Transcript chapt16_lecture

Chapter 16
Respiratory System
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Introduction
• The respiratory system consists of tubes that filter
incoming air and transport it into the microscopic alveoli
where gases are exchanged.
• Respiration is defined as the process of inhalation of oxygen
and the exhalation of carbon-di-oxide with the help of
certain organs of the human body. These organs include the
nose, pharynx, larynx, trachea, bronchi and the lungs. These
organs together make the human respiratory system.
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Functions of the Respiratory
System
• Respiration
The most important function of the respiratory
system is the process of respiration.
• The entire process of exchanging gases between
the atmosphere and body cells is called and
consists of the following: ventilation, gas exchange
between blood and lungs, gas transport in the
bloodstream, gas exchange between the blood
and body cells, and cellular respiration.
.
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Respiration
How does the respiratory system function?
1. Inhalation
When a person breathes air (which contains oxygen), it passes
through the nasal passages containing mucous. This mucous helps in
filtering out contaminants like dust, pollen and smoke. The nasal
epithelium naturally adds moisture and heat to the air. The larynx
prevents food or liquid entering the respiratory tract. The air then
passes through the larynx and enters the trachea or the windpipe.
Here it gets divided into the two bronchi that connect the trachea
to the lungs. The bronchi again gets split into many smaller tubes
known as bronchioles. These bronchi end in air sacs, also known as
alveoli, which contain blood capillaries. These blood capillaries carry
blood which comes through veins from all other parts of the body.
Here the carbon dioxide from the blood is exchanged for the
oxygen in the alveoli. The blood containing oxygen then goes to the
heart where it is later pumped to other parts of the body.
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How does the respiratory system function?
2. Exhalation
Exhalation in human beings is the process of expelling out of air
containing carbon dioxide. The movement of the air while
exhalation is through the bronchi, then through the airways and
then it passes out through the nose. The exhaled air is completely
depleted of oxygen.
The lungs are the most important organs of the human
respiratory system. There is a muscle located below the lungs
known as the diaphragm which also plays an important role in the
process of respiration. During inhalation, the diaphragm
contracts, creating a vacuum that helps in pulling air into the
lungs. On the other hand, during exhalation, the diaphragm
relaxes which helps in forcing the air out of the lungs.
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How does the respiratory system function?
3.Vocalization
Vocalization is also one of the major respiratory system
functions. Vocalization is the process which enables humans
to speak and also to make sound. When the air passes
through the pharynx and larynx, it makes the vocal cords in
larynx to vibrate which helps in production of sound and
speech in humans.
4. Coughing/Sneezing
When any foreign particles enter the nasal passages, it can
result into irritation. Therefore, expelling out these foreign
bodies or irritants is one of the functions of the respiratory
system. These irritants are forced out of the respiratory
tract through cough or even sneeze
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To Put It Simply…
• The principle functions of the
respiratory system are:
– Ventilate the lungs
– Extract oxygen from the air and
transfer it to the bloodstream
– Excrete carbon dioxide and water vapor
– Maintain the acid base of the blood
– Screen and filter air from foreign
particles
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Organs of the Respiratory System
• The organs of the
respiratory tract can
be divided into two
groups: the upper
respiratory tract
(nose, nasal cavity,
sinuses, and pharynx),
and the lower
respiratory tract
(larynx, trachea,
bronchial tree, and
lungs).
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Nose
•
supported by bone and cartilage, provides an entrance for air in
which air is filtered by coarse hairs inside the nostrils
Nasal Cavity
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•
space posterior to the nose that is divided medially by the nasal
septum
nasal conchae divide the cavity into passageways that are lined with
mucous membrane, and help increase the surface area available to
warm and filter incoming air
Particles trapped in the mucus are carried to the pharynx by ciliary
action, swallowed, and carried to the stomach where gastric juice
destroys any microorganisms in the mucus.
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Paranasal Sinuses
• Sinuses are air-filled spaces within the maxillary,frontal,
ethmoid, and sphenoid bones of the skull.
• These spaces open to the nasal cavity and are lined with mucus
membrane that is continuous with that lining the nasal cavity.
• The sinuses reduce the weight of the skull and serve as a
resonant chamber to affect the quality of the voice.
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Pharynx
aka Throat
• common passageway for air and food
• aids in producing sounds for speech
Larynx
• an enlargement in the airway superior to the trachea and
inferior to the pharynx
• helps keep particles from entering the trachea and also
houses the vocal cords
• composed of a framework of muscles and cartilage bound by
elastic tissue
•
Note: Epiglottis & vestibular folds prevent swallowed material from moving into larynx (can
move to cover trachea)
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Larynx continued…
• Inside the larynx, two pairs of folds of muscle and connective
tissue covered with mucous membrane make up the vocal cords
• The upper pair is the false vocal cords
• The lower pair is the true vocal
cords
• Changing tension on the vocal cords controls pitch, while increasing the
loudness depends upon increasing the force of air vibrating the vocal
cords
• During normal breathing, the vocal cords are relaxed and the
glottis is a triangular slit
• During swallowing, the false vocal cords and epiglottis close off
the glottis
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Trachea
• Extends downward
anterior to the
esophagus and into the
thoracic cavity, where it
splits into right and left
bronchi
• inner wall of the
trachea is lined with
ciliated mucous
membrane with many
goblet cells that serve
to trap incoming
particles
• tracheal wall is
supported by 20
incomplete cartilaginous
rings
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Bronchial Tree
• consists of branched tubes leading from the trachea to the
alveoli
• begins with the two primary bronchi, each leading to a lung
• branches of the bronchial tree from the trachea are right
and left primarybronchi; these further subdivide until
bronchioles give rise to alveolar ducts which terminate in
alveoli
• it is through the thin epithelial cells of the alveoli that gas
exchange between the blood and air occurs
Primary bronchi
Secondary bronchi
Tertiary bronchi
bronchioles
Terminal bronchioles
Respiratory bronchioles
Alveolar ducts
Alveolar sacs
alveoli
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Alveoli
– Extremely thin-walled
sacs covered w/
capillaries
– CO2 & O2 move by
diffusion across the
respiratory membrane
– About 300 million
alveoli in two lungs
– Size of a tennis court
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Lungs
• the right and left soft, spongy, cone-shaped lungs are
separated medially by the mediastinum and are enclosed by
the diaphragm and thoracic cage
• the bronchus and large blood vessels enter each lung
• A layer of serous membrane, the visceral pleura, folds back
to form the parietal pleura
• The visceral pleura is attached to the lung, and the parietal
pleura lines the thoracic cavity; serous fluid lubricates the
“pleura cavity” between these two membranes
• the right lung has three lobes, the left has two
• Each lobe is composed of lobules that contain air passages,
alveoli, nerves, blood vessels, lymphatic vessels, and
connective tissues.
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Breathing Mechanism
• Ventilation (breathing), the movement of air in and out of
the lungs, is composed of inspiration and expiration
Inspiration
• Atmospheric pressure is the force that moves air into the lungs
• When pressure on the inside of the lungs decreases, higher
pressure air flows in from the outside
• Air pressure inside the lungs is decreased by increasing the
size of the thoracic cavity; due to surface tension between the
two layers of pleura, the lungs follow with the chest wall and
expand
• Muscles involved in expanding the thoracic cavity include the
diaphragm and the external intercostal muscles
• As the lungs expand in size, surfactant keeps the alveoli
from sticking to each other so they do not collapse when
internal air pressure is low.
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Expiration
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• The forces of expiration are due to the elastic recoil of lung
and muscle tissues and from the surface tension within the
alveoli
• Forced expiration is aided by thoracic and abdominal wall
muscles that compress the abdomen against the diaphragm
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Changing Alveolar Volume
• Lung recoil
– Causes alveoli to collapse resulting from
• Elastic recoil and surface tension
– Surfactant: Reduces tendency of lungs to collapse
• Pleural pressure
– Negative pressure can cause alveoli to
expand
– Pneumothorax is an opening between
pleural cavity & air that causes a loss of
pleural pressure
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Compliance
• Measure of the ease with which lungs &
thorax expand
– The greater the compliance, the easier it is
for a change in pressure to cause expansion
– A lower-than-normal compliance means the
lungs and thorax are harder to expand
• Conditions that decrease compliance
– Pulmonary fibrosis
– Pulmonary edema
– Respiratory distress syndrome
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Respiratory Air Volumes and Capacities
• The measurement of different air volumes is called
spirometry, and it describes four distinct respiratory
volumes
• One inspiration followed by expiration is called a respiratory
cycle; the amount of air that enters or leaves the lungs
during one respiratory cycle is the tidal volume
• During forced inspiration, an additional volume, the
inspiratory reserve volume, can be inhaled into the lungs.
IRV + TV gives us the inspiratory capacity
• During a maximal forced expiration, an expiratory reserve
volume can be exhaled, but there remains a residual volume
in the lungs. Adding the two together gives us the functional
reservecapacity
• Vital capacity is the tidal volume plus inspiratory reserve and
expiratory reserve volumes combined
• Vital capacity plus residual volume is the total lung capacity
• Anatomic dead space is air remaining in the bronchial tree
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Control of Breathing
• Normal breathing is a rhythmic, involuntary
act even though the muscles are under
voluntary control
Respiratory Center
• Groups of neurons in the brain stem
comprise the respiratory center, which
controls breathing by causinginspiration
and expiration and by adjusting the rate
and depth of breathing
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Factors Affecting Breathing
• Chemicals, lung tissue stretching, an
emotional state affect breathing
• Chemosensitive areas (central chemoreceptors) are
associated with the respiratory center and
are sensitive to changes in the blood
concentration of carbon dioxide and
hydrogen ions
• If either carbon dioxide or hydrogen ion concentrations
rise, the central chemoreceptors signal the respiratory
center, and breathing rate increases
• Peripheral chemoreceptors in the carotid sinuses and
aortic arch sense changes in blood oxygen concentration,
transmit impulses to the respiratory center, and
breathing rate and tidal volume increase
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More Factors Affecting Breathing
• An inflation reflex, triggered by stretch receptors in the
visceral pleura, bronchioles, and alveoli, helps to prevent over
inflation of the lungs during forceful breathing
• Hyperventilation lowers the amount of carbon dioxide in the
blood
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Alveolar Gas Exchanges
• The alveoli are the only sites of gas exchange between the
atmosphere and the blood.
Alveoli
•
The alveoli are tiny sacs clustered at the distal ends of the alveolar
ducts
Respiratory Membrane
• The respiratory membrane consists of the epithelial cells of
the alveolus, the endothelial cells of the capillary, and the
two fused basement membranes of these layers.
• Gas exchange occurs across this respiratory membrane
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Hemoglobin and Oxygen Transport
• Oxygen is transported by hemoglobin (98.5%) and is
dissolved in plasma (1.5%)
Transport of Carbon Dioxide
•Carbon dioxide is transported as bicarbonate ions
(70%) in combination with blood proteins (23%) and in
solution with plasma (7%)
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Disorders
Asthma— spasms of smooth muscle in the bronchioles
Lung cancer
– Constant irritation produces excess mucous and puts unnecessary
stress on the bronchi
– Alveoli destroyed by WBC’s acting on the irritation
– Structural cells disappear and cancer cells take over
Emphysema— alveolar walls lose their elasticity
– Some alveoli merge and reduce volume
– Have to work voluntarily to exhale
Bronchitis— inflammation of the bronchi
– Creates site for infection and increases mucous
Pneumonia— infection or inflammation of the alveoli
Tuberculosis (TB)— bacterial infection that destroys lung tissue and is
replaced by non-elastic connective tissue
Respiratory Distress Syndrome (RDS)
– Lack of surfactant makes breathing difficult
– Alveoli are sticking together
– Occurs in infants
Pulmonary Embolism
– blood clot obstructs circulation to lung tissue & tissue dies
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Disorders
Respiratory Failure
– Not enough O2 to maintain metabolism
– Cannot eliminate enough CO2
– Caused by:
• Drugs
• Stroke
• CO poisoning
• Shock
Colds and Flu— viral infections
Sudden Infant Death Syndrome (SIDS)
– Crib death
– Occurs between 1 week and 12 months
– Cause is unknown
– Baby stops breathing
Laryngitis— vocal cords
Pharyngitis— sore throat
Rhinitis— lining of the nose
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Effects of Aging
• Vital capacity and maximum minute ventilation decrease
• Residual volume and dead space increase
• Ability to remove mucus from respiratory passageways
decreases
• Gas exchange across respiratory membrane is reduced
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