Nasal cavity and larynx histology

The nasal cavity is separated into two spaces, or fossae, by the nasal septum.The nasal septum can be seen along the midline.The nasal turbinates project into the nasal cavity in order to help increase the total available surface area.Both the paranasal sinuses, as well as the majority of the nasal cavity, are lined with respiratory mucosa.Only the roof of the nasal cavity is lined with olfactory mucosa instead.This image of a human’s nasal mucosa, at 10x magnification, was prepared with Alcian blue and Van Gieson stains.If we zoom in, to 40x magnification, we can see that the epithelium consists of pseudostratified ciliated columnar cells, along with many goblet cells that can be easily identified in light blue, because of the Alcian Blue stain.This epithelium is also referred to as respiratory epithelium and generally can be found in the conducting portions of the respiratory tract.The supporting connective tissue called the lamina propria is deep to the epithelium and contains many blood vessels and seromucous glands.If we compare the respiratory epithelium to the olfactory epithelium, we can see that the olfactory epithelium also has pseudostratified columnar cells, but it’s significantly thicker and is composed of a combination of olfactory, sustentacular, and basal cells.The surface of the olfactory epithelium is also lined with modified cilia that function as olfactory receptors, which allows the olfactory cells to sense smells.Moving on to the larynx, this image is a low power, coronal section of the larynx.There are two pairs of folds within the larynx, the upper folds are the vestibular folds (or false vocal cords), and the lower folds are the actual vocal folds, (or true vocal cords).Between the folds on each side are narrow spaces simply called ventricles.Each true vocal cord will need relatively large muscles in order to move the vocal cords for speech.These muscles, called the vocalis muscles are stained darker within the vocal folds.The long structures on both sides of the larynx are portions of the thyroid cartilage, and the cricoid cartilage is partially seen at the bottom as well.Both of these support structures contain a large amount of hyaline cartilage that can be identified by their dark glassy appearance under higher magnification.The structure at the top is this image is the epiglottis.Now, let’s take a closer look at an upper vestibular fold stained with Haemotoxylin and Eosin or H&E for short.Within the fold, there are many seromucous glands that help trap contaminants as well as increasing moisture in the air that’s breathed in.The surface is lined with pseudostratified ciliated epithelium with goblet cells, or in other words, respiratory epithelium.When stained with H&E, the goblet cells can be identified as the clear oval structures within the epithelium.The vestibular folds may also have patches of stratified squamous epithelium in many non-smoking adults, but almost all smokers will have these patches.Moving down to the true vocal cords, we can zoom in and see that portions of the vocal cords are lined with pseudostratified ciliated epithelium with goblet cells, or respiratory epithelium, similar to the upper vestibular folds.Between the epithelium and the vocalis muscle is a relatively thick ligament that runs the length of the vocal cord called the vocalis ligament.In this image, it’s cut transversely and can be difficult to identify, but it’s normally seen as a band of connective tissue just underneath the epithelium, near the apex of the vocal fold.The epithelium that covers this ligament is under a lot of mechanical stress when the vocal cords vibrate and hit one-another in order to create sound during speech.So instead of respiratory epithelium, this portion of the vocal cords are lined with stratified squamous non-keratinized epithelium, which helps prevent physical damage to the surface of these folds.The remaining tissue between the epithelium and surrounding the vocalis ligament is the lamina propria, which consists of dense connective tissue with poor vasculature and no lymphatic vessels.Since the vocal cords are exposed to a lot of mechanical stress and harmful substances in the environment, there are quite a lot of conditions involving the epithelium of the vocal cords in particular.For example, vocal cord nodules, or singer’s nodules, can form from frequent overuse or misuse of the voice.The nodules are benign reactive polyps that often form in the stratified squamous epithelium of the true vocal cords.Also, both cigarette smoke and alcohol consumption increase the risk of hyperplasia or dysplasia of the squamous epithelium within the larynx, leading to benign squamous papillomas or invasive squamous cell carcinoma.And neonates can be infected by human papillomavirus or HPV from their infected mother during birth.This can lead to the development of laryngeal papillomatosis, where tumors grow in the infant’s airway, which can cause respiratory difficulties and may eventually lead to suffocation if not treated.##SummaryAlright, as a quick recap.The nasal cavity is mainly lined with respiratory epithelium, which consists of pseudostratified ciliated columnar cells with goblet cells.But the roof of the nasal cavity will have olfactory epithelium instead, which has a significantly thicker epithelium with modified cilia that function as olfactory receptors.The Larynx consists of two folds: the vestibular folds and the vocal folds.The vestibular folds are primarily respiratory epithelium and have a large number of seromucous glands; while the vocal folds have respiratory epithelium as well, and stratified squamous epithelium that covers the vocalis ligament.