The Pulmonary System

• The pulmonary system is responsible for respiration

Objectives of Studying the Pulmonary System

• Describe the upper and lower respiratory tracts, detailing the functions of their components
• Discuss gas exchange and transport within the body
• Define lung volumes and capacities
• Discuss respiration regulation through the nervous system and chemical mediation

Divisions of the Respiratory System

• The respiratory system consists of the upper and lower respiratory tracts
• The upper respiratory tract includes structures located outside the chest cavity, such as the nose, nasal cavities, pharynx, larynx, and upper trachea.
• The lower respiratory tract includes structures within the chest cavity like the lower trachea, lungs (including bronchial tubes and alveoli), pleural membranes, diaphragm, and intercoastal muscles

Upper Respiratory Tract

• The upper respiratory tract includes the nose, Nasal Cavities, Pharynx, and Larynx.
• The nose has hair inside the nostrils which blocks the entry of dust
• Nasal Cavities contains nasal mucosa which is made of ciliated epithelium with goblet cells
• Paranasal sinuses open into nasal cavities, and lighten the skull and provide voice resonance
• The pharynx is posterior to nasal and oral cavities
• Nasopharynx sits above the soft palate and is a passageway for air only; Eustachian tubes open into it and contains the adenoid
• The Oropharynx sits behind the mouth and its a passageway for air and food; Palatine tonsils are on its lateral walls.
• The Laryngopharynx is a passageway for both air and food, it opens anteriorly into the larynx and posteriorly into the esophagus
• The larynx is the voice box and airway joining the pharynx and trachea containing 9 cartilages
• The thyroid cartilage is the largest and most anterior
• The epiglottis is the uppermost cartilage which covers the larynx when swallowing
• Vocal cords are lateral to the glottis, and vibrate when speaking as exhaled air passes over them making sound
• The trachea extends from the larynx to primary bronchi
• C-shaped cartilages in the wall keep it open.
• The mucosa consists of ciliated epithelium with goblet cells, cilia sweep mucus, trapped dust, and microorganisms to the pharynx.

Lower Respiratory Tract

• The bronchial tree extends from the trachea to the alveoli.
• The right and left primary bronchi branch from the trachea and delivers air to each lung
• Secondary bronchi go to the lobes of each lung with 3 on the right, 2 on the left
• Walls of the Bonchioles do not have cartilage

Lungs and Pleural Membranes

• Lungs stretch form the diaphragm up to the clavicles
• The rib cage protects them from mechanical injury
• The hilus is an indentation on the medial side, where entry occurs for the primary bronchus, pulmonary artery and veins, and bronchial vessels
• The pleural membranes are serous membranes of the thoracic cavity
• Parietal pleura lines the chest walls, while visceral pleura covers the lungs
• Serous fluid between the layers prevents friction and keeps them together during breathing

Alveoli

• Alveoli are the site of gas exchange
• They are made of simple squamous epithelium where thinness permits diffusion
• They are surrounded by pulminary capillaries and pulminary artieroles constrict in response to the hypoxia of poorly ventilated alveoli
  • Blood gets shunted to better ventilated alveoli
• Elastic connective tissue is located between alveoli and is important for normal exhalation
• The alveolus is lined by a thin layer of fluid mixed with surfactant which decreases surface tension and permits inflation
• Macrophages and neutrophils phagocytize foreign material

Mechanism of Breathing

• Ventilation is the movement of air in and out of the lungs, including phases of inhalation and exhalation
• Ventilation is regulated by respiratory centers in the medulla and pons in the brain
• Key respiratory muscles involved are the diaphragm and external intercostal muscles
• Atmospheric pressure at sea level averages 760 mm Hg
• Intrapleural pressure within the potential pleural space is always slightly below atmospheric pressure
• Intrapulmonic pressure in the bronchial tree and alveoli fluctuates

Inhalation

• The medulla triggers motor impulses via phrenic nerves to stimulate the diaphragm to contract down and flatten
• Impulses get sent along intercostal nerves to the external intercostal muscles, which contract to pull the ribs up and out
• The chest cavity expands with parietal pleura and visceral pleura adheres to the parietal pleura and expands and causes lung expansion
• Intrapulmonic pressure reduces and air rushes into lungs

Exhalation

• Normally passive involving the diaphragm and external intercostals relaxing
• Motor impulses from the medulla decrease diaphragm and external intercostals to relax
• The chest cavity becomes smaller to compress the lungs, elastic lung tissue recoils to further compress the alveoli
• Intrapulmonic pressure increases --> air gets forced out of lungs
• Forced exhalation which utilizes accessory muscles of expiration
  • Internal intercostals pull ribs down and inward and abdominal muscles force the diaphragm upward

Pulmonary Volumes

• Lung capacity varies based on the individual size and age
• Taller have larger lungs
• Lung capacity diminishes with age due to a loos of tissue elasticity and decreased efficiency of respiratory muscles
• Tidal volume (TV) refers to the air amount inhaled and exhaled in normal quiet breathing ~500 mL
• Minute respiratory volume (MRV) is amount of air inhaled and exhaled in 1 minute
• MRV - TV x number of respirations per minute
  • Avg respiratory rate is 12 to 20 per minute
  • Equals 500 mL x 12 breaths/min = 6000 mL/min
• Shallo breathing with smaller TV requires RR to achieve required MRV
• Inspiratory reserve volume (IRV) is volume that can inhaled beyond TV
  • The normal IR is 2000-3000 mL
• Expiratory reserve volume (ERV) is the volume that can be exhaled beyond TV
  • The Normal ER IS 1000-1500 mL
• Residual volume (RV) is amount of air left in lungs after maximum forceful exhalation
• The average range is 1000-1500 mL, the ensures some amount of air stays in lungs at all times and helps maintain gas exchange

Pulmonary Capacities

• Inspiratory capacity is total of TV and IRV, refers to the amount of air that can be inhaled when starting from tidal exhalation.
• Functional residual capacity is total of RV and ERV, which refers to remaining amount of air in lungs following tidal exhalation.
• Vital capacity (VC) refers to amount of air in lungs with volitional control
  • TV + IRV + ERV
  • Ave VC is 3500 - 5000 mL/min
• Total lung capacity (TLC) is TV + IRV + ERV +RV

Gas Exchange

• Exchange occurs in the lungs and in the body tissues
• Air we breathe in is 21% O₂, 0.04%CO₂ and we exhale air with 16%O₂, 4.5%CO₂
• Some oxygen is retained internally and CO₂ that cells produced is exhaled
• External respiration is the exchange of gases between the air in the alveoli and the blood in pulmonary capillaries
• Oxygen in the air diffuses from the air in the alveoli to the blood in pulminary capillaries
• Carbon Dioxide diffuses from the blood to the air in the alveoli
• Internal respiration is the exchange of gases between the blood in systemic capillaries and the interstitial fluid
• The arteriole blood in systemic capillaries has high PO₂ and low PCO₂ so the oxygen can diffuse into the interstitial fluid
• The body and tissue fluid has low oxygen, high carbod dioxide and carbon dioxide diffuses into blood

Partial Pressure

• Partial pressure reflects the concentration of a gas in a particular site
• Partial pressure equals the % of gas mixture multiplied by total pressure
• Oxygen in the atmosphere averages to 21% x 760mm hg = 160 mmHG (PO₂)

Transport of Gases In Blood

• Roughly 1.5% of oxygen is dissolved in blood and the rest is transported while bonded to hemoglobin in RBCs
• Oxygen hemoglobin bonds form in the lungs
• The bond relatively unstable allowing oxygen to readily dissasociate as it passes through tissues with low PO₂
• The lower the oxygen in tissue the more oxygen released which ensures adequate supply to active tissues
• A high PCO₂, a lower pH, and high tissue temperature increase oxygen release
• A small amount of carbon dioxide is dissolved in blood and some is bound to hemoglobin (cabaminohemoglobin), accounting for around 20% of transport
  • The majority of cabon dioxide is transported in plasma in the form of bicarbonate ions.
  • Once carbon dioxide enters RBCs the carbonic anhydrase catalyes the reaction of CO₂ and H₂O to make carbonic acid.
  • CO₂ + H₂O -> H₂CO₃
• Carbonic acid then dissociates, H₂CO₃ = H+ + HCO₃-
• The bicarbonate ions diffuse out of RBCs into plasma
• This leaves hydrogen ions in the RBCs.
• hemoglobin acts as a buffer to prevent acidosis with hydrogren ions.
• chloride ions shift from plasma into RBC maintains ionic equilibrium
• Reaction reverses when blood moves to the lungs causing carbon dioxide to reform and diffuse into alveoli.

Nervous System Regulation

• The medulla houses inspiration and expiration centers
• The inspiration center automatically generating impulse in spurts
• These impulses travel to respiratory muscles causing contraction and subsequent lung expansion.
• There are receptors in lung tissue which detect stretching as send impulses to the medulla
• The hering breuer reflex prevents overinflation of the lungs
• Expiration center, ventral respiratory group, gets triggered via stimulation with inspiration center when forceful exhalations happen
  • Generates impulses forinternal intercostal and abdominal muscles.
• Pons help regulate normal breathing rhythm
• The Apneustic center prolongs inhalation
• Pneumotaxic center brings about exhalation.
• Hypothalamus facilitates changes to breathing with emotional situations
• The Cerebal cortex permits voluntary changes in breathing.
• The Reflex centers in medulla facilitate coughing and sneexing which help remove irritants from airways

Chemical Regulation of Respiration

• Chemoreceptors detect change in blood and pH
• They are located in the carotid and adortic bodies as in the the medulla
• chemoreceptors detect blood CO₂ levels and trigger respiration to exhale more CO₂
• CO₂ is the major regulator of normal respiration
• High CO₂ will decrease pH of body fluids which leads to acidosis.
• Excess hydrogen ions lower pH, and hypercapnia is abnormally elevated CO₂.
• Oxygen regulates respiration when central chemoreceptors are desensitized to carbon dioxide
• This is the result from severe chronic pulminary disesase
• Decreased blood oxygen is detected by chemoreceptors in carotids and adortic bodies and sends sensory imputls to to the medulla
• The medulla increase depth and rate to bring in air.