Respiration Flashcards
respiration
exchange of O2 and CO2 between animals and environment
what does respiration involve?
gas exchange structure (i.e., lungs), circulation and release to tissues
series of processes involved in respiration
bulk transport, then diffusion, then convection, then diffusion
what process in respiration do very small animals (especially invertebrates) skip?
bulk transport
bulk transport AKA
ventilation of large volumes of air via a gas exchange structure (lungs)
what happens after bulk transport?
diffusion into circulatory system, then diffusion into tissues
Fick’s law
describes rate of diffusion
rate = K x A x ((C2-C1)/L)
K = constant, A = SA, C = concentration (2 = lungs; 1 = blood), L = distance of diffuson
how can you increase diffusion rate?
increase surface area, decrease distance of diffusion, increase concentration gradient (increase concentration in lungs or decrease concentration in blood)
how are lungs adapted to increase diffusion rate?
very high surface area, very thin tissue (decreases distance), and constant ventilation to keep concentration gradient high
lung structure in order
trachea > bronchi > bronchioles > respiratory bronchioles > alveolar ducts > alveolar sac > alveoli
conducting zone
bronchioles, bronchi, trachea
respiratory zone
where respiration occurs
respiratory bronchioles, alveolar ducts, alveolar sac, and alveoli
trachea
tube in throat - linked to pharynx in humans
respiratory bronchioles
special bronchioles where gas exchange can occur
what role does the conducting zone play?
- has mucus escalator - goblet cells secrete mucus; cillia beat upward to move mucus to pharynx (then swallowed)
- captures particulates (like dust)
what happens in cystic fibrosis
mucus escalator is compromised - mucus thickened, which obstructs airways and affects respiratory system
features of the respiratory zone (specifically alveoli)
super thin tissue (0.2-15 microns), huge surface area (1 human lung = 250 million alveoli, 65 sq m), thin and coated with watery solution (act like bubbles - high surface tension)
pleural sac/cavity
fluid-filled sac that encompasses lung and provides lubrication for smooth movement and holds lungs open
2 membranes (one by lungs - visceral and one by chest wall - parietal)
pleurisy
inflammation of pleural sac membrane due to infection
diaphragm
muscle at base of lungs - connected to pleural sac but not lungs
diaphragm shape when relaxed vs contracted
relaxed = arched (lengthens when relaxes)
contracted = flattened (shortens when contracts)
chest wall
rib cage, sternum, thoracic vertebrae, connective tissue, intercostal muscles
intercostal muscles
in between ribs; 2 sets: external and internal (antagonistic muscles)
connected to pleural sac (along with ribs)
external intercostal muscles
outside of ribcage - function is to lift ribcage
internal intercostal muscles
inside ribcage - function is to depress ribcage
at rest, the lung has a tendency toward collapse - why?
- of weight of chest cavity
- elasticity of lung tissue (always in a slightly stretched state - tendency of recoiling)
- surface tension in alveoli (has tension pulling inwards - collapsing while air inside has outward force)
collapse is opposed by
pleural sac and production of surfactant
how does the pleural sac oppose collapse?
fluid-filled (think about a syringe, liquids cannot be compressed or expanded) and drags lung along with any force applied on it
pleural sac is attached to diaphragm and ribs hold lung open
how does the production of surfactant oppose collapse?
detergent-like substance secreted by cells in alveoli - decreases surface tension in alveoli so they stay open
why does surfactant decrease surface tension
cannot blow bubbles with just water (too high surface tension) - need soap to decrease it
what is the release of surfactant triggered by?
stretch (inhaling)
why is surfactant important for mammalian newborns?
first breath of baby is to break open alveoli - lots of surfactant is produced right before birth to reduce surface tension so baby can inflate lungs
what role does the ventilator play for premature babies?
holds lungs open + supplies artificial surfactant
infant respiratory distress syndrome
baby is born before surfactant production begins (first breath is unable to open lungs due to high surface tension)
what is the consequence of the opposing collapse in the lungs?
there’s always some air in the lungs (retention of stale air)
3 main parts of the breathing cycle
tidal ventilation, inhalation, exhalation
tidal ventilation
like a tide = air enters and exit on same path
what happens during inhalation?
- contract external intercostals and diaphragm, expansion of chest cavity
- pulls on pleural sac and generates negative pressure below ambient in pleural fluid
- fluid follows pleural sac, pulls on lungs, lungs expand, negative pressure in lung so air is sucked in
what happens during exhalation at rest?
exhalation is completely passive - weight and elastic recoil makes lung volume smaller, positive pressure inside lung so it pushes air out
what happens during exhalation during activity?
same as rest (positive pressure in lung) PLUS contract internal intercostals, contract muscles of abdomen = helps reduce lung volume and increase positive pressure further, expelling air
what is a limitation of mammalian lung anatomy?
dead space
2 types of dead space
anatomical (structural) and alveolar (functional)
anatomical dead space
arises due to conducting structure of lung - volumes of air in conducting zone don’t contribute to gas exchange and lungs are open all the time (stale air mixes with fresh air reducing effectiveness)
alveolar dead space
not all alveoli are receiving air or blood all the time (so they don’t contribute physiologically)
physiological dead space
sum of anatomical + alveolar
very significant - normal resting breath = 350 mL fresh air in inhale but lung capacity is 3 L
what is the consequence of dead space?
significantly less O2 in air inside lung than in atmospheric air
what is the driving force of gases?
partial pressure
why is partial pressure used?
gas diffusion into a liquid is more accurately described by partial pressure than concentration gradient
what moves O2 into blood and CO2 out of blood?
partial pressure = driving force!
partial pressure
portion of total pressure that a single gas is exerting
sea level atmospheric air pressure
760 mmHg
partial pressure of O2 at sea level
0.21 x 760 = 160 mmHg
partial pressure of CO2 at sea level
0.03 x 760 = ~0 mmHg
partial pressure is dependent on
altitude
atmospheric air pressure in Calgary
667 mmHg
partial pressure of O2 in Calgary
0.21 x 667 = 140 mmHg
partial pressure of O2 in lungs is lower than atmospheric because
large presence of water vapour in lungs
higher pp of O2/lower pp of CO2 in atmospheric air than lungs does what?
drives O2 into and drives CO2 out of lungs
what does the solubility of O2 and CO2 depend on?
dissolvability in water depends on:
1. partial pressure of gas
2. temperature
3. salinity
how does partial pressure affect solubility?
higher pressure gradient means more dissolved gas - gas dissolves until pp in fluid = pp in air
how does temperature affect solubility
cold water means more gas dissolved
how does salinity affect solubility?
less salt means more gas can dissolve
is O2’s partial pressure higher or lower at the top of Mt. Everest than in Calgary?
lower
Assuming constant pp, is there more O2 in salt or fresh water at the same temperature?
fresh water
Assuming constant pp, is there more O2 in a Petri dish containing fresh water or a plasma sample at same temperature?
fresh water - plasma = H2O based solution but has higher salinity
Assuming constant pp, is there more O2 in hot or cold tap water?
cold tap water
comparative ventilation
gas exchange surface area (lungs, alveoli, gill tissue, etc.) matches O2 demand
as body size increases, how does gas exchange surface area change?
also increases
bigger animals have more cells because they have a greater demand for cellular respiration and O2
how does gas exchange surface area differ in endotherms and ectotherms?
more SA in endotherms (i.e., frog and mouse may have same body weight but gas exchange SA higher in mouse)
heat regulation requires more energy and O2
bird ventilation steps
inhale #1 = to posterior air sac (expands)
exhale #1 = to rigid lungs and some back to main airway
inhale #2 = to anterior air sac
exhale #2 = out of body
what is one difference between bird and mammalian lungs?
bird lungs are rigid - do not change in shape or size
why do birds need to extract more O2 than mammals?
because they fly which requires lots of O2
do birds have tidal ventilation?
no - one way continuous flow (doesn’t go out/in on the same path)
does bird ventilation have dead space?
no - stale air and fresh air do not mix (the air that goes back to main airway from posterior air sac is still fresh!)
insect ventilation systems tend to involve
a network of gas-filled tubes (no lungs)
what is the network of gas-filled tubes in insects called?
tracheal system
how does fresh air enter the tracheal system in insects?
through pores of body surface or aquatic insects may have gill-like structures or hollow hairs
invertebrates that don’t fly use what for gas exchange?
diffusion (no lungs or tracheal system)
why are insect ventilation systems so specialized?
flying is energetically costly - air movement through passive diffusion (no active pumping)
what are some challenges that might make breathing hard for aquatic organisms?
water has higher density than hair, O2 is less soluble in water than air (low O2 content), water is viscous and heavy (hard to move)
gills
external filamentous tissues used for gas exchange
gills can be either
fully externalized (no protective structure around them) or covered gills (external to body cavity but have hard structure covering them)
fish gills have a specialized type of flow
countercurrent (opposite)
blood: flows posterior to anterior
water: flow anterior to posterior
flow of water in/out fish body
active pumping into mouth, over gills and out through operculum opening (anterior to posterior)
how does countercurrent flow affect O2 pickup capabilities?
higher efficiency of extraction - consistent concentration gradient exists along whole length of the gill
what type of flow do mammalian lungs use?
concurrent (same direction)
may have some limitations but gets the job done (air also has more O2 than water)
what type of flow do bird lungs use?
cross-current (specialized flow system) - better than concurrent but not as good at countercurrent
flow of respiratory medium (air) is almost perpendicular to flow of blood (like a grid)
why are ventilation and perfusion matched?
too much movement = waste of energy while moving too little = not meeting energy demands
perfusion
blood flow
V/Q ratio
V = ventilation; Q = perfusion (volumetric flow rate)
e.g. 1:1 = 1 unit of air per 1 unit of blood; 2:1 = 2 units of air per 1 unit of blood
V/Q ratio of mammals (whole lung)
1:1
V/Q ratio of fishes (whole gill)
~10 (10 units of water:1 unit of blood)
challenge for fish in terms of V/Q
water has less O2 than air and fish blood carries half the amount of O2 as mammalian blood (not good at carrying O2)
2 opposing problems
how do fishes overcome lower solubility of O2 in water?
increase ventilation (increase V - send more water), reduce blood flow (decrease Q)
how do fishes overcome their blood carrying less O2?
reduce water flow (decrease V), send more blood (increase Q)
net effect of fish overcoming its 2 challenges of less O2 in water and in blood
an overall increase V and decrease Q to make V/Q ratio ~ 10 (10 units of water for 1 unit blood)
what is the underlying issue of low V/Q
too much blood (Q too high) and not enough air (V too low)
how does the mammalian lung correct for too much blood - high Q?
too much CO2 present
smooth muscles in alveolar duct are sensitive to CO2 increases - triggers them to relax and opens alveolar duct to let air carry CO2 away
how does the mammalian lung correct for too little air - low V?
too little O2 present
vascular smooth muscle in capillaries are sensitive to O2 decreases - contract when O2 low (constricts blood vessels and reduces blood flow Q)
what does decreased O2 usually lead to in smooth muscle?
relaxation - but in vascular smooth muscle, causes constriction to decrease Q since V is so low
at altitude, how does the partial pressure of O2 change?
decreases
at altitude, how does blood flow change?
decreases
pulmonary edema
happens at high altitudes (low blood flow) where constriction raises blood pressure in lung and causes rupture of capillaries
also drives fluid out of vessels and into alveoli, reducing gas exchange abilities
what is the problem with the dissolved O2 levels in our blood?
not enough to supply tissues
metabolic demand at rest (resting metabolic rate, VO2 rest)
consume 250 mL O2/min
blood flow at rest
heart circulates 5 L blood/min
blood plasma O2 solubility
3 mL O2/L blood (really low solubility)
how much O2 does blood plasma deliver?
5 L blood/min x 3 mL O2/L = 15 mL O2/min
(less than our VO2 rest = 250 mL O2/min)
steps of oxygen getting taken up by blood + Hb
- High PO2 in lung causes O2 to dissolve in the plasma (low PO2 in blood)
- Raise PO2 of blood with dissolution - drives Hb to pick up blood
- O2 binding to Hb reduces blood PO2
- Low blood PO2 now lets more O2 dissolve (loops back to step 1)
oxygen dissociation curve
shows relationship between amount of O2 dissolved in body and held by Hb
what are the axes labels on an oxygen dissociation curve?
y-axis = % saturation of Hb (100% = 4 O2, 50% = 2 O2, etc.)
x-axis = PO2
for Hb, what is the shape of the oxygen dissociation curve?
s-shaped - shows cooperativity
increases O2 affinity as more O2 binds
for Mb, what is the shape of the oxygen dissociation curve?
square-root (curved) - no cooperativity
only 1 O2 binding site
Mb
myoglobin - supplies O2 to muscles
lungs on oxygen dissociation curve
at plateau - some wiggle room to change PO2 without affecting O2
tissues on oxygen dissociation curve
at increase (slope) - change in PO2 changes saturation
exercising muscle uses O2; what does this do to the PO2 in this tissue?
lowers PO2 (decrease due to decrease in O2 saturation)
fresh blood arrives to exercising muscle; how does Hb respond to the decreased PO2 in that tissue?
decrease in saturation of O2 = Hb will release its O2
how is affinity for Hb for O2 measured?
P50
P50
partial pressure needed to saturate Hb to 50%
how does affinity for O2 changes with P50?
higher the P50, the lower the affinity
(need to work harder to get Hb to pick up oxygen)
myoglobin vs hemoglobin affinity for O2
higher affinity in Mb (lower P50) - O2 preferentially binds to Mb
Hb affinity for O2 is reduced by
heat, presence of organic phosphates (ATP), lowered pH, increase in CO2
properties of muscle use (exercise)
Bohr shift
right shift in Hb affinity for O2 based on pH (more acidic - pH<7.4)
reverse Bohr shift
left shift in Hb affinity for O2 based on pH (more basic - pH>7.4)
Hb affinity for O2 at lower pH
lower (higher P50) when acidic
Hb affinity for O2 at higher pH
higher (lower P50) when basic
why does a lower pH cause lower Hb affinity for O2?
more acidic conditions indicate increased CO2, so encourages Hb to release O2
Root shift
down shift in Hb affinity for O2 based on pH
which is given more priority: Bohr shift or Root shift?
Root shift (down shift)
what happens with a root shift?
max out at <100% saturation
which animals can root shift?
some animals like fish (NOT mammals)
mechanism for root shift in fish
fill swim bladder - secrete lactic acid into tissues near swim bladder, causes root shift and helps force Hb to release O2 which gets shuttled to swim bladder
some fish do this in eye + brain - keeps metabolism higher here for higher function
after exposing a respiratory pigment to H+, you find that its P50 for O2 has increased; how has its affinity for O2 changed?
decreased affinity
name 4 ways Hb’s affinity for O2 can be reduced
heat, presence of H+ ions, organic phosphates, CO2
thinking about the V/Q ratio at the whole-lung scale, if we observe that V is increasing, what is happening?
V = ventilation - breathing faster
after CO2 dissolves in water, what happens?
enter carbonic acid reaction
carbonic acid reaction
CO2 + H2O ⇔ H2CO3 (carbonic acid) ⇔ H+ + HCO3- (bicarbonate) ⇔ 2H+ + CO3(2-) (carbonate)
what catalyzes the carbonic acid reaction?
carbonic anhydrase (enzyme)
which is favoured more in the carbonic acid reaction: bicarbonate or carbonate ion?
bicarbonate (yields 1 H+)
3 places CO2 can be found in blood
dissolved (20x more soluble than O2), bound to Hb, tied up in a bicarbonate
where is the majority of CO2 in blood found?
tied up in bicarbonate (70-80%)
what type of CO2 counts toward PCO2?
dissolved CO2 (~10% of CO2)
Haldane effect
Hb with less O2 has higher affinity for CO2 and H+ so Hb carries more CO2 and H+
chloride shift
rapid anion exchange protein exchanges bicarbonate for chloride ion (moves bicarbonate ion out of the RBC)
what range of pH do we tolerate?
7.0-7.6 (blood is usually ~7.4)
methods for regulating blood pH
use bicarbonate, get rid of H+, adjust ventilation
how do we use bicarbonate to regulate blood pH?
shift carbonic acid reaction toward CO2 + H2O (shift left) to use up extra H+
kidneys: expel bicarbonate (reaction shifts right), causing increase in H+ and lowers pH
how is H+ regulated to regulate blood pH?
kidneys: expels H+, raises pH
proteins: “soak up” H+ (including some H+ on Hb) to raise pH - very effective
difference between changing pH in blood vs water
500,000x more H+ required to changes pH of blood than water
most of blood pH regulation is through
breathing (adjusting ventilation)
how do we adjust ventilation to regulate blood pH?
respiratory alkalosis or respiratory acidosis
respiratory alkalosis
breathe faster - increases V which increases V/Q ratio which decreases CO2 in blood; this uses up H+ in carbonic acid reaction (to replenish CO2) and raises pH
respiratory acidosis
breathe slower - decreases V and lowers V/Q ratio which causes build-up/backlog of CO2, pushing carbonic acid reaction toward H+ and lowers pH
how else do aquatic animals regulate blood pH?
exchange ions over skin and gills
how are ions exchanged in aquatic animals to regulate blood pH?
- active H+ pumps - use ATP to move H+ outside of body (raises pH)
- pump bicarbonate out through chloride shift and carbonic acid reaction shifts right to replenish + increases H+ (lowers pH)
2 categories of sensors for respiratory gases
peripheral sensors (PNS) and central sensors (CNS - monitor cerebrospinal fluid)
what is sensed to control respiratory gases?
O2 and pH (proxy for CO2)
3 major sensors in mammals
aortic arch, carotid arteries, medulla
aortic arch
peripheral sensor, shuttle blood to body from heart - sense O2, blood volume and hematocrit
carotid arteries
peripheral sensor, supplies blood to brain - sense O2, blood volume and hematocrit
medulla
central sensor, at base of brain leading to spinal cord - senses pH in CBSF
why do air-breathing animals primarily monitor pH?
always have 21% O2 in air, O2 is consumed and CO2 is produced at same rate, both are moved using the lungs at the same time
SO if we monitor for CO2, we end up with right amount of O2
role of O2 sensors in air-breathing animals
back-up plan - we don’t use these sensors in healthy, normal conditions unless O2 levels get very low
water-breathing animals primarily monitor
O2 - peripheral sensors
air-breathing animals primarily monitor
pH (CO2) - central sensors
why do water-breathing animals primarily monitor O2?
- very little O2 in water
- O2 levels in water vary a lot (e.g. temp affects solubility)
SO must adjust breathing to compensate for changes in O2
to control respiratory gases, how do we respond to change?
increase or decrease ventilation
how does your breathing changes when you start to exercise (ways mammals change V)?
breathe faster or breathe deeper
hypoxia
low O2 in tissues - a form of respiratory stress
why is hypoxia rare for air-breathers under normal function?
tons of O2 present in air
causes of hypoxia
breathing very slowly, lung diffusion limitations, altitude, suffocation (not enough O2 in air), impaired ability to carry O2 in blood
what are some examples of lung diffusion limitations that could lead to hypoxia?
infant respiratory distress syndrome, pulmonary edema, emphysema (loss of alveolar SA, stiff lungs)
what would impair ability to carry O2 in blood?
severe blood loss, anemia, CO poisoning
why is hypoxia more common in water-breathers
limited O2 levels in water
how are the low levels of O2 in water dealt with by water breathers?
increase V, grow more gill tissue (increase SA), metabolic depression (reduce BMR to reduce O2 consumption)
how is respiratory stress dealt with by diving mammals?
some hypoxic tissues during dives - can prioritize which tissues get O2
how is respiratory stress dealt with by carps (goldfish)?
they can tolerate anoxia (no O2) via a fermentation system where they produce lactic acid and convert it to alcohol which is diffused out of gills
O2 demands varies based on
activity level
how can O2 demand higher than the VO2 max (aerobic MR) be met?
by supplementing with anaerobic metabolism to reach the highest activity level
O2 needs during submaximal activity (<VO2 max) - e.g. easy job
real O2 consumption lags behind activity’s O2 demand
O2 deficit on O2 demand vs time graph
takes time for body to ramp up and supply O2 to match demand
EPOC
excessive postexercise oxygen consumption - consuming more O2 than activity demands (recovering from fatigue)
how does EPOC change with activity
increases - longer with higher level of activity (need more time to cool down)
why is our O2 demand non-zero at rest?
we have non-zero MR (BMR)
O2 needs during supermaximal activity (at >VO2 max)
prolongs EPOC and O2 demand is supplied by anaerobic metabolism
