Anatomy chapter 4

Langerhans cells

Found in the stratum spinosum. play an important role in initiating an immune response against pathogens that have pen- etrated the superficial layers of the epidermis and epidermal cancer cells.

Apocrine Sweat Glands

Sweat glands that release their secretions into hair follicles in the axillae (armpits), around the nipples (areolae), and in the groin.coiled tubular glands that produce a viscous, cloudy, and potentially odorous secretion.

dermal papillae

Projections from the dermis toward the epidermis,

Keratohyalin

accumulates in electron-dense granules called keratohyalin granules. These granules form an intracellular matrix that surrounds the keratin filaments. Cells of this layer also contain membrane-bound granules that release their contents by exocytosis, which forms sheets of a lipid-rich substance that begins to coat the cells of the stratum granulosum. This substance will form a complete water-resistant layer around the cells of the more superficial layers of the epidermis. This water-resistant layer will protect the epidermis, but it will also prevent the diffusion of nutrients and wastes into and out of the cells, thereby causing cells in the more superficial epidermal layers to die.

Intermediate hairs

are hairs that change in their distribution, such as the hairs of the upper and lower limbs.

Terminal hairs

are heavy, more deeply pigmented, and sometimes curly. The hairs on your head, including your eyebrows and eyelashes, are ex- amples of terminal hairs.

Melanocytes

are pigment-producing cells in the epidermis. Melanocytes are scattered among the basal cells of the stratum basale. They have numer- ous cytoplasmic processes that inject melanin, a black, yellow-brown, or brown pigment, into the keratinocytes in this layer and in more superficial layers.

Vellus hairs

are the fine "peach fuzz" hairs found over much of the body surface.

reticular layer

consists of fibers in an interwoven meshwork of dense irregular connective tissue that surrounds blood vessels, hair follicles,nerves, sweat glands, and sebaceous glands.

Melanin

pigments help prevent skin damage by absorbing ultraviolet (UV) radiation in sunlight.protects the underlying dermis. Within each kera- tinocyte, the melanosomes are most abundant around the cell's nucleus. This increases the likelihood that the UV radiation will be absorbed before it can damage the nuclear DNA. Melanocytes respond to UV exposure by increasing their rates of mel- anin synthesis and transfer. Tanning then occurs, but the response is not quick enough to prevent a sunburn on the first day at the beach;

Functions of Hair

protect from uv light filters nose and ears. provide sensory information

Merocrine Sweat Glands

A type of sweat gland that is far more nu- merous and widely distributed than apocrine sweat glands.do not extend as far into the dermis. Palms and soles have the highest numbers. Coiled tubular glands that discharge their secretions directly onto the surface of the skin.

subcutaneous layer

Although the subcutaneous layer is sometimes not consid- ered to be a part of the integument, it is important in stabilizing the position of the skin in relation to underlying tissues, such as skeletal muscles or other organs, while still permitting independent movement.The subcutaneous layer consists of loose connective tissue with abundant adi- pocytes (Figure 4.7c). Infants and small children usually have extensive "baby fat," which helps reduce heat loss. Subcutaneous fat also serves as a substantial energy reserve and a shock absorber for the rough-and-tumble activities of our early years.

Langerhans cells

Are wandering phagocytic cells that are important in the body's immune response.

cutaneous plexus

Arteries and veins supplying the skin form an interconnected network in the subcutaneous layer along the border with the reticular layer. This network is called the cutaneous plexus

Stratum Spinosum

Each time a basal cell divides, one of the daughter cells is pushed into the next, more superficial layer, the stratum spinosum ("spiny layer"), where it begins to differentiate into a keratinocyte.he stratum spinosum is several cells thick. Each keratinocyte in the stratum spinosum contains bundles of protein fila- ments that extend from one side of the cell to the other. These bundles, called tonofibrils, begin and end at a macula adherens (desmosome) that connects the keratinocyte to its neighbors.Melanocytes are common in this layer,

Hair follicles

Hairs are nonliving structures that are formed in organs called hair follicles. The epithelium at the follicle base surrounds a small hair papilla, a peg of connective tissue containing capillaries and nerves. The hair bulb consists of epithelial cells that surround the papilla.Hair production involves a specialization of the keratinization process. The hair matrix is the epithelial layer involved in hair production. When the super- ficial basal cells divide, they produce daughter cells that are pushed toward the surface as part of the developing hair. Most hairs have an inner medulla and an outer cortex. The medulla contains relatively soft and flexible soft keratin. Matrix cells closer to the edge of the developing hair form the relatively hard cortex. The cortex contains hard keratin that gives hairits stiffness. A single layer of dead, keratinized cells at the outer surface of the hair overlap and form the cuticle that coats the hair.

Stratum Lucidum

In thick skin only In the thick skin of the palms and soles, a glassy clear layer covers the stratum granulosum. The cells in this layer lack organelles and nuclei and are flattened, densely packed, and filled with keratin filaments that are ori- ented parallel to the surface of the skin

The accessory structures

Include hair, nails, and a variety of multicellular exocrine glands. These structures are located in the dermis and protrude through the epidermis to the surface.

callus

Increased friction against the skin stimu- lates increased keratohyalin and keratin synthesis by keratinocytes within the stratum granulosum. This results in a localized thickening of the skin and the formation of a callus

The Nerve Supply to the Skin

Nerve fibers in the skin control blood flow, adjust gland secretion rates, and monitor sensory receptors in the dermis and the deeper layers of the epidermis. We have already noted the presence of Merkel cells in the deeper layers of the epidermis. These cells are touch receptors monitored by sen- sory nerve endings known as tactile discs.The epidermis also contains the dendrites of sensory nerves that are believed to respond to pain and temperature.

Follicle Structure

The cells of the follicle walls are organized into concentric layers (Figure 4.10a). Beginning at the hair cuticle, these layers include the following:

Skin Color

The color of the epidermis is due to a combination of the dermal blood supply, the thickness of the stratum corneum, and variable quantities of two pigments: carotene and melanin.

Stratum Basale

The deepest epidermal layer.This single layer of cells is firmly attached to the basal lamina that separates the epidermis from the loose connective tissue of the adjacent dermis. Large stem cells, termed basal cells, dominate the stratum basale.

Local Control of Integumentary Function

The integumentary system displays a significant degree of functional inde- pendence. It responds directly and automatically to local influences without the involvement of the nervous or endocrine systems.stem cells in the stratum basale di- vide more rapidly, and the depth of the epithelium increases. That is why cal- luses form on your palms when you perform manual labor

keratinocytes

The most abundant epithelial cells,

Nails

The nail body covers the nail bed, but nail production occurs at the nail root, an epithelial fold not visible from the surface. The deepest portion of the nail root lies very close to the periosteum of the bone of the fingertip. The nail body is recessed beneath the level of the surrounding epi- thelium, and it is bounded by nail grooves and nail folds.

Sweat Glands

The skin contains two different groups of sweat glands: apocrine sweat glands and merocrine sweat glands.Both gland types con- tain myoepithelial cells (myo-, muscle), specialized epithelial cells located between the gland cells and the underlying basal lamina.

Glands in the Skin

The skin contains two types of exocrine glands: sebaceous glands and sweat (sudoriferous) glands.

Epidermal Ridges

The stratum basale of the epidermis forms epidermal ridges that extend into the dermis, increasing the area of contact between the two regions.

Functions of sweat

Thermoregulation. Sweat cools the surface of the skin.Excretion. Protection. Merocrine sweat gland secretion provides protection from en- vironmental hazards by diluting harmful chemicals and discouraging the growth of microorganisms.

Glassy membrane:

This is a thickened basal lamina, wrapped in a dense connective tissue sheath.

external root sheath:

This layer extends from the skin surface to the hair matrix. Over most of that distance it has all the cell layers found in the superficial epidermis. However, where the external root sheath joins the hair matrix, all the cells resemble those of the stratum basale.

The internal root sheath

This layer surrounds the hair root and the deeper portion of the shaft. It is produced by the cells at the periphery of the hair matrix. Because the cells of the internal root sheath disintegrate relatively quickly, this layer does not extend the entire length of the fol- licle, typically ending where the duct of the sebaceous gland attaches to the hair follicle.

Stratum Granulosum

consists of keratinocytes displaced from the stra- tum spinosum. By the time cells reach this layer, they have begun to manu- facture large quantities of the proteins keratohyalin (ker-a-tō-HĪ-a-lin) and keratin (KER-a-tin; keros, horn)

The superficial papillary layer

consists of loose connective tissue (Figure 4.7a). This region contains the capillaries supplying the epidermis and the axons of sensory neurons that monitor receptors in the papillary layer and the epidermis.

Myoepithelial cell

contractions squeeze the gland and discharge the accumulated secretions. The secretory activities of the gland cells and the contractions of myoepithe- lial cells are controlled by both the autonomic nervous system and by circu- lating hormones.

Sebaceous Glands

discharge a waxy, oily secretion into hair follicles.This secretion, called sebum (SĒ-bum), provides lubrication and inhibits the growth of bacteria. Keratin is a tough protein, but dead, keratinized cells become dry and brittle once exposed to the environment. Sebum lubricates and protects the keratin of the hair shaft and conditions the surrounding skin. Shampooing removes the natural oily coating, and excessive washing can make hairs stiff and brittle. Large Glands

keratin

forms the basic structural component of hair and nails. It is a very versatile material, however, and in other vertebrates it forms the claws of dogs and cats, the horns of cattle and rhinos, the feathers of birds, the scales of snakes, the baleen of whales, and a variety of other interesting epidermal structures.

Thick skin

found on the palms of the hands and soles of the feet, may be cov- ered by 30 or more layers of keratinized cells. As a result, the epidermis in these locations exhibits all five layers and may be as much as six times thicker than the epidermis covering the general body surface

Accessory Structures

hair follicles, sebaceous glands, sweat glands, and nails

Merkel

have a role in detecting sensation.Skin surfaces that lack hair. These cells are found among the cells of the stratum basal. and when compressed, Merkel cells release chemicals that stimulate sensory nerve endings, providing information about objects touching the skin.

INTEGUMENTARY SYSTEM

is composed of the skin and its derivatives: hair, nails, sweat glands, oil glands, and mammary glands. clinicians can use the appearance of the skin to detect signs of underlying disease. protects you from the surrounding environment; its receptors tell you a lot about the outside world; and it helps regulate your body temperature.The integument covers the entire body surface, including the anterior surfaces of the eyes and the tympanic membranes (eardrums) at the ends of the external auditory canals.

stratum corneum

is the most superficial layer of both thick and thin skin. It consists of numerous layers of flattened, dead cells that possess a thickened plasmalemma. These dehydrated cells lack organelles and a nucleus, but still contain large amounts of keratin filaments. Because the interconnections established in the stratum spinosum remain intact, the cells of this layer are usually shed in large groups or sheets, rather than individually.

There are four cell types in the epidermis

keratinocytes, melano- cytes, Merkel cells, and Langerhans cells.

As you pick up a piece of lumber, a splinter pierces the palm of your hand and lodges in the third layer of the epidermis. Identify this layer. 2 What is keratinization? What are the stages of this process? 3 Identify the sources of color of the epidermis. 4 Describe the relationship between epidermal ridges and dermal papillae.

n

thin skin.

only four layers are present because the stratum lucidum is typically absent. Here the epidermis is a mere 0.08 mm thick, and the stratum corneum is only a few cell layers deep

Carotene

orange-yellow pigment.It can be converted to vitamin A, which is required for epithelial maintenance and the synthesis of visual pigments by the photore- ceptors of the eye. Carotene normally accumulates inside keratinocytes, and it becomes especially evident in the dehydrated cells of the stratum corneum and in the subcutaneous fat.

skin

the superficial epithelium, termed the epidermis (epi-, above + derma, skin) and the underlying connective tissues of the dermis. Deep to the dermis, the loose connective tis- sue of the subcutaneous layer, also known as the hypodermis, or su- perficial fascia, separates the integument from the deep fascia around other organs, such as muscles and bones.