The respiratory system is divided into Conducting portion & Respiratory portion

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.

Respiratory portion:

gaseous exchange occurs.

This portion includes:

Respiratory bronchioles.

& lung Alveoli.

exchange of gases between the blood and the inspired air takes place.

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

Mucosa

Submucosa

Fibro-Cartilagenous coat

Adventitia

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.

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

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

THE LUNGThe lung represent the main part of the respiratory portion of the respiratory tract . They consist of air containing chamberscalled pulmonary or lung alveoli

PULMONARY ALVEOLIStructural & 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.

Type-1- PneumocytesThe most numerous 97%

L/M: - Flat squamous cells with flat deeply stained nucleus.

Type-2- PneumocytesLess numerous 3%

L/M: Cuboidal cells with rounded large nuclei with prominent nucieoli

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.

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

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.

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

Interalveolar septumPart in() lung Alveoli

Capillary network.

Highly vascular C.T.

rich in reticular fibres & elastic fibres which are important for elasticity & support of lung tissue.

BLOOD AIR BARRIERThe 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.

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.

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.

Types: Dust cells:

phagocytose dust or

Carbon particles that are

inspired with air. That

appear as black particles

within them.

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.