HLTAP301A ANATOMY & PHYSIOLOGY
LECTURE 10 - THE RESPIRATORY SYSTEM
Out of all of the basic life support systems, the respiratory system is the only
one under voluntary control.
It shares the responsibility with the
cardiovascular system to obtain the oxygen necessary to create energy for
body functions and to eliminate carbon dioxide produced during cellular
metabolism. The organs of the respiratory system include the nose, pharynx,
larynx, trachea, bronchus and the lungs. Since gas exchange only occurs in
the alveoli, the rest of the respiratory system are really just conducting
passageways that allow air to reach the lungs. However, these passageways
also purify, humidify, and warm the incoming air.
The nose is divided into two portions - the external nose, which is formed by
hyaline cartilage and bones of the skull, and the nasal cavity, which is entirely
within the skull. It moistens, warms, filters, and cleans incoming air; provides
a resonance chamber for speech; and houses olfactory receptors.
The nasal cavity consists of two types of epithelium: olfactory mucosa, which
contains olfactory receptors for the sense of smell and respiratory mucosa,
which produces sticky mucus to moisten incoming air and trap incoming
bacteria and other foreign debris. The nasal cavity also has superficially
located thin-walled veins that warm incoming air. When a nosebleed occurs,
it is from these veins that the blood leaks.
The nasal cavity is separated from the oral cavity by the palate. Anteriorly, it
is supported by bone (hard palate) and posteriorly, the unsupported part is
known as the soft palate.
The pharynx is about 13cm long and is divided into three areas – the
nasopharynx, oropharynx and laryngopharynx . It’s major role is to trap and
destroys airborne pathogens.
The eustachian tubes open into the
nasopharynx and help equalize pressure in the head, nose and pharynx. The
oropharynx is the part of the throat that you can see if you open your mouth.
Air enters the nasopharynx, descends through the oropharynx and
laryngopharynx to enter the larynx. Food enters the mouth, travels with air
through the oropharynx and laryngopharynx but enters the esophagus, which
sits posterior to the larynx.
The larynx (voice box) attaches superiorly to the hyoid bone, opening into the
laryngopharynx, and attaches inferiorly to the trachea. The larynx provides an
open airway, routes food and air into the proper passageways, and produces
sound through the vocal cords. The larynx consists of hyaline cartilage and
the epiglottis, which is elastic cartilage. The epiglottis protects the entry to the
larynx. When we swallow food, the epiglottis folds back over the superior
opening of the larynx and allows food to pass through into the esophagus. If
anything other than air enters the larynx, a cough reflex is triggered to expel
the substance and prevent it from entering the lungs.
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HLTAP301A ANATOMY & PHYSIOLOGY
The trachea (windpipe) is about 10-12cm long and descends from the larynx
through the neck into the mediastinum, where it terminates at the primary
bronchi. The trachea is lined with ciliated mucosa that propels mucus that is
loaded with dust particles towards the throat where it can be swallowed or
spat out. The ‘C-shaped’ rings of hyaline cartilage of the trachea serve a
double purpose. The open part abuts the esophagus and allows the
esophagus to expand when swallowing a large piece of food. The solid
portion of the ‘C’ supports the walls of the trachea and keeps it open,
regardless of pressure changes that occur during breathing.
The bronchi are a continuation of the structural framework of the trachea
(except that they have more smooth muscle). They consist of right and left
primary bronchi that enter each lung and diverge into secondary bronchi that
serve each lobe of the lungs. The right bronchus is wider, shorter and straighter
than the left. This makes it the more common bronchus for an inhaled foreign
object to become lodged.
Secondary bronchi branch into several orders of tertiary bronchi, which
ultimately branch into bronchioles. As the conducting airways become
smaller, the supportive cartilage changes in character until it is no longer
present in the bronchioles. The respiratory zone begins as the terminal
bronchioles feed into respiratory bronchioles that terminate in alveolar ducts
within clusters of alveolar sacs, which consist of alveoli.
The lungs occupy all of the thoracic cavity except for the mediastinum, which
houses the heart, major blood vessels and the esophagus. Each lung is
suspended within its own pleural cavity and connected to the mediastinum by
vascular and bronchial attachments called the lung root.
There are two circulations that serve the lungs: the pulmonary network carries
systemic blood to the lungs for oxygenation, and the bronchial arteries provide
systemic blood to the lung tissue.
Lung tissue consists largely of air spaces, with the balance of lung tissue, its
stroma, comprised mostly of elastic connective tissue. The pleurae form a
thin, double-layered serosa. The parietal pleura lines the thoracic cavity. The
visceral pleura covers the external lung surface, following its contours and
fissures. The pleural membranes produce a slippery serous secretion, pleural
fluid, which allows the lungs to glide over the thorax wall during breathing
movements without friction.
Pleurisy (inflammation of the pleura) can be caused by decreased secretion of
pleural fluid whereby the pleural surfaces become dry and rough, resulting in
friction and stabbing pain with each breath.
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HLTAP301A ANATOMY & PHYSIOLOGY
The major function of the respiratory system is to supply the body with oxygen
and dispose of carbon dioxide. To do this, at least four distinct events must
occur – these four events are collectively called respiration. The four events
are pulmonary ventilation, external respiration, respiratory gas transport and
internal respiration.
Pulmonary Ventilation
Pulmonary ventilation, more commonly known as breathing, is a mechanical
process causing gas flow into and out of the lungs according to volume
changes in the thoracic cavity.
External respiration involves O2 uptake and CO2 unloading from
hemoglobin in red blood cells. O2 diffuses rapidly from the alveoli (in the
lungs) into the blood, and carbon dioxide moves in the opposite direction.
The respiratory membrane is normally very thin, and presents a huge surface
area for efficient gas exchange.
Respiratory Gas Transport – is the transport of oxygen and carbon dioxide
in the blood to/from the cells of the body. Oxygen binds to hemoglobin to be
transported and carbon dioxide is dissolved as bicarbonate ions in the blood
(70%) and some binds to hemoglobin, but at different sites to oxygen.
Internal Respiration occurs in the capillaries to all cells in the body. The
actual use of oxygen and production of carbon dioxide by the cells of the body
is the cornerstone of all energy-producing chemical reactions in the body.
Respiratory Adjustments
During vigorous exercise, deeper and more vigorous respirations, (called
hyperpnea), ensure that tissue demands for oxygen are met. Three neural
factors contribute to the change in respiration: psychic stimuli, cortical
stimulation of skeletal muscles and respiratory centers, and excitatory
impulses to the respiratory areas from active muscles, tendons, and joints.
At high altitude, acute mountain sickness (AMS) may result from a rapid
transition from sea level to altitudes above 8000 feet. A long-term change
from sea level to high altitudes results in acclimatization of the body, including
an increase in ventilation rate, lower than normal hemoglobin saturation, and
increased production of erythropoietin.
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Homeostatic Imbalances of the Respiratory System
Chronic obstructive pulmonary diseases (COPD) are seen in patients that
have a history of smoking, and result in progressive dyspnea, coughing and
frequent pulmonary infections, and respiratory failure.
Obstructive emphysema is characterized by permanently enlarged alveoli
and deterioration of alveolar walls.
Chronic bronchitis results in excessive mucus production, as well as
inflammation and fibrosis of the lower respiratory mucosa.
Asthma is characterized by coughing, dyspnea, wheezing, and chest
tightness, brought on by active inflammation of the airways.
Tuberculosis (TB) is an infectious disease caused by the bacterium
Mycobacterium tuberculosis and spread by coughing and inhalation.
Lung Cancer
Lung cancer is the most common type of malignancy, and is strongly
correlated with smoking. Squamous cell carcinoma arises in the epithelium of
the bronchi, forming masses that hollow out and bleed. Adenocarcinoma
originates in peripheral lung areas and small cell carcinoma forms clusters
within the mediastinum and rapidly metastasize.
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