Histology of the Respiratory System

Zhihua GaoSchool of Medicine Zhejiang University

zhihuagao@zju.edu.cn

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