BIO Exam 2: Gas Exchange Flashcards
Gas Transport
To harvest energy from glucose, the glucose is burned
Glucose + 6 O2 → 6 CO2 + 6
H2ORequires O2 and generates CO2 as a waste product
These gasses are poorly soluble in water
Moving O2 and CO2 is largely done by the erythrocytes (red blood cells)
Erythrocytes (1)
Highly abundant: 25 trillion per adult~ 5 million per mL of blood
Biconcave disk: Higher SA/V than sphere
Moves single file through most capillaries
No nucleus – terminal, nondividing cell
No mitochondria
Highly specialized for O2 transport
Erythrocytes (2)
limited lifespan of about 100 days
2-3 million erythrocytes die per second
~2-3 million new erythrocytes per second
Macrophages consume old erythrocytes in liver and spleen by phagocytosis. Proteins are degraded to amino acids for recycling
Erythropoiesis
Stem cells in bone marrow
Stimulated by low oxygen levels in tissue through erythropoietin
Hemoglobin (1)
Each erythrocyte contains ~250 million molecules of hemoglobin (Hb)
Tetramer: Two a-globin and two b-globin proteins
Each protein is bound to a heme prosthetic group includes Fe2+, leading to the red color
The Fe2+ in heme binds to O2 when in hemoglobin. Reversible binding, depending on O2 concentration
Hemoglobin (2): Sequence and Structure
Sequence determines structure.
Structure determines function.
Gas Transport (2)
Erythrocytes move through circulation about every 60 seconds.
From pulmonary circuit to systemic circuit, repeat.
Gas Exchange in the Lungs
Air enters the lungs through the trachea
Branches to clustered air sacs (the alveoli)
Muscular diaphragm contracts, pulling down, to inflate lungs.
Tidal inflation
Each alveolus has a capillary network
O2 moves to erythrocytes
In other tissues, such as muscle, O2 leaves erythrocytes
Hemoglobin/O2 Binding
Cooperative
When one protein binds, it encourages the others to bind
Concentration of a gas (like O2) expressed as Torr or mm Hg
Alveoli capillaries:
about 100 mm Hg
Resting muscle: about 40 mm Hg
Active muscle: about 20 mm Hg
Myoglobin
Muscles produce a similar protein:
Myoglobin
monomer. No cooperative binding.
Short-term oxygen storage
Fetal Gas Exchange
different as:
Two a-globin subunits and two g-globin
CO2 Transport
Produced as a waste product
Crosses membranes by simple diffusion
Needs to be removed in the blood~10% of CO2 is dissolved in the plasma
Some diffuse into erythrocytes
Contains Carbonic Anhydrase
Carbonic Anhydrase
in muscle tissue, lots of CO2, leading to lots of bicarbonate
Bicarbonate is carried in the erythrocyte
In alveoli, CO2 is lost by diffusion into air
Carbonic Anhydrase catalyzes the reverse reaction
How Carbonic Anhydrase Affects Plasma pH
In muscle tissue, lots of H+ is produced. Blood is made slightly more acidic pH 7.4 → 7.2
In lung tissue, lots of H+ is removed. Blood is made slightly more basic pH 7.2 → 7.4
Hemoglobin/O2 Binding and pH: The pH change affects
hemoglobin’s O2 affinity
Acidic conditions in muscles cause a “right shift”
Some CO2 directly binds to hemoglobin at an allosteric site
Also leads to a right shift
Happens in addition to pH-dependent shift
Gas Exchange: In Alveoli and Tissues
In alveoli, hemoglobin binds lots of O2 due to:
High O2 concentration
Low CO2
More basic pH
In tissues, hemoglobin releases lots of O2 due to:
Low O2 concentration
High CO2
More acidic pH
