Gas transport and exchange Flashcards
what is the primary function of the respiratory system?
it is to exchange oxygen and carbon dioxide
what three processes are essential for the transfer of oxygen from the outside air to the blood flowing through the lungs?
ventilation
diffusion
perfusion
ventilation?
it is the process by which air moves in and out of the lungs
what is diffusion?
it is the spontaneous movement of gases without the use of any energy or effort by the body, between the gas in the alveoli and the blood in the capillaries in the lungs
what is perfusion?
it is the process by which the cardiovascular system pumps blood throughout the lungs
alveoli are sites of?
gas exchange
where does inhaled oxygen diffuse?
diffuses from the alveoli to the blood in the capillaries
where does carbon dioxide diffuse?
it diffuses from the blood in the capillaries to the air in the alveoli
diffusion distance is small (0.7um) so?
gas exchange is extensive
pulmonary venous blood will have the same concs of gases as?
as alveolar air
it is the process by which the cv system pumps blood throughout the lungs
what is partial pressure?
it is the pressure that would be exerted by one of the gases in a mixture if it occupied the same volume on its own
what are gas partial pressures determined by?
by total number of gas molecules per unit volume
where will a gas diffuse from and to?
from high to low partial pressure
partial pressures are sometimes displayed in?
in kPa
what does solubility of gases depend on?
partial pressure of a gas in mixture
chemical properties of gas e.g. CO2 is 20 x more soluble than O2
what are oxygen and carbon dioxide transported in?
in an aqueous liquid - the blood
which has the lower partial pressure of oxygen, alveoli/air?
alveolar
describe why the partial pressure of oxygen is lower in the alveoli than the air?
small proportion of alveolar air exchanged
continuous uptake of O2 into blood
contribution of pH2O (water vapour)
what can alveolar ventilation be determined from?
from arterial pO2 and pCO2
optimal gas exchange requires?
requires optimum ratio of ventilation (V) to blood flow (Q)
what does V/Q represent?
ratio of ventilation to blood flow
V/Q can be different for?
for different alveoli
describe V/Q in humans:
in humans, the base of the lung has a low V/Q compared to the top
what balances the V/Q across the lungs?
deeper breathing in exercise balances V/Q across the lungs
describe the V/Q of quadrupeds?
they have much more uniform V/Q already
what is V/Q mismatch?
it is when ventilation or perfusion is altered such that gas exchange is no longer optimal
lung disease (reduced V)
positional (large animal anaesthesia) (variable V and Q dependent on position)
Hypoxic vasoconstriction (reduced Q)
why is CO2 exchange less affected by V/Q mismatch?
due to higher diffusion gradient
what are the two oxygen carrying proteins?
haemoglobin
myoglobin
where is haemoglobin found?
in red blood cells in the bloodstream
where is myoglobin found?
in vertebrate muscle cells
how many oxygens can myoglobin carry?
it has one haem group so can carry one oxygen molecule
how many oxygens can myoglobin carry?
each haemoglobin molecules binds up to four oxygen molecules
as it has four haem groups
each bound oxygen molecule makes the next binding more likely - cooperative
each gram of haemoglobin can combine with?
combine with 1.34 mL of O2 and so for a haemoglobin concentration [Hb] of 150g/L blood can contain a maximum of 200mL/L of O2 (O2 capacity)
what does the actual amount of O2 bound to haemoglobin (O2 content) depend on?
depends on the pO2 and the percentage O2 saturation = content/capacity x 100
describe the left shift of the HbO2 dissociation curve:
high pO2 in the lungs facilitates O2 binding to haemoglobin
describe the right shift of the HbO2 dissociation curve:
low pO2 in the tissues facilitates O2 release from haemoglobin
what would cause the left shift of the HbO2 dissociation curve?
haemoglobin holds onto O2 more avidly
increased pH (metabolic alkalosis)
decreased temp
decreased pCO2
decreased 2,3-diphosphoglycerate (2,3-DPG) –> (metabolic by-product of glycolysis)
what don’t bind to 2,3-DPG?
foetal Hb and ruminant Hb don’t bind so are left shifted compared to adults or other species
what would cause the right shift of the HbO2 dissociation curve?
haemoglobin releases o2 more easily
decreased pH (metabolic acidosis)
increased temp
increased pCO2
increased 2,3-diphosphoglycerate
carboxyhaemoglobin?
haem sites bind carbon monoxide 210 times more tightly than o2
cherry red appearance of skin in humans
methaemoglobin?
iron in haem groups is Fe3+
normally Fe2+
can be a response to drug toxicity or genetic
consequence of paracetamol poisoning in cats
what is co2 produced by?
by tissues as by-product of metabolism
where does CO2 diffuse along?
along partial pressure gradient from cells to ISF to blood
what are the three ways in which carbon dioxide is carried in?
dissolved in plasma (10%)
bound to haemoglobin (20%)
as bicarbonate (hydrogen carbonate, HC03-) (70%)
carbaminohaemoglobin?
carbon dioxide does NOT bind to the haem group (compare with CO)
binds instead to amino (NH2) groups within the globin portion
binds more easily to deoxyhaemoglobin
describe the regulation of ventilation?
breathing is an automatic process
depth and frequency can be controlled voluntarily
breath holding is possible until pCO2 stimulis overrides
what is ventilation controlled by?
by the respiratory centre located within medulla oblongata
what is responsible for the rhythm of ventilation?
central pattern generator (Pre-Botzinger complex)
and it is influenced by sensory input form CO2, O2 and H+ chemoreceptors
where are central chemoreceptors located?
in the medulla oblongata and form synapses with neurones in the respiratory centre
exercise results in?
an increase in cellular metabolism which increases o2 demand and co2 production
why must cardiac output be higher during exercise?
to increase velocity of blood flow to the capillaries
what is erythropoietin a major regulator of?
major regulators of the oxygen-carrying capacity blood
acclimatisation factors for high altitude?
increased pulmonary ventilation
increased number of RBCs
increased vascularity in pulmonary capillaries and increased diffusing capacity of lungs
Increased levels of 2,3-DPG
increased cellular components
how can blood be adapted to function in a low oxygen environment?
higher haemoglobin concs
higher haematocrit
higher erythrocytic concs of 2,3-DPG
lower mean corpuscular haemoglobin concs
overall higher Hb but spread over more and smaller cells
smaller red blood cells
why do most animals have some form of oxygen carrying protein?
in order to increase oxygen carrying capacity
what oxygen carrying protein do most vertebrates have?
haemoglobin - gives the red colour
how is oxygen transported?
dissolved in plasma
cold liquids can carry more?
they can carry more dissolved gas
what is 2,3-diphosphoglycerate?
it is a metabolic by-product of glycolysis (increases any time oxygen delivery is insufficient for demand e.g. exercise, higher altitude, anaemia and resp distress)
what enzyme do erythrocytes contain?
they have the enzyme carbonic anhydrase
where is HCO3- transported for carbon dioxide transport and by what?
it is transported out of erythrocytes by carrier proteins in exchange for Cl-
describe the transport of carbon dioxide?
HCO3- is transported out of erythrocyte by carrier protein in exchange for Cl-
chloride shift
H+ remains inside the cell
H+ binds more readily to deoxyHb
Facilitates O2 unloading (Bohr effect)
holding your breath is possible until?
until partial pressure (pCO2) of co2 stimulus overrides
what initiates inspiration?
pacemaker inspiratory neurons initiate inspiration via a series of action potentials
after depolarisation, what does the elasticity of the lungs allow for?
allows for expiration
what is responsible for forced expiration?
expiratory neurones
what is the regulation of ventilation controlled by?
controlled by the resp centre located within medulla oblongata
what is the central pattern generator influenced by?
influenced by sensory input from CO2, O2 and H+ chemoreceptors
