BIO 226 Chap 21: The Respiratory System

Anatomy of the Respiratory System

• Respiratory System includes structures involved in breathing, known as pulmonary ventilation, which allows air flow for gas exchange

Upper and Lower Respiratory System

• Respiratory tract is the branching passageway for air movement to and from gas exchange surfaces in the lungs
• The respiratory tract has two divisions:
  • Conducting portion from the nasal cavity to larger bronchioles
  • Respiratory portion from the smallest bronchioles to alveoli, where gas exchange occurs
• The upper respiratory tract Includes the upper respiratory tract, filters, warms, and humidifies incoming air, protects the lower tract, and reabsorbs heat and water from outgoing air
• The lower respiratory tract includes the lower respiratory tract, and it conducts air to and from gas exchange

Functions of the Respiratory System

• Provides a large surface area for gas exchange between air and circulating blood
• Moves air to and from the exchange surfaces
• Protects respiratory surfaces, prevents dehydration, temperature impactsand pathogenic invasion
• Produces sounds for speaking and other forms of communication
• Detects odors through olfactory receptors in the nasal cavity

Respiratory Defense System

• The respiratory defense system works as a series of filtration mechanisms
• Respiratory mucosa will line the nasal cavity through to the large bronchioles
  • It consists of pseudostratified ciliated columnar epithelium and mucous cells
  • The underlying areolar tissue of the Lamina propria supports the respiratory epithelium and includes mucous glands in the trachea and bronchi
• The respiratory tract features a mucociliary escalator composed of mucous and trapped debris
  • Sticky mucus, from mucous cells and glands, traps debris particles
  • Beating cilia moves debris
  • The pharynx sweeps debris to be swallowed, then acids in the stomach destroy it or coughed it out
  • Epithelial stem cells replace damages and old cells that were pushed along by escalator flow
• Specific types of epithelia vary along the tract
• Respiratory mucosa lines the nasal cavity and superior pharynx
• It also lines the superior portion of the lower respiratory tract
• Stratified squamous epithelium lines the inferior porting of the pharynx
• Simple squamous epithelium forms gas exchange surfaces
• Distance between air and blood in capillaries measures less than one micrometer (1µm)
• Cystic fibrosis (CF) is the mist common lethal inherited disease among individuals with Northern European descent
• It results in the production of thick mucus that cannot be transported
• The mucociliary escalator stops, causing frequent infections, and the average lifespan for those living to adulthood is 37
  • Death is usually from heart failure and chronic bacterial lung infections

Upper Respiratory System

• The nose is the primary air route
• The dorsum of the nose (bridge) is formed by two nasal bones
• Hyaline cartilage aids in support
• Nasal cartilages are small elastic cartilages, and extend laterally from the bridge to keep the nostrils open
• Nostrils (external nares) are paired openings into the nasal cavity
• The nasal cavity contains superior, middle, and inferior nasal conchae (bones)
• Also contains superior, middle, and inferior nasal meatuses, act as passages between nasal conchae
• Passages swirl air to trap small particles, moves chemicals to olfactory receptors, and warms & humidifies air
• The paranasal sinuses consist of the frontal sinus, ethmoidal air cells, maxillary sinus, and sphenoidal sinus
• These sinuses secret mucus to moisten and clean the nasal cavity; their surfaces drain with tears through the nasolacrimal duct
• The nasal septum is formed by the vomer and perpendicular plate of the ethmoid
• Extensive network of veins exist within nasal cavities
  • These veins release heat to warm inhaled air
  • Water then evaporates to humidify the air
• Heated air moves from the nasal cavity to the lungs to almost body temp and saturate with water vapor
• During exhalation the reverse happens, the mucosa reabsorbs heat and water reducing heat and water loss
• Mouth breathing benefits are eliminated
• The pharynx is used by both respiratory and digestive systems
  • Includes nasopharynx which is the most superior part of the pharynx - It has pharyngeal opening into the auditory tube
  • Oropharynx extends from soft palate to the base of tongue - It consists of stratified squamous epithelium
  • Laryngopharynx extends from the hyoid to the larynx
• The trachea conducts to bronchi
• The nasal vestibule is where the nasal cavity begins - It contains course hairs that traps large airborne particles
• The nasal cavity opens into the nasopharynx through the choanae
• The bony hard palate forms the floor of the nasal cavity, separating it from the oral cavity
• The soft palate is the fleshy part posterior to the hard palate
• The glottis opens into the larynx
• The larynx is mostly cartilage and surrounds/protects the glottis
• The trachea conducts air toward lungs

Larynx

• The larynx surrounds and protects the glottis (voice box)
• The epiglottis, thyroid cartilage, and cricoid cartilage represent the larynx's three large cartilages
• The epiglottis projects superior to the glottis forming a lid
• While swallowing, the larynx elevates and the epiglottis folds back over the glottis, blocking entry into the respiratory tract
• The thyroid cartilage is shield-shaped (or thyroid) and the anterior surface is the laryngeal prominence (Adam's apple)
• The thyrohyoid ligament attaches it to the hyoid bone
• Other ligaments attach it to the epiglottis and smaller cartilages
• The cricoid cartilage encircles the larynx
• Together the thyroid cartilage protects the glottis and larynx by providing attachment for laryngeal muscles/ligaments
• Small pairs of laryngeal cartilages consist of:
  • Cuneiform cartilages are within the folds of tissue between each arytenoid cartilage and epiglottis
  • Corniculate cartilages that articulate with arytenoid cartilages
    • Work with arytenoid muscles to open and close the glottis
  • Arytenoid, ladle-shaped, cartilages articulate with the superior surface of the cricoid cartilage
• The glottis allows air to pass through the larynx
• It is made of vocal folds and rima glottidis (opening between folds)
• The vocal cords are vibrating tissues that produce sound waves and they are opened and closed by the rotation of the arytenoid cartilages
• Vestibular folds are folds that contain vestibular ligaments, and they help prevent foreign objects from entering the glottis
• Phonation refers to sound production from the larynx
• Includes the vibration of vocal cords, produces sound waves
• Articulation refers to the modification of sounds by the tongue, teeth, and lips
• Additionally, resonance and amplification from the pharynx, nasal cavities, and paranasal sinuses are significant

Trachea, Bronchi, and Bronchial Branches and Air Flow

• The trachea (windpipe) is tough and flexible
• It starts at the C6 of the vertebrae and ends at the T5 vertebrae branching into bronchi
• 15-20 C-shaped tracheal cartilages prevent collapse and overexpansion
• Elastic ligaments and the trachealis muscle connect the ends of each cartilage in the trachea
• The contraction of trachealis narrows the trachea and restricts airflow
• The tracheal diameter changes often, controlled by sympathetic stimulation which typically increases airflow
• Cartilage is incomplete posteriorly to allow for expansion when swallowing
• Right and left main bronchi go to lungs
• The right bronchus is wider, at a steeper angle, so foreign objects often go to the right bronchus
• The trachea bifurcates into main bronchi, then the lobar bronchi, the segmental bronchi and thereafter, they give rise to bronchioles
• There is no cartilage in bronchiole as they are primarily consisted of thick smooth muscle, modulated by the nervous system

Sympathetic and Parasympathetic Modulations

• Sympathetic nervous system causes bronchodilation, increasing airflow The parasympathetic nervous system causes bronchoconstriction, decreasing airflow An extreme form of bronchoconstriction occurs during allergic reactions such as asthma
• Terminal bronchioles lead to pulmonary lobules which is the site of gas exchange
• The route after the pulmonary lobules travels through the respiratory bronchioles, marking the final division
• Airflow and diameter changes as air travels from:
  • the trachea from the larynx in mediastinum towards main bronchi and have complete cartilage rings
• main bronchi towards in the lungs three lobar bronchi in the right lung which carries one per lobe
• segmental bronchi then give rise to bronchioles followed by bronchioles to terminal branches then to the respiratory and and pulmonary divisions

Lung Anatomy

• Lungs are divided into lobes
• Right lung (3) features a superior, middle, and inferior lobe
• Left lung (2) has a superior and inferior lobe
• Each lobe has bronchopulmonary segments Each segmental bronchus supplies the bronchopulmonary segment
• The cone shaped lungs have a horizontal fissure between the superior / middle lobes the right lung, where the oblique fissure between the middle/inferior lobes
• Left lung has oblique fissure between the superior/inferior lobes
• The apex(tip) of the lungs extends to superior border of first rib
• The concave base rests on diaphragm
• The left lung contains a cardiac notch in order to accommodate pericardium with the heart
• The root of the lung consist of dense connective tissue holding bronchi, and major nerves, blood vessels, and lymphatics
• The hilum a medial depression on each lung facilitating the above passage
• Grooves on surface of lungs mark positions of vessels

Pulmonary Lobules and Alveoli

• Segmental bronchus supplies bronchopulmonary segment
• Bronchioles branch into terminal bronchioles which supplies the pulmonary lobule at the terminal site
• Terminal bronchioles then branch into respiratory bronchioles
• Respiratory bronchioles lead to alveolar ducts, which lead to alveolar sacs (alveolar saccules)
• This culminates to 150 million alveoli per lung, which gives lungs an open and spongy appearance
• These are surrounded by extensive capillary networks where there is a gas exchange
• These are surround by elastic fibers which allows for expansion or recoil to aid in air movements
• The two layers the pleurae are serous membrane sacs surrounding the lungs
• Visceral pleura covers the outer surfaces of lungs
• Parietal pleura covers inner surface of thoracic wall - extending over diaphragm and mediastinum
• Pleural cavity is a potential space between visceral and parietal layers of pleural sac
• It contains pleural fluid to reduce friction

Alveolar Cells

• The three major alvelor cell types are:

1. Pneumocytes type I : thin, delicate, allowing gas of diffusion
2. Pneumocytes type II : produce surfactant oily secretion; reduces the surface tension of water in alveoli to prevent collapse
3. Roaming alveolar macrophages : phagocytize particles that could clog the alveoli

Blood Air Barrier

• The blood air barrier is where gas exchange occurs between blood and alveolar air
• It will consist of three layers:
  • alveolar cell epithelium
• fused basement membranes alveoli vessels
• capillary endothelium
• There is minimal distance (~ 0.5 µm ) and because both O2 and CO2 gases are lipid soluble, this leads to very rapid diffusion

Respiration

• Respiration are a set of two key processes of internal and external respiration
• Exchange of gases between blood, lungs, and external environment is termed external respiration
  • The exchange involves gas diffusion at blood air barrier and and all involce alveolar capillaries
  • Pulmonary ventilation will involve air movement in out if the lungs maintainig the right air volumes
• Internal respiration occurs between blood and tissues which absorb oxygen from blood by releasing release CO2
• If externalities affect respiration it will gas concentrations in interstitial fluids
• Low tissue oxygen levels = Hypoxia results in metabolic activities limited
• Not enough oxygen supply = Anoxia which leads is damage from attacks and strokes of localized hypoxia
• The volume and pressure dictates pulmonary ventilation which drives air flow

Gas Laws

• The gas laws operate according to the following principles of volume and pressure
  • Gas molecules will bounce independently
    • When contained, collisions with container wall cause pressure
    • More collisions = more pressure
    • More collisions occur when molecules are in a smaller container Pressure and inversed to volume ( P = 1/volume) otherwise known as Boyles Law i.e. Volume Increase = Pressure Decrease
• Volume within the thoracic cavity dictates volume of of lungs which change which changes pressure of the area
• A breath is dictated by pressures relative to with the thorax, therefore
  • pressures must be equal for movement with parietals being attachend to the thoracic wall where pressure forms bonds beteeen layers while the visceral holds lungs - when injured with airflow the lung might collapses i.e. atelectasis Thoracic cavity and volumes influence air and pressure flows The larger the cavity the more the volume will occur during increased conditions P outside > P inside = Air will force high to low
• The tidal volume is related to volume moved into/out of lungs in an event breath therefore: During Inhalation: Intrapulmonary pressure and pressure pulls air lungs that may be negative or atmosphere related During exhaling : intrapulmonary and pressure pushes air and will be more atmosphere and positve

Respiratory and Pressure Measurement

• The units for determining such is mm Hg and the average is 760 (Millimeters of mercury) : normal average/blood pressure
• The torr unit of measurement and unit is in 1 mm Hg with average normal is 760
• cm H₂O, is another alternative anesthetic/ oxygen pressure to calculate and One cm. is 0.735 mm Hg (centimeters of water) and average amount at 1033.6 cm
• psi pounds per square inch. At the sea levels is to be approximately 15 psi and often is used for compressed gases

Muscles

• The inspiratory muscles have 2 primary that do -75% movement = Diaphragm/ external intercostals and are also 25% - Diaphragm flattens cavity while external elevates the lungs
• During inhalation the main assist = Accessory Muscles will the sternocleidomastoid / scalenes/ pectoralis minor that often Increase to assist movement
• there is no primary Expiratory but it passively in process via recoil but rather accessory muscle during recoil is via gravity - Assist during the External/ internal and obliques/ transverus/ rectus to abdominals and to the transversus lowering lungs quicking for good force change