Transcript Chapter 3

Chapter 23
The Respiratory System
Lecture Outline
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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.
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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
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Respiratory System Anatomy (Figure 23.1).
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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.
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External Nasal Structures
• Skin, nasal bones, & cartilage lined with mucous membrane
• Openings called external nares or nostrils
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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).
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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.
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Nose -Internal
Structures
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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
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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
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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
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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).
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Pharynx
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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
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Nasopharynx
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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
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Oropharynx
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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
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Laryngopharynx
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Extends from epiglottis to cricoid cartilage
Common passageway for food & air & ends as esophagus inferiorly
– stratified squamous epithelium
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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.
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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)
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Larynx
• Cartilage & connective tissue tube
• Anterior to C4 to C6
• Constructed of 3 single & 3 paired cartilages
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Vocal Cords
• False vocal cords (ventricular folds) found above vocal folds
(true vocal cords)
• True vocal cords attach to arytenoid cartilages
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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
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Movement of Vocal
Cords
• Opening and closing of the
vocal folds occurs during
breathing and speech
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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
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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.
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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.
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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
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Trachea and Bronchial Tree
• Full extent of airways is visible starting at the larynx and trachea
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Histology of the Trachea
• Ciliated pseudostratified columnar epithelium
• Hyaline cartilage as C-shaped structure closed by trachealis muscle
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Airway Epithelium
• Ciliated pseudostratified columnar epithelium with goblet cells
produce a moving mass of mucus.
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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
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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.
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Bronchi and Bronchioles
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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
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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
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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
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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).
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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).
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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
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Mediastinal Surface of Lungs
• Blood vessels & airways enter lungs at hilus
• Forms root of lungs
• Covered with pleura (parietal becomes visceral)
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Structures within a
Lobule of Lung
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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
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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).
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Histology of Lung Tissue
Photomicrograph of
lung tissue showing
bronchioles, alveoli
and alveolar ducts.
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Details of
Respiratory
Membrane
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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
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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
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Details of
Respiratory
Membrane
• Find the 4 layers that comprise the respiratory membrane
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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
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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.
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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).
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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
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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.
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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
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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.
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Quiet Inspiration
• Diaphragm moves 1 cm & ribs lifted by muscles
• Intrathoracic pressure falls and 2-3 liters inhaled
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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.
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Quiet Expiration
• Passive process with no muscle action
• Elastic recoil & surface tension in alveoli pulls inward
• Alveolar pressure increases & air is pushed out
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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
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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
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Summary of Breathing
• Alveolar pressure decreases & air rushes in
• Alveolar pressure increases & air rushes out
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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
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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
– pulmonary edema --- fluid in lungs & reduced surfactant
– paralysis
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Airway Resistance
• Resistance to airflow depends upon airway size
– increase size of chest
• airways increase in diameter
– contract smooth muscles in airways
• decreases in diameter
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Breathing Patterns
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Eupnea is normal variation in breathing rate and depth.
Apnea refers to breath holding.
Dyspnea relates to painful or difficult breathing.
Tachypnea involves rapid breathing rate.
Costal breathing requires combinations of various patterns
of intercostal and extracostal muscles, usually during need
for increased ventilation, as with exercise.
• Diaphragmatic breathing is the usual mode of operation to
move air by contracting and relaxing the diaphragm to
change the lung volume (Figure 23.14).
• Modified respiratory movements are used to express
emotions and to clear air passageways. Table 23.1 lists
some of the modified respiratory movements.
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Modified Respiratory Movements
• Coughing
– deep inspiration, closure of rima glottidis & strong
expiration blasts air out to clear respiratory passages
• Hiccuping
– spasmodic contraction of diaphragm & quick closure of
rima glottidis produce sharp inspiratory sound
• Chart of others on page 794
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LUNG VOLUMES AND CAPACITIES
• Air volumes exchanged during breathing and rate of ventilation are
measured with a spiromometer, or respirometer, and the record is called
a spirogram (Figure 23.17)
• Among the pulmonary air volumes exchanged in ventilation are tidal
(500 ml), inspiratory reserve (3100 ml), expiratory reserve (1200 ml),
residual (1200 ml) and minimal volumes. Only about 350 ml of the tidal
volume actually reaches the alveoli, the other 150 ml remains in the
airways as anatomic dead space.
• Pulmonary lung capacities, the sum of two or more volumes, include
inspiratory (3600 ml), functional residual (2400 ml), vital (4800 ml), and
total lung (6000 ml) capacities (Figure 23.17).
• The minute volume of respiration is the total volume of air taken in
during one minute (tidal volume x 12 respirations per minute = 6000
ml/min).
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Lung Volumes and Capacities
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•
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Tidal volume = amount air moved during quiet breathing
MVR= minute ventilation is amount of air moved in a minute
Reserve volumes ---- amount you can breathe either in or out above
that amount of tidal volume
Residual volume = 1200 mL permanently trapped air in system
Vital capacity & total lung capacity are sums of the other volumes
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EXCHANGE OF OXYGEN AND CARBON DIOXIDE
• To understand the exchange of oxygen and carbon dioxide
between the blood and alveoli, it is useful to know some gas
laws.
• According to Dalton’s law, each gas in a mixture of gases
exerts its own pressure as if all the other gases were not
present.
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Dalton’s Law
• Each gas in a mixture of gases exerts its own
pressure
– as if all other gases were not present
– partial pressures denoted as p
• Total pressure is sum of all partial pressures
– atmospheric pressure (760 mm Hg) = pO2 +
pCO2 + pN2 + pH2O
– to determine partial pressure of O2-- multiply 760
by % of air that is O2 (21%) = 160 mm Hg
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What is Composition of Air?
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•
•
•
Air = 21% O2, 79% N2 and .04% CO2
Alveolar air = 14% O2, 79% N2 and 5.2% CO2
Expired air = 16% O2, 79% N2 and 4.5% CO2
Observations
– alveolar air has less O2 since absorbed by blood
– mystery-----expired air has more O2 & less CO2 than
alveolar air?
– Anatomical dead space = 150 ml of 500 ml of tidal
volume
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EXCHANGE OF OXYGEN AND CARBON DIOXIDE
• The partial pressure of a gas is the pressure exerted by that
gas in a mixture of gases. The total pressure of a mixture is
calculated by simply adding all the partial pressures. It is
symbolized by P.
• The partial pressures of the respiratory gases in the
atmosphere, alveoli, blood, and tissues cells are shown in
the text.
• The amounts of O2 and CO2 vary in inspired (atmospheric),
alveolar, and expired air.
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Henry’s Law
• Henry’s law states that the quantity of a gas that will
dissolve in a liquid is proportional to the partial pressure of
the gas and its solubility coefficient (its physical or chemical
attraction for water), when the temperature remains
constant.
• Nitrogen narcosis and decompression sickness (caisson
disease, or bends) are conditions explained by Henry’s law.
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Henry’s Law
• Quantity of a gas that will dissolve in a liquid depends upon
the amount of gas present and its solubility coefficient
– explains why you can breathe compressed air while scuba
diving despite 79% Nitrogen
• N2 has very low solubility unlike CO2 (soda cans)
• dive deep & increased pressure forces more N2 to
dissolve in the blood (nitrogen narcosis)
• decompression sickness if come back to surface too
fast or stay deep too long
• Breathing O2 under pressure dissolves more O2 in blood
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Hyperbaric Oxygenation
• A major clinical application of Henry’s law is hyperbaric
oxygenation.
– Use of pressure to dissolve more O2 in the blood
– treatment for patients with anaerobic bacterial infections
(tetanus and gangrene)
– anaerobic bacteria die in the presence of O2
• Hyperbaric chamber pressure raised to 3 to 4 atmospheres
so that tissues absorb more O2
• Used to treat heart disorders, carbon monoxide poisoning,
cerebral edema, bone infections, gas embolisms & crush
injuries
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Respiration
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External Respiration
• O2 and CO2 diffuse from
areas of their higher partial
pressures to areas of their
lower partial pressures
(Figure 23.18)
• Diffusion depends on partial
pressure differences
• Compare gas movements in
pulmonary capillaries to
tissue capillaries
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Rate of Diffusion of Gases
• Depends upon partial pressure of gases in air
– p O2 at sea level is 160 mm Hg
– 10,000 feet is 110 mm Hg / 50,000 feet is 18 mm Hg
• Large surface area of our alveoli
• Diffusion distance (membrane thickness) is very small
• Solubility & molecular weight of gases
– O2 smaller molecule diffuses somewhat faster
– CO2 dissolves 24X more easily in water so net outward
diffusion of CO2 is much faster
– disease produces hypoxia before hypercapnia
– lack of O2 before too much CO2
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Internal Respiration
• Exchange of gases between
blood & tissues
• Conversion of oxygenated blood
into deoxygenated
• Observe diffusion of O2 inward
– at rest 25% of available O2
enters cells
– during exercise more O2 is
absorbed
• Observe diffusion of CO2
outward
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TRANSPORT OF OXYGEN AND CARBON DIOXIDE
IN THE BLOOD
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Oxygen Transport
• In each 100 ml of oxygenated blood, 1.5% of the O2 is
dissolved in the plasma and 98.5% is carried with
hemoglobin (Hb) inside red blood cells as oxyhemglobin
(HbO2) (Figure 23.19).
• Hemoglobin consists of a protein portion called globin and a
pigment called heme.
• The heme portion contains 4 atoms of iron, each capable of
combining with a molecule of oxygen.
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Hemoglobin and Oxygen Partial Pressure
• The most important factor that determines how much
oxygen combines with hemoglobin is PO2.
• The relationship between the percent saturation of
hemoglobin and PO2 is illustrated in Figure 23.20, the
oxygen-hemoglobin dissociation curve.
• The greater the PO2, the more oxygen will combine with
hemoglobin, until the available hemoglobin molecules are
saturated.
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Hemoglobin and Oxygen Partial Pressure
•
•
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Blood is almost fully saturated
at pO2 of 60mm
– people OK at high altitudes
& with some disease
Between 40 & 20 mm Hg, large
amounts of O2 are released as
in areas of need like contracting
muscle
80
Oxygen Transport in the Blood
• Oxyhemoglobin contains 98.5% chemically combined
oxygen and hemoglobin
– inside red blood cells
• Does not dissolve easily in water
– only 1.5% transported dissolved in blood
• Only the dissolved O2 can diffuse into tissues
• Factors affecting dissociation of O2 from hemoglobin are
important
• Oxygen dissociation curve shows levels of saturation and
oxygen partial pressures
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Hemoglobin and Oxygen Partial Pressure
•
•
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Blood is almost fully saturated
at pO2 of 60mm
– people OK at high altitudes
& with some disease
Between 40 & 20 mm Hg, large
amounts of O2 are released as
in areas of need like contracting
muscle
82
Other Factors Affecting Hemoglobin Affinity for
Oxygen
• In an acid (low pH) environment, O2 splits more readily from
hemoglobin (Figure 23.21). This is referred to as the Bohr
effect.
• Low blood pH (acidic conditions) results from high PCO2.
• Within limits, as temperature increases, so does the amount
of oxygen released from hemoglobin (Figure 23.22). Active
cells require more oxygen, and active cells (such as
contracting muscle cells) liberate more acid and heat. The
acid and heat, in turn, stimulate the oxyhemoglobin to
release its oxygen.
• BPG (2, 3-biphosphoglycerate) is a substance formed in red
blood cells during glycolysis. The greater the level of BPG,
the more oxygen is released from hemoglobin.
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Acidity & Oxygen Affinity for Hb
• As acidity
increases, O2
affinity for Hb
decreases
• Bohr effect
• H+ binds to
hemoglobin &
alters it
• O2 left behind
in needy tissues
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pCO2 & Oxygen Release
• As pCO2 rises with
exercise, O2 is
released more
easily
• CO2 converts to
carbonic acid &
becomes H+ and
bicarbonate ions &
lowers pH.
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Temperature & Oxygen Release
• As temperature
increases, more O2 is
released
• Metabolic activity &
heat
• More BPG, more O2
released
– RBC activity
– hormones like
thyroxine & growth
hormone
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Oxygen Affinity & Fetal Hemoglobin
• Differs from adult in
structure & affinity for
O2
• When pO2 is low, can
carry more O2
• Maternal blood in
placenta has less O2
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Review
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Fetal Hemoglobin
• Fetal hemoglobin has a higher affinity for oxygen because it
binds BPG less strongly and can carry more oxygen to
offset the low oxygen saturation in maternal blood in the
placenta (Figure 23.23).
• Because of the strong attraction of carbon monoxide (CO) to
hemoglobin, even small concentrations of CO will reduce
the oxygen carrying capacity leading to hypoxia and carbon
monoxide poisoning. (Clinical Application)
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Carbon Monoxide Poisoning
•
•
•
•
CO from car exhaust & tobacco smoke
Binds to Hb heme group more successfully than O2
CO poisoning
Treat by administering pure O2
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Carbon Dioxide Transport
• CO2 is carried in blood in the form of dissolved CO2 (7%),
carbaminohemoglobin (23%), and bicarbonate ions (70%).
• The conversion of CO2 to bicarbonate ions and the related
chloride shift maintains the ionic balance between plasma
and red blood cells (Figure 23.24).
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Carbon Dioxide Transport
• 100 ml of blood carries 55 ml of
CO2
• Is carried by the blood in 3 ways
– dissolved in plasma
– combined with the globin part
of Hb molecule forming
carbaminohemoglobin
– as part of bicarbonate ion
• CO2 + H2O combine to
form carbonic acid that
dissociates into H+ and
bicarbonate ion
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Summary of Gas Exchange and Transport in Lungs
and Tissues
• CO2 in blood causes O2 to split from hemoglobin.
• Similarly, the binding of O2 to hemoglobin causes a release
of CO2 from blood.
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Summary of Gas Exchange & Transport
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CONTROL OF RESPIRATION
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Respiratory Center
• The area of the brain from which nerve impulses are sent to
respiratory muscles is located bilaterally in the reticular
formation of the brain stem. This respiratory center consists
of a medullary rhythmicity area (inspiratory and expiratory
areas), pneumotaxic area, and apneustic area (Figure
23.15).
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Role of the Respiratory Center
• Respiratory mm.
controlled by neurons
in pons & medulla
• 3 groups of neurons
– medullary
rhythmicity
– pneumotaxic
– apneustic centers
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Medullary Rhythmicity Area
• The function of the medullary rhythmicity area is to control
the basic rhythm of respiration.
• The inspiratory area has an intrinsic excitability of
autorhythmic neurons that sets the basic rhythm of
respiration.
• The expiratory area neurons remain inactive during most
quiet respiration but are probably activated during high
levels of ventilation to cause contraction of muscles used in
forced (labored) expiration (Figure 23.26).
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Medullary Rhythmicity Area
•
•
•
•
Controls basic rhythm of respiration
Inspiration for 2 seconds, expiration for 3
Autorhythmic cells active for 2 seconds then inactive
Expiratory neurons inactive during most quiet breathing only active
during high ventilation rates
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Pneumotaxic Area
• The pneumotaxic area in the upper pons helps coordinate
the transition between inspiration and expiration (Figure
23.25).
• The apneustic area sends impulses to the inspiratory area
that activate it and prolong inspiration, inhibiting expiration.
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Regulation of Respiratory Center
• Cortical Influences
– voluntarily alter breathing patterns
– Cortical influences allow conscious control of respiration
that may be needed to avoid inhaling noxious gasses or
water.
– Voluntary breath holding is limited by the overriding
stimuli of increased [H+] and [CO2].
• inspiratory center is stimulated by increase in either
• if you hold breathe until you faint----breathing will
resume
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Chemoreceptor Regulation of Respiration
• A slight increase in PCO2 (and thus H+), a condition called
hypercapnia, stimulates central chemoreceptors (Figure
23.26).
• As a response to increased PCO2, increased H+ and
decreased PO2, the inspiratory area is activated and
hyperventilation, rapid and deep breathing, occurs (Figure
23.28).
• If arterial PCO2 is lower than 40 mm Hg, a condition called
hypocapnia, the chemoreceptors are not stimulated and the
inspiratory area sets its own pace until CO2 accumulates
and PCO2 rises to 40 mm Hg.
• Severe deficiency of O2 depresses activity of the central
chemoreceptors and respiratory center (Figure 23.29).
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Chemical Regulation of Respiration
• Central chemoreceptors in medulla
– respond to changes in H+ or pCO2
– hypercapnia = slight increase in
pCO2 is noticed
• 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
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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
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Control of Respiratory Rate
• Proprioceptors of joints and muscles activate the inspiratory
center to increase ventilation prior to exercise induced
oxygen need.
• The inflation (Hering-Breuer) reflex detects lung expansion
with stretch receptors and limits it depending on ventilatory
need and prevention of damage.
• Other influences include blood pressure, limbic system,
temperature, pain, stretching the anal sphincter, and
irritation to the respiratory mucosa.
• Table 23.2 summarizes the changes that increase or
decrease ventilation rate and depth.
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Regulation of Ventilation Rate and Depth
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Hypoxia
• Hypoxia refers to oxygen deficiency at the tissue level and is
classified in several ways (Clinical Application).
– Hypoxic hypoxia is caused by a low PO2 in arterial blood
(high altitude, airway obstruction, fluid in lungs).
– In anemic hypoxia, there is too little functioning
hemoglobin in the blood (hemorrhage, anemia, carbon
monoxide poisoning).
– Stagnant hypoxia results from the inability of blood to
carry oxygen to tissues fast enough to sustain their
needs (heart failure, circulatory shock).
– In histotoxic hypoxia, the blood delivers adequate oxygen
to the tissues, but the tissues are unable to use it
properly (cyanide poisoning).
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EXERCISE AND THE RESPIRATORY SYSTEM
• The respiratory system works with the cardiovascular system to make
appropriate adjustments for different exercise intensities and durations.
• As blood flow increases with a lower O2 and higher CO2 content, the
amount passing through the lung (pulmonary perfusion) increases and is
matched by increased ventilation and oxygen diffusion capacity as more
pulmonary capillaries open.
• Ventilatory modifications can increase 30 times above resting levels, in
an initial rapid rate due to neural influences and then more gradually due
to chemical stimulation from changes in cell metabolism. A similar, but
reversed, effect occurs with cessation of exercise.
• Smokers have difficulty breathing for a number of reasons, including
nicotine, mucous, irritants, and that fact that scar tissue replaces elastic
fibers.
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Smokers Lowered Respiratory Efficiency
• Smoker is easily “winded” with moderate exercise
– nicotine constricts terminal bronchioles
– carbon monoxide in smoke binds to hemoglobin
– irritants in smoke cause excess mucus secretion
– irritants inhibit movements of cilia
– in time destroys elastic fibers in lungs & leads to
emphysema
• trapping of air in alveoli & reduced gas exchange
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DEVELOPMENT OF THE RESPIRATORY SYSTEM
• The respiratory system begins as an outgrowth of the
foregut called the respiratory diverticulum (Figure 23.29).
• The endoderm of the diverticulum gives rise to the
epithelium and glands of the trachea, bronchi, and alveoli.
• The mesoderm of the diverticulum produces the connective
tissue, cartilage, smooth muscle, and pleural sacs.
• Epithelium of the larynx develops from the endoderm of the
respiratory diverticulum while pharyngeal arches 4 and 6
produce the cartilage and muscle of the structure.
• Distal ends of the respiratory diverticulum develop into the
tracheal buds and a little later the bronchial buds
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The time line for development of the respiratory
system
• 6 – 16 weeks the basic structures are formed
• 16 – 26 weeks vascularization and the development of
respiratory bronchioles, alveolar ducts and some alveoli
begins
• 26 weeks to birth many more alveoli develop
• By 26 – 28 weeks there is sufficient surfactant for survival.
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Developmental Anatomy of Respiratory System
• 4 weeks endoderm of foregut
gives rise to lung bud
• Differentiates into epithelial lining
of airways
• 6 months closed-tubes swell into
alveoli of lungs
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Aging & the Respiratory System
•
•
•
•
•
•
Respiratory tissues & chest wall become more rigid
Vital capacity decreases to 35% by age 70.
Decreases in macrophage activity
Diminished ciliary action
Decrease in blood levels of O2
Result is an age-related susceptibility to pneumonia or
bronchitis
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Disorders of the Respiratory System
• Asthma
• Chronic obstructive pulmonary disease
– Emphysema
– Chronic bronchitis
– Lung cancer
• Pneumonia
• Tuberculosis
• Coryza and Influenza
• Pulmonary Edema
• Cystic fibrosis
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Pneumothorax
• Pleural cavities are sealed cavities not open to the outside
• Injuries to the chest wall that let air enter the intrapleural
space
– causes a pneumothorax
– collapsed lung on same side as injury
– surface tension and recoil of elastic fibers causes the
lung to collapse
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DISORDERS: HOMEOSTATIC IMBALANCES
• Asthma is characterized by the following: spasms of smooth muscle in
bronchial tubes that result in partial or complete closure of air
passageways; inflammation; inflated alveoli; and excess mucus
production. A common triggering factor is allergy, but other factors
include emotional upset, aspirin, exercise, and breathing cold air or
cigarette smoke.
• Chronic obstructive pulmonary disease (COPD) is a type of respiratory
disorder characterized by chronic and recurrent obstruction of air flow,
which increases airway resistance.
– The principal types of COPD are emphysema and chronic bronchitis.
– Bronchitis is an inflammation of the bronchial tubes, the main
symptom of which is a productive (raising mucus or sputum) cough.
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DISORDERS: HOMEOSTATIC IMBALANCES
• In bronchogenic carcinoma (lung cancer), bronchial epithelial cells are
replaced by cancer cells after constant irritation has disrupted the
normal growth, division, and function of the epithelial cells. Airways are
often blocked and metastasis is very common. It is most commonly
associated with smoking.
• Pneumonia is an acute infection of the alveoli. The most common cause
in the pneumococcal bacteria but other microbes may be involved.
Treatment involves antibiotics, bronchodilators, oxygen therapy, and
chest physiotherapy.
• Tuberculosis (TB) is an inflammation of pleurae and lungs produced by
the organism Mycobacterium tuberculosis. It is communicable and
destroys lung tissue, leaving nonfunctional fibrous tissue behind.
• Coryza (common cold) is caused by viruses and usually is not
accompanied by a fever, whereas influenza (flu) is usually accompanied
by a fever greater than 101oF.
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DISORDERS: HOMEOSTATIC IMBALANCES
• Pulmonary edema refers to an abnormal accumulation of interstitial fluid
in the interstitial spaces and alveoli of the lungs. It may be pulmonary or
cardiac in origin.
• Cystic fibrosis is an inherited disease of secretory epithelia that affects
the respiratory passageways, pancreas, salivary glands, and sweat
glands.
• Asbestos related diseases develop as a result of inhaling asbestos
particles. Diseases such as asbestosis, diffuse pleural thickening, and
mesothelioma may result.
• Sudden infant death syndrome (SIDS) is the sudden unexpected death
of an apparently healthy infant. Peak incidence is ages two to four
months. The exact cause is unknown.
• Severe acute respiratory syndrome (SARS) is an emerging infectious
disease.
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end
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