respiratory gas transport
DESCRIPTION
RESPIRATORY GAS TRANSPORT. OXYGEN TRANSPORT. 98.5% oxygen in arterial blood is bound to hemoglobin and 1.5% is dissolved in plasma Each heme group of 4 globin chains in a hemoglobin molecule may bind O 2 - PowerPoint PPT PresentationTRANSCRIPT
RESPIRATORY GAS TRANSPORT
OXYGEN TRANSPORT• 98.5% oxygen in arterial blood is bound to
hemoglobin and 1.5% is dissolved in plasma• Each heme group of 4 globin chains in a
hemoglobin molecule may bind O2
• After binding with O2, hemoglobin changes shape to allow further uptake (positive feedback)
• An oxyhemoglobin dissociation curve shows relationship between hemoglobin saturation and oxygen partial pressure - PO2.
Oxyhemoglobin Dissociation Curve
CARBON DIOXIDE TRANSPORT
• 90% as carbonic acid in plasma CO2 + H2O H2CO3 HCO3
- + H+
• 5% as carbaminohemoglobin (HbCO2)- binds to amino groups of Hb (and plasma proteins)
• 5% as dissolved gas in plasma
SYSTEMIC GAS EXCHANGE• CO2 loading
– carbonic anhydrase in RBC catalyzes• CO2 + H2O H2CO3 HCO3
- + H+
– chloride shift• keeps reaction proceeding, exchanges HCO3
- for Cl- (H+
binds to hemoglobin)• O2 unloading
– H+ binding to HbO2 causes affinity for O2
• Hb arrives 97% saturated, but leaves 75% saturated
(venous reserve) – Utilization coefficient (amount of oxygen Hb has
released) is 22%
ALVEOLAR GAS EXCHANGE
• Reactions are the reverse of systemic gas exchange
• O2 loading & CO2 unloading– as Hb loads O2 its affinity for H+ decreases, H+
dissociates from Hb and binds with HCO3-
• CO2 + H2O H2CO3 HCO3- + H+
– reverse chloride shift• HCO3
- diffuses back into RBC in exchange for Cl-
and free CO2 diffuses into alveoli to be exhaled
Alveolar Gas Exchange
Systemic Gas Exchange
FACTORS FAVORING OXYGEN UNLOADING
• Metabolic needs of tissues affect O2 unloading (HbO2 releases O2)– Low ambient PO2
: tissue has PO2
– Increased temperature of tissue– Bohr effect: tissue has CO2, which raises H+ and lowers
pH– bisphosphoglycerate (BPG):BPG produced by RBCs as a
metabolic intermediate binds to Hb and causes HbO2 to release O2
body temp. (fever), TH, GH, testosterone, and epinephrine raise BPG and cause O2 unloading
Oxygen Dissociation & pH
Bohr effect: release of O2 in response to low pH
Active tissue - more O2 released
• Metabolic needs of tissues affect CO2 loading– Haldane effect: low level of oxyhemoglobin
(HbO2) enables blood to transport more CO2
• HbO2 does not bind CO2 as well as deoxyhemoglobin (HHb) does.
• HHb binds more H+ than HbO2 - The CO2 + H2O HCO3
- + H+ reaction therefore
shifts to the right
FACTORS FAVORING CARBON DIOXIDE LOADING
CHEMORECEPTORS
• Monitor pH, PCO2, PO2
of body fluids
– Peripheral chemoreceptors• aortic bodies - signal medulla by vagus
nerves• carotid bodies - signal medulla by
glossopharyngeal nerves– Central chemoreceptors on surface of medulla
• primarily monitor pH of cerebrospinal fluid
Peripheral Chemoreceptor Pathways
DIRECT CARBONDIOXIDE EFFECT ON CHEMORECEPTORS
CO2 may directly stimulate peripheral chemoreceptors and trigger ventilation more quickly than central chemoreceptors
DIRECT EFFECT OF OXYGEN ON CHEMORECEPTORS
• Usually, oxygen has little effect on chemoreceptors.
• Chronic hypoxemia, PO < 60 mmHg, as is associated with emphysema & pneumonia may cause increased ventilation .