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HN220 > Chapter 17: Respiratory System - Gas Exchange > Flashcards

Chapter 17: Respiratory System - Gas Exchange Flashcards

1
Q

what is pulmonary circulation?

A

a system of blood vessels that forms a closed circuit between the heart and the lungs

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2
Q

why are concentrations of O2 and CO2 constant?

A
  • oxygen moves from alveoli to blood at the same rate it is consumed by tissue cells
  • CO2 moves into alveoli from the blood at the same rate it is produced in the tissues
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3
Q

what is the circulatory pathway for pulmonary loop?

A

deoxygenated blood exits the right ventricle of the heart –> through the pulmonary trunk –> right and left pulmonary arteries –> arterioles and capillary beds in the lungs –> CO2 is released into the alveoli and O2 is absorbed into the blood –> blood passes through the capillary beds –> venules –> the pulmonary veins –> left atrium of the heart

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4
Q

what is the cirulatory pathway for systemic loop?

A

oxygenated blood is pumped from the left ventricle –> through the aorta –> through the systemic arteries –> arterioles and capillary beds that supply body tissues –> oxygen and nutrients are released and carbon dioxide and other waste substances are absorbed –> deoxygenated blood then moves from the capillary beds –> venules –> systemic veins –> inferior and superior venae cavae –> right atrium of the heart.

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5
Q

percentage composition of air

A

nitrogen = 79.04%
oxygen = 20.9%
carbon dioxide = 0.03%

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6
Q

how does oxygen and carbon dioxide move?

A
  • O2 and CO2 move between alveolar air and blood via diffusion down concentration gradients
  • the rate of transport is proportional to the magnitude of the concentration gradient and the surface area and permeability of the membrane
    –> oxygen is at a higher concentration in the alveoli = diffuses into the blood
    –> carbon dioxide is at a higher concentration in the blood = diffuses into the alveoli.
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7
Q

what is daltons law of partial pressure?

A
  • each gas contributes to the total pressure in proportion to its number of molecules
    partial pressure = total pressure / fraction of a gas
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8
Q

gas solubility in a liquid

A
  • gas molecules dissolved in a liquid have a certain partial pressure.
  • when a gas mixture and a liquid are in contact, gas molecules dissolve in the liquid until equilibrium is reached.
  • at equilibrium, the rate of gas molecules dissolving in the liquid equals the rate of gas molecules leaving the liquid and entering the gaseous phase.
  • dissolved gas molecules and those in the gaseous phase have the same partial pressure at equilibrium.
  • the concentration of gas molecules in the liquid is proportional to the partial pressure of the gas
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9
Q

physiological significance of solubility of gases

A
  • oxygen and carbon dioxide, the primary respiratory gases, must dissolve in the blood to facilitate gas exchange in the lungs
  • CO2 is more soluble in water (blood) than O2 is. N2 is almost insoluble.
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10
Q

what mechanism allows gas exchange to occur?

A
  • gas exchange in the lungs occurs via diffusion
  • gases move down pressure gradients, from high partial pressure to low partial pressure.
  • each gas diffuses down its own partial pressure gradient, and the presence of other gases is irrelevant to its diffusion.
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11
Q

what does gas exchange depend on?

A

1) thickness & surface area of respiratory membrane
2) solubility and partial pressure of gases

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12
Q

what happens if diffusion of gases is impaired?

A
  • hypoxia = too little oxygen to tissue
  • hypercapnia = too much CO2
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13
Q

gas exchange at the lung

A
  • the diffusion between alveoli and blood is rapid
  • this is due to a thin diffusion barrier and large surface area
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14
Q

what causes partial pressure to vary?

A
  • the amount of oxygen (O2) and carbon dioxide (CO2) exchanged in a vascular bed depends on the metabolic activity of the tissue.
    –> greater metabolic activity leads to a greater exchange of gases.
  • partial pressure of oxygen (PO2) and carbon dioxide (PCO2) in different systemic veins can vary.
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15
Q

gas exchange at respiring tissue

A
  • gases diffuse down their partial pressure gradients simultaneously
  • when the partial pressure of oxygen (PO2) in tissues is less than the normal (40 mmHg), and the PO2 in systemic arteries is higher (around 100 mmHg) = oxygen will diffuse from the blood into the cells to meet cellular metabolic demands.
  • when the partial pressure of carbon dioxide (PCO2) in cells exceeds the normal (46 mmHg), and the PCO2 in systemic arteries is lower (around 40 mmHg), carbon dioxide will diffuse from the cells into the blood for removal from the body.
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16
Q

partial pressure in veins/arteries

A
  • PO2 in systemic veins = 40 mmHg.
  • PCO2 in systemic veins = 46 mmHg
  • PO2 in systemic arteries = 100 mmHg
  • PCO2 in systemic arteries = 40 mmHg
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17
Q

3 factors affecting alveolar partial pressures

A

1) the partial pressure of O2 and CO2 of inspired air
2) the minute alveolar ventilation (the volume of air reaching the alveoli each minute)
3) the rates at which respiring tissue use O2 and produce CO2

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18
Q

hypernea

A
  • increased ventilation due to increased demand
    –> minimal changes to arterial PO2 and PCO2
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19
Q

hypoventilation

A
  • ventilation is insufficient to meet the metabolic demands of the body
    –> arterial PO2 decreases (not enough oxygen in the blood stream)
    –> arterial PCO2 increases (CO2 is not being effectively removed)
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20
Q

hyperventilation

A
  • ventilation exceeds the metabolic demands of the body
    –> arterial PO2 increases (excess of oxygen available in the bloodstream)
    –> arterial CO2 decreases (CO2 is effectively being removed)
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21
Q

how is oxygen transported in the blood?

A
  • oxygen is transported via binding to hemoglobin
  • oxygen is not soluble in plasma so only 1.5% of arterial blood O2 dissolved into plasma
    –> Hb = deoxyhemoglobin
    –> HbO2 = oxyhemoglobin
22
Q

steps to oxygen transport in blood

A
  • hemoglobin consists of 4 subunits containing a globin and heme group
  • each heme group can bind to one oxygen molecule, so it can carry 4 oxygens total
  • in the lungs, as oxygen moves from alveolar air to capillary blood, O2 binds to the hemoglobin
  • when the blood reaches respiring tissues, the O2 molecules dissociates and diffuses into cells
23
Q

what is key about oxygen binding to blood

A
  • hemoglobin MUST bind to oxygen reversibly (both bind and release O2 as needed)
  • it must be tight enough to pick up large quanities of O2 in the lungs but not too tight that it cannot release the O2 at the tissues
  • the binding or release of oxygen depends on PO2 in the fluid surrounding the hemoglobin:
    –> high PO2 of surrounding fluid = facilitates the binding of oxygen with hemoglobin in lungs
    –> low PO2 of surrounding fluid facilitates release of oxygen from hemoglobin (typically in tissues)
24
Q

oxygen carrying-capacity of blood

A
  • oxygen-carrying capacity of blood is primarily determined by hemoglobin, a protein in red blood cells.
  • hemoglobin can carry approximately 200 mL of oxygen per liter of blood.
    –> in arterial blood, hemoglobin is typically 98.5% saturated with oxygen = nearly all oxygen-binding sites on hemoglobin molecules are occupied.
    –> in venous blood, hemoglobin is 75% saturated with oxygen = less oxygen-binding sites on hemoglobin molecules are occupied
25
Q

saturation of hemoglobin

A
  • saturation of hemoglobin is a measure of how many binding sites on hemoglobin are occupied by oxygen.
  • hemoglobin can bind up to four oxygen molecules, and is said to be 100% saturated when there are 4
  • the binding of oxygen to hemoglobin follows the law of mass action: more oxygen leads to more binding to hemoglobin.
  • the ability of hemoglobin to bind oxygen depends on how many oxygen molecules are already bound
26
Q

what increases the affinity of O2 on hemoglobin?

A
  • once one O2 molecule binds to hemoglobin, it makes it easier for subsequent oxygen molecules to bind.
  • this is because it induces a conformational change that increases the affinity for remaining subunits of O2
  • therefore more O2 = greater percent concentration
    –> called positive cooperativitiy
27
Q

what is the hemoglobin-oxygen saturation curve?

A
  • represents the relationship between the percentage of hemoglobin saturation and the partial pressure of oxygen
  • as the partial pressure of oxygen (PO2) rises, the percentage saturation of hemoglobin also increases, but this trend is not linear.
  • this pattern is non-linear because hemoglobin eventually reaches a saturation point when PO2 levels/affinity are high causing all binding sites become occupied
28
Q

how does the concentration of O2 affect affinity to hemoglobin?

A
  • at low PO2 levels, hemoglobin has low affinity for oxygen, resulting in minimal saturation with a small increase in PO2.
  • as PO2 rises, hemoglobin binds more oxygen and its affinity for additional oxygen increases.
  • at very high PO2 levels, hemoglobin’s affinity increases, but fewer binding sites are available, causing saturation to plateau.
29
Q

what causes right or left shifts on the hemoglobin-oxygen curve?

A

RIGHT:
- decreases in affinity cause the curve to shift rightward, indicating that a higher PO2 is required to achieve any given level of saturation.
- a rightward shift also suggests that oxygen is unloaded more easily from hemoglobin, making it more available to the tissue.

LEFT:
- increases in affinity cause leftward shifts, indicating that a lower PO2 is required to achieve any given level of saturation.
- a leftward shift also suggests that oxygen is loaded more easily onto hemoglobin.

30
Q

what other factors affect affinity of hemoglobin for oxygen?

A

1) temperature
2) pH
3) CO2
4) 2,3-BPG
5) carbon monoxide

31
Q

how does temperature affect affinity of hemoglobin?

A
  • temperature alters the structure of the hemoglobin molecule which therefore affects its ability to bind to oxygen
  • as tissue metabolism and temperature increases, the affinity of hemoglobin for oxygen decreases = more oxygen is readily unloaded (released) and delivered to active tissues
  • as temperature decreases, the affinity of hemoglobin for oxygen increases = more oxygen loading (held onto) and blood has more O2 in it
    –> higher temps = decreased affinity = more unloading
    –> lower temps = increased affinity = more loading
32
Q

what is the Bohr effect?

A
  • based on the fact that when oxygen binds to hemoglobin, certain amino acids released hydrogen ions
33
Q

how does pH affect affinity of hemoglobin?

A
  • the effect of pH on the hemoglobin/oxygen curve is called the Bohr effect
    —> at low pH (acidic) = decreased affinity and oxygen readily dissociates from hemoglobin = more O2 unloading
    –> at high pH (basic) = increased affinity and oxygen sticks to hemoglobin = more O2 loading
  • when O2 binds to hemoglobin, an amino acids in a protein release H+. the ions can bind to hemoglobin which changes its conformation, consequently decreases its affinity for O2
34
Q

how does CO2 affect affinity of hemoglobin

A
  • CO2-carbamino effect leads to increased oxygen unloading in tissues
  • active tissues with high metabolic activity release CO2
  • CO2 binds with hemoglobin to form HbCO2
  • HbCO2 has lower affinity for oxygen compared to Hb
  • decreased affinity of HbCO2 for oxygen facilitates more oxygen unloading in active tissues
35
Q

how does 2,3-BPG affect affinity of hemoglobiin

A
  • 2,3-BPG is produced in red blood cells during low oxygen conditions (e.g., anemia, high altitudes).
  • High levels of oxyhemoglobin (HbO2) inhibits 2,3-BPG synthesis = no real affect on affinity
  • however when oxyhemoglobin levels are low (when O2 supply is low), 2,3-BPG synthesis increases = reducing hemoglobin’s affinity for oxygen = unloading of oxygen to tissues
  • the lower affinity facilitates oxygen unloading in tissues with high metabolic demands
36
Q

how does carbon monoxide affect affinity of hemoglobin

A
  • carbon monoxide is toxic
  • when CO is present, it binds to hemoglobin far more readily than O2 does
  • as a results, it prevents O2 from binding to haemoglobin and decreasing the oxygen carrying capacity of blood
  • this leads to decreased oxygen transport in the bloodstream
37
Q

presence of CO2 in blood

A

CO2 is more soluble in plasma than O2, but still not very soluble
–> 5-6% of CO2 is dissolved in plasma
–> 5-8% of CO2 is bound to hemoglobin as carbaminohemoglobin
–> 86-90% is dissolved in plasma as bicarbonate ions (HCO3-)

38
Q

how is CO2 present in bicarbonate ions?

A
  • the enzyme carbonic anhydrase facilitates the conversion of carbon dioxide (CO2) and water into carbonic acid (H2CO3).
  • carbonic acid dissociates into ions: H+ and HCO3-
    –> this follows the law of mass action as the increase in Co2 presence causes an increase in bicarbonate ad hydrogen ion concentration and VICE VERSA
39
Q

steps to carbon dioxide transport in blood

A
  • CO2 produced in tissues diffuses into the blood and then into erythrocytes (RBC).
  • inside the erythrocytes, carbonic anhydrase catalyzes the conversion of CO2 to bicarbonate (HCO3-) and hydrogen ions (H+).
  • bicarbonate (HCO3-) exits erythrocytes into the plasma in exchange for a chloride ion, a process known as the chloride shift.
  • hydrogen ions produced during bicarbonate formation bind to hemoglobin, acting as a buffer to maintain pH levels.
  • when erythrocytes reach the lungs, oxygen (O2) binds to hemoglobin, releasing the hydrogen ions (H+) from hemoglobin.
  • the released hydrogen ions (H+) react with bicarbonate ions (HCO3-) that have reentered the erythocyte to produce CO2 and water (H2O).
  • the CO2 produced in this reaction diffuses from the blood into the alveoli for exhalation.
40
Q

effects of oxygen on CO2 transport in blood

A

Haldane Effect: oxygenation of blood in the lungs displaces carbon dioxide (CO2) from hemoglobin, increasing the removal of CO2

  • oxygenated blood has a reduced capacity for CO2
    –> this is because O2 alters hemoglobin’s conformation = decreasing its affinity for CO2 = increased release of CO2 from hemoglobin into the bloodstream.
  • deoxygenation of blood increases its ability to carry CO2
    –> this is because a less of O2 creates a conformation on hemoglobin that enhancing affinity for CO2 = Increased binding of CO2 to hemoglobin in tissues = CO2 can be transported from tissues to lungs
41
Q

what are the effects of PO2 and PCO2 on loading and unloading?

A
  • in systemic tissues, as PO2 decreases and PCO2 increases = O2 offloads and CO2 loads onto hemoglobin because of low concentration of oxygen (therefore decreased affinity)
  • in the lungs, as PO2 increases and PCO2 decreases = CO2 offloads and and O2 loads onto hemoglobin because of high concentration of oxygen (therefore higher affinity)
42
Q

what are chemoreceptors?

A
  • monitor partial pressures of oxygen and carbon dioxide in arterial blood
  • they relay this information to the respiratory control center so it can adjust ventilation in response to changes in these variables
43
Q

role of central chemoreceptors

A
  • detect changes in the arterial partial pressure of carbon dioxide (PCO2) and hydrogen ion (H+) concentration
  • since CO2 can pass the blood-brain barrier and convert to bicarbonate (HCO3-) and H+ ions, changes in PCO2 indirectly influence H+ concentration in the cerebrospinal fluid.
  • are NOT activated by PO2 levels like peripheral receptors
  • when changes are detected, the receptors send impulses to the respiratory centres in the brainstem that initiate changes in ventilation to restore normal PCO2.
    –> detection of an increase in pCO2 = increase in ventilation = more CO2 is exhaled and the pCO2 level within the blood decreases to normal.
    –> detection of a decrease in pCO2 = decrease in ventilation = less CO2 is exhaled and the pCO2 level in the blood increase to normal
44
Q

role of peripheral chemoreceptors

A
  • are sensitive to cells in direct contact with arterial blood and communicate with afferent neurons
  • they detect large changes in the partial pressure of oxygen (pO2) but can also respond to changes in blood CO2 and pH
45
Q

peripheral vs central chemoreceptors

A
  • peripheral chemoreceptors are located in the carotid bodies near the carotid sinus
  • central chemoreceptors are located in the medulla oblongata
46
Q

importance of neural control in breathing

A
  • alveolar ventilation (the rate and depth of breathing) must be regulated to serve the metabolic demands of the body
  • this includes regulation the delivery/removal of CO2 and O2
47
Q

what motor neurons control breathing?

A

the muscles of respiration are skeletal muscles, so they must be stimulated to contract via neural input
- phrenic nerve = innervate the diaphragm
- intercostal nerves = innervate external and internal intercostal muscles
- respiratory centre in CNS

48
Q

2 respiratory centers

A

1) medulla oblongata
- contains both inspiratory and expiratory neurons that regulate transition between respiratory cycles
2) pons
- primarily responsible for setting the pace of respiration

49
Q

two groups in the medulla oblongata respiratory centre

A

1) Dorsal Respiratory Group (DRG):
- activates inspiratory muscles like external intercostals and diaphragm for inhalation
- involved in quiet breathing

2) Ventral Respiratory Group (VRG):
- engages during forced breathing or increases respiratory demand
- recruits accessory muscles for inspiration and expiration

50
Q

5 respiratory reflexes

A

1) chemoreceptors
- sensitive to PCO2, PO2, or pH of blood or cerebrospinal fluid
- peripheral (carotid and aortic bodies) and central (medulla)
2) baroreceptors
- sensitive to changes in blood pressure
- in aortic or carotid sinuses
3) stretch receptors
- respond to changes in lung volume
4) irritating stimuli
- in nasal cavity, larynx or bronchial tree
5) other sensations
- pain, body temp, sensations

51
Q

effects of blood CO2 and O2 on breathing

A
  • partial pressure of carbon dioxide (PCO2) is the primary stimulus for reflex control of ventilation.
    –> changes in PCO2 levels strongly influence respiratory drive and the rate of breathing
    –> high PCO2 levels stimulate ventilation, low PCO2 levels suppress it.
  • partial pressure of oxygen (PO2) modulates chemoreceptor sensitivity to PCO2.
    –> whne PO2 levels decrease (as in hypoxia), chemoreceptors become more sensitive to changes in PCO2.
    –> heightened sensitivity leads to an increase in ventilation, facilitating greater removal of CO2 from the body

HN220 (12 decks)

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