Transcript Respiration2

Gas Exchange
Gas Exchange
• Animals need a supply of O2 and a means of
expelling CO2
• They are the reactants and products of cellular
respiration
Respiratory medium
• Atmosphere has O2 at a partial pressure of
~159 mmHg
– Varies with altitude, its about half as much at
18,000 feet above sea level
• Water has ~ 1 ml of O2 per 100 ml of H2O at
0o Celsius
– Varies with solubility, pressure, salts, and
temperature
– 0.7 ml of O2 per 100 ml of H2O at 15o Celsius
– 0.5 ml of O2 per 100 ml of H2O at 35o Celsius
Water vs. air as a medium
• Water
• Keeps the cells moist
• Lower oxygen
concentration than
air
• Concentration varies
more
• Water is heavier
•
•
•
•
Air
Higher conc. of O2
Faster diffusion
Needs less
ventilation
• Water is lost by
evaporation
• So lungs have to be
interior
Diffusion
• Cells are aquatic
• O2 has to be dissolved across a respiratory
surface to get to cells
• O2 can diffuse through a few mm of cells
• If a part of your body is more than a few mm
thick then you need a way to carry the oxygen
• Need a large respiratory surface area
Skin breathers
• Earthworms
– Keep skin moist and exchange gases across their
entire surface
• Amphibians
– Supplement their lungs with gills
Form and function
• Depends on whether
environment is terrestrial or aquatic
• Simple animals have nearly every plasma
membrane in contact with the outside
environment
–
–
–
–
Protozoans
Sponges
Cnidarians – hydra, anemones
Flat worms
• Lungs/gills
– Highly folded or branched body region
– Creates a large surface area for absorption
• Gills
– External
– Problem - losing water due to
osmolarity of salt water
• Lungs
– Internal – prevents drying out of
membranes
– Allow use of air as a medium
– Terrestrial life poses problem of
dessication
Gills
• Invertebrates can have simple gills
– Echinodermata: have simple flaps over
much of their body
– Crustaceans: have regionalized gills
• Ventilation: have to keep water
moving over the gills, either by
paddling water in or staying on the
move
– This requires energy
– Gill slits of fish are believed to be
evolutionary ancestors of Eustachian
tubes
Invertebrate gills
Gills
•Specialized for gas exchange in water.
•Have to be efficient – 10,000X less O2 in water than in air.
•O2 and CO2 readily diffuse between blood and water.
•Countercurrent Exchange: blood in capillaries flows
in opposite direction from the water passing over the
gills.
Along the capillary, a steep
diffusion gradient favors transfer
of oxygen into the blood.
Countercurrent Flow in Sharks
Countercurrent vs. Concurrent Flow
Countercurrent exchange
• Speeds transfer of O2 to blood
• Blood and water move toward each
other in gills so as blood is more loaded
with O2 it’s running into water with even
more O2 dissolved so it can take on the
maximum load
– Gills can remove 80% of the oxygen from
the water passing over it
Tracheae
•
•
•
•
Spiracles are holes all over an insect’s body.
From the spiracles, tubes branch out
Finest branches (0.001mm) reach every cell
Insects still have circulatory system to carry
other materials
Respiratory Exchange
in Insects
Spiracles of Two Insects
Lungs
• Dense networks of capillaries under epithelium forms
the respiratory surface
• Snails: Internal mantle
• Spiders: book lungs
• Frogs: balloon like lungs
• Vertebrates: highly folded epithelium
– humans (~ 100m2 surface area)
Lungs
• Enclosed by double walled sac
whose layers are stuck together
by surface tension, allowing them
to slide past each other
• System of branching ducts
• Nasal cavity  pharnyx  open
glotis  larynx (voicebox) 
trachea (windpipe)  2 bronchi
(bronchus)  many bronchioles 
cluster of air sacs called alveoli
(alveolus)
Pulmonary Circulation
Alveolar Exchange
Ventilating the Lungs
• Frogs use positive pressure breathing:
gulp air and push it down
• Mammals: negative pressure breathing
– Suction pulls air down into a vacuum
– During exercise rib muscles pull up ribs
increasing lung volume, and lowering
pressure
– But ribs are only ~ 1/3 of Shallow breathing
Diaphragm
• Sheet of muscle at bottom of thoracic cavity
• During inhalation: it descends
• During exhalation: it contracts
Volumes
• Tidal volume: The volume of air inhaled/exhaled
– ~500 ml in humans
• Tidal capacity: maximum volume
– ~3400 ml for girls 4800ml for boys
• Residual volume: air left in alveoli after exhalation
Control
• Medulla oblongata and pons
– negative feedback loop: when
stretched too much lungs send
message back to brain to
exhale
– CO2 levels are monitored
in the brain
• CO2 dissolves in water and
forms carbonic acid with
sodium carbonate salts
• More carbonic acid lowers
pH of blood and the medulla
responds by increasing
depth and rate of breathing
Hyperventilating
• Trick the brain by
purging blood of CO2
so breathing slows
Loading/Unloading Gases
•
•
•
•
•
•
Substances diffuse down the Conc. Grad.
In the atm. there’s 760 mmHg of gas
O2 is 21% of this so 0.21 x 760 = 159 mmHg
This is the partial pressure of oxygen PO2
CO2 partial pressure(PCO2): 0.23 mmHg
Liquids in contact with air have the same partial
pressure
Gas Exchange at Alveoli
•
•
•
•
Blood at lung: high PCO2 and low PO2
At lungs CO2 diffuses out and O2 diffuses in
Now blood has a low PCO2 and high PO2
In cells doing respiration there is a high PCO2 and low
PO2 so the CO2 diffuses into blood and O2 diffuses
into the cells
Gas Exchange Throughout
the Body
Respiratory pigments
• Colored by metals
• Invertebrates have hemocyanin which
uses copper making blood blue
• Vertebrates: hemoglobin which uses
iron to carry the oxygen. Each
hemoglobin can carry 4 O2s, each blood
cell has many hemoglobins
If blood is red why do your veins
look blue?
• Blood is a bright red in its oxygenated form (i.e., leaving
the lungs), when hemoglobin is bound to oxygen to form
oxyhemoglobin. It's a dark red in its deoxygenated form
(i.e., returning to the lungs), when hemoglobin is bound
to carbon dioxide to form carboxyhemoglobin. Veins
appear blue because light, penetrating the skin, is
absorbed and reflected back to the eye. Since only the
higher energy wavelengths can do this (lower energy
wavelengths just don't have the *oomph*), only higher
energy wavelengths are seen. And higher energy
wavelengths are what we call "blue."
• From straightdope.com
Dissociation curves
• Changes in PO2 will cause hemoglobin to pick up or
dump oxygen
• Lower PO2 means hemoglobin will dump oxygen
• Bohr shift: Drops in pH makes hemoglobin dump O2
Diving mammals
•
•
•
•
Weddell seals
Dive 200 – 500 m
20 min – 1 hr. under water
Compared to us it has ~ 2x
as much O2 per kg of weight
• 36% of our O2 is in lungs 51% in blood
• Seals have 5% and 70% respectively
– more blood, huge spleen stores 24L blood
– More myoglobin (dark meat)
– Slow pulse
Liquid Ventilation
• Perfluorocarbon liquids –
• ~65 mL O2 per 100 mL
• Problems with expelling the
CO2
• Remember this is a liquid
1.8 times as dense as water
so it is hard to breath
• Could someday be used for
diving, or medical
applications (ex: supporting
injured lungs, radiology)