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Functional Human Physiology
The Respiratory System
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Overview of Respiratory Function
Respiration = the process of gas exchange
Two levels of respiration:
Internal respiration (cellular respiration)
The use of O2with mitochondria to generate ATP
by oxidative phosphorylation
CO2is the waste product
External respiration (ventilation) The exchange of O2and CO2between the
atmosphere and body tissues
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Internal respiration (cellular
respiration)
Involves gas exchange between capillaries andbody tissues cells Tissue cells continuously use O2and produce CO2during
metabolism
Partial pressure (P) The PO2is always higher in arterial blood than in the
tissues
The PCO2is always higher in the tissues than in arterialblood
O2and CO2move downtheir partial pressuregradients O2moves out of the capillary into the tissues
CO2moves out of the tissues into the capillary
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External respiration (ventilation)
4 Processes: Pulmonary Ventilation Movement of air into the lungs (inspiration) and
out of the lungs (expiration)
Exchange of O2and CO2between lung airspaces and blood
Transportation of O2and CO2between the
lungs and body tissues Exchange of O2and CO2between the blood
and tissues
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Overview of Pulmonary Circulation
Deoxygenated blood
Under resting conditions, 5 liters of deoxygenated
blood are pumped to the lungs each minute from
the right ventricle CO2blood concentration is higher than O2blood
concentration in:
Systemic veins
Right atrium
Right ventricle
Pulmonary arteries
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Overview of Pulmonary Circulation
Oxygenated blood Transported from the pulmonary capillaries pulmonary
veins left atrium left ventricle aorta systemicarterial circulation
O2blood concentration is higher than CO2bloodconcentration in:
Alveoli
Pulmonary capillaries
Pulmonary veins
Left atrium
Left ventricle
Systemic arteries
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The Respiratory System
Cells continually useO2 & 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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Nose -- Internal Structurestwo nasal cavitieswith bony
outgrowths = nasal conchae(superior,
middle, inferior)nasal cavities separated by nasal
septumand nasal bone
lined with: pseudostratified ciliated
epithelial cells - mucus production
also are receptors for odors -lead to
nerves -> brain (smell)lacrimal glandsdrain into nasal
cavities
nasal cavities communicate with
cranial sinuses(air-filled chambers
within the skull)
nasal cavities empty into thenasopharynx- upper portion of the
pharynx
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
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Nasopharynx
From choanae to soft palate
openings of auditory (Eustachian) tubes frommiddle ear cavity
adenoids or pharyngeal tonsil in roof
Passageway for air only
pseudostratified ciliated columnar epithelium
with goblet
From soft palate to epiglottis
fauces is opening from mouth intooropharynx
palatine tonsils found in side walls, lingual
tonsil in tongue
Common passageway for food & air
stratified squamous epithelium
Oropharynx
Laryngopharynx
Extends from epiglottis to cricoid
cartilage
Common passageway for food &
air & ends as esophagus inferiorly
stratified squamous epithelium
The Pharynx
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Tortora & Grabowski 9/e2000 JWS 23-15
The Larynx
triangular box = voicebox top of the larynx - hole = glot t iswith the
epiglottis
Constructed of 3 single & 3 paired
cartilages
Epiglott is---leaf-shaped piece of elasticcartilage
during swallowing, larynx moves upward
epiglottis bends to cover glottis
thyro id cart i lage(Adams apple)
cr ico id cart i lage
arytenoid cart i lage for the attachment of truevocal cords
functions:
filters, moistens,
vocal
production
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Vocal Cords False vocal cord s
(ventricular folds) found
above the true vocalcords
True vocal cordsattach
to arytenoid cartilages True vocal cord contains
both skeletal muscle andan elastic ligament (vocal
ligament)
When intrinsic muscles of
the larynx contract they
move the cartilages &stretch vocal cord tight
When air is pushed past
tight ligament, sound is
produced
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The tighter the ligament, the higher the pitch
To increase volume of sound, push air harder
Vocal Cords
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Tortora & Grabowski 9/e2000 JWS 23-18
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Trachea
flexible cylindrical tube - Size is 5 in long & 1in diameter
sits anterior (in front of) the esophagus - Extends from larynx to T5
anterior to the esophagus and then splits into bronchi held upon by C rings of hyaline cartilage = tracheal cart i lage
16 to 20 incomplete rings
open side facing esophagus contains smooth muscle
layers:
mucosa= pseudostratified columnar with cilia & goblet cellssubmucosa= loose connective tissue & seromucous glands
splits into the right and left primary bronchi - enter the lungs
functions
:conducts
air into thelungs,
filtration,
moistens
mucosasubmucosa
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Trachea and Bronchial Tree
Pr imary bronc hisupply each lung
Secondary bronc hisupply each lobe of the lungs (3 right + 2 left)
Tert iary bron chisplits into successive sets of in t ralobular b ronchio lesthatsupply each bronchopu lmonary segment ( right = 10, left = 8)
IL bronchioles split into Terminal b ronch io les-> these split into RespiratoryBronchio les
each RB splits into multiple alveolar ducts which end in an alveolar sac
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Structure of Respiratory System
Respiratory zoneregion of gas exchange occurs only in
respiratory bronchioles and the terminal alveoli sacs
Conducting zoneairways that conduct air to therespiratory zone
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Anatomy of the Respiratory Zone
Gas exchange occurs
between the air and
the blood within the
alveoli
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Anatomy of the Respiratory Zone
Alveoli (singular is alveolus)
Tiny air sacs clustered at the distal ends of
the alveolar ducts
Alveoli have a thin respiratory membraneseparating the air from blood in pulmonary
capillaries
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Respiratory Membrane
The thin alveolar wall consists of:
The fused alveolar and capillary walls
Alveolar epithelial cells
Capillary endothelial cells
The basement membrane
Sandwiched between the alveolar epithelial cells
and the endothelial cells of the capillary
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Lung Alveoli and Pulmonary
Capillaries
Gas exchange occurs
across the 300 million
alveoli (60-80 m2total
surface area)
Alveolusone cell-layer
thick
Total air-blood barrier
only 2 thin cells across
Between lung air and
blood: 1 alveolar cell
and 1 endothelial cell
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Respiratory Membrane
Gas exchanges occurs across therespiratory membrane
It is < 0.1 m thick
Lends to very efficient diffusion
It is the site of external respiration and
diffusion of gases between the inhaled air
and the blood
Occurs in the pulmonary capillaries
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Structures of the Thoracic Cavity
A container with a single opening, the
trachea
Volume of the container changes
Diaphragm moves up and down
Muscles move the rib cage in and out
Volume of the thoracic cavity increases by
enlarging all diameters diameter = volume
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Conducting Zone
Warms and humidifies inspired airreaches respiratory
zone at 37 C Mucus lining filters and cleans inspired airmucous
moved by cilia to be expectorated
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Boyles Law
Volume and pressure are inverselyrelated
volume = pressure
Air always flows from an area of higher
pressure to an area of lower pressure
Decreased pressure in the thoracic cavity in
relation to atmospheric pressure causes air
to flow into the lungs The process of inspiration
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Structures of the Thoracic Cavity
Pleura
Parietal pleura: A membrane that lines the
interior surface of the chest wall
Visceral pleura: A membrane that lines theexterior surface of the lungs
Intrapleural space
A thin compartment between the two pleurae
filled with intrapleural fluid
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Pulmonary Pressures
Pressure gradient
The difference between intrapulmonary and
atmospheric pressures
4 Pulmonary Pressures Atmospheric pressure
Intra-alveolar (Intrapulmonary) pressure
Intrapleural pressure
Transpulmonary pressure
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Pulmonary Pressures
Atmospheric pressure
The pressure exerted by the weight of the air in theatmosphere (~ 760 mmHg at sea level)
Intra-alveolar (Intrapulmonary) pressure
The pressure inside the lungs
Intrapleural pressure
The pressure inside the pleural space
Transpulmonary pressure The difference between the intrapleural and intra-
alveolar pressure
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Pleural Pressures
Intrapleural pressure
The pressure inside the pleural space or cavity
This cavity contains intrapleural fluid, necessary
for surface tension
Surface tension
The force that holds moist membranes together
due to an attraction that water molecules have
for one another
Responsible for keeping lungs patent
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Intrapulmonary and Intrapleural Pressures
During inspiration, intrapulmonary pressure is about -3 mm
Hg pressure; during expiration is about +3 mm Hg Positive transmural pressure (intrapulmonary minus
intrapleural pressure) keeps lungs inflated
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Surface Tension
The force of attraction between liquidmolecules
Type II alveolar cells secrete surfactant Creates a thin fluid film in the alveoli
Surfactant (a phospholipoprotein) reducesthe surface tension in the alveoli It interferes with the attraction between fluid
molecules
Decreasing surface tension reduces theamount of energy required to expand thelungs
Laplaces Law
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Surface Tension
Law of Laplacestates that pressure in
alveolus is directly
proportional to ST; and
inversely to radius of
alveoli Thus, pressure in smaller
alveoli would be greater
than in larger alveoli, if
ST were same in both
Greater pressure of
smaller alveolus would
cause it to its empty air
into the larger one
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Inspiration
Drawing or pulling air into the lungs Atmospheric pressure forces air into the lungs
The diaphragm moves downward, decreasing
intra-alveolar pressure
The thoracic rib cage moves upward and outward,
increasing the volume of the thoracic cavity
Surface tension
Holds the pleural membranes together, which assistswith lung expansion
Surfactant reduces surface tension within the alveoli
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Inspiration
During inspiration, forces are generated that
attempt to pull the lungs away from the
thoracic wall
Surface tension of the intraplueral fluid holdthe lungs against the thoracic wall,
preventing collapse
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Expiration
Pushing air out of the lungs Results due to the elastic recoil of tissues
and due to the surface tension within thealveoli
Expiration can be aided by: Thoracic and abdominal wall muscles that pull
the thoracic cage downward and inward,decreasing intra-alveolar pressure
This compresses the abdominal organs upwardand inward, decreasing the volume of thethoracic cavity
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Muscles of Breathing - Inspiration
Quiet Breathing Muscles include: External intercostals
Diaphragm
Contract to expand the rib cage and stretch the
lungs = volume of the thoracic cavity intrapulmonary volume
intrapulmonary pressure (relative to atmosphericpressure)
Decreased pressure inside the lungs pulls air intothe lungs down its pressure gradient untilintrapulmonary pressure equals atmosphericpressure
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Forced or Deep Inspiration Involves several accessory muscles:
Sternocleidomastoid
Pectoralis minor
Scalenes (neck muscles)
Maximal in thoracic volume
Greater in intrapulmonary pressure
More air moves into the lungs At the end of inspiration, the intrapulmonary
pressure equals atmospheric pressure
Muscles of Breathing - Inspiration
M l f B hi E i i
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Quiet Breathing Passive process Depends on the elasticity of the lungs
Muscles of inspiration relax The rib cage descends
The lungs recoil
intrapulmonary volume
intrapulmonary pressure Alveoli are compressed, thus forcing air out
of the lungs
Muscles of Breathing - Expiration
M l f B thi E i ti
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Forced Expiration
It is an active process
Occurs in activities such as blowing up a balloon,
exercising, or yelling
Abdominal wall muscles are involved in forcedexpiration
Function to the pressure in the abdominal cavity forcing
the abdominal organs upward against the diaphragm
volume of thethoracic cavity
pressure in the thoracic cavity
Air is forced out of the lungs
Muscles of Breathing - Expiration
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Brain (medulla
and higher
centers) sendsimpulse to
inspire.
Diaphragm contracts down,
increasing the vertical dimension
of the thorax.
Intercostals and
interchondral
muscles contract
expanding lateral
and anterior-
posterior
dimensions of the
thorax.
Negative air
pressure iscreated in the
lungs
Pressure is
equalized
in the
lungs.
Air isdrawn
into the
lungs.
Gas is
expelled
from thelungs.
Diaphragm and rib-
cage relax
decreasing the
vertical, lateral and
anterior-posterior
dimensions of the
thorax.
Contraction of the
diaphragm,
intercostals and
interchondral
muscles stop and
elastic recoil brings
them to released
position.
Abdominal and
intercostals
muscles contract
decreasing
thoracic volume.
Positive air
pressure is
created in thelungs.
INSPIRATION EXPIRATION
F t Aff ti P l
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Factors Affecting Pulmonary
Ventilation
Lung compliance
The ease with which the lungs may be
expanded, stretched, or inflated
Depends primarily on the elasticity of thelung tissue
Elasticity refers to the ability of the lung to recoil
after it has been inflated
F t Aff ti P l
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Factors Affecting Pulmonary
Ventilation
Lung and thoracic cavity tissue has a
natural tendency to recoil, or become
smaller
Lung recoil is essential for normal expirationand depends on the fibroelastic qualities of
lung tissue
In normal lungs there is a balance betweencompliance and elasticity
F t Aff ti P l
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Recoil pressure is inverselyproportional to
compliance
Increased compliance results in decreased recoil
Example: Emphysema Results in difficulty resuming the shape of the lung
during exhalation
Decreased compliance results in increased recoil
Example: Cysitc fibrosis Results in difficulty expanding the lung because of
increased fibrous tissue and mucous
Factors Affecting Pulmonary
Ventilation
F t Aff ti P l
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Airway Resistance (Poiseuilles Law) Opposition to air flow in the respiratory passageways
Resistance and air flow are inverselyrelated
airway resistance = air flow (and vice versa)
Airway resistance is most affected by changes in thediameter of the bronchioles
diameter of the bronchioles = airway resistance
Examples:
Asthma
Bronchiospasm during an allergic reaction
A high resistance to air flow produces a greater energy costof breathing
Factors Affecting Pulmonary
Ventilation
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To Be Continued
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