Week 2:
Respiratory Disorders and Alterations in Acid/Base Balance,
Fluid and Electrolytes
Chapter 35: Structure and Function of the Pulmonary System
Tara Morgan
• The primary function of the pulmonary system is the exchange of gases between
the environmental air and the blood.
• There are three steps in this process:
○ Ventilation, the movement of air into and out of the lungs
○ Diffusion, the movement of gases between air spaces in the lungs and the
bloodstream
○ Perfusion, the movement of blood into and out of the capillary beds of the
lungs to body organs and tissues
• The first two functions (ventilation and diffusion) are carried out by the
pulmonary system and the third (perfusion) by the cardiovascular system.
• Normally the pulmonary system functions efficiently under a variety of conditions
and with little energy expenditure.
Structures of the Pulmonary System
• The pulmonary system includes two lungs and the upper and lower airways, and
the blood vessels that serve them; the chest wall, or thoracic cage; and the
diaphragm.
• The lungs are divided into lobes:
○ 3 in the right lung (upper, middle, lower)
○ 2 in the left lung (upper, lower)
• Each lobe is further divided into segments and lobules.
• The mediastinum is the space between the lungs and contains the heart, great
vessels, and esophagus.
• A set of conducting airways, or bronchi, delivers air to each section of the lung.
• The diaphragm is a dome-shaped muscle that separates the thoracic and
abdominal cavities and is involved in ventilation.
•
• FIGURE 35.1 Structural Plan of the Respiratory System. The inset shows alveolar
sacs where the interchange of oxygen and carbon dioxide takes place through the
walls of the grapelike alveoli. Capillaries surround the alveoli.
• The lungs are protected from a variety of exogenous contaminants by a series of
mechanical and cellular defenses.
• These defense mechanisms are so effective that in the healthy individual,
contamination of the lung tissue itself, particularly by infectious agents, is rare.
STRUCTURE MECHANISM OF DEFENSE
OR
SUBSTANCE
Upper Maintains constant temperature and humidification of gas entering
respiratory tract the lungs; traps and removes foreign particles, some bacteria, and
mucosa noxious gases from inspired air
Nasal hairs and Trap and remove foreign particles, some bacteria, and noxious
turbinates gases from inspired air
Advanced Patho Page 1
, turbinates gases from inspired air
Branching Disrupt laminar flow and enhance deposition of particles and
airways pathogens on ciliated mucosa
Mucous blanket Protects trachea and bronchi from injury; traps most foreign
particles and bacteria that reach the lower airways
Innate immune Lysozyme, lactoferrin, defensins, collectins (surfactant protein A
proteins [SP-A] and surfactant protein D [SP-D]), and immunoglobulin A
(IgA); recognize and promote killing of pathogens
Cilia Propel mucous blanket and entrapped particles toward the
oropharynx, where they can be swallowed or expectorated
Alveolar Ingest and remove bacteria and other foreign material from alveoli
macrophages by phagocytosis (see Chapter 7)
Surfactant Enhances phagocytosis of pathogens and allergens in alveoli;
down-regulates inflammatory responses
Irritant receptors Stimulation by chemical or mechanical irritants triggers sneeze
in nares reflex, which results in rapid removal of irritants from nasal
(nostrils) passages
Irritant receptors Stimulation by chemical or mechanical irritants triggers cough
in trachea and reflex, which results in removal of irritants from the trachea and
large airways large airways
Conducting Airways
• The conducting airways provide a passage for the movement of air into and out of the
gas-exchange structures of the lung.
• The nasopharynx, oropharynx, and related structures are called the upper airway.
• Lined with ciliated mucosa with a rich vascular supply that warms and humidifies
inspired air and removes foreign particles from it as it passes into the lungs.
• The mouth and oropharynx provide for ventilation when the nose is obstructed or
when increased flow is required, for example, during exercise. Filtering and
humidifying are not as efficient with mouth breathing.
FIGURE 35.2 Structures of the Upper Airway.
• The larynx connects the upper and lower airways and consists of the endolarynx and
its surrounding triangular-shaped bony and cartilaginous structures.
• The endolarynx is formed by two pairs of folds: the false vocal cords (supraglottis)
and the true vocal cords.
• The slit-shaped space between the true cords forms the glottis.
• The vestibule is the space above the false vocal cords.
• The laryngeal box is formed by three large cartilages
• Epiglottis
Advanced Patho Page 2
, • Epiglottis
• Thyroid
• Cricoid
○ And three smaller cartilages-connected by ligaments
▪ Arytenoid
▪ Corniculate
▪ Cuneiform
• The supporting cartilages prevent collapse of the larynx during inspiration and
swallowing.
• The internal laryngeal muscles control vocal cord length and tension, and the external
laryngeal muscles move the larynx as a whole.
• The internal muscles contract during swallowing to prevent aspiration into the trachea
and contribute to voice pitch.
• The trachea, which is supported by U-shaped cartilage, connects the larynx to the
bronchi, the conducting airways of the lungs.
• The trachea divides into the two main airways, or bronchi, at the carina
• This area is very sensitive and when stimulated can cause coughing and airway
narrowing.
• The left mainstem bronchus branches from the trachea at about a 45 -degree angle.
The right mainstem bronchus is slightly larger and more vertical than the left
(branches at about a 20- to 30-degree angle from the trachea).
• Aspirated fluids or foreign particles thus tend to enter the right lung rather than
the left.
• The right and left main bronchi enter the lungs at the hila, or “roots” of the lungs,
along with the pulmonary blood and lymphatic vessels.
• From the hila the main bronchi branch into lobar bronchi and then to segmental and
subsegmental bronchi, and finally end at the sixteenth division in the smallest of the
conducting airways, the terminal bronchioles
FIGURE 35.3 Conducting Airways and Respiratory Unit. A, Structures of respiratory
airways. B, Changes in bronchial wall with progressive branching. C, Electron
micrograph of alveoli: long white arrow identifies type II alveolar cells (pneumocytes -
secretes surfactant); short white arrowhead identifies pores of Kohn; red arrow
identifies alveolar capillary. D, Plastic cast of pulmonary capillaries at high
magnification.
• The bronchial walls have 3 layers:
• Epithelial lining
• Smooth muscle layer
• Connective tissue layer
• In the large bronchi (up to approximately the tenth division), the connective tissue
layer contains cartilage.
• The epithelial lining of the bronchi contains single -celled exocrine glands—the mucus-
secreting goblet cells—and ciliated cells.
• High columnar pseudostratified epithelium lines the larger airways and becomes
progressively thinner, changing to columnar cuboidal epithelium in the bronchioles
and squamous epithelium in the alveoli
• The submucosal glands of the bronchial lining produce a mucous blanket that
protects the bronchial epithelium.
• The ciliated epithelial cells rhythmically beat this mucous blanket toward the trachea
and pharynx, where it can be swallowed or expectorated by coughing.
Advanced Patho Page 3
, and pharynx, where it can be swallowed or expectorated by coughing.
• Toward the terminal bronchioles, ciliated cells and goblet cells become more sparse,
and smooth muscle and connective tissue layers thin
Gas-Exchange Airways
• The conducting airways terminate in the respiratory (terminal) bronchioles, alveolar
ducts, and alveoli
• These thin-walled structures participate in gas exchange, and the clusters of
alveoli are sometimes called the acinus
• The bronchioles from the sixteenth through the twenty-third divisions contain
increasing numbers of alveoli and are called respiratory bronchioles.
• The walls of the respiratory bronchioles are very thin, consisting of an epithelial
layer devoid of cilia and goblet cells, very little smooth muscle fiber, and a very
thin and elastic connective tissue layer.
• These bronchioles end in alveolar ducts, which lead to alveolar sacs made up
of numerous alveoli.
• The alveoli are the primary gas-exchange units of the lung, where oxygen enters the
blood and CO2 is removed
• Tiny passages called pores of Kohn permit some air to pass through the septa from
alveolus to alveolus, promoting collateral ventilation and even distribution of air
among the alveoli. The lungs contain approximately 50 million alveoli at birth and
about 480 million by adulthood.
FIGURE 35.4 Alveoli. Bronchioles subdivide to form tiny tubes called alveolar ducts that end in
clusters of alveoli called alveolar sacs.
• Lung epithelial cells provide a protective interface with the environment
• Essential for adequate gas exchange
• Preventing entry of foreign agents
• Regulates ion and water transport
• Maintains mechanical stability of the alveoli
• The alveolar septa consist of an epithelial layer and a thin, elastic basement
membrane but no muscle layer
• Two major types of epithelial cells (pneumocytes) appear in the alveolus.
• Type I alveolar cells provide structure
• Type II alveolar cells secrete surfactant, a lipoprotein that coats the inner
surface of the alveolus and facilitates its expansion during inspiration, which
lowers alveolar surface tension at end-expiration, thereby preventing lung
collapse (atelectasis).
• Surfactant
• Contribute to control of lung inflammation by decreasing release of
proinflammatory mediators
• Prevents oxidative injury
• Regulates the role of fibroblasts in airway remodeling.
• Bacteriostatic and function as opsonins in presenting pathogens to alveolar
macrophages.
• Macrophages are the most numerous immune cells present in the lung environment
and provide innate immune defense of the airway from the bronchi to the alveoli.
• In the alveoli, alveolar macrophages provide protection by clearing surfactant from the
lung and ingesting foreign material and pathogens that reach the alveolus, preparing
these substances for removal through the lymphatics -Phagocytosis
• Surfactant and alveolar macrophages work together with the normal pulmonary
microbiota to prevent lower lung infection.
Pulmonary and Bronchial Circulation
• The pulmonary circulation;
• provides an extensive surface area for gas exchange
• delivers nutrients to lung tissues
• acts as a blood reservoir for the left ventricle
• serves as a filtering system that removes clots, air, and other debris from the
circulation
Advanced Patho Page 4
Respiratory Disorders and Alterations in Acid/Base Balance,
Fluid and Electrolytes
Chapter 35: Structure and Function of the Pulmonary System
Tara Morgan
• The primary function of the pulmonary system is the exchange of gases between
the environmental air and the blood.
• There are three steps in this process:
○ Ventilation, the movement of air into and out of the lungs
○ Diffusion, the movement of gases between air spaces in the lungs and the
bloodstream
○ Perfusion, the movement of blood into and out of the capillary beds of the
lungs to body organs and tissues
• The first two functions (ventilation and diffusion) are carried out by the
pulmonary system and the third (perfusion) by the cardiovascular system.
• Normally the pulmonary system functions efficiently under a variety of conditions
and with little energy expenditure.
Structures of the Pulmonary System
• The pulmonary system includes two lungs and the upper and lower airways, and
the blood vessels that serve them; the chest wall, or thoracic cage; and the
diaphragm.
• The lungs are divided into lobes:
○ 3 in the right lung (upper, middle, lower)
○ 2 in the left lung (upper, lower)
• Each lobe is further divided into segments and lobules.
• The mediastinum is the space between the lungs and contains the heart, great
vessels, and esophagus.
• A set of conducting airways, or bronchi, delivers air to each section of the lung.
• The diaphragm is a dome-shaped muscle that separates the thoracic and
abdominal cavities and is involved in ventilation.
•
• FIGURE 35.1 Structural Plan of the Respiratory System. The inset shows alveolar
sacs where the interchange of oxygen and carbon dioxide takes place through the
walls of the grapelike alveoli. Capillaries surround the alveoli.
• The lungs are protected from a variety of exogenous contaminants by a series of
mechanical and cellular defenses.
• These defense mechanisms are so effective that in the healthy individual,
contamination of the lung tissue itself, particularly by infectious agents, is rare.
STRUCTURE MECHANISM OF DEFENSE
OR
SUBSTANCE
Upper Maintains constant temperature and humidification of gas entering
respiratory tract the lungs; traps and removes foreign particles, some bacteria, and
mucosa noxious gases from inspired air
Nasal hairs and Trap and remove foreign particles, some bacteria, and noxious
turbinates gases from inspired air
Advanced Patho Page 1
, turbinates gases from inspired air
Branching Disrupt laminar flow and enhance deposition of particles and
airways pathogens on ciliated mucosa
Mucous blanket Protects trachea and bronchi from injury; traps most foreign
particles and bacteria that reach the lower airways
Innate immune Lysozyme, lactoferrin, defensins, collectins (surfactant protein A
proteins [SP-A] and surfactant protein D [SP-D]), and immunoglobulin A
(IgA); recognize and promote killing of pathogens
Cilia Propel mucous blanket and entrapped particles toward the
oropharynx, where they can be swallowed or expectorated
Alveolar Ingest and remove bacteria and other foreign material from alveoli
macrophages by phagocytosis (see Chapter 7)
Surfactant Enhances phagocytosis of pathogens and allergens in alveoli;
down-regulates inflammatory responses
Irritant receptors Stimulation by chemical or mechanical irritants triggers sneeze
in nares reflex, which results in rapid removal of irritants from nasal
(nostrils) passages
Irritant receptors Stimulation by chemical or mechanical irritants triggers cough
in trachea and reflex, which results in removal of irritants from the trachea and
large airways large airways
Conducting Airways
• The conducting airways provide a passage for the movement of air into and out of the
gas-exchange structures of the lung.
• The nasopharynx, oropharynx, and related structures are called the upper airway.
• Lined with ciliated mucosa with a rich vascular supply that warms and humidifies
inspired air and removes foreign particles from it as it passes into the lungs.
• The mouth and oropharynx provide for ventilation when the nose is obstructed or
when increased flow is required, for example, during exercise. Filtering and
humidifying are not as efficient with mouth breathing.
FIGURE 35.2 Structures of the Upper Airway.
• The larynx connects the upper and lower airways and consists of the endolarynx and
its surrounding triangular-shaped bony and cartilaginous structures.
• The endolarynx is formed by two pairs of folds: the false vocal cords (supraglottis)
and the true vocal cords.
• The slit-shaped space between the true cords forms the glottis.
• The vestibule is the space above the false vocal cords.
• The laryngeal box is formed by three large cartilages
• Epiglottis
Advanced Patho Page 2
, • Epiglottis
• Thyroid
• Cricoid
○ And three smaller cartilages-connected by ligaments
▪ Arytenoid
▪ Corniculate
▪ Cuneiform
• The supporting cartilages prevent collapse of the larynx during inspiration and
swallowing.
• The internal laryngeal muscles control vocal cord length and tension, and the external
laryngeal muscles move the larynx as a whole.
• The internal muscles contract during swallowing to prevent aspiration into the trachea
and contribute to voice pitch.
• The trachea, which is supported by U-shaped cartilage, connects the larynx to the
bronchi, the conducting airways of the lungs.
• The trachea divides into the two main airways, or bronchi, at the carina
• This area is very sensitive and when stimulated can cause coughing and airway
narrowing.
• The left mainstem bronchus branches from the trachea at about a 45 -degree angle.
The right mainstem bronchus is slightly larger and more vertical than the left
(branches at about a 20- to 30-degree angle from the trachea).
• Aspirated fluids or foreign particles thus tend to enter the right lung rather than
the left.
• The right and left main bronchi enter the lungs at the hila, or “roots” of the lungs,
along with the pulmonary blood and lymphatic vessels.
• From the hila the main bronchi branch into lobar bronchi and then to segmental and
subsegmental bronchi, and finally end at the sixteenth division in the smallest of the
conducting airways, the terminal bronchioles
FIGURE 35.3 Conducting Airways and Respiratory Unit. A, Structures of respiratory
airways. B, Changes in bronchial wall with progressive branching. C, Electron
micrograph of alveoli: long white arrow identifies type II alveolar cells (pneumocytes -
secretes surfactant); short white arrowhead identifies pores of Kohn; red arrow
identifies alveolar capillary. D, Plastic cast of pulmonary capillaries at high
magnification.
• The bronchial walls have 3 layers:
• Epithelial lining
• Smooth muscle layer
• Connective tissue layer
• In the large bronchi (up to approximately the tenth division), the connective tissue
layer contains cartilage.
• The epithelial lining of the bronchi contains single -celled exocrine glands—the mucus-
secreting goblet cells—and ciliated cells.
• High columnar pseudostratified epithelium lines the larger airways and becomes
progressively thinner, changing to columnar cuboidal epithelium in the bronchioles
and squamous epithelium in the alveoli
• The submucosal glands of the bronchial lining produce a mucous blanket that
protects the bronchial epithelium.
• The ciliated epithelial cells rhythmically beat this mucous blanket toward the trachea
and pharynx, where it can be swallowed or expectorated by coughing.
Advanced Patho Page 3
, and pharynx, where it can be swallowed or expectorated by coughing.
• Toward the terminal bronchioles, ciliated cells and goblet cells become more sparse,
and smooth muscle and connective tissue layers thin
Gas-Exchange Airways
• The conducting airways terminate in the respiratory (terminal) bronchioles, alveolar
ducts, and alveoli
• These thin-walled structures participate in gas exchange, and the clusters of
alveoli are sometimes called the acinus
• The bronchioles from the sixteenth through the twenty-third divisions contain
increasing numbers of alveoli and are called respiratory bronchioles.
• The walls of the respiratory bronchioles are very thin, consisting of an epithelial
layer devoid of cilia and goblet cells, very little smooth muscle fiber, and a very
thin and elastic connective tissue layer.
• These bronchioles end in alveolar ducts, which lead to alveolar sacs made up
of numerous alveoli.
• The alveoli are the primary gas-exchange units of the lung, where oxygen enters the
blood and CO2 is removed
• Tiny passages called pores of Kohn permit some air to pass through the septa from
alveolus to alveolus, promoting collateral ventilation and even distribution of air
among the alveoli. The lungs contain approximately 50 million alveoli at birth and
about 480 million by adulthood.
FIGURE 35.4 Alveoli. Bronchioles subdivide to form tiny tubes called alveolar ducts that end in
clusters of alveoli called alveolar sacs.
• Lung epithelial cells provide a protective interface with the environment
• Essential for adequate gas exchange
• Preventing entry of foreign agents
• Regulates ion and water transport
• Maintains mechanical stability of the alveoli
• The alveolar septa consist of an epithelial layer and a thin, elastic basement
membrane but no muscle layer
• Two major types of epithelial cells (pneumocytes) appear in the alveolus.
• Type I alveolar cells provide structure
• Type II alveolar cells secrete surfactant, a lipoprotein that coats the inner
surface of the alveolus and facilitates its expansion during inspiration, which
lowers alveolar surface tension at end-expiration, thereby preventing lung
collapse (atelectasis).
• Surfactant
• Contribute to control of lung inflammation by decreasing release of
proinflammatory mediators
• Prevents oxidative injury
• Regulates the role of fibroblasts in airway remodeling.
• Bacteriostatic and function as opsonins in presenting pathogens to alveolar
macrophages.
• Macrophages are the most numerous immune cells present in the lung environment
and provide innate immune defense of the airway from the bronchi to the alveoli.
• In the alveoli, alveolar macrophages provide protection by clearing surfactant from the
lung and ingesting foreign material and pathogens that reach the alveolus, preparing
these substances for removal through the lymphatics -Phagocytosis
• Surfactant and alveolar macrophages work together with the normal pulmonary
microbiota to prevent lower lung infection.
Pulmonary and Bronchial Circulation
• The pulmonary circulation;
• provides an extensive surface area for gas exchange
• delivers nutrients to lung tissues
• acts as a blood reservoir for the left ventricle
• serves as a filtering system that removes clots, air, and other debris from the
circulation
Advanced Patho Page 4
