gas transport & control of respiration. gas transport blood transports oxygen and carbon dioxide...
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GAS TRANSPORT &
CONTROL OF RESPIRATION
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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 plasma2. Chemically combined with hemoglobin3. Converted to a different molecule
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Oxygen Transport
• Due to low solubility, only 1.5 % of oxygen is dissolved in plasma
• 98.5 % of oxygen combines with hemoglobin
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• 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
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• 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)
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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
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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
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• 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)
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BOHR EFFECT
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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)
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• SHIFT to the RIGHT Decreased affinity of Hb for Oxygen Increased delivery of Oxygen to tissues
• It is brought about by
1. Increased partial pressure of Carbon Dioxide
2. Lower pH (high [H+])
3. Increased temperature
4. Increased levels of 2,3 DPGA
• Ex: increased physical activity, high body temperature (hot weather as well), tissue hypoxia (lack of O2 in tissues)
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• SHIFT to the LEFT Increased affinity of Hb for Oxygen Decreased delivery of Oxygen to tissues
• It is brought about by
1. Decreased partial pressure of Carbon Dioxide
2. Higher pH (low [H+])
3. Decreased temperature
4. Decreased levels of 2,3 DPGA
• Ex: decreased physical activity, low body temperature (cold weather as well), satisfactory tissue oxygenation
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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
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• 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
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• Other gases have different affinities for hemoglobin
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• 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)
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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
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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
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That’s exactly why sportsmen (real football players for instance-
wrongfully called “soccer players” here) train in the mountains
To improve physical performance !
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• 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
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• 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
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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
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Carbon dioxide is the most important factor controlling depth and rate of breathing
For all other inquiries, please refer back to the BOHR Effect.
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• 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
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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