Download The Respiratory System 2

The Respiratory System 2
Chapter 15
The Lower Respiratory Tract
• Contains the trachea, bronchi,
bronchioles, and alveoli
• Structurally similar throughout
• Tubes made of hyaline cartilage, smooth
muscle, and connective tissue dense with
elastic protein fibers
• Lined with ciliated mucous membrane
(PSCC epithelial tissue) to protect from
foreign particles
• Mucous is produced by goblet cells
• The cilia beat synchronously to “sweep”
mucous toward pharynx where it is usually
swallowed
• This system is called the mucociliary
transport system
• Digestive processes destroy microbes
Trachea
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•
•
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Extends from larynx to bronchi
Approx. 4 inches long and 1 inch wide
Located anterior to esophagus
Walls supported by rings of cartilage that
are open in the back to accommodate
expansion of esophagus when swallowing
(shaped like “C”)
• The rings prevent closure of main air
passage
Bronchial Tree
• Main branches of “bronchial tree” are called
“bronchi”
• Extend toward right and left lungs; left branches
at sharper angle than right—inhaled particles
usually end up in right lung
• Branch off into progressively smaller tubes
called bronchioles; amount of cartilage
decreases as tubes get smaller
• Terminate in alveolar ducts which lead to alveoli
Alveoli
• Tiny air sacs where gases are exchanged
• Average adult has between 300 and 500
million alveoli
• Comprise a surface area of approximately
70 square meters
• Massive surface area necessary to
support metabolism
• Walls of alveoli are only 0.5 micrometers
thick; diameter is approx. 10 micrometers
• Walls are made of a single layer of simple
squamous epithelial tissue
• Alveoli must remain moist to dissolve
gases
• At this microscopic scale, the force from
surface tension holding the walls of alveoli
together are significant (this force arises
from the polarity of water molecules)
• A surfactant is produced to allow alveoli to
re-inflate easily following expiration
Lungs
• Made of the many branches of tubes that
form the bronchial tree, the alveoli and
capillaries, along with supportive tissues
• Lungs are soft, spongy, and cone-shaped
• Occupy most of the thoracic cavity, from
the diaphragm to just above the clavicles
• Blood vessels mirror the pathway of the
bronchial tree beginning from the medial
surface of each lung; convergence called
a root
Serous Membranes
• Two layers of serous membranes
surround each lung, collectively called the
pleurae
• Animation: The Pleural Membranes
• Outer layer is called parietal pleura; lines
the thoracic wall and mediastinum; links
with layer from opposite lung to form a
ligament that supports each lung from its
root
• The visceral pleura is attached firmly to
the surface of each lung
• Between the two layers is a potential
space called the pleural cavity
• Contains a thin film of fluid produced by
serous cells
• Acts as a lubricant between the two
membranes as lungs expand and contract
during breathing
Divisions of Lungs
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Each lung is divided into smaller compartments
Right lung has 3 lobes; left has two
Lines of division called fissures
Each lobe is divided into segments
Within each segment are numerous lobules,
each of which receives a single bronchiole, an
arteriole, a venule, and a lymphatic vessel
• Lobules contain alveolar ducts, their alveoli and
capillaries
Mechanics of Breathing
• Pulmonary
ventilation relies
heavily upon
Boyle’s Law
(pressure is
inversely
proportional to
volume at a
constant
temperature)
• Recall that the pressure of a gas is the
result of collisions between atoms and
molecules with the walls of its container
• An expansion of the thoracic cavity causes
an increase in the volume of the space
within and the gases inside decrease in
pressure
• This creates a pressure gradient between
the inside of the lungs and the atmosphere
• Air rushes into the lungs following this
gradient
• This is how your lungs fill with air when
you inhale
• To exhale, the volume of the thoracic
cavity is decreased, resulting in an
increase in pressure which forces the air
out
Expansion and Contraction of
the Thoracic Cavity
• The thoracic cage is formed by the ribs,
sternum, and clavicles
• Muscles responsible for the movement of
these bones are primarily the diaphragm
and intercostal muscles
• To a lesser extent, the pectoralis minor
and abdominal muscles play a role
• Recall that there are no muscles attached
directly to the surface of the lungs
• Surface tension from serous fluid between
the layers of the plurae holds the outer
surface of the lungs to the inner surface of
the thoracic cavities
Inspiration
• For inspiration, or breathing in, the
diaphragm (pulls down toward the
abdominal cavity) and external intercostals
contract (pull each inferior rib up)
• For a deep breath, the pectoralis minor
can assist with further lifting of the ribs
Expiration
• For normal expiration, or breathing out,
these same muscles relax
• On a forced expiration, the abdominal
muscles and internal intercostals contract
to further shrink the cavity
• These muscular movements are
stimulated by the respiratory center found
in the pons and medulla
Respiratory Volumes
• The amounts of gases that need
exchanged vary according to how much
energy is required to meet the body’s
immediate needs
• This need is determined by the several
areas of the autonomic nervous system
which monitor things like the amount of
carbon dioxide in the blood and the degree
of stretch in the bronchial tree
Type
Definition
Average Volume
tidal volume
amount of air moving into or out of lungs during
quiet breathing
500 ml
inspiratory
reserve volume
maximum amount of air that can be inhaled
forcibly over the tidal volume
3100 ml
expiratory
reserve volume
maximum amount of air that can be exhaled
forcibly over the tidal volume
1200 ml
residual volume
amount of air remaining in the lungs following a
forced expiration
1200 ml
vital capacity
the total amount of exchangeable air, determined 4800 ml
by the sum of the tidal volume, inspiratory
reserve volume, and expiratory reserve volume
total lung
capacity
the total amount of air contained in the fully
6000 ml
inflated respiratory system, determined by the
sum of the vital capacity and the residual volume