Which of the following is NOT a component of the extracellular matrix?

A. papillary layer of dermis – fingerprints and toeprints
Correct match. The dermal papillae in this layer interlock with the epidermis and form ridges that result in fingerprints and toeprints.

B. stratum basale – most mitotically active layer of epidermis
Correct match. The stratum basale contains basal cells that divide continuously to replenish the upper layers.

C. reticular layer of dermis – arranged in lines of cleavage
Correct match. The dense irregular connective tissue in this layer has collagen fibers oriented in specific directions (cleavage lines), which is clinically important for surgical incisions.

D. epidermis – structural strength of the skin
Incorrect match. The dermis provides the structural strength of the skin due to its collagen and elastic fibers. The epidermis offers protection but does not contribute significant structural strength.

A. hyaluronic acid + proteoglycan monomers: Hyaluronic acid forms the central stalk (handle of the "toilet brush"), and proteoglycan monomers attach along its length, forming a large aggregate that traps water and gives ground substance its gel-like consistency.

B. reticular fibers + collagen fibers: These are structural protein fibers in connective tissue but are not components of proteoglycan aggregates.

C. chondroblasts and chondroclasts: These are cartilage cells involved in formation (chondroblasts) and resorption (chondroclasts) but not part of the ground substance's molecular structure.

D. collagen fibers + fibroblasts: Collagen fibers are structural; fibroblasts produce extracellular matrix components, but neither directly forms the proteoglycan aggregate.