Lecture 6: 20 Jan.
Gas Exchange
• CO2 exchange
• Regulating breathing
• Reading: 677-685, 620638
• If you need to review:
pg. 654-677
1
Quiz Date Confirmed
• Fri. 3 Feb., in class
• matching, labelling, calculations
• ~20 multiple choice
• practice questions on OWL soon
• office hours posted on OWL soon
2
1
Respiratory Pigments
• covered in Bio 2601…right?
• you’re expected to know it
• hematocrit?
3
Antarctic
• lives at –1.9oC
• no respiratory pigments
Icefish
• how does it get enough O2?
• possible advantage(s) to not having pigments?
• any other animals that don’t “need” pigments?
23.29
sort of
4
2
Pigments & O2 Carrying Capacity
24.4
what’s this?
5
𝐻𝑏 𝐻 + 𝑂2 ՞ 𝐻𝑏 𝑂2 + 𝐻 +
6
3
𝐻𝑏 𝐻 + 𝑂2 ՞ 𝐻𝑏 𝑂2 + 𝐻 +
7
𝐻𝑏 𝐻 + 𝑂2 ՞ 𝐻𝑏 𝑂2 + 𝐻 +
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4
What can change P50?
9
What can change P50?
what do we call this effect?
10
5
Hb at working tissues
11
CO2 Excretion
24.21
• where is CO2 produced?
• diffuses freely across
epithelia/membranes but…
• not very soluble “as is”
• interconvertable to HCO3- (bicarbonate)
• carbonic anhydrase within RBC
• most CO2 transported as HCO3-
CO2 + H2O  H2CO3  H+ + HCO3CA
12
6
CO2 Excretion: Working Tissues
• CO2 diffuses from tissue to plasma & RBC
• very little binds to Hb
• most converted to H2CO3 by CA, then to HCO3• what happens to H+? effect on Hb? name of effect?
• HCO3- transported to plasma
• band 3 (rapid anion exchange) protein, exchanges for Cl-
• CO2 transported as HCO3- in plasma
13
CO2 Excretion: Gas X Surface
• HCO3- can’t diffuse across membranes
• most re-converted to CO2 which diffuses out of lung/gill
• effect on equilibrium, process below?
CO2 + H2O  H2CO3  H+ + HCO3-
14
7
CO2 Excretion
• air breathers: a bit of a challenge
• fairly low [CO2] in air…but…
15
Blood Gases & Breathing
• mammal (air breather) chemoreceptors
• peripheral
• carotid, aortic bodies: detect?
• central
• medulla: detects?
• which is most important in regulating
breathing?
16
8
What regulates breathing?
• in air-breathers
• interpret the data
17
Unusual Air-Breathers
• where might CO2 be an issue for air breathers?
• how do they cope?
18
9
CO2 Excretion
• water breathers: usually pretty easy
– low [CO2] in water
– what happens to excreted CO2?
– consequences?
CO2 + H2O  H2CO3  H+ + HCO3-
 P − P2 
J = D  A 1

 X 
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What about water breathers?
filled circles
20
10
Gas Exchange: Bimodal Breathers
• O2: mostly lungs from air
• CO2: mostly gills to water
• requires re-routing of blood
video
21
Gas Exchange: Skin Breathers
• O2: lungs in air, permeable skin in water
• CO2: interpret the adult data
23.15
22
11
Unusual Water Breathers
• what nitrogenous waste do FW fish excrete?
• NH3: can diffuse across gill but NH4+ can’t
• NH3 basic (high pK’), so converted to NH4+ in most water: always a [gradient] for NH3
excretion
• “soda lake”: Lake Magadi, Kenya
• CO2 + HCO3 + CO32- = 180 mM, pH 10.5
• inhibits diffusion of CO2 across gills
• also inhibits excretion of NH3
• at pH 10.5, much NH4+ converted back to NH3, so reduced diffusion gradient for NH3
• Tilapia incorporate NH4+ & CO2 into urea, excrete in urine
23
Ornitihine-Urea
Cycle
24
12