Which of the following is the outermost layer of skin? Group of answer choices Dermis Epidermis Hyperdermis Hypodermis
The correct answer and explanation is:
Correct Answer: Epidermis
Explanation (300 words):
The epidermis is the outermost layer of the skin, and it serves as the body’s first line of defense against the external environment. It is composed mainly of keratinized stratified squamous epithelial cells, which are tough and water-resistant due to the presence of the protein keratin.
The skin is made up of three main layers:
- Epidermis – the outermost layer
- Dermis – the middle layer beneath the epidermis
- Hypodermis (or Subcutaneous layer) – the innermost layer, also sometimes referred to as the hyperdermis, though this term is less commonly used and considered incorrect in anatomical terminology.
The epidermis itself is avascular, meaning it does not contain blood vessels. Instead, it receives nutrients through diffusion from the underlying dermis. It contains several sub-layers or strata, including:
- Stratum corneum (outermost, made of dead keratinized cells)
- Stratum lucidum (only in thick skin like palms and soles)
- Stratum granulosum
- Stratum spinosum
- Stratum basale (deepest layer where new cells are produced)
Functions of the epidermis include:
- Protection: Forms a barrier against pathogens, chemicals, and physical trauma.
- Water regulation: Prevents excess water loss through evaporation.
- Sensation: Contains sensory receptors for pain, temperature, and touch.
- Vitamin D synthesis: Begins the process of vitamin D production when exposed to sunlight.
In contrast, the dermis contains blood vessels, nerves, sweat glands, and hair follicles, and the hypodermis stores fat and helps insulate the body.
To summarize, the epidermis is the correct answer and is essential for protection and maintaining homeostasis as the outermost layer of the skin.