Dermis and Hypodermis of Skin

Dermis and Hypodermis

Overview

  • The dermis lies beneath the epidermis.
  • The hypodermis is underneath the dermis, sometimes considered a layer of skin or fascia; in these notes, it will be considered a skin layer.

Location of Skin Layers

  • Epidermis: The top layer of skin, characterized by a wavy bottom that extends to form hair follicles.
  • Dermis: The pink layer between the epidermis and hypodermis, packed with muscles, glands, nerves, nerve endings, and blood vessels.
  • Hypodermis: The yellow area at the bottom.

Dermis Layers

  • The dermis consists of two layers:
    • Papillary Layer
    • Reticular Layer
Papillary Layer
  • The very top layer of the dermis fills indentations between the dermis and epidermis.
  • Composed mostly of areolar connective tissue.
  • Contains different cell types; the most common is the fibroblast, which makes fibers (reticular, collagen, and elastic).
  • Cushions the small blood vessels present, which supply nutrients to the avascular epidermis.
  • Damage to these blood vessels results in a black and blue mark (blood leaking into the epidermis).
Reticular Layer
  • Below the papillary layer.
  • Composed of dense irregular connective tissue.
  • Collagen fibers provide strength and resilience to the skin.
  • Contains a small amount of elastic connective tissue, for extra stretchiness.
  • The reticular layer contains hair follicles, sweat/oil glands, nerve cells, and blood vessels.

Tissues in the Reticular Layer

  • Dense irregular connective tissue:
    • Pink, swirly collagen fibers produced by fibroblasts
    • Visible darkly stained nuclei due to DNA content
  • Blood vessels:
    • Enmeshed in dense irregular tissue.
    • Lined with simple squamous epithelial tissue which facilitates the movement of oxygen into and out of the bloodstream.
    • Surrounded by smooth muscle tissue that aids in moving blood along its length.
  • Sweat glands:
    • Often appear in cross-sections.
    • Have a central pore/duct through which sweat travels.
    • Composed of cuboidal epithelial cells that produce sweat.

Hypodermis

  • Adipose connective tissue.
  • Contains individual adipose cells filled with fat; the nucleus is pushed to the side.
  • Functions as a storage place for fat in the body.