lecture note 6 - hcc learning
TRANSCRIPT
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Chapter 23
The Respiratory
System
Upper respiratory tract
Lower respiratory tract
Respiratory System Anatomy Structurally, the respiratory system is divided into upper
and lower divisions or tracts.
The upper respiratory tract
consists of the nose, pharynx
and associated structures.
The lower respiratory tract
consists of the larynx,
trachea, bronchi and
lungs.
Respiratory System Anatomy Functionally, the respiratory system is divided into the
conducting zone and the respiratory zone.
The conducting zone is involved with bringing air to
the site of external respiration and consists of the
nose, pharynx, larynx, trachea, bronchi, bronchioles
and terminal bronchioles.
The respiratory zone is the main site of gas
exchange and consists of the respiratory bronchioles,
alveolar ducts, alveolar sacs, and alveoli.
Air passing through the respiratory
tract traverses the:
Nasal cavity
Pharynx
Larynx
Trachea
Primary (1o) bronchi
Secondary (2o) bronchi
Tertiary (3o) bronchi
Bronchioles
Alveoli (150 million/lung)
Respiratory System Anatomy
The external nose is visible on the face.
The internal nose is a large cavity beyond the nasal
vestibule.
The internal nasal
cavity is divided by a
nasal septum into
right and left nares.
Respiratory System Anatomy Three nasal conchae (or turbinates)
protrude from each lateral wall into the
breathing passages.
Tucked under each nasal concha is an
opening, or meatus, for a duct that drains
secretions of the sinuses and tears into the
nose.
Receptors in the
olfactory epithelium
pierce the bone
of the cribriform plate.
Respiratory System Anatomy
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Respiratory System Anatomy The pharynx is a hollow tube that starts
posterior to the internal nares and
descends to the opening of the larynx in
the neck.
It is formed by a complex arrangement of
skeletal muscles that assist in deglutition.
It functions as:
a passageway for air and food
a resonating chamber
a housing for the tonsils
Respiratory System Anatomy The pharynx has 3 anatomical regions:
The nasopharynx; oropharynx; and
laryngopharynx
In this graphic, slitting the muscles of the posterior
pharynx shows the
back of the tongue
in the laryngopharynx.
The nasopharynx is separated
from the oropharynx by the
hard and soft palate.
The nasopharynx lies behind the internal nares.
It contains the pharyngeal tonsils (adenoids)
and the
openings of the
Eustachian tubes
(auditory tubes)
which come off
of it and travels
to the middle
ear cavity.
Respiratory System Anatomy Respiratory System Anatomy
The oropharynx lies behind the mouth and
participates in both respiratory and digestive
functions.
The main palatine tonsils (those usually taken
in a tonsillectomy) and small lingual tonsil are
housed here.
The laryngopharynx lies inferiorly and opens
into the larynx (voice box) and the esophagus.
It participates in both respiratory and digestive
functions.
Respiratory System Anatomy Respiratory System Anatomy The larynx, composed of 9 pieces of cartilage,
forms a short passageway connecting the
laryngopharynx with the trachea (the “windpipe”).
The thyroid cartilage (the large
“Adam’s apple”) and the one
below it (the cricoid cartilage)
are landmarks for making an
emergency airway (called a
cricothyrotomy).
Anterior view of the larynx
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The epiglottis is a flap of elastic cartilage covered with a
mucus membrane, attached to the root of the tongue.
The epiglottis guards the entrance of the glottis, the
opening between the vocal folds.
For breathing, it is held
anteriorly, then pulled back-
ward to close off the glottic
opening during
swallowing.
Respiratory System Anatomy Respiratory System Anatomy The rima glottidis (glottic opening) is formed by a
pair of mucous membrane vocal folds (the true
vocal cords).
The vocal folds are situated high in the larynx
just below where the larynx and the esophagus
split off from the pharynx.
Cilia in the upper respiratory tract move mucous
and trapped particles down toward the pharynx.
Cilia in the lower respiratory tract move them up
toward the larynx.
Respiratory System Anatomy
Upper respiratory tract
Lower respiratory tract
Respiratory System Anatomy As air passes from the laryngopharynx into the
larynx, it leaves the upper respiratory tract and
enters the lower respiratory tract.
Air passing through the respiratory
tract
Nasal cavity
Pharynx
Larynx
Trachea
Primary bronchi
Secondary bronchi
Tertiary bronchi
Bronchioles
Alveoli (150 million/lung)
Respiratory System Anatomy The trachea is a semi-rigid pipe made of semi-
circular cartilaginous rings, and located anterior to
the esophagus.
It is about 12 cm long and extends from the
inferior portion of the larynx into the mediastinum
where it divides into right and left primary (1o,
“mainstem”) bronchi.
It is composed of 4 layers: a mucous secreting
epithelium called the mucosa, and three layers of
CT (submucosa, hyaline cartilage, and
adventitia).
The tracheal cartilage rings are incomplete
posteriorly, facing the esophagus.
Esophageal masses can press into this soft
part of the trachea and make it difficult
to breath, or even
totally obstruct
the airway.
Respiratory System Anatomy
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Respiratory System Anatomy The right and left primary (1o or “mainstem”) bronchi
emerge from the inferior trachea to go to the lungs,
situated in the right and left pleural cavities.
The carina is an internal
ridge located at the junction
of the two main stem
bronchi – a very sensitive
area for triggering the
cough reflex.
Respiratory System Anatomy The 1o bronchi divide to form 2o and 3o bronchi which
respectively supply the lobes and segments of each lung.
3o bronchi divide into
bronchioles which in
turn branch through
about 22 more divisions
(generations).
The smallest are the
terminal bronchioles.
Respiratory System Anatomy The bronchi and bronchioles go through structural
changes as they branch and become smaller.
The mucous membrane changes and then
disappears.
The cartilaginous rings become more sparse,
and eventually disappear altogether.
As cartilage decreases, smooth muscle (under
the control of the Autonomic Nervous System)
increases. Sympathetic stimulation causes airway dilation, while
parasympathetic stimulation causes airway constriction.
Respiratory System Anatomy All the branches from the trachea to the
terminal bronchioles are conducting
airways – they do not
participate in gas
exchange.
Respiratory System Anatomy The cup-shaped outpouchings which participate in gas
exchange are called alveoli.
The first alveoli don’t appear until
the respiratory
bronchioles
where they are
rudimentary and
mostly
nonfunctioning.
Respiratory System Anatomy
Respiratory bronchioles give way to alveolar
ducts, and the epithelium (simple cuboidal)
changes to simple squamous, which comprises
the alveolar ducts, alveolar sacs, and alveoli.
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Taken together, these structures form the
functional unit of the lung, which is the
pulmonary lobule.
Wrapped in elastic
C.T., each pulmonary
lobule contains a
lymphatic vessel, an
arteriole, a venule
and a terminal
bronchiole. The pulmonary lobule
Respiratory System Anatomy Respiratory System Anatomy As part of the pulmonary lobule, alveoli are delicate
structures composed chiefly of type I alveolar cells,
which allow for exchange of gases with the pulmonary
capillaries.
Alveoli make up a large
surface area (750 ft2).
Type II cells secrete a
substance called surfactant
that prevents collapse of the
alveoli during exhalation.
Respiratory System Anatomy Alveoli macrophages (also called “dust cells”) scavenge
the alveolar surface to engulf and remove microscopic
debris that has made it past the “mucociliary blanket” that
traps most foreign particles higher in
the respiratory tract.
The alveoli (in close proximity
to the capillaries) form the
alveolar-capillary membrane
(“AC membrane”).
Blood Supply to the Lungs
The lungs receive blood via two sets of
arteries
Pulmonary arteries carry deoxygenated blood
from the right heart to the lungs for oxygenation
Bronchial arteries branch from the aorta and
deliver oxygenated blood to the lungs primarily
perfusing the muscular walls of the bronchi and
bronchioles
Ventilation-Perfusion Coupling
Ventilation-perfusion coupling is the coupling of
perfusion (blood flow) to each area of he lungs to
match the extent of ventilation (airflow) to alveoli in
that area
In the lungs, vasoconstriction in response to
hypoxia diverts pulmonary blood from poorly
ventilated areas of the lungs to well-ventilated
regions
In all other body tissues, hypoxia causes dilation
of blood vessels to increase blood flow
As organs, the lungs are divided into lobes by fissures.
The right lung is divided by the oblique fissure and the
horizontal fissure into 3 lobes .
The left lung is divided into
2 lobes by the oblique fissure.
Each lobe receives it own 2o
bronchus that branches into
3o segmental bronchi (which
continue to further divide).
Respiratory System Anatomy
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The apex of the lung is superior, and extends slightly
above the clavicles. The base of the
lungs rests on the diaphragm.
The cardiac notch –
in the left lung (the
indentation for the
heart) makes the left
lung 10 % smaller
than the right lung.
Respiratory System Anatomy The lungs are separated from each other
by the heart and other structures in the
mediastinum.
Each lung is enclosed by a double-layered
pleural membrane.
The parietal pleura line the
walls of the thoracic cavity.
The visceral pleura adhere
tightly to the surface of
the lungs themselves.
Respiratory System Anatomy
Respiratory System Anatomy On each side of the thorax, a pleural cavity is formed.
The integrity of this space (really potential space)
between the parietal and visceral pleural layers is
crucial to the mechanism of breathing.
Pleural fluid reduces friction and produces a surface
tension so the layers can slide across one another.
The pleura, adherent to the chest wall and to the lung,
produces a mechanical coupling for the two layers to
move together.
Understanding Gases
To understand how this mechanical
coupling between the lungs, the pleural
cavities and the chest wall results in
breathing, we first need to discuss some
physics of gases called the
gas laws.
Understanding Gases The respiratory system depends on the
medium of the earth’s atmosphere to
extract the oxygen necessary for life.
The atmosphere is composed of these
gases:
Nitrogen (N2) 78%
Oxygen (O2) 21%
Carbon Dioxide (CO2) 0.04%
Water Vapor variable, but on average
around 1%
Understanding Gases The gases of the atmosphere have a
mass and a weight (5 x 1018 kg, most
within 11 km of the surface).
Consequently, the atmosphere exerts a
significant force on every object on the
planet (recall that pressure is measured as
force applied per unit area, P = F/A.)
We are “accustomed” to the tremendous
force pressing down on every square inch of
our body.
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Understanding Gases A barometer is an
instrument that
measures atmospheric
pressure.
Baro = pressure or
weight
Meter = measure
Air pressure varies
greatly depending on the
altitude and the
temperature.
Understanding Gases There are many different units used to
measure atmospheric pressure. At sea
level, the air pressure is:
14.7 lb/in2 = 1 atmosphere
760 mmHg = 1 atmosphere
76 cmHg = 1 atmosphere
29.9 inHg = 1 atmosphere
At high altitudes, the atmospheric pressure
is less; descending to sea level,
atmospheric pressure is greater.
Understanding Gases Gases obey laws of physics called the
gas laws.
These laws apply equally to the gases of the
atmosphere, the gases in our lungs, the
gases dissolved in the blood, and the gases
diffusing into and out of the cells of our body.
To understand the mechanics of ventilation
and respiration, we need to have a basic
understanding of 3 of the 5 common gas
laws.
Understanding Gases Boyle’s law applies to containers with
flexible walls – like our thoracic cage.
It says that volume and pressure are
inversely related.
If there is a decrease
in volume – there will
be an increase in
pressure: V ∝ 1/P
Understanding Gases Dalton’s law applies to a mixture of
gases.
It says that the pressure of each gas is
directly proportional to the percentage of that
gas in the total mixture: PTotal = P1 + P2 + P3
…
Since O2 = 21% of atmosphere, the partial
pressure exerted by the contribution of just
O2 (written pO2 or PAO2) = 0.21 x 760 mmHg
= 159.6 mmHg at sea level.
Understanding Gases Henry’s law deals with gases and solutions.
It says that increasing the partial pressure of a
gas “over” (in contact with) a solution will
result in more of the gas dissolving into the
solution.
The patient in this picture is getting
more O2 in contact with
his blood - consequently,
more oxygen goes
into his blood.
Medicimage/Phototake
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Understanding Gases
Gas will always move from a region of
high pressure to a region of low pressure.
Applying Boyle's law: If the volume inside
the thoracic cavity , the pressure .
Ventilation and Respiration Pulmonary ventilation is the movement of air
between the atmosphere and the alveoli, and
consists of inhalation and exhalation.
Ventilation, or
breathing, is made
possible by
changes in the
intrathoracic
volume.
Ventilation and Respiration In contrast to ventilation,
respiration is the exchange of
gases.
External respiration
(pulmonary)
is gas exchange between the
alveoli and the blood.
Internal respiration (tissue)
is gas exchange between
the systemic capillaries and
the tissues of the body.
Ventilation and Respiration External respiration in the lungs is possible
because of the implications of Boyle’s law:
The volume of the thoracic cavity can be
increased or decreased by the action of the
diaphragm, and other muscles of the chest
wall.
By changing the volume of the thoracic cavity
(and the lungs – remember the mechanical
coupling of the chest wall, pleura, and lungs),
the pressure in the lungs will also change.
Ventilation and Respiration
Changes in air pressure result in
movement of the air.
Contraction of the diaphragm and external
intercostal (rib) muscles increases the size of
the thorax. This decreases the intrapleural
pressure so air can flow in from the
atmosphere (inspiration).
Relaxation of the diaphragm, with/without
contraction of the internal intercostals,
decreases the size of the thorax, increases the
air pressure, and results in exhalation.
Ventilation and Respiration Certain thoracic
muscles participate
in inhalation;
others aid
exhalation.
The diaphragm
is the primary
muscle of
respiration – all
the others are
accessory.
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Ventilation and Respiration The recruitment of accessory muscles
greatly depends on whether the respiratory
movements are quiet (normal), or forced
(labored).
Airflow and Work of Breathing Differences in air pressure drive airflow, but 3
other factors also affect the ease with which we
ventilate:
1. The surface tension of alveolar fluid causes
the alveoli to assume the smallest possible
diameter and accounts for 2/3 of lung elastic
recoil. Normally the alveoli would close with
each expiration and make our “Work of
Breathing” insupportable.
Surfactant prevents the complete collapse
of alveoli at exhalation, facilitating
reasonable levels of work.
Airflow and Work of Breathing
2. High lung compliance means the lungs and
chest wall expand easily.
Compliance is decreased by a
broken rib, or by diseases such
as pneumonia or emphysema.
Airflow and Work of Breathing
Measuring Ventilation Ventilation can be measured using spirometry.
Tidal Volume (VT) is the volume of air inspired (or
expired) during normal quiet breathing (500 ml).
Inspiratory Reserve Volume (IRV) is the volume
inspired during a very deep inhalation (3100 ml –
height and gender dependent).
Expiratory Reserve Volume (ERV) is the volume
expired during a forced exhalation (1200 ml).
Measuring Ventilation
Spirometry continued
Vital Capacity (VC) is all the air that can be
exhaled after maximum inspiration.
It is the sum of the inspiratory reserve + tidal volume
+ expiratory reserve (4800 ml).
Residual Volume (RV) is the air still present in
the lungs after a force exhalation (1200 ml).
The RV is a reserve for mixing of gases but is not
available to move in or out of the lungs.
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Measuring Ventilation
Old and new spirometers used to measure ventilation.
Measuring Ventilation
A graph of spirometer volumes and capacities
Measuring Ventilation Only about 70% of the tidal volume reaches the
respiratory zone – the other 30% remains in the
conducting zone (called the anatomic dead space).
If a single VT breath = 500 ml, only 350 ml will
exchange gases at the alveoli.
In this example, with a respiratory rate of 12, the
minute ventilation = 12 x 500 = 6000 ml.
The alveolar ventilation (volume of air/min that
actually reaches the alveoli) = 12 x 350 = 4200ml.
Exchange of O2 and CO2 Using the gas laws and understanding the
principals of ventilation and respiration,
we can calculate the
amount of oxygen and
carbon dioxide
exchanged between
the lungs and
the blood.
Exchange of O2 and CO2
Dalton’s Law states that each gas in a mixture of gases
exerts its own pressure as if no other gases were present.
The pressure of a specific gas is the partial pressure
Pp.
Total pressure is the sum of all the partial pressures.
Atmospheric pressure (760 mmHg) = PN2 + PO2 + PH2O
+ PCO2 + Pother gases
Since O2 is 21% of the atmosphere, the PO2 is
760 x 0.21 = 159.6 mmHg.
Exchange of O2 and CO2 Each gas diffuses across a permeable membrane (like
the AC membrane) from the side where its partial
pressure is greater to the side where its partial pressure is
less.
The greater the difference, the faster the rate of
diffusion.
Since there is a higher PO2 on the lung side of the AC
membrane, O2 moves from the alveoli into the
blood.
Since there is a higher PCO2 on the blood side of the
AC membrane, CO2 moves into the lungs.
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Exchange of O2 and CO2
PN2 = 0.786 x 760 mmHg = 597.4 mmHg
PO2 = 0.209 x 760 mmHg = 158.8 mmHg
PH2O = 0.004 x 760 mmHg = 3.0 mmHg
PCO2 = 0.0004 x 760 mmHg = 0.3 mmHg
Pother gases = 0.0006 x 760 mmHg = 0.5 mmHg
Total = 760.0 mmHg
Partial pressures of gases in inhaled air for sea level
Exchange of O2 and CO2 Henry’s law states that the quantity of a gas
that will dissolve in a liquid is proportional to the
partial pressures of the gas and its solubility.
A higher partial pressure of a
gas (like O2) over a liquid (like
blood) means more of the gas
will stay in solution.
Because CO2 is 24 times more
soluble in blood (and soda pop!) than in O2,
it more readily dissolves.
Exchange of O2 and CO2 Even though the air we breathe is mostly
N2, very little dissolves in blood due to its
low solubility.
Decompression sickness (“the bends”) is a
result of the comparatively insoluble N2 being
forced to dissolve into the blood and tissues
because of the very high pressures associated
with diving.
By ascending too rapidly, the N2 rushes out of the
tissues and the blood so forcefully as to cause
vessels to “pop” and cells to die.
Transport of O2 and CO2 In the blood, some O2 is dissolved in the
plasma as a gas (about 1.5%, not enough
to stay alive – not by a long shot!). Most
O2 (about 98.5%) is carried attached to
Hb.
Oxygenated Hb is called oxyhemoglobin.
Transport of O2 and CO2
CO2 is transported in the blood in three different
forms:
1. 7% is dissolved in the plasma, as a gas.
2. 70% is converted into carbonic acid through the
action of an enzyme called carbonic anhydrase.
CO2 + H2O H2CO3 H+ + HCO3
-
3. 23% is attached to Hb (but not at the same binding
sites as oxygen).
Transport of O2 and CO2 The O2 transported in the blood (PO2 = 100 mmHg) is
needed in the tissues to continually make ATP (PO2 = 40
mmHg at the capillaries).
CO2 constantly diffuses
from the tissues
(PCO2 = 45 mmHg) to
be transported in
the blood
(PCO2 = 40 mmHg) Internal Respiration occurs at
systemic capillaries
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Transport of O2 and CO2 The amount of Hb saturated with O2 is called
the SaO2.
Each Hb molecule can carry 1, 2, 3, or 4
molecules of O2. Blood leaving the lungs
has Hb that is fully saturated (carrying 4
molecules of
O2 – oxyhemoglobin).
The SaO2 is close to 95-98% .
When it returns, it still has 3 of
the 4 O2 binding sites occupied.
SaO2 = 75%
Transport of O2 and CO2 The relationship between the amount of O2
dissolved in the plasma and the saturation
of Hb is called the oxygen-hemoglobin
saturation curve.
The higher the PO2
dissolved in the plasma,
the higher the SaO2.
Transport of O2 and CO2
Measuring SaO2 has
become as
commonplace in
clinical practice as
taking a blood
pressure.
Pulse oximeters
which used to cost
$5,000 can now be
purchased at your local
pharmacy.
3660 Group,
Inc/NewsCom
Transport of O2 and CO2
Although PO2 is the most important
determinant of SaO2, several other factors
influence the affinity with which Hb binds O2
Acidity (pH), PCO2 and blood temperature shift
the entire O2 –Hb saturation
curve either to the left
(higher affinity for O2), or
to the right (lower affinity
for O2).
Transport of O2 and CO2
Transport of O2 and CO2 As blood flows from the lungs toward the tissues,
the increasing acidity (pH decreases) shifts the
O2–Hb saturation curve “to the right”, enhancing
unloading of O2 (which is just what we want to
happen).
This is called the Bohr effect.
At the lungs, oxygenated blood has a reduced
capacity to carry CO2 ,and it is unloaded as we
exhale (also just what we want to happen).
This is called the Haldane effect.
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Fetal and Maternal Hemoglobin Fetal hemoglobin (Hb-F) has a higher
affinity for oxygen (it is shifted to the left)
than adult hemoglobin A, so it binds O2
more strongly. The fetus is thus able
to attract oxygen
across the placenta
and support life,
without lungs.
The medulla rhythmicity area, located in the brainstem, has centers
that control basic respiratory patterns for both inspiration and
expiration.
The inspiratory center
stimulates the diaphragm
via the phrenic nerve, and
the external intercostal
muscle via intercostal nerves.
Inspiration normally lasts about 2 sec.
Control of Respiration
Control of Respiration Exhalation is mostly a passive process,
caused by the elastic recoil of the lungs.
Usually, the expiratory center is inactive
during quiet breathing (nerve impulses
cease for about 3 sec).
During forced exhalation,
however, impulses from this
center stimulate the internal
intercostal and abdominal
muscles to contract.
Control of Respiration Other sites in the pons help the medullary centers manage
the transition between inhalation and exhalation.
The pneumotaxic center limits inspiration to prevent
hyperexpansion.
The apneustic
center coordinates
the transition between
inhalation and exhalation.
Control of Respiration Other brain areas also play a role in respiration:
Our cortex has voluntary control of breathing.
Stretch receptors sensing over-inflation arrests
breathing temporarily (Herring Breuer reflex).
Emotions (limbic system) affect respiration.
The hypothalamus, sensing a fever, increases
breathing, as does moderate pain (severe pain
causes apnea.)
Initial Response
Mucous layer thickens.
Goblet cells over-secrete
mucous.
Basal cells proliferate.
Advanced Response to Irritation
Mucous layer and goblet cells disappear.
Basal cells become malignant & invade deeper tissue.
Normal columnar epithelium
in the respiratory tract
Response to Pollutants
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Diseases and Disorders Asthma is a disease of hyper-reactive airways
(the major abnormality is constriction of smooth
muscle in the bronchioles, and inflammation.) It
presents as attacks of wheezing, coughing, and
excess mucus production.
It typically occurs in response to allergens;
less often to emotion.
Bronchodilators and anti-
inflammatory corticosteroids
are mainstays of treatment.
Pulse Picture Library/CMP mages /Phototake
Diseases and Disorders Chronic bronchitis and emphysema are
caused by chronic irritation and
inflammation leading to lung destruction.
Patients may cough up
green-yellow sputum due to
infection and increased mucous
secretion (productive cough).
They are almost exclusively
diseases of cigarette smoking.
Diseases and Disorders
Pneumonia is an acute infection of the
lowest parts of the respiratory tract.
The small bronchioles and alveoli become filled
with an inflammatory fluid exudate.
It is typically caused by infectious agents such as
bacteria, viruses, or fungi.
Diseases and Disorders Normal Lungs Pneumonia
Patient
Du Cane Medical Imaging, Ltd./Photo Researchers, Inc