The Integumentary System and Burns | Real 3D Anatomy
by Robert Tallitsch, PhD | March 24, 2022
Video explanation of the Integumentary System and Burns Explanation using 3D Anatomy Software!
Written by: Robert Tallitsch, PhD
The integumentary system, or integument, is composed of the skin and its derivatives (nails, hair, and glands). The functions of the integument include:
- Synthesis and storage of lipids
- Excretion of wastes
- Regulation of body temperature
- Synthesis of vitamin D3
- Coordination of immune responses involving cancers and other pathogens of the skin
- Sensing environmental stimuli
Even though the skin is one of, if not the largest organ of the body, a description is often omitted from human anatomy texts, and skin is seldom studied in the dissection laboratory. This Brain Builder will describe the skin and the various types of burns that can affect it.
The skin, or integument, is composed of two layers: a superficial epidermis, and a deeper dermis. The epidermis is composed of a keratinized stratified squamous epithelium. There are two types of skin: thick and thin. Thick skin, which typically lacks hair, is found on the palms of the hands and soles of the feet, and has five layers. These layers are, from deep to superficial, the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.
The deepest layer of thick skin is the stratum basale (also termed the stratum germinativum). This layer, which is one cell thick, is the epidermal layer with the highest rate of mitotic activity. As new cells are formed they move superficially. This upward migration of new cells allows for the replacement of cells that are sloughed off and lost from more superficial layers of the epidermis.
Scattered within the stratum basale are pigment-producing cells called melanocytes. These cells possess cytoplasmic processes that inject pigment into adjacent cells within the stratum basale, as well as cells of more superficial layers. The pigment produced by melanocytes varies in color, from black to brown or yellow-brown. Differences in skin color is due to the rate of pigment synthesis, rather than the number of melanocytes present.
The next layer is the stratum spinosum. New cells produced by mitosis within the stratum basale migrate superficially into the stratum spinosum, which is several cell layers thick. Cells within the deepest part of the stratum spinosum continue to undergo mitosis, contributing to the thickness of this layer.
Cells within the stratum spinosum are characterized by possessing intracellular and intercellular specializations that tightly tie all of the cells within this layer together.
Melanocytes and Langerhans cells (also termed dendritic cells) are frequently found within this layer. Langerhans cells contribute to the immune response of the skin against skin cancers and pathogens that have penetrated the skin.
Superficial to the stratum spinosum is the stratum granulosum. Cells within this layer have moved superficially out of the stratum spinosum. This is the last layer of the skin where all of the cells possess a visible and functioning nucleus. Cells of the stratum granulosum synthesize large amounts of two intracellular proteins: keratin and keratohyalin. These proteins, once fully formed, will assist in protecting the skin from environmental microorganisms.
Stratum granulosum cells release granules by exocytosis. These granules contain a lipid-rich substance that will, in more superficial layers, completely coat all of the cells and contribute to the cells’ water resistance.
The stratum lucidum, which is superficial to the stratum spinosum, is found only within thick skin. Cells within this layer lack organelles and a functioning nucleus, and are densely packed together. The keratin proteins are fully formed and bind the cells of this layer tightly together.
The most superficial layer is the stratum corneum. This layer is composed of dead cells that possess a very thick cellular membrane, lack any organelles or nucleus, and possess a high amount of keratin. The intercellular connections formed within the stratum spinosum are still fully intact and bind the cells tightly together. In addition, the lipid-rich substance formed by the cells of the stratum granulosum completely surrounds the cells of this layer. These characteristics contribute to the protective nature of the stratum corneum against environmental pathogens and contribute to the cells’ water resistance.
Deep to the epidermis is the dermis, which is composed of two layers: a reticular layer and a papillary layer.
The reticular layer is the deepest layer of the dermis. This layer is composed of densely interwoven connective tissue fibers that surround blood vessels, nerves, hair follicles, sweat glands and sebaceous glands. The connective tissue fibers of this layer extend deeper into the subcutaneous tissue, and superficially into the papillary layer. As a result all of these layers are held tightly together.
The papillary layer of the dermis, which serves to mechanically anchor the epidermis to the dermis, is composed of loose connective tissue. The papillary layer contains a large number of capillaries and neuronal axons. The capillaries nourish the epidermis and remove epidermal wastes by diffusion. The neurons provide sensory input coming from epidermal sensory receptors.
Burns are one of the most painful injuries to the human body. Smoking and open flames are the most common causes of burns in older adults, while scalding by hot water is the leading cause of burns in infants and children.
Burns are classified as first-, second-, and third-degree, depending on the depth of the burn injury.
A first-degree burn is a superficial injury, in that it only affects the epidermis of the skin. The site of the burn is red, dry, and lacks blisters. Although long-term tissue damage is rare, if it does occur it typically involves an alteration is the color of the skin.
Second-degree burns extend through the entire epidermis and part of the underlying dermis. The site of the burn is red, blistered, and often swells.
Third-degree burns (also termed full-thickness burns) completely destroys the epidermis and underlying dermis. It is not uncommon for third-degree burns to also damage muscles, tendons, and bones. The burn site has a white or charred appearance. The burn victim lacks feeling in the area of the third-degree burn, as all of the nerve endings within the burn area have been destroyed.
Epidermis - The most superficial layer of the skin.
Dermis - The layer of skin deep to the epidermis.
Reticular layer - The deepest layer of the dermis.
Papillary layer - The most superficial layer of the dermis.
Keratin - An intracellular protein synthesized by cells within the granular layer of the epidermis. This protein, once fully formed, serves to protect the skin from environmental microorganisms.
Stratum corneum - The most superficial layer of the epidermis.
Melanocytes - Cells of the epidermis that contain pigment-producing granules.
Langerhans cells - Specialized cells of the stratum spinosum. These cells contribute to the immune response of the skin against skin cancers and pathogens that have penetrated the skin.
Third-degree burn - Also termed a full-thickness burn, this type of burn completely destroys the epidermis and dermis. It may also destroy deeper tissues, such as muscles, bones, and ligaments.
- List the layers of the epidermis (in thin skin) from superficial to deep.
A: Stratum corneum; stratum granulosum; stratum spinosum; stratum basale
- What cell type contributes to the immune response of the skin against cancers and pathogens that have penetrated the skin?
A: Langerhans cells
- True or False? Melanocytes are only found within the stratum basale of the epidermis.
A: False. Melanocytes are also found within the stratum granulosum of the epidermis.
- True or False? Mitosis only occurs within the stratum basale of the epidermis.
A: False. Mitotic activity is seen within the stratum basale and the stratum granulosum of the epidermis.
- Which layer of the epidermis is found in thick skin but not in thin skin?
A: Stratum lucidum
- True or False? The papillary layer of the dermis anchors the dermis to underlying connective tissue.
A: False. The papillary layer of the dermis attaches the epidermis to the dermis of the skin.
- The synthesis of keratin and keratohyalin begins within which layer of the skin?
A: Stratum granulosum of the epidermis
- True or False? Patients with third-degree burns feel extreme pain at the burn area immediately following experiencing the burn.
A: False. Third-degree burn patients do not feel pain in the burn area due to the complete destruction of nerve endings within the burn area.
- Which degree(s) of burn blisters?
A: Second degree burns blister.
- What is a skin graft?
A: A surgical procedure where a section of healthy skin is used to replace the scar tissue caused by deep burns.
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