Overview
This lecture explains the structure and functions of the dermis and hypodermis, describing their layers, tissue types, and clinical relevance, especially in burn diagnosis.
Layers of the Skin
- The skin has three main layers: epidermis (top), dermis (middle), and hypodermis (bottom).
- The bottom-most layer of the epidermis is called the stratum basale (basal layer).
- The dermis sits below the epidermis and consists of two layers: the papillary dermis (upper) and the reticular dermis (lower).
Dermis Structure and Function
- The dermis is composed of connective tissue, in contrast to the epidermis, which is made of epithelial tissue.
- Papillary dermis contains thin, loose connective tissue allowing flexibility and movement.
- Reticular dermis contains dense connective tissue to anchor structures like glands and hair follicles.
- Connective tissues include proteins such as collagen, actin, laminin, elastin, and desmin.
- The papillary dermis contains blood vessels that nourish both the dermis and the avascular epidermis.
- Nerve endings in the dermis allow sensation of touch and pain.
Structures Within the Dermis
- Sweat glands and other exocrine glands originate in the reticular dermis and extend to the skin’s surface.
- Hair follicles are anchored in the reticular dermis; hair grows through the epidermis.
- The erector pili muscle, attached to hair follicles, causes hair to stand up in response to cold or fear.
Hypodermis (Subcutaneous Layer)
- The hypodermis, or subcutaneous fat, is located below the dermis and is mostly composed of fat.
- Functions of hypodermal fat include shock absorption and insulation.
- Below the hypodermis are muscle and bone.
Clinical Application: Burns
- First-degree burns affect only the epidermis and cause pain.
- Second-degree burns reach the dermis and may destroy nerve endings, reducing pain in affected areas.
- Third-degree burns penetrate past the hypodermis into fat, muscle, or bone and cause no pain due to nerve destruction.
- Understanding skin layers helps clinicians assess burn severity.
Key Terms & Definitions
- Dermis — middle skin layer below the epidermis with two sublayers.
- Papillary dermis — upper dermal layer with loose connective tissue and blood vessels.
- Reticular dermis — lower dermal layer with dense connective tissue anchoring glands and follicles.
- Connective tissue — tissue type providing structure and support, rich in proteins like collagen.
- Hypodermis (subcutaneous fat) — bottom layer under dermis, primarily fat for insulation and shock absorption.
- Erector pili muscle — small muscle that causes hair to stand up.
Action Items / Next Steps
- Review the anatomy of skin layers and their components.
- Study the classification of burns based on the affected skin layers.