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THE RESPIRATORY SYSTEM 2, Factors affecting gas exchange at alveoli
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THE RESPIRATORY SYSTEM 2
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Control of Respiration
Medullary chemoreceptors (from brain) Triggered by
- Decreased pH
- Increased CO2
- Exercise
- CO2 increases
- Anhydrase pathway "produces" H+
- Respiratory control centers (medulla) react by increasing respiratory rate
Carotid and aortic chemoreceptors (from heart)Triggered by
CO2 transport in blood
- CO2 transfer from tissue to blood
- In blood, 23% of CO2 gets attached to Hb
- CO2 + H20 > H2CO3 then disassociate to H+ and HCO3-
- H+ binds with Hb to maintain pH
- Erythrocyte expels HCO3 to tissue and receive Cl- (chloride), to maintain electrical neutrality of erythrocyte (you don't want them to repel/attract to one another)
CO2 breakdown
- 23% in Hb
- 70% handled by carbonic anhydrase pathway (see equation above)
- 7% dissolved in plasma
Chemical Control of Breathing
- PCO2
- Main respiratory regulator
- Mainly affect on central chemoreceptors
- CO2 can pass blood-brain barrier
- H+ cannot pass the barrier
- [H+]
- Monitored by carotid & aortic bodies
- PO2
- Monitored by carotid & aortic bodies
- Arterial PO2< 60 mmHg to stimulate peripheral chemoreceptors
Factors affecting gas exchange at alveoli
- Factors influencing efficiency of diffusion alveolar-capillary barrier
- Partial pressures of gases
- Thickness of barrier
- Surface area
- Blood Flow
- Rate of blood flow through alveoli
- Perfusion of alveoli
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Revision
- Right Ventricle (RV) > Main pulmonary artery (PA), branches successively into several pulmonary arteries (accompany bronchioles)
- Arterioles > Capillary bed around alveoli
- Small pulmonary veins > Large pulmonary veins > Left Atrium (LA)
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In order for gas exchange to occur
- Fresh air must reach the alveoli: ventilation (alveolar ventilation vs dead space)
- Alveoli must be perfused by blood
- Diffusion at alveoli should be efficient
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