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Chapter 16 – The Respiratory System
- Pulmonary ventilation – movement of air between
the external environment and the air sac w/in lungs
- External respiration – exchange of gases between
the lungs and bloodstream
- Internal respiration – movement of oxygen and
carbon dioxide between the bloodstream and body
cells
- Respiration – entire process of gas exchange
between external environment and body cells
Organs of the Respiratory System
- Upper respiratory system – head and neck
-organs: nose, pharynx, larynx
-Lower respiratory system
-organs: trachea, bronchi, bronchioles, alveoli,
lungs (bronchi, bronchioles, alveoli, and
supporting tissues)
-Conduction zone – organs that conduct air
between the external atmosphere and air sacs in
lungs;
-warm and humidify air as it passes through
-includes nose, pharynx, trachea, bronchi, and
bronchioles
-Respiratory Zone – organs involved in actual gas
exchange
-includes alveoli and associated structures
Nose
-provides and internal chamber for inhaled air;
formed by 2 nasal bones and numerous cartilages
-external nares (nostrils) – openings at base of nose
separated by a partition at the midline called the
nasal septum – divides nasal cavity in half, opens
into vestibule
-vestibule – chamber that contains hairs that help
filter particles from inhaled air; opens into larger
space (nasal cavity)
-nasal conchae – bony projections that separate the
nasal cavity into narrow passageways called meati
-nasal cavity is lined w/ mucous membranes w/
abundant blood vessels which warm and moisten
air
-external layer of mucous membranes is lined w/
cilia which beat together to create a flow of mucous
that moves toward pharynx; traps particles that are
swallowed
-paranasal sinuses – connected to nasal cavity by
small ducts; lined w/ mucous membranes
-sinusitis – tubes become swollen/plugged up,
causing infection
Pharynx
-Throat – chamber that extends from the back of
the nasal cavity to larynx; skeletal muscle walls lined
w/ mucous membranes; receives air from nasal
cavity through 2 small openings called internal
nares
-divided into 3 segments
1) nasopharynx – superior section, receives
internal nares and auditory tubes (connect to
ear)
2) oropharynx – visible
3) laryngopharynx – below tongue level, unites
w/ larynx in neck
-oropharynx and laryngopharynx – common
passageway for air and food
Larynx
- voicebox – connects pharynx w/ trachea
-prevents solid material from entering trachea
-houses vocal cords which produce sound
-cartilage walls (9 pieces in a box shape) lined w/
mucous membranes
-thyroid cartilage – front piece (enlarged in males =
Adam’s apple)
-epiglottis – suspended by muscles and ligaments
over the glottis  opening of larynx
-upright position to allow air to pass through,
except during swallowing  epiglottis moves
downward to seal off glottis
-false vocal cords – move larynx up during
swallowing, do not function in sound production
-true vocal cords – vibrate back and forth in
response to air, produce sound, mucous sometimes
accumulates b/c there is no cilia present to move it
 must clear throat
Trachea
-windpipe – tubular passageway in front of
esophagus (food tube)
-12cm long + 2.5cm wide
-extends from larynx to thoracic cavity where it
divides into left and right bronchi
-walls are supported by cartilage rings (C’s open
in back), smooth muscle, and elastic fibers
-rigid – prevents collapse and closing off air
passage
-C’s allow esophagus to expand as food moves
through
-internally lined w/ ciliate mucous membranes –
contain large #’s of mucous-secreting cells
-mucociliary transport system – mucous
covered cilia move trapped particles upward
toward pharynx where they are swallowed
Bronchial Tree
-trachea splits into a left and right primary
bronchus, which lead into each lung
-left bronchus branches off at a sharper angle, so
accidentally inhaled substances usually go into right
lung
-each bronchus branches extensively into smaller
and smaller tubes resembling a tree
-bronchi are similar to trachea – C cartilage rings,
smooth muscle, ciliated mucous membrane
-as tubes branch and get smaller, cartilage rings
gradually disappear, mucous membranes get
thinner, resulting in bronchioles  small tubes
supported only by a band of smooth muscle and
elastic fibers lined w/ a thin mucous membrane
layer; very numerous in each lung
-bronchioles divide to form smaller tubes called
alveolar ducts; which terminate as round,
microscopic pouches called alveoli
Alveoli and Respiratory Membranes
-300 to 500 million alveoli in lungs of average adult
-provides only site of gas exchange between
external environment and bloodstream
-surface area of lung is size of tennis court:
necessary to meet metabolic needs of body
-each alveolus consists of a microscopic air space
surrounded by a thin wall, which separates one
alveolus from another and from capillaries
-wall is made of a single layer of squamous
epithelium w/ cells that secrete surfactant (layer of
lipid molecules)
-surfactant lines inner surface of alveolar wall along
w/ thin watery fluid layer
-necessary for surface to be moist for diffusion of
gases to occur
-water in fluid has surface tension  strong,
attractive force that causes alveolar walls to
collapse when air is exhaled
-surfactant counters this force; reinflating alveoli
-wall of each alveolus is very close to a capillary wall
to promote rapid diffusion of gases
-respiratory membrane – close arrangement of
epithelial wall of alveolus and capillary wall,
basement membrane of connective tissue
Lungs
- consist of bronchial tree, alveoli, capillaries, and
supporting tissues
 General Characteristics
- soft, spongy, cone-shaped
-extend from diaphragm to just below clavicles,
bordered by ribs
-right lung is thicker and broader b/c of liver
-apex – narrow, superior region
-base – broad, inferior region
-costal surface – lies against ribs in front and back
-medial surface – faces the midline toward the
heart
-each lung attaches to the trachea and heart only
on medial surface
-root – collection of attachments including primary
bronchus, large blood vessels, and nerves
 Serous Membranes
-pleurae – 2 layers of serous membranes
surrounding each lung
-parietal pleura – outer layer, lines thoracic wall and
mediastinum, continues around heart and between
lungs where it combines w/ parietal pleura of other
lung and forms a ligament supporting both lungs
-visceral pleura – inner layer, surrounds each lung,
firmly attached to outer surface
-pleural cavity – space between 2 pleural layers
containing fluid secreted by serous cells in pleurae
-reduces friction between membranes as lungs
expand or contract
-pleurisy – inflammation of membrane or
reduction in fluid causing membranes to scrape
against one another
Divisions
-right lung has 3 compartments or lobes and is
larger than left lung – only 2 lobes
-fissures – lines of division between lobes
-each lobe is supplied by a major branch of
bronchial tree and enclosed by connective tissue
-lobes are divided into segments
-each segment contains many lobules