呼吸系统

  • Anatomy of the respiratory system
    • 图
    • The upper respiratory tract
      • nose, nasal cavity, pharynx
      • 鼻子、鼻腔、咽部
    • The lower respiratory tract
      • larynx, trachea, bronchi, lungs
      • 喉、气管、支气管、肺
    • Lungs
      • The right lung has 3 lobes，the left lung has 2 lobes
    • Pleura胸膜
      • Pleura = visceral pleura (胸膜脏层) + parietal pleura (胸膜壁层)
      • The visceral pleura covers the surface of the lung and extends into the fissures裂缝 between lobes
      • The parietal pleura adheres附着 to the mediastinum (纵隔), the rib cage and the diaphragm (膈)
      • The space between the two pleurae is the pleural cavity胸膜腔，it contains a thin film of lubricating pleural fluid润滑性胸膜液
    • Trachea & bronchi 气管 & 支气管
      • Cross section of trachea, esophagus and thyroid gland
      • Branching of airways from the trachea
      • cellular transition from trachea to alveolus，从气管→毛细支气管→肺泡，气管的gland腺分泌mucus粘液
    • Alveoli 肺泡
      • Type Ⅰ alveolar cells (40%)
        • cover 95% of the alveoli surface
        • form the air-blood barrier
      • Type Ⅱ alveolar cells (60%)
        • secrete surfactant分泌表面活性剂
        • can divide into type Ⅰ alveolar cells
      • Alveolar macrophages
        • remove fine dust particle
      • 图
    • Respiratory muscles
      • Muscles of inhalation
        • the diaphragm隔膜 & external intercostals (肋间外肌)
        • sternocleidomastoid胸锁乳突肌 & scalenes斜角肌
      • Muscles of exhalation
        • the abdominal腹部的 & internal intercostals (肋间内肌)
      • direction of respiratory muscles contraction
  • Pulmonary ventilation通气
    • basic
      • Pulmonary ventilation, or breathing, is the flow air into and out of the lungs
      • Inhalation permits O2 to enter the lungs and exhalation permits CO2 to leave the lungs
      • The differences in pressure between the alveoli and the air drives pulmonary ventilation
      • Lack of muscles, lungs themselves can not contract or relax
      • Passive changes in lung volume are caused by the contraction/relaxation of respiratory muscles
    • Respiratory movement
      • ①Inhalation
        • the diaphragm隔膜 & external intercostals contract 肋间外肌
      • ②Exhalation
        • the diaphragm & external intercostals relax.
        • 正常呼气没有肌肉收缩，肌肉放松自动呼气
      • ③Forced inhalation
        • ① plus the sternocleidomastoid胸锁乳突肌 and scalenes斜角肌 contract.
      • ④Forced exhalation
        • ② plus the abdominal腹部的 & internal intercostals contract 肋间内肌
    • Alveolar & pleural pressure
      • 图
      • 呼吸时压力变化，transpulmonary pressure 跨肺压，胸膜压力随胸腔体积变化，肺泡压力＜0，肺体积变大，压力＞0，肺体积变小
    • Breathing patterns
      • Eupnea (平静呼吸)
        • 12~18breaths/min, active inhalation, passive exhalation, only muscles of inhalation participate.
      • Forced/deep breathing ( 用力呼吸/ 深 呼吸)
        • active inhalation & exhalation, all muscles of respiration participate.
      • Thoracic/costal breathing (胸式呼吸)
        • movements of chest due to contraction of external intercostal muscles.
      • Abdominal/diaphragmatic breathing (腹式/膈式呼吸)
        • movements of the abdomen due to contraction of the diaphragm.
        • 婴儿都是腹式呼吸，因为肋骨还没有长到胸骨上
    • Resistance to airflow
      • Elastic resistance 平静呼吸时占70%
        • elastic resistance of the lungs
          • Elastic forces of the lung tissue 1/3
          • Elastic forces caused by surface tension of the fluid that lines the inside walls of the alveoli, 2/3
            • The elastic resistance of lungs resists inhalation but drives exhalation
            • Pressure in alveoli caused by surface tension P = 2T / r，T是肺泡表面张力(N/m)
            • 根据上面那个公式，小的肺泡表面张力更大，会把气全都吹到大的肺泡里
            • 因此有 Surfactant表面活性剂 reduces the surface tension to about 1/10
            • Surfactant is a mixture of phospholipids (90%) and proteins, which is secreted by type Ⅱ alveolar cells
        • elastic resistance of the thoracic cage
          • The thoracic cage at rest, no elastic resistance, 2/3 lung capacity (end of inhalation during eupnea)
          • <2/3 lung capacity (exhalation), the elastic resistance resists exhalation but drives inhalation

          • 2/3 lung capacity (forced inhalation), the elastic resistance resists inhalation but drives exhalation

      • Inelastic resistance 平静呼吸时占30%
        • airway resistance (气道阻力) 80~90%
          • factors that influence airway resistance
            • ①inhalation/exhalation
            • ②airway smooth muscles
        • inertial resistance (惯性阻力)
        • viscous resistance (黏滞阻力)
    • Spirometry 肺活量测定
      • 传统方法是弄个水桶倒着插进来个柱状体往里吹气
      • 图
      • Total lung capacity (肺总量) is the maximum amount of air the lungs can contain. ≈5800ml
      • Tidal volume (潮气量) is the amount of air inhaled or exhaled in a cycle during eupnea. ≈500ml
      • Inspiratory reserve volume (补吸气量) is the amount of air in excess of tidal volume that can be inhaled with maximum effort. ≈3000ml
      • Inspiratory capacity (深吸气量) is the maximum amount of air that can be inhaled. ≈3500ml
      • Expiratory reserve volume (补呼气量) is the amount of air in excess of tidal volume that can be exhaled with maximum effort. ≈1100ml
      • Residual volume (余气量) is the amount of air remaining in the lungs after maximum exhalation. ≈1200ml
      • Functional residual capacity (功能余气量) is the amount of air remaining in the lungs after a normal exhalation. ≈2300ml
      • Vital capacity (肺活量) is the maximum amount of air that can be inhaled and then exhaled with maximum effort. ≈4600ml
      • Forced vital capacity (用力肺活量) is the maximum amount of air exhaled as rapidly as possible.
      • Forced expiratory volume during the first second (1秒用力呼气量) is the amount of air exhaled within the first second of FVC.
    • Alveolar ventilation 肺泡通气
      • The rate at which new air reaches the respiratory zone is called alveolar ventilation (肺泡通气量).
      • Areas where gas exchange does not occur are called dead spaces (无效腔).
      • Anatomic dead space (解剖无效腔) = conducting zone ≈ 150ml
      • Alveolar dead space (肺泡无效腔) is due to absent or poor blood flow. ≈0
      • Physiological dead space (生理无效腔) = total dead space
  • Gas exchange
    • gas law
      • Dalton’s law
        • Atmospheric pressure = PN2 +PO2 +PAr +PH2O +PCO2 + ···
      • Henry’s law
        • The quantity of a gas that will dissolve in a liquid is proportional to the partial pressure of the gas and its solubility
      • Factors that influence gas diffusion
        • Partial pressure difference
        • Molecular weight
        • Solubility (air-liquid interface)
        • Surface area
        • Diffusion distance
        • Temperature
        • 速度
    • Alveolar gas exchange
      • Respiratory unit
        • A respiratory bronchiole 呼吸性细支气管
        • Alveolar ducts 肺泡管
        • Alveolar sacs 肺泡囊，连接着好几个肺泡
        • Alveoli 肺泡
        • 图
      • Respiratory membrane
        • A layer of fluid containing surfactant that lines the alveolus
        • The alveolar epithelium 上皮
        • An epithelial basement membrane 上皮基底膜
        • A thin interstitial间质的 space
        • A capillary basement membrane 毛细基底膜
        • The capillary endothelial membrane 毛细血管内皮膜
        • 图
      • The total surface area of the respiratory membrane is about 70m²
      • The total quantity of blood in the capillaries of the lungs at any given instant is 60~140ml
      • Ventialtion/perfusion ratio (通气/血流比值)
        • VA / Q ≈ 0.84
        • 我们看作血流Q 60~140 ≈100
        • VA ≈ 84mL
    • Systemic gas exchange
      • The directions of gas diffusion is different.
      • The interface is different.
  • Gas transport
    • Oxygen transport
      • O2 does not dissolve easily in water, thus about 1.5% of inhaled O2 is dissolved in blood plasma
      • About 98.5% of blood O2 is bound to hemoglobin in RBCs
      • Each 100ml of oxygenated blood contains the equivalent of 20ml of O2.
      • 动脉里氧气分压约为95mmHg，静脉里约为40mmHg，运动时静脉可以更低
      • 血红蛋白
        • relaxed有O2，tight没有O2
        • When O2 binds to hemoglobin, allostery T→R, affinity to O2↑, more O2 binds to hemoglobin
        • When O2 dissociates from hemoglobin, allostery R→T, affinity to O2↓, more O2 dissociates from hemoglobin
        • 正反馈调节，O2越多，O2越多，O2越少，O2越少
      • Factors affecting the affinity of hemoglobin for oxygen
        碱冷利氧
        • ①pH
          • pH↑, affinity↑
          • pH↓, affinity↓
        • ②PCO2
          • PCO2 ↑, affinity↓
          • PCO2 ↓, affinity↑
        • ③temperature
          • temp↑, affinity↓
          • temp↓, affinity↑
        • ④DPG(二磷酸甘油酸)
          • DPG↑, affinity↓
          • DPG↓, affinity↑
          • 胎儿血红蛋白构成与成人不同
          • 胎儿血红蛋白的affinity比母亲的大
        • ⑤CO
          • The affinity of hemoglobin for CO is 250 times greater than that for O2.
    • Carbon dioxide transport
      • Each 100ml of deoxygenated blood contains 53ml of CO2
      • 7% dissolved in plasma
      • 23% combines with proteins (such as hemoglobin) in the blood to form carbamino compounds (氨基甲酰化合物)
      • 70% as HCO3-
      • 在动脉里40mmHg，静脉里45mmHg
      • systemic gas exchange
      • alveolar gas exchange
      • 神奇的CAH既可以催化CO2变成H2CO3又可以催化反向反应
  • Regulation of respiration
    • receptors
      • Peripheral chemoreceptors
        • 位于主动脉体和颈动脉体，传递信号到延髓
        • aortic bodies 主动脉体连着vagus nerve 迷走神经
        • carotid body 颈动脉体连着glossopharyngeal nerve 舌咽神经
        • sensitive to PO2，less sensitive to PCO2 and H+
        • Ⅰ型细胞感受到以下条件时，会通过导致K+通道失活，细胞去极化导致Ca2+通道打开，Ca2+浓度升高释放神经递质
        • PO2 ↓, impulses↑
        • PCO2 ↑, impulses↑
        • H+↑, impulses↑
      • Central chemoreceptors
        • Central chemoreceptors are located on the ventral腹部 surface of rostral/caudal medulla延髓头端/尾端
        • Central chemoreceptors do not monitor PO2 or PCO2 , but H+ in the cerebrospinal fluid (脑脊液).
        • They are 25 times more sensitive to H+ than peripheral chemoreceptors.
        • H+ is produced by CO2 diffused across the blood-brain barrier.
      • Stretch receptors
        • Pulmonary stretch receptors (肺牵张感受器) are located in the smooth muscle of bronchi and bronchioles.
        • When the lungs become overly inflated膨胀 (the tidal volume > 1.5L), these receptors transmit signals through the vagi into the respiratory center.
        • It appears to be mainly a protective mechanism for preventing excess lung inflation rather than an important ingredient in normal control of respiration
    • respiratory center
      • Brainstem (脑干) = midbrain (中脑) + pons (脑桥) + medulla (延髓)
      • The lower brainstem = pons + medulla
      • The lower brainstem实验
        • 切哈基米的低位脑干，观察呼吸变化，图里蓝的是呼吸中枢位置
        • 切A
          • transection between the midbrain中脑 and the pons脑桥
          • No change in breathing with vagi intact
          • Eupnea changes to deep breathing with vagi cut
          • 说明中枢在A下面
        • 切D
          • transection between the medulla延髓 and the spinal cord脊髓
          • Breathing ceases with/without vagi
          • 说明中枢在D上面
        • 切B
          • transection at the middle of pons
          • Breathing becomes deep with vagi intact
          • Breathing becomes apneusis (长吸式呼吸) with vagi cut.
          • Pneumotaxic center (呼吸调整中枢) in the upper zone of pons
        • 切C
          • transection between the pons脑桥 and the medulla延髓
          • Breathing becomes gasping
          • Apneustic长呼吸 center in the lower zone of pons
          • Gasping喘息 center in the medulla
        • 结论
          • The pneumotaxic center呼吸调整中枢 inhibits apneustic center and switches inhalation to exhalation.
          • The apneustic center长呼吸中枢 promotes inhalation.
          • The gasping center喘息中枢 maintains a basic respiratory rhythm.
          • The vagi promotes exhalation and inhibits inhalation
      • DRG与VRG位于延髓，PRG位于脑桥
      • DRG
        • Neurons of dorsal respiratory group ( 背侧呼吸组 ) are located within NTS (孤束核).
        • During eupnea, neurons of DRG generate impulses to the diaphragm via phrenic nerves隔运动神经 and the external intercostal肋间 muscles via intercostal nerves.
        • The impulses last for 2s, and DRG become inactive for 3s
      • VRG
        • Neurons of ventral respiratory group (腹侧呼吸组) remain almost totally inactive during eupnea.
        • They do not appear to participate in the basic respiratory rhythm.
        • During forced inhalation, neurons of VRG send impulses to the accessory muscles辅助肌 of inhalation.
        • During forced exhalation, these neurons send impulses to muscles of exhalation.
      • PRG
        • The pontine respiratory group ( 脑桥呼吸组 ) is the pneumotaxic area呼吸调整中枢
        • Neurons of PRG transmit impulses to DRG, modifying the basic rhythm of breathing
        • 限制吸气，使吸气向呼气转换
      • Cortex 大脑皮层
        • Because the cerebral cortex has connections with the respiratory center, we can voluntarily alter the pattern of breathing
        • Nerve impulses from the hypothalamus (下丘脑) and limbic system (边缘系统) also alter breathing via emotional stimuli
    • motor nerve
      • 图
      • C3-C5 control diaphragm
      • T1-T5 control intercostals肋间肌 and abdominal腹肌