The Respiratory System – Notes Part I
Why do we breathe? “To live? Because our lungs need it? Because it is vital to life?” Yes, but
why? The correct answer is, “for aerobic respiration.” Oxygen is the final electron acceptor in
the electron transport chain (ETC). But what is Aerobic Respiration? It is the process that the
cells use to break down glucose for energy.
Aerobic respiration:
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 34 ATP
During aerobic
respiration, which occurs
in all of our cells,
glucose is broken down
for its energy. Oxygen is
the final electron
acceptor in the electron
transport chain (ETC)
which is the final step of
aerobic respiration. At
the end of the ETC, one
molecule of oxygen
combines with two
electrons and two
hydrogen atoms to form
water. When the ETC is
functioning properly
with oxygen available,
the electrons of the ETC produce 34 ATP per glucose molecule. (This is a large amount of
energy.) Without ATP, the cells of the body would not function. Therefore, without oxygen,
ATP can only be produced in small amounts which are not sufficient to support life.
Lactic acid fermentation (no oxygen available):
C6H12O6 → + 2 C3H6O3 + 2 ATP
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Importance of the Respiratory System:
The cardiovascular system and respiratory system have a shared responsibility to supply the
body with oxygen and rid it of carbon dioxide. The cardiovascular system and lymphatic system
combined are sometimes called the circulatory system.
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Organs of the Respiratory System:
Nasal cavity, pharynx, larynx, trachea, bronchi and their smaller
branches, and the lungs which serve to purify (of dust and bacteria),
humidify, warm, and transport oxygen to and carbon dioxide from the
bloodstream.
The Nasal Cavity
Nose – contains the
external nares (anterior
naris) or nostrils that
allow air to enter
Nasal Cavity – The
nasal cavity is lined with
a ciliated mucosa (a
mucus membrane
containing cells with tiny
hairs) overlaying a
blood-rich connective
tissue layer (nose
bleeds). The blood is
used to warm the air.
The mucus moistens the
air, traps bacteria, and
traps dust as the air
passes by. In addition
the cilia (tiny hairs) are
able to push the mucus
toward the pharynx
where it is swallowed.
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The nasal cavity is divided by a midline of tissue
called the nasal septum. Three conchae bones can
be found on the walls of the nasal cavity to increase
the surface area of the mucosa.
Olfactory receptors – located near the cribiform
plates of the Ethmoid bone which is located on the
superior surface of the nasal cavity.
Hard Palate – surface of the mouth supported by
bone that separates the nasal cavity from the oral
cavity
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Soft Palate – also located on the surface of the oral cavity, but is not supported by bone
Paranasal Sinuses – found within the frontal, sphenoid, ethmoid, and maxillary bones
surrounding the nasal cavity; produce mucus which drains into the nasal cavity and is removed
by nose blowing
http://www.sinuscure.com.au/nasanat.htm
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The Pharynx:
Pharynx (throat) – a muscular passageway about 13cm long that functions as a passageway for
air and food. From the pharynx, air enters the larynx, where as food goes into the esophagus.
Clusters of lymphatic tissue
(fight infection) called tonsils are
found in the pharynx.
o The pharyngeal tonsils
(adenoids) are located in
the superior portion of the
larynx.
o The palatine tonsils are
located at the end of the
soft palate
o The lingual tonsils are
located at the base of the
tongue.
1 Pharyngeal tonsil
2 Palatine tonsil
3 Lingual tonsil
4 Epiglottis
Inflammation of the tonsils
(tonsillitis) blocks air flow to
nose and restricts it to the mouth.
Previously treated by removing
tonsils, tonsillitis is now typically
treated with antibiotics.
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The Larynx:
Larynx (voicebox) – located
inferior to the pharynx, formed
by eight rigid hyaline cartilages,
and a flap of elastic cartilage
(epiglottis). The largest ridge of
hyaline cartilage is the thyroid
cartilage (Adam’s apple).
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Epiglottis
The epiglottis is responsible for
directing food and water into the
esophagus and air into the
trachea. A cough results when
food or water enter the trachea.
Part of the mucous membrane of
the larynx forms a pair of folds
called the vocal cords which
vibrate with expelled air. The slit-like passage
between the vocal cords is the glottis.
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Glottis
The Trachea:
Trachea (windpipe) – located inferior to the larynx (about 10-12 cm long) and travels to the
right and left primary bronchi.
The trachea is lined with ciliated mucosa. The cilia beat upward in order to remove debris so
that it too may be swallowed. Smoking creates too much mucus which eventually kills the cilia
and leaves coughing as the only means to cleanse the trachea.
C-shaped rings of hyaline cartilage support the trachea and do not allow it too collapse in on
itself. The open part of the “C” also allows us to swallow large parts of food by folding inward
allowing more room for the esophagus within the neck.
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Heimlich maneuver – used to remove an obstruction that
has closed off the airways (trachea)
Tracheostomy/ Tracheotomy – surgical opening in the
trachea to provide an alternate route for air to pass
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The Lungs:
Lungs – large organs that occupy most of the thoracic cavity
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Mediastinum – occupies the remainder (center) of the
thoracic cavity and includes the heart, great blood
vessels, bronchi, and esophagus
Pulmonary (Visceral) Pleura – a type of serous
membrane that lines the outside of each lung
Parietal Pleura – a type of serous membrane that lines
the walls of the thoracic cavity.
Together the parietal and visceral pleura secrete
serous fluid (pleural fluid) that lubricates the two
membranes, reducing friction and allowing the lungs to
slide past one another and to glide along the thoracic
walls.
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Apex of lung –
narrow superior
portion of each lung
located just deep to
the clavicle
Base of lung –
broad inferior
portion of each lung
that rests on the
diaphragm
Note: In humans,
the left lung has two
lobes and the right
lung has three lobes
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Airway passages:
Primary Bronchi – right and left divisions of the trachea that continue to divide into smaller and
smaller branches before reaching the bronchioles and finally the alveoli of the lungs
Secondary Bronchi – branch off the primary bronchi and are smaller in diameter
Tertiary Bronchi – branch off the secondary bronchi and are even smaller in diameter
Bronchioles – smallest of the conducting passageway between the bronchi and the alveoli
Alveoli (alveolar sacs) – terminal grape-shaped air sacs
found within the lungs, located at the end of the
bronchioles, where gas exchange occurs between the
lungs and the blood; compose the bulk of the lungs
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The Respiratory Membrane (air-blood barrier) –
composed of thin simple squamous epithelial of the alveoli
and a “cobweb” of pulmonary capillaries that allows gas
exchange to occur by simple diffusion (Oxygen into the
blood and Carbon Dioxide out of the blood)
The surface area provided for gas exchange in a healthy
individual is 70 to 80 square meters. Bigger than the surface
area of the floor in our classroom!
Macrophages – the last line of defense within the lungs;
phagocytotic cells that are capable of consuming bacteria,
carbon particles, and debris within the alveoli
Cuboidal cells – larger cells that are found within the simple squamous epithelial cells of the
alveoli – these cells secrete surfactant that coats the alveoli and is important in lung function lowers the surface tension of the film of water lining each alveolar sac so that the alveoli do not
collapse between each breath
Premature babies may not have cells that make enough surfactant until they mature a bit
more. This is why premature babies needs to be on respirators.
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The Respiratory System – Notes Part II
Respiratory Physiology: The process of Respiration
4 Parts to Respiration:
1. Pulmonary Ventilation (breathing) – air must move in and out of the lungs
2. External Respiration – oxygen must enter the blood from the alveoli and carbon dioxide
must leave to blood and enter the alveoli
3. Respiratory Gas Transport – blood must carry the respiratory gases between the lungs
and the tissues of the body
4. Internal Respiration - oxygen must enter the cells from the blood and carbon dioxide
must leave the cells and enter the blood in order to be transported back to the lungs
Mechanisms of Pulmonary Ventilation / Breathing (Page 383)
Inspiration – air is flowing into the lungs
Expiration – air is flowing out of the lungs
1. Process of Inspiration:
As the diaphragm contracts it moves inferiorly and flattens. At the same time the
intercostal muscles contract lifting the rib cage. The lungs must follow the
diaphragm and the thoracic walls because they are connected by the pleural
membrane. This
increases the size of each
lung (increasing
intrapulmonary volume)
and decreases
intrapulmonary pressure
causing a vacuum which
draws air into the lungs.
2. Process of Expiration:
The process of expiration
is a passive process in which the diaphragm and the external intercostal muscles
relax, compressing the lungs, causing the intrapulmonary pressure to exceed
atmospheric pressure. The air within the lungs then flows out to equalize the
pressure.
During exercise, we breathe more deeply and at a faster rate. At this time
expiration becomes an active process. Various chest and abdominal muscles
capable of lowering the ribs may be used to aid in expiration. (Various diseases
of the lung may also require the person to use active expiration as well.)
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External Respiration, Gas Transport, and Internal Respiration
Respiratory Gases / Partial Pressures
What causes carbon dioxide to move out of the body and oxygen to move in?
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Oxygen transportation:
Oxygen is transported in the blood in two ways:
Most attaches to hemoglobin in the RBCs to form oxyhemoglobin (HbO2)
The remaining small amount of oxygen is transported in the plasma (fluid of blood)
During internal respiration, oxygen leaves the blood and diffuses into the tissues.
Carbon dioxide transportation:
During internal respiration, carbon dioxide diffuses into the blood from the tissues and
combines with water to form carbonic acid which quickly splits into hydrogen ions and
bicarbonate ions
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3Most carbon dioxide is transported in the plasma as bicarbonate ion (HCO3-)
The remaining 20-30% is carried inside the RBCs attached to a different site than oxygen
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External respiration: In order for carbon dioxide to be released into the alveoli, HCO3must first combine with hydrogen (H+) to form carbonic acid (H2CO3) which is quickly
split into water and carbon dioxide. The carbon dioxide then diffuses into the alveoli
from the blood stream.
Relationship between carbon dioxide and pH
The pH of blood decreases (= becomes more acidic) when more carbon dioxide is
present. This is due to increased levels of carbonic acid and subsequently hydrogen and
bicarbonate ions. The body responds to pH levels by increasing or decreasing respiration
rates, driving the equation above either towards the carbon dioxide side to increase pH or
towards the bicarbonate side to decrease pH.
Hypoventilation – slow or shallow breathing that increases carbonic acid (carbon
dioxide) and may lead to acidosis (homeostasis is disrupted because body fluids are too
acidic)
Hyperventilation – fast, deep breathing that decreases carbonic acid (carbon dioxide)
and may lead to alkalosis (homeostasis is disrupted because body fluids are too basic)
Breathing into a paper bag during hyperventilation reduces the amount of carbon dioxide
you will be able to get rid of and decreases the chances of alkalosis
Respiratory Rates, Volumes, and Capacities
Respiratory rates throughout life:
o In the fetus the lungs are filled with fluid and all respiratory exchanges are made
though the placenta.
o 40-80 respirations per minute in newborns
o 30 respirations per minute in infants
o 25 respirations per minute at 5 years old
o 12-15 respirations per minute in adults
o Increasing respirations per minute in old age
Control of Respiratory Rate
1. The diaphragm and the intercostals are
regulated by the phrenic and intercostal nerves
respectively. The control centers for these
nerves are located in the medulla and Pons.
2. Rate of respiration can be modified by
physical, emotional, and chemical factors
o Physical Factors: demand for more oxygen
or removal of carbon dioxide
o Emotional Factors: being scared or
frightened increases respiration
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http://www.scottsdalecc.edu/ricker/psy101/
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o Chemical Factors: change in pH levels in the blood
o Consciously controlling breathing = Volition on breathing: one can only
hold their breath for only so long before the unconscious control takes over
Respiratory capacity
o Respiratory capacity is regulated by size, sex, age, and physical condition
o Average lung capacity of a healthy adult is 6 liters or 6000 ml
1. Tidal Volume – is referred to as the amount of air transferred in one normal resting
breath (500 ml or 1 pint)
2. Inspiratory Reserve Volume (IRV) – the amount of air that can be taken in forcibly
over the tidal volume (2100 – 3100ml)
3. Expiratory Reserve Volume (ERV) – the amount of air that can be forcibly exhaled
after a tidal expiration (1000ml)
4. Residual Volume – the amount of air that remains after the ERV is exhaled; air that is
always present allowing gas exchange to continue uninterrupted (1100ml)
5. Vital Capacity (TV + IRV + ERV) – the total amount of exchangeable air (4500ml)
6. Dead Space Volume – air within the conducting respiratory passageways (150ml)
7. Functional Volume – air that actually reaches the respiratory zone and contributes to gas
exchange
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Respiratory Conditions and Disorders
Hypoxia
A condition in which inadequate oxygen is available to tissue (increases with old age, anxiety, asthma, and
other respiratory diseases)
Carbon Monoxide Poisoning
Carbon monoxide (CO) binds to hemoglobin at the same site as oxygen usually does and competes vigorously
for those binding sites
Chronic obstructive pulmonary diseases (COPD) – a series of diseases including chronic bronchitis and
emphysema, commonly brought on by smoking, leading to coughing and frequent pulmonary infections and
ultimately respiratory failure
Emphysema – the alveoli enlarge as the walls of adjacent chambers break through and chronic inflammation
promotes fibrosis (scarring) of the lungs. The process of exhalation must become active instead of passive (the
person must work to breathe out) and since oxygen is always left in large amounts in the lungs, results in
cyanosis (deficient oxygenation of the blood)
Chronic Bronchitis – the mucosa of the lower respiratory passages become severely inflamed and produces
excessive amounts of mucus impairing both ventilation and gas exchange and increasing the likelihood of
infection
Lung Cancer – accounts for 1/3 of all cancer deaths in the U.S. (90% of patients are smokers)
Due to the effects of chemicals in cigarettes, the nasal hairs, mucous glands, and cilia which protect the lungs
become overwhelmed. Cigarettes also depress the activity of lung macrophages (WBCs). Finally, the 15 or so
carcinogenic chemicals in cigarettes enter the lungs and translate into lung cancer by causing the mucosal cells
to mutate and divide rapidly
Squamous cell carcinoma (20-40% of cases) – arises in the epithelium of the larger bronchi and tends
to form masses that hollow out and bleed
Adenocarcinoma – (25-35% of cases) – originates in the peripheral areas of the lungs as solitary
nodules that develop from bronchial mucous glands and alveolar epithelial cells
Small cell carcinoma (10-20% of cases) & Oat Cell Carcinoma – consist of lymphocyte-like epithelial
cells that originate in the primary bronchi and grow aggressively in cords or small grape-like clusters
within the mediastinum. Treatment – removal of diseased lung, radiation, and chemotherapy. The
overall 5 year survival rate is only 7% and the average person survives only 9 months after diagnosis.
Pneumonia bacterial or viral infection in the lungs. Pneumonia causes the alveoli to become filled with fluid
which interferes with the process of external respiration. The bronchioles are often also affected by the
infection as well.
Asthma is a chronic condition in which the airways spasm and narrow and may even become inflammed.
Because the airways are narrowed, the ability to bring air in and out of the lung becomes difficult.
Atelectasis (collapsed lung) – results when the pressure within the pleural space (which is always negative)
becomes equal to the atmospheric pressure
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