Histology of the Respiratory System

The respiratory system consists of 3 principle regions: 1. conducting portion, consisting of the nasal cavity, nasopharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles. 2. respiratory portion, consisting of respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli.3. structures of ventilating mechanism, which creates pressure differences that move air. It includes the diaphragm, rib cage, intercostal muscles, abdominal muscles and elastic connective tissue in the lungs.

Conducting Portion

System of ducts --- conducts air to alveoli in the lungs

Function --- Conditioning of the air --- Warming, moistening and removal of particulate materials

Details of organization: 1.presence of hyaline cartilage in the larynx, trachea,

extrapulmonary and intrapulmonary bronchi. 2.elasticity of the lungs.

3. Ciliated cells and goblet cells in the epithelium4. Changes in the epithelium from the nasal cavity to

the alveoli of the lungs:Pseudostratified Columnar => Simple Columnar

=>Simple Cuboidal => Simple Squamous.

Conducting Portion

Larynx Tube kept open hyaline or elastic (Epiglottis)

cartilage Skeletal muscle surrounds cartilage on outside

and present between the cartilage and mucosa

Mucosa Pseudostratified columnar epithelium containing

cilia and goblet cells Unkeratinized stratified squamous epithelium –

only in the epiglottis and the vocal folds

Mucosa has pseudostratified columnar epithelium with cilia and goblet cells

Submucosa has mixed glands 20 C-shaped hyaline cartilages

Trachea

Low Magnification of a Cross Section Through the Trachea

1. Lumen2. Pseudostratified ciliated

columnar epithelium3. Submucosa4. Hyalin cartilage5. Perichondrium6. Adventitia7. Mixed glands8. Secretory duct

Epithelium of the Trachea

1. Lumen2. Cilia3. Columnar epithelial cells4. Prominent thick basal membrane5. Lamina propria6. Basal cell layer7. Goblet cell

Bronchianatomy:

Two main extrapulmonary bronchi -- histologically similar to the trachea

Intrapulmonary bronchi– Primary bronchi - Lobar bronchi - Secondary bronchi -- Segmental bronchi- Tertiary bronchi - interlobular bronchi

Intrapulmonary Bronchi Pseudostratified columnar epithelium

containing cilia and goblet cellsSmooth muscle - between mucosa

and cartilage Mixed glands lie between muscle

layer and cartilagous plates Cartilage - Irregular shaped

cartilaginous plates

Bronchi Three-dimensional Representation of an Intrapulmonary Bronchus

cartilage platelamina propria

pseudostratified columnar epithelium with cilia and goblet cells

smooth muscle

Bronchioles – smallest branches of bronchi:

Preterminal bronchiole penetrate lobule at its apex and enter inside the lobule, branches into terminal bronchioles

Bronchioles:Epithelium

in the larger bronchioles -- Simple columnar, in smaller bronchioles --- tall cuboidal

Goblet cells have disapeared and cells of Clara (tall, non-ciliated

secretory cells, produce surfactant) – apeare

BronchiolesNo glands or cartilage are present

Bronchioles Three-dimensional

Representation of a Preterminal

Bronchiole Schematic

Representation of the Cells of Clara

mucosasimple columnar epitheliumlamina propriacells of Clara

smooth muscle

neuro-epithelial body

cells of Clara

Respiratory Portion

Respiratory Portion

Consists of smaller ducts and sacs Lie inside lung lobules Provides exchange of gases

Lung Lobules Schematic Representation of a Lung Lobule

bronchiolus

pulmonary artery

lymphatic vessel

pulmonary vein

preterminal bronchiole

respiratory bronchioles

alveoli

visceral layer

parietal layer

Respiratory Bronchioles

Branch from terminal bronchioles and have Alveoli - thin bulging sacs - in walls

Gas exchange takes place in alveoli

Respiratory Bronchioles Schematic of the Respiratory

Portion of a Lung Lobule

Smooth musclerespiratory bronchiole

alveolar ductsalveoli

interalveolar septum

sacculus alveolaris

Respiratory Bronchiole

1. High cuboidal epithelium2. Alveolus

3. Interalveolar septum4. Lumen

Alveolar ducts -- long air passages , Alveolar sacs – round air spaces surrounded by clusters of

alveoli

Interalveolar septa – connective tisue - separate neighboring alveoli

Alveolar pores -- direct contact between 2 alveoli

The Lung Demonstrating the Basic Structures

1. Alveolar sacs2. Alveoli3. Interalveolar septa

Epithelium of Alveoli

Has two types of cells 1. Pneumocyte (or alveolocytes) type I (Simple

squamous alveolar epithelium)

2. Pneumocyte type II (Surfactant secreting cells) (NOTE: surfactant decrease surface tension in alveoli preventing their collapsing)

Alveolar macrophages (dust cells) – present in the cavity

1. Carbon particles2. Pneumocyte type II (Surfactant secreting cells)3. Pneumocyte type I

Barrier between Air and Blood

Cytoplasm of epithelium lining the alveoli Basal lamina of the epithelium Basal lamina of the capillary endothelium Cytoplasm of capillary endothelium

Blood Vessels

Branches of pulmonary artery form capillaries in interalveolar septa (carry deoxygenated blood)

Bronchial arteries supply walls of bronchi and connective tissue

Acinus is Structural and Functional Unit of the Lung

Control questions

Name, group Topic of the lecture Air-conducting structures – general plane

of organization:

-- epithelium – cells?

----another layers ?