Hyaline

Hyaline is a descriptive term used in biology and medicine to indicate a glassy, translucent appearance of tissue. The word derives from the Greek hyalos, meaning glass. In pathology and histology, hyaline does not denote a single substance but a class of materials or changes that look smooth, homogeneous, and pink to eosinophilic under light microscopy. The term is applied across different tissues to convey a similar glistening, glassy quality.

One prominent example is hyaline cartilage, a type of connective tissue found at the ends of long bones, in the nose, trachea, and larynx. Its matrix is rich in type II collagen and proteoglycans, producing a clear, resilient tissue that supports and cushions joints and respira­tory structures. Hyaline cartilage differs from other cartilage types by its relatively glassy appearance and uniform matrix.

In pathology, hyaline describes several specific phenomena. Hyaline membranes line alveoli in acute respiratory distress syndrome, consisting of a protein-rich, eosinophilic layer that impairs gas exchange. Hyaline casts can appear in urine as concentrated protein aggregates formed in the renal tubules. Hyaline degeneration or change refers to the accumulation of homogeneous, eosinophilic material in various tissues, often reflecting chronic injury or aging.

Hyaline arteriolosclerosis involves thickening of small arteries and arterioles with eosinophilic, glassy material, seen in hypertension and diabetes. Across contexts, hyaline remains a descriptive term for a glassy, pink-staining appearance rather than a specific substance or mechanism.