2. Function of Respiratory System
• Gets air into and out of the body and allows
• Conducting portion
– Nasal cavity, nasopharynx, larynx, trachea,
bronchi, bronchioles, terminal bronchioles
– Warms, moistens air
• Respiratory portion
– Respiratory bronchioles, alveolar ducts, alveoli
– Gas exchange occurs
4. Layers of Wall
– Lamina propria (loose CT)
– Smooth muscle
– Dense irregular CT
– Glands often present
5. Respiratory Epithelium
• In the conducting portion:
– Ciliated columnar cells
– Mucous goblet cells
– Brush cells (microvilli)
• Sensory receptor cells
– Basal cells
• Generative stem cells that replace other cells
– Small granule cell (DNES)
• Produce biogenic amines (NE, Ep, 5-HT); paracrine
9. Small Granule Cell
Electron micrograph of a cell
of the diffuse neuroendocrine
system. Note the
accumulation of secretory
granules (arrows) in the basal
region of the cell. The Golgi
complex seen in the upper
part of the micrograph shows
some secretory granules.
10. Nasal Passage
11. Nasal Cavity
• Vestibule (outer nasal area)
– Keratinized epithelium transitions to respiratory
– Short hairs filter
• Nasal Fossae
• Respiratory epith (pseudostratified squamous)
• Swell bodies; extensive venous system for
countercurrent flow to warm air.
• Olfactory epithelium of superior choncha
12. Nasal Mucosa
E – Epithelium
M – Mucous glands of
S – Serous glands of
V – Thin walled venules
13. Olfactory Mucosa
14. Diagram of the
16. Epithelium Lining of Sinus
• The pharynx connects the nasal cavity with the
• Depending on the extent of abrasive forces on the
epithelium, the pharynx is either lined with
respiratory epithelium (nasopharynx or
epipharynx) or with a stratified squamous
epithelium (oropharynx or meso- and
hypopharynx), which also covers the surfaces of
the oral cavity and the oesophagus.
• Lymphocytes frequently accumulate beneath the
epithelium of the pharynx.
• Accumulations of lymphoid tissues
surrounding the openings of the digestive
and respiratory passages form the tonsils.
• The nasal cavity and pharynx form the
upper respiratory passages.
19. Respiratory Structures
• The larynx connects the pharynx and trachea.
• The vocal folds of the larynx control airflow and
allow the production of sound.
• The vocal folds are lined by stratified squamous
epithelium and contain the muscle (striated,
skeletal) and ligaments needed to control the
tension of the vocal folds.
• The larynx is supported by a set of complexly
Core of Elastic Cartilage covered by a respiratory
24. The Larynx
a Resp Mucus
Membrane w/ a
rich in elastic
is seen in the wall
25. Vocal Chord – a fold in the laryngeal wall
with St Sq
• A fairly short tube (10-12 cm) with a diameter of
• Epithelium, Mucosa and Submucosa
- lined by respiratory epithelium
- cells: basal cells, ciliated cells, goblet cells,
brush cells, endocrine cells (or small granule cells,
function not clear), surfactant-producing cells (or
Clara cells), and serous cells.
- lamina propria: loose CT with many elastic
fibres, which condense at the deep border of
the lamina propria to form an elastic
- submucosa: muco-serous glands
supplement the secretions of cells in the
epithelium. The submucosa ends with the
perichondrium of the tracheal cartilages.
• Tracheal cartilages
– The trachea is stabilised by 16-20 C-shaped cartilages (hyaline
– The free dorsal ends of the cartilages are connected by bands of
smooth muscle (trachealis muscle) and connective tissue fibres.
– Longitudinal collagenous and elastic connective tissue fibres
(annular ligaments) link the individual cartilages and allow both
the lengthening and shortening of the trachea for example during
swallowing or movements of the neck. They are inseparable from
the fibres of the perichondrium.
– The tracheal cartilages may ossify with age.
30. Trachea - Mucus Membrane
Pseudostratified ciliated cells and mucous (goblet) cells are the two
major components of the epithelium. Cilia beat at 1,000 to 1,500 cycles
per minute resulting in movement of the mucus blanket at 0.5-1 mm
/min in small airways and 5-20 mm/min in the trachea and main
32. Trachea x40
34. Mucous Glands in Upper Resp Tract
37. Glands of Trachea
• The main bronchi divide into lobar bronchi which
in turn give rise to segmental bronchi.
• The latter supply the bronchopulmonary segments
of the lungs.
• Bronchial branches are accompanied by branches
of the pulmonary artery, nerves and lymph
• These structures usually travel in intersegmental
and interlobar sheets of connective tissue.
• Conductive structures of a size down to ~1
mm are termed bronchi.
• Smaller ones are called bronchioles.
• Aside from their different sizes, bronchi are
characterized by the presence of glands and
• The cartilage supporting the bronchi is
typically found in several small pieces.
• The histological structure of the epithelium
and the underlying connective tissue of the
bronchi corresponds largely to that of the
trachea and the main bronchi.
• bronchi are surrounded by a layer of smooth
muscle, which is located between the
cartilage and epithelium.
41. BRONCHIAL TREE
42. BRONCHIAL TREE
• 1, 2, 3 Bronchi
– Cartilage plates, glands present, smallest is
5mm, many lymphocytes present
– No cartilage, no glands
• Alveolar Duct
• Alveolar Sac
– Gas exchange
43. HISTOLOGY OF BRONCHIAL
– Rings, plates, disappears
Smooth Muscle Layer
Begins in bronchi, more prominent in
bronchioles, then disappears
– Pseudostratified, Simple columnar, cuboidal,
• > 5mm diameter
• No cartilage or glands in mucosa
• Epithelium changes from pseudostratified to
cuboidal epith., shortening along the way.
• Only scattered goblet cells initially.
• Clara cells secrete protective proteins.
• Lamina propria contains only smooth muscle and
• Vagus nerve, sympathetic neurons
48. Bronchiole x40
49. Alveolus, Bronchiole
50. Respiratory Structures in the
• Bronchioles divide into respiratory bronchioles,
which are the first structures that belong to the
respiratory portion of the respiratory system.
• Small outpouchings of the walls of the respiratory
bronchioles form alveoli, the site of gas exchange.
• The number of alveoli increases as the respiratory
bronchioles continue to divide.
• They terminate in alveolar ducts. The "walls" of
alveolar ducts consists of entirely of alveoli.
51. Histological Structure of Alveoli
• The wall of the alveoli is formed by a thin
sheet (~2µm) of tissue separating two
• This sheet is formed by epithelial cells and
intervening connective tissue.
• Collagenous (few and fine), reticular and
elastic fibres are present.
52. Histological Structure of Alveoli
• Between the connective tissue fibres we find a
dense, anastomosing network of pulmonary
• The wall of the capillaries are in direct contact
with the epithelial lining of the alveoli.
• The basal laminae of the epi- and endothelium
may actually fuse. Neighbouring alveoli may be
connected to each other by small alveolar pores.
53. Location of Gas Exchange
54. ALVEOLUS AND CAPILLARY
55. GAS EXCHANGE
• Respiratory membrane
• Cells present in alveolus
– Simple squamous epithelium
• Other cells in alveolus
– Surfactant cells
56. Section of a terminal bronchiole with a small portion of a respiratory
bronchiole continuous with an alveolar duct and many alveoli. Low
57. Diagram of a
portion of the
Note that the
smooth muscle in
the alveolar duct
disappears in the
58. Transition of a terminal bronchiole into an alveolar duct (arrow). Note
the Clara cells (arrowheads). Medium magnification.
59. Respiratory Duct With Alveoli
61. Alveolar Sac
62. Blood Vessel in Lung
63. Alveolus with Capillary
65. Interface Between Capillary, Alveolus
66. Alveoli and interalveolar septum
showing capillaries and epith. Cells
type I and II
67. Cells Located in Alveolus
• Type I alveolar cells
– Simple squamous cells
• Type II cells
• Macrophages (dust cells)
68. Development of the Lungs
• The formation of the lower respiratory
passages begins in the fourth foetal week.
• An outpouching of the foregut gives rise to
the laryngotracheal tube.
• The lining of this tube will eventually give
rise to the epithelia covering the surfaces of
the larynx, trachea, bronchi, bronchioles
69. Development of the Lungs
• Most of the other tissues of the lower
respiratory passages are derived from
• The laryngotracheal tube divides distally to
form two lung buds.
• Dependent of the state of maturity of the
lung, development is divided into three
70. Development of the Lungs
The bronchi grow and branch during the glandular
period, which last until approx. the 17th foetal week.
Alveoli are not present at this time.
Bronchi and bronchioles expand and branch during the
canalicular period. The lung tissue is vascularised during
the canalicular period. Bronchi and bronchioli begin to
form terminal sacs (developing primitive alveoli), in
which cuboidal and squamous cells become associated
with vessels. Respiration becomes possible towards the
end of this period around the 25th foetal week.
71. Development of the Lungs
3. The number of terminal sacs increases
during the intial part of the alveolar
• The capillary network is developing
between the terminal sacs.
• The late alveolar period is marked by the
development of mature alveoli from the
72. Development of the Lungs
• The period begins shortly before birth, but the first
mature alveoli appear only after birth.
• Alveolar sacs continue to be formed during early
childhood (up to year 8) and mature into alveoli.
• Alveolar maturation and growth continue for
another decade, but their numbers do not increase