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Pl. V · Epiglottis

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3–4 minutes

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Pl. V · FAM. OPERCULIDAE

Operculum stratificatus var. dionaeus

the trapdoor  ·  epiglottis

The plate

The specimen, drawn

Pl. V

Hand-drawn field-guide plate: a Venus flytrap with one trap open on its hinge, the teeth and trigger hairs drawn on the lobes. Below, a schematic of the epiglottis in section showing a core of elastic cartilage with chondrocytes in lacunae among dark branching elastic fibres, stratified squamous epithelium on the lingual face and ciliated pseudostratified epithelium on the laryngeal face. A circular inset at ×400 shows the transition where one epithelium becomes the other.

The specimen as it was drawn, with the wall below it and the lining in the circle.

Habitat & range

Where it lives

Body map

Body map: a simple hatched human figure on a transparent background with four numbered markers at the throat. Key: 1 the epiglottis, at the tongue root; 2 the laryngeal inlet beneath it; 3 the hyoid, just above; 4 where food and air have to cross. Where the epiglottis is found in the body.

Where this one lives.

Range

  • At the root of the tongue, above the laryngeal inlet.
  • Elastic cartilage, the same tissue as the external ear and the auditory tube.
  • Moves about once a minute while you are awake, and on every single swallow.
  • The lingual face meets food; the laryngeal face meets air. One organ, two jobs, two linings.

Collection record

  • Add your slide numbers here.

Niche

What it does for a living

It is a lid. It folds back over the laryngeal inlet when you swallow and springs forward the rest of the time, and it has to do that roughly once a minute for a lifetime without ever staying bent. Elastic cartilage is the only tissue that will take that; hyaline would fatigue and fail. The epiglottis is the reason the other four plates in this volume stay dry, which is the argument for putting a lid in a volume about airways.

field collected specimen

How to know it on sight

  • A core of elastic cartilage: chondrocytes in lacunae, in a matrix stuffed with dark branching elastic fibres — not the clear glassy matrix of the trachea’s hyaline.
  • Two different linings on the two faces. Stratified squamous on the lingual side, respiratory pseudostratified ciliated on the laryngeal side.
  • A transition between them, somewhere near the tip. Finding it is the best thing to do on this slide.
  • Taste buds sometimes on the lingual surface, and sero-mucous glands under the laryngeal side.
Histological slide of elastic cartilage, likely from the epiglottis. Hematoxylin and Eosin (H&E) staining highlights cell structures and extracellular matrix. Pink staining indicates the extracellular matrix, containing collagen fibers and elastic fibers. Round or oval chondrocytes, with distinct nuclei, occupy lightly colored lacunae. Overall composition is a dense network of stained fibers and cellular structures.

Specimen 1

Light microscopy image of Pseudostratified Ciliated Columnar epithelium. The tissue structure is displayed with elongated cells arranged in a seemingly stratified manner, stained pink. Apical surface displays cilia as small parallel projections. Nuclei are darkly stained, positioned at varied levels within the cell layer. Stromal elements below show less dense arrangement.

The laryngeal face: pseudostratified, ciliated, the same lining as Pl. I.

Specimen 2

Photomicrograph of the esophagus showcasing layered tissue section, stained in varying pink dyes. The upper portion displays stratified squamous epithelium, exhibiting rounded nuclei within cells. Below it, the lamina propria appears less cellular. Muscularis mucosae shows layers of smooth muscle fibers. High magnification.

The lingual face: stratified squamous, built to be scraped by food.

Specimen 3

Light microscopy image of Masson's Trichrome stained hyaline cartilage. Chondrocytes, visible within lacunae, are scattered throughout a pale blue matrix. Ovoid chondrocytes are surrounded in a light purple halo around darker nuclei with bright white spots. The compositional arrangement emphasizes the typical cell distribution of hyaline cartilage.

Hyaline cartilage for comparison, in Masson’s trichrome. Note how little the matrix has going on in it.

Illustration showing the anterior view of the human hyoid bone and related structures. The hyoid bone is the light-brown, horseshoe-shaped bone near the top, connected by tissue in a light-gray color. Below sits the blue larynx and the trachea.

People keep calling her by the wrong name

Look-alikes

Two plates. Read the line underneath each one before you decide.

Hyaline cartilage

High magnification microscopic image of hyaline cartilage within the trachea. The dominant purple matrix contains chondrocytes, small cells appearing encapsulated in circular or oval lacunae that vary in darkness and internal detail. The overall composition is dense, showcasing fine cellular structure.
Hyaline cartilage — the same chondrocytes in lacunae, a completely different matrix.

Tell them apart by the matrix, not the cells. Hyaline is clear and glassy; elastic is full of dark branching fibres. If the section is stained for elastin there is no argument left to have.

Hyaline with glands

A microscope image shows the cartilage and surrounding tissue of a trachea. The cartilage appears as a deep purple band with lacunae, each containing a cell. Connective tissue appears on the right side, with glands, and blood vessels visible in the pink-stained tissue. The image shows a section of tissue prepared for microscopic examination, likely for diagnostic or research purposes.
Hyaline cartilage of the trachea, with submucosal glands beside it.

Tell them apart by where you are as well as what you see. Both organs carry cartilage and glands, but only the epiglottis has two different epithelia on its two faces.

Examine it yourself

The virtual slide

Walk along one face until the lining changes, and stop at the moment it does. That boundary is the whole point of this slide — one organ with food on one side of it and air on the other.

Virtual slide courtesy of Histology Guide.

YOur missions

Field Notes for Future Missions

Mission 1: label the wall

Mission 2: quick check

Field notes

Why this organism

A flytrap is a hinged flap that swings across an opening, springs back to exactly the shape it was, and does it again. Both it and the epiglottis are doors that decide what gets in, and both are built to bend an enormous number of times without fatiguing — which is what elastic cartilage is for. One cross-reference worth making: Ordo Conjunctiva Pl. VIII, The Bouncer, is the fennec fox, and it teaches this same tissue. That plate is about elastic cartilage. This one is about the lid it gets built into.

Back · Frontispiece

Ordo Pneumatica

the air-movers · the five specimens.

Back to the Frontispiece →

In the wild  ·  photograph to come.

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← Epithelial Tissues: A Guided Journey

All plates — The Tissue Field Guide: Epithelium

Frontispiece Ordo Epithelia (main page)
Pl. I · Simple squamous
Pl. II · Simple cuboidal
Pl. III · Simple columnar
Pl. IV · Stratified squamous
Pl. V · Stratified cuboidal
Pl. VI · Stratified columnar
Pl. VII · Transitional
Pl. VIII · Pseudostratified columnar
Epithelial Identification Game

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