Histology of the Respiratory System
Zhihua GaoSchool of Medicine Zhejiang University
Components of the respiratory system
NosePharynxLarynxTracheaBronchiLung
Upper respiratory tract
Lower respiratory tract
Portions of the respiratory system
The conducting portionNasal cavity, pharynx, larynx, trachea, bronchi, bronchiolesTerminal bronchiolesFunctions: to warm, humidify and clean inhaled air
The respiratory portionRespiratory bronchioles, aveolar ducts, alveolar sac, alveoliFunction: to exchange gas
Main divisions of the respiratory tract
Bronchial trees 气管树
Trachea (气管) and main bronchi (主支气管)
General structure of the trachea
Layers of trachea
• Mucosa 粘膜– Epithelium– Lamina propria (loose CT)– Smooth muscle
• Submucosa 粘膜下层– Loose CT– Glands often present
• Adventitia 外膜
MucosaSubmucosa
Adventitia
Mucosa Submucosa Adventitia
Three layers of the trachea
Epithelium: pseudostratified ciliated columnar epithelium Lamina propria: CT, contain LC, PC, MC, BV, LV
Mucosa
Epithelium
Lamina propria
Pseudostratified ciliated columnar epithelium
• Ciliated cells: columnar with cilia• Goblet cells• Basal cells:• Brush cells• Small granule cells
Pseudostratified ciliated cells and mucous (goblet) cells are the two major components of theepithelium.* Clear basement membrane
*
---pyramidal shape,---basally-located---undifferentiated cells, can differentiate intociliated cell or goblet cell
Basal cells
Surface of Respiratory Mucosa
Ciliated cell Goblet cell Brush cell
Loose connective tissue with blood vessels, lymphatic vessels and nodes
Tracheal glands, mixed glands
Submucosa 黏膜下层
• 16-20 “C ” shaped cartilage rings• Circular ligament: elastic fibers
Adventitia
In the posterior part of the trachea (membrane part), the adventitia contains smooth muscle, elastic fiber, tracheal glands
Adventitia
Lung 肺
paired organ, Located in thoracic Cavity.
Capsule: visceral layer of pleura-serous membrane mesotheliumand connective tissueParenchyma: all branches ofbronchi and alveoli (right 3, left 2)Interstitial substance:connective tissue, blood vessels, lymphatic vessels, nerves
General structure of the lung
Bronchial trees 气管树
Primary bronchi
Intrapulmonary bronchial
lobar bronchial
small bronchi
segmental bronchi
bronchioles
terminal bronchioles
Respiratory bronchioles
Conducting portion
Respiratory portion
Alveolar duct
Alveolar Sac
Alveoli
The conducting portion 导气部
Mucosa respiratory epithelium lamina propria: thinner, SM
Submucosa: mixed glands Adventitia: cartilage plate
Lobar bronchi to smallbronchi
Small bronchi 小支气管
Diameter<1mm Gradually reduced goblet cells, glands and cartilage (may even disappear) smooth muscles appear circular mucosa plica
Bronchiole 细支气管
Bronchiole (细支气管) and Pulmonary lobule (肺小叶)
• Cone or pyramidal-shaped: apex pointed toward the hilum and basal(1.0 cm in D) faced the surface
• More CT between them
All branches and alveoli of a bronchiole
Diameter < 0.5 mm Absence of goblet cells, glands and cartilage (may even disappear) Simple columnar epithelium: two types of cells Smooth muscles form a whole circumferential layer Circular mucosa plica
Terminal bronchiole 终末细支气管
Ciliated cells Exocrine cells/
Clara /club cells
Two types of cells in the simple columnar epithelium
EM: dome-shaped apical SER Secreting granules contain
proteolytic enzyme and oxidase
Clara cells Clara cells
Various functions of Club cells
Secretion of surfactant lipoproteins and mucins in fluid layer on the epithelialsurface
Detoxification of inhaled xenobioticcompounds by enzymes of the SER,
Secretion of antimicrobial peptides and cytokines for local immune defense.
Summary of the conducting portion
Bronchi
Bronchiole
Terminal bronchiole
The respiratory portion 呼吸部/换气部
The respiratory portion consists of:– Respiratory bronchioles– Alveolar ducts– Alveolar sacs– Alveoli
• Similar to terminal bronchioles• Simple ciliated columnar cells simple cuboidal cellssimple squamous
epithelium• Thin smooth muscle• Some alveoli openings to the lumen
The respiratory portionRespiratory bronchiole 呼吸性细支气管
• Simple cuboidal epi. or squamous epi.• SM: single, EF- knob-liked structure
Alveolar duct 肺泡管
Connection with 20-60 alveoliThe wall is incomplete due to the openingsResidual smooth muscles and elastic fibers form the knobs between alveoli
Alveolar sac 肺泡囊
alveolar sac
many alveoli openningsno proper wall, no knob-liked structure
3
Alveoli 肺泡Polygonal, with opening sac- 0.2mm in diameter, 300-400 million/per lung, total area: 70-80 mm2
Wall: epithelium and basal laminaAlveolar septum: connective tissue rich in blood vessels and elastic fibers
Alveolar epithelium: type I alveolar cell
LM: flattened, 0.2um, round nucleusEM:Plasma lemmal vesicles, tight junctionFunction: constitute the blood-air barrier
Type II alveolar cellScattered, 5-8/per alveolus
LM: cuboidal or round, with round nucleus, pale-stained, foamy cytoplasm
EM: secreting granules: Osmiophilic multilamellar body, 0.1-1.0 um, contains: phospholipid,glycosaminoglycan and protein, microvilli, mitochondria, lysosome, RER, Golgi complex
Function: to secret surfactant
Summary of the respiratory portion
Features of the air ways within the lung
Connective tissue, elastic fibers, fibroblasts, macrophages, plasma cells, mast cellsCapillaries: endothelium & basement membrane
Alveolar septum
the structure through whichthe exchange takes place
The blood-air barrier comprises: A layer of liquid Type I alveolar cell andBM Connective tissue Capillary endothelial cell and BM
Blood-air barrier 血-气屏障
The interface between the capillary and the alveolus
Alveolar pore: 10-15 umEqualize (balance) the air-pressure between alveoliLobe pneumonia - bacteria or inflammatory agents spread through the pores
Alveolar macrophages
dust cells: macrophages that phagocytose carbon or dust particles
Questions
1.Compare the structure of bronchiole with that of terminalbronchiole.
2.D the morphology and function of type I cell and type II cell in lung in detail.
3.What is the air-blood barrier (or respiratory memebrane) composed of ?
4. Describe the blood circulation of lung.
heart failure cell:
the alveolar marcophage phagocytose RBC
digest the hemoglobin
hemosiderin (pigment)
accumulated them withinmacrophage
In congestive heart failure
Clinical Considerations
1. Asthma(哮喘)
• B. Emphysema(肺气肿)
• -results from destruction of alveolar walls and formation oflarge cyst like sacs, reducing the surface available for gasexchange.
• - is marked by decreased elasticity of the lungs, whichare unable to recoil adequately during expiration. In time,the lungs become expanded and enlarge the thoraciccavity(“barrel chest”)
• - is associated with exposure to cigarette smoke andother substances that inhibit α1–antitrypsin, a protein thatnormally protects the lungs from the action of elastaseproduced by alveolar macrophages.
neonatal respiratory distress syndrome