Pl. VII · Sustinens hyalinus — hyaline cartilage

The plate

The specimen, drawn

Pl. VII

A matrix so fine-grained it looks like frosted glass. The fibres are there; they are just too small and too close in refractive index to see.

Habitat & range

Where it lives

Body map

Hyaline is the commonest cartilage in the body, and it goes wherever something has to slide or stay open.

Range

• The articular surface of every synovial joint.
• The rings of the trachea and the plates of the bronchiThe large airways that branch from the trachea into the lungs, dividing into smaller bronchioles..
• Where each rib meets the sternumFlat bone forming the center of the chest; anchor for ribs and clavicles. Appears as a vertical dagg, as costal cartilage.
• The end of the nose, and most of the larynxThe voice box; contains vocal cords and connects the pharynx to the trachea..
• The whole fetal skeleton, before bone replaces it.

Collection record

• Add your slide numbers here.

Niche

What it does for a living

Being slippery and staying open. Articular hyaline is the lowest-friction surface in biology, and it does that with a smooth matrix and a great deal of bound waterThe universal solvent essential for life.. It is avascularTo be devoid of blood capillaries. Epithelial tissue is avascular, kind of like a cap of dead cells — chondrocytes are fed by diffusionPassive movement of molecules from areas of high to low concentration. through the matrix — which is why cartilage heals so badly, and why a torn knee surface does not simply grow back.

field collected specimen

How to know it on sight

• A smooth glassy matrix with no visible fibres at all.
• ChondrocytesMature cartilage cells housed in lacunae. sitting in lacunae — little holes with a cell in each.
• Cells often in pairs or small groups, where one divided and the daughters stayed put.
• A perichondrium at the edge, unless the surface is articular, in which case there is none.

Specimen 1

Trachea at high power. The matrix is purple here; find a lacunaSmall spaces in bone tissue where osteocytes reside. with two cellsThe basic structural and functional units of life. in it.

Specimen 2

Trachea at low power. The cartilage is the deepAway from the surface of the body. block; follow it to its edge and find the perichondrium.

Specimen 3

Masson’s trichrome. A different stain, the same glassy matrix and the same lacunae.

People keep calling her by the wrong name

Look-alikes

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

Elastic cartilage

Both have chondrocytes in lacunae. Hyaline matrix is featureless; elastic matrix has a dark fibre network running through it.

Fibrocartilage

Fibrocartilage has obvious thick collagenA structural protein in the dermis that provides strength and elasticity. bundles between its cells. If you can see bundles, it is not hyaline.

Examine it yourself

The virtual slide

Find the tracheal cartilage and travel from its middle out to its edge. The cells get flatter and smaller as you approach the perichondrium, because that is where new cartilage is added.

Virtual slide courtesy of Histology Guide.

Field notes

Why this organism

Snow fungus is a cluster of translucent gelatinous lobes that looks like it should not hold its own weight and does. There is structure in it, but you cannot see the structure — it is dispersed through a clear gel, which is the whole trick. Hyaline cartilage is exactly that: collagen II is in there in quantity, but the fibrils are thin and the matrix around them bends light the same way, so the tissue reads as frosted glass with cells in it.