Dermis

Tactile Receptors

Also called corpuscles of touch or Meissner corpuscles, these receptors are nerve endings that are sensitive to touch.

Capillary Loops

Blood vessels within dermal papillae.

Reticular Region

Deeper portion of dermis (about four-fifths); consists of dense irregular connective tissue with bundles of thick collagen and some coarse elastic fibers. Spaces between fibers contain some adipose cells, hair follicles, nerves, sebaceous glands, and sudoriferous glands.

Free Nerve Endings

Dendrites that lack any apparent structural specialization. Different free nerve endings initiate signals that give rise to sensations of warmth, coolness, pain, tickling, and itching.

Dermal Papillae

Small, nipple-shaped structures that project into the undersurface of the epidermis. All dermal papillae contain capillary loops (blood vessels). Some also contain tactile receptors called corpuscles of touch or Meissner corpuscles, nerve endings that are sensitive to touch. Still other dermal papillae also contain free nerve endings, dendrites that lack any apparent structural specialization. Different free nerve endings initiate signals that give rise to sensations of warmth, coolness, pain, tickling, and itching.

Papillary Region

Superficial portion of dermis (about one-fifth); consists of areolar connective tissue with thin collagen and fine elastic fibers; contains dermal ridges that house blood capillaries, corpuscles of touch, and free nerve endings.

Elasticity

The ability to return to original shape after stretching.

Extensibility

The ability to stretch.

Extensibility and Elasticity

The combination of collagen and elastic fibers in the reticular region provides the skin with strength, extensibility, the ability to stretch, and elasticity, the ability to return to original shape after stretching.

Dermis

The second deeper part of the skin, the dermis, is composed of dense irregular connective tissue containing collagen and elastic fibers. This woven network of fibers has great tensile strength (resists pulling or stretching forces). The dermis also has the ability to stretch and recoil easily. It is much thicker than the epidermis, and this thickness varies from region to region in the body, reaching its greatest thickness on the palms and soles. The few cells present in the dermis include predominantly fibroblasts, with some macrophages, and a few adipocytes near its boundary with the subcutaneous layer. Blood vessels, nerves, glands, and hair follicles (epithelial invaginations of the epidermis) are embedded in the dermal layer. The dermis is essential to the survival of the epidermis, and these adjacent layers form many important structural and functional relations. Based on its tissue structure, the dermis can be divided into a thin superficial papillary region and a thick deeper reticular region.

Epidermal Ridges

The surfaces of the palms, fingers, soles, and toes have a series of ridges and grooves. They appear either as straight lines or as a pattern of loops and whorls, as on the tips of the digits. These epidermal ridges are produced during the third month of fetal development as downward projections of the epidermis into the dermis between the dermal papillae of the papillary region. The epidermal ridges create a strong bond between the epidermis and the dermis in a region of high mechanical stress. The epidermal ridges also increase the surface area of the epidermis and thus increase the grip of the hand or foot by increasing friction. Finally, the epidermal ridges greatly increase surface area, which increases the number of corpuscles of touch and thus increases tactile sensitivity. Because the ducts of sweat glands open on the tops of the epidermal ridges as sweat pores, the sweat and ridges form fingerprints (or footprints) on touching a smooth object. The epidermal ridge pattern is in part genetically determined and is unique for each individual.