Epidermis Layers Overview

Overview

This lecture reviews the five layers of the epidermis, explaining their cell types, functions, and importance in skin structure and protection.

Skin has three main layers: the epidermis (top), dermis (middle), and subcutaneous tissue/hypodermis (bottom).

The epidermis is the outermost skin layer and is made of five distinct sublayers called strata.
The five strata of the epidermis, from deepest to most superficial, are: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.

Stratum basale is the deepest epidermal layer and lies just above the dermis.
This layer contains keratinocytes (cells that produce keratin for toughness) and melanocytes (cells that produce melanin pigment for skin color).
Rapid cell division occurs here, generating new keratinocytes.
Skin color depends on the amount of melanin produced, not the number of melanocytes.

Stratum spinosum (spiny layer) contains keratinocytes connected by desmosomes, giving a spiny appearance when dehydrated.
Langerhans cells (immune system cells) are present here and help defend against pathogens.

Stratum granulosum (granular layer) features keratinocytes packed with keratohyalin granules (proteins that manage keratin).
Lamellar bodies in this layer release lipids to form a waterproof barrier on the skin’s surface.

Stratum lucidum (clear layer) contains dead, transparent keratinocytes that lack nuclei and organelles.
This layer is only present in thick skin (like palms and soles).

Stratum corneum is the topmost layer, consisting of 15-20 stacked layers of flat, dead keratinocytes.
Cells continuously shed from this layer to be replaced by new ones from below.
In reptiles, this layer is shed all at once, as in molting.

Epidermis — outermost layer of skin, made up of five sublayers (strata).
Stratum basale — deepest layer of the epidermis where cell division occurs and melanin is produced.
Keratinocyte — skin cell that produces keratin protein, providing strength to skin.
Melanocyte — cell in the stratum basale that produces melanin pigment.
Melanin — pigment giving skin its color; amount determines darkness of skin.
Desmosome — structure connecting keratinocytes, giving the spiny appearance in the stratum spinosum.
Langerhans cell — immune cell in the epidermis that defends against pathogens.
Keratohyalin granule — protein-filled structure in the stratum granulosum involved in managing keratin.
Lamellar body — lipid-containing structure creating the skin’s waterproof barrier.
Stratum corneum — outermost, dead cell layer of the epidermis that continuously sheds.

Review diagrams of skin structure and memorize the five epidermal layers in order.
Prepare for a discussion on the dermis and subcutaneous (hypodermis) layers in the next lecture.