Ch 22: The Respiratory System
The respiratory system
• The respiratory system:
– supplies the body with oxygen & disposes of
carbon dioxide
• Respiration – 4 steps:
– 1. Pulmonary ventilation –
• Movement of air into and out of the lungs
• Air movement = ventilation
– 2. External respiration –
• Between the blood & alveoli
– 3. Transport of respiratory gases –
• Between the lungs and tissue cells of the body
– 4. Internal respiration –
• Between the systemic blood & tissue cells
Functional anatomy
• Organs include:
– Nose, nasal cavity, pharynx, larynx, trachea,
and bronchi
• Respiratory zone –
– Actual site of gas exchange
– Composed of: respiratory bronchioles, alveolar
ducts, and alveoli
• Conducting zone –
– All other respiratory passageways
– The organs cleanse, humidify, and warm the
incoming air
Respiratory organs
Nose & Paranasal Sinuses
• Function of the nose –
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–
–
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Provides an airway for respiration
Moistens, warms, filters, & cleans incoming air
Resonance chambers for speech
Houses olfactory receptors
• 2 divisions of the nose –
– External:
• External nares
• Formed by hyaline cartilage
• Includes bones from the skull – nasal, frontal, and
maxillary bones
Nose cont.
– Nasal cavity:
• Air enters this cavity through the external nares
• Divided by the nasal septum
• Contain internal nares (posterior nasal apertures a.k.a.
choanae “funnels”) – continuous w/ the pharynx
• Roof formed by ethmoid & sphenoid bones
• Floor of cavity – palate (separates the nasal & oral
cavities) – supported by maxillary processes &
palatine bones = hard palate
Nasal Cavity
Lining of Nasal Cavity
• Nasal vestibule lined with sebaceous and sweat glands and
hair follicles (vibrissae = hairs, filter coarse particles)
• Olfactory mucosa – receptors for the sense of smell
• Respiratory mucosa – pseudostratified ciliated columnar
epithelium & goblet cells
• Mucous glands secrete mucus to trap dust and bacteria,
serous glands secrete watery fluid with lysozyme
• Epithelial cells secrete defensins (natural antibiotics that
help get rid of invading microbes)
• Cilia creates a gentle current that moves the mucus
towards the throat – mucus builds up in the cold because
the cilia move more slowly
Nasal Cavity cont.
• Nasal mucosa richly supplied with sensory
nerve endings
– Sneeze reflex
• Plexuses of capillaries and thin-walled veins
warm incoming air
• Mucosa-covered projections (conchae)
increase mucosal surface area
– Groove below = meatus
• Rhinitis = inflamation of nasal mucosa
Paranasal Sinuses
• Nasal cavity is surrounded by:
– paranasal sinuses found w/in the frontal,
maxillary, sphenoid, & ethmoid bones
• Sinuses –
– lighten the skull,
– warm & moisten air, &
– produce mucus
The Pharynx
• The pharynx connects the nasal cavity and
mouth superiorly to the larynx and
esophagus inferiorly.
• The throat
• 3 regions (superior to inferior)
– Nasopharynx
– Oropharynx
– Laryngeopharynx
• Muscular wall = skeletal muscle
Phayrnx
• Nasopharynx –
– Posterior to the nasal cavity & inferior to
sphenoid bone & superior to the soft palate
– Serves only as an air passageway
– Uvula closes off during swallowing to prevent
food from entering nasal cavity
– Continuous w/ nasal cavity through the internal
nares
– Pseudostratified ciliated columnar epithelium
– Contains adenoids (pharyngeal tonsil) –
• Trap & destroy airborne pathogens entering
Nasopharynx
Pharynx
• Oropharynx –
– Posterior to oral cavity – inferior to the soft palate to
the epiglottis
– Passageway for food & air
– Stratified squamous epithelium – accommodates the
trauma caused by food and digestive enzymes
• Larygopharynx –
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–
–
–
–
Air & food passageway
Posterior to epiglottis
Extends to the larynx
Continues inferiorly w/ the esophagus
Stratified squamous epithelium
Oropharynx & Laryngopharynx
Larynx
• Voice box
• Attaches superiorly to the hyoid bone, opening
into the laryngopharynx, and attaches inferiorly to
the trachea.
• Provides/functions:
– Open (patent) airway
– Routes food and air into proper passageways
– Produces sound through the vocal cords
• Composition –
– nine hyaline cartilages connected w/ membranes &
ligaments
Larynx
• Hyaline cartilages –
– Thyroid:
• Shield shaped
• Midline laryngeal prominence forms the Adam’s apple
• Larger in males than females (male sex hormones during
puberty)
– Cricoid:
• Ring shaped
• Attaches & anchored to the trachea inferiorly
– Three pairs
• Arytenoid
– Anchors the vocal folds (cords)
• Corniculate:
– Helps reinforce vocal folds
• Cuneiform:
– Reinforces epiglottis & vocal folds
• Epiglottis
Larynx
– Elastic cartilage
– Flexible, spoon shaped
– Posterior aspect of tongue to the anterior rim of
the thyroid cartilage where it anchors
– Breathing –
• epiglottis is free and projecting upward allowing air
to flow freely into the larynx
– Swallowing –
• larynx pulled superiorly causing the epiglottis to tip
and cover the laryngeal inlet
– Coughing reflex –
• when anything other than air entering the larynx
Larynx
• Vocal ligaments –
– Attach to the thyroid cartilage
– Elastic fibers
– Form the core of the mucosal folds (true vocal cords)
• pearly white in color because they lack blood vessels
• Vibrate as air passes over them to produce sound
– Glottis =
• medial opening through which air passes between the vocal
folds
• Opening & closing along with expired air = voice production
– Laryngitis =
• Inflammation of the vocal folds interfering w/ their vibrations
• Below vocal folds, epithelium is pseudostratified ciliated
columnar type that directs power stroke of cilia upward
Trachea
• The trachea (windpipe) descends from the larynx
through the neck into the mediastinum, where it
terminates at the primary bronchi.
• Very flexible
• Thick lamina propria w/ pseudostratified ciliated
epithelium
• Smoking –
– Kills cilia preventing them from propelling mucus &
dust towards the pharynx
– Coughing is the only way to prevent mucus from
accumulating in the lungs
Trachea
Tracheal Wall
• Mucosa
– Propels debris-laden mucus toward pharynx
• Submucosa
– Connective tissue layer
– Contains seromucous glands that help produce the mucus sheets
• Adventitia
– Connective tissue reinforced by C-shaped rings of hyaline cartilage
– Trachealis muscle can contract to cause expired air to rush upward
with greater force
– Carina = last tracheal cartilage, marks point of bronchi branching
• Muscosa highly sensitive – trigger coughing
Bronchial tree
• Conducting zone –
– R & L bronchi – run obliquely in the mediastinum
before plunging into the hilum (depression on the lung
for blood vessel & bronchial attachment) of the lung on
its respective side
– Secondary bronchi branch into several orders of the
tertiary bronchi, which ultimately branch into
bronchioles
– Bronchi segments –
• Primary, secondary (lobar), tertiary (segmental), bronchioles
(>1 mm), and terminal bronchioles (>0.5 mm)
Conducting vs. Respiratory
1. Support structures change
–
As conducting airways become smaller – supportive
cartilage changes in character until it is no longer
present in the bronchioles
2. Epithelium type changes
–
Columnar -> cuboidal
3. Amount of smooth muscle increases
–
Complete layer of circular smooth muscle in
bronchioles provides substantial resistance under
certain conditions
Bronchial tree
• Respiratory zone –
– Defined by the presence of alveoli
– Begins at the terminal bronchioles which feed into the
respiratory bronchioles & terminate in the alveolar
ducts w/in clusters of alveolar sacs (made up of a
cluster of alveoli ~300 million)
Respiratory Membrane
• Respiratory membrane =
– Type I Cells - Single cell layer of squamous epithelium
surrounded by basal lamina
– Gas on one side blood flowing past on the other
– Simple diffusion allows for gas exchange
– alveolar wall + capillary walls + fused basal laminas
– Type II Cells – secrete fluid containing surfactant that
coats the alveolar surfaces and reduces surface tension
• Alveoli surrounded by elastic fibers, contain
open alveolar pores (air pressure
equalization), & have alveolar
macrophages
Lungs
• Occupy the thoracic cavity except the
mediastinum
• Each lung is suspended w/in its own pleural cavity
& connected to the mediastinum by vascular &
bronchial attachments = lung roots
• Apex – narrow superior tip of the lung
• Base – concave inferior surface of the lung that
rests on the diaphragm
• All conducting & respiratory passageways distal
to the primary bronchi are w/in the lungs
• Left lung –
– Cardiac notch – impression for the heart
– 2 lobes – upper & lower
• Right lung –
– 3 lobes- upper, middle, & lower
Lungs
• Each lobe contains a number of
bronchopulmonary segments, each served
by its own artery, vein, and tertiary
bronchus
• Lobule – smallest division of the lungs that
can be seen w/ the naked eye
– Smokers – connective tissue between lobules
becomes blackened w/ carbon
• Lung tissue consists largely of air spaces,
with a balance of lung tissue (stroma)
composed of elastic connective tissue
Lung blood supply & Innervation
• 2 circulations that serve the lungs (enter through
the hilum) –
– Pulmonary network –
• Carries systemic blood to the lungs for oxygenation
• Picks up O2 and unloads CO2 for blood returning to
the body
– Bronchial arteries –
• Provide systemic blood to the lung tissue
• Oxygenates the lung tissue
• Lungs innervated by parasympathetic (constrict)
and sympathetic (dilate) motor fibers, and visceral
sensory fibers
– Enter through the pulmonary plexus on the lung root
Pleura
• Pleura –
– Thin, double-layered serosa (moist membrane found in closed
cavities)
• Parietal pleura –
– Covers the thoracic wall, superior surface of the diaphragm, &
continues around the heart between the lungs
• Visceral pleura –
– Covers the external surface of the lungs
– Follows the lungs contours
• Pleural fluid –
– Allows the lungs to slide easily over the thoracic wall during
breathing
• Pleurisy –
– Inflammation of the pleurae
– Results from pneumonia
– Prevents pleura from producing fluid causing friction & stabbing
pain w/ each breath
Mechanics of Breathing
• Pulmonary ventilation is a mechanical process
causing gas flow into (inspiration) and out of
(expiration) the lungs according to volume
changes in the thoracic cavity.
• Atmospheric pressure (Patm) =
760 mm Hg
– A negative respiratory pressure
indicates that the pressure is lower
than 1 ATM
• Intrapulmonary pressure (Ppul)
= pressure in the alveoli
– Eventually equalizes with Patm
• Intrapleural pressure (Pip) =
pressure in the pleural cavity
– About -4 mm Hg
• Transpulmonary pressure keeps
air spaces of lungs open
Pulmonary Ventilation:
Inspiration and Expiration
• Pulmonary ventilation is a mechanical
process that depends on volume changes
• Volume changes lead to pressure
changes, pressure changes lead to the
flow of gases to equalize the pressure.
– Gases always fill their container.
Breathing
• Quiet inspiration –
– Diaphragm & intercostals muscles contract
– Thoracic volume increases
– Intrapulmonary pressure drops below atmospheric
pressure
– Air flows into the lungs
– Any time intrapulmonary pressure is less than
atmospheric pressure air will rush into the lungs
• Forced inspiration –
– Accessory muscles of the neck & thorax contract raise
the ribs even more
– Thoracic volume increases beyond the increase in
volume during quiet inspiration
Breathing
• Quiet expiration –
– Passive process
– Relies on elastic recoil of the lungs as the
thoracic muscles relax
– Ribcage descends & the lungs recoil
• Forced expiration –
– Active process
– Relies on the contraction of the abdominal
muscles (oblique & transverse)
– Increases intra-abdominal pressure & depresses
the ribcage
Inspiration
•Figure 22.13.1
Expiration
•Figure 22.13.2
Physical Factors Influencing
Pulmonary Ventilation
• Airway Resistance
– Diameters of conducting tubes
• Alveolar Surface Tension
– Liquid molecules are more strongly attracted to
each other than gas molecules
– Water molecules are highly polar
• Lung Compliance
– Distensibility of lungs (the higher the lung
compliance, the easier to expand the lungs)
Respiratory volume & pulmonary ventilation
• Respiratory volumes include…
– Tidal, inspiratory reserve, expiratory reserve, & residual volumes
• Tidal volume –
– Amount of air that moves in & out of the lungs with each breath
during quiet breathing
– About 500 ml
• Inspiratory reserve volume –
– Amount of air that can be forcibly inspired beyond the tidal
volume
– About 2100-3200 ml
• Expiratory reserve volume –
– Amount of air that can be evacuated from the lungs after tidal
expiration
– About 1000-1200 ml
• Residual volume –
– Amount of air that remains in the lungs after maximal forced
expiration
– About 1200 ml
– Helps to keep the alveoli open & prevent lung collapse
R.V & P. V cont
• Inspiratory capacity (IC) –
– Total amount of air that can be inspired after a tidal
expiration
– Sum of the tidal volume & inspiratory reserve volume
• Vital Capacity (VC) –
– Total amount of exchangeable air
• Total lung capacity –
– Sum of all lung volumes
– About 6000 ml in males
– Less in women – smaller in size
Pulmonary Function
• Anatomical dead space: volume of air
within the conducting zone that do not
contribute to gas exchange in alveoli
• Alveolar Ventilation Rate
– Index of effective ventilation
– Includes dead space and measures flow of fresh
gases in and out
– 12 breathes per min.
Nonrespiratory Air Movements
• Most result from reflex activity, some
produced voluntarily
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Cough
Sneeze
Crying
Laughing
Hiccups *spasms of diaphragm
Yawn *not believed to be triggered by levels of O2 or CO2
Gas Exchanges Between the
Blood, Lungs, and Tissues
• Partial Pressure = pressure exerted by
each gas (proportional to percentage of that
gas in the mixture.
– Henry’s Law – when a mixture of gases is in
contract with a liquid, each gas will dissolve in
the liquid in proportion to its partial pressure.
– Also depends on solubility of the gas in the
liquid (temp. can affect this)
• I.e. Warm vs. Cold Pop
Alveolar Gas
• Atmosphere is almost entirely O2 and N2;
the alveoli contain more CO2 and water
vapor
• The relative proportions of gases in the
alveoli reflect;
– gas exchange occurring in the lungs,
– humidification of air by conducting passages,
– and mixing of alveolar gas that occurs with
each breath
External Respiration: Pulmonary
Gas Exchange
• Three factors influence the movement of O2
and CO2 across the respiratory
membrane (from alveoli to blood):
1. Partial Pressure gradients and gas solubilities
2. Matching of alveolar ventilation and
pulmonary blood perfusion
3. Structural characteristics of respiratory
membrane
Partial Pressure gradients and gas
solubilities
• Oxygen moves from alveoli to blood stream
due to high partial pressure gradient
• Carbon dioxide moves in the opposite
direction with a lesser gradient, but it has a
much higher solubility
Matching of alveolar ventilation
and pulmonary blood perfusion
• Ventilation = the amount of gas reaching
the alveoli
• Perfusion = the blood flow in pulmonary
cappilaies
Structural characteristics of
respiratory membrane
• Healthy lungs – respiratory membrane is
only 0.5 to 1 micrometer thick
• Greater surface area, the more gas can
diffuse across it in a given time period
– Spread flat, tiny sacs have surface area 40 times
greater than the skin
Internal Respiration
• Capillary gas exchange in body tissues
driven by simple diffusion
• Partial pressure and diffusion gradients are
switched
• Tissue cells use oxygen for metabolic
activities and produce carbon dioxide
Transport of Respiratory Gases
by Blood
• Oxygen
– Bound to hemoglobin (98.5%)
– Dissolved in plasma (1.5%)
• Carbon dioxide
– Dissolved in plasma (7-10%)
– Bound to hemoglobin (~20%)
– Bicarbonate ion in plasma (~70%)
• Quickly enters the RBCs
Transport and Exchange
•Figure 22.22a
Transport and Exchange
•Figure 22.22b
Respiratory adjustments
• Adjustments during exercise –
– Ventilation can increase 10-20 fold
– During vigorous exercise, deeper and more vigorous
respirations, called hyperpnea, ensure that tissue
demands for oxygen are met
• 3 neural factors –
– Psychic stimulation:
• Anticipation of exercise
– Cortical stimulation:
• Stimulation of skeletal muscles and respiratory centers
– Excitatory impulses:
• Signals being sent from active muscles, tendons, & joints to
the respiratory area
Respiratory adjustments cont.
• Adjustments at high altitude:
– High altitude = lower density & lower partial
pressure of oxygen (pO2)
• Acute mountain sickness –
– Rapid transition from sea level to altitudes above
8000 ft.
– Headache, dizziness, shortness of breath, nausea
• Adjustments/acclimatization –
– Increased ventilation rate
– Lower hemoglobin saturation (less O2 available)
– Increased production in erythropoietin (stimulate
bone marrow to produce more RBC’s)
Homeostatic imbalances
• Chronic Obstructive Pulmonary Disease (COPD)
– Chronic bronchitis and emphysema
• Asthma –
– Coughing, wheezing, chest tightness, & dyspnea (labored
breathing – “air hunger”)
– Caused by – active inflammation of the airways
• Tuberculosis –
– Fever, night sweats, weight loss, cough, & spitting up blood
– Infectious disease caused by the bacterium Mycobacterium
tuberculosis
– Spread by coughing & inhalation
• Lung Cancer –
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Leading cause of cancer death for both men and women in N.A.
Squamous cell carcinoma (25-30%)
Adenocarcinoma (40%)
Small cell carcinoma (20%)
Developmental Aspects
• During fetal life, the lungs are filled with fluid and
exchanges are made by the placenta
• By 28 weeks, the respiratory system has developed
sufficiently to allow a baby to breathe on its own
• Cystic fibrosis –
– Lethal genetic disease – most common in young children – 2
children die every day
– Over secretion of mucus that clogs respiratory passageways –
breeding ground for bacteria
– Can impair food digestion by clogging pores that deliver bile to the
intestines
• Respiratory Rate
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Newborn infants: 40-80 resp./min.
5 years: 25 resp./min.
Adults: 12-18 resp./min.
Old Age: increases again
Alveoli develop and mature until young adulthood