Chapter 7 The Respiratory System Copyright 2010, John Wiley & Sons, Inc.

Respiration: Three Major Steps Pulmonary ventilation Moving air in and out of lungs External respiration Gas exchange between alveoli and blood Internal respiration Gas exchange between blood and cells Copyright 2010, John Wiley & Sons, Inc.

Organs of the Respiratory System Upper respiratory system Nose and pharynx Lower respiratory system Trachea, larynx, bronchi, bronchioles, and lungs “Conducting zone” consists of All airways that carry air to lungs: Nose, pharynx, trachea, larynx, bronchi, bronchioles, and terminal bronchioles “Respiratory zone” Sites within lungs where gas exchange occurs Respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli Copyright 2010, John Wiley & Sons, Inc.

Organs of the Respiratory System Copyright 2010, John Wiley & Sons, Inc.

Upper Respiratory System: Nose Structure External nares  nasal cavity  internal nares Nasal septum divides nose into two sides Nasal conchae covered by mucous membrane Functions Warm, humidify, filter/trap dust and microbes Mucus and cilia of epithelial cells lining nose Detect olfactory stimuli Modify vocal sounds Copyright 2010, John Wiley & Sons, Inc.

Upper Respiratory System: Pharynx Known as the “throat” Structure Funnel-shaped tube from internal nares to larynx 3 parts Three regions (with tonsils in the upper two) Upper: nasopharynx; posterior to nose Adenoids and openings of auditory (Eustachian) tubes Middle: oropharynx; posterior to mouth Palatine and lingual tonsils are here Lower: laryngeal pharynx Connects with both esophagus and larynx: food and air The adenoid, also known as a pharyngeal tonsil or nasopharyngeal tonsil, is a mass of lymphatic tissue situated posterior to the nasal cavity, Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc.

Respiratory System: Head and Neck Copyright 2010, John Wiley & Sons, Inc.

Lower Respiratory System: Larynx “Voice box” Made largely of cartilage Thyroid cartilage: V-shaped “Adam's apple”: projects more anteriorly in males Vocal cords “strung” here (and to arytenoids) Epiglottis: leaf-shaped piece; covers airway During swallowing, larynx moves up so epiglottis covers opening into trachea Cricoid cartilage: inferior most portion Arytenoids (paired, small) superior to cricoid Copyright 2010, John Wiley & Sons, Inc.

Lower Respiratory System: Larynx Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc. Voice Production Mucous membrane of larynx forms two pairs of folds Upper = false vocal cords Lower = true vocal cords Contain elastic ligaments When muscles pull elastic ligaments tight, vocal cords vibrate  sounds in upper airways Pitch adjusted by tension of true vocal cords Lower pitch of male voice Vocal cords longer and thicker; vibrate more slowly Copyright 2010, John Wiley & Sons, Inc.

Lower Respiratory System: Trachea “Windpipe” Location Anterior to esophagus and thoracic vertebrae Extends from end of larynx to primary bronchi Structure Lined with pseudostratified ciliated mucous membrane: traps and moves dust upward C-shaped rings of cartilage support trachea, keep lumen open during exhalation Tracheostomy: opening in trachea for tube Copyright 2010, John Wiley & Sons, Inc.

Lower Respiratory System: Bronchi, Bronchioles Structure of bronchial tree Bronchi contain cartilage rings Primary bronchi enter the lungs medially In lungs, branching secondary bronchi One for each lobe of lung: 3 in right, 2 in left Tertiary bronchi    terminal bronchioles These smaller airways Have less cartilage, more smooth muscle. In asthma, these airways can close. Can be bronchodilated by sympathetic nerves, epinephrine, or related medications. Copyright 2010, John Wiley & Sons, Inc.

Lower Respiratory System: Lungs Two lungs: left and right Right lung has 3 lobes Left lung has 2 lobes and cardiac notch Lungs surrounded by pleural membrane Parietal pleura attached to diaphragm and lining thoracic wall Visceral pleura attached to lungs Pleural cavity with little fluid between pleurae Broad bottom of lungs = base; pointy top = apex Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc. Lung Lobes Divided into lobules fed by tertiary bronchi Further divisions  terminal bronchioles  Respiratory bronchioles Lined with nonciliated epithelium  Alveolar ducts  Alveolar sacs  Surrounded by alveoli Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc. Lung Lobes Copyright 2010, John Wiley & Sons, Inc.

Lower Respiratory System: Alveoli Cup-shaped outpouchings of alveolar sacs Alveoli: composed of three types of cells Lined with thin alveolar cells (simple squamous); sites of gas exchange Scattered surfactant-secreting cells. Surfactant: Lowers surface tension (keeps alveoli from collapsing) Humidifies (keeps alveoli from drying out) Alveolar macrophages: “cleaners” Respiratory membrane: alveoli + capillary Gases diffuse across these thin epithelial layers: air  blood Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc. Lobule of the Lung Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc. Lobule of the Lung Copyright 2010, John Wiley & Sons, Inc.

Structure of an Alveolus Copyright 2010, John Wiley & Sons, Inc.

Respiration Step: 1. Pulmonary Ventilation Air flows: atmosphere   lungs due to difference in pressure related to lung volume Lung volume changes due to respiratory muscles Inhalation: diaphragm + external intercostals Diaphragm contracts (moves downward)   lung volume Cohesion between parietal-visceral pleura   lung volume as thorax volume . Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc. Exhalation Exhalation is normally passive process due to muscle relaxation Diaphragm relaxes and rises   lung volume External intercostals relax   lung volume Active exhalation: exhale forcefully Example: playing wind instrument Uses additional muscles: internal intercostals, abdominal muscles Copyright 2010, John Wiley & Sons, Inc.

Muscles of Inhalation and Exhalation Copyright 2010, John Wiley & Sons, Inc.

Muscles of Inhalation and Exhalation Copyright 2010, John Wiley & Sons, Inc.

Volume-Pressure Changes in Lungs Volume and pressure are inversely related As  lung volume  alveolar pressure As  lung volume  alveolar pressure Contraction of diaphragm  lowers diaphragm   lung volume  alveolar pressure so it is < atmospheric pressure  air enters lungs = inhalation Relaxation of diaphragm  raises diaphragm   lung volume   alveolar pressure so it is > atmospheric pressure  air leaves lungs = exhalation Copyright 2010, John Wiley & Sons, Inc.

Volume-Pressure Changes in Lungs Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc. Air Flow Terms Frequency = breaths/min; normal: 12 Tidal volume (TV) = volume moved in one breath. Normal ~ 500 ml About 70% of TV reaches alveoli (350 ml) Only this amount is involved in gas exchange 30% in airways = anatomic dead space Minute ventilation (MV) = f x TV = 6000 mL/min Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc. Lung Volumes Measured by spirometer Inspiratory reserve volume (ERV) = volume of air that can be inhaled beyond tidal volume (TV) Expiratory reserve volume (IRV) = volume of air that can be exhaled beyond TV Air remaining in lungs after a maximum expiration = residual volume (RV) Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc. Lung Capacities Inspiratory capacity = TV + IRV Functional residual capacity (FRC) = RV + ERV Vital capacity (VC) = IRV + TV + ERV Total lung capacity (TLC) = VC + RV Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc. Lung Capacities Copyright 2010, John Wiley & Sons, Inc.

Respiration Step 2: Pulmonary Gas Exchange: External Respiration Diffusion across alveolar-capillary membrane O2 diffuses from air (PO2 ~105 mm Hg) to pulmonary artery (“blue”) blood (PO2 ~40 mm Hg). (Partial pressure gradient = 65 mm Hg) Continues until equilibrium (PO2 ~100-105 mm Hg) Meanwhile “blue” blood (PCO2 ~45) diffuses to alveolar air (PCO2 ~40) (Partial pressure gradient = 5 mm Hg) Copyright 2010, John Wiley & Sons, Inc.

Respiration Step 3: Systemic Gas Exchange: Internal Respiration Occurs throughout body O2 diffuses from blood to cells: down partial pressure gradient PO2 lower in cells than in blood because O2 used in cellular metabolism Meanwhile CO2 diffuses in opposite direction: cells  blood Copyright 2010, John Wiley & Sons, Inc.

Internal and External Respiration Copyright 2010, John Wiley & Sons, Inc.

Transport of Oxygen within Blood 98.5% of O2 is transported bound to hemoglobin in RBCs Binding depends on PO2 High PO2 in lung and lower in tissues O2 dissolves poorly in plasma so only 1.5% is transported in plasma Tissue release of O2 to cells is increased by factors present during exercise: High CO2 (from active muscles) Acidity (lactic acid from active muscles) Higher temperatures (during exercise) Copyright 2010, John Wiley & Sons, Inc.

Transport of Carbon Dioxide CO2 diffuses from tissues into blood  CO2 carried in blood: Some dissolved in plasma (7%) Bound to proteins including hemoglobin (23%) Mostly as part of bicarbonate ions (70%) CO2 + H2O  H+ + HCO3- Process reverses in lungs as CO2 diffuses from blood into alveolar air  exhaled Copyright 2010, John Wiley & Sons, Inc.

Transport of Oxygen and Carbon Dioxide Copyright 2010, John Wiley & Sons, Inc.

Control of Respiration Medullary rhythmicity area in medulla Contains both inspiratory and expiratory areas Quiet breathing Inspiratory area  nerve signals to inspiratory muscles for ~2 sec  Inspiration  Inspiration ends and muscles relax  Expiration  Expiratory center active only during forceful breathing Two areas in pons adjust length of inspiratory stimulation Copyright 2010, John Wiley & Sons, Inc.

Control of Respiration Copyright 2010, John Wiley & Sons, Inc.

Control of Respiration Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc.

Regulation of Respiratory Center Cortical input: voluntary adjustment of patterns For talking or cessation of breathing while swimming Chemoreceptor input will override breath-holding Copyright 2010, John Wiley & Sons, Inc.

Regulation of Respiratory Center Chemoreceptor input to  increase ventilation Central receptors in medulla: sensitive to  H+ or PCO2 in CSF Peripheral receptors in arch of aorta + common carotids: respond to  PO2 as well as  H+ or PCO2 in blood Blood and brain pH can be maintained by these negative feedback mechanisms Copyright 2010, John Wiley & Sons, Inc.

Regulation of Respiratory Center Copyright 2010, John Wiley & Sons, Inc.

Other Regulatory Factors of Respiration Respiration can be stimulated by Limbic system: anticipation of activity, emotion Proprioception as activity is started Increase of body temperature Sudden pain can  apnea: stop breathing Prolonged somatic pain can increase rate Airway irritation cough or sneeze Inflation reflex Bronchi wall stretch receptors inhibit inspiration Prevents overinflation Copyright 2010, John Wiley & Sons, Inc.

Aging and the Respiratory System Lungs lose elasticity/ability to recoil  more rigid; leads to Decrease in vital capacity Decreased blood PO2 level Decreased exercise capacity Decreased macrophage activity and ciliary action  Increased susceptibility to pneumonia, bronchitis and other disorders Copyright 2010, John Wiley & Sons, Inc.