Respiratory System - Histology

Introduction

This page contains information and images associated with respiratory system histology.

This can be initially divided into the 2 regions of the upper and lower respiratory tract.

For the upper respiratory tract observe the epithelial specialisations, sensory regions and associated cartilages.
For the lower respiratory tract observe the basic structure of the lung, alveoli and ducts, and associated cardiovascular elements.

Historic Embryology - Respiratory
1902 The Nasal Cavities and Olfactory Structures \| 1906 Lung \| 1912 Upper Respiratory Tract \| 1912 Respiratory \| 1913 Prenatal and Neonatal Lung \| 1914 Phrenic Nerve \| 1918 Respiratory images \| 1921 Respiratory \| 1922 Chick Pulmonary Vessels \| 1934 Right Fetal Lung \| 1936 Early Human Lung \| 1937 Terminal Air Passages \| 1938 Human Histology

Fetal Respiratory: late canalicular | unlabeled late canalicular | Hyaline cartilage | Respiratory Histology


Nasal respiratory epithelium (inferior concha)	Nasal respiratory epithelium (detail)

Nasal cavity olfactory epithelium cells

Olfactory cells
Sustentacular cells - located mainly in the superficial cell layer of the epithelium (difficult to distinguish from olfactory cells).
Basal cells - identified by their location.

Epithelium

Lamina Propria

olfactory axon bundles (lightly stained, rounded areas) connected to olfactory cells.
Bowman's glands - (small mucous glands, olfactory glands) function to moisturise the epithelium.


Nasal cavity olfactory	Nasal cavity olfactory (detail)

Nasal Olfactory Histology: overview image | detail image | Smell Development | Histology | Histology Stains

trachea histology

Mucosa - formed by epithelium and underlying lamina propria.

respiratory epithelium - (pseudostratified columnar and ciliated) ciliated cells, goblet cells, brush cells, endocrine cells, surfactant-producing cells (Clara cells), serous cells, basal cells, basement membrane.
lamina propria - loose connective tissue, many elastic fibres.
elastic lamina - forming the border between the mucosa and submucosa is not visible in H&E stained slides.

Submucosa - connective tissue and submucosal glands.

(muco-serous) serous (dark) and mucous (light) parts have different staining appearance.

Mucous secretions - "slimy" (high viscosity) mucous acini cells appear "foamy" or "frothy" and poorly stained (light). nuclei dark and smaller than serous.
Serous secretions - "watery" (low viscosity) serous acini cell apical cytoplasm is usually well-stained (dark). nuclei round to ovoid located in cell basal cytoplasm.

perichondrium - surface of cartilage.
tracheal cartilage - hyaline cartilage, 16 to 20 C-shaped cartilages.
trachealis muscle - (smooth muscle) Not visible in this section, together with connective tissue fibres, join ends of the cartilages together.

forms from mesenchymal cells.
precursor cells become rounded and form densely packed cellular masses, chondrification centres.
chondroblasts - (cartilage-forming cells) begin secreting the extracellular matrix components of cartilage.
- extracellular matrix - ground substance (hyaluronan, chondroitin sulfates and keratan sulfate) and tropocollagen (polymerises into fine collagen fibres, not visible).

Alveolar type I cells

small alveolar cells or type I pneumocytes
are extremely flattened (the cell may be as thin as 0.05 µm)
form the bulk (95%) of the surface of the alveolar walls.
The shape of the cells is very complex, and they may actually form part of the epithelium on both faces of the alveolar wall.

Alveolar type II cells

large alveolar cells or type II pneumocytes
about as many type II cells as type I cells (cell shape accounts for small contribution to alveolar area).
irregularly (sometimes cuboidal) shaped.
form small bulges on the alveolar walls.
contain are large number of granules called cytosomes (or multilamellar bodies)
- consist of precursors to pulmonary surfactant (mixture of phospholipids that keep surface tension in the alveoli low).