Ch 15: Respiratory System Descriptive Histology CLS 222

Objectives  Classification of the respiratory system  Structure of nose  Structure of larynx  Structure of Trachea  Structure of Bronchioles  Structure of terminal Bronchioles  Structure of lung

Respiratory system  The complex of organs and tissue which are necessary to exchange blood carbon dioxide (CO 2 ) with air oxygen (O 2 ) is called the respiratory system. The respiratory system is divided into:-  Conducting part : Consists of passageways which carry air to the respiratory portion  Respiratory portions: In which the exchange of CO 2 and O 2 is occurring

Conducting portion  The conducting portion includes parts which are outside the lung or extra-pulmonary  Nasal cavities  Nasal pharynx  Larynx  Trachea  Primary bronchi  Bronchioles

Respiratory portion  All of the respiratory portion are of course, intrapulmonary and consists of:  Respiratory bronchioles  Alveolar ducts  Alveoli

Respiratory system

Nose  When looking at a frontal section of the nose Identify  Nasal septum  Nasal cavities.  The epithelial lining the nasal cavity show a gradual change from keratinized stratified squamous epithelium of the skin, in the nasal vestibule, to the pseudostratified columnar ciliated epithelium that is characteristic of the nasal mucosa, so name as respiratory epithelium  Olfactory epithelium, specialized for smell, lines the roof of the nasal cavity

Nose  The nasal mucosa lining the bulk of the nasal cavity is made up of respiratory epithelium and an underlying layer of connective tissue

Larynx  The passageway for air between the oropharynx and trachea is the larynx.  This complex tubular region is formed by irregularly shaped plates of hyaline and elastic cartilage (the epiglottis and the vocal processes of the arytenoids cartilages).

Larynx  In addition to serving as a conduit for air, the larynx serves as the organ for producing sounds.  The vocal folds, also referred to as vocal cords, are two folds of mucosa that project into the lumen of the larynx  The mucosal surface of the conducting portion is lined by respiratory epithelium, except the true vocal fold in the larynx, which is lined by a stratified squamous epithelium (sometimes keratinized).

Vocal cord

Trachea  The trachea is a wide flexible tube, the lumen of which is kept open by tracheal cartilages, which are C-shaped rings of hyaline cartilage.  The gaps between the rings of cartilage are filled by the trachealis muscle - a bundle of smooth muscle, and fibroelastic tissue.  Together these hold the lumen of the trachea open, but allow flexibility during inspiration and expiration.

Trachea

Mucosa and sub-mucosa of Trachea  The respiratory mucosa is made up of the following: 1- Ciliatted columnar pseudostratified epithelium and supporting lamina propria 2- Goblet cell: produce mucus  The sub-mucosa contains glands which are mixed sero-mucous glands produce;  Watery secretions from the serous glands humidify the inspired air.  Mucous, together with mucous from the goblet cells traps particles from the air.

Bronchi  The trachea branches to give rise to two primary bronchi.  These then branch successively to give rise in turn to secondary and tertiary bronchi.  These then branch to give rise to several orders of progressively smaller airways called bronchioles, the smallest of which are called terminal bronchioles.  These are the last components of the conducting portion, and the beginning of the respiratory portion where is actual gas exchange takes place.

Trachea

Bronchioles  The epithelium is made up of ciliated columnar cells in larger bronchioles, or non-ciliated in smaller bronchioles.  There are no goblet cells, but there are secretory cells called Clara cells.  Clara cells are non ciliated cells that have a characteristic rounded or dome-shaped apical surface projection.

Ciliated columnar cells

Terminal bronchioles  The final branches of the bronchioles are called terminal bronchioles.  These have a layer smooth muscle surrounding their lumens.  There is no cartilage or glands, some smooth muscle is still present, there are no goblet cells.  The epithelium is either columnar or cuboidal.  Small sacs are found extending from the walls of the terminal bronchii called respiratory bronchioles.

Lung Normal Lung:-  Sections of lung tissue have the appearance of fine lace because most of the lung is composed of thin-walled alveoli.  The alveoli are composed of a single layer of squamous epithelium.  Between the alveoli you may see a thin layer of connective tissue and numerous capillaries also lined with simple squamous epithelium.

Respiratory Bronchioles  Bronchioles can be recognized by the fact that they are lined by ciliated columnar epithelium (larger bronchioles) or by cuboidal epithelium (smaller bronchioles leading to alveoli).  A pulmonary lobule is the portion of the lung ventilated by one bronchiole.  Bronchioles are approximately 1mm or less in diameter and their walls consist of ciliated cuboidal epithelium and a layer of smooth muscle.  Bronchioles divide into even smaller bronchioles called terminal bronchioles which are 0.5mm or less in diameter  Terminal bronchioles in turn divide into smaller respiratory bronchioles which divide into alveolar ducts, where the actual exchange of air occur.

Respiratory system

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