Gas Exchange and Transport Flashcards
Atmospheric air
a gaseous mixture of approximately 78% nitrogen, 21% oxygen, 0.04% carbon dioxide, and minute amounts of other gases.
partial pressure of oxygen in atmospheric air
(pO2)
approximately 160 mmHg
partial pressure of carbon dioxide
(pCO2)
approximately 0.3 mmHg
When air and water meet at the respiratory membrane
each gas diffuses along its concentration gradient until its partial pressure in air equals its partial pressure in water
pO2
relatively higher in alveolar air, blood “loads” oxygen in the lungs
pCO2
relatively higher in alveolar blood, it “unloads” carbon dioxide in lungs
pO2 in alveolar air versus pO2 in the blood
pO2 in alveolar air is approximately 104 mmHg, while pO2 in the blood entering the capillaries is approximately 40 mmHg
oxygen in alveolar gas exchange
will diffuse along a pressure gradient out of the alveoli and into the blood
pCO2 in the blood versus in alveolar air
pCO2 in the blood entering the capillaries is approximately 46 mmHg while pCO2 in alveolar air is approximately 40 mmHg
The rate of alveolar gas exchange at high altitudes
the pO2 is low; pressure gradient is smaller and less oxygen diffuses into blood
The rate of alveolar gas exchange under hyperbaric conditions
pO2 is very high; pressure gradient is great, more oxygen diffuses into blood
Solubility of the gases in respiratory fluids
- Oxygen is only 5% soluble in blood plasma
- nitrogen is only 2.5% soluble in blood plasma
- carbon dioxide is the most soluble of the gases in blood plasma
it quickly diffuses even though it has smallest pressure gradient
Respiratory membrane
relatively thin so gases diffuse across it without difficulty
Surface area of the respiratory membrane
large enough to facilitate gas exchange
oxygen carried in the blood plasma
oxygen does not dissolve easily, so only 1.5% is carried in the blood plasma
formation of oxyhemoglobin (HbO2)
oxygen diffuses into the blood and quickly moves into erythrocytes where it combines with the heme portion of hemoglobin to form oxyhemoglobin
amount of oxygen carried as oxyhemoglobin
98.5%
oxyhemoglobin dissociation curve
the extent to which oxygen binds reversibly with hemoglobin depends on pO2 according to the oxyhemoglobin dissociation curve
oxyhemoglobin dissociation curve- at low pO2
(in tissue capillaries)- hemoglobin is only partially saturated
oxyhemoglobin dissociation curve- at high pO2
(in pulmonary capillaries) - hemoglobin becomes fully saturated
pCO2 in tissue cells
is approximately 45 mmHg, while pCO2 in tissue capillaries is about 40 mmHg
carbon dioxide diffusion
CO2 will diffuse along its pressure gradient out of the cells through interstitial space, into tissue capillaries where much of it will enter erythrocytes
carbonic anhydrase (CAH)
catalyzes reaction between carbon dioxide and water to form carbonic acid which dissociates into bicarbonate and hydrogen ions
Chloride shift
most bicarbonate ions are pumped out of erythrocytes and replaced with chloride ions duirng chloride shift, which maintains balance of anions
hyrdogen ions combine with
hemoglobin to prevent a change in blood pH
pO2 in tissue capillaries versus tissue cells
pO2 in tissue capillaries is about 95 mmHg, while pO2 in tissue cells is about 40 mmHg
oxygen diffusion
O2 will diffuse along its pressure gradient out of the blood through interstitial fluid into cells
how does pO2 in the tissues affect the rate at which oxygen is unloaded from oxyhemoglobin
low pO2 in the tissues promotes elease of oxygen from oxyhemoglobin
how does temperature affect the rate at which oxygen is unloaded from oxyhemoglobin
an increase in temperature causes more oxygen to be released from oxyhemoglobin
how does pH affect the rate at which oxygen is unloaded from oxyhemoglobin
a drop in pH causes more oxygen to be released from oxyhemoglobin (Bohr effect)
What affect do hydrogen ions have when they bind to hemoglobin
when hydrogen ions bind to hemoglobin- the 3-dimensional structure is altered and it reduces its oxygen- carrying capacity
BPG
a metabolic byproduct produced when erythrocytes break down glucose by glycolysis and its presence promotes oxygen unloading
Carbon monoxide
a colorless, odorless gas produced by incomplete combustion
carbon monoxide binding to hemoglobin versus oxygen binding to hemoglobin
carbon monoxide binds to hemoglobin 200 times more tightly than oxygen binds to hemoglobin, which drastically reduces oxygen-carrying capacity of hemoglobin
How much of the carbon dioxide generated is trasnported as dissolved gas in blood plasma
5%
The carbon dioxide transported as dissolved gas in blood plasma accounts for how much of carbon disoxide exchange between the blood and the alveolar capillaries
7%
How much of the carbon dioxide generated is trasnported as carbaminohemoglobin
5%
carbaminohemoglobin
when carbon dioxide binds to amino groups on the polypeptide chains of hemoglobin
The carbon dioxide transported as carbaminohemoglobin accounts for how much of carbon disoxide exchange between the blood and the alveolar capillaries
23%
a low pO2
results in less saturated Hemoglobin
How much of the carbon dioxide generated is trasnported as bicarbonate ions in blood plasma
90%
The carbon dioxide transported as bicarbonate ions in blood plasma accounts for how much of carbon disoxide exchange between the blood and the alveolar capillaries
70%
bicarbonate ions combine with hydrogen ions to do what
reform carbonic acid; carbonic anhydrase enzyme breaks it down into carbon dioxide and water
reverse chloride shift
chloride ions are removed from erythrocytes
where does carbon dioxide diffuse in order to be exhaled
out of the blood into alveoli
blood gives up dissolved carbon dioxide gas and carbon dioxide from carbaminohemoglobin _____ _____ than it gives up CO2 from bicarbonate ions
more easily
an increase of pCO2 has what affect on oxyhemoglobin
causes oxyhemoglobin to release its oxygen and transport more carbon dioxide
Chemoreceptors
in the medulla oblongata, carotid arteries, and aorta are senstive to changes in hydrogen ions, carbon dioxide, and oxygen in the blood
control of breathing during rest
aimed primarily at regulating the concentration of hydrogen ions in the brain
drowning victims
have water in their lungs because H+ builds up as result of insufficient ventilation (involuntary inspiration)
Normal blood pH
between 7.35 and 7.45
respiratory acidosis
when blood pH falls below 7.35 because of problems with pulmonary ventilation
respiratory alkalosis
when blood pH rises above 7.45 because of problems with pulmonary ventilation
common cause of respiratory acidosis
a slight increase in pCO2
when pCO2 rises above 43 mmHg
hypercapnia occurs and causes acidosis
what do chemoreceptors signal when acidosis occurs and why
inspiratory area to increase rate and depth of breathing
hyperventilation
allows the body to exhlae carbon dioxide faster than it forms; will shift carbonic acid reaction to left and get rid of hydrogen ions to bring pH up to “normal”
common cause of respiratory alkalosis
a slight decrease in pCO2
when pCO2 falls below 37 mmHg
hypocapnia occurs and causes alkalosis
what do chemoreceptors signal when alkalosis occurs
they do not signal inspiratory area- so rate and depth of brathing remain slow and shallow
hypoventilation
allows body to accumulate carbon dioxide faster than it can be exhaled; will shift carbonic acid reaction to right and produce more hydorgen ions to bring pH down to “normal”
oxygen concentration and the impact on respiration
oxygen concentration usually has little impact on respiration because hemoglobin is usually highly saturated
- only if arterial pO2 falls dramatically will ventilation be affected.
