Lab 5: Dermis and hypodermis

Dermis

• is deep to the epidermis and ranges in thickness from 0.5 mm to 3.0 mm.

• This layer of the integument is composed of connective tissue proper contains primarily collagen fibers, although both elastic and reticular fibers also are found within the dermis.

• Additionally, researchers recently have discovered motile cells in the dermis called dendritic cells.

• These cells are similar to the epidermal dendritic cells in that they serve an immune function, except they are located in the dermis.

• Other structures within the dermis are blood vessels, sweat glands, sebaceous glands, hair follicles, nail roots, sensory nerve endings, and smooth muscle tissue associated with hair follicles (arrector pili).

• Two major regions of the dermis can be distinguished:

  • A superficial papillary layer

  • a deeper reticular layer

Papillary Layer of the Dermis

• The papillary (pap'i-lär-ē) layer is the superficial part of the dermis that is deep to the epidermis.

• It is composed of areolar connective tissue, and it derives its name from the projections of the dermis called dermal papillae (der'mãl pã-pil'ē; papilla = a nipple).

• The dermal papillae interdigitate with deep projections of the epidermis called epidermal ridges.

• Together, the dermal papillae and epidermal ridges increase the area of contact between the two layers and interlock them.

• Each dermal papilla contains the capillaries that supply nutrients to the cells of the epidermis.

• Additionally, dermal papillae contain sensory nerve endings that serve as tactile receptors these receptors continuously monitor touch on the surface of the epidermis.

Reticular Layer of the Dermis

• The reticular layer forms the deeper, major portion of the dermis that extends from the papillary layer to the underlying subcutaneous layer.

• The reticular layer consists primarily of dense irregular connective tissue through which large bundles of collagen fibers extend in all directions.

• These fibers are interwoven into a meshwork that surrounds structures in the dermis, such as the hair follicles, sebaceous glands and sweat glands, nerves, and blood vessels.

• The word reticular means "network" and refers to this meshwork of collagen fibers.

• Note that the reticular layer is different from reticular connective tissue,

hypodermis (subcutaneous) layer

• Deep to the integument is the subcutaneous (sub-kü-ta ne-us; sub = beneath, cutis = skin) layer, also called the hypodermis, or superficial fascia.

• It is not considered a part of the integument.

• this layer consists of both areolar connective tissue and adipose connective tissue

• In some locations of the body, adipose connective tissue predominates; thus, the subcutaneous layer is called subcutaneous fat.

• The connective tissue fibers of the reticular layer of the dermis are extensively interwoven with those of the subcutaneous layer to stabilize the position of the skin and bind it to the underlying structures.

• The subcutaneous layer pads and protects the body, acts as an energy reservoir, and provides thermal insulation. Drugs often are injected into the subcutaneous layer (using hypodermic needles) because its extensive vascular network promotes rapid absorption of the drugs.

• Normally the thickness and distribution of the subcutaneous layer are influenced by sex hormones (testosterone, or estrogen and progesterone).

• Under the influence of testosterone, subcutaneous fat tends to accumulate primarily at the neck, upper arms, abdomen, lower back, and buttocks.

• Under the influence of estrogen and progesterone, subcutaneous fat tends to be thicker overall and tends to accumulate primarily in the mammary regions, buttocks, hips, and thighs.