Chapter 23
Chapter 23
The Respiratory System
Lecture Outline
INTRODUCTION
• The two systems that cooperate to supply O2 and eliminate CO2 are the cardiovascular and the respiratory system.
• The respiratory system provides for gas exchange.
• The cardiovascular system transports the respiratory gases.
• Failure of either system has the same effect on the body: disruption of homeostasis and rapid death of cells from oxygen starvation and buildup of waste products.
• Respiration is the exchange of gases between the atmosphere, blood, and cells. It takes place in three basic steps: ventilation (breathing), external (pulmonary) respiration, and internal (tissue) respiration.
Chapter 23 The Respiratory System
• Cells continually use O2 & release CO2
• Respiratory system designed for gas exchange
• Cardiovascular system transports gases in blood
• Failure of either system
– rapid cell death from O2 starvation
Respiratory System Anatomy (Figure 23.1).
• Nose
• Pharynx = throat
• Larynx = voicebox
• Trachea = windpipe
• Bronchi = airways
• Lungs
• Locations of infections
– upper respiratory tract is above vocal cords
– lower respiratory tract is below vocal cords
• The conducting system consists of a series of cavities and tubes - nose, pharynx, larynx, trachea, bronchi, bronchiole, and terminal bronchioles - that conduct air into the lungs. The respiratory portion consists of the area where gas exchange occurs - respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.
External Nasal Structures
• Skin, nasal bones, & cartilage lined with mucous membrane
• Openings called external nares or nostrils
External Anatomy
• The external portion of the nose is made of cartilage and skin and is lined with mucous membrane. Openings to the exterior are the external nares.
• The external portion of the nose is made of cartilage and skin and is lined with mucous membrane (Figure 23.2a).
• The bony framework of the nose is formed by the frontal bone, nasal bones, and maxillae (Figure 23.2).
Internal Anatomy
• The interior structures of the nose are specialized for warming, moistening, and filtering incoming air; receiving olfactory stimuli; and serving as large, hollow resonating chambers to modify speech sounds.
• The internal portion communicates with the paranasal sinuses and nasopharynx through the internal nares.
• The inside of both the external and internal nose is called the nasal cavity. It is divided into right and left sides by the nasal septum. The anterior portion of the cavity is called the vestibule (Figure 7.14a).
• The surface anatomy of the nose is shown in Figure 23.3.
• Nasal polyps are outgrowths of the mucous membranes which are usually found around the openings of the paranasal sinuses.
Nose -- Internal Structures
• Large chamber within the skull
• Roof is made up of ethmoid and floor is hard palate
• Internal nares (choanae) are openings to pharynx
• Nasal septum is composed of bone & cartilage
• Bony swelling or conchae on lateral walls
Functions of the Nasal Structures
• Olfactory epithelium for sense of smell
• Pseudostratified ciliated columnar with goblet cells lines nasal cavity
– warms air due to high vascularity
– mucous moistens air & traps dust
– cilia move mucous towards pharynx
• Paranasal sinuses open into nasal cavity
– found in ethmoid, sphenoid, frontal & maxillary
– lighten skull & resonate voice
Rhinoplasty
• Rhinoplasty (“nose job”) is a surgical procedure in which the structure of the external nose is altered for cosmetic or functional reasons (fracture or septal repair)
• Procedure
– local and general anesthetic
– nasal cartilage is reshaped through nostrils
– bones fractured and repositioned
– internal packing & splint while healing
Pharynx - Overview
• The pharynx (throat) is a muscular tube lined by a mucous membrane (Figure 23.4).
• The anatomic regions are the nasopharynx, oropharynx, and laryngopharynx.
• The nasopharynx functions in respiration. Both the oropharynx and laryngopharynx function in digestion and in respiration (serving as a passageway for both air and food).
Pharynx
Pharynx
• Muscular tube (5 inch long) hanging from skull
– skeletal muscle & mucous membrane
• Extends from internal nares to cricoid cartilage
• Functions
– passageway for food and air
– resonating chamber for speech production
– tonsil (lymphatic tissue) in the walls protects entryway into body
• Distinct regions -- nasopharynx, oropharynx and laryngopharynx
Nasopharynx
• From choanae to soft palate
– openings of auditory (Eustachian) tubes from middle ear cavity
– adenoids or pharyngeal tonsil in roof
• Passageway for air only
– pseudostratified ciliated columnar epithelium with goblet
Oropharynx
• From soft palate to epiglottis
– fauces is opening from mouth into oropharynx
– palatine tonsils found in side walls, lingual tonsil in tongue
• Common passageway for food & air
– stratified squamous epithelium
Laryngopharynx
• Extends from epiglottis to cricoid cartilage
• Common passageway for food & air & ends as esophagus inferiorly
– stratified squamous epithelium
Larynx - Overview
• The larynx (voice box) is a passageway that connects the pharynx with the trachea.
• It contains the thyroid cartilage (Adam’s apple); the epiglottis, which prevents food from entering the larynx; the cricoid cartilage, which connects the larynx and trachea; and the paired arytenoid, corniculate, and cuneiform cartilages (Figure 23.5).
• Voice Production
– The larynx contains vocal folds (true vocal cords), which produce sound. Taunt vocal folds produce high pitches, and relaxed vocal folds produce low pitches (Figure 23.6). Other structures modify the sound.
Cartilages of the Larynx
• Thyroid cartilage forms Adam’s apple
• Epiglottis---leaf-shaped piece of elastic cartilage
– during swallowing, larynx moves upward
– epiglottis bends to cover glottis
• Cricoid cartilage---ring of cartilage attached to top of trachea
• Pair of arytenoid cartilages sit upon cricoid
– many muscles responsible for their movement
– partially buried in vocal folds (true vocal cords)
Larynx
• Cartilage & connective tissue tube
• Anterior to C4 to C6
• Constructed of 3 single & 3 paired cartilages
Vocal Cords
• False vocal cords (ventricular folds) found above vocal folds (true vocal cords)
• True vocal cords attach to arytenoid cartilages
The Structures of Voice Production
• True vocal cord contains both skeletal muscle and an elastic ligament (vocal ligament)
• When 10 intrinsic muscles of the larynx contract, move cartilages & stretch vocal cord tight
• When air is pushed past tight ligament, sound is produced (the longer & thicker vocal cord in male produces a lower pitch of sound)
• The tighter the ligament, the higher the pitch
• To increase volume of sound, push air harder
Movement of Vocal Cords
• Opening and closing of the vocal folds occurs during breathing and speech
Speech and Whispering
• Speech is modified sound made by the larynx.
• Speech requires pharynx, mouth, nasal cavity & sinuses to resonate that sound
• Tongue & lips form words
• Pitch is controlled by tension on vocal folds
– pulled tight produces higher pitch
– male vocal folds are thicker & longer so vibrate more slowly producing a lower pitch
• Whispering is forcing air through almost closed rima glottidis -- oral cavity alone forms speech
Application
• Laryngitis is an inflammation of the larynx that is usually caused by respiratory infection or irritants. Cancer of the larynx is almost exclusively found in smokers.
Trachea
• The trachea (windpipe) extends from the larynx to the primary bronchi (Figure 23.7).
• It is composed of smooth muscle and C-shaped rings of cartilage and is lined with pseudostratified ciliated columnar epithelium.
• The cartilage rings keep the airway open.
• The cilia of the epithelium sweep debris away from the lungs and back to the throat to be swallowed.
Trachea
• Size is 5 in long & 1in diameter
• Extends from larynx to T5 anterior to the esophagus and then splits into bronchi
• Layers
– mucosa = pseudostratified columnar with cilia & goblet
– submucosa = loose connective tissue & seromucous glands
– hyaline cartilage = 16 to 20 incomplete rings
• open side facing esophagus contains trachealis m. (smooth)
• internal ridge on last ring called carina
– adventitia binds it to other organs
Trachea and Bronchial Tree
• Full extent of airways is visible starting at the larynx and trachea
Histology of the Trachea
• Ciliated pseudostratified columnar epithelium
• Hyaline cartilage as C-shaped structure closed by trachealis muscle
Airway Epithelium
• Ciliated pseudostratified columnar epithelium with goblet cells produce a moving mass of mucus.
Tracheostomy and Intubation
• Reestablishing airflow past an airway obstruction
– crushing injury to larynx or chest
– swelling that closes airway
– vomit or foreign object
• Tracheostomy is incision in trachea below cricoid cartilage if larynx is obstructed
• Intubation is passing a tube from mouth or nose through larynx and trachea
Bronchi
• The trachea divides into the right and left pulmonary bronchi (Figure 23.8).
• The bronchial tree consists of the trachea, primary bronchi, secondary bronchi, tertiary bronchi, bronchioles, and terminal bronchioles.
• Walls of bronchi contain rings of cartilage.
• Walls of bronchioles contain smooth muscle.
Bronchi and Bronchioles
• Primary bronchi supply each lung
• Secondary bronchi supply each lobe of the lungs (3 right + 2 left)
• Tertiary bronchi supply each bronchopulmonary segment
• Repeated branchings called bronchioles form a bronchial tree
Histology of Bronchial Tree
• Epithelium changes from pseudostratified ciliated columnar to nonciliated simple cuboidal as pass deeper into lungs
• Incomplete rings of cartilage replaced by rings of smooth muscle & then connective tissue
– sympathetic NS & adrenal gland release epinephrine that relaxes smooth muscle & dilates airways
– asthma attack or allergic reactions constrict distal bronchiole smooth muscle
– nebulization therapy = inhale mist with chemicals that relax muscle & reduce thickness of mucus
Pleural Membranes & Pleural Cavity
• Visceral pleura covers lungs --- parietal pleura lines ribcage & covers upper surface of diaphragm
• Pleural cavity is potential space between ribs & lungs
Lungs - Overview
• Lungs are paired organs in the thoracic cavity; they are enclosed and protected by the pleural membrane (Figure 23.9).
• The parietal pleura is the outer layer which is attached to the wall of the thoracic cavity.
• The visceral pleura is the inner layer, covering the lungs themselves.
• Between the pleurae is a small potential space, the pleural cavity, which contains a lubricating fluid secreted by the membranes.
• The pleural cavities may fill with air (pneumothorax) or blood (hemothorax).
• A pneumorthorax may cause a partial or complete collapse of the lung.
• The lungs extend from the diaphragm to just slightly superior to the clavicles and lie against the ribs anteriorly and posteriorly (Figure 23.10).
Lungs - Overview
• The lungs almost totally fill the thorax (Figure 23.10).
• The right lung has three lobes separated by two fissures; the left lung has two lobes separated by one fissure and a depression, the cardiac notch (Figure 23.10).
• The secondary bronchi give rise to branches called tertiary (segmental) bronchi, which supply segments of lung tissue called bronchopulmonary segments.
• Each bronchopulmonary segment consists of many small compartments called lobules, which contain lymphatics, arterioles, venules, terminal bronchioles, respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli (Figure 23.11).
Gross Anatomy of Lungs
• Base, apex (cupula), costal surface, cardiac notch
• Oblique & horizontal fissure in right lung results in 3 lobes
• Oblique fissure only in left lung produces 2 lobes
Mediastinal Surface of Lungs
• Blood vessels & airways enter lungs at hilus
• Forms root of lungs
• Covered with pleura (parietal becomes visceral)
Structures within a Lobule of Lung
• Branchings of single arteriole, venule & bronchiole are wrapped by elastic CT
• Respiratory bronchiole
– simple squamous
• Alveolar ducts surrounded by alveolar sacs & alveoli
– sac is 2 or more alveoli sharing a common opening
Alveoli
• Alveolar walls consist of type I alveolar (squamous pulmonary epithelial) cells, type II alveolar (septal) cells, and alveolar macrophages (dust cells) (Figure 23.12).
• Type II alveolar cells secrete alveolar fluid, which keeps the alveolar cells moist and which contains a component called surfactant. Surfactant lowers the surface tension of alveolar fluid, preventing the collapse of alveoli with each expiration.
• Respiratory Distress Syndrome is a disorder of premature infants in which the alveoli do not have sufficient surfactant to remain open.
• Gas exchange occurs across the alveolar-capillary membrane (Figure 23.12).
Histology of Lung Tissue
Details of Respiratory Membrane
Cells Types of the Alveoli
• Type I alveolar cells
– simple squamous cells where gas exchange occurs
• Type II alveolar cells (septal cells)
– free surface has microvilli
– secrete alveolar fluid containing surfactant
• Alveolar dust cells
– wandering macrophages remove debris
Alveolar-Capillary Membrane
• Respiratory membrane = 1/2 micron thick
• Exchange of gas from alveoli to blood
• 4 Layers of membrane to cross
– alveolar epithelial wall of type I cells
– alveolar epithelial basement membrane
– capillary basement membrane
– endothelial cells of capillary
• Vast surface area = handball court
Details of Respiratory Membrane
• Find the 4 layers that comprise the respiratory membrane
Double Blood Supply to the Lungs
• Deoxygenated blood arrives through pulmonary trunk from the right ventricle
• Bronchial arteries branch off of the aorta to supply oxygenated blood to lung tissue
• Venous drainage returns all blood to heart
• Less pressure in venous system
• Pulmonary blood vessels constrict in response to low O2 levels so as not to pick up CO2 on there way through the lungs
Clinical Applications
• Nebulization, a procedure for administering medication as small droplets suspended in air into the respiratory tract, is used to treat many different types of respiratory disorders.
• In the lungs vasoconstriction in response to hypoxia diverts pulmonary blood from poorly ventilated areas to well ventilated areas. This phenomenon is known as ventilation – perfusion coupling.
PULMONARY VENTILATION
• Respiration occurs in three basic steps: pulmonary ventilation, external respiration, and internal respiration.
• Inspiration (inhalation) is the process of bringing air into the lungs.
• The movement of air into and out of the lungs depends on pressure changes governed in part by Boyle’s law, which states that the volume of a gas varies inversely with pressure, assuming that temperature is constant (Figure 23.13).
Breathing or Pulmonary Ventilation
• Air moves into lungs when pressure inside lungs is less than atmospheric pressure
– How is this accomplished?
• Air moves out of the lungs when pressure inside lungs is greater than atmospheric pressure
– How is this accomplished?
• Atmospheric pressure = 1 atm or 760mm Hg
Boyle’s Law
• As the size of closed container decreases, pressure inside is increased
• The molecules have less wall area to strike so the pressure on each inch of area increases.
Dimensions of the Chest Cavity
• Breathing in requires muscular activity & chest size changes
• Contraction of the diaphragm flattens the dome and increases the vertical dimension of the chest
Inspiration
• The first step in expanding the lungs involves contraction of the main inspiratory muscle, the diaphragm (Figure 23.14).
• Inhalation occurs when alveolar (intrapulmonic) pressure falls below atmospheric pressure. Contraction of the diaphragm and external intercostal muscles increases the size of the thorax, thus decreasing the intrapleural (intrathoracic) pressure so that the lungs expand. Expansion of the lungs decreases alveolar pressure so that air moves along the pressure gradient from the atmosphere into the lungs (Figure 23.15).
• During forced inhalation, accessory muscles of inspiration (sternocleidomastoids, scalenes, and pectoralis minor) are also used.
• A summary of inhalation is presented in Figure 23.16a.
Quiet Inspiration
• Diaphragm moves 1 cm & ribs lifted by muscles
• Intrathoracic pressure falls and 2-3 liters inhaled
Expiration
• Expiration (exhalation) is the movement of air out of the lungs.
• Exhalation occurs when alveolar pressure is higher than atmospheric pressure. Relaxation of the diaphragm and external intercostal muscles results in elastic recoil of the chest wall and lungs, which increases intrapleural pressure, decreases lung volume, and increases alveolar pressure so that air moves from the lungs to the atmosphere. There is also an inward pull of surface tension due to the film of alveolar fluid.
• Exhalation becomes active during labored breathing and when air movement out of the lungs is impeded. Forced expiration employs contraction of the internal intercostals and abdominal muscles (Figure 23.15).
• A summary of expiration is presented in Figure 23.16b.
Quiet Expiration
• Passive process with no muscle action
• Elastic recoil & surface tension in alveoli pulls inward
• Alveolar pressure increases & air is pushed out
Labored Breathing
• Forced expiration
– abdominal mm force diaphragm up
– internal intercostals depress ribs
• Forced inspiration
– sternocleidomastoid, scalenes & pectoralis minor lift chest upwards as you gasp for air
Intrapleural
Pressures
• Always subatmospheric (756 mm Hg)
• As diaphragm contracts intrathoracic pressure decreases even more (754 mm Hg)
• Helps keep parietal & visceral pleura stick together
Summary of Breathing
• Alveolar pressure decreases & air rushes in
• Alveolar pressure increases & air rushes out
Alveolar Surface Tension
• Thin layer of fluid in alveoli causes inwardly directed force = surface tension
– water molecules strongly attracted to each other
• Causes alveoli to remain as small as possible
• Detergent-like substance called surfactant produced by Type II alveolar cells
– lowers alveolar surface tension
– insufficient in premature babies so that alveoli collapse at end of each exhalation
Compliance of the Lungs
• Ease with which lungs & chest wall expand depends upon elasticity of lungs & surface tension
• Some diseases reduce compliance
– tuberculosis forms scar tissue
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