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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. Nose -- Internal Structures. entrance – external nares

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the respiratory system
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
nose internal structures
Nose -- Internal Structures
  • entrance – external nares
  • two nasal cavities with bony outgrowths = nasal conchae(superior, middle, inferior)
  • nasal cavities separated by nasal septum and nasal bone
  • superior most region of the cavity – site for olfactory epithelium - olfactory receptors for odors (smell)
  • lacrimal glands drain into nasal cavities
  • nasal cavities communicate with cranial sinuses (air-filled chambers within the skull)
  • nasal cavities empty into the nasopharynx - upper portion of the pharynx
  • connection between nasal cavity and nasopharnyx – internal nares
  • functions:warm, moisten, and filter incoming air
  • 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

Eustacian tube

With tubal tonsil


From internal nares to soft palate

Anatomical Landmark: openings of auditory (Eustachian) tubes from middle ear cavity

adenoids or pharyngeal tonsil in roof

Passageway for air only

The Pharynx



  • From soft palate to epiglottis
    • Anatomical Landmark: behind the uvula
    • palatine tonsils found in side walls, lingual tonsil in tongue
  • Common passageway for food & air
  • Extends from epiglottis to cricoid cartilage
  • Anatomical Landmark: the epiglottis
  • Common passageway for food & air & ends as esophagus inferiorly

The Larynx

  • triangular box = “voicebox”
  • top of the larynx is a hole = glottis
  • covered with the epiglottis
  • contains the vocal cords - mucosal folds supported by elastic ligaments
  • Epiglottis---leaf-shaped piece of elastic cartilage
    • during swallowing, larynx moves upward bringing the glottis up to the epiglottis
    • epiglottis bends slightly to cover glottis
  • Laryngeal cartilages:
  • 1. thyroid cartilage (Adam’s apple)
  • 2. cricoid cartilage
  • 3. arytenoid cartilage – for the attachment of true vocal cords and arytenoideus muscles
  • filters, moistens, vocal production

Tortora & Grabowski 9/e 2000 JWS

vocal cords
Vocal Cords
  • False vocal cords (ventricular folds) found above the true vocal cords
  • True vocal cords attach to arytenoid cartilages
  • True vocal cord contains both skeletal muscle and an elastic ligament (vocal ligament)
  • When intrinsic muscles of the larynx contract they move the artytenoid cartilages & stretch the true vocal cords tighter
  • When air is pushed past the tightened vocal ligament, sound is produced
larnyx and vocal cords
Larnyx and Vocal Cords
  • true vocal cords vibrate upon passage of air -> speech
  • thickness determines frequency of vibration and timber of sound
  • thicker the cords – slower they vibrate – lower the pitch
  • thinner the cords – faster they vibrate – higher the pitch
  • thickness also controlled by testosterone
  • pitch can also be controlled by tightening the vocal cords voluntarily

-arytenoideus muscle and the intrinsic muscles of the true vocal cords can alter the “tightness” of the cords

  • tighter the cords – faster they will vibrate


  • flexible cylindrical tube - Size is 5 in long & 1 in diameter
  • sits anterior (in front of) the esophagus
  • splits into right and left primary bronchi – enter the lungs
  • held open by “C” rings of hyaline cartilage = tracheal cartilage
    • 16 to 20 incomplete rings
      • open side facing esophagus contains smooth muscle = tracheal ligament
  • layers:
    • innermost layer (mucosa) = pseudostratified columnar with cilia & goblet cells
    • outer layer (submucosa) = loose connective tissue & mucous glands
  • functions:conducts air into the lungs, filtration, moistens



trachea and bronchial tree
Trachea and Bronchial Tree
  • Primary bronchisupply each lung
  • Secondary bronchisupply each lobe of the lungs (3 right + 2 left)
  • Tertiary bronchisplits into successive sets of Intralobular bronchiolesthat supply each bronchopulmonary segment ( right = 10, left = 8)
  • IL bronchioles split into Terminal bronchioles-> these split into Respiratory Bronchioles
  • each RB splits into multiple Alveolar ducts which end in an Alveolar sac
gross anatomy of lungs
Gross Anatomy of Lungs
  • Blood vessels & airways enter lungs at hilus
  • Forms root of lungs
  • Covered with pleura (parietal becomes visceral)
  • 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


  • Respiratory bronchioles branch into multiple Alveolar ducts
  • Alveolar ducts end in a grape-like cluster = alveolar sac or lobule
  • -each grape = alveolus

Respiratory membrane = 1/2 micron thick



  • site of gas exchange by simple diffusion
  • from heart (right ventricle)-> Pulmonary artery  multiple branches ending as the Pulmonary arteriole  Capillary bed over Alveolus  Pulmonary venule multiple veins  Pulmonary vein  heart (left atrium)
  • deoxygenated blood flows over the alveolus & picks up O2 via diffusion because the alveolar wall is very thin
cells types of the alveoli
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



  • Respiratory membrane = 1/2 micron thick
  • surrounded by “ring” of bronchiolar smooth muscle that can control the diameter of the bronchiole

smooth muscle

pleural membranes pleural cavity
Pleural Membranes & Pleural Cavity
  • Visceral pleuracovers lungs
  • Parietal pleuralines ribcage & covers upper surface of diaphragm
  • Pleural cavityis space between the two pleura
    • contains a small amount of fluid
mechanism of breathing boyle s law
Mechanism of Breathing: Boyle’s Law
  • As the size of closed container decreases, pressure inside is increased
  • As the size of a closed container increases, pressure decreases

Mechanism of Breathing


-at rest: pressure inside lung = pressure outside lungs (atmospheric pressure)

-inhale - diaphragm contracts and drops, external intercostal muscles swing the ribcage up and out

-increase in thoracic cavity volume results

-due to the cohesiveness of intrapleural fluid – lung volume increases also

-pressure inside the lung drops = Boyle’s Law

-air rushes in to equalize

-SO: muscles of inspiration do not act directly on the lungs but act to change the volume of the thoracic and pleural cavities


Mechanism of Breathing

Expiration: occurs because of the elasticity of the lungs - PASSIVE

-in addition: relaxation of diaphragm and intercostal muscles returns thoracic and pleural cavity volume to normal

-pressure of air in the lungs increases over atmospheric pressure

-air leaves lungs to equalize

summary of breathing
Summary of Breathing
  • Alveolar pressure decreases & air rushes in
  • Alveolar pressure increases & air rushes out
labored breathing
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

Respiratory Volumes and Capacities

  • tidal volume (TV) =amnt of air that enters or exits the lungs
  • 500 ml per inhalation
  • inspiratory reserve volume (IRV) = max. amnt of air taken in after
  • a normal inhalation, 3000 ml
  • expiratory reserve volume
  • (ERV) = amnt of air forcefully
  • exhaled, 1100 ml
  • residual volume (RV) =amnt of air
  • left in lungs after forced expiration
  • 1200 ml

O2 and CO2 transport

Body tissue

CO2 transport

from tissues

CO2 produced




  • most O2 is carried in the blood bound to hemoglobin of the RBC
    • some is dissolved in blood plasma ( O2 not very soluble in water)
  • CO2 is carried by the blood in 3 ways:
  • 90% of the CO2 enters the RBC - combines with water of the cytosol to form carbonic acid
    • immediately dissociates into bicarbonate and H+ ions (binds to Hb)
    • catalyzed by the RBC enzyme called carbonic anhydrase
  • 2. some CO2 dissolves in the water of the plasma as carbonic acid  H+ and bicarbonate
  • 3. CO2 can combine directly with hemoglobin to form carbaminohemoglobin
  • in the lungs – Hb releases its H+ ion – it combines with the HCO3- to reform carbonic acid
  • carbonic acid breaks up into H2O and CO2
  • CO2 is also released by Hb
  • CO2 diffuses into the alveolar air and is breathed out


within capillary






Hemoglobin (Hb)

picks up

CO2 and H+.












To lungs

CO2 transport

to lungs






CO2 and H+.








Alveolar space in lung


Respiration Rate: controlled by a respiratory centermade up of a

Medullary rhythmicity areain the medulla and two nuclei in the pons

-MRA -group of neurons with an automatic, rhythmic discharge

-groups are called the dorsal and ventral respiratory groups

-controls rate and depth of breathing

-dorsal group is called the inspiratory center which send signals via the motor neurons of the phrenic nerve and intercostal nerves that supply the inspiratory muscles (diaphragm and external intercostals)

-ventral group contains expiratory neurons – inactive during normal quiet breathing but called into play with active breathing

respiratory center
Respiratory Center
  • Pneumotaxic Area
    • constant inhibitory impulses to inspiratory area
      • inhibits inspiration before lungs become too expanded
  • Apneustic Area
    • stimulatory signals to inspiratory area to prolong inspiration
  • Respiration also controlled by neurons in pons

Chemical regulation

    • Central chemoreceptors in medulla
    • respond to changes in H+ or pCO2
    • Peripheral chemoreceptors
    • respond to changes in H+ , pO2 or pCO2
    • aortic body---in wall of aorta
      • nerves join vagus
    • carotid bodies--in walls of common carotid arteries
      • nerves join glossopharyngeal nerve

Respiratory Center

  • Cortical Influences
    • voluntarily alter breathing patterns
    • limitations are buildup of CO2 & H+ in blood
    • inspiratory center is stimulated by increase in either

Tortora & Grabowski 9/e 2000 JWS

negative feedback regulation of breathing
Negative Feedback Regulation of Breathing
  • Negative feedback control of breathing
  • Increase in arterial pCO2
  • Stimulates receptors
  • Inspiratory center
  • Muscles of respiration contract more frequently & forcefully
  • pCO2 Decreases