Trachea, Bronchial Tree, and Lungs

Chapter 19 – Respiratory System
Trachea, Bronchial Tree, Lungs
• Extends from larynx into the thoracic cavity
where it splits into the left and right bronchial
• Structure
– Lined with ciliated mucous membrane
• Membrane filters out particles and moves them up to
the pharynx where they can be swallowed
• Structure
– Tracheal wall contains about twenty C-shaped
pieces of hyaline cartilage with smooth muscle
and connective tissues between them
• The cartilage prevents the trachea from collapsing and
preventing air flow while the soft tissues between allow
the esophagus to expand when food passes through it
Bronchial Tree
• Branched airways that lead from the trachea
to microscopic air sacs in the lungs
Bronchial Tree
• Branches
1. Right and left primary bronchi arise from the trachea
These are separated by a ridge of cartilage called the
2. Secondary (or lobar) bronchi branch from the
primary bronchi
Three branch on the right and two branch on the left
3. Tertiary (or segmental) bronchi split from the
secondary bronchi
These supply a portion of the lung called the
bronchopulmonary segment
Typically ten segments are in right lung and eight
segments are in the left lung
Bronchial Tree
• Branches
4. Intralobular bronchioles branch from the tertiary bronchi
These enter the basic units of the lung (called lobules)
5. Terminal bronchioles branch from the intralobular
• There are fifty to eighty terminal bronchioles in a lobule of the
6. Respiratory bronchioles branch from each terminal
These have air sacs that bud from their sides and allow them to
participate in gas exchange
There are typically two or more that branch from each terminal
Bronchial Tree
• Branches
7. Alveolar ducts branch from each respiratory
8. Alveolar sacs come off of the alveolar ducts
9. Alveoli (which are thin-walled microscopic air
sacs) open to the alveolar sacs
Bronchial Tree
• Structure of respiratory tubes
– Bronchus
• Structured similar to the trachea
• C-shaped rings of cartilage are replaced by plates of
cartilage that completely surround the bronchus (unlike
the c-shaped rings which open posteriorly) when the
bronchus enters the lung
Bronchial Tree
• Structure of respiratory tubes
– Smaller branches
• As the branches of the respiratory tree become smaller:
– The amount of cartilage decreases and the amount of smooth
muscle becomes more prominent
» Cartilage disappears completely in the bronchioles
» The muscular layer remains prominent until the alveolar
ducts which only have a few muscle fibers
– The number of goblet cells and the amount of cilia decrease
– The type of tissue in the walls also changes
Bronchial Tree
• Structure of respiratory tree
– Elastic fibers are scattered throughout the smooth
muscle and connective tissue that surround the
respiratory tubes
Bronchial Tree
• Functions of the respiratory tubes and alveoli
– Branches serve as passageways for air, filter
incoming air, and distribute air evenly to alveoli in
all parts of the lungs
– Alveoli provide a large surface area for gas
• During gas exchange:
– Oxygen diffuses through the alveolar walls and enters blood in
nearby capillaries
– Carbon dioxide diffuses from the blood through alveolar walls
and enters the alveoli
• Suspended in the thoracic cavity by a bronchus
and various large blood vessels
– These tubular structures enter each lung on the
medial surface through a region called the hilum
• Covered by the visceral pleura which fold back to
become the parietal pleura at the hilum
– The visceral pleura and parietal pleura essentially
touch each other and are separated only by a thin film
of serous fluid (located in the pleural cavity) that
serves as lubrication to reduce friction during
breathing and helps to hold the pleural membranes
• Right lung is larger than the left lung
– The right lung is divided by fissures into the
superior, middle, and inferior lobes
– The left lung is divided by fissures into the
superior and inferior lobes
• Lobes
– Each lobe is supplied by a lobar bronchus, has
connections to blood and lymphatic vessels, and is
enclosed by connective tissues
– Each lobe is further divided by connective tissues
into lobules
– Each lobule contains terminal bronchioles (along
with their respective alveolar ducts, alveolar sacs,
alveoli, nerves, blood vessels, and lymphatic

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