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Anatomy Chapter 13.docx

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University of Toronto Scarborough
Biological Sciences
Connie Soros

Chapter 13 Respiratory System • Terminology (different from text) - pulmonary ventilation: breathing - external respiration: gas exchange between the blood and alveoli (air sacs) - gas transport: blood transports gases to tissues (CV system) - internal respiration: gas exchange between the blood and tissues (CV/tissues) - cellular respiration: use of O 2o produce ATP (cells) • Functions - obtain O ,2eliminate CO 2 - nonrespiratory functions 1. route for water and heat loss 2. enhance venous return 3. acid-base balance (CO ) 2 4. vocalization 5. defense against inhaled invaders 6. sense of smell 7. alters blood composition • Functional anatomy - airways 1. smallest bronchioles have no cartilage; smooth muscle regulates air flow (bronchoconstriction and bronchodilation) - alveoli (air sacs) 1. thin walled and surrounded by capillaries a. large surface area for gas exchange b. type I cells - simple squamous epithelium c. type II cells - secrete surfactant d. macrophages fight invaders - pleural sacs 1. each lung is separate 2. intrapleural fluid lubricates surfaces and helps lungs stick to thoracic wall • Respiratory mechanics - in ventilation air flows down a pressure gradient 1. 3 important pressures a. atmospheric pressure (760 mmHg at sea level) b. intra-alveolar a.k.a. intrapulmonary pressure (varies) c. intrapleural pressure a.k.a. intrathoracic pressure is within the pleural sac (756 mmHg at rest) 2. lungs will always expand to fill the thoracic cavity a. intrapleural fluid (sticky) b. transmural pressure gradient (1) intra-alveolar pressure always equilibrates with atmospheric pressure (2) greater pressure outward than inward 3. inspiration a. inspiratory muscles contract (diaphragm and external intercostals) b. volume of thoracic cavity and lungs increases c. intra-alveolar pressure decreases d. air flows in 4. expiration a. inspiratory muscles relax (quiet breathing) b. volume of thoracic cavity and lungs decreases c. intra-alveolar pressure increases d. air flows out 5. forced expiration a. expiratory muscles contract (abdominal wall muscles and internal intercostals) - airway resistance 1. adjusted to meet the body's needs a. parasympathetic stimulation  bronchoconstriction  increased resistance  decreased airflow b. sympathetic stimulation/epinephrine  bronchodilation  decreased resistance  increased airflow - matching airflow to blood flow (ventilation-perfusion coupling) 1. local controls act on bronchiolar smooth muscle and on arteriolar smooth muscle 2. bronchioles a. increased CO  2ronchodilation  increased airflow b. decreased CO  b2onchoconstriction  decreased airflow 3. arterioles a. decreased O  2asoconstriction  decreased blood flow b. increased O  vasodilation  increased blood flow 2 4. simultaneous adjustments mean air and blood not wasted a. examples: (1) if blood flow > airflow, increased CO a2d decreased O in al2eoli, so bronchodilation and vasoconstriction (2) if airflow > blood flow, decreased CO and increased O in alveoli, so 2 2 bronchoconstriction and vasodilation - elastic behavior of lungs 1. healthy lungs recoil after stretching and are compliant (easy to inflate) 2. two main factors a. elastin fibers in lung connective tissue b. alveolar surface tension (1) water molecules lining alveoli attract each other, creating surface tension (2) surfactant decreases surface tension (without it lungs would collapse) (3) surfactant also increases compliance and reduces work needed to breathe (4) surfactant may also enhance phagocytosis 3. in healthy lungs breathing requires little energy a. 3% of total energy at rest b. 5% during exercise c. up to 30% at rest with obstructive lung disease • Gas Exchange - gases diffuse down partial pressure gradients (pressure exerted by a particular gas in a mixture of gases or dissolved in a body fluid) 1. alveolar PO i2 lower than atmospheric PO and al2eolar PCO is higher 2han atmospheric PCO 2 a. water vapor in lungs dilutes gases b. newly inspired air mixes with old air (15% new air with inspiration) 2. CO 2equires a smaller gradient for efficient transfer because it is more soluble (usually about equal amounts of O /CO2excha2ged) 3. at lungs a. PO a2ways higher in alveoli, O  b2ood b. PCO al2ays higher in blo
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