呼吸系統(tǒng)氣體交換英文版

1、respiratory system()gas exchangelalveolar-blood gas exchangelgas exchange in the tissuesltransport in bloodthe blood that enters the pulmonary capillaries is , of course ,systemic venous blood pumped to the lungs via the pulmonary arteries.having come from the tissues, it has a relatively high pco2

2、and a relatively low po2.lthe differences in the partial pressures of oxygen and carbon dioxide on the two sides of the alveolar-capillary membrane result in the net diffusion of oxygen from alveoli to blood and of carbon dioxide from blood to alveoli.las this diffusion occurs, the capillary blood p

3、o2 rises and its pco2 falls . the net diffusion of these gases ceases when the capillary partial pressures become equal to those in the alveoli. in a normal person ,the rate at which oxygen and carbon dioxide diffuse are so rapid and the blood flow through the capillaries so slow that compete equili

4、brium is reached well before the end of the capillaries.thus ,the blood that leaves the pulmonary capillaries to return to the heart and be pumped into the systemic arteries has essentially the same po2 and pco2 as alveolar air.in lung affections or pulmonary edema ,some of the alveoli may become fi

5、lled with fluid .diffusion may also be impaired if the alveolar walls become thickened. very importantly ,diffusion problems in the lung are restricted to oxygen and do not affect elimination of carbon dioxide ,which is much more diffusible than oxygen.gas exchange in the tissuesmetabolic reactions

6、occurring within cells are constantly consuming oxygen and producing carbon dioxide .therefore , intracellular po2 is lower and pco2 higher than in blood .as the result ,there is a net diffusion of oxygen from blood into cells ,and a net diffusion of carbon dioxide from cells into blood. in this man

7、ner, as blood flows through systemic capillaries, its po2 decreases and its pco2 increases.transport-o2hemoglobin molecule each iron atom can bind one molecule of oxygen, a single hemoglobin molecule can bind four molecules of oxygen.a protein made up of four subunits bound togetherleach hemoglobin

8、molecule is a protein made up of four subunits bound together. each subunit consists of molecular group known as heme and a polypeptide attached to the heme .each of the four heme groups in a hemoglobin molecule contains one atom of iron ,to which oxygen binds.transport-co2lin a resting person ,meta

9、bolism about 200ml of carbon dioxide per minute. carbon dioxide is much more soluble in water than oxygen, and so more dissolved carbon dioxide than dissolved oxygen is carried in the blood. leven so, only a small amount of blood carbon dioxide is transported in this way ; only 10% of the carbon dioxide entering the blood remain physically dissolved in the plasma and erythrocytes.lanother 30% of the carbon dioxide molecules entering the blood reacts reversibly with amino groups of proteins, particularly