General structural plan of the skin
The general integument of the body (integumentum commune) consists of the skin (cutis) and the underlying hypodermis. Within the skin, there are sensory nerve endings, blood and lymphatic vessels, as well as glands, hair, and nails.
Functionally and histologically, the skin is divided into two main layers:
- Epidermis (epidermis) — the outer layer.
- Skin proper, or dermis (dermis, corium) — the inner connective tissue framework.
Below the dermis lies the hypodermis (tela subcutanea). It is important to remember that anatomically it does not belong to the layers of the skin itself, although it is closely connected to it topographically.
The epidermis and its layers
The epidermis is a derivative of the ectoderm and is a keratinized stratified squamous epithelium. It lacks its own blood vessels, so the cells are nourished exclusively by diffusion from the underlying layer.
Layers of the epidermis (from deepest to superficial):
- Stratum basale (stratum basale). Formed by a single row of columnar cells. This is an active germinative layer where mitosis constantly occurs. It also contains melanocytes, which produce the pigment melanin.
- Stratum spinosum (stratum spinosum). Consists of several rows of cells. They are characterized by the presence of special intercellular "spines" that firmly bind the cells together and provide mechanical strength to the entire epidermis.
- Stratum granulosum (stratum granulosum). Includes 3–5 rows of cells. Keratohyalin granules accumulate in their cytoplasm.
- Stratum lucidum (stratum lucidum). Not present everywhere — it is found only in so-called thick skin (soles and palms). The cells of this layer lack nuclei and are completely filled with eleidin.
- Stratum corneum (stratum corneum). The most superficial layer. Consists of flat, keratinized dead cells that constantly desquamate and renew. It performs the primary protective function.
The skin proper (dermis)
The dermis (dermis, corium) is a derivative of the mesoderm. It consists of strong fibrous connective tissue.
The dermis has two distinct layers:
- Papillary layer (stratum papillare). Formed by loose connective tissue. It forms specific projections (papillae) that extend into the epidermis. This layer contains blood and lymphatic capillaries that nourish the outer epithelium, as well as nerve endings.
- Reticular layer (stratum reticulare). Formed by dense irregular connective tissue. It contains a dense network of collagen and elastic fibers, which provides high mechanical strength and elasticity to the skin.
Skin relief
The skin surface is not completely smooth. It forms a complex pattern of relief:
- Sulci (sulci cutis) and ridges (cristae cutis). The pattern they create is strictly individual for each person and remains constant throughout life (this exact fact is used in dermatoglyphics/fingerprinting).
- Skin creases/folds. They can be permanent or temporary (most commonly forming in the area of joints during movement).
Hypodermis (Subcutaneous layer)
The hypodermis (tela subcutanea) lies beneath the dermis. It consists of loose connective tissue, in the meshes of which lie fat lobules — adipose tissue. In certain anatomical regions (e.g., eyelids, auricle, scrotum), adipose tissue is completely absent.
Main functions of the hypodermis:
- thermal insulation of the body;
- cushioning against mechanical impacts and pressure;
- ensuring skin mobility relative to underlying fascia and muscles;
- energy storage (fat reserves).
Briefly: answers to topical questions
What skin derivatives (appendages) are distinguished in human anatomy, and what specific types of glands belong to them?
Skin derivatives (appendages) in human anatomy include hair, nails, and glands. The following types of glands are distinguished:
- Sweat glands (glandulae sudoriferae).
- Sebaceous glands (glandulae sebaceae) — their excretory ducts open into hair follicles.
- Mammary glands — are modified sweat glands.
Hair and nails are also derivatives of the cutaneous ectoderm.
What encapsulated and free nerve endings are located in the various layers of the skin?
Both free and encapsulated nerve endings are located in the various layers of the skin.
- The epidermis contains free nerve endings and Merkel touch discs (which are classified as free receptors).
- The papillary layer of the dermis houses encapsulated Meissner corpuscles, as well as unencapsulated (non-free) endings.
- The reticular layer of the dermis contains deep encapsulated receptors: Vater-Pacini corpuscles (lamellar corpuscles), Ruffini corpuscles, and Krause end bulbs.
What cells, aside from keratinocytes and melanocytes, are present in the epidermis?
In addition to keratinocytes and melanocytes, the stratified squamous keratinizing epithelium of the epidermis contains other specialized cells. These include:
- Langerhans cells — specialized antigen-presenting dendritic cells of macrophage lineage.
- Merkel cells — tactile epithelial cells that perform a receptor function.
- T lymphocytes — predominantly cytotoxic CD8+ lymphocytes localized in the basal and spinous layers.
Other dendritic and neuroectodermal cells are also present in the epidermis.
What are Langer's lines (cleavage lines) and how do they relate to the structure of the reticular layer of the dermis?
Langer's lines are skin tension lines that determine the direction of wrinkle and fold formation. Their formation is related to the orientation of collagen fibers. The principle of Langer's lines applies to all areas of the body, including those where visible lines are absent. The reticular layer of the dermis (stratum reticulare), consisting of dense irregular connective tissue, contains these collagen and elastic fibers, which provide strength and elasticity to the skin.
To remember the layers of the epidermis from bottom to top, use the mnemonic: Basal, Spinous, Granular, Lucid, Cornified.
Class and exam questions
Are hair, nails, and subcutaneous tissue part of the skin?
Hair, nails, and glands are skin derivatives and are located within its thickness. However, the hypodermis (tela subcutanea) lies beneath the dermis and does not belong to the skin layers proper.
How are the stratum corneum and other epidermal layers nourished?
The epidermis contains no blood capillaries of its own. All nutrients arrive via diffusion from the capillaries of the papillary layer of the dermis.
What is the difference between thin and thick skin?
In thick skin (on the palms and soles), there is an additional layer — the stratum lucidum of the epidermis, which is absent in other areas of the body covered by thin skin.
Where in the skin is the pigment melanin produced?
Melanin is synthesized by specialized cells — melanocytes. They are located in the deepest, basal layer of the epidermis.
What else to study on this topic
- Cellular composition of the epidermis (keratinocytes, melanocytes, Langerhans cells, and Merkel cells)
- Process of keratinization: from keratohyalin synthesis to the formation of cornified scales
- Anatomy and physiology of skin appendages (structure of the hair follicle, sebaceous and sweat glands)
- Morphological basis of fingerprinting: how ridges and furrows are formed
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