Download bio20 9.2 - Stirling School

Gas Exchange and
Transport
Section 9.2
Dalton’s Law of Partial
Pressure
 Each gas in a mixture exerts its own pressure or partial
pressure.
Partial Pressure
 Oxygen has its highest partial pressure in the
atmosphere.
 Gasses move from areas of high concentration to areas
of low concentration.
 Therefore, oxygen moves from the atmosphere and
diffuses in the lungs.
Arteries Capillaries and Veins
 Picture here
Arteries
 Carry oxygenated blood away from the heart.
Veins
 Carry deoxynated blood back to the heart
Capillaries
 Connect arteries and veins
 The site of gas exchange
Partial Pressure cont.
 Carbon dioxide has its highest pressure in the tissues
of the body.
 Therefore, carbon dioxide will diffuse out of the tissues.
Oxygen Transport
 Oxygen moves from atmosphere, to the the alveoli, to
the blood and dissolves in blood plasma.
 Plasma: Colorless fluid part of the blood
Hemoglobin
 The Oxygen carrying molecule.
 Contains iron that binds with oxygen.
 Oxyhemoglobin: Hemoglobin bonded to oxygen.
 Hemoglobin drastically increases the bloods capacity to
carry oxygen. (70 times greater)
Breakdown of Oxyhemoglobin
 Ultimately, oxygen must be released in order for uptake
by the cells.
 Partial pressure dictates the dissociation of the
oxyhemoglobin molecule.
 At 5.3 kpa dissociation occurs.
So What?
 Important because this is the partial pressure at the
capillaries.
 Oxygen is made available at the site of gas exchange.
 Nice adaptation eh?
Venous Blood
 Is the blood returning to the heart void of oxygen?
 No!
 70% of the hemoglobin still carry oxygen at their
binding sites.
Carbon Dioxide Transport
 Carbon D. is 20 times more soluble in the blood than
oxygen.
 9% of Caron D. is carried in the blood
 27% combines with hemoglobin
 64% combines with water to form carbonic acid
Formation of Carbonic Acid
Carbonic Anhydrase
 An enzyme
 Speeds up chemical rxn’s
 Carbonic Anhydrase speeds the conversion to carbonic
acid by 250 times.
Carbonic Acid
 This allows for a rapid way to deal with build up of
Carbon D. in the blood plasma
 The rxn also maintains a low partial pressure of Carbon
D. in the blood (carbon d. continues to diffuse into
blood.)
Problem
 Carbonic acid will lower the pH of the blood.
 If we alter the pH of the blood too much the
consequences could be catastrophic.
Solution
 Hemoglobin can work as a buffer.
 Carbonic acid dissociates to bicarbonate ions and
hydrogen ions.
Dissociation of Carbonic acid
Hemoglobin Buffer
 Hydrogen ions help dislodge oxygen from hemoglobin.
 Hemoglobin bind with hydrogen ions, thus, removing H
ions from the solution. (raises pH or buffers the soln.)
 Oxygen that has been removed is now free for
exchange at capillaries.
 At lungs, oxygen dislodges hydrogen ions from
hemoglobin.
 Free Hydrogen ions and bicarbonate combine to form
water and Carbon D.
 Highly concentrated Carbon D. diffuses out of blood
into alveoli, and expelled through exhalation.
At Lungs
Maintaining Gas Levels
 Chemical receptors are commonly employed to ensure
carbon d. and oxygen levels are maintained at proper
levels.
Maintenance of Carbon D.
Levels (Example)
 Exercise leads to a build up of carbon d.
 Chemical receptors are triggered in the brainstem
 Causes muscles that control breathing rate to operate
at increased levels
 Carbon D. is flushed from the body
Summary
Summary