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Physiology 208 > Gas Exchange and Transport > Flashcards

Gas Exchange and Transport Flashcards

1
Q

Hypoxia

A

too little oxygen

- a result of impaired diffusion from alveoli to blood or impaired blood transport

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2
Q

Hypercapnia

A

excess CO2

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3
Q

Hypoxic Hypoxia

A
  • low arterial PO2
  • causes: high altitude; alveolar hypoventilation; decreased lung diffusion capacity; abnormal ventilation-perfusion ratio
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4
Q

What Three Variables does the Body Respond to to Avoid Hypoxia

A
  1. Oxygen: ATP production
  2. Carbon Dioxide: CNS depressant/acid precursor
  3. pH: denaturing of protein
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5
Q

How do Gases Diffuse?

A
  • gases diffuse down partial pressure gradients
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6
Q

Alveolar Gas Exchange is Influenced by…

A
  1. O2 reaching the alveoli
  2. Gas diffusion between alveoli and blood
  3. Adequate perfusion of alveoli
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7
Q

Two Causes of Low Alveolar PO2

A
  1. inspired air has low O2 content
    - > alterations in atmospheric PO2
  2. alveolar ventilation (hypoventilation)
    - > increase airway resistance, decrease lung compliance, or CNS issue, decrease rate and/or depth of breathing
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8
Q

What Could be Another cause of Hypoxia

A

problems within gas exchange between the alveoli and blood

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9
Q

Diffusion

A
  • random movement of molecules from a region of high concentration to a region of low concentration
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10
Q

Factors that Affect the Random Movement of Gas Molecules Between the Alveoli and Capillaries

A
  1. Concentration Gradient**
  2. Surface Area
  3. Barrier Permeability
    - diffusion distance, solubility of gas
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11
Q

Emphysema

A
  • decreased surface area
  • causes hypoxia
  • destruction of alveoli means less surface area for gas exchange
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12
Q

Fibrotic Lung Disease

A
  • decreased barrier permeability
  • causes hypoxia
  • thickened alveolar membrane slows gas exchange
  • loss of lung compliance may decrease alveolar ventilation
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13
Q

Pulmonary Edema

A
  • increased diffusion distance
  • causes hypoxia
  • fluid interstitial space increases diffusion distance
  • arterial PCO2 may be normal due to higher CO2 solubility in water
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14
Q

Asthma

A
  • decreased concentration gradient
  • causes hypoxia
  • increased airway resistance decrease alveolar ventilation
  • bronchiole constricted
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15
Q

Gas Solubility and Diffusion

A
  • alveoli are lined with liquid, the small interstitial space between alveoli and capillaries contains liquid and blood itself is liquid
  • respiratory gases must be soluble in liquids
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16
Q

Movement of Gas Molecules is Directly Proportional to…

A
  1. the pressure gradient of the gas
  2. solubility of gas in liquid
  3. temperature-relatively constant (not really relevant)
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17
Q

Gas Transport in Blood

A
  • demonstrates the general principles of mass flow and mass balance
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18
Q

O2 consumption by _______ tissues

A

systemic

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19
Q

Fick Equation

A

CO x (Arterial [O2] - Venous [O2]) = QO2

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20
Q

Cellular Oxygen Consumption

A

QO2 = arterial O2 transport - venous O2 transport

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21
Q

Oxygen Transport

A
  • > 98% of oxygen in blood is bound to hemoglobin in RBCs

- <2% is dissolved in plasma

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22
Q

Oxygen Binding Reaction Equation

A

Hb + O2 ⇌ HbO2

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23
Q

What Law does Oxygen Binding Obey?

A
  • law of mass action
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24
Q

Oxygen Binding: Law of Mass Action

A
  • as [free O2] increases, more oxygen binds to Hb –> HbO2
  • free O2 is taken up until plasma and Hb reach equilibrium
  • transfer of O2 happens rapidly
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25
Q

How long does RBC spend in pulmonary capillary?

A

~0.75 sec

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26
Q

How long does it take for RBC to become saturated?

A

~0.40 sec

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27
Q

Reverse Reaction of Oxygen Binding

A
  • blood travels to tissues with low PO2
  • O2 drawn out of plasma
  • equilibrium is disrupted
  • Hb releases its O2 into plasma
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28
Q

at rest we consume about ____ ml O2/min

A

250

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29
Q

Plasma O2 is determined by?

A

alveolar PO2

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30
Q

Alveolar PO2 depends on:

A
  1. composition of inspired air
  2. alveolar ventilation rate
  3. efficiency of gas exchange
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31
Q

PO2 determines what?

A

Oxygen-Hb binding

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32
Q

Plasma O2 determines

A

% saturation of Hb

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33
Q

Amount of Hb determines

A

Total # of Hb binding sites

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34
Q

How to calculate total # of Hb binding sites

A

Hb content per RBC x # of RBCs

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35
Q

Oxygen Binding is expressed as…

A

percentage

- percent saturation of hemoglobin

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36
Q

Resting Cell PO2?

A

40 mmHg

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37
Q

Alveoli PO2

A

100 mmHg

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38
Q

Can active cells have a lower PO2?

A

yes

  • active muscle cells can have 20 mmHg
  • results in larger release of O2
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39
Q

Physical Factors Altering Hb’s Affinity for O2

A
  1. pH
  2. PCO2
  3. temperature
  4. 2,3-DPG
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40
Q

Effect of pH

A
  • max exertion produces excess CO2 and pushes a cell into anaerobic metabolism
  • increased H+ and lactic acid in cytoplasm and extracellular space
  • more oxygen delivered @ low pH
41
Q

Bohr Effect

A
  • shift in Hb saturation as a result in pH or CO2 change
42
Q

Increased Aerobic Metabolism results in…

A

increased CO2 production

43
Q

Effects of PCO2

A
  1. readily binds Hb altering conformation and decreases binding spots for O2
    * *2. CO2 is readily converted to carbonic acid
44
Q

Carbonic Anhydrase

A
  • enzyme in reaction of CO2 to carbonic acid (H2CO3)
45
Q

Effect of Temperature

A
  • increased heat causes a conformational change in Hb
  • decreased affinity and more O2 to be dropped at very active muscles
  • increased heat = increased delivery
46
Q

2,3-DPG

A
  • diphosphoglycerate
  • metabolic compound
  • by-product of glycolysis in RBCs
47
Q

Increase Production of 2,3-DPG

A
  • chronic hypoxia increase 2,3-DPG production
  • RBCs release ATP during hypoxia
  • ascent to higher altitude and anemia can increase 2,3-DPG
48
Q

Effect of 2,3-DPG

A
  • increase 2,3-DPG = increased delivery
49
Q

Fetal Hemoglobin

A
  • two alpha, two gamma globulin subunits

- gamma increases oxygen binding

50
Q

Importance of Removing CO2 from Body

A
  • elevated PCO2 causes acidosis, low pH leads to interruptions in H bonds and denaturing of proteins
  • abnormally high PCO2 depresses CNS causing confusion, coma, death
51
Q

Cells produce far ___ CO2 than plasma is capable of carrying

A

more

52
Q

How much CO2 is carried by venous blood dissolved in plasma

A

7%

53
Q

What happens to remaining 93% of CO2

A
  • diffuses into RBCs
54
Q

____ of CO2 binds to Hb

A

23%

55
Q

carbaminohemoglobin

A
  • HbCO2
56
Q

70% of CO2 is converted to ____

A

HCO3- (bicarbonate)

57
Q

CO2 Transport

A
  1. dissolve in plasma (7%)
  2. Bound to Hb (23%)
  3. Converted to HCO3- (70%)
58
Q

Purposes of HCO3-

A
  1. provides additional means of CO2 transport from cells to lungs
  2. HCO3- is available to act as a buffer for metabolic acids, stabilizing body’s pH
59
Q

Carbonic Acid

A
  • H2CO3

- intermediate step (ignored)

60
Q

To Ensure Equilibrium is not Reached in CO2->HCO3-

A
  1. remove HCO3- from RBC

2. mop up excess H+

61
Q

Hb acts as a ____ and binds excess H+ ions

A

buffer

62
Q

Why does Hb act as a buffer?

A
  1. prevents large changes in body’s pH

2. if blood CO2 is elevated too high Hb can’t soak up al H+ which can result in acidosis

63
Q

Where does CO2 bind to Hb

A
  • at exposed amino groups (-NH2)

- forms carbaminohemoglobin

64
Q

CO2 Removal at the Lungs

A
  • plasma CO2 diffuses into alveoli –> RBC CO2 diffuses into plasma
  • causes CO2 to unbind from Hb and diffuse out of RBC
  • CO2 levels drop = reverse reaction
65
Q

as [HCO3-] drops, ____ exchanger ______

A

Cl-/HCO3-

reverses

66
Q

Breathing

A
  • rhythmic process

- occurs subconsciously

67
Q

Skeletal Muscles that Control Ventilation

A
  • can’t contract spontaneously
68
Q

Regulation of Ventilation

A
  • spontaneously firing networks of neurons in the brainstem

- network influenced by sensory and chemoreceptors, high brain enters

69
Q

Blackbox

A
  • considered as the neural control of ventilation
70
Q

Neurons in the Medulla

A
  • control inspirator and expiratory muscles
71
Q

Neurons in the Pons

A
  • integrate sensory info

- interact with medullary neurons to influence ventilation

72
Q

Rhythmic Pattern of Breathing comes from…

A
  • a neural network with spontaneously discharging neurons
73
Q

How is Ventilation Continuously Modulated?

A
  • by various chemo and mechanical receptor-linked reflexes

- by higher brain centers

74
Q

What Neurons are in the Medulla that Control Breathing

A
  1. nucleus tractus solitaris (NTS)
  2. dorsal respiratory group (DRG)
  3. pontine respiratory group (PRG)
  4. ventral respiratory group (VRG)
75
Q

NTS

A
  • contains the DRG

- receives input from the peripheral mechanical and chemoreceptors

76
Q

DRG

A
  • mainly control inspiratory muscles via phrenic nerve and intercostal nerve
77
Q

PRG

A
  • provides tonic input to DRG to help medullary network coordinate a smooth rhythm
  • doesn’t create the rhythm
78
Q

VRG

A
  • has a few areas with different functions
  • Pre-botzinger complex
  • control muscles of active inspiration and expiration
  • outputs that keep upper airways open
79
Q

Pre-Botzinger Complex

A
  • contain pacemaker neurons that may initiate respiration
80
Q

Slow Output in VRG

A
  • slows down too much while asleep
  • sleep apnea
  • snoring
81
Q

Upper Airways

A
  • tongue, larynx, pharynx
82
Q

Neural Activity During Quiet Breathing

A
  • believed to be initiated by a pacemaker
  • positive feedback loop recruits more neurons “ramping” recruiting more outputs to inspiratory muscles
  • activity shuts off abruptly after inspiration
83
Q

Peripheral Chemoreceptors

A
  • aortic and carotid bodies
  • sense changes in arterial PO2, PCO2, and pH
  • adjust ventilation accordingly
  • structurally similar to neruons
84
Q

Type I (Glomus) Cell

A
  • sensing changes in oxygen and pH
  • excitable cells
  • can send vesicles
  • has a variety of neurotransmitters (dopamine)
85
Q

Type II (Sustentacular) cells

A
  • like glia cells

- support cells

86
Q

It takes a _____ drop in arterial PO2 to trigger peripheral chemoreceptors

A

large

87
Q

Carotid Body

A
  • oxygen sensor

- releases neurotransmitter when PO2 decreases

88
Q

What Triggers Peripheral Chemoreceptors

A
  • can respond to increases in H+

- primarily respond to increases in CO2

89
Q

Glomus Cells Process

A
  1. Low PO2
  2. K+ channels close
  3. Cell depolarizes
  4. voltage-gated CA2+ channel opens
  5. Ca2+ enters
  6. exocytosis of neurotransmitters
  7. signal to medullary enters to increase ventilation
90
Q

Central Chemoreceptors

A
  • located in the medulla
  • provide continuous input to respiratory control centre
  • explained to respond mainly to changes in PCO2
  • respond to changes in pH in CSF caused by CO2, but not to changes in plasma pH
  • neurons in this region contain ASIC
91
Q

Can H+ cross the blood brain barrier well.

A

NO

92
Q

ASIC

A
  • H+ sensitive channel

- become activated and transmit AP’s to the respiratory control centre

93
Q

Decreased Arterial O2

A

d. inspired PO2
d. alveolar PO2
d. arterial PO2
peripheral chemoreceptor i.fire
respiratory muscles i.contract
i. ventilation
return of alveolar and arterial PO2 toward normal

94
Q

Increased Arterial H+

A
  • increase in H+ independent of CO2 increase

- peripheral mediated

95
Q

Increased Arterial CO2

A
  • most sensitive to changes in CO2

- mediated by both central chemoreceptors (70% primary) and peripheral chemoreceptors (30%)

96
Q

Irritant Receptors

A
  • in the lungs
  • respond to inhaled particles or noxious gases
  • send input to CNS, parasympathetic outputs and results in bronchoconstriction
  • leads to rapid shallow breathing and turbulent airflow to deposit irritant in mucosa
  • reflexes: coughing/sneezing
97
Q

Stretch Receptors

A
  • in the lung
  • prevent over inflation of the lungs
  • “Hering-Breuer inflation reflex”
98
Q

High Brain Centers

A
  • cerebral cortex
  • voluntary control over breathing
  • we can actively hold our breath until chemoreceptors take over
  • can breath out for set amounts of time –> higher control

Physiology 208 (11 decks)

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