School of Anatomy and Human Biology - The University of Western Australia
|Blue Histology - Respiratory System|
Lab Guides and Images
Respiratory Region of the Nasal
Olfactory Region of the Nasal Cavity
Trachea - H&E, Alcian blue/van Gieson
Lung - H&E, reticulin, elastin
Foetal Lung - developing alveoli, developing cartilage, H&E
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The complex of organs and tissue which are necessary to exchange blood carbon dioxide (CO2) with air oxygen (O2) is called the respiratory system. It consists of
The Nasal cavity is divided into three structurally and functionally different parts.
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.
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.
Inferior Concha, human - Alcian blue & van Gieson
Thin structures which consist of tissues with very different physical properties - like loose connective tissue and bone - may easily get damaged during tissue preparation. Find a spot where the layers from epithelium to bone appear intact. Identify goblet cells, basal cells and ciliated cells in the epithelium. Now have a look at the lamina propria. Depending on the exact location you may only see connective tissue between the epithelium and bone or large spaces (either empty or filled with red blood cells) which represent the cavernous sinusoids, or glandular tissue (mucous glands appear green and muco-serous glands appear brownish-green in this preparation), or combinations of these features. Lamellae and osteocytes in lacunae may be visible in the bone, while Haversian systems are rare or absent. Which type of bone is it?
Draw a survey of the tissue which includes bone, the lamina propria and structures within it, and epithelium.
Nasal Cavity, Olfactory Region, rat - Alcian blue &
In humans, olfactory epithelium lines the superior concha and parts of the nasal septum. The bony structures beneath the epithelium form an irregular surface, which increases turbulence in the air passing them and thereby the chances that odorants come into contact with the olfactory epithelium. In macrosmatic animals, like the rat, the olfactory epithelium also covers the middle conchae and the surface is considerably more irregular than in humans.
The olfactory epithelium is formed by olfactory cells, sustentacular cells and basal cells. Basal cells can be identified by their location. Sustentacular cells are preferentially located in the superficial cell tier of the epithelium but are difficult to distinguish from olfactory cells in this preparation. Cilia are not visible and goblet cells are absent from the olfactory epithelium. Lightly stained rounded areas in the lamina propria represent bundles of olfactory axons in the lamina propria. Small mucous glands, olfactory glands or Bowman's glands, in the lamina propria moisturise the epithelium.
Draw the olfactory epithelium and underlying lamina propria at high magnification. Label the features included in your drawing.
Larynx, trachea, bronchi and bronchioles form the lower respiratory passages.
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.
The trachea is a fairly short tube (10-12 cm) with a diameter of ~2 cm.
The trachea is lined by respiratory epithelium. The number of goblet cells
is variable and depends on physical or chemical irritation of the epithelium
which increase goblet cell number. Prolonged intense
irritation of the epithelium may lead to its transformation to a stratified
squamous epithelium (squamous metaplasia).
In addition to the staple of basal cells, ciliated cells and goblet cells , the respiratory epithelium also contains brush cells, endocrine cells (or small granule cells, function not clear), surfactant-producing cells (or Clara cells), and serous cells.
Epithelium and underlying lamina propria are called the mucosa. The lamina propria consists of loose connective tissue with many elastic fibres, which condense at the deep border of the lamina propria to form an elastic membrane. This elastic membrane forms the border between the mucosa and the connective tissue below it, which is called the submucosa. Muco-serous glands in the submucosa (submucosal glands) supplement the secretions of cells in the epithelium. The submucosa ends with the perichondrium of the 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.
Cartilages, annular ligaments and the trachealis muscle form the "skeleton" of the trachea which sometimes is referred to as tunica fibromusculocartilaginea. If you want to impress someone with this term make sure that you can pronounce and/or spell it.
The trachea bifurcates to give rise to the main bronchi. Their histological structure corresponds largely to that of the trachea.
Trachea, human - H&E
In the lungs we find the last segments of the conductive portion of the respiratory system. 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. 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.
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. In addition, bronchi are surrounded by a layer of smooth muscle, which is located between the cartilage and epithelium.
Bronchioles are the terminal segments of the conductive portion. At the transition from bronchi to bronchioles the epithelium changes to a ciliated columnar epithelium, but most of the cell types found in the epithelium of other parts of the conductive portion are still present. Glands and cartilage are absent. The layer of smooth muscle is relatively thicker than in the bronchi.
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.
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. 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.
The epithelium of the alveoli is formed by two cell types:
Cilia are absent from the alveolar epithelium and cannot help to remove particulate matter which continuously enters the alveoli with the inspired air. Alveolar macrophages take care of this job. They migrate freely over the alveolar epithelium and ingest particulate matter. Towards the end of their life span, they migrate either towards the bronchioles, where they enter the mucus lining the epithelium to be finally discharged into the pharynx, or they enter the connective tissue septa of the lung.
Lung, human - H&E, elastin
Lung, cat - reticulin
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. 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:
Foetal lung, human - H&E
The lung tissue on the slides available in the tray should according to the above scheme come from the late canalicular period. Mucous connective tissue fills fairly wide spaces between the terminal sacs. Both slides contain developing bronchi and cartilage. Have a quick look at the developing cartilage and note that histologically it somewhat resembles the intramembranous formation of bone.
Draw a small section of developing lung including terminal sacs and connective tissue at high magnification.
page content and construction: Lutz Slomianka
last updated: 6/08/09