THE RESPIRATORY SYSTEM III
Dr. Mah Jabeen Muneera
Assistant professor
Department of Anatomy
KEMU
RESPIRATORY BRONCHIOLE

Arise from terminal bronchiole

Diameter < 0.5mm

Transition between conducting &
respiratory subdivisions

Structurally similar to terminal
bronchioles EXCEPT

Walls interrupted by out pocketings
(alveoli)– gas exchange

Epithelium
 Ciliated cuboidal in larger
 Simple cuboidal in smaller

Lamina propria
 Smooth muscles
 Fibroelastic tissue
ALVEOLAR DUCT
 Arise from respiratory
bronchioles
 Completely lined by alveoli
 Epithelium
 Simple squamous
 Smooth Muscles
 Smooth muscles DISAPPEAR
at end of alveolar duct
 Only elastic & collagen fibers
support the wall
ALVEOLAR SACS
 Arise from alveolar duct
 Epithelium
 Simple squamous
 Wall has:
 Elastic fibers-for
expansion
 Reticular fibers- to
prevent over distension
 Capillaries embedded in
this CT
ALVEOLI

Sac like evaginations open on one
side

Size 200 µm

Between adjacent alveoli is
interalveolar septum
 Elastic & reticular fibers
 Macrophages, fibroblast, mast cells
 Continuous capillary bed (from
pulmonary artery  vein)

Air in alveoli separated from capillary
blood by respiratory membrane made
of
 Alveolar cells
 Fused basal lamina of alveolar cell
& capillary endothelium
 Cytoplasm of endothelial cell
Jeanne Adiwinata Pawitan
 Alveoli surrounded by fine elastic fibers
 Alveoli interconnect via alveolar pores of Kohn– equalize air
pressure, collateral ventilation
 Alveolar macrophages – free floating “dust cells”—Heart
Failure Cells
 Alveolar cells
 Type I pneumocytes/alveolar cells - squamous alveolar cells) – tight
junction – basal lamina – very thin region  permeable to gasses
 Type II pneumocytes/alveolar cells - great alveolar cell – septal cells –
surfactant – surface tension decreased
 prevents collapse
 Alveolar lining regeneration
 This “Air-blood barrier” (the respiratory membrane)
is where gas exchange occurs
 Oxygen diffuses from air in alveolus (singular of alveoli) to
blood in capillary
 Carbon dioxide diffuses from the blood in the capillary
into the air in the alveolus
Alveolar cells
Surfactant
 Type II alveolar cells scattered in alveolar walls
 Microvilli over free surface
 Lamellar bodies
 Phospholipids, surfactant proteins (A, B, C & D)
 Surfactant is a detergent-like substance which is secreted in
fluid coating alveolar surfaces – it decreases surface tension
 Without it the walls would stick together during expiration
 Respiratory Distress Syndrome
 Premature babies – problem breathing is largely because they
lack surfactant
 Role of Steroids
Pleura
Around each lung is a
flattened sac of serous
membrane called pleura
Parietal pleura
Visceral pleura
Pleural cavity – slit-like potential space filled with
pleural fluid
Pleura
 Mesothelial cells
 Connective tissue
 Pleural effusion - fluid
 Haemothorax - blood
 Pneumothorax - air
 Pleuritis - infection
Clinical correlation
 Emphysema
 Asthma
 prolonged contraction – expiration
 Lumen << – wheezing, dyspnea
 Hypersecretion goblet cell, mucus/serous gl
 Steroids, Β2-agonist -relax
 Longterm exposure- cigarette smoke ≈ inh
– antitrypsin >< elastase – dust cells –
elastic fiber destructed
 Fibrosis
 Increased activity of fibroblasts in response
to diseases causing distress
normal
emphysema
Clinical correlations
 Metaplasia
 Tumors – squamous cell carcinoma
you might want to think twice about
smoking….
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