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Anatomy and Physiology

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									                              Anatomy and Physiology 2402
                                      Chapter 22
                                  Respiratory System

Major Function: Supply the body with oxygen and dispose of carbon dioxide

Respiration: Four Processes
 1. Pulmonary Ventillation – movement of air into and out of the lungs
    (commonly called breathing.)
 2. External respiration – movement of oxygen from the lungs to the blood
    and carbon dioxide from the blood to the lungs
 3. Transport of respiratory gases – transport of oxygen from lungs to the
    tissue cells and of carbon dioxide from tissue cells to the lungs
 4. Internal respiration – movement of oxygen from blood to the tissue
    cells and of carbon dioxide from tissue cells to blood

Functional Anatomy of the Respiratory System:

Nose
Nasal cavity
Pharynx
Larynx
Trachea
Bronchi and smaller branches
Lungs
Alveoli

Respiratory Zone: Actual sites of gas exchange
   Respiratory bronchioles
   Alveolar ducts               all microscopic structures
   Alveoli

Conduction Zone: all other respiratory passageways
    Rigid conduits: cleanse, humidify and warm incoming air

Nose and Paranasal Sinuses

     Functions of the nose:
     1. Provides an airway
     2. Moistens and warms entering air
     3. Filters and cleans inspired air
     4. Serves as a resonating chamber for speech
     5. Houses olfactory receptors
Parts of the Nose:

Nasal cavity:
External nares:
Nasal septum:
Posterior nasal apertures (internal nares or conchae[funnels]): nasal portion of nasopharynx
Palate: separates the nasal cavity from the oral cavity
     Soft palate: not supported by bone – posterior portion
     Hard palate: supported by bone – anterior portion
Vestibule: Part of nasal cavity just superior to the nostrils
     Lined with skin containing sebaceous and sudoriferous glands and numerous hair follicles
Vibrissae: hairs – filter coarse particles

The rest of the nasal cavity is lined with two types of mucous membranes:
     Olfactory mucosae: lines superior region, contains olfactory (smell) receptors
     Respiratory receptors: scattered goblet cells
              Underlining lamina propria contains mucus glands and serous glands
              That secrete mucus and serous fluid which contains enzymes
                      (lysozyme) and defensins (both antibacterials)
              Secrete about a quart of mucus per day.

      Sensory nerve endings Abundant in nasal mucosa – contact with irritating particles stimulates
       the sneeze reflex to expel the irritant.

      Rich plexuses of capillaries and veins underlie nasal epithelium to warm incoming air
       Dilate when cold
       Being so close to the surface and thin walled and in abundance, explains nose bleeds

      Nasal conchae (superior, middle and inferior conchae)
       Increase the mucosal surface area exposed to the air and enhance air turbulence.
       Heavier nongaseous particles tend to deflect onto the mucus coated surfaces and get trapped, so
              few particles larger than 4µ make it past the nasal cavity.
       Surfaces serve to enhance heating, humidifying and filtering of the air breathed in.
       Also serve to reclaim moisture from exhaled air.

Paranasal sinuses:
    Frontal
    Sphenoid                  Lighten the skull
    Ethmoid                   Warm and moisten air
    Maxillary                 Mucus produced in them flows into nasal cavity

∆    Rhinitis – inflammation of the nasal mucosa
    Sinusitis: inflamed sinuses.
    Cause: cold viruses, streptococcal bacteria and various allergens.
       What causes the “sinus headache”?
Pharynx: connects the nasal cavity and mouth superiorly to the larynx and esophagus inferiorly
    Commonly called the “throat”.
    Divided into three parts:

     1. Nasopharynx: Lies above where food enters - serves as air passageway only
                       During swallowing, the soft palate and uvula move superiorly closing off
                       nasopharynx – prevents food from going up into nasal cavity.
                       Pharyngeal tonsil (adenoids) destroys pathogens entering the nasopharynx
                        in air
                          ∆ Infected adenoids: if enlarged, may block passage forcing person to
                          breathe through the mouth. Air is not properly warmed and moistened or
                          filtered. Can affect sleep and speech.

      2. Oropharynx: Lies posterior to the oral cavity seen through the fauces (archway)
                       Both food and air pass through here
                       Paired palatine tonsils: lateral walls
                       Lingual tonsil: Covers base of tongue

      3. Laryngopharynx: Serves as passage for both food and air
                         Posterior to epiglottis extending to larynx where food and air passages
                         diverge.
                         Laryngopharynx continues with the esophagus
                         Larynx continues with the trachea.

     Larynx: Voice box
           Functions 1. Provide open airway
                     2. Switching mechanism to route air and food to proper channels
                     3. Houses vocal cords (sound conduction)

 Epiglottis: Made of elastic cartilage covered in taste buds
    Open when air is moving through passage
    Closes when swallowing
 Vocal Ligaments: form vocal folds or true vocal cords         Voice Production: How does it work?
    Vibration produces sounds
    Glottis: opening between Vocal ligmaments
 Vestibular folds: False vocal cords
    Superior to True Vocal Cords
    Do not produce sound – help close epiglottis
Laryngitis: Inflammation of the vocal folds
      Vocal folds swell, interfering with vibration (causes hoarseness or inability to speak
      above a whisper (vocal folds do not have to vibrate to whisper)

Valsalva’s maneuver: _____________________________________________________

                                            Trachea

Trachea: Windpipe
      Divides into the bronchi (going to each lung)
      Three layers –
      1. Mucosa: contains goblet cells and pseudostratified ciliated epithelium
             with thick underlying lamina propria (alveolar tissue)
      2. Submucosa – connective tissue layer deep to mucosa
             Contains seromucous glands that helps produce “mucus sheets” of trachea
      3. Adventitia – Outermost layer. Connective tissue layer reinforced by 20 C-shaped
             rings of hyaline cartilage which prevent collapsing.

                                The Bronchi and Subdivisions
                                    The Bronchial Tree

Bronchial tree: site where conduction zone gives way to respiratory zone
Conduction zone:
      1. Right and left primary (main) bronchi:
          Splits from the trachea and enters the hilus of each lung.
          The right is shorter, wider and more vertical so it is easier to inhale foreign objects.
          Air is already warmed, filtered and humidified before entering bronchi.
      2. Secondary (lobar) bronchi: Bronchi divide inside the lung
          (3 on the right and 2 on the left)
      3. Tertiary (segmental) bronchi: Bronchioles divide into smaller and smaller branches
          (fourth and fifth order bronchi… 23 order)
      4. Bronchioles: any that are smaller than 1mm in diameter
      5. Terminal bronchioles (bronchial or respiratory tree): the smallest bronchioles less
          than 0.5mm in diameter.

The smaller the passage becomes:
   1. Support structures change: cartilage rings are replaced by irregular plates of cartilage
      until it becomes absent. Elastic fibers are found in bronchial tree instead.
   2. Epithelium type changes: Pseudostratified columnar to columnar to cuboidal.
      Cilia is sparse and mucus producing cells are absent in the bronchioles.
               Airborne particles that enter bronchioles must be removed by macrophages.
   3. Amount of smooth muscle increases: allows bronchioles to be constricted at times.

Respiratory Zone: Defined by the presence of alveoli
             Begins as the terminal bronchioles feed into the respiratory bronchioles
   1. Alveoli: Thin walled sacs at the terminal end of the respiratory zone.
                  Sites for gas exchange (one alveolus is a single sac)
                  About 300 million of them account for most of lung volume
                  Greatly increase surface area.
        2. Respiratory bronchioles: Covered in scattered alveoli
        3. Alveolar ducts: lead into terminal clusters of alveoli
        4. Alveolar sacs: clusters of alveoli (like a bunch of grapes).

 Terminal                  Respiratory
bronchioles                bronchioles with             Alveolar ducts                       Alveoli
                           alveolar sacs


                                           Respiratory Membrane

    Respiratory membrane: capillary walls and alveolar walls and their basal lamina fused
          This forms an air-blood barrier – gas flows on one side and blood flows on the other

              Type I cells: single layer of squamous epithelial cells with flimsy basal lamina thinner
              than tissue paper (form walls of alveoli) surrounded by thin cobweb of capillaries.

              Type II cells: scattered cuboidal cells secrete fluid containing surfactant.
                    Coats surface of alveoli: reduces surface tension of alveolar fluid

              Alveoli:                                                    Huge numbers of pathogens are inhaled,
              1. Are surrounded in elastic fibers                         but alveolar surfaces are generally sterile
              2. Have alveolar pores: connect adjacent alveoli            because of macrophages crawling over
                     Equalizes pressure                                   their surfaces. However, ~ 2 million dead
                     Alternate routes if some alveoli are diseased        macrophages must be removed from
              3. Have alveolar macrophages: crawl over alveolar           dead ended alveoli per hour. Cilia
                      surfaces (remove pathogens inhaled)                 currents created from higher regions
                                                                          they are passively swept up and then
                                                                          swallowed.
                                            Lungs and Pleurae
                                        Gross Anatomy of the Lungs

    Root: vascular and bronchial attachments to the mediastinum
    Apex: Narrow superior tip of the lungs
    Base: concave inferior surface that rests on the diaphragm
    Costal surface: anterior and posterior lung surfaces that are in close contact with the ribs
    Hilus: an indentation through which pulmonary and systemic blood vessels and the primary
    bronchus enter and leave the lungs
    Cardiac Notch: Only in the smaller left lung; a concavity that allows for the heart
    Lobes: Left lung is divided into upper and lower lobes
           Right lung is divided into upper, middle and lower lobes
    Bronchopulmonary segments: Each is served by its own blood vessels and air passageways
         Lobules: smallest subdivision of lung visible to the unaided eye.
         Stroma: part of the lung that is not air spaces
               Mostly elastic connective tissue

                                    Blood Supply and Innervation of the Lungs
                                                                                                      All except
                                                                                                      alveoli which
         Pulmonary Circulation:                                                                       are supplied
           Pulmonary arteries: blood coming to lungs from heart (deoxygenated)                        with oxygen by
           Pulmonary capillary networks: surround alveoli where gas exchange occurs                   pulmonary
           Pulmonary veins: blood leaving lungs to heart (oxygenated)                                 circulation.
         Bronchial Circulation:
           Bronchial arteries: provide oxygenated systemic blood too lung tissue, arise from the aorta

            Pulmonary Plexus: Nerve fibers enter the lungs through here
               Sympathetic nerves constrict air tubes
               Parasympathetic nerves dilate air tubes          1. Compartmentalizes organs so their
               Visceral sensory nerves allows for sensation     functions don’t interfere with each
Review                                                                other, which also helps to inhibit the
         Pleurae: (2401) Thin double layered serosae                 spread of infection. 2. Reduces friction
               Parietal pleura: covers the thoracic wall
               Visceral pleura: covers the lung outer surface
               Pleural fluid: fills the pleural cavity (lubrication – reduces friction)
               Pleural cavity: thin space between the layers of the pleura

         ∆ Pleurisy: Inflammation of the pleura – dry kind and wet kind.
            Pleural effusion: fluid accumulation in pleural cavity (blood, watery fluid…)
                Usual cause: right sided heart failure

                                                Mechanics of Breathing

                                    Breathing (pulmonary ventilation):
                                          Inspiration: air flows into lungs
                                          Expiration: air flows out of lungs


                                  Pressure Relationships in the Thoracic Cavity

         Respiratory pressures are described relative to atmospheric pressure (Patm)
                Positive respiratory pressure – area of lung is below atmospheric pressure
                Negative respiratory pressure -
                Zero respiratory pressure -
         Intrapulmonary pressure (Ppul) – pressure in the alveoli
                Rises and falls with breathing but always eventually equalizes with atmospheric pressure
         Intrapleural pressure (Pip) pressure in pleural cavity
                Fluctuates with breathing, but is always ~ 4mmHg less than Ppul
                So Pip is negative relative to both Patm and Ppul.
             Why?
                  Opposing forces
                        a. Two forces act to pull lungs away from the thorax wall causing lungs to collapse
The surface tension
of the alveolar fluid
                            1. Lungs’ natural tendency to recoil
constantly acts to          2. Surface tension of alveolar fluid
draw the alveoli to     b. Natural elasticity of the chest wall tends to pull thorax outward and enlarge lungs
their smallest              Which wins? Neither, if healthy.
possible dimension                Why? The fluid between the pleurae make them difficult to separate.

                          Pleural fluid must be kept at a minimum to maintain negative intrapleural pressure, so it
                          is constantly being pumped out into the lymphatics. If not, pressure builds and becomes
                          positive relative to intrapulmonary pressure and lungs collapse.


           In summary, it is the Transpulmonary Pressure – (Ppul - Pip ) difference between
           intrapulmonary pressure and intrapleural pressure keeps lungs from collapsing.

                                                 Homeostatic Imbalance
           Atelectasis – Lung collapse
                  Usually caused by air entering the pleural cavity through a chest wound, but may be from
                  a rupture of visceral pleura or as a sequel to pneumonia
           Pneumothorax – presence of air in the intrapleural space
                  Treated by withdrawing the air with a chest tube and closing the hole.

                                 Pulmonary Ventilation: Inspiration and Expiration

           Volume changes lead to pressure changes which lead to flow of gases to equalize pressure

           Inspiration: 1. Action of diaphragm (most important for quiet inspiration)
                        2. Action of intercostal muscles

           Diaphragm contracts – flattens inferiorly increases thoracic space
           Intercostals contract – lifts rib cage and pulls sternum up
                  This causes them to swing outward expanding diameter of rib cage (front to back and
                  side to side) only a few millimeters, but enough for 500mL air

           Lungs are stretched and Ppul drops below Patm and air rushes in until pressure equalizes.

           Deep (forced) inspiration: accessory muscles become involved
                  Scalenes and sternocleidomastoid of neck and pectoralis of chest lifts rib cage more
                  Erector spinae muscles straighten thoracic curvature

           Expiration: A passive process
                                                                                                            Lungs are
                 Muscles simply relax and elasticity of lungs causes them to recoil.
                                                                                                            stretched
                 Pressure within lungs increase and air is pushed out until pressure is equalized.          during
                                                                                                            inspiration
           Forced expiration: Abdominal muscles contract (oblique and transvesus mostly)                    and recoil
                                                                                                            passively
                                                                                                            during
                                                                                                            expiration
             1. Increases intra-abdominal pressure
                Forces abdominal organs superiorly against diaphragm
             2. Depresses rib cage (internal intercostals may help some)

                          Physical Factors Influencing Pulmonary Ventilation

                                           1. Airway Resistance

     Homeostatic Imbalance:
     Constriction of air passages increases resistance
            Causes: inhaled chemicals or inflammatory chemicals such as histamine

     Asthma attack: respiratory passages can close almost completely
          Epinephrine can open constricted passages

     Mucus, infectious material or tumors can block airways (increasing resistance)
           Breathing becomes more labored.

                                       2. Alveolar Surface Tension

     Surface Tension: at the gas-liquid boundary liquid molecules are more strongly attracted to each
     other than to the gas molecules
             1. Draws liquid molecules together reducing contact with gas molecules
             2. Resists any force that tends to increase the surface area of the liquid

     Alveolar film (fluid coating alveoli) being mostly water, and water being highly polar tends to
     reduce alveoli to smallest size. If it were pure water, alveoli would collapse between breaths.
     Surfactant: in alveolar film prevents this

     Homeostatic Imbalance:
     Infant Respiratory Syndrome: Too little surfactant is produced. Alveoli collapse
     between breaths and must be forcibly re-inflated with each breath. Very energy consuming and
     stressful. Most often with premature babies.

     Bronchopulmonary dyspplasia: suffered by many survivors of IRDS. A chronic lung disease
     form childhood into adulthood results from inflammatory injury by the respirators used to treat
     IRDS.
                                  3. Lung Compliance

Lung compliance – refers to great distensibility of lungs (unbelievably stretchy)!

The more or easier a lung expands for a given rise in transpulmonary pressure is lung compliance.
     Determined by:
     1. Distensibility of lung tissue and thoracic cage
     2. Alveolar surface tension
Compliance can be diminished by
    1. Reduced natural resilience of lungs
           a. Fibrosis from diseases like tuberculosis         The lower the lung compliance, the
    2. Blockage of smaller air passages                        more energy is needed just to breathe.
    3. Reduced surfactant
    4. Decreased flexibility of thoracic cage

Homeostatic Imbalance
Deformities of thorax, ossification of costal cartilages (as is common in old age) and paralysis of
intercostals muscles all reduce lung compliance.

                       Respiratory Volumes and Pulmonary Function Tests

                                       1. Respiratory Volumes

Tidal Volume (TV) Air that moves in and out with each breath (usually about 500mL)
Inspiratory Reserve Volume (IRV) What can be forced into the lungs past tidal volume
                   (2100-3200 mL)
Expiratory Reserve Volume (ERV) What can be forced out of the lungs after tidal expiration
                           (1000-1200 mL)
Residual Volume (RV) What is left in the lungs after even the most strenuous
            exhalation (about 2100 mL)
            Helps to keep alveoli the lungs from collapsing

                                      2. Respiratory Capacities

Inspiratory Capacity (IC) total amount of air that can be inspired after a tidal expiration

                                    IC = TV + IRV

Functional Residual Capacity (FRC) represents the amount of air remaining in the lungs after
                  a tidal expiration.
                                                                        All but TV tend to
                                  FRC = RV + ERV                        be smaller in women
                                                                        because of women’s
Vital Capacity (VC) the total amount of exchangeable air                smaller size.

                                    VC = TV + IRV + ERV

Total Lung Capacity (TLC)the sum of all lung volumes and is normally around 6000mL in males

                                               3. Dead Space

Anatomical Dead Space: Air that fills the conducting zone conduits and never contributes to gas
exchange in the alveoli. (about 150mL – in healthy young adults is 1mL for each pound body weight)
 Total Dead Space: if some alveoli fail to act in gas exchange for whatever reason,
      Alveolar dead space + anatomical dead space = total dead space

                                         Pulmonary Function Tests

 Spirometer –
            a. Forced vital capacity (maximum amount of gas expelled after a deep breath)
            b. Forced expiratory capacity (amount of air expelled in one second)

                                      Non-respiratory Air Movement

What other than breathing, moves air in and out of the lungs
      Hiccupping, coughing, sneezing, crying laughing…

                                        Gas Exchange in the Body

Dalton’s Law of Partial Pressures: the total pressure exerted by a mixture of gasses is the sum of the
pressures exerted independently by each gas in the mixture.
       The Partial Pressure of each gas is directly proportional to the percentage of that gas in the mixture.

Henry’s Law: When a mixture of gases is in contact with a liquid, each gas will dissolve in proportion to its
partial pressure.
        a. Depends on solubility of gas in the liquid, concentration of the gas, and the temperature of the
           liquid
        b. This law is demonstrated in soft drinks

								
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