RESPI

• Organs and structures of the respiratory system

  • Conducting zone
  • Respiratory zone
• Conducting zone


  • Organs and structures not involved directly in gas exchange
• Structures of the nose

  • Root
  • Bridge
  • Dorsum nasi
  • Apex
  • Ala
  • Philtrum
  • Nasal bone
  • Alar cartilage
• Internal nose


  Nasal cavity
• Nasal septum


  • Formed anteriorly by septal cartilage and posteriorly by the perpendicular plate of ethmoid bone and vomer bones
  • Lateral walls have conchae - upper, middle, and lower, which increase surface area of nasal cavity and disrupt air flow and causing turbulence against nasal epithelium, cleaning, warming, and moisturizing the air
  • Conchae and meatuses (spaces between conchae) also conserve water and prevent dehydration of nasal epithelium by trapping exhaled water
• Palate


  Floor of nasal cavity - hard palate (bone) anteriorly and soft palate (muscle) posteriorly
• Paranasal sinuses


  • Spaces within bones forming walls of nasal cavity; named for associated bones: frontal sinus, maxillary sinus, sphenoidal sinus, ethmoidal sinus
  • Sinuses produce mucus and lighten weight of skull
• Respiratory epithelium


  Pseudostratified ciliated columnar epithelial tissue with goblet cells (produce mucus to trap debris)
• Regions of the pharynx

  • Nasopharynx
  • Oropharynx
  • Laryngopharynx
• Nasopharynx


  Superior portion of the pharynx located between the soft palate and the internal nares; lined with pseudostratified columnar epithelium and houses the pharyngeal tonsils (adenoids)
• Oropharynx


  Extends between the soft palate and the base of the tongue at the level of the hyoid bone; epithelial tissue changes from pseudostratified columnar to stratified squamous epithelium to accommodate the movement of food through this region and protects against abrasion; houses the palatine tonsils on either side of the fauces (archways formed by the soft palate and uvula) and the lingual tonsils attached to the back of the tongue
• Laryngopharynx


  Inferior to the oropharynx and posterior to the larynx; continuous common route for ingested materials and air until it diverges into respiratory and digestive openings; lined with stratified squamous epithelium
• Larynx


  Cartilaginous structure inferior to the laryngopharynx; surrounds and protects the glottis; commonly called the "voice box"; lined with pseudostratified columnar epithelium
• Glottis


  Narrow opening through which inhaled air leaves the pharynx and enters the larynx
• Cartilages of the larynx

  • Epiglottis
  • Thyroid cartilage
  • Cricoid cartilage
  • Arytenoid cartilages
  • Cuneiform cartilages
  • Corniculate cartilages
• Epiglottis


  Flexible flap of elastic cartilage that covers the glottis during swallowing to prevent food from entering respiratory passageways
• Thyroid cartilage


  • Large single piece of hyaline cartilage forming the anterior and lateral walls of the larynx
  • Laryngeal prominence, also "Adam's Apple" - prominent anterior surface of thyroid cartilage
  • Superior portion of thyroid cartilage is connected to the hyoid bone by the thyrohyoid membrane
• Cricoid cartilage


  A single piece of hyaline cartilage with an expanded posterior portion to provide support; together the cricoid and thyroid cartilages protect the glottis and the entrance to the trachea; their broad surfaces provide muscle and ligament attachment sites
• Arytenoid cartilages


  Two small pieces of hyaline cartilage which articulate with the superior surface of the cricoid cartilage; help anchor the vocal cords
• Cuneiform cartilages


  Two long, curved pieces of hyaline cartilage; lie within the folds of tissue that extend between the lateral surface of each arytenoid cartilage and the epiglottis
• Corniculate cartilages


  Two small pieces of hyaline cartilage that articulate with the arytenoid cartilages to function in the opening and closing of the glottis and the production of sound
• Vestibular and Vocal Ligaments

  • Bands of connective tissue that extend between the thyroid cartilage and arytenoid cartilages
  • Vocal folds - house the vocal ligaments; inferior to the vestibular folds; vocal folds vibrate as air passes over them - involved in production of sound; also known as vocal cords
  • Vestibular folds - house an inelastic pair of vestibular ligaments that are not associated with sound production; help prevent foreign objects from entering the glottis and contacting the more delicate vocal folds; also known as false vocal cords
• Trachea


  • Tough flexible tube connecting larynx to bronchi of lungs
  • 16-20 stacked, C-shaped hyaline cartilage rings connected by dense connective tissue keep airway open
  • Trachealis muscle and elastic connective tissue form the fibroelastic membrane that connects C-shaped rings at the posterior of trachea
  • Lined with pseudostratified ciliated columnar epithelium
  • Esophagus borders posteriorly
• Bronchial tree


  • Highly branching pattern of bronchi and bronchioles as they approach and travel through the lungs; rings of cartilage provide support and prevent collapse
  • Primary bronchi - trachea branches at site of Carina to form a right and left primary bronchus; transport air to right and left lung
  • Secondary bronchi - right primary bronchus branches to form three secondary bronchi; left primary bronchus branches to form two secondary bronchi
  • Tertiary bronchi - each secondary bronchus branches to form tertiary bronchi; cartilage begins to shrink forming cartilage plates rather than C-shaped rings
  • Terminal bronchioles (> 1000 per lung) are the LAST branch of the conducting zone
• Respiratory zone


  • Gas exchange occurs
• Respiratory bronchiole


  Smallest bronchioles; lead to alveolar duct which opens to cluster of alveoli
• Alveoli


  • Small, grape-like sacs at ends of alveolar ducts; responsible for gas exchange
  • ~200 µL in diameter with elastic walls; connected to neighboring alveoli by alveolar pores to maintain equal air pressure throughout lung
  • 3 types of cells make up alveolar walls: Type I alveolar cells - simple squamous cells that make up 97% of alveolar surface area; highly permeable to gases
  • Type II alveolar cells – interspersed among type I cells; secrete pulmonary surfactant – substance composed of phospholipids and proteins that reduce surface tension in alveoli
  • Alveolar macrophages – phagocytic immune cell specific to alveoli
• Lungs


  • Pyramid-shaped, paired organs connected to trachea by right and left bronchi
  • Bordered inferiorly by the diaphragm – a dome-shaped muscle at the base of the thoracic cavity
  • Right lung – shorter and wider than left lung; composed of three lobes: superior, middle and inferior lobe divided by two fissures
  • Left lung – occupies smaller volume than right lung; composed of two lobes: superior and inferior lobe divided by the oblique fissure
  • Cardiac notch – indentation in surface of left lung which allows space for the heart
  • Lobes are subdivided into bronchopulmonary segments, each with its own tertiary bronchus and its own artery
  • Segments further subdivide into lobules, each with its own large bronchiole with multiple branches
  • Pulmonary hilum – an indention in each lung where primary bronchi, pulmonary blood vessels, nerves, and lymphatics enter into and exit out of the lungs
• Pulmonary arteries and veins

  • Pulmonary arteries (often shown in blue) exit the right atrium of the heart and transport deoxygenated blood to the lungs; the pulmonary veins (often shown in red) leave the lungs and transport oxygenated blood to the left atrium
  • As pulmonary arteries and arterioles branch and approach alveoli, they become the pulmonary capillary network; wraps around respiratory bronchioles and alveoli, where they contribute to the respiratory membrane
  • Oxygenated blood drains into pulmonary veins which exit through the hilum to return to systemic circulation via the left atrium of the heart
• Nervous innervation of the lungs

  • Sympathetic and parasympathetic systems control dilation and constriction of the airway
  • Bronchoconstriction = parasympathetic
  • Bronchodilation = sympathetic
  • Reflexes like coughing and regulation of oxygen and carbon dioxide are also under autonomic control
  • Pulmonary plexus = nerves enter lungs at the hilum, then follow bronchi to branch for innervation of muscle, glands, and blood vessels
• Pleura of the lungs

  • Serous membrane surrounding each lung; composed of two distinct layers: Visceral pleura – lines external surface of lungs, extending into fissures
  • Parietal pleura – lines the interior of the thoracic cavity and extends over the diaphragm and mediastinum
  • Pleural cavity and pleural fluid – the space between the parietal and visceral pleura; contains a small volume of pleural fluid that coats the pleural surfaces and reduces friction
• Mechanisms of breathing


  • Major mechanisms driving pulmonary ventilation are atmospheric pressure (Patm), intra-alveolar pressure (Palv), and intrapleural pressure (Pip)
  • Pressure differential of 0 mmHg exists when atmospheric and alveolar pressures are equal; positive Palv will push air out of the lungs while negative Palv will pull air into the lungs
  • Air flows from an area of higher pressure to an area of lower pressure
• Atmospheric pressure (Patm)


  The force exerted by the mixture of air surrounding the body; normal atmospheric pressure at sea level is 760 mmHg (1 atm)
• Intra-alveolar pressure (Palv)


  Also, intrapulmonary pressure; the force exerted by the air within the alveoli of the lungs; this pressure rises and falls as the phases of breathing progress; equalizes with Patm
• Intrapleural pressure (Pip)


  Pressure within the pleural cavity; always 4 mmHg lower than the alveolar pressure so the alveoli will be able to inflate
• Boyle's Law


  • P1V1 = P2V2; volume is inversely proportional to pressure; as volume increase, pressure decreases, and as volume decreases, pressure increases
  • If the volume of the thoracic cavity is reduced by half, pressure within the thoracic cavity will double; if the volume of the thoracic cavity is doubled, pressure within will decrease by half
• Physical factors affecting ventilation

  • Changes in intra-alveolar pressure are the result of variations in lung and thoracic volume; contraction and relaxation of respiratory muscles alter the volume of the thoracic cavity; lungs are passive
  • Resistance – force that slows the flow of gases; primarily impacted by size of airway; regulated by bronchodilation and bronchoconstriction
  • Surface tension – water present in respiratory membrane is cohesive; surface tension inhibits expansion of alveoli; type II alveolar cells (pneumocytes) secrete surfactant which reduces surface tension
  • Thoracic wall compliance – ability of thoracic wall to stretch while under pressure; directly influences capacity of lungs to expand
• Pulmonary ventilation


  1. Inspiration - as the diaphragm contracts, it moves downward which increases the volume of the thoracic cavity; intra-alveolar pressure decreases [758 mm Hg], which causes atmospheric air to be pulled into the lung spaces

  2. Expiration - as the diaphragm relaxes, the thoracic cavity volume decreases, intra-alveolar pressure increases [760 mm Hg], and air is pushed out of the lungs
• Factors that affect volume of thoracic cavity

  • Contraction and relaxation of respiratory muscles
• Resistance


  Force that slows the flow of gases; primarily impacted by size of airway; regulated by bronchodilation and bronchoconstriction