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Pierce College
Putman/Biol 242
Lecture Unit 05 notes: Respiratory System
FUNCTION
Facilitate exchange of oxygen and carbon dioxide between the blood and environment.
CARBON DIOXIDE ISSUES:
1. In aqueous solution, carbon dioxide may dissolve (in other words, remain as carbon dioxide)
or it may combine with water to form carbonic acid.
2. Carbonic acid is the major source of hydrogen ions in blood, thus is of major importance to
blood pH.
3. Increasing carbon dioxide levels in blood makes the blood more acidic (lowers pH);
decreasing carbon dioxide levels in blood makes the blood less acidic (increases pH).
RESPIRATORY SYSTEM FUNCTIONAL ANATOMY
1. Functions of upper respiratory system structures.
a. External nares. Opening into nasal vestibule, area through which respiratory gases may
pass.
b. Nasal vestibule. Contains vibrissae (hairs) that allows air to be filtered; space allows air
to begin to be heated. Tissue type is stratified squamous epithelium, serving to protect the
inside of the nose.
c. Nasal cavity. Function is to warm and moisten air entering the respiratory passages,
secrete mucus that traps and kills pathogens, as well as trapping other particles, and to
absorb water as you exhale, thus helping to retard dehydration. Superior nasal cvty
contains olfactory mucosa (smell receptors); remainder of nasal cavity is lined with
respiratory mucosa (pseudostratified ciliated columnar epithelium with goblet cells). Also
serve as resonating chambers in sound production!
d. Nasal conchae (superior, middle, inferior) increase surface area of nasal cavity. They are
a moist, warm, closely-fit labrynth of tissue.
e. Nasal meatus (superior, middle, inferior). Short passages in the back of the nasal cavity,
serve the same functions as the nasal conchae.
f. Internal nares. Allow for passage of air from the nasal sinus cavities into and from the
nasopharynx.
g. Nasopharynx. Allows for passage of air into or from internal nares down into or from the
oropharynx. Tissue type: pseudostratified ciliated columnar epithelium.
h. Oropharynx. Allows for passage of air into or from nasopharynx down to or from
laryngopharynx. Tissue type: stratified squamous epithelium.
i. Laryngopharynx. Allows for passage of air from nasopharynx down to or from trachea.
Tissue type: stratified squamous epithelium.
j. Oriface (opening) of auditory (eustachian) tube. Air passage to/from middle ear. A major
source of infection as it provides access to pathogens to middle ear, leading to otis
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media—middle ear infection. The middle ear is, of course, connected to the mastoid,
leading to possibility of mastoiditis.
k. Lips. Major function in digestive system; allows for passage of respiratory gases to and
from respiration system.
l. Vestibule. Major function in digestive system; allows for passage of respiratory gases to
and from respiration system.
m. Teeth. Major function in digestive system; allows for passage of respiratory gases to and
from respiration system.
n. Tongue. Major function in digestive system; allows for passage of respiratory gases to
and from respiration system.
o. Hard palate. Major function in digestive system; allows for passage of respiratory gases
to and from respiration system.
p. Soft palate. Major function in digestive system; allows for passage of respiratory gases to
and from respiration system.
q. Uvula. Major function in digestive system; allows for passage of respiratory gases to and
from respiration system.
r. Fauces (arch in back of throat). Major function in digestive system; allows for passage of
respiratory gases to and from respiration system.
s. Palatine tonsil, lingual tonsil. Tonsils are made of lymphatic tissue and help to intercept
and kill pathogens being inhaled.
t. Frontal sinus, ethmoid sinus, sphenoid sinus, maxillary sinus. The paranasal sinuses, all
connected to the nasal passages, serve to lighten and strengthen the skull. They also serve
as resonating chambers in sound production. They are sites of infection.
u. Epiglottis. Covers the glottis when you swallow.
v. Glottis. Allows respiratory gases through the larynx.
w. Larynx. The voice box, helps keep the respiratory passages open and serves to produce
sounds used in communication.
x. Hyoid bone. Important insertion point for many muscles, including those used in
respiration and vocal communication.
y. Thyroid cartilage, cuneiform cartilage, corniculate cartilage, arytenoid cartilage,
arytenoid muscle, cricoid cartilage. Protect and articulates the larynx.
z. Vestibular folds (false vocal cords).
aa. Vocal folds (true vocal cords). Allow for sound production
bb. Trachea. Allows for passage of air into lungs. Is lined with pseudostratified ciliated
columnar epithelium that secretes mucus, trapping particles; cilia move mucus with
trapped particles up into esophagus where it is swallowed.
cc. Tracheal cartilages. Keep airways open.
2. Anatomy and functions of trachea (cross section). Note the “U”-shaped hyaline cartilaginous
rings that keep the trachea open. This structure allows the trachea to be bent if under a
compression load without breaking.
a. The trachealis muscle is smooth muscle, anchored to the open side of the hyaline
cartilage rings. Constriction of this muscle reduces air flow; this happens in anaphylaxis,
asthma, etc. Relaxation of the muscle allows cartilage rings to open trachea. Drugs of
importance: Epinephrine, ephedrine, pseudoephedrine.
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b. Smoking destroys cilia of trachea. Without cilia, mucus produced continues to be
produced. A smoker will sit up in the morning, collected mucus will slide down his/her
throat and collect at the carina, which contains a patch of very sensitive tissue, causing
coughing. Unfortunately, cilia destroyed by smoke generally don’t grow back.
3. At the carina, the trachea bifurcates into R and L primary bronchi.
a. R primary bronchus shorter than the left as it does not have to pass over the heart in the
mediastinum.
b. Primary bronchi divide into secondary bronchi (lobar bronchi), which divide into the
tertiary bronchi (segmental bronchi), which divide into the bronchioles, which divide into
the terminal bronchioles.
c. Although the primary bronchi have tracheal rings and pseudostratified ciliated columnar
epithelium like the trachea, the secondary bronchi, tertiary, etc. bronchi have cartilage
plates and have increasingly more simple columnar epithelium without cilia or goblet
cells.
d. Bronchioles and the rest of the gas conduction structures making up the respiratory tree
do not have cartilage, it being replaced entirely by smooth muscle.
e. The bronchioles and terminal bronchioles are lined with simple cuboidal epithelium.
f. Terminal bronchioles branch even smaller into respiratory bronchioles, which then
branch into alveolar ducts.
g. Alveolar ducts lack smooth muscle and are lined only with cuboidal epithelium.
h. The alveoli, which are lined only with simple squamous epithelium, line the alveolar
ducts.
RESPIRATORY SYSTEM PHYSIOLOGY
1. The alveolus is the site of gas exchange. Type 1 cells line/make up the walls of the alveolus;
it is through these cells that respiratory gases diffuse. Type 2 cells secrete surfactant,
decreasing surface tension of water in alveoli, helping to overcome the cohesion of alveoli in
breathing so that the lungs can expand and also reducing the tendency of the lungs to
collapse. Surfactant secretion is particularly important in allowing new-born infants to take
their first breath, and is important is allowing for deep breathing. Particles smaller than 0.5
micrometers make it into the alveoli. Macrophages attack them. Cigarette ash particles range
from 0.7 to 0.3 micrometers, so can obstruct alveoli. Asbestos fibers are easy to breathe in,
act like needles, damaging both alveolar cells and macrophages.
2. Respiratory gases diffuse from high partial pressures to low partial pressures. In the alveoli, a
higher partial pressure of oxygen than in the lung capillaries allows oxygen to diffuse out
into the blood; a lower partial pressure of carbon dioxide in the alveoli than in the blood
allows carbon dioxide to diffuse out of the blood into the lungs. In the tissues, a lower partial
pressure of oxygen than in the blood allows oxygen to diffuse into the tissues; a higher partial
pressure of carbon dioxide in the tissues than in the blood allows carbon dioxide to diffuse
from the tissues into the lungs.
3. At sea level, the partial pressure of oxygen is 159 torr of a total of 760 torr; at 20,000 feet,
the partial pressure of oxygen is 73 torr of 349 total. At lower partial pressures, oxygen has a
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hard time diffusing into the blood leading to high altitude sickness: nausea, dizziness,
headache, shortness of breath.
4. Arterial pO2 in fingertip = same as pO2 in pulmonary vein! No O2 used up in transport! This
used to determine how well lungs are exchanging O2!
5. Hemoglobin facilitates the transportation of respiratory gases. It is always as saturated as it
can be, given its surroundings. At 104 torr, hemoglobin is 100% saturated with oxygen; at 40
torr, the partial pressure of oxygen in the tissues, it can only be about 75% saturated—so it
unloads some of its oxygen to the tissues. Recall that Hb in within biconcave erythrocytes;
the thinness of erythrocytes facilitates the loading & unloading of respiratory gasses.
6. The affinity of hemoglobin for oxygen decreases with both temperature and acidity;
consequently, Hb can unload more oxygen when it enters working muscle tissue because it is
both warm and acidic (producing carbon dioxide or lactic acid). Hyperventilation does not
deliver more oxygen to the tissues—in fact, the harder you breathe, the more carbon dioxide
you remove from your blood, causing the Hb disassociation curve to move to the left,
decreasing your blood’s ability to carry oxygen! Carbon monoxide is bad because it has a
stronger affinity for hemoglobin than does oxygen.
7. Carbon dioxide is produced by mitochondria in cells, diffuses across extracellular fluid,
across endothelium of capillaries, dissolves in plasma. A significant amount of carbon
dioxide is transported as a gas in solution; some carbon dioxide reacts with water to form
carbonic acid. Some plasma proteins act as buffers, resisting changes in pH, by absorbing
excess hydrogen ions.
8. Most plasma carbon dioxide diffuses into erythrocytes. Carbonic anhydrase catalyses the
formation of carbonic acid; carbonic acid disassociates into bicarbonate and hydrogen ions.
The bicarbonate diffuses out into the plasma as chloride ions enter (= chloride shift). The
hydrogen ions are picked up by hemoglobin. Carbon dioxide may also be picked up and
transported by hemoglobin (= carbaminohemoglobin) or any plasma protein! Thus, carbon
dioxide is transported from the tissues a) as gas dissolved in the plasma, b) as carbonic acid,
c) as bicarbonate ion, d) as carbaminohemoglobin and e) as a carbondioxide-protein
complex. Note that at low oxygen levels, the affinity of carbondioxide for Hb increases (=
Haldane effect).
9. The small amount of oxygen dissolved in the plasma diffuses into the tissues. Hydrogen ion
binding to hemoglobin decreases hemoglobin’s affinity for oxygen, helping remove it.
Oxygen diffuses out into plasma, then into tissues.
10. A small amount of carbon dioxide diffuses from the plasma into the lungs (across the
capillary endothelium, across the lamina, across the type 1 cells of the alveoli). The largest
amount of carbon dioxide diffuses from the erythrocytes. Carbonic anhydrase catalyzes the
conversion of carbonic acid into water and carbon dioxide, which diffuses out into the lungs.
High levels of oxygen, which you have in the lungs, bond onto hemoglobin, kicking
hydrogens off, which go into combining with bicarbonate, brought in by the chloride shift,
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making carbonic acid. Another small amount of carbon dioxide disassociates from
carbaminohemoglobin and protein-carbon dioxide complexes, and diffuses into the lungs.
11. In the lungs, oxygen diffuses from the alveolar air spaces, through alveolar type-1 cells,
through the lamina, through the capillary endothelium, into the plasma. A small amount of
oxygen dissolves and is transported in the plasma. Most of the oxygen diffuses into
erythrocytes, where it is picked up by hemoglobin. When oxygen combines with
hemoglobin, it kicks the hydrogen ions off that it has been carrying. The hydrogens facilitate
the conversion of carbonate into carbonic acid (see above for significance). High levels of
oxygen saturation of Hb decreases the affinity of Hb for carbon dioxide, hence facilitating
the unloading of carbon dioxide (= Bohr Effect).
CONTROL OF BREATHING
1. Breathing controlled by respiratory center in medulla oblongata. Medulla receives
innervation from carotid and aortic bodies. The medulla sends out depolarizations every 1517 seconds, propagating automatic breathing. Medullary sensors, which analyze CNS, aortic
and carotid sensors, which analyze plasma, respond to changes in blood chemistry, not
erythrocyte chemistry. Thus, toxins that bond to Hb, lowering Hb’s ability to pick up oxygen,
don’t cause respiratory distress!
2. Chemoreceptors respond most sensitively to carbon dioxide, increasing respiratory rate and
volume with higher levels. At 80 torr, oxygen becomes important. Lowered levels of
hydrogen ions, seen after eating a big meal, depress respiration (= alkaline tide). At 2 atm,
oxygen interferes with glycolysis—a problem with deep divers using rebreathers.
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