Respiratory System
• The major function of the respiratory system is to
supply the body with oxygen and dispose of carbon
dioxide. To accomplish this function, at least four
processes, collectively called respiration, must
happen:
• 1. Pulmonary ventilation: movement of air into
and out of the lungs so that the gases there are
continuously changed and refreshed (commonly
called breathing).
• 2. External respiration: movement of oxygen from
the lungs to the blood and of carbon dioxide from
the blood to the lungs.
• 3. Transport of respiratory gases: transport of
oxygen from the lungs to the tissue cells of the
body, and of carbon dioxide from the tissue cells to
the lungs. This is accomplished by the
cardiovascular system using blood as the
transporting fluid.
• 4. Internal respiration: movement of oxygen from
blood to the tissue cells and of carbon dioxide from
tissue cells to blood.
The respiratory system
Respiration is much more than the simple mechanical
actions of breathing. Breathing consists of:
-Inhalation provides the body with the oxygen that is
necessary for the production of ATP in the process of
cell respiration.
-Exhalation removes the CO2 that is a product of cell
respiration.
-Breathing also regulates the level of CO2 within the
body, and this contributes to the maintenance of the
acid–base balance of body fluids.
Functional Anatomy of the Respiratory System
Functionally, the Respiratory System consists of two
zones.
The respiratory zone, the actual site of gas exchange,
is composed of the respiratory bronchioles,
alveolar ducts, and alveoli, (all microscopic
structures).
The conducting zone includes all other respiratory
passageways, which provide fairly rigid canals for air
to reach the gas exchange sites. The conducting
zone organs also cleanse, humidify, and warm
incoming air. Thus, air reaching the lungs has fewer
irritants (dust, bacteria, etc.) than when it entered
the system, and it is warm and damp.
• The respiratory system moves air into and out of
the lungs, which are the site of exchange for O2 and
CO2 between the air and the blood.
• The functioning of the respiratory system depends
directly on the proper functioning of the circulatory
system.
• The respiratory tract consists of two parts
1. The upper respiratory tract consists of those parts
outside the chest cavity.
2. The lower respiratory tract consists of those parts
within the chest cavity.
The nose
1-provides an airway for respiration;
2- warms(many capillaries in submucosa),
moistens, and cleanses incoming air; and
3- houses the olfactory receptors that respond to
vapors in inhaled air.
-The external nose is shaped by bone and cartilage
plates.
-The nasal cavity, which opens to the exterior, is
divided by the nasal septum.
-Paranasal sinuses and nasolacrimal ducts drain
into the nasal cavities.
- The roof of the nasal cavity is formed by the
ethmoid and sphenoid bones of the skull.
-The floor is formed by the palate, which separates
the nasal cavity from the oral cavity below.
Anteriorly, where the palate is supported by the
maxillary processes and palatine bones, it is called
the hard palate. The unsupported posterior
portion is the muscular soft palate.
-Hairs inside the nostrils block the entry of dust.
-Nasal mucosa is ciliated epithelium with goblet
cells; surface area is increased by the conchae.
- Nasal mucosa warms and moistens the incoming
air; dust and microorganisms are trapped on mucus
and swept by the cilia to the pharynx.
-Paranasal sinuses in the maxillae , frontal , sphenoid,
and ethmoid bones open into the nasal cavities:
functions are to lighten the skull and provide
resonance for the voice.
• HOMEOSTATIC IMBALANCE Cold viruses, streptococcal
bacteria, and various allergens can cause rhinitis (rini′tis), inflammation of the nasal mucosa accompanied
by excessive mucus production, nasal congestion, and
postnasal drip.
• The nasal mucosa is continuous with that of the rest of
the respiratory tract, explaining the typical nose to
throat to chest progression of colds. Because the
mucosa extends tentacle-like into the nasolacrimal
(tear) ducts and paranasal sinuses, nasal cavity
infections often spread to those regions, causing
sinusitis (inflamed sinuses).
• When the passageways connecting the sinuses to the
nasal cavity are blocked with mucus or infectious
material, the air in the sinus cavities is absorbed. The
result is a partial vacuum and a sinus headache
localized over the inflamed areas.
Pharynx—posterior to nasal and oral cavities
1. Nasopharynx—above the level of the soft palate,
which blocks it during swallowing; a passageway for
air only. The eustachian tubes from the middle ears
open into it. The adenoid is a lymph nodule on the
posterior wall.
2. Oropharynx—behind the mouth; a passageway for
both air and food. Palatine tonsils are on the lateral
walls. Two kinds of tonsils lie embedded in the
oropharyngeal mucosa. The paired palatine tonsils
and the lingual tonsil .
3. Laryngopharynx—a passageway for both air and
food; opens anteriorly into the larynx and posteriorly
into the esophagus.
HOMEOSTATIC IMBALANCE
High on its posterior wall is the pharyngeal tonsil
(or adenoids), which traps and destroys pathogens
entering the nasopharynx in air.
Infected and swollen adenoids block air passage
in the nasopharynx, making it necessary to breathe
through the mouth. As a result, the air is not
properly moistened, warmed, or filtered before
reaching the lungs. When the adenoids are
chronically enlarged, both speech and sleep may
be disturbed.
Larynx—the voice box and the airway between the
pharynx and trachea
1. Made of nine cartilages; the thyroid cartilage is the
largest and most anterior.
2. The epiglottis is the uppermost cartilage; covers
the larynx during swallowing.
3. The vocal cords are lateral to the glottis, the opening
for air .
4. During speaking, the vocal cords are pulled across
the glottis and vibrated by exhaled air, producing
sounds that may be turned into speech.
5. The cranial nerves for speaking are the vagus and
accessory.
-HOMEOSTATIC IMBALANCE
Inflammation of the vocal folds, or laryngitis, causes
the vocal folds to swell, interfering with their vibration.
This produces hoarseness, or in severe cases inability to
speak above a whisper.
Laryngitis is also caused by overuse of the voice, very
dry air, bacterial infections, tumors on the vocal folds,
and inhalation of irritating chemicals.
-Sphincter Functions of the Larynx
*Under certain conditions, the vocal folds act as a
sphincter that prevents air passage. During abdominal
straining associated with defecation, the glottis closes
to prevent exhalation and the abdominal muscles
contract, causing the intra-abdominal pressure to rise.
These events, collectively known as Valsalva’s
maneuver, help empty the rectum and can also splint
(stabilize) the body trunk when one lifts a heavy load.
Trachea—extends from the larynx to the primary
bronchi
1. Sixteen to 20 C-shaped cartilages in the tracheal
wall keep the trachea open.
2. Mucosa is ciliated epithelium with goblet cells; cilia
sweep mucus, trapped dust, and microorganisms
upward to the pharynx.
Bronchial Tree—extends from the trachea to the alveoli
1. The right and left primary bronchi are branches of
the trachea; one to each lung; same structure as the
trachea.
2. Secondary bronchi: to the lobes of each lung (three
right, two left)
3. Bronchioles—no cartilage in their walls.
HOMEOSTATIC IMBALANCE
Smoking inhibits and ultimately destroys cilia, after
which coughing is the only means of preventing
mucus from accumulating in the lungs. For this
reason, smokers with respiratory congestion should
avoid medications that prevents cough.
HOMEOSTATIC IMBALANCE
Many people have suffocated after choking on a piece
of food that suddenly closed off their trachea. The
Heimlich maneuver, a procedure in which air in the
victim’s lungs is used to “pop out,” or expel, an
obstructing piece of food, has saved many people.
The maneuver is simple ,but cracked ribs are a
distinct possibility when it is done incorrectly .
The Lungs
-The paired lungs occupy all of the thoracic cavity
except the mediastinum, which houses the heart, great
blood vessels, bronchi, esophagus, and other organs .
-The anterior, lateral, and posterior lung surfaces lie in
close contact with the ribs and form the continuously
curving costal surface.
- Just deep to the clavicle is the apex, the narrow
superior tip of the lung. The concave, inferior surface
that rests on the diaphragm is the base.
-On the mediastinal surface of each lung is an
indentation, the hilum, through which pulmonary and
systemic blood vessels enter and leave the lungs. All
conducting and respiratory passageways distal to the
main bronchi are found in the lungs.
The alveoli—the sites of gas exchange in the lungs
-Made of simple squamous epithelium(Alveolar type
I); thin to permit diffusion of gases.
-Surrounded by pulmonary capillaries, which are also
made of simple squamous epithelium
-Elastic connective tissue between alveoli is important
for normal exhalation.
-A thin layer of tissue fluid lines each alveolus .
- Alveolar type II cells produce pulmonary surfactant
that mixes with the tissue fluid lining to decrease
surface tension to permit inflation of the alveoli.
-Have efficient alveolar macrophages crawl freely
along the internal alveolar surfaces.
-Although the number of microorganisms is huge,
alveolar surfaces are usually sterile. Most
macrophages simply get swept up by the ciliary
current of superior regions and carried passively to
the pharynx. In this manner, we clear and swallow
over 2 million alveolar macrophages per hour!
The Respiratory Membrane The walls of the alveoli
are composed of a single layer of squamous
epithelial cells on a basement membrane. A sheet
of tissue paper is much thicker.
-The external surfaces of the alveoli are densely
covered with a pulmonary capillaries .
-Together, the alveolar and capillary walls and their
fused basement membranes form the respiratory
membrane, a 5-µm-thick air-blood barrier that has
gas on one side and blood flowing past on the other
-Gas exchanges occur readily by simple diffusion
across the respiratory membrane— O2 passes from
the alveolus into the blood, and CO2 leaves the
blood to enter the gas-filled alveolus.
Pleural Membranes( Pleurae)
are serous membranes of the thoracic cavity
1. Parietal pleura lines the chest wall.
2. Visceral pleura covers the lungs.
Serous fluid between the two layers prevents
friction and keeps the membranes together
during breathing.
• HOMEOSTATIC IMBALANCE
-Pleurisy (ploo′rĭ-se), inflammation of the pleurae,
results in friction and stabbing pain with each
breath. As the disease progresses, the pleurae may
produce an excessive amount of fluid that may exert
pressure on the lungs and hinder breathing
movements.
-Other fluids that may accumulate in the pleural
cavity include blood (leakage from damaged blood
vessels) and blood filtrate (the watery fluid that
oozes from the lung capillaries when right-sided
heart failure occurs).
-The general term for fluid accumulation in the
pleural cavity is pleural effusion.
Mechanism of Breathing
1. Ventilation is the movement of air into and out of
the lungs: inhalation and exhalation. Gases travel from
an area of higher pressure to an area of lower
pressure.
2. Respiratory centers are in the medulla and pons.
3. Respiratory muscles are the diaphragm and external
and internal intercostal muscles .
Pressures in the Thoracic Cavity
1-Intrapulmonary pressure is the pressure within the
bronchial tree and alveoli; fluctuates during breathing.
2-Intrapleural pressure is the pressure within the pleural
cavity; it is always negative (slightly below)relative to
intrapulmonary pressures.
3- Atmospheric pressure is air pressure:760 mmHg at
sea level.
• HOMEOSTATIC IMBALANCE
Atelectasis (at″ĕ-lik′tah-sis), or lung collapse, occurs
when a bronchiole becomes plugged (as may follow
pneumonia). Its associated alveoli then absorb all of
their air and collapse.
Atelectasis can also occur when air enters the pleural
cavity either through a chest wound, or due to rupture
of the visceral pleura, which allows air to enter the
pleural cavity from the respiratory tract.
Pneumothorax ,the presence of air in the intrapleural
space .Drawing air out of the intrapleural space with
chest tubes, allows the lung to reinflate and resume its
normal function. Note that because the lungs are in
separate cavities, one lung can collapse without
interfering with the function of the other
Inhalation (inspiration)
1. Motor impulses from medulla travel along phrenic
nerves to diaphragm, which contracts and moves
down. Impulses are sent along intercostal nerves to
external intercostal muscles, which pull ribs up and out.
2. The chest cavity is expanded and expands the
parietal pleura.
3. The visceral pleura adheres to the parietal pleura
and is also expanded and in turn expands the lungs.
4. Intrapulmonic pressure decreases, and air rushes
into the lungs.
Exhalation (expiration)
1. Motor impulses from the medulla decrease, and the
diaphragm and external intercostal muscles relax.
2. The chest cavity becomes smaller and compresses
the lungs.
3. The elastic lungs recoil and further compress the
alveoli.
4. Intrapulmonic pressure increases, and air is forced
out of the lungs. Normal exhalation is passive.
5. Forced exhalation: contraction of the internal
intercostal muscles pulls the ribs down and in;
contraction of the abdominal muscles forces the
diaphragm upward.
Pulmonary Volumes
Measured by Respirometer
1. Tidal volume—the amount of air in one normal inhalation
and exhalation.
2. Minute respiratory volume—the amount of air inhaled and
exhaled in 1 minute.
3. Inspiratory reserve—the amount of air beyond tidal in a
maximal inhalation.
4. Expiratory reserve—the amount of air beyond tidal in the
most forceful exhalation.
5. Vital capacity—the sum of tidal volume, inspiratory and
expiratory reserves.
6. Residual volume—the amount of air that remains in the
lungs after the most forceful exhalation; provides for
continuous exchange of gases.
• Anatomic dead space—air still in the respiratory passages at
the end of inhalation (is normal).
Alveolar Surface Tension
Surface tension:
(1) draws the liquid molecules closer together and
(2) resists any force that tends to increase the surface
area of the liquid.
Because water is the major component of the liquid
film that coats the alveolar walls, it is always acting to
reduce the alveoli to their smallest possible size. If
the film was pure water, the alveoli would collapse
between breaths. But the alveolar film contains
surfactant (ser-fak′tant), a complex of lipids and
proteins produced by the type II alveolar cells.
Surfactant decreases the surface tension of alveolar
fluid, and discourage alveolar collapse.
HOMEOSTATIC IMBALANCE When too little surfactant is
present, surface tension forces can collapse the
alveoli. Once this happens, the alveoli must be
completely reinflated during each inspiration, an effort
that uses tremendous amounts of energy. This is the
problem faced by newborns with infant respiratory
distress syndrome (IRDS), a condition peculiar to
premature babies. Since inadequate pulmonary
surfactant is produced until the last two months of
fetal development, babies born prematurely often are
unable to keep their alveoli inflated between breaths.
IRDS is treated with positive-pressure respirators that
force air into the alveoli, keeping them open between
breaths. Spraying natural or synthetic surfactant into
the newborn’s respiratory passageways also helps.
Nonrespiratory Air Movements
Exchange of Gases
1. External respiration is the exchange of gases
between the air in the alveoli and the blood in the
pulmonary capillaries.
2. Internal respiration is the exchange of gases
between blood in the systemic capillaries and
tissue fluid (cells).
3. Inhaled air (atmosphere) is 21% O2 and 0.04%
CO2. Exhaled air is 16% O2 and 4.5% CO2.
4. Diffusion of O2 and CO2 in the body occurs
because of pressure gradients , gas will diffuse
from an area of higher partial pressure to an area
of lower partial pressure.
5. External respiration: PO2 in the alveoli is high,
and PO2in the pulmonary capillaries is low, so
O2 diffuses from the air to the blood. PCO2 in
the alveoli is low, and PCO2 in the pulmonary
capillaries is high, so CO2 diffuses from the
blood to the air and is exhaled .
6. Internal respiration: PO2 in the systemic
capillaries is high, and PO2 in the tissue fluid is
low, so O2 diffuses from the blood to the
tissue fluid and cells.
PCO2 in the systemic capillaries is low, and
PCO2 in the tissue fluid is high, so CO2
diffuses from the tissue fluid to the blood .
Transport of Oxygen in the Blood
1. Oxygen is carried by the iron of hemoglobin (Hb) in
the RBCs. The O2–Hb bond is formed in the lungs
where the PO2 is high.
2. In tissues, Hb releases much of its O2; the important
factors are low PO2 in tissues, high PCO2 in tissues,
and a high temperature in tissues.
3. Oxygen saturation of hemoglobin (SaO2) is 95% to
97% in systemic arteries and averages 70% to 75% in
systemic veins.
• Oxygen is carried in blood in two ways:
1-bound to hemoglobin within red cells(main way) and
2-dissolved in plasma
• Because the iron atoms bind oxygen, each hemoglobin
molecule can combine with four molecules of O2, and
oxygen loading is rapid and reversible.
• The hemoglobin-oxygen combination, called
oxyhemoglobin (ok″sĭ-he″mo-glo′bin), is
written HbO2. Hemoglobin that has released
oxygen is called reduced hemoglobin, or
deoxyhemoglobin, and is written HHb.
Loading and unloading of O2 can be indicated
by a single reversible equation:
Carbon Dioxide Transport
Normally active body cells produce about 200 ml of
CO2 each minute—exactly the amount excreted by
the lungs. Blood transports CO2 from the tissue cells
to the lungs in three forms :
• 1. Dissolved in plasma (7–10%). The smallest
amount of CO2 is transported simply dissolved in
plasma.
• 2. Chemically bound to hemoglobin (just over
20%). In this form, CO2 is carried in the RBCs as
carbamino- hemoglobin .
• Because carbon dioxide binds directly to the amino
acids of globin (and not to the heme), carbon
dioxide transport in RBCs does not compete with
the oxyhemoglobin transport mechanism.
• CO2 loading and unloading to and from Hb are
directly influenced by the PCO2.
- Carbon dioxide rapidly dissociates from
hemoglobin in the lungs, where the PCO2 of alveolar
air is lower than that in blood.
- Carbon dioxide is loaded in the tissues, where the
PCO2 is higher than that in the blood.
3. As bicarbonate ion in plasma (about
70%). Most carbon dioxide molecules
entering the plasma quickly enter the
RBCs, where it combines with water,
forming carbonic acid (H2CO3). H2CO3 is
unstable and quickly dissociates into
hydrogen ions and bicarbonate ions
which is carried in plasma:
Nervous Regulation of Respiration
1. The medulla contains the inspiration center and expiration
center.
2. Impulses from the inspiration center to the respiratory
muscles cause their contraction; the chest cavity is
expanded.
3. Baroreceptors in lung tissue detect stretching and send
impulses to the medulla to depress the inspiration center.
This prevents overinflation of the lungs.
4. In the pons: the apneustic center and the pneumotaxic
center work with the inspiration center in the medulla to
produce a normal breathing rhythm.
5- The cerebral cortex permits voluntary changes in breathing.
6. The hypothalamus influences changes in breathing in
emotional situations.
7. Coughing and sneezing remove irritants from the upper
respiratory tract; the centers for these reflexes are in the
medulla.
Chemical Regulation of Respiration
1. Decreased blood O2 is detected by
chemoreceptors in the carotid body and aortic
body leading to increased respiration to take more
air into the lungs.
2. Increased blood CO2 level is detected by
chemoreceptors in the medulla leading to
increased respiration to exhale more CO2.
3. Increased CO2 (low pH)is the major regulator of
respiration
4. Oxygen becomes a major regulator of respiration
when blood level is very low, as may occur with
severe, chronic pulmonary disease.
Respiration and Acid–Base Balance
1. Respiratory acidosis: a decrease in the rate or
efficiency of respiration permits excess CO2 to
accumulate in body fluids, resulting in the formation
of excess H+ ions, which lower pH. Occurs in severe
pulmonary disease.
2. Respiratory alkalosis: an increase in the rate of
respiration increases the CO2 exhaled, which
decreases the formation of H+ ions and raises pH.
Occurs during hyperventilation or when first at a high
altitude.
3. Respiratory compensation for metabolic acidosis:
increased respiration to exhale CO2 to decrease H+
ion formation to raise pH to normal.
4. Respiratory compensation for metabolic alkalosis:
decreased respiration to retain CO2 to increase H+ ion
formation to lower pH to normal.
Related Clinical Terms
• Adenoidectomy (adenotonsillectomy): Surgical
removal of an infected pharyngeal tonsil (adenoids).
• Aspiration: (1) The act of inhaling or drawing
something into the lungs or respiratory passages.
Pathological aspiration in which vomit or excessive
mucus is drawn into the lungs may occur when a
person is unconscious or anesthetized; turning the
head to one side is preventive.
(2) Withdrawal of fluid by suction (use of
an aspirator); done during surgery to keep an area
free of blood or other body fluids; mucus is
aspirated from the trachea of tracheotomy patients.
• Bronchoscopy: (scopy = viewing) Use of a viewing
tube inserted through the nose or mouth to
examine the internal surface of the main bronchi in
the lung. Forceps attached to the tip of the tube
can remove trapped objects or take samples of
mucus for examination.
• Epistaxis: (epistazo = to bleed at the nose)
Nosebleed; commonly follows trauma to the nose
or excessive nose blowing. Most nasal bleeding is
from the highly vascularized anterior septum and
can be stopped by pinching the nostrils closed or
packing them with cotton.
• Cheyne-Stokes breathing: Abnormal breathing
pattern sometimes seen just before death and in
people with combined neurological and cardiac
disorders. It consists of bursts of tidal volume
breaths (increasing and then decreasing in depth)
alternating with periods of apnea.
• Deviated septum Condition in which the nasal
septum takes a more lateral course than usual and
may obstruct breathing; often manifests in old age
or from nose trauma.
• Endotracheal tube: A thin plastic tube threaded
into the trachea through the nose or mouth; used
to deliver oxygen to patients who are breathing
inadequately, in a coma, or under anesthesia.
• Orthopnea: (ortho = straight, upright) Inability to
breathe in the horizontal (lying down) position.
• Otorhinolaryngology: (oto = ear; rhino = nose)
Branch of medicine that deals with diagnosis and
treatment of diseases of the ears, nose, and throat.
• Pneumonia: Infectious inflammation of the lungs,
in which fluid accumulates in the alveoli; the
seventh most common cause of death in the
United States. Most of the more than 50 different
varieties of pneumonia are viral or bacterial.
• Pulmonary embolism: Obstruction of the
pulmonary artery or one of its branches by an
embolus (most often a blood clot that has been
carried from the lower limbs and through the right
side of the heart into the pulmonary circulation).
Symptoms are chest pain, productive bloody cough,
tachycardia, and rapid, shallow breathing. Can
cause sudden death unless treated quickly .
• Stuttering A problem of voice production in which
the first syllable of words is repeated in “machinegun” fashion. Primarily a problem with neural
control of the larynx and other voice-producing
structures.
• Sudden infant death syndrome (SIDS): Unexpected
death of an apparently healthy infant during sleep.
Commonly called crib death, SIDS is one of the
most frequent causes of death in infants under 1
year old. Believed to be a problem of immaturity of
the respiratory control centers. Most cases occur in
infants placed in a prone position (on their
abdomen) to sleep—a position which may result in
hypoxia and hypercapnia due to rebreathing
exhaled (CO2-rich) air.
• Tracheotomy: Surgical opening of the trachea;
done to provide an alternate route for air to reach
the lungs when more superior respiratory
passageways are obstructed (as by food or a
crushed larynx).