Integumentary System What is integument ? The integument as an organ, and is an alternative name for skin. The integumentary system includes the skin and the skin derivatives hair, nails, and glands. The integument can also be thought of as a cutaneous membrane that covers the outer surface of the body. We lose almost a kg Introduction of skin epithelium a year that becomes a The Integument major part of household o Is the largest system of the body “dust”. o 16% of body weight o The integument is made up of two parts: 1. Cutaneous membrane a. Epidermis– Superficial epithelium b. Dermis – underlying CT with blood supply c. Hypodermis 2. Accessory structures a. Hair b. Nails c. Exocrine Glands Functions Protection o First line of defense against • Bacteria • Viruses o Protects underlying structures from • Ultraviolet (UV) radiation • Dehydration Vitamin D production o Needed for calcium absorption Sensation o Sensory receptors Funcitons Body temperature regulation o If too hot • Dermal blood vessels dilate • Vessels carry more blood to surface so heat can escape o If too cold • Dermal blood vessels constrict • Prevents heat from escaping Excretion o Small amounts of waste products are lost through perspiration Structure Understanding how the skin can function in these many ways starts with understanding the structure of the 3 layers of skin The Epidermis o Epithelial tissue Dermis o Dense connective tissue proper – irregular Hypodermis o Subcutaneous tissue- loose connective tissue proper and adipose tissue Structure /subcutaneous layer Structure/Epidermis The Epidermis is •A stratified squamous epithelia, composed of four to five layers (depending on body region) of epithelial cells. •Nutrients and oxygen diffuse from capillaries in the dermis Structure/Cells of Epidermis The epidermis is composed of five types of cells Structure/Cells of Epidermis • Stem cells are undifferentiated cells that divide and give rise to the keratinocytes described next. They are found only in the deepest layer of the epidermis, called the stratum basale. Basal cells are an example of tissue-specific stem cells, meaning they can turn into a variety of cell types found in that tissue. Under normal conditions, daughter basal cells most commonly replace lost keratinocytes. Structure/Cells of Epidermis • Keratinocytes are the great majority of epidermal cells. They are named for their role in synthesizing keratin. In ordinary histological specimens, nearly all of the epidermal cells you see are keratinocytes. • The keratinocytes on the most superficial layer of the epidermis are dead, and periodically slough away, being replaced by cells from the deeper layers. As keratinocytes move superficially from the deeper layers, they lose cytoplasm and become flattened, allowing for many layers in a relatively small space. Structure/Cells of Epidermis • Melanocytes also occur only in the stratum basale, amid the stem cells and deepest keratinocytes. They synthesize the brown to black pigment melanin. They have branching processes that spread among the keratinocytes and continually shed melanin- containing fragments from their tips. • The keratinocytes phagocytize these fragments and accumulate melanin granules on the “sunny side” of the nucleus. Like a parasol, the pigment shields the DNA from ultraviolet radiation. Structure/Cells of Epidermis • Tactile (Merkel) cells, relatively few in number, are receptors for the sense of touch. They, too, are found in the basal layer of the epidermis and are associated with an underlying dermal nerve fiber. The tactile cell and its nerve fiber are collectively called a tactile (Merkel) disc. Structure/Cells of Epidermis • Dendritic (Langerhans) cells are found in two layers of the epidermis called the stratum spinosum and stratum granulosum. They are macrophages that originate in the bone marrow but migrate to the epidermis and epithelia of the oral cavity, esophagus, and vagina. • The epidermis has as many as 800 dendritic cells per square millimeter. They stand guard against toxins, microbes, and other pathogens that penetrate into the skin. When they detect such invaders, they alert the immune system so the body can defend itself. Stucture/Epidermal Strata • Cells of the epidermis are arranged in four to five zones, or strata (five in thick skin). • Thin Skin (A) Covers most of the body Has four layers of keratinocytes • Thick Skin (B) Covers the palms of the hands and soles of the feet Has five layers of keratinocytes • The following description progresses from deep to superficial, and from the youngest to the oldest keratinocytes. Stucture/Epidermal Strata • The stratum basale consists mainly of a single layer of cuboidal to low columnar stem cells and keratinocytes resting on the basement membrane. • Scattered among these are the melanocytes and tactile cells. As stem cells of the stratum basale divide, they give rise to keratinocytes that migrate toward the skin surface and replace lost epidermal cells. • The stratum basale is attached to basement membrane by hemidesmosomes. • Forms a strong bond between epidermis and dermis. • Dermal papillae (tiny mounds) Increase the area of basement membrane Strengthen attachment between epidermis and dermis Stucture/Epidermal Strata • The stratum they produce more spinosum consists of and more keratin several layers of filaments, which keratinocytes. In cause the cells to most skin, this is the flatten. Therefore, thickest stratum, but the higher up you in the thick skin it is look in the stratum usually exceeded by spinosum, the flatter the stratum the cells appear. corneum. Eight to ten layers. • Dendritic cells are also found • The deepest cells of throughout the the stratum stratum spinosum spinosum remain but are not usually capable of mitosis, visible in tissue but as they are sections. pushed farther upward, they cease dividing. Instead, Stucture/Epidermal Strata • The stratum spinosum is named for an artificial appearance (artifact) created by the histological fixation of tissue specimens. • Keratinocytes are firmly attached to each other by numerous desmosomes, which partly account for the toughness of the epidermis. • Histological fixatives shrink the keratinocytes so they pull away from each other, but they remain attached by the desmosomes—like two people holding hands while they step farther apart. • The desmosomes thus create bridges from cell to cell, giving each cell a spiny appearance from which we derive the word spinosum. «spiny layer» Stucture/Epidermal Strata • The stratum granulosum consists of three to five layers of flat keratinocytes—more in the thick skin than in the thin skin. The keratinocytes of this layer contain coarse, dark-staining keratohyalin granules that give the layer its name. • Epidermal keratinocytes are also bound to each other by tight junctions, which make an essential contribution to water retention by the skin. • Stops dividing, starts producing Keratin A tough, fibrous protein Makes up hair and nails Keratohyalin Dense granules Cross-link keratin fibers «grainy layer» Stucture/Epidermal Strata • The stratum lucidum is a thin zone superficial to the stratum granulosum, seen only in the thick skin. Here, the keratinocytes are densely packed with a clear protein named eleidin. The cells have no nuclei or other organelles. This zone has a pale, featureless appearance with indistinct cell boundaries «clear layer» Stucture/Epidermal Strata • The stratum corneum consists of up to 30 layers of dead, scaly, keratinized cells that form a durable surface layer. This layer is especially resistant to abrasion, penetration, and water loss. • Shed and replaced every 2 weeks. «horn layer» Stucture/Epidermis/Skin Pigments • Skin Pigments • Melanin is produced by melanocytes in the stratum basale • Eumelanin (brown to black) • Pheomelanin (yellow to red) •Freckles are clusters of concentrated melanin triggered by exposure to sunlight. Stucture/Epidermis/Skin Pigments • Vitiligo is a chronic disorder that causes depigmentation patches in the skin. The precise pathogenesis, or cause, is not known, but is most likely a combination of genetic factors coupled with a disorder of the immune system (autoimmune disease). • Albinism is a congenital disorder characterized by the complete or partial absence of pigment in the skin, hair, and eyes due to a defect of an enzyme involved in the production of melanin. Stucture/Dermis The Dermis Located between epidermis and subcutaneous layer Anchors epidermal accessory structures (hair follicles, sweat glands) Two components 1. Outer papillary layer 2. Deep reticular layer Stucture/Dermis The Papillary Layer Consists of areolar connective tissue Contains smaller capillaries, lymphatics, and sensory neurons Has dermal papillae projecting between epidermal ridges The Reticular Layer Consists of dense irregular connective tissue Contains larger blood vessels, lymphatic vessels, and nerve fibers Contains collagen and elastic fibers Contains connective tissue proper Stucture/Dermis/Dermatitis An inflammation of the papillary layer Caused by infection, radiation, mechanical irritation, or chemicals Characterized by itch or pain Characteristics Strong, due to collagen fibers Elastic, due to elastic fibers Flexible Stucture/HypoDermis • The subcutaneous layer is also called the hypodermis, and it attaches the skin to underlying tissues and organs. • It contains blood vessels and nerves in transit to the more superficial layers. • It also contains lamellated (pacinian) corpuscles that detect external pressure applied