Chapter 5: The Integumentary System Flashcards
What is the integumentary system?
The integumentary system is composed of the skin, hair, oil and sweat glands, nails, and sensory receptors.The integumentary system helps maintain a constant body temperature, protects the body, and provides sensory information about the surrounding environment.
Describe the layers of the skin.
The skin, also known as the cutaneous membrane, consists of two main parts. The superficial, thinner portion, which is composed of epithelial tissue, is the epidermis. The deeper, thicker connective tissue portion is the dermis. While the epidermis is avascular, the dermis is vascular. Deep to the dermis, but not part of the skin, is the subcutaneous (subQ) layer. Also called the hypodermis, this layer consists of areolar and adipose tissues. Fibers that extend from the dermis anchor the skin to the subcutaneous layer, which in turn attaches to underlying fascia, the connective tissue around muscles and bones. This region (and sometimes the dermis) also contains nerve endings called lamellated corpuscles or pacinian corpuscles that are sensitive to pressure.
Describe the 4 kinds of cells that make up the epidermis.
The epidermis is composed of keratinized stratified squamous epithelium. It contains four principal types of cells: keratinocytes, melanocytes, intraepidermal macrophages, and tactile epithelial cells.
About 90% of epidermal cells are keratinocytes, which are arranged in four or five layers and produce the protein keratin, a tough, fibrous protein that helps protect the skin and underlying tissues from abrasions, heat, microbes, and chemicals. Keratinocytes also produce lamellar granules, which release a water-repellent sealant that decreases water entry and loss and inhibits the entry of foreign materials.
About 8% of the epidermal cells are melanocytes, which produce the pigment melanin, a yellow-red or brown-black pigment that contributes to skin color and absorbs damaging ultraviolet (UV) light.
Intraepidermal macrophages or Langerhans cells arise from red bone marrow and migrate to the epidermis where they constitute a small fraction of the epidermal cells. They participate in immune responses mounted against microbes that invade the skin, helping other cells of the immune system recognize an invading microbe and destroy it.
Tactile epithelial cells, or Merkel cells, are the least numerous of the epidermal cells. They are located in the deepest layer of the epidermis, where they contact the flattened process of a sensory neuron (nerve cell), a structure called a tactile disc or Merkel disc. Tactile epithelial cells and their associated tactile discs detect touch sensations.
Describe the 2 regions of the dermis.
The second, deeper part of the skin, the dermis, is composed of dense irregular connective tissue containing collagen and elastic fibers. Based on its tissue structure, the dermis can be divided into a thin superficial papillary region and a thick deeper reticular region.
The papillary region makes up about one-fifth of the thickness of the total layer. It contains thin collagen and fine elastic fibers. Its surface area is greatly increased by dermal papillae, small, nipple-shaped structures that project into the undersurface of the epidermis. All dermal papillae contain capillary loops (blood vessels). Some also contain tactile receptors called corpuscles of touch or Meissner corpuscles, nerve endings that are sensitive to touch. Still other dermal papillae also contain free nerve endings, dendrites that lack any apparent structural specialization. Different free nerve endings initiate signals that give rise to sensations of warmth, coolness, pain, tickling, and itching.
The reticular region, which is attached to the subcutaneous layer, contains bundles of thick collagen fibers, scattered fibroblasts, and various wandering cells (such as macrophages). Some adipose cells can be present in the deepest part of the layer, along with some coarse elastic fibers. Blood vessels, nerves, hair follicles, sebaceous (oil) glands, and sudoriferous (sweat) glands occupy the spaces between fibers.
Explain the basis for different skin colours.
Melanin, hemoglobin, and carotene are three pigments that impart a wide variety of colors to skin. The amount of melanin causes the skin’s color to vary from pale yellow to reddish-brown to black. Because the number of melanocytes is about the same in all people, differences in skin color are due mainly to the amount of pigment the melanocytes produce and transfer to keratinocytes.
Identify the parts of the Integumentary System on a diagram.
Describe the location, distribution, and function of hair.
Each hair is composed of columns of dead, keratinized epidermal cells bonded together by extracellular proteins. The hair shaft is the superficial portion of the hair, which projects above the surface of the skin. The hair root is the portion of the hair deep to the shaft that penetrates into the dermis, and sometimes into the subcutaneous layer. Surrounding the root of the hair is the hair follicle, which is made up of an external root sheath and an internal root sheath. The external root sheath is a downward continuation of the epidermis. The internal root sheath is produced by the matrix (described shortly) and forms a cellular tubular sheath of epithelium between the external root sheath and the hair. Together, the external and internal root sheath are referred to as the epithelial root sheath. The dense dermis surrounding the hair follicle is called the dermal root sheath. The base of each hair follicle and its surrounding dermal root sheath is an onion-shaped structure, the hair bulb. This structure houses a nipple-shaped indentation, the papilla of the hair, which contains areolar connective tissue and many blood vessels that nourish the growing hair follicle. The bulb also contains a germinal layer of cells called the hair matrix.
Describe the the 3 kinds of skin glands.
Glands are epithelial cells that secrete a substance. Several kinds of exocrine glands are associated with the skin: sebaceous (oil) glands, sudoriferous (sweat) glands, and ceruminous glands.
Sebaceous glands or oil glands are simple, branched acinar (rounded) glands. With few exceptions, they are connected to hair follicles. Sebaceous glands secrete an oily substance called sebum, a mixture of triglycerides, cholesterol, proteins, and inorganic salts.
Sudoriferous glands, or sweat glands, release sweat, or perspiration, into hair follicles or onto the skin surface through pores. Sweat glands are divided into two main types, eccrine and apocrine, based on their structure and type of secretion. Eccrine sweat glands are simple, coiled tubular glands that are much more common than apocrine sweat glands. They are distributed throughout the skin of most regions of the body, especially in the skin of the forehead, palms, and soles. The main function of eccrine sweat glands is thermoregulation. Sweat that evaporates from the skin before it is perceived as moisture is termed insensible perspiration. Sweat that is excreted in larger amounts and is seen as moisture on the skin is called sensible perspiration. Apocrine sweat glands are also simple, coiled tubular glands but have larger ducts and lumens than eccrine glands. They are found mainly in the skin of the axilla (armpit), groin, areolae (pigmented areas around the nipples) of the breasts, and bearded regions of the face in adult males. Apocrine sweat glands, along with eccrine sweat glands, are active during emotional sweating. In addition, apocrine sweat glands secrete sweat during sexual activities. In contrast to eccrine sweat glands, apocrine sweat glands do not play a role in thermoregulation.
Ceruminous glands are modified sweat glands in the external ear. They produce a waxy lubricating secretion. Their excretory ducts open either directly onto the surface of the external auditory canal (ear canal) or into ducts of sebaceous glands. The combined secretion of the ceruminous and sebaceous glands is a yellowish material called cerumen, or earwax.
Describe the nails.
Nails are plates of tightly packed, hard, dead, keratinized epidermal cells that form a clear, solid covering over the dorsal surfaces of the distal portions of the digits. Each nail consists of a nail body, a free edge, and a nail root. The nail body (plate) is the visible portion of the nail. Most of the nail body appears pink because of blood flowing through the capillaries in the underlying dermis. The free edge is the part of the nail body that may extend past the distal end of the digit. The free edge is white because there are no underlying capillaries. The nail root is the portion of the nail that is buried in a fold of skin. The whitish, crescent-shaped area of the proximal end of the nail body is called the lunula. Nails have a variety of functions:
- They protect the distal end of the digits.
- They provide support and counterpressure to the palmar surface of the fingers to enhance touch perception and manipulation.
- They allow us to grasp and manipulate small objects, and they can be used to scratch and groom the body in various ways.
Beneath the free edge is a thickened region of stratum corneum called the hyponychium. It is the junction between the free edge and skin of the fingertip and secures the nail to the fingertip. The nail bed is the skin below the nail plate that extends from the lunula to the hyponychium. The epidermis of the nail bed lacks a stratum granulosum. The eponychium or cuticle is a narrow band of epidermis that extends from and adheres to the margin (lateral border) of the nail wall. It occupies the proximal border of the nail and consists of stratum corneum. The portion of the epithelium proximal to the nail root is the nail matrix, which divides mitotically to produce new nail cells.
Compare structural and functional differences in thin and thick skin.
In most regions of the body, the epidermis has four strata or layers - stratum basale, stratum spinosum, stratum granulosum, and a thin stratum corneum. This is called thin skin. Where exposure to friction is greatest, such as in the fingertips, palms, and soles, the epidermis has five layers—stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and a thick stratum corneum. This is called thick skin.
Describe the five layers of the epidermis.
The deepest layer of the epidermis is the stratum basale, composed of a single row of cuboidal or columnar keratinocytes.
Superficial to the stratum basale is the stratum spinosum. This stratum mainly consists of numerous keratinocytes arranged in 8–10 layers.
At about the middle of the epidermis, the stratum granulosum consists of three to five layers of flattened keratinocytes that are undergoing apoptosis. The stratum granulosum marks the transition between the deeper, metabolically active strata and the dead cells of the more superficial strata.
The stratum lucidum is present only in the thick skin of areas such as the fingertips, palms, and soles. It consists of four to six layers of flattened clear, dead keratinocytes that contain large amounts of keratin and thickened plasma membranes.
The stratum corneum consists, on average, of 25 to 30 layers of flattened dead keratinocytes, but can range in thickness from a few cells in thin skin to 50 or more cell layers in thick skin. Its multiple layers of dead cells help the stratum corneum to protect deeper layers from injury and microbial invasion.
Describe how the skin contributes to the regulation of body temperature, storage of blood, protection, sensation, excretion and absorption, and the synthesis of vitamin D.
Thermoregulation
The skin contributes to thermoregulation in two ways: by liberating sweat at its surface and by adjusting the flow of blood in the dermis.
Blood Reservoir
The dermis houses an extensive network of blood vessels that carry 8–10% of the total blood flow in a resting adult.
Protection
The skin provides protection to the body in various ways. Keratin protects underlying tissues from microbes, abrasion, heat, and chemicals, and the tightly interlocked keratinocytes resist invasion by microbes. Lipids released by lamellar granules inhibit evaporation of water from the skin surface, thus guarding against dehydration; they also retard entry of water across the skin surface during showers and swims. The oily sebum from the sebaceous glands keeps skin and hairs from drying out and contains bactericidal chemicals (substances that kill bacteria). The acidic pH of perspiration retards the growth of some microbes. The pigment melanin helps shield against the damaging effects of ultraviolet light. Two types of cells carry out protective functions that are immunological in nature. Intraepidermal macrophages alert the immune system to the presence of potentially harmful microbial invaders by recognizing and processing them, and macrophages in the dermis phagocytize bacteria and viruses that manage to bypass the intraepidermal macrophages of the epidermis.
Cutaneous Sensations
Cutaneous sensations are sensations that arise in the skin, including tactile sensations—touch, pressure, vibration, and tickling—as well as thermal sensations such as warmth and coolness. Another cutaneous sensation, pain, usually is an indication of impending or actual tissue damage.
Excretion and Absorption
Besides removing water and heat from the body, sweat also is the vehicle for excretion of small amounts of salts, carbon dioxide, and two organic molecules that result from the breakdown of proteins—ammonia and urea. The absorption of water-soluble substances through the skin is negligible, but certain lipid-soluble materials do penetrate the skin. These include fat-soluble vitamins (A, D, E, and K), certain drugs, and the gases oxygen and carbon dioxide.
Synthesis of Vitamin D
Synthesis of vitamin D requires activation of a precursor molecule in the skin by ultraviolet (UV) rays in sunlight. Enzymes in the liver and kidneys then modify the activated molecule, finally producing calcitriol, the most active form of vitamin D.
