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 Upper respiratory tract and associated structures.
– The
lower respiratory tract
consists of the larynx, Lower respiratory tract 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.
Respiratory System Anatomy
Air passing through the respiratory tract traverses the: – Nasal cavity – Pharynx – Larynx – Trachea – Primary (1
o
) bronchi – Secondary (2
o
) bronchi – Tertiary (3
o
) 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 back ward 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 Pharynx Larynx Trachea Primary bronchi Secondary bronchi Tertiary bronchi Bronchioles Alveoli (150 million/lung) Upper respiratory tract Lower respiratory tract
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 (1
o
, “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
(1
o
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
The
1 o bronchi
divide to form
2 o
and
3 o bronchi
which respectively supply the lobes and segments of each lung.
– 3
o
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, increases.
smooth muscle
(under the control of the Autonomic Nervous System) •
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 ft
2
).
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.
Each lobe receives it own 2
o
bronchus that branches into 3
o
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 (N 2 ) – Oxygen (O 2 ) – Carbon Dioxide (CO 2 ) – Water Vapor 78% 21% 0.04% variable, but on average around 1%
Understanding Gases
The gases of the atmosphere have a mass and a weight (5 x 10
18
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:
P Total = P 1 + P 2 + P 3 …
– Since O 2 = 21% of atmosphere, the partial pressure exerted by the contribution of just O 2 (written pO 2 or
P A O 2
) = 0.21 x 760 mmHg =
159.6 mmHg
at sea level.
Gas Exchange
Gas Exchange
You must be connected to the internet to run this animation
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 O 2 in contact with his blood - consequently, more oxygen goes into his blood.
Medicimage/Phototake