

Carbon dioxide

This is in contrast to carotid and aortic chemoreceptors (aka peripheral) which also monitor oxygen and pH.

50
Q

What types of neurons signal to the respiratory control centers and what effect does that have?

A

Sensory neurons signal to respiratory control centers to change ventilation

intro bio ii exam 2 (8 decks)

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