Extracellular accumulations: hyalinosis, fibrinoid swelling
A reminder, that extracellular tissue consists of:
- Fibrous structural proteins (elastin and collagens)
- Water hydrated gels (proteoglycans and hyaluronan)
- Adhesive glycoproteins
Pathologies lead to a change in quantity and/or quality of these normal components.
We classify accumulations in the ECM as follows:
- Disorders in the metabolism and structure of collagen
- Disorders in the metabolism and structure of elastin
- Disorders in the content of the proteoglycans
- Abnormal accumulations in the ECM
- Including proteins
- Fibrinoid
- Hyalin
- Amyloid
- Inorganics
- Ca²⁺
- Urates (e.g. Uric acid)
Hyalinosis
Hyaline is a morphological description of a non-structured ‘glassy’ structure, made of a heterogenous mix of proteins, lipids and carbohydrates. Hyalinisation can occur in the ECM of any tissue, below we explore some examples:
- Vascular hyaline
- Due to nonenzymatic glycosylation of proteins in the basement membrane of vessels (in diabetes)
- Is associated with hypertension, usually a secondary product, as high pressure forces proteins into the ECM
- Can lead to nephrosclerosis
- Benign nephrosclerosis
- High pressure in the afferent arteries of the kidneys leads to build up of Hyaline around the glomeruli. (NOTE SLIDE - HYALINOSIS RENIS)
H&E, kidney: hyaline arteriolosclerosis – the arteriole wall (arrows) is replaced by homogeneous, glassy pink hyaline that narrows the lumen; glomerulus on the right.
Image: “Histopathology of renal arteriolar hyalinosis, annotated” by Mikael Häggström , M.D. Author info - Reusing images - Conflicts of interest: None Mikael Häggström , M.D. Consent note , CC0, via Wikimedia Commons.
Examples: hyaline arteriolosclerosis of the renal afferent arterioles in benign hypertension and diabetes (gives benign nephrosclerosis: small, finely granular kidneys); hyalinised old scars and keloids; hyalinised glomeruli in end-stage kidneys; corpora albicantia in the ovary; thickened, glassy capsules over the spleen ('sugar-coated spleen').
We can also divide hyalinosis according to the mechanism of formation:
- Hyaline as a product of of fibrinoid changes
- A product of damaged perivascular stroma
- Hyaline in the finale of plasmatic impregnation
- A product of buildup in the vascular wall
- Local hyalinosis as product of inflammation
- Hyalinosis as a product of necrosis
- Hyalinosis as a product of sclerosis (hardening of tissue)
Fibrinoid swelling
Fibrinoid swelling, quite simply means swellings that have the characteristics of fibrin. It is the morphological description of non-structured heterogeneous substance predominantly made of plasma proteins. It is stained by Van Gieson (yellow).
There are three main forms of Fibrinoid swelling
- Fibrinoid in precipitation of immune complexes
- A product of systemic connective tissue diseases
- Fibrinoid in accumulation of plasma proteins