THE RESPIRATORY SYSTEM III

Dr. Mah Jabeen MuneeraAssistant 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

Pleural cavity – slit-like potential space filled with pleural fluid

Around each lung is a flattened sac of serous membrane called pleura

Parietal pleura Visceral pleura

Pleura

Mesothelial cells

Connective tissue

Pleural effusion - fluid

Haemothorax - blood

Pneumothorax - air

Pleuritis - infection

Clinical correlation

Asthma prolonged contraction – expiration

Lumen << – wheezing, dyspnea

Hypersecretion goblet cell, mucus/serous gl

Steroids, Β2-agonist -relax

Emphysema 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

Metaplasia

Tumors – squamous cell carcinoma

Clinical correlations

16

you might want to think twice about smoking….