System overview: anatomy, zones, basic function
Anatomy
• The respiratory system consists of tubes and cavities and the
lungs. Two zones are distinguished:
• The conducting zone: nasal cavity (cavum nasi), naso-
pharynx, oropharynx, laryngo-
pharynx, larynx, trachea, bronchi,
bronchioles.
• The respiratory zone: respiratory bronchioles, alveolar
ducts, alveoli.
• Pulmonary circulation is the movement of de-oxygenated blood from the heart
to the lungs, and oxygenated blood back to the heart again. Gas exchange (CO2
for O2) takes place in the capillary bed around the lung alveoli.
• The ventilatory pump consists of the thoracic cage, the respiratory muscles and
the elastic tissue in the lung.
Function
• The conducting zone transports and conditions (warming, moistening, cleaning)
air and plays a role in mucus transport.
• The respiratory zone and the pulmonary circulation primarily serve the gas
exchange.
• The ventilatory pump replenishes the alveoli with fresh air and expels alveolar
gas from the lungs.
Mediastinum
Key Mediastinal Structures:
• The mediastinum contains key structures like the Heart, Trachea (or main
bronchi), Aorta, Esophagus, and Superior Vena Cava (SVC).
Clinical Importance of Mediastinum:
• The mediastinum forms a complete partition between the left and right pleural
cavities.
• This is clinically important because it prevents bilateral lung collapse if one
side is punctured (pneumothorax protection) and helps localize disease or
infection to one side.
Gross lung anatomy and topography
Apex Location:
• It’s the cranial part (apex) of each lung extends above the level
of the clavicle, rising into the root of the neck.
• It typically extends about 2–3 cm (approximately 1 inch) above the
clavicle (or the first rib). The cupula (cervical pleura) also rises
above the clavicle, enclosing the lung apex.
• The apex lies posterior to the clavicle and subclavian vessels and
is covered by the suprapleural membrane (Sibson’s fascia).
Largest Lung Mass:
• The largest part of the lung mass lies posteriorly and inferiorly, primarily within
the lower lobes.
• This is because the bases are broad and rest on the diaphragm, and the
posterior thoracic cavity is deeper.
,Surfaces in Contact with Adjacent Structures:
• Costal surface (lateral): Convex surface in
contact with ribs
and intercostal
muscles (especially
ribs 1–10) and costal cartilages.
• Mediastinal surface (medial):
• In contact with the mediastinum, including the heart and pericardium
(forming the cardiac impression, especially on the left side), great vessels
(aorta, superior and inferior vena cava, pulmonary vessels), trachea and
main bronchi, and esophagus (especially posterior to the right lung).
• Diaphragmatic surface (base): Concave surface resting on the diaphragm, which
separates the lungs from the liver (right) and the
stomach/spleen (left).
• The external intercostal muscles (m. intercostalis externus (12)) are involved
in pulling up the ribs during respiration. When you exhale (detraction), the ribs
go down.
Key Characteristics and Structure:
• Bronchopulmonary segments are generally pyramid-shaped parts.
• The base of the segment is oriented toward the lung surface.
• The top of the segment points in the direction of the lung hilum.
• These segments are large divisions separated by connective tissue.
• Each segment is connected to its own segmental or tertiary bronchus (bronchus
segmentalis).
• Each segment is also connected to its own segmental arteries (arteria
segmentalis).
• The nomenclature (numbering) of the segmental bronchi and lung segments
corresponds (is analogous).
Lung hilum
• The hilum (70) is the specific area where bronchi and blood vessels enter and
leave the lungs.
• The structures that are located within the hilum of the lung (collectively known
as the root of the lung) include the pulmonary artery, the two pulmonary veins,
the principal bronchus, bronchial vessels, nerves, and lymphatics.
• A key anatomical point is that the arrangement of these structures in the lung
hilum differs between the left and right sides.
Differences Between Right and Left Lungs:
• In general, the right lung consists of 10 segments (3 in
superior lobe, 2 in middle lobe, 5 in inferior lobe)
• The left lung consists of 8–10 segments.
• The left lung is smaller due to the cardiac notch, leading
to the fusion or reduction of some segments.
The lingula of the left upper lobe is homologous to the right middle lobe.
• Specifically, segments 1+2 and/or 7+8 are sometimes combined or left out in the
left lung.
, Conducting zone structure and histology
Trachea- Respiratory epithelium
• A large part of the airways is covered by respiratory epithelium (2, misleading
name).
• This is a pseudo-layered (pseudo-stratified) columnar epithelium, containing
the following cell types:
• Ciliated columnar cells (3), with long cilia (4), and centrally located nuclei.
The cilia transport mucus towards the pharynx.
• Mucous goblet cells (5), with a basally located nucleus. The apical part of the
cells is filled with mucus.
• Brush cells (6, not indicated), with short cilia. These are sensory receptor
cells. They are very rare.
• Basal cells (7) are the stem cells of the respiratory epithelium.
• All cells reside on a basal membrane.
• The trachea is a stiff straight tube starting at the larynx and ending at the first
ramification (separation into the two principal bronchi).
Tachea wall
• The wall consists of the following layers:
A) respiratory mucosa (1) with
respiratory epithelium (2), and the
lamina propria (8) with tracheal
glands (9);
B) submucosa (12) with cartilage (13) and connective tissue in the
curved part, and the musculus trachealis (15) in the straight
membranous wall (14);
C) adventitia (16).
The lamina propria is markedly
vascularized. This supports the
warming and moistening of the
inspired air.
• In the submucosa, packages of tracheal glands are present, sometimes
surrounded by adipocytes.
• Adipocytes present as large empty cells, because the fat was washed away
during the fixation and embedding procedures.
Tracheal Bifurcation (Carina):
• The trachea begins at C6 and ends at the level of T4/T5 (sternal angle) where it
bifurcates.
• The internal ridge of cartilage marking the bifurcation is the carina.
Glands:
The tracheal glands are mixed glands: there are both mucous (10) and serous (11)
gland cells present.
• Serous glands produce a watery secretion; proteins in the serous fluid are not or
only lightly glycosylated.
Anatomy
• The respiratory system consists of tubes and cavities and the
lungs. Two zones are distinguished:
• The conducting zone: nasal cavity (cavum nasi), naso-
pharynx, oropharynx, laryngo-
pharynx, larynx, trachea, bronchi,
bronchioles.
• The respiratory zone: respiratory bronchioles, alveolar
ducts, alveoli.
• Pulmonary circulation is the movement of de-oxygenated blood from the heart
to the lungs, and oxygenated blood back to the heart again. Gas exchange (CO2
for O2) takes place in the capillary bed around the lung alveoli.
• The ventilatory pump consists of the thoracic cage, the respiratory muscles and
the elastic tissue in the lung.
Function
• The conducting zone transports and conditions (warming, moistening, cleaning)
air and plays a role in mucus transport.
• The respiratory zone and the pulmonary circulation primarily serve the gas
exchange.
• The ventilatory pump replenishes the alveoli with fresh air and expels alveolar
gas from the lungs.
Mediastinum
Key Mediastinal Structures:
• The mediastinum contains key structures like the Heart, Trachea (or main
bronchi), Aorta, Esophagus, and Superior Vena Cava (SVC).
Clinical Importance of Mediastinum:
• The mediastinum forms a complete partition between the left and right pleural
cavities.
• This is clinically important because it prevents bilateral lung collapse if one
side is punctured (pneumothorax protection) and helps localize disease or
infection to one side.
Gross lung anatomy and topography
Apex Location:
• It’s the cranial part (apex) of each lung extends above the level
of the clavicle, rising into the root of the neck.
• It typically extends about 2–3 cm (approximately 1 inch) above the
clavicle (or the first rib). The cupula (cervical pleura) also rises
above the clavicle, enclosing the lung apex.
• The apex lies posterior to the clavicle and subclavian vessels and
is covered by the suprapleural membrane (Sibson’s fascia).
Largest Lung Mass:
• The largest part of the lung mass lies posteriorly and inferiorly, primarily within
the lower lobes.
• This is because the bases are broad and rest on the diaphragm, and the
posterior thoracic cavity is deeper.
,Surfaces in Contact with Adjacent Structures:
• Costal surface (lateral): Convex surface in
contact with ribs
and intercostal
muscles (especially
ribs 1–10) and costal cartilages.
• Mediastinal surface (medial):
• In contact with the mediastinum, including the heart and pericardium
(forming the cardiac impression, especially on the left side), great vessels
(aorta, superior and inferior vena cava, pulmonary vessels), trachea and
main bronchi, and esophagus (especially posterior to the right lung).
• Diaphragmatic surface (base): Concave surface resting on the diaphragm, which
separates the lungs from the liver (right) and the
stomach/spleen (left).
• The external intercostal muscles (m. intercostalis externus (12)) are involved
in pulling up the ribs during respiration. When you exhale (detraction), the ribs
go down.
Key Characteristics and Structure:
• Bronchopulmonary segments are generally pyramid-shaped parts.
• The base of the segment is oriented toward the lung surface.
• The top of the segment points in the direction of the lung hilum.
• These segments are large divisions separated by connective tissue.
• Each segment is connected to its own segmental or tertiary bronchus (bronchus
segmentalis).
• Each segment is also connected to its own segmental arteries (arteria
segmentalis).
• The nomenclature (numbering) of the segmental bronchi and lung segments
corresponds (is analogous).
Lung hilum
• The hilum (70) is the specific area where bronchi and blood vessels enter and
leave the lungs.
• The structures that are located within the hilum of the lung (collectively known
as the root of the lung) include the pulmonary artery, the two pulmonary veins,
the principal bronchus, bronchial vessels, nerves, and lymphatics.
• A key anatomical point is that the arrangement of these structures in the lung
hilum differs between the left and right sides.
Differences Between Right and Left Lungs:
• In general, the right lung consists of 10 segments (3 in
superior lobe, 2 in middle lobe, 5 in inferior lobe)
• The left lung consists of 8–10 segments.
• The left lung is smaller due to the cardiac notch, leading
to the fusion or reduction of some segments.
The lingula of the left upper lobe is homologous to the right middle lobe.
• Specifically, segments 1+2 and/or 7+8 are sometimes combined or left out in the
left lung.
, Conducting zone structure and histology
Trachea- Respiratory epithelium
• A large part of the airways is covered by respiratory epithelium (2, misleading
name).
• This is a pseudo-layered (pseudo-stratified) columnar epithelium, containing
the following cell types:
• Ciliated columnar cells (3), with long cilia (4), and centrally located nuclei.
The cilia transport mucus towards the pharynx.
• Mucous goblet cells (5), with a basally located nucleus. The apical part of the
cells is filled with mucus.
• Brush cells (6, not indicated), with short cilia. These are sensory receptor
cells. They are very rare.
• Basal cells (7) are the stem cells of the respiratory epithelium.
• All cells reside on a basal membrane.
• The trachea is a stiff straight tube starting at the larynx and ending at the first
ramification (separation into the two principal bronchi).
Tachea wall
• The wall consists of the following layers:
A) respiratory mucosa (1) with
respiratory epithelium (2), and the
lamina propria (8) with tracheal
glands (9);
B) submucosa (12) with cartilage (13) and connective tissue in the
curved part, and the musculus trachealis (15) in the straight
membranous wall (14);
C) adventitia (16).
The lamina propria is markedly
vascularized. This supports the
warming and moistening of the
inspired air.
• In the submucosa, packages of tracheal glands are present, sometimes
surrounded by adipocytes.
• Adipocytes present as large empty cells, because the fat was washed away
during the fixation and embedding procedures.
Tracheal Bifurcation (Carina):
• The trachea begins at C6 and ends at the level of T4/T5 (sternal angle) where it
bifurcates.
• The internal ridge of cartilage marking the bifurcation is the carina.
Glands:
The tracheal glands are mixed glands: there are both mucous (10) and serous (11)
gland cells present.
• Serous glands produce a watery secretion; proteins in the serous fluid are not or
only lightly glycosylated.
