Dermis - Skin

Dermis

The dermis lies between the epidermis and the sub-cutaneous layer and has two major components: a superficial papillary layer and a deeper reticular layer. The dermis also contains all cells of connective tissue proper. Epidermal accessory organs extend into the dermis, and both the papillary and reticular layers of the dermis contain many blood vessels, lymph vessels, and nerve fibers. The dermis is the second major skin structure and is a strong and flexible connective tis-sue. Dermal cells contain fibroblasts, macrophages, and smaller amounts of mast cells and white blood cells. The major portions of hair follicles, oil glands, and sweat glands are found in the dermis, even though they derive from the epidermal tissue.

The papillary layer consists of areolar tissue and contains capillaries, lymphatics, and sensory neurons. The papillary layer is named for the dermal papillae that project between the epidermal ridges. It is a thin and superficial areolar connective tissue with interwo-ven collagen and elastic fibers. The papillary layer is loose, allowing phagocytes and various defensive cells to move freely, searching for bacteria that have gotten through the skin. Dermal papillae often contain loops of capillaries or may contain pain receptors and touch receptors. In the thicker skin of the palms or soles, these papillae are above larger dermal ridges, which then cause the epidermis to form its epidermal ridges. These ridges leave pressure marks that are commonly referred to as fingerprints, unique to every individual human being.

The deeper reticular layer is made up of connec-tive tissue containing collagen and elastic fibers. The boundary between the papillary and reticular layers is not distinct. The reticular layer makes up approxi-mately 80% of the overall thickness of the dermis. It is nourished by the cutaneous plexus. Collagen fibers mostly run parallel to the skin surface, with less dense regions known as separations forming cleavage lines in the skin. Also known as tension lines, these lines are used for surgeries to make parallel incisions, meaning better healing afterward. A third type of skin marking, flexure lines, occur close to joints, where the dermis is more tightly secured to deeper structures. Examples include the creases on the palms of the hands. In the papillary layer, small arteries form a branched net-work known as the papillary plexus, which provides arterial blood to the capillaries along the epidermis– dermis boundary.

The collagenous and elastic fibers of the dermis make it both tough and elastic. The skin’s water content helps it to be flexible and resilient, which is known as skin turgor. A sign of dehydration is the loss of skin turgor. Processes from nerve cells are located through-out the dermis. Motor processes carry impulses to the dermal glands and muscles, whereas sensory processes carry impulses back to the brain and spinal cord. Cuta-neous sensations include touch, hot, cold, and pain.

1. Describe the layer of the dermis that determines a person’s fingerprints.

2. What forms cleavage lines in the skin?

3. What are the functions of the dermis?