呼吸生理 黃基礎

呼吸的主要作用 細胞與外界之間的氣體交換

氣體交換的方式 單細胞生物：簡單擴散 多細胞生物：需要呼吸系統 與循環系統

Five steps for gas exchange 1. Ventilation 2. Gas exchange between alveoli and lung capillaries 3. Gas transport by circulation 4. Gas exchange between tissue cells and tissue capillaries 5. O2 consumption and CO2 production

呼吸系統包括： 呼吸道 與肺臟

哺乳類的呼吸系統 上呼吸道：鼻腔、咽喉、喉頭 肺：氣管、支氣管、小支氣管 、終末小支氣管、呼吸小 支氣管、肺泡道及肺泡

呼吸上皮

Inspiration

側面觀

呼吸體積 潮氣容積吸氣儲備容積 呼氣儲備容積 肺餘容積 肺活量 功能肺餘量

以肺量計測定肺換氣體積

Dead space air that not participate gas exchange between alveoli and lung capillaries

Bird

氣囊

Unidirectional flow

青蛙的呼吸

魚的呼吸

Water versus air breathing (1) Higher viscosity of water entails higher frictional energy loss Higher density of water causes a higher energy cost in the respiratory cycle low diffusitivity of O2 in water (need a small diffusion distance for gas transfer) Low solubility of O2 in water

Comparison of physical properties of water and air

Water versus air breathing (2) Morphological adaptation: the filaments and secondary lamellae providing a large surface area and entailing a very short diffusion distance for gas exchange between water and blood

Water versus air breathing (3) Good physiological performance: a higher arterial partial pressure of oxygen (PaO2) than that of expired water this is due to the countercurrent arrangement of water and blood which entails the blood in the outflow end from the secondary lamellae has gas exchange contact with inflowing waster

Pulmonary gas transfer in birds versus mammals (1) There are two kinds of air filling structures in birds vs the lung in mammals No alveoli in bird but parabronchi from which air capillaries extending to contact with blood capillaries lung volume change during respiratory cycle in mammals vs volume change in air sac in bird

Pulmonary gas transfer in birds versus mammals (2) Unidirectional airflow in the parabronchi in birds vs a pool of gas in the alveoli in mammals/ gas exchange occurs in alveoli in mammals vs in air capillaris in bird crosscurrent model in bird show a more efficiency of gas exchange comparing with the pool model in mammals higher arterial PO2 than expired in bird

Gas Transport in blood O2 carriage by blood CO2 carriage by blood

O2 carriage: 1. physical dissolve 2. bound to hemoglobin Hb + O2 ←→ HbO2 HbO2 + O2 ←→ Hb(O2)2 Hb(O2)2 + O2 ←→ Hb(O2)3 Hb(O2)3 + O2 ←→ Hb(O2)4 3. oxygen dissociation curve

Factors that modified the O2 dissociation curve 1. CO2 increase (Bohr effect) 2. pH decrease 3. temperature increase 4. 2,3-DPG increase shift the curve to the right and favor unloading of O2 from HbO2

O2 dissociation curve Myoglobin Hemoglobin

Decrease in pH

Hemo-cyanin display Bohr effect

Root effect

CO2 carriage 1. Physical dissolve 2. Carbamino compounds 3. Bicarbonate CO2 dissociation curve

Haldane effect

The increase in HbO2 formation in pulmonary capillaries favors unloading of CO2 from bicarbonate and carbamino compound

O2 consumption, CO2 production and tissue gas exchange

Oxygen extraction