RESPIRATORY SYSTEM

Function of Respiratory System

• Gets air into and out of the body and allows gas exchange

• Conducting portion– Nasal cavity, nasopharynx, larynx, trachea,

bronchi, bronchioles, terminal bronchioles – Warms, moistens air

• Respiratory portion– Respiratory bronchioles, alveolar ducts, alveoli– Gas exchange occurs

Main Divisions of Respiratory

Tract

Layers of Wall

• Mucosa– Epithelium– Lamina propria (loose CT)– Smooth muscle

• Submucosa– Dense irregular CT– Glands often present

• Adventitia

Respiratory Epithelium

• In the conducting portion:– Ciliated columnar cells– Mucous goblet cells– Brush cells (microvilli)

• Sensory receptor cells

– Basal cells• Generative stem cells that replace other cells

– Small granule cell (DNES)• Produce biogenic amines (NE, Ep, 5-HT); paracrine

cells

Respiratory Epithelium

Ciliated Columnar

Cells

Surface of Respiratory

Mucosa

Ciliated cell

Goblet cell

Brush cell

Small Granule Cell(DNES)

Electron micrograph of a cell of the diffuse neuroendocrine system. Note the accumulation of secretory granules (arrows) in the basal region of the cell. The Golgi complex seen in the upper part of the micrograph shows some secretory granules.

Nasal Passage

Turbinates

Nasal Cavity

• Vestibule (outer nasal area)– Keratinized epithelium transitions to respiratory– Short hairs filter

• Nasal Fossae– Chonchae

• Respiratory epith (pseudostratified squamous)

• Swell bodies; extensive venous system for countercurrent flow to warm air.

• Olfactory epithelium of superior choncha

Nasal Mucosa

E – EpitheliumM – Mucous glands of lamina propriaS – Serous glands of lamina propriaV – Thin walled venules

Olfactory Mucosa

Diagram of the Olfactory

Epithelium

Sinuses

Epithelium Lining of Sinus

Thinner respiratoryepithelium thatcontains fewgoblet cells.

Pharynx

• The pharynx connects the nasal cavity with the larynx.

• Depending on the extent of abrasive forces on the epithelium, the pharynx is either lined with respiratory epithelium (nasopharynx or epipharynx) or with a stratified squamous epithelium (oropharynx or meso- and hypopharynx), which also covers the surfaces of the oral cavity and the oesophagus.

• Lymphocytes frequently accumulate beneath the epithelium of the pharynx.

Pharynx

• Accumulations of lymphoid tissues surrounding the openings of the digestive and respiratory passages form the tonsils.

• The nasal cavity and pharynx form the upper respiratory passages.

Respiratory Structures

LARYNX

Anterior Posterior

LARYNX

Larynx

• The larynx connects the pharynx and trachea. • The vocal folds of the larynx control airflow and

allow the production of sound. • The vocal folds are lined by stratified squamous

epithelium and contain the muscle (striated, skeletal) and ligaments needed to control the tension of the vocal folds.

• The larynx is supported by a set of complexly shaped cartilages.

Epiglottis

Core of Elastic Cartilage covered by a respiratory mucus membrane

The Larynx

a Resp Mucus Membrane w/ a lamina propria rich in elastic

Cartilage support is seen in the wall

Vocal Chord

Vocal Chord – a fold in the laryngeal wall

covered with St Sq Non-K Epith with fibroelastic LP and core of skeletal muscle (VM)

TRACHEA

TRACHEA

• A fairly short tube (10-12 cm) with a diameter of ~2 cm

• Epithelium, Mucosa and Submucosa

- lined by respiratory epithelium

- cells: basal cells, ciliated cells, goblet cells, brush cells, endocrine cells (or small granule cells, function not clear), surfactant-producing cells (or Clara cells), and serous cells.

TRACHEA

- lamina propria: loose CT with many elastic fibres, which condense at the deep border of the lamina propria to form an elastic membrane.

- submucosa: muco-serous glands supplement the secretions of cells in the epithelium. The submucosa ends with the perichondrium of the tracheal cartilages.

TRACHEA

• Tracheal cartilages – The trachea is stabilised by 16-20 C-shaped cartilages (hyaline

cartilage). – The free dorsal ends of the cartilages are connected by bands of

smooth muscle (trachealis muscle) and connective tissue fibres. – Longitudinal collagenous and elastic connective tissue fibres

(annular ligaments) link the individual cartilages and allow both the lengthening and shortening of the trachea for example during swallowing or movements of the neck. They are inseparable from the fibres of the perichondrium.

– The tracheal cartilages may ossify with age.

Trachea - Mucus Membrane

Trachea

Pseudostratified Epithelium

Pseudostratified ciliated cells and mucous (goblet) cells are the two major components of the epithelium. Cilia beat at 1,000 to 1,500 cycles per minute resulting in movement of the mucus blanket at 0.5-1 mm/min in small airways and 5-20 mm/min in the trachea and main bronchi.

Trachea x40

Trachea

Mucous Glands in Upper Resp Tract

Trachea x10

Trachea x10

Glands of Trachea x40

Bronchi

• The main bronchi divide into lobar bronchi which in turn give rise to segmental bronchi.

• The latter supply the bronchopulmonary segments of the lungs.

• Bronchial branches are accompanied by branches of the pulmonary artery, nerves and lymph vessels.

• These structures usually travel in intersegmental and interlobar sheets of connective tissue.

Bronchi

• Conductive structures of a size down to ~1 mm are termed bronchi.

• Smaller ones are called bronchioles. • Aside from their different sizes, bronchi are

characterized by the presence of glands and supporting cartilage.

• The cartilage supporting the bronchi is typically found in several small pieces.

Bronchi

• The histological structure of the epithelium and the underlying connective tissue of the bronchi corresponds largely to that of the trachea and the main bronchi.

• bronchi are surrounded by a layer of smooth muscle, which is located between the cartilage and epithelium.

BRONCHIAL TREE

Primary

SecondaryTertiary

BRONCHIAL TREE

• 1, 2, 3 Bronchi– Cartilage plates, glands present, smallest is

5mm, many lymphocytes present

• Bronchioles– No cartilage, no glands

• Alveolar Duct• Alveolar Sac

– Gas exchange

• Alveolus

HISTOLOGY OF BRONCHIAL TREE

• Cartilage– Rings, plates, disappears

Smooth Muscle LayerBegins in bronchi, more prominent in bronchioles, then disappears

• Epithelium– Pseudostratified, Simple columnar, cuboidal,

squamous

Bronchus

Cartilage

BronchusLamina propria

Bronchioles

• > 5mm diameter• No cartilage or glands in mucosa• Epithelium changes from pseudostratified to

cuboidal epith., shortening along the way.• Only scattered goblet cells initially.• Clara cells secrete protective proteins.• Lamina propria contains only smooth muscle and

elastic fibers.• Vagus nerve, sympathetic neurons

Bronchiole x10

Bronchiole x40

Alveolus, Bronchiole

Respiratory Structures in the Lung

• Bronchioles divide into respiratory bronchioles, which are the first structures that belong to the respiratory portion of the respiratory system.

• Small outpouchings of the walls of the respiratory bronchioles form alveoli, the site of gas exchange.

• The number of alveoli increases as the respiratory bronchioles continue to divide.

• They terminate in alveolar ducts. The "walls" of alveolar ducts consists of entirely of alveoli.

Histological Structure of Alveoli

• The wall of the alveoli is formed by a thin sheet (~2µm) of tissue separating two neighbouring alveoli.

• This sheet is formed by epithelial cells and intervening connective tissue.

• Collagenous (few and fine), reticular and elastic fibres are present.

Histological Structure of Alveoli

• Between the connective tissue fibres we find a dense, anastomosing network of pulmonary capillaries.

• The wall of the capillaries are in direct contact with the epithelial lining of the alveoli.

• The basal laminae of the epi- and endothelium may actually fuse. Neighbouring alveoli may be connected to each other by small alveolar pores.

Location of Gas Exchange

ALVEOLUS AND CAPILLARY

GAS EXCHANGE

• Respiratory membrane– Layers

• Cells present in alveolus– Simple squamous epithelium

• Other cells in alveolus– Macrophages– Surfactant cells

Section of a terminal bronchiole with a small portion of a respiratory bronchiole continuous with an alveolar duct and many alveoli. Low magnification.

Diagram of a portion of the bronchial tree. Note that the smooth muscle in the alveolar duct disappears in the alveoli. (Redrawn from Baltisberger.)

Transition of a terminal bronchiole into an alveolar duct (arrow). Note the Clara cells (arrowheads). Medium magnification.

Respiratory Duct With Alveoli

Alveolus

                                                                            

Alveolar Sac

Blood Vessel in Lung

Alveolus with Capillary

Interfacebetweencapillary

and alveolus

Interface Between Capillary, Alveolus

Alveoli and interalveolar septum showing capillaries and epith. Cells

type I and II

Cells Located in Alveolus

• Type I alveolar cells– Simple squamous cells

• Type II cells– Surfactant

• Macrophages (dust cells)

Development of the Lungs

• The formation of the lower respiratory passages begins in the fourth foetal week.

• An outpouching of the foregut gives rise to the laryngotracheal tube.

• The lining of this tube will eventually give rise to the epithelia covering the surfaces of the larynx, trachea, bronchi, bronchioles and alveoli.

Development of the Lungs

• Most of the other tissues of the lower respiratory passages are derived from splanchnic mesoderm.

• The laryngotracheal tube divides distally to form two lung buds.

• Dependent of the state of maturity of the lung, development is divided into three periods:

Development of the Lungs

1. The bronchi grow and branch during the glandular period, which last until approx. the 17th foetal week. Alveoli are not present at this time.

2. Bronchi and bronchioles expand and branch during the canalicular period. The lung tissue is vascularised during the canalicular period. Bronchi and bronchioli begin to form terminal sacs (developing primitive alveoli), in which cuboidal and squamous cells become associated with vessels. Respiration becomes possible towards the end of this period around the 25th foetal week.

Development of the Lungs

3. The number of terminal sacs increases during the intial part of the alveolar period.

• The capillary network is developing between the terminal sacs.

• The late alveolar period is marked by the development of mature alveoli from the terminal sacs.

Development of the Lungs

• The period begins shortly before birth, but the first mature alveoli appear only after birth.

• Alveolar sacs continue to be formed during early childhood (up to year 8) and mature into alveoli.

• Alveolar maturation and growth continue for another decade, but their numbers do not increase further.