Biomedical Engineering Reference
In-Depth Information
4.2.3
Dermis
The dermis is a complex, dynamic microenvironment that harbors a collection of
specialized cells within an intricate matrix (formed by soluble and non-soluble
molecules.) It is subdivided into the papillary dermis (superficial) and the reticular
dermis (deep.) The dermis is responsible for a wide variety of functions, including
maintaining the elastic and mechanical integrity of the skin, cutaneous nutrition,
immunosurveillance, sensory perception and temperature regulation.
In a normal physiological state, the dermis contains an ensemble of cells that
includes (1) fibroblasts, (2) endothelial cells, (3) monocytes/macrophages, (4)
dendritic cells (also called dermal dendrocytes), (5) mast cells, (6) lymphocytes,
(7) Schwann cells, axons and specialized nerve endings, (8) pericytes and glomus
cells and (9) mesenchymal elements with presumed differentiation plasticity
(mesenchymal stem cells.) These cells are contained within an acellular matrix,
composed mainly of collagen and glycosaminoglycan.
The dermis contains an extensive network (plexus) of blood vessels that
provides nourishment for itself and the epidermis. The superficial microvascular
plexus defines the boundary between the papillary dermis and the reticular dermis.
Endothelial cells, expressing surface markers CD31 (short for cluster of differen-
tiation-31), CD34, and CD144 (vascular epithelium-cadherin or VE-cadherin) line
the lumen of the dermal microvessels.
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Endothelial cells participate in transmural
shuttling of macromolecules and are important facilitators of immune cell
trafficking.
Dermal microvessels are surrounded by a complement of immune cells, includ-
ing macrophages, mast cells and dendritic cells. Collectively, these cells collaborate
to coordinate intradermal antigen presentation, induction of inflammation and
homeostasis in the immediate perivascular microenvironment.
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The dermis is supplied with sensory (myelinated up to their terminal branches)
and autonomic (unmyelinated) nerves. Found mostly in the papillary dermis
(especially near microvessels), autonomic nerves (derived from the sympathetic
system) control vascular flow and secretory functions of skin appendages, includ-
ing sweat glands, but not sebaceous glands (endocrine stimulated.)
Detection of cutaneous sensation is performed by several specialized nerve
endings, including free nerve endings, Meissner's corpuscles, Vater-Pacini cor-
puscles and, in lower vertebrates - Merkel cells (also found in the basal cell layer
of the epidermis and the bulge region of hair follicles.)
Free nerve endings are
involved with temperature, pain and itch (a variant of pain) perceptions. Meissn-
er's corpuscles are structured nerve endings that detect touch; they are found
exclusively in the papillary dermis of the ventral aspects of hands and feet. Vater-
Pacini corpuscles mediate pressure and vibrational sensation; they are found in the
deep dermis and subcutis of palms and soles. Protective roles of these neural
components become evident in patients with tissue injury (such as sensory
neuropathy.)
