GAS TRANSPORT
&
CONTROL OF RESPIRATION
GAS TRANSPORT
•
Blood transports Oxygen and Carbon
dioxide between lungs and the tissues of
the body
• These gases are transported in different
states
1. Dissolved in plasma
2. Chemically combined with hemoglobin
3. Converted to a different molecule
Oxygen Transport
• Due to low solubility,
only 1.5 % of oxygen is
dissolved in plasma
• 98.5 % of oxygen
combines with
hemoglobin
• Each Hb consists of a globin portion composed of 4
polypeptide chains
• Each Hb also contains 4 iron containing pigments called
heme groups
• Up to 4 molecules of O2 can bind one Hb molecule
because each iron atom can bind one oxygen molecule
• There are about 250 million Hb hemoglobin molecules
in one Red Blood Cell
• When 4 oxygen molecules are bound to Hb, it is 100%
saturated, with fewer, it is partially saturated
• Oxygen binding occurs in response to high partial
pressure of Oxygen in the lungs
• Oxygen + Hb  Oxyhemoglobin (Reversible)
• Cooperative binding  Hb’s affinity for O2
increases as its saturation increases (similarly its
affinity decreases when saturation decreases)
• In the lungs where the partial pressure of oxygen
is high, the rxn proceeds to the right forming
Oxyhemoglobin
• In the tissues where the partial pressure of oxygen
is low, the rxn reverses. OxyHb will release
oxygen, forming again Hb (or properly said
deoxyhemoglobin)
Oxygen-Hemoglobin Dissociation Curve
• Hb saturation is determined by the partial
pressure of Oxygen
• @ High partial pressures of O2 – lungs – Hb is
98% saturated
• @ Low partial pressures of Oxygen – tissues –
Hb is only 75% saturated
• “S” shape is a trademark of its cooperative
binding interaction – the binding of one oxygen
molecule increases Hb’s affinity for binding
additional oxygen molecules
Other factors altering Hb saturation
• Low pH (Carbonic Acid, Lactic Acid)
• High Temperature
• High 2,3 DiphosphoGlycerate concentration
(DPG)
• High partial pressure of Carbon Dioxide
• These conditions decrease Hb’s affinity for
oxygen, releasing more oxygen to active cells
• Example: Vigorous physical exercise
• Contracting muscles produce metabolic acids such as
lactic acid which lower the pH, more heat and more
carbon dioxide.
• In addition 2,3 DPGA is produced during conditions of
higher temperature and lower partial pressures of oxygen
Acting together or individually, these
conditions lead to a decrease in
Hemoglobin’s activity for Oxygen,
releasing more Oxygen to the tissues
(muscles)
BOHR EFFECT
Bohr Effect
• Bohr Effect refers to the changes in the affinity
of Hemoglobin for oxygen
• It is represented by shifts in the Hb-O2
dissociation curve
• Three curves are shown with progressively
decreasing oxygen affinity indicated by
increasing P(50)
•
•
•
•
1.
2.
3.
4.
•
SHIFT to the RIGHT
Decreased affinity of Hb for Oxygen
Increased delivery of Oxygen to tissues
It is brought about by
Increased partial pressure of Carbon Dioxide
Lower pH (high [H+])
Increased temperature
Increased levels of 2,3 DPGA
Ex: increased physical activity, high body
temperature (hot weather as well), tissue
hypoxia (lack of O2 in tissues)
•
•
•
•
1.
2.
3.
4.
•
SHIFT to the LEFT
Increased affinity of Hb for Oxygen
Decreased delivery of Oxygen to tissues
It is brought about by
Decreased partial pressure of Carbon Dioxide
Higher pH (low [H+])
Decreased temperature
Decreased levels of 2,3 DPGA
Ex: decreased physical activity, low body
temperature (cold weather as well), satisfactory
tissue oxygenation
Carbon Dioxide Transport
• Produced by cells thru-out the body
• CO2 diffuses from tissue cells and into the
capillaries
• 7% dissolves in plasma
• 93% diffuses into the Red Blood Cells
• Within the RBC ~23% combines with Hb (to
form carbamino hemoglobin) and ~ 70% is
converted to Bicarbonate Ions which are then
transported in the plasma
• In the lungs, which have low Carbon Dioxide partial
pressure, CO2 dissociates from CarbaminoHemoglobin,
diffuses back into lungs and is exhaled
• Within the RBC, CO2 combines with water and in the
presence of carbonic anhydrase it transforms into
Carbonic acid
• Carbonic acid then dissociate into H+ and HCO3• In the lungs CO2 diffuses out into the alveoli. This
lowers the partial press. Of Co2 in blood, causing the
chemical reactions to reverse
• Other gases have different affinities for hemoglobin
• CO carbon monoxide has more than 250 times the
affinity for Hb than oxygen. It will quickly and
almost irreversibly bind to Hb  CO poisoning
• NO nitrogen oxide has more than 200,000 times
the affinity for Hb than oxygen. Irreversible bind
• CO and O2 bind to same site on Hb
• CO2 and O2 bind to different sites on Hb
• Myoglobin (in muscle cells) binds more tightly to
oxygen than Hb but NOT cooperatively (Mb
serves as temporary intracellular O2 storage
mechanism useful in muscle contraction)
Llama and Vicuna
• Llama & Vicuna live in
the Andes Mts. South
America
• Oxygen dissociation
curves are located to the
left of other mammals
• Higher oxygen affinity
of the blood of these
animals aids in oxygen
uptake at the low
pressure of high altitude
High Altitude Adaptations for us…
• Chronic Mountain Sickness (ventilatory
depression, polycythemia, heart failure) R.I.P.
• At high altitude initially the person is
hyperventilating
• After some time however…
• Hb/RBC production increases (more oxygen
carrying capacity)
• 2,3 DPGA concentration rises in RBCs shifting
the curve to the right, improving O2 tissue
delivery
• Increased sensitivity to concentrations of [H+],
CO2, pH and their respective variations
That’s exactly why sportsmen (real
football players for instancewrongfully called “soccer players”
here) train in the mountains
To improve physical performance !
• At similar pH and Co2, small mammals have lower
oxygen affinity. Improved delivery of oxygen in the
tissues to sustain the high metabolic rate of a small animal
• Higher oxygen
affinity of the fetal
blood helps in the
transfer of oxygen to
the fetal blood in the
placenta
• Fetus – higher
affinity- shift left
• Fetus [Hb]~200g/L
• Mother [Hb]~135g/L
• Normal [Hb]~150g/L
Control of Respiration
• Basic rhythm is controlled by respiratory centers
located in medulla and brainstem
• An inspiratory center sends impulses via nerves to the
effectors: diaphragm and intercostals muscles
• Normal breathing rate @ rest is about 12 to 15 breaths a
minute
• Chemo receptors located thru out the body modify the
breathing rhythm by responding to changes in partial
pressures of Co2, O2, pH.
• Central chemoreceptors  medulla  changes in pH
• Peripheral chemoreceptors: carotid body, aortic bodies
monitor values of arterial blood: Pco2, Po2, pH
Carbon dioxide is the most important factor
controlling depth and rate of breathing
For all other inquiries, please refer back to the BOHR Effect.
• HYPERVENTILATION
• Increased rate and depth
of breathing if
• Low pp. O2
• High pp. CO2
• Low pH, High [H+]
• High Temperature
• High 2,3 DPGA
• High metabolic
requirements
• Shift to the RIGHT
• HYPOVENTILATION
• Decreased rate and depth
of breathing if
• High pp O2
• Low pp CO2
• High pH, Low [H+]
• Low Temperature
• Low 2,3 DPGA
• Low metabolic
requirements
• Shift to the LEFT
Other factors that affect respiration
• Pain & strong emotion
• Pulmonary Irritants (dust, smoke, noxious fumes, excess
mucus)
• Voluntary control (ALWAYS OVERIDDEN)
• Lung Hyperinflation (stretch receptors in pleurae send
inhibitory signals protecting against hyperinflation)
• Exercise and ventilation