The respiratory system is divided into a conducting portion and respiratory portion. The conducting portion carries air but does not allow for gas exchange, including the nasal cavities, pharynx, larynx, trachea, and bronchi. The respiratory portion, including respiratory bronchioles and alveoli, is where gas exchange occurs between inhaled air and blood. Alveoli are the basic structural and functional units of the lungs that allow for diffusion of oxygen and carbon dioxide across the blood-air barrier, composed of a thin epithelial layer, basement membrane, and endothelial lining.

2. The respiratory
system is divided
into Conducting
portion &
Respiratory
portion

3. Conducting portion:
no gaseous
exchange can occur
this part includes:
1.Nasal cavities.
2.Nasopharynx.
3.Oroopharynx.
4.Larynx.
5.Trachea.
6.Bronchi.
7.Bronchioles.

4. Respiratory portion:
gaseous exchange occurs.
This portion includes:
Respiratory bronchioles.
& lung Alveoli.
exchange of gases between the
blood and the inspired air
takes place.

5. TRACHEA
11 length x 2 width.
Starts at the end of
the Larynx & end by
dividing into 2
bronchi
The wall of the
trachea consists of 4
layers:
11
2

6. Mucosa
Submucosa
Fibro-Cartilagenous coat
Adventitia

7. Mucosa:
(A) Epithelium:
Pseudo-stratified columnar ciliated with many
goblet cells resting on clear but thin basement
membrane .
(B) The C.T.Corium:
Thin with lymphocytes & blood vessels & nerves .
Rich in elastic fibres which condenses to form
elastic membrane between the corium and the
submucosa.

8. Submucosa:
Loose areolar
connective tissue
contains
mucoserous
tracheal glands
which Open into
the surface
epithelium by
short ducts.

9. Fibro-Cartilagenous coat:
16-20 C-shaped rings of
hyaline cartilage embedded in
CT that fuse with the
perichondrium of the cartilage.
The 2 ends of the cartilage
plates are connected by smooth
muscle fibres & flattened
posteriorly opposite the
oesophagus
(4) Adventitia:
Formed of CT

12. THE LUNG
The lung represent
the main part
of the respiratory
portion of the
respiratory tract .
They consist of air
containing
chambers
called pulmonary or
lung alveoli

13. PULMONARY ALVEOLI
Structural & functional units
of the lung.
minute air spaces unit with
each other & form air sacs.
There are pores in () lung
alveoli that allow
communication.
The alveoli separated from
each other by thin inter
alveolar septum.
They are lined by two types
of cells called pneumocytes
type-1 & type-2.

14. Type-1- Pneumocytes
The most numerous 97%
L/M: - Flat squamous
cells with flat deeply
stained nucleus.
Type-2- Pneumocytes
Less numerous 3%
L/M: Cuboidal cells with
rounded large nuclei with
prominent nucieoli

15. E/M:-
little cytoplasm contains
few organells
Cells attached to each
other by tight junctions to
avoid escape of tissue
fluids to alveoli .
They can not divide.
EM:
Abundant vaculated cytoplasm
rich in rER. Mitochondria, Golgi
Complex. Multilamellar bodies
cytosomes contain
phospholipids.
Their apical surface have
microvilli.
Have the capacity to divide and
give the 2 types of pneumocytes.

16. Lamellar
bodies: electron
dense
lamellated
globules, rich in
phospholipid
and surrounded
by membrane.

17. Functions: -
Provide a very thin
membrane through which
gaseous exchange takes
place.
Secrete pulmonary surfactant
that forms a thin film over the
epithelial lining which reduce
the surface tension of lung
alveoli & help their expantion.

18. N.B.: surfactant is only secreted late in pregnancy
so premature babies usually have respiratory
distress due to deficiency of surfactant.

19. Interalveolar septum
Part in() lung Alveoli
Capillary network.
Highly vascular C.T.
rich in reticular fibres &
elastic fibres which are
important for elasticity &
support of lung tissue.

20. BLOOD AIR BARRIER
The wall through which gas
exchange occur. It is present
in() blood in the capillaries & air
within lung alveoli.
structure:
1)Thin film of pulmonary
surfactant
2)cytoplasm of pneumocyte
type I.
3)The fused basement
membrane of type I
pneumocyte and capillary
endothelium.
4)capillary endothelium.

21. ALVEOLAR phagocytes
Definition:
phagocytic cells present in
the cavities of lungs
alveoli or the
interalveolar septum.
Free cells migrating over
the luminal surface of the
lung alveoli.

22. Origin: blood monocytes
Staining : vital stain as
trypan blue
Function : phagocytose
bacteria & dust particles
& rich in lysosomes.
Fate: coughed in the
sputum or they may die
& remain in the
interalveolar septum or
the near by lymph node.

23. Types:
Dust cells:
phagocytose dust or
Carbon particles that are
inspired with air. That
appear as black particles
within them.

24. Heart failure cells:
Not present in normal persons
but in patient with heart
failure.
Congestion of blood capillaries
rupture  escape of RBCs
to alveolar cavities.
Macrophage phagocytose HB
& destroy it to red colored
hemosidrin granules that
appear within them.