Respiratory system
•
It
consists of paired lungs and a series of air passages that lead to and form the
lungs.
Function
•
Air
conduction
•
Air
filtration
•
Gas
exchange
•
In
addition, air passing through the larynx produce speech
•
The
olfactory mucosa of nasal cavities carries sense of smell
The air passages of respiratory system consists of a
conducting portion and a respiratory portion
Extrapulmonary region
•
Nasal
cavities
•
Pharynx
•
Larynx
•
Trachea
•
Bronchi
The intrapulmonary
region
•
Intrapulmonary
bronchi
•
Bronchioles
•
Terminal
bronchioles
•
Respiratory
bronchioles
•
Alveolar
duct
•
Alveoli
Olfactory epithelium
The olfactory chemoreceptors are located in the olfactory
epithelium, a specialized area of the mucous membrane in the superior conchae,
located in the roof of the nasal cavity.
It is a pseodostratified ciliated columnar epithelium
composed of three types of cells
•
Supporting
cell
•
Olfactory
cell
•
Basal
cell
Lamina propria is
richly vascularized and possesses Bowman’s glands which produce a watery mucus
The respiratory epithelium
•
Most
of the conducting portion is lined with ciliated pseudostratified columnar
epithelium that contain rich population of goblet cells and is known as
respiratory epithelium
Typical respiratory epithelium
consists of 5 cell types
Ciliated cells: Tall columnar cells with cilia that project
into the mucus covering the surface of epithelium
Goblet cells : That synthesize and
secrete mucus
Brush cells: Bear short, blunt
microvilli
Small granule cells: That resemble basal cells
but contain secretory granules
Basal cells : Stem cells from which the other
cell types arise
Trachea
is a short, flexible, air tube about 2.5 cm in
diameter and about 10 cm long
The wall of the trachea consists of four
definable layers
Mucosa: Composed of a ciliated pseusostratified
epithelium and an elastin, fiber-rich lamina propria
Submucosa : Contains denser conn. tissue than the
lamina propria
Cartilaginous
layer : Composed the C shaped hyaline cartilages. Fibroelastic tissue &
smooth muscle , the trachealis muscle , bridge the gap between the free ends of
the C shaped cartilages at the posterior border of the trachea
Adventitia:
Composed of conn. Tissue that binds the trachea to adjacent structures
Bronchus
Bronchus are
two type extra pulmonary bronchus and intra pulmonary bronchus
a
bronchus is lined by the respiratory
epithelium with goblet cells and columnar ciliated cells.
lamina propria (connective tissue ) contains
serous glands and smooth muscle (SM).
Extra
pulmonary Bronchus is surrounded by a continuous plate of cartilage but intra
pulmonary bronchus is surrounded by discontinuous cartilaginous plates
Outer most
part of bronchus is covered by adventitia a collagen fibres rich connective
tissue
Terminal bronchiole
Difference between bronchus
and bronchioles are : bronchus is surrounded by cartilage and bronchiole is not
surrounded by cartilage
• The smallest conducting bronchioles are referred to as
terminal bronchioles
• They are lined with the simple cuboidal epi. Interspersed
with clara cells
• No cartilage plates
• No glands
• No goblet cell
• Well developed and continuous smooth muscle cells layer are surrounded the thin lamina propria of terminal
bronchiole
• Outer most part is surrounded by the adventitia
Respiratory
bronchioles
The
difference between terminal and respiratory bronchiole are :
Terminal
bronchiole contain continuous layer of smooth muscles cells and respiratory bronchiole
contain discontinuous smooth muscle cells layer
• It is lined by simple cudoidal epithelium consisting of
some ciliated cells and clara cells
• Clara cells have three functions:
- They produce one components of surfactant
- They act as a reserve cells
- They detoxify the noxious substances
• Alveolar outpocketing are found in the wall of respi.
bronchioles
• A thin, incomplete layer of smooth muscle surrounded the
epithelium
• Each res. Bronchioles gives rise to an alveolar ducts into
which open numerous alveoli.
Alveoli
• They are the site of gas exchange
• Each alveoli consists of a pocket, open at one side and
surrounded by a rich network of pulmonary capillaries
• the wall between adjacent alveoli is called the alveolar
septum. It is formed by two layers of alveolar epithelium with their
basement membranes and capillaries. The alveolar septa contain small
openings called alvealar pores which allow equalisation of pressure
between alveali and provide a collateral air circulation
Alveoli:
its
epithelium is composed of type I & II alveolar cells & occasional brush
cells
Type I
alveolar cells/ type I pneumocytes are extremely thin squamous cells that line
most (95%) of surface of the alveoli. But number of type II alveolar cells are
more than the type I alveolar cells
They are
not capable of cell division
•
Type II pneumocytes or
septal cells are secretory cells
•
These are cuboidal
cells
•
The number of the cell
is more than the type I pneumocytes
•
They retain capacity
for cell division & can differentiate into type I pneumocyte
•
They secrete
surfactant
Surfactant: A surface-active material which reduces surface tension within the
alveoli , preventing alveolar collapse
during expiration
•
Secretion of
surfactant by a type II cell. Surfactant is a protein-lipid complex synthesized
in the rough endoplasmic reticulum and Golgi complex and stored in the lamellar
bodies. It is continuously secreted by means of exocytosis (arrows)
