A

Dermis and Hypodermis Overview

Dermis Structure and Function

  • The dermis is the second official layer of the skin, lying just beneath the epidermis.

  • Composition:

    • Consists entirely of connective tissue.

    • Functions to bind the body together.

Papillary Layer of the Dermis

  • Description:

    • This is the superficial most layer of the dermis.

    • Highly vascularized (rich blood supply).

  • Contrast with Epithelial Tissue:

    • Unlike epithelial tissue, the epidermis, which is avascular (lacking blood vessels).

  • Features:

    • Houses epidermal ridges (formed by projections into the epidermis).

    • Attachment site for epidermis via desmosomes.

Sensory Receptors in the Dermis

  • Merkel's Discs:

    • Location: found in the stratum basale and the dermis.

    • Function: Detect light touch.

  • Meissner's Corpuscles:

    • Function: Also detects light touch;

    • Important for the sensitivity of skin in areas like fingertips.

  • Pacinian Corpuscles:

    • Function: Detect deep pressure and vibration.

    • Example: Allows sensing of vibrations when placing a hand on a running car or a cat.

  • Root Hair Plexus:

    • Description: Nerve endings surrounding the root of a hair.

    • Function: Detect slight movements, contributing to hair sensitivity.

  • Free Nerve Endings:

    • Function: Detect pain, responding to cuts or chemical signals related to injury.

Reticular Layer of the Dermis

  • Description:

    • This layer constitutes the majority of the dermis.

  • Composition:

    • Contains a high concentration of collagen and elastin fibers.

    • Provides hydration and elasticity to the skin.

    • Consists of dense irregular connective tissue.

  • Features:

    • Houses larger blood vessels.

Blisters

  • Cause: Friction can damage desmosomes in the epidermis, leading to interstitial fluid accumulation.

  • Advice: Do not pop blisters as they protect the skin and aid in healing (they are referred to as nature's Band Aids).

Hypodermis (Subcutaneous Tissue)

  • Classification: Not officially a skin layer; lies beneath the dermis.

  • Other Names: Also known as subcutaneous tissue or superficial fascia.

  • Composition:

    • Contains a larger amount of adipose (fat) tissue.

  • Function:

    • Acts as an energy reservoir; adipose tissue is an excellent insulator.

  • Medical Relevance:

    • Site for hypodermic injections due to fewer capillaries and absence of vital organs. This allows for better absorption of injected substances.

Subcutaneous Fat

  • Impacts of Hormones:

    • The distribution of subcutaneous fat is influenced by sex hormones (testosterone and estrogen).

    • Higher testosterone leads to male-pattern fat distribution, primarily around the belly, thighs, and buttocks.

    • Higher estrogen leads to fat accumulation around the thighs, belly, buttocks, breasts, upper arms, and neck.

Conclusion

  • Future Learning:

    • More detailed information about sex hormones will be covered in subsequent courses (Bio 202).