Download day 4 ch 13

Day 4 ch 13
1. Clearly explain the difference between external and internal respiration.
External respiration is the process of gas exchange that occurs between the blood of the
pulmonary capillaries and the external environment (alveolar air). Internal respiration is the
process of gas exchange that occurs between the blood of the systemic capillaries and the tissue
cells. (pp. 448–449)
2. Trace the route of air from the nares to an alveolus.
External nares to nasal cavities to nasopharynx to oropharynx to laryngopharynx to larynx to
trachea to right or left primary bronchus to secondary (tertiary, etc.) bronchi to bronchioles (to
alveolar ducts) to alveolus. (pp. 441–447)
3. Why is it important that the trachea be reinforced with cartilaginous rings? What is the
advantage of the fact that the rings are incomplete posteriorly?
The cartilaginous reinforcements keep the trachea patent during the pressure changes that occur
during breathing. The incomplete rings of the posterior tracheal surface make it flexible, allowing
a food bolus traveling through the posterior esophagus to bulge anteriorly. (p. 444)
4. Where in the respiratory tract is the air filtered, warmed, and moistened?
Primarily in the nasal cavities, but the warming and moistening process continues for the entire
length of the respiratory passageways. (pp. 441–442)
5. The trachea has goblet cells that produce mucus. What is the specific protective function of
the mucus?
Mucus serves to trap dust, bacteria, and other foreign debris that manage to enter the
respiratory passageways. (pp. 441–445)
6. In terms of general health, what is the importance of the fact that the pharyngotympanic .
tubes and the sinuses drain into the nasal cavities and nasopharynx?
If either the middle ear or the sinuses are infected, the exudate will drain into the nasal passages
and possibly lead to congestion, or “postnasal drip.” Conversely, a nasopharyngeal infection can
easily spread to the middle ear cavity or the sinuses because of the continuity of their mucosae,
thus causing otitis media or sinusitis, respectively. (pp. 443–444)
7. What is it about the structure of the alveoli that makes them an ideal site for gas exchange?
Their walls are extremely thin (one layer of squamous epithelium plus a basement membrane)
for easy gas exchange, and combined, they present an extremely large surface area. (p. 447)
Respiratory Physiology
The major function of the respiratory system is to supply the body with oxygen and to dispose of
carbon dioxide. To do this, at least four distinct events, collectively called respiration, must occur:
1. Pulmonary ventilation. Air must move into and out of the lungs so that the gases in the air
sacs (alveoli) of the lungs are continuously refreshed. This process of pulmonary ventilation is
commonly called breathing.
2. External respiration. Gas exchange (oxygen loading and carbon dioxide unloading) between
the pulmonary blood and alveoli must take place. Remember that in external respiration, gas
exchanges are being made between the blood and the body exterior.
3. Respiratory gas transport. Oxygen and carbon dioxide must be transported to and from the
lungs and tissue cells of the body via the bloodstream.
4. Internal respiration. At systemic capillaries, gas exchanges must be made between the blood
and tissue cells. * In internal respiration, gas exchanges are occurring between the blood and
cells inside the body.
Although only the first two processes are the special responsibility of the respiratory system, all
four processes are necessary for it to accomplish its goal of gas exchange.
Mechanics of Breathing
Breathing, or pulmonary ventilation, is a completely mechanical process that depends on volume
changes occurring in the thoracic cavity. Here is a rule to keep in mind about the mechanics of
breathing: Volume changes lead to pressure changes, which lead to the flow of gases to equalize
the pressure.
Let’s see how this relates to the two phases of breathing—inspiration, when air is flowing into
the lungs, and expiration, when air is leaving the lungs.
Inspiration
When the inspiratory muscles, the diaphragm and external intercostals, contract, the size of the
thoracic cavity increases. The lungs adhere tightly to the thorax walls (because of the surface
tension of the fluid between the pleural membranes), so they are stretched to the new, larger
size of the thorax. As intrapulmonary volume (the volume within the lungs) increases, the gases
within the lungs spread out to fill the larger space. The resulting decrease in the gas pressure in
the lungs produces a partial vacuum (pressure less than atmospheric pressure), which sucks air
into the lungs. Air continues to move into the lungs until the intrapulmonary pressure equals
atmospheric pressure. This series of events is called inspiration (inhalation).
Changes in intrapulmonary pressure and
air flow during inspiration and
expiration.
Expiration
Expiration (exhalation) in healthy people is largely a passive process that depends more on the
natural elasticity of the lungs than on muscle contraction. As the inspiratory muscles relax and
resume their initial resting length, the rib cage descends and the lungs recoil. Thus, both the
thoracic and intrapulmonary volumes decrease. As the intrapulmonary volume decreases, the
gases inside the lungs are forced more closely together, and the intrapulmonary pressure rises to
a point higher than atmospheric pressure. This causes the gases to flow out to equalize the
pressure inside and outside the lungs.
The normal pressure within the pleural space, the intrapleural pressure, is always negative, and
this is the major factor preventing collapse of the lungs.
If for any reason the intrapleural pressure becomes equal to the atmospheric pressure, the lungs
immediately recoil completely and collapse.
Respiratory Volumes and Capacities
Many factors affect respiratory capacity—for example, a person’s size, sex, age, and physical
condition. Normal quiet breathing moves approximately 500 ml of air (about a pint) into and out
of the lungs with each breath. This respiratory volume is referred to as the tidal volume (TV).
As a rule, a person can inhale much more air than is taken in during a normal, or tidal, breath.
The amount of air that can be taken in forcibly over the tidal volume is the inspiratory reserve
volume (IRV). Normally, the inspiratory reserve volume is between 2100 and 3200 ml.
Similarly, after a normal expiration, more air can be exhaled.
The amount of air that can be forcibly exhaled after a tidal expiration, the expiratory reserve
volume (ERV), is approximately 1200 ml.
Even after the most strenuous expiration, about 1200 ml of air still remains in the lungs, and it
cannot be voluntarily expelled. This is the residual volume. Residual volume air is important
because it allows gas exchange to go on continuously even between breaths and helps to keep
the alveoli open (inflated).
The total amount of exchangeable air is typically around 4800 ml in healthy young men, and this
respiratory capacity is the vital capacity (VC). The vital capacity is the sum of the TV + IRV + ERV.
Much of the air that enters the respiratory tract remains in the conducting zone passageways
and never reaches the alveoli. This is called the dead space volume.
Respiratory Sounds
As air flows into and out of the respiratory tree, it produces two recognizable sounds that can be
picked up with a stethoscope.
Bronchial sounds are produced by air rushing through the large respiratory passageways
(trachea and bronchi).
Vesicular breathing sounds occur as air fills the alveoli. The vesicular sounds are soft and
resemble a muffled breeze.
Diseased respiratory tissue, mucus, or pus can produce abnormal sounds such as crackle (a
bubbling sound) and wheezing (a whistling sound).
REVIEW
What is the most basic function of respiration?
To exchange gases between the external environment and the blood—oxygen in, carbon dioxide
out.
What causes air to flow out of the lungs during expiration?
Increased air pressure in the lungs as they recoil.
Which is the largest respiratory volume—ERV, IRV, TV, or VC? Which is the smallest?
VC is largest; TV is smallest.
Dead space volume accounts for about 150 ml of tidal volume. How much of a tidal breath
actually reaches the exchange chambers (alveoli)?
About 350 ml reaches the alveoli.
Jimmy broke a left rib during his fall from his bike. It punctured the chest wall. What happened to
his left lung? Why?
His left lung collapsed because the pressure in the intrapleural space (normally negative) became
equal to atmospheric pressure.
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