呼吸系统 (NXPowerLite).ppt

Chapter 8,呼吸系统 Respiratory System,绍兴文理学院生命科学学院潘伟槐,要点,重点：呼吸道的鼻旁窦、喉的结构、肺的结构特点；呼吸运动的主要呼吸肌，气体交换的基本机理以及呼吸的主要调节。,概述 呼吸器官的结构 肺通气 呼吸气体的交换和运输 呼吸的调节,概述overview,呼吸概念及意义 conception and Significance,The gas exchange process between organization and environment is named respiration uptake oxygen output carbon dioxide,呼吸过程process of respiration,呼吸过程是通过三个连续的环节 外界空气与肺泡之间以及肺泡与肺毛细血管之间的气体交换称外呼吸(external respiration)，包括肺通气和肺换气二个过程。 血液气体运输(gas transportation) 组织细胞与组织毛细血管之间的气体交换称内呼吸(internal respiration),组成 Components of respiratory system,习惯上把进行外呼吸的肺脏称为呼吸器官，它与那些协助肺泡完成通气功能的器官和支气管等共同构成呼吸系统。 呼吸系统包括呼吸道和肺 呼吸道分上呼吸道(鼻、咽、喉)和下呼吸道(气管、支气管) 肺由支气管及分支和肺泡构成。,呼吸器官的结构 Fundamental structure of respiratory organs,呼吸道respiratory tract,鼻Nose 由外鼻、鼻腔和鼻旁窦组成。 鼻腔Nasal Cavity A chamber that transfers air and gases back and forth between the nostrils and the pharynx. The design of this cavity allows for air filtration, air conditioning (warming, cooling), air monitoring (smelling odors) and mucus production for protection against foreign substances (bacteria, dust, pollen, etc.).,上呼吸道upper respiratory tract,鼻旁窦paranasal sinus 鼻旁窦共四对，分别为上颌窦、额窦、筛窦和蝶窦，是鼻腔周围相应的含气骨性鼻旁窦补以粘膜而成的，都有开口于鼻腔。对发音有共鸣作用，同时具有温暖和湿润被吸入的空气的作用。,咽Pharynx 垂直的肌性管道，略呈漏斗形，前后较窄，位于鼻腔、口腔和喉的后方。几乎没有前壁，经鼻后孔、口咽峡、喉口分别与鼻腔、口腔和喉相通。咽的下方在第六颈椎下缘高度与食管相续。 The pharynx also has sensory capability to monitor the flow of materials and assists swallowing of food and drink.,咽腔鼻部(鼻咽部、上部) 鼻腔向后方的直接延续，鼻后孔为界，下部为软腭，吞咽时，软腭抵达咽的后壁，使鼻咽部与口腔隔开，防止食物流入，呼吸时下垂。 咽腔口部(口咽部、中部) 口腔后方延续的部分，位于口咽峡的后方，软腭、舌根和会厌上缘之间，侧壁在舌腭弓和咽腭弓之间有一凹陷叫扁桃体窦，容纳腭扁桃体(扁桃体)。 咽腔喉部(喉咽部、下部) 较狭窄，上端约在舌骨水平处与口咽部相通，下端约在第六颈椎下缘处与食管相接，向前正对喉与喉口。,喉Larynx A set of cartilaginous structures and membranes that allow air to pass back and forth between the glottis and the trachea. The larynx (voicebox) also contains cord-like membranes that produce sounds for communicating (talking, singing, noisemaking).,喉外部有颈部的血管和神经及甲状腺侧叶等重要结构。 喉的结构复杂，由软骨(单块的甲状软骨、环状软骨、会厌软骨和成对的杓状软骨)、韧带、喉肌和粘膜构成。喉上部甲状软骨借韧带连于舌骨。甲状软骨下端与环状软骨相关节，环状软骨后部上缘在中线二侧与杓状软骨相关节，会厌软骨下缘借韧带连于甲状软骨内面，上端宽并游离于喉口上方。,喉肌为横纹肌，作用是运动喉的软骨和关节，使声门开大或缩小，并能紧张或松驰声韧带。 喉腔上通咽部(开口为喉口)，下通气管，喉腔内粘膜与舌根及咽的粘膜相续。,甲状软骨,环状软骨,会厌软骨,会厌软骨,小角软骨,杓状软骨,在喉腔中部的侧壁，可见上、下两对矢状位的粘膜皱襞。 上方一对为室襞，由喉粘膜覆盖室韧带而成，有保护作用，室襞间的裂隙称前庭裂。 下方一对为声襞或称声带，是喉粘膜覆盖声韧带和声带肌而成。成年男子长约23mm，女子长约17mm，二侧声襞之间的裂隙为声门裂或称声门。,声门裂是喉腔中最狭窄的部分，气体通过声门裂时，声带振动而发音。 活体通过喉镜对喉进行观察，可见到声带位于内下方，呈白色，表面光滑，边缘很薄。 室襞位于外上方，呈淡红色，边缘较厚。,在平静呼吸时，声门裂呈近三角形。 深呼吸时裂增大，呈菱形。 发音时，两侧声带紧张并靠近，呈一窄的裂隙，甚至关闭，由于气流冲击声带而发生振动。,气管和支气管一般称为下呼吸道。 气管呈圆筒形管道，长912cm，上起处第6、7颈椎间，下至第4、5胸椎间分为左右支气管。 由1416个“C”形软骨环和连于其间的环韧带构成。气管软骨环开口向后，由平滑肌纤维和弹性纤维构成膜性壁封闭。,下呼吸道lower respiratory tract,软骨环使管腔保持开放状态，膜壁适于后方的食管腔扩长。 支气管左支细长(45cm)，走向平坦，右支粗短(长3cm)，走向陡直，因此进入气管的异物易落入右支气管。左支经肺门入左肺，右支入右肺。 气管和支气管壁由内向外由粘膜层、粘膜下层和外膜组成。,气管外观,气管纵切,气管横切,clara细胞为一类无纤毛、无粘液,而有着丰富分泌颗粒的呼吸道上皮细胞。,气管粘膜,肺Lung,The organ for breathing, air transfer and gas exchange.,Located in the pleural cavity of the thorax. Covered or lined with a thin epithelium called the visceral pleura.,Primary Bronchus A tubular structure that passes air back and forth between the trachea and secondary bronchi.,导管部Conducting Zone,The overall structure and function of larger bronchial tubes is similar to the trachea. The epithelial lining of these tubes produce protective mucus and possess cilia which “brush” material up toward the pharynx.,Secondary Bronchus A tubular passageway that passes air back and forth between a primary bronchus and the remainder of a bronchial tree (third, fourth, fifth degree branches, etc. ). Retains the structural features of the trachea and the primary bronchi.,Terminal Bronchiole One of the smallest tubular passageways in the lung that passes air back and forth between the smallest bronchial tube and the respiratory bronchiole.,终末细支气管杯状细胞、腺体、软骨消失，而平滑肌形成完整的环形肌层，所以细支气管、终末细支气管平滑肌的收缩和舒张直接影响到管腔的大小，控制肺泡的气体流量。,细支气管、终末细支气管平滑肌受交感和迷走神经双重支配，交感神经通过型肾上腺素能受体(2)降低平滑肌的紧张性使之舒张，减少气流的阻力；迷走神经通过M型胆碱能受体使平滑肌收缩加强，紧张性增高，细支气管口径缩小，气流阻力增加。,支气管哮喘的病人，平滑肌发生痉挛性收缩，使管腔变窄，甚至阻塞，从而气流量减少，会引起呼吸困难。 临床上常用拟交感药物治疗那些呼吸道平滑肌紧张性过高的病症。,支气管树,呼吸部Respiratory Zone,指能够进行气体交换的部分，包括呼吸性细支气管(Respiratory Bronchiole)、肺泡管(Alveolar duct)、肺泡囊(Alveolar Sac)和肺泡(Alveolus)。,呼吸性细支气管是终末细支气管的分支，其管壁有少量囊状肺泡，管壁单层纤毛上皮变成柱状或立方上皮。 肺泡管是呼吸性细支气管的分支，管壁四周都是肺泡囊或肺泡的开口。 肺泡囊是肺泡管的分支，为数个肺泡的共同开口。,肺泡是半球形的囊泡，为气体交换场所。 Polyhedral in shape and clustered like units of honeycomb. 300 million air sacs. Large surface area (60 80 m2). Each alveolus is 1 cell layer thick. Total air barrier(气屏障) is 2 cells across. 2 types of cells: Alveolar type I: Structural cells. Alveolar type II: Secrete surfactant(表面活性物质).,肺泡隔alveolar septum 相邻两个肺泡之间的薄层结缔组织称肺泡隔，膈内有丰富的毛细血管及弹性纤维等，故肺泡有良好的弹性，膈内具有尘细胞(巨噬细胞)，它可穿过肺泡上皮进入肺泡腔内，吞噬尘粒，对肺起净化作用。 在肺泡隔毛细血管间隙中往往有10-15m的圆形或椭圆形小孔，称Kohn氏小孔。,Region of gas exchange between air and blood. Includes respiratory bronchioles. Must contain alveoli. Gas exchange occurs by diffusion.,Basil lamina,肺泡壁由单层上皮细胞组成，下面衬有一层基膜，与肺毛细血管之间有间质，肺毛细血管壁由内皮细胞构成，其下方有基膜，肺泡表面还有液体分子层和II型细胞分泌的表面活性剂形成表面活性物质层，这七层共同构成血-气屏障，其厚度在0.20.6m。有很好的通透性，有利于肺泡与血液之间的气体交换。,血-气屏障或呼吸膜 (Blood air barrier， Alveolar Respiratory membrane),Surface Tension表面张力 抵抗肺扩张的一种力。 吸气时增加肺作功。 由液体分子层形成。 Pulmonary surfactant表面活性剂 由II型细胞分泌。 最重要的是二棕榈酰卵磷脂(DPPC)。 作用 调节表面张力，稳定肺泡内压。 降低肺泡表面张力。减少吸气阻力，防止因回缩过大而阻碍肺泡的扩张，甚至导致肺泡的塌陷。 减少肺泡液的生成，防止肺水肿，抽吸作用下降。,肺表面活性物质的组成 (Conformation of Pulmonary Surfactant) Saturation lecithin(饱和卵磷脂) is 41%(90% is DPPC) DPPC binding to apolipoprotein(载脂蛋白) exist as lipoprotein(脂蛋白) Non-saturation lecithin is 25% Cholesterol(胆固醇) is 8,DPPC is an important Pulmonary Surfactant （1）Quantity is large. it is 1/3 of all （2）Character of molecule structure Strong hydrophobicity(疏水性) Strong hydrophilicity(亲水性) （3）Strong suspending stability,1974年，King报告，DPPC载脂蛋白(疏水氨基酸，可溶性蛋白)降表面张力的有效成分为其中脂类，脂质分子彼此间和对水分子吸引力较小，在表面稀释了水分子，故能降低肺泡表面张力。,胸膜和胸膜腔 pleura and Pleural Cavity,胸膜为浆膜，分壁胸膜和脏胸膜。肺的表面有一层膜称脏胸膜Visceral Pleura(胸膜脏层、肺胸膜)，同时在胸廓内面，膈上面及纵膈上的胸膜称壁胸膜Parietal Pleura(胸膜壁层)，二层在肺门处互相连续。二层间围成一个完全封闭的胸膜腔Pleural Cavity，腔内为负压，使二层胸膜紧密相贴，在呼吸运动时，可随胸壁和膈的运动而扩张或回缩，同时腔内有少量浆液，以减少呼吸时二层胸膜之间的磨擦。,肺通气Pulmonary Ventilation,Pulmonary ventilation is the gas exchange process between lungs and environment.,All the structures through air passes before reaching the respiratory zone. Warms and humidifies inspired air. Filters and cleans: Mucus secreted trap particles in the inspired air. Mucus moved by cilia to be expectorated.,呼吸道在肺通气中的作用 Effect of respiratory tract in Pulmonary Ventilation,肺通气是指与外界环境间的气体交换过程。 实现肺通气的器官包括呼吸道、肺泡和胸廓等。 胸廓节律性呼吸运动则是实现通气的动力。肺本身没有肌纤维，没有主动地扩张和缩小能力(舒缩能力)，其舒缩的动力完全依赖呼吸肌的舒缩引起胸腔扩大和缩小而实现，也即呼吸运动才是肺通气的动力。 气体通过呼吸道进出肺是由于肺泡与外界之间的气压差所引起的。,肺通气的动力 Power of pulmonary ventilation,呼吸运动respiratory movement,胸廓的前后、左右壁是由肋骨、胸骨和脊椎骨以及附着在它们上面的肌肉所形成的。,胸腔的扩大和缩小实际上是肋骨、胸骨和膈运动的结果，胸腔的节律性扩大与缩小称为呼吸运动。 与呼吸运动相关的骨骼肌称为呼吸肌。 吸气肌 能使胸腔扩大引起吸气的肌肉，如肋间外肌、膈肌、胸锁乳突肌、胸肌等。 呼气肌 能使胸腔缩小的引起呼气的肌肉，如肋间内肌、腹壁肌等。,平静呼吸常起作用的是吸气肌中的肋间外肌和膈肌。 深呼吸运动时，除肋间外肌、膈肌收缩加强外，其它辅助吸气肌，如胸锁乳突肌、胸大肌等也参与活动，呼气肌如肋间内肌和腹壁肌也在呼气时收缩，使肋骨更加下降，腹壁肌收缩，腹内压长高，膈上移。,External Intercostals Elevate ribs,Internal Intercostals Depress ribs,Diaphragm Inspiration,平静吸气时，穹窿下降约12cm，而中心腱不下降。 深吸气时，肋间外肌、膈肌收缩加强，特别是膈肌收缩加强，使中心腱也明显下降可达710cm。,腹壁肌 Compress Abdomen,精索,肋间肌收缩和舒张引起肋骨和胸骨的升降运动的呼吸方式称胸式呼吸(Thoracic breathing)。 膈肌的长降造成腹壁的起伏的呼吸方式称腹式呼吸(Abdominal breaghing)。 正常情况下二种方式同时存在，安静时，一般女子以胸式呼吸为主，男子及婴儿以腹式呼吸为主。,胸内压(Intrapleural Pressures)和肺内压(Intrapulmonary Pressures),Intrapleural Pressures,Visceral and parietal pleurae are flush against each other. The intrapleural space contains only a film of fluid secreted by the membranes. lack of air in the intrapleural space. Lungs normally remain in contact with the chest wall. Lungs expand and contract along with the thoracic cavity.,Elasticity Tendency to return to initial size after distension. High content of elastin proteins. Very elastic and resist distension. Recoil ability. Elastic tension increases during inspiration and is reduced by recoil during expiration.,平静呼气末期约为-3-5mmHg(0.4-0.7Kpa)，而在吸气末期则更低，约为-5-10mmHg (0.81.3Kpa)。 由于胸廓自然容量比肺的自然容量大，同时由于两层膜不能分开，胸膜腔不能增大，只有肺被动地随之扩张，所以肺不认论在吸气还是呼气时，总是处于一定的扩张状态,Intrapleural Pressures = Atmospheric pressure(大气压)- Elastic tension(肺泡回缩力),Intrapleural pressureis negative.,Intrapulmonary Pressures,Intrapulmonary pressure: Intra-alveolar pressure (pressure in the alveoli). During inspiration: Atmospheric pressure is than intrapulmonary pressure (- 3 mm Hg). During expiration: Intrapulmonary pressure (+ 3 mm Hg) is atmospheric pressure.,Changes in intrapulmonary pressure occur as a result of changes in lung volume. Pressure of gas is inversely proportional to its volume. Increase in lung volume decreases intrapulmonary (alveolar) pressure. Air goes in. Decrease in lung volume, raises intrapulmonary pressure above atmosphere. Air goes out.,正常呼吸时肺泡压、胸膜腔内压与肺容量的变化,Assessed by spirometry. Spirogram,肺总量total lung capacity,Tidal volume(潮气量) The volume of gas inspired or expired in an unforced respiratory cycle. 400-500ml Inspiratory reserve volume(补吸气量) The maximum volume of gas that can be inspired during forced breathing in addition to tidal volume. 1500-1800ml,Expiratory reserve volume(补呼气量) The maximum volume of gas that can be expired during forced breathing in addition to tidal volume. 900-1200ml Residual volume(残气量) The volume of gas remaining in the lungs after a maximum expiration. 1000(female) -1500ml(male),Inspiratory capacity(深吸气量) The maximum amount of gas that can be inspired after a normal tidal expiration. IC=TV+IRV Functional residual capacity(机能残气量) The amount of gas remaining in the lungs after a normal tidal expiration. 2000-2500ml FRC= ERV+RV,Vital capacity(肺活量) The maximum amount of gas that can be expired after a maximum inspiration. 2500(female)-3500ml(male) VC= TV+IRV+ERV Total lung capacity(肺总量) The total amount of gas in the lungs after a maximum inspiration. TC=VC+RV,肺通气量和肺泡通气量 lung ventilation volume and alveolar ventilation,每分通气量 每分通气量=潮气量呼吸频率(次/分) 成人呼吸频率为12-18次/分，女性快2-3次 平静时每分通气量为68升，运动时，不仅呼吸频率增加，且呼吸深度加大，每分通气量增加，可达到70120L,肺泡通气量 Anatomical Dead Space(解剖无效腔，死腔) Not all of the inspired air reached the alveoli. As fresh air is inhaled it is mixed with anatomical dead space(150ml). Conducting zone and alveoli where 02 concentration is lower than normal and C02 concentration is higher than normal. Alveolar ventilation: F (TV-DS) F = frequency (breaths/min.). TV = tidal volume. DS = dead space.,肺泡无效腔指肺泡内不能与血液进行气体交换的那一部分空间，正常人近于0。 生理无效腔(无效腔)=解剖无效腔+肺泡无效腔。 成人肺泡通气量约为肺通气量70%，因为潮气量中约有150ml为无效腔气量，即(500-150)/500=70%。肺中的机能余气量约为2500ml，实际每次进入肺泡的新鲜空气却为500-150=350ml，故每次呼吸仅能使肺泡中气体更新1/7左右。,时间肺活量,指单位时间内，肺活动所能呼吸的最大气量，在到第1秒末、第2秒末和第3秒末呼出的气体量约占肺活量的83%、96%和99%。,呼吸气体的交换和运输 Gas Exchange and Transport,Movement of gases between the alveoli, blood and cells depends on the partial pressure difference of a gas across these regions.,气体交换Gas Exchange,According to the Law of Diffusion, gases always move from a region of high partial pressure to a region of low partial pressure. If your lungs have a higher gas pressure than your blood, then the gas will move into your blood and visa versa.,Examine the following slide in order to observe the gas partial pressure differences that exist in different regions of the body. Predict the direction of oxygen and carbon dioxide movement from one region to another using the gas pressures.,Daltons Law Total pressure of a gas mixture is = to the sum of the pressures that each gas in the mixture would exert independently. PATM=PN2+P02+PCO2=760 mm Hg H20 humidified(saturated). H20 contributes to partial pressure (47 mm Hg). P02 (sea level) = 160 mm Hg. *1mm Hg=0.133322KPa,Significance of Blood P02 and PC02 Measurements,At normal P02 arterial blood is about 100 mm Hg. P02 level in the systemic veins is about 40 mm Hg. PC02 is 46 mm Hg in the systemic veins.,从上面的梯度图可非常明显地看出，Po2从空气到组织呈下波，且斜率较大，而Pco2从组织到空气呈下波，但斜率较小，所以在这样的分压差的推动下，O2从空气扩散到组织，而CO2则从组织向空气扩散。,虽然Pco2的梯度差较小，但并不影响CO2的交换，因为气体扩散速度与它在液体中的溶解度密切相关，扩散速度与溶解度成正比。同时分子量对扩散速率也有影响，分子量的平方根的倒数与扩散速度成正比。,37时 CO2 48.0ml/100ml全血/大气压 51.5ml/100ml血浆/大气压 O2 2.36ml/100ml全血/大气压 2.14ml/100ml血浆/大气压。 CO2/O2=51.5/2.14=24，即在血浆中CO2比O2的扩散速度快24倍。,影响气体交换的因素 呼吸膜的厚度、通透性和面积等。 肺泡通气量与肺血流量的比值,O2和CO2在血液中均以物理溶解和化学结合二种方式运输，但绝大部分是以化学结合形式运输的。以物理溶解的量很少，却十分重要，因为肺和组织进行气体交换时进入血液的气体首先必须溶解于血液中，反之当气体从血液释放出来时，首先是溶解状态的气体，结合状态的气体再分离出来成为溶解气体。,气体的运输 O2 and CO2 Transport,Oxygen Transport,Dissolved in Plasma,1.5 % Arteries 0.3mlO2/100ml blood. Veins 0.12mlO2/100ml blood.,Combined with Hemoglobin,Loading/unloading depends P02 of environment Affinity between hemoglobin and 02,98.5 % Oxyhemoglobin(氧合血红蛋白) Formation Oxyhemoglobin forms when an oxygen molecule reversibly attaches to the heme portion of hemoglobin. The heme unit contains iron(+2) which provides the attractive force.,280 million hemoglobin/ RBC. Each hemoglobin has 4 polypeptide chains and 4 hemes. Each heme has 1 atom iron that can combine with 1 molecule 02.,1gHb可结合1.34-1.36mlO2，健康的人100ml血含Hb15g，则完全饱和时可结合氧约20ml，这称为血红蛋白氧容量，在一个大气压下，百分之百Hb与氧结合为氧合血红蛋白的称氧饱和，血红蛋白在一定条件下实际结合的氧量称血红蛋白氧含量，血红蛋白氧含量占血红蛋白氧容量的百分比称为血红蛋白氧饱和度。,血液能结合氧的量称为血氧容量，它是血红蛋白氧容量和物理溶解氧容量之和，但由于物理溶解量很少，所以常把血红蛋白氧容量称为血氧容量。 安静时，动脉血氧饱和度达97%以上，可视为100%，为20.30ml%(mlO2/100ml全血)，静脉血的饱和度为75%，为15ml%，也就是说每100 ml血流经组织后，释放出5 ml O2。,氧离曲线 Oxyhemoglobin Dissociation Curve,表达血红蛋白氧饱和度与血液O2分压之间关系的曲线称氧离曲线。从氧离曲线可以看出，随着氧分压的逐渐升高，血红蛋白的氧饱和度缓慢上升，但它们不是直线的正比关系，而是呈“S”形曲线关系。,The Oxygen Dissociation Curve,曲线上段，即PO2在 60-100mmHg时，坡度小，说明这个范围内O2分压的变化虽然较大，但血氧饱和饱和度的变化却不大。当血O2分压从100mmHg下降到80mm Hg时，血氧饱和度从98%下降到96%。这一特征表明，即使外界或肺泡中O2分压有所下降，但血氧饱和度仍可维持在较高的水平上，从而保证全身组织氧的供应。实际上，动脉中O2分压如果低于80mmHg时，肺通气能力通过调节将很明显加强。,曲线下段，即O2分压在60mmHg以下时，坡度很陡，表明O2分压略有下降，血氧饱和度就迅速下降。当O2分压到40-10mmHg时(正是组织内O2分压波动的范围)，坡度更陡，O2分压稍有下降，血氧饱和度就大幅度下降，使较多的O2释放出来，供组织利用。血红蛋白的这种特性使血液在O2分压高的部位即肺能迅速与O2结合，达到很高的氧饱和度，而在O2分压低的组织部位又能促进O2的释放。,影响氧离曲线的因素,The loading and unloading of O2 influenced by the affinity of hemoglobin for 02. Decreased pH, increased temp., and increased 2,3-DPG(2,3-二磷酸甘油酸) affinity of Hb for 02 decreases. Shift to the right greater unloading.,pH和CO2影响 Increased H+ from acids When the CO2 content of the blood increases, the oxygen dissociation curve shifts to the right. This right shift decreases the ability of hemoglobin to hold oxygen. Consequently, additional oxygen is unloaded and made available to the body.,温度影响 血温度升高，降低O2和血红蛋白的亲合力，曲线右移，如运动时，体温升高，促进HbO2解离。 2,3二磷酸甘油酸(2,3-DPG) 其与Hb结合，降低Hb对O2亲合力，有利HbO2解离。红细胞中的无氧代谢可产生大量的DPG，曲线右移。如长时间运动时(或贫血)，红细胞产生大DPG，促进HbO2解离。,Carbon Dioxide Transport,Dissolved in Plasma,7-10 % 3.09 mlCO2/100ml blood.,Chemically Bound,Chemically Bound to Hemoglobin in RBC(Carbaminohemoglobin氨基甲酰血红蛋白) 20 - 30 % As Bicarbonate Ion(HCO3-) in Plasma 60 -70 %,Carbaminohemoglobin氨基甲酰血红蛋白 Carbaminohemoglobin forms when a carbon dioxide molecule reversibly attaches to an amino portion of hemoglobin. The process is summarized as follows:,该过程无需酶，其主要因素是氧合作用。去氧血红蛋白与CO2结合成氨基甲酰血红蛋白的能力比氧合血红蛋白强，故在体循环毛细血管中HbO2氧离后就可多结合一些CO2。,Bicarbonate Ion(HCO3-) in Plasma Carbonic acid forms abundantly in the RBC when the enzyme carbonic anhydrase(CA,碳酸酐酶) stimulates water to combine quickly with carbon dioxide. The process is summarized as follows:,CA,At the tissues, C02 diffuses into the RBC, reaction shifts to the right. Increased HC03- in RBC, HC03- diffuses into the plasma. RBC becomes more +. Cl- diffuses in (Cl- shift). HbC02 formed, give off 02.,CA,At the alveoli, C02 diffuses into the alveoli, reaction shifts to the left. Decreased HC03- in RBC, HC03- diffuses into the RBC. RBC becomes more -. Cl- diffuses out (Cl- shift). Hb02 formed, give off HbC02.,呼吸的调节 Regulation of Breathing,呼吸肌是骨骼肌，可作随意运动，接受大脑皮质的控制。但呼吸运动又是一种自动的节律性活动。应用分段横截脑干的方法证明，其调节中枢在延髓和脑桥，正常的呼吸运动就是在各级呼吸中枢的相互配合调节下进行的。在多种传入冲动的作用下，反射性地调节呼吸的频率和深度，从而改变肺通气量，以适应机体代谢的需要。,脊髓呼吸运动神经元,各级呼吸中枢Respiratory centers,颈髓35节的前角运动神经元发出膈神经，支配膈肌的运动。 胸髓111节的前角运动神经元发出肋间神经，支配肋间肌的运动。,支配呼吸肌的运动神经元胞体位于脊髓，但在延髓下部横切后的脊髓动物不能进行呼吸运动，这说明其受脑部中枢控制的。保留延髓的去大脑动物，就能进行节律性的呼吸运动，所以延髓是调节节律性呼吸运动的主要中枢。,脑干呼吸中枢 Brain stem respiratory centers,Medulla oblongata The medulla contains the medullary respiratory center that operates as the primary breathing center.,Neurons in the medulla oblongata forms the rhythmicity center Controls automatic breathing. The medullary respiratory center stimulates basic inspiration for about 3 seconds and then basic expiration for about 2 seconds (12breaths/min).,Rhythmicity Center,Dorsal respiratory group(DRG，背侧群) Regulate activity of phrenic nerve. Project to and stimulate spinal interneurons that innervate respiratory muscles(ig.external intercostal muscles). Ventral respiratory group(VRG，腹侧群 ) Passive process. Controls motor neurons to the internal intercostal muscles肋间内肌. Activity of expiratory neurons inhibit inspiratory neurons.,Pons. The pons contains the apneustic respiratory center(长吸中枢) and the pneumotaxic respiratory center(呼吸调节中枢). Both of these centers are considered secondary respiratory centers. This means they do not set the basic respiratory rhythm. Instead, they modify the basic respiratory rate.,Apneustic center(长吸中枢) Promote inspiration by stimulating the inspiratory neurons in the medulla. Provide constant stimulus for inspiration. Pneumotaxic center(呼吸调节中枢) Antagonize the apneustic center. Inhibits inspiration