Histology of Respiratory system

Portion of respi tract

Conducting part

Respiratory part

From nose to terminal bronchiole

To piping air to and from the lungs

From respiratory bronchiole to alveoli

Gaseous exchange btw air and blood

Structurally

Upper respiratory tract

Lower respiratory tract

Trachea

Bronchi

Bronchioles

Pulmonary alveoli

Nasal cavity

Pharynx

Larynx

Conducting portion

Respiratory portion

Principle feature

Trachea

Epithelium

Hyaline cartilage

Elastic Fibers

Smooth ms

Cleansing the inspired air

Humidify

Warming

Changes along respi tract

Nasal to end bronchus

Pseudostratified ciliated columnar epithelium

Bronchus to conducting bronchiole (terminal bronchiole)

Simple ciliated columnar epithelium

Respiratory bronchiole

Simple ciliated cuboidal epithelium

Alveolar duct

Simple CUBOIDAL epithelium

Alveoli

Simple SQUAMOUS epithelium

Up to end of bronchus

Below bronchus have no cartilage

Found thru out respi tract up to alveoli

Line the tract up to alveolar duct

3 layers

Mucosa

Submucosa

Adventitia

Epithelium

Pseudostratified ciliated columnar AND Goblet cell

Lamina propria

Thin, loose connective tissue and abundance fibroelastic fibres

Dense connective tissue

Contain seromucous gland

Mucus is thick sticky substance that act in collecting debris for swallowing

Serous fluid is thinner runny substance that keep the epithelial tissue moist and lubricated

Consist of loose connective tissue with blood vessel, nerve and fat cell

Contain cartilage connected by fibrous membrane

C-shaped hyaline cartilage ring open posteriorly

Open interval is filled in by fibro-elastic tissue and trachealis ms

Bronchus

Trachea divide into right and left primary bronchi (extra-pulmonary) at sternal angle

Bronchus enter lung and subdivide into intra-pulmonary bronchi within lung

Primary bronchi has same basic structural pattern as trachea EXCEPT

Cartilage are arranged in complete circular rings

Smooth ms layer within cartilage ring in spiral fashion

Mucosa

Epithelium

PSCCE with globlet cell

Lamina propria

Separated from submucosa by discontinuous layer of smooth ms (Muscularis mucosae)

Run in spiral manner and progressively become more prominent in lower part of the airway

Submucosa

Contain sero-mucous gland

Gland decrease in number and size as the bronchi grow smaller

Solitary lymph nodules are presents

Adventitia

Extra pulmonary bronchus, hyaline cartilage ring completely encircle the lumen

Intra pulmonary bronchus, hyaline cartilage arranged in isolated plates

Bronchioles

No cartilage

No glands

Each bronchioles subdivided and branches into 5-7 terminal bronchioles

Each terminal bronchioles subdivided into 2 or more respiratory bronchioles

Respiratory bronchioles is similar to terminal bronchioles except its wall are interrupted by numerous alveoli

Mucosa

Simple ciliated columnar epithelium

Gradually replaced by simple ciliated cuboidal epithelium in respi bronchioles

Goblet cell less

Submucosa

Lamina propria is loose connective tissue with blood vessel

Many elastic fiber

Intermingle wif smooth ms forming spiral network

Smooth ms is the most prominent feature of bronchiole and effectively controls resistance to airflow within lung

No gland and no lymphoid tissue

Adventitia

Thin consist of collagen fibers

No cartilage

Terminal Bronchiole

Clara cell

Non-ciliated cell, apical projection

Protein secreting cell

Prevent luminal adhesion and airway collapse

Respiratory bronchioles

Simple ciliated cuboidal epithelium

No cartilage ,no gland ,no goblet cell

lamina propria is thin and loose and consist of spiral network of smooth ms and elastic fibers

Wall is interrupted by little out - pouching of alveoli (increase in number)

Each respi bronchioles divides into long thin walled tubes called alveolar ducts

Alveolar Duct

Discontinuous wall

Simple cuboidal cell

Spiral smooth ms are reduced to tiny local knobs

Lead to alveolar sacs

Alveolar sac

Simple squamous

Alveolar pore in the wall of alveolus communicate wif adjacent alveoli

Wall consist of elastic fibres

No ms, No cartilage no gland

Alveolus

Simple squamous

2 type of cell

Type I

Simple squamous cell

Gaseous exchange

Type II

Cuboidal cell

Produce surfactant

Interalveolar septum

Supporting tissue btw 2 alveoli

Consist of elastic fibers ,reticular cell and fibers ,dust cell (alveolar macrophage) and capillary

Blood-air barrier

3 layers

Epithelium of capillary

Epithelium of alveoli

Basement membrane