Transcript Chapter 23

Chapter 23
The Respiratory
System
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.
Upper
respiratory
tract
Lower
respiratory
tract
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.
Respiratory System Anatomy
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
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.
Respiratory System Anatomy
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
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
Respiratory System Anatomy
• 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 backward to close off the glottic
opening during
swallowing.
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.
Respiratory System Anatomy
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
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
Upper
respiratory
tract
Pharynx
Larynx
Trachea
Primary bronchi
Secondary bronchi
Tertiary bronchi
Bronchioles
Alveoli (150 million/lung)
Lower
respiratory
tract
Respiratory System Anatomy
The trachea is a semi-rigid pipe made of semicircular 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
o
primary (1 , “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).
Respiratory System Anatomy
• 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
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 mainstem
bronchi – a very sensitive
area for triggering the
cough reflex.
Respiratory System Anatomy
o
o
o
The 1 bronchi divide to form 2 and 3 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.
Respiratory System Anatomy
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
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
Respiratory System Anatomy
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.
o
Each lobe receives it own 2
bronchus that branches into
o
3 segmental bronchi (which
continue to further divide).
Respiratory System Anatomy
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
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)
– Oxygen (O2)
– Carbon Dioxide (CO2)
– Water Vapor
78%
21%
0.04%
variable, but on average
around 1%
Understanding Gases
The gases of the atmosphere have a mass
18
and a weight (5 x 10 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.
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.
Gas Exchange
Gas Exchange
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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